Research in the central and southern Transantarctic Mountains has yielded many significant discoveries and results (Table 1) over the 40 years since the International Geophysical Year when the U.S. Antarctic Program was established. These results have been obtained by a combination of numerous individual remote field projects and five major field camps (between 1969-70 and 1995-96) with varying numbers of projects and scientists supported by helicopters. These results laid the foundation for on-going and anticipated research efforts directed at addressing specific questions.
Table 1. Major advances in geology in CTM from helicopter-supported field camps
1969-1971 helicopter-supported camps near Beardmore, Shackleton and Amundsen glaciers
Geologic quadrangle maps (1:250,000) of Beardmore Glacier region (Barrett, et al., 1970; Lindsay et al., 1973; Barrett & Elliot, 1973; Elliot et al., 1974).
Anatomically well preserved plant fossils in silicified Permian peat deposits (Schopf, 1970).
Lower Triassic Lystrosaurus Zone fauna of reptiles and amphibians at Coalsack Bluff (Elliot et al., 1970) and the Cumulus Hills near the Shackleton Glacier (Kitching et al., 1972).
Middle (Upper?) Triassic anatomically well preserved plant fossils in silicified peat (Schopf, 1978).
Pre-Pleistocene glacial deposits of the Sirius Formation (Mercer, 1972).
Recycled Pliocene marine microfossils in pre-Pleistocene glacial deposits (Webb et al., 1984).
1985-1986 helicopter-supported camp in Beardmore Glacier region
Lower Permian turbidites (Miller & Collinson, 1994).
Upper Permian silicified ("petrified") forest (Isbell, 1990; Taylor et al., 1992).
Paleocurrent reversal documented as Late Permian and tied to change from basement to volcaniclastic alluvial fan from West Antarctica. (Isbell, 1991).
Lower (Middle?) Triassic Cynognathus Zone reptile and amphibian fauna (Hammer et al., 1990).
Middle (Upper?) Triassic silicified ("petrified") forest and anatomically well preserved plant fossils in silicified peat (Taylor & Taylor, 1993).
Well preserved wood fragments and pollen in pre-Pleistocene glacial deposits (Askin & Markgraf, 1986; Carlquist, 1987; Webb & Harwood, 1987; McKelvey et al., 1991).
1990-1991 helicopter-supported camp in Beardmore Glacier region
Jurassic vertebrate fauna including dinosaurs and a pterosaur (Hammer & Hickerson, 1994).
Pre-Pleistocene glacial marine deposits along Beardmore Glacier (Webb et al., 1994; 1996).
Nothofagus (Southern Beech) leaves in pre-Pleistocene glacial deposits (Webb & Harwood, 1991).
1995-1996 helicopter-supported camp in Shackleton Glacier region (preliminary)
Archeocyathids in Hansen Member of Fairweather Formation dating it as Early Cambrian. Late Middle Cambrian trilobites and brachiopod fauna from previously undated Taylor Formation (Rowell & Grunow). Well constrained age of 505 Ma on zircons from volcanic beds above and below trilobite horizon (Encarnación).
Permian crayfish and Triassic crayfish burrows (Isbell & Miller).
Uppermost Permian silicified ("petrified") fossil forest with large mature trees (Isbell & E.L. Taylor).
Possible shocked quartz grains from Upper Permian Buckley Formation (Retallack).
Lower Triassic silicified ("petrified") fossil forest and peat containing anatomically well preserved plant fossils immediately below strata with abundant vertebrate skeletons (Collinson, Hammer, T.N. & E.L. Taylor).
Well preserved unmineralized moss in pre-Pleistocene Sirius Formation (Webb & Harwood).
Stratigraphically diagnostic Triassic palynomorphs (Askin).
Recent changes in the logistic operations, particularly the change to a civilian contractor for helicopter operations and the increasing availability of Twin Otter support, seem to offer new and more cost-effective ways of conducting research in remote field areas.
Thus the time seemed appropriate for a workshop to explore both the compelling scientific questions that can be addressed by further research in the central and southern Transantarctic Mountains, and how this research can best be achieved given the new possibilities for logistic support. This workshop builds on an earlier evaluation of the geodynamic evolution of the Transantarctic Mountains and associated West Antarctic Rift System as a whole (Wilson and Finn, 1996). This workshop also dealt with two aspects of the geology not specifically considered in that earlier report: the pre-Devonian basement rocks and the Beacon Supergroup.
II. WORKSHOP ORGANIZATION
The first day of this two-day workshop was devoted to science presentations and discussions, and the second to: science summaries; map, imagery and photographic needs; logistics questions; and preliminary planning of possible logistic requirements.
Established research scientists in each of four areas gave overviews of the science and important problems. Each overview was followed by short presentations by individual participants. At the start of the second day, the four groups met to refine their goals and objectives, and these were then presented to the workshop as a whole. Jean Claude Thomas, U.S.G.S., followed these presentations with a discussion of the potential for new imagery of the central and southern Transantarctic Mountains. The Antarctic Geology and Geophysics Program Manager, Scott Borg, then discussed current thinking in OPP about logistic opportunities and capabilities; this was followed by a general discussion of this topic. The workshop then proceeded to identify possible areas of concentrated research interest, and concluded with a tentative framework for science and a summary of the logistics required to address these goals.
III. WORKSHOP RESULTS/CONCLUSIONS
Research was initially discussed under four general topics:
a. Basement geology
b. Gondwana stratigraphy and paleontology
c. Mesozoic-Cenozoic tectonics, including magmatism, structure, geophysics (hereafter separated into: magmatism and continental break-up; geodynamic evolution of rifts)
d. Cenozoic glacial history (hereafter separated into: Cenozoic glaciation and climate history; landscape evolution)
Discussions of these general topic areas were broad-ranging and directed toward identifying the high priority science that could be addressed by research in the Transantarctic Mountains south of the Byrd Glacier. Details of the science are given in Appendix A and Abstracts of presentations in Appendix B.
A. High Priority Science Objectives
The highest priority can be attached to those aspects of the geology that make a unique contribution to earth sciences. These objectives provide the rationale for further research in the central and southern Transantarctic Mountains, and are listed below (NOTE that the topic areas have NOT been evaluated relative to each other and that these topics are NOT rank ordered).
1. Pre-Gondwana tectonic history. The SWEAT hypothesis is an example of application of the principles of plate tectonics to the Precambrian. The Neoproterozoic to Early Paleozoic record in Antarctica provides critical information for testing that hypothesis and understanding Rodinia- and Gondwana-wide tectonic events.
2. Biotic evolution and paleoclimates at high latitudes. Antarctica provides a unique opportunity to study a sedimentary sequence, deposited in a polar and near-polar position, that contains a nearly complete record of changes from "icehouse" to "greenhouse" conditions. This succession of upper Paleozoic to Mesozoic clastic sedimentary rocks contains exceptional vertebrate, invertebrate, plant and trace fossils. Fundamental questions concerning biotic evolution, the physical changes that occur during an "icehouse" to "greenhouse" transition, paleoclimate, paleoclimatic models, and tectonic evolution of southern Pangea can be addressed by studies of these rocks.
3. Magmatism and continental break-up processes. Assembly and break-up of supercontinents is a first order event in crustal history. The Ferrar tholeiites are an integral part of the flood basalt magmatism associated with the initial fragmentation of Gondwanaland. They contain unique information on source regions and evolution of mantle-derived magmas and their plumbing systems. They bear on the role of plumes, whether as heat sources alone or as heat and magma sources, plate-scale mantle processes, and the evolution of large igneous provinces (LIPs) in general. The tectonic setting of the linear belt of Ferrar tholeiites is critical in evaluating competing models for break-up processes.
4. Geodynamic evolution of continental rifts. The linked Transantarctic Mountains and West Antarctic Rift System, one of earth's major rift systems, have unique attributes that relate to intraplate deformation during Mesozoic break-up and subsequent rifting and uplift. These attributes include aspects such as the consistent asymmetry of the rift shoulder, the long duration of the crustal thickness and thermal boundaries between the two provinces, and the apparent aseismicity yet active volcanism, uplift and faulting. Furthermore, uplift is related to the glacial history and climate, which themselves have feedback into the denudation history.
5. Landscape evolution. Development of the landscape reflects the interplay of tectonics, climate and denudation. In the Transantarctic Mountains it links adjacent sedimentary basins to uplift of the range and to Cenozoic climate trends. The Transantarctic Mountains, and other high elevation ranges in East Antarctica, may be among the planet's least modified ancient mountain landscapes, parts of which may date from the Early Miocene or earlier. These mountains provide a unique window into Cenozoic history.
6. Cenozoic glaciation and climate history. Terrestrial sequences are an essential counterpart to marine sequences in the study of glaciation and climate history. The Sirius Group, with the most diverse geomorphic settings of any glacial unit in the Transantarctic Mountains, has been interpreted in terms of a dynamic East Antarctic ice sheet which attained its present state during mid-Pliocene cooling; this contrasts with the conventional view of long-term stability with the present polar conditions and East Antarctic ice sheet existing essentially unmodified since the early Miocene. These contrasting hypotheses have profoundly different implications for the course of Cenozoic climate.
B. Field and Laboratory Objectives
Research objectives for the central and southern Transantarctic Mountains are presented in full in Appendix A. Considerable overlap exists between the various areas. The goals are not exclusive; in due course other research objectives and endeavors will be formulated and will augment or supersede those listed here. Field and laboratory objectives for the six general areas, listed in the same order as above, are summarized here.
1. Basement geology (Pre-Gondwana tectonic history). Isotope mapping of igneous, metamorphic and sedimentary rocks. Neoproterozoic rift-margin history and relations to Laurentia. Crustal architecture of basement terrains. Early Paleozoic orogenic history and intercontinental correlations. Post-orogenic, pre-Devonian, uplift and denudation.
2. Beacon rocks (Biotic evolution and paleoclimate at high latitudes). Late Paleozoic to Early Mesozoic biotic and environmental changes, from a polar perspective, with respect to an icehouse to greenhouse climate shift. Data acquisition for testing general circulation models developed for modern climates.
3. Ferrar tholeiites (Mesozoic magmatism and continental break-up). Spatial diversity of Ferrar Dolerite geochemistry. Ferrar magma origin and source region. Ferrar plumbing system. Ferrar tectonic setting.
4. Mesozoic-Cenozoic tectonics (Geodynamic evolution of continental rifts). Structural architecture of the Transantarctic Mountains and adjacent regions. Post-Jurassic tectonic history and relationships to adjacent sedimentary basins to understand the evolution of a unique rift margin. Lithospheric structure in transects from the Ross embayment to the Wilkes-Pensacola basin. Relationships between uplift history and glaciation.
5. Landscape evolution. Extensive mapping of landscape elements. Systematic sample collection for cosmogenic nuclide, radiogenic isotope and fission-track dating, to provide a framework for landscape analysis.
6. Cenozoic glacial history (Cenozoic glaciation and climate history). Mapping and analysis of glacial deposits to develop a chronology of glaciation from inception, through growth and fluctuations, to present day conditions. Collection of fossil flora and fauna for paleoenvironmental studies.
C. Logistics to Accomplish the Science Objectives
1. Available mix. Potentially, the basic logistic support consists of the heavy lift, ski-equipped LC-130 aircraft, the limited load-capacity and range performance Twin Otter, and helicopters. The LC-130 aircraft have placed many small parties in the field for self-contained operations with surface transport (snowmobiles). These aircraft have also serviced various helicopter-supported field camps, providing the ability to build temporary housing and other facilities at remote field sites and supply the large amounts of fuel needed for sustained helicopter operations. Twin Otter aircraft are a more recent addition to the logistic capabilities and have provided invaluable support for small parties needing transport to distant localities for short durations as well as for camp moves. Helicopter support was formerly provided exclusively by the US Navy UH-1N Bell helicopters, but recently small Squirrel (A Star) helicopters have proven to be most effective in support of fieldwork.
2. Research support scenarios. Three basic scenarios can be envisaged:
i) A traditional large field camp. The Shackleton 1995-96 field camp is an example. It accommodated 12 individual projects with 56 scientists who were supported by 7 ASA camp personnel; two helicopters were deployed for eight weeks (three UH-1N helicopters provided equivalent support for previous remote field camps of this type); two separate weeks of Twin Otter time provided additional logistic resources.
ii) A small helicopter-supported field camp. The Beardmore 1990-91 field camp is an example. It accommodated eight projects with 29 scientists who were supported by 5 ASA personnel. Field projects also operated, prior to the 4 weeks of helicopter support, with surface transport. Twin Otter-type support (Ganovex Dornier aircraft) was also provided for a limited time.
iii) Individual field projects. Perhaps two to four projects located in the same region, placed in the field by LC-130 or Twin Otter, and requiring limited helicopter or Twin Otter support. Such support might be one to two weeks duration and perhaps split into two periods during the field season.
The principal science objectives to emerge from the workshop require a mix of the different modes of operation outlined above. The groups considered priorities within their subdisciplines and identified regions where objectives could best be met. Given the need for helicopter support to attain the objectives, the workshop as a whole then considered whether priorities in different groups had sufficient geographic overlap to justify seeking helicopter-supported field camps. The conclusion was that there are a number of localities where concentrated interest from one or more groups justifies deployment of helicopters to remote field camps for extended time periods. Rationales for possible camps are described below.
Table 2. Priorities for each interest group with respect to potential camp sites. Note that only the three highest priorities are listed (with 3 as the highest). Note that there is no ranking between subdisciplines; Table 2 does not reflect an absolute ranking. Note that potential camp sites are ordered geographically.
3. Field objectives for each possible camp site (Fig. 2). NOTE: the order is geographic from north to south.
Figure 2. Map of the Ross Sea sector of the Transantarctic Mountains. The region of interest lies between the Byrd Glacier and the Ohio Range and beyond to the Thiel Mountains (see Figure 1). Sites for possible Beardmore "South" and Shackleton camps are those used previously. Sites for other possible camps are approximate and would require detailed evaluation.
i) Nimrod Glacier. The Nimrod Glacier region has the most extensive exposures of basement rocks between south Victoria Land and the Scott Glacier region. It is a prime target for study because of the thick siliciclastic and carbonate sequences, the rich biota in the carbonate beds, the post-orogenic coarse clastic sequences, the cross-strike extent of the sequences, and the structural relations between them. Furthermore, high-grade metamorphic assemblages cropping out at the head of the Nimrod Glacier represent deeper crustal levels in the Ross Orogen. Ongoing studies may answer many of the questions raised.
ii) Beardmore Glacier region (Beardmore South camp). The Queen Alexandra Range has the most complete Gondwana sequence of any region in the Transantarctic Mountains. It is of prime importance paleontologically; every season of fieldwork, starting in 1969-70, has turned up new vertebrate material and new paleobotanical discoveries. It is a key area for establishing Gondwana paleoenvironments, from glaciation, through wet-temperate forested conditions, to drier alluvial plains. The recent discovery of fossil crayfish and fossil-bearing lacustrine beds provides an additional focus, as does the presence of sequences crossing the Permian/Triassic boundary.
It is also a key area for addressing the sequence of magmatic events following cessation of Gondwana sedimentation. It is the only region where silicic pyroclastic rocks preceding basaltic volcanism occur in situ, and thus the stratigraphic relations and tectonic settings can be clarified. The basaltic pyroclastic rocks have greater variety here than anywhere else in the Transantarctic Mountains; paleovolcanological studies on the extensive exposures will clarify and elaborate on the processes and environments preceding eruption of the flood basalts. In this region the extensive exposure of dolerite sills will facilitate studies on geochemical variability, magma transport and the magma plumbing system.
Landforms have been developed primarily on the Beacon. There are indications of relict pre-glacial surface events preserved in toreva blocks resting on mesa and butte topography. There are also numerous surfaces suitable for exposure age dating. An array of glacial deposits occurs in this region in different geomorphic settings and at different elevations.
Basement rocks exposed to the north of the Queen Alexandra Range provide a transect across the Transantarctic Mountains. This is a key area for understanding relationships between various crustal terranes and between various lithostratigraphic units. Much of this would be more easily accomplished from a camp adjacent to the Nimrod Glacier (see: i. Nimrod Glacier).
A camp in this region could provide a convenient staging post in support of the meteorite program.
iii) Mill Glacier. The upper Beardmore Glacier region has the most extensive Cenozoic glacial deposits south of McMurdo. The Oliver Bluffs region has been particularly important and still has much to offer. In the Mill Glacier region as a whole, there are large expanses of relatively flat terrain where other glacial deposits undoubtedly occur. These deposits will augment and build on the current database and yield much information on landscape evolution as well as glacial history. The possibility exists for developing a substantially larger database for interpretation of the landscape and glacial history and for comparison with other regions in the Transantarctic Mountains. Furthermore, inferred neotectonic displacements have been mapped on the Dominion Range and, given the significance of these features for uplift scenarios, need to be examined more closely.
iv) Shackleton Glacier. The frontal fault system, expressed by a series of tilted fault blocks from Cape Surprise southward for about 100 km, represents a prime target for investigating the structural evolution of the Transantarctic Mountains. Wide expanses of exposed rock in this region provide a prime target for landscape analysis. Inferred neotectonic faults reported from the head of the Shackleton Glacier are a significant target for structural studies related to the Late Cenozoic history of uplift and glaciation.
v) Scott Glacier region. This region provides the most extensive transect of the Transantarctic Mountains basement rocks apart from north Victoria Land. Although high-grade metamorphic basement (craton) is not exposed, all the components of the Ross Orogen are present and exposed over a wide area. It is the best place to conduct a geological transect of the range, with primary emphasis on the structural and tectonic history. Relatively short distance projection of the geological boundaries of basement rock units along strike will intersect corridors where oversnow and aerogeophysical traverses can be conducted parallel to Scott Glacier. The geophysical traverses can be linked to ongoing surveys in West Antarctica, and extended onto the polar plateau, thus contributing to the major transect corridors identified in previous reports (e.g., Polar Research Board, 1986; Wilson and Finn, 1996).
This region is key to distinguishing the geometry and kinematics of fault arrays related to Cretaceous and Cenozoic uplift episodes documented by fission-track data. The exposures of Cenozoic volcanic rocks may offer the opportunity to develop constraints on timing of faulting. This area, and the mountains to the east, are pivotal in establishing structural-kinematic links between development of the Transantarctic Mountains and motions of West Antarctic blocks, particularly the Ellsworth-Whitmore block.
This general region is also of prime importance for studies of Cenozoic glacial history. Sirius Group deposits are known (e.g., along the flanks of the Reedy Glacier), but require detailed studies. To date, geomorphological studies have been cursory; this region has extensive areas of outcrop and will provide a contrast and complement to the Beardmore-Mill Glacier region and to south Victoria Land where most landscape evolution studies have been conducted so far.
Knowledge of the Ferrar Dolerite in this part of the range is extremely limited; it is important for assessing geographic trends in geochemistry and time of emplacement, as well as the magma plumbing system. This region provides the link to the Dufek Intrusion and the Weddell Sea end of the Transantarctic Mountains.
Although only Permian Beacon strata (glacials to coal measures) are exposed along the plateau edge, those outcrops will yield critical information on the along-axis basin trends identified in the Beardmore-Shackleton region.
Because of the distance from McMurdo Station, a camp could facilitate support of the meteorite program, both in providing helo-supported reconnaissance of icefields as well as Twin Otter access to a variety of locations.
D. Community Action
The Workshop agreed that Letters of Intent from individual investigators and groups of investigators will be submitted directly to OPP. For major field camps, it is the intent that one scientist will co-ordinate Letters of Intent and provide an overview of the science that might be conducted and the logistics required. Letters of Intent will include, as appropriate: brief summary of the proposed science, the scale of logistics, preferred field year(s), and associated or related field projects.
A. Major Field Operations
Based on the expressed interests of participants in the workshop, and recognizing the logistics constraints imposed by rebuilding of South Pole Station, it is recommended that OPP announce that opportunities exist for helicopter-supported remote field camps.
Locations for possible Beardmore "South" and Shackleton Glacier camp sites are known quantities. The specific sites for possible camps in the other areas considered will require evaluation based on scientific need and logistics considerations. Suggested locations (see Table 2 and Figure 2) are not exclusive and specific scientific needs may well determine different sites.
B. Community Participation
It is recommended that OPP encourage individual investigators and groups of investigators to submit proposals that take advantage of the new and more cost-effective ways of conducting research in remote field areas.
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APPENDIX A - GROUP REPORTS
Basement Rocks of the Central Transantarctic Mountains (TAM)
Late Precambrian - Early Paleozoic
Compiled by: A.J. (Bert) Rowell
Discussants: John Encarnación, John Goodge, Anne Grunow, Tim Paulsen, and Terry Wilson
Introduction and Background
Recent studies of basement rocks near the Weddell Sea terminus of the Transantarctic Mountains challenge traditional interpretations for the origin and subsequent tectonic history of the east Antarctic cratonic margin (Rowell et al., 1994, 1997; Millar and Storey, 1995, Gose et al., 1997). Although it is probable that the SWEAT hypothesis (Moores, 1991; Dalziel, 1991, 1992; Hoffman, 1991) correctly describes first-order relationships among Proterozoic cratons, it is no longer clear whether the entire margin of the TAM was the product of Neoproterozoic rifting. Investigations in several sectors of the TAM also question the existence of a distinct Beardmore orogeny (Goodge, 1997; Rowell et al., 1997) and associated late Neoproterozoic magmatism (Encarnación and Grunow, 1996). Perhaps even more significantly, a clearer understanding of the timing of the Ross orogeny, the oldest of the Phanerozoic orogenies, is emerging (Rowell et al., 1992, 1997; Goodge et al., 1993).
Rifting and passive-margin sedimentation are characteristic features of the late Neoproterozoic to Cambrian period globally. During the Neoproterozoic, many thousands of kilometers of new continental margin were formed (Bond et al., 1984) by the breakup of the supercontinent Rodinia (Moores, 1991; Dalziel, 1991). Most of these margins continued in a passive state during the early Paleozoic and accumulated thick lower Paleozoic sedimentary successions as a consequence of thermal subsidence and lithospheric thinning that occurred during the rift phase. The Transantarctic margin of East Antarctica was unusual because, contrary to widespread opinion (Stump 1995), its passive-margin history was brief at best. By middle Early Cambrian time, subduction-related magmatism was widespread in the Queen Maud sector of the TAM (Rowell et al., 1995, in press; Encarnación and Grunow, 1995, 1996; Van Schmus et al., 1997), and although periods of relative tranquillity occurred at various places along the margin of the East Antarctic craton, it was an active margin for much of the Cambrian. Tectonic activity appears synchronous with Gondwana-wide consolidation. Folding and magmatism continued into the Early Ordovician as an expression of the Ross orogeny (Laird, 1981; Stump, 1995). In the Pensacola Mountains, however, it is now apparent that by the close of the Cambrian, orogenic effects were modest and that maximum deformation occurred much earlier during the mid-Early and early Middle Cambrian interval (Rowell et al., 1997). Data are permissive, but not conclusive, that this time period also witnessed maximum deformation in the Beardmore - Byrd sector of the range (Rowell et al., 1992).
Understanding the nature and timing of orogenic events along the Neoproterozoic to early Paleozoic active margin is critical to our global understanding of Cambrian sea-level changes and major episodes of biotic diversification and extinction (e.g., Kirschvink et al., 1997). To do this adequately, it is important to ensure that isotopic dates are tied to series and stage boundaries using the best possible correlations. Most major events in the lower Paleozoic are still expressed in terms of their position relative to stage and series boundaries (thus, the upper Toyanian extinctions and the early Middle Cambrian Hawke Bay event). Commonly a disconnect exists between these biostratigraphic events and magmatic or deformation episodes, which are normally measured isotopically. Can episodes of increased tectonic activity be correlated to abrupt changes in sea-level and accommodation known from many parts of the world? Is it possible to recognize a common driving force for abrupt changes in sea level, magmatism, and deformation? Were relative plate movements superimposed on true polar wander?
These are fundamental problems that need to be addressed and the Antarctic is seemingly one of the best places to address them. The active Antarctic margin was continuous with that of eastern Australia (Flottmann et al., 1993), yet despite extensive cover by ice and snow, outcrops in the Transantarctic Mountains are generally more revealing than those in Australia. No place in Australia, for example, affords documentation of Early and Middle Cambrian volcanic activity as well as the Queen Maud Mountains. Modern logistics available to USAP are adequate to overcome the problems inherent in remote field work and we believe the following objectives are attainable.
Critical Scientific Problems
The group focused its efforts on problems associated with initiation of sedimentation along the margin of the East Antarctic craton, together with its subsequent history prior to Devonian deposition of the unconformably overlying Beacon Supergroup. We recognize two general classes of problems of wide significance because they relate to processes that operate on a global scale. These processes are associated with large-scale plate motions and commonly initiate eustatic sea-level changes and associated biotic reactions that are potentially detectable over all the Earth. The third group of problems is of regional significance within Antarctica.
Problems of Global Significance
A. Inferred rift-margin phase
i) What was the Neoproterozoic geographic position of the TAM margin of East Antarctica relative to the other cratons (Laurentia in particular)? Given that the TAM contain one of the most extensive geologic records from the Neoproterozoic to early Paleozoic period in Antarctica, can we obtain reliable paleopole positions for the craton?
ii) When was rifting initiated? What lithostratigraphic units were deposited during this interval, what was their provenance, and what are their ages?
iii) What was the structural geometry of the rift margin? Has this inherited basement geometry controlled subsequent events?
iv) Can this rifting phase be correlated with well-known rift and passive-margin deposits of the Windermere Group or other units along the margin of Laurentia? Were the margins formerly contiguous?
B. Orogenic history
i) How many phases of deformation occurred and what was their timing?
ii) What was the style and geometry of deformation?
iii) For any given episode of deformation, how do geometry and timing vary along the length of the orogen? Is there evidence for postulated translation or partitioned oblique motion? What about syn-tectonic sedimentation?
iv) How did magmatism vary in composition, space and time? What was the role of magmatism in deformation and strain history?
v) What was(were) the inferred plate-tectonic setting(s) of orogenesis?
Problems of regional significance
C. Post-orogenic history
i) What were the magnitudes and/or rates of post-orogenic exhumation and denudation? By
what mechanism did post-orogenic exhumation occur? How much variation is recorded along the orogen?
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Goodge, J.W., V.L. Hansen, and N.W. Walker. 1993. Neoproterozoic-Cambrian basement - involved orogenesis within the Antarctic margin of Gondwana. Geology, 21, 37-40.
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Moores, E.M. 1991. Southwest U.S.- East Antarctic (SWEAT) connection: A hypothesis. Geology, 19, 425-428.
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The Role of Antarctica in Changing Global Systems as Shown by the Late Paleozoic and Early Mesozoic Succession:
"Icehouse" to "Greenhouse" Transition and Biotic Response
Compiled by : John L. Isbell
Discussants: Rosemary A. Askin, Loren E. Babcock, James W. Collinson, William R. Hammer, Molly F. Miller, Edith L. Taylor, and Thomas N. Taylor
Studies of Pangean rocks, primarily in Europe and North America, have shown that dramatic biotic changes and a climatic change from an "icehouse" to a "greenhouse" state occurred during the late Paleozoic and early Mesozoic. Because of the equatorial location of the Euramerican rocks, our understanding of the biotic and climatic record of Pangea is biased toward events that occurred at low paleolatitudes. Antarctica, however, provides a unique opportunity to study upper Paleozoic and lower Mesozoic rocks deposited in a polar and near-polar position. The thick succession of siliciclastic sedimentary rocks in the central and southern Transantarctic Mountains contains vertebrate, invertebrate, plant, and trace fossils that provide a nearly complete record of changing high-latitude conditions within southernmost Pangea. Fundamental questions concerning biotic evolution, the physical changes that occur during an "icehouse" to a "greenhouse" transition, paleoclimate, paleoclimatic models, and the tectonic evolution of southern Pangea can be addressed by studies of these rocks.
Pangea formed by the collision of Gondwanaland and Euramerica in the Carboniferous and by a collision with Siberia in the Early Permian (Ross and Ross, 1985; Veevers, 1988; Scotese and McKerrow, 1990). Surrounded by the Panthalassan Ocean, this supercontinent stretched from pole to pole. Pangea drifted northward throughout the Permian and Triassic, resulting in changing paleolatitudes for many sectors within the landmass (Scotese and McKerrow, 1990; Powell and Li, 1994; Ziegler et al., 1997). Antarctica, however, was unique within Pangea as it was located in a near-south-polar position throughout the supercontinent's northward drift.
Major changes in dominant fauna and flora occurred globally during the late Paleozoic to early Mesozoic, resulting in tremendous taxonomic diversification. Diversification occurred in spite of a major extinction at the end of the Permian. In the marine realm, Paleozoic faunas, dominated by complexly tiered, epifaunal suspension feeders, were replaced by a more modern-type fauna dominated by predators and a mobile, highly tiered infauna (Sepkoski, 1990). A parallel change in dominant elements in the terrestrial realm occurred in vascular plants and in tetrapods. In the latest Paleozoic, floras dominated by seed ferns and cordaites were replaced in the Mesozoic by conifers in the northern hemisphere and corystosperms in the southern hemisphere (Niklas et al., 1983). Also during this time, a late Paleozoic labyrinthodont, anapsid, and synapsid-dominated tetrapod fauna was superseded by a Mesozoic diapsid, dinosaur, and pterosaur-dominated fauna (Benton, 1985). Pangean floras display a change from low provinciality and broad latitudinal distributions during the Early Carboniferous (Raymond, 1985), to high provinciality with apparent latitudinal gradients during the Late Carboniferous and Permian (Ziegler, 1990; Ziegler et al., 1993; Hallam, 1994). Not enough studies of late Paleozoic terrestrial tetrapods have been conducted to define latitudinal zonations; however, early Mesozoic faunas appear to be dominated by cosmopolitan taxa (Shubin and Sues, 1991). Much of the work done on the biota of Pangea is from low paleolatitudes (e.g., Embry et al., 1994; Hallam, 1994). The role that high latitude communities played within Pangea is unclear at the present time. The study of high latitude late Paleozoic and early Mesozoic terrestrial fossils in Antarctica, which include decapods, tetrapods, and vascular plants (e.g., Babcock et al., 1996; Taylor and Taylor, 1990; Hammer, 1990; Hammer and Hickerson, 1994; Isbell et al., in press) may provide answers to this problem.
Within Pangea, Late Carboniferous and Early Permian ice sheets extended across much of the southern Gondwanan portion of the continent. Their waxing and waning resulted in cyclic sedimentation and peat accumulation in equatorial Euramerica (Veevers and Powell, 1987; Scotese and McKerrow, 1990). Extensive glacial deposits and cyclothems within Pangea suggest high latitudinal climatic gradients with mean annual temperatures colder than at present (Frakes et al., 1992; Ziegler et al., 1990, 1997). An absence of glacial deposits and associated ice rafted debris, coupled with widespread evaporites, red beds, and the expansion of carbonates (bioherms/reefs) during the Late Permian and Triassic suggest a warmer-than-present world climate punctuated with arid intervals (Parrish, 1990; Frakes et al., 1992). Although Late Carboniferous to Triassic climatic amelioration occurred within northward-drifting sectors of Pangea, a progressive change from glacial, to coal-bearing, to tetrapod-bearing fluvial deposits in Antarctica indicates that the polar regions also experienced a change from cold-glacial to warm-temperate conditions during the same interval (Collinson et al., 1994). The transition from glacial to post-glacial deposits represents a change from an "icehouse" to a "greenhouse" world (e.g., Fischer, 1981, 1984a, 1984b). However, present numerical simulations based on general circulation patterns and on energy balance models cannot explain the apparent latest Paleozoic and early Mesozoic climatic conditions in the south polar sectors of Pangea. The models suggest seasonal extremes in climate (Crowley et al., 1989; Kutzbach and Gallimore, 1989; Kutzbach and Ziegler, 1993), whereas the Antarctic rocks suggest temperate conditions (Collinson et al., 1994).
A complete picture of changing conditions within Pangea requires documentation of the rocks and fossils from low and high paleolatitudes. Because of late Paleozoic and early Mesozoic plate motion, most sectors of Pangea moved northward from one latitudinal and climatic zone to another. Antarctica's constant near-polar position was unique, which therefore makes it the best place in Pangea to investigate high latitude depositional, biotic and climatic conditions. Fundamental questions that can be addressed using such a "stable high latitudinal platform" include: 1) How did individual faunal and floral elements adapt to polar latitudes? 2) What role did high latitude communities play in terms of evolutionary innovations within the Earth's biota? 3) What changes were occurring within the polar landmass during the change from an "icehouse" to a "greenhouse" world? 4) What was the paleogeography of Antarctica like? 5) How can the physical and biological events within Antarctica be dated? and 6) How can geological and biological evidence be used to calibrate physical climate models? These questions are addressed below.
High Latitude Faunas and Floras as Sources of Evolutionary Innovation
Documentation of late Mesozoic and Cenozoic biota of the polar regions over the last century has shown that these areas have been home to thriving communities of organisms. In several examples (e.g., Hickey et al., 1983; Zinsmeister and Feldmann, 1984), groups of organisms described from polar regions predate their descendants in low latitudes by tens of millions of years. This concept (heterochroneity) seems to apply to a wide variety of terrestrial and marine organisms. Recognition of heterochroneity within various groups of organisms suggests that the high latitude regions have played an important role in the development and diversity of late Mesozoic and Cenozoic biotas (Zinsmeister and Feldmann, 1984). Rather than acting merely as conduits for dispersal (or, alternatively, as refugia from originally much larger geographic distributions), high latitude regions may have acted as major areas of biological innovation (Hickey et al., 1983; Zinsmeister and Feldmann, 1984).
The possibility exists that high-latitude-to-low-latitude dispersal patterns documented for the late Mesozoic and Cenozoic may have a parallel in late Paleozoic and early Mesozoic biotas. This would contrast with more conventional interpretations that low latitude areas acted as centers of most biological innovation (e.g., Schram, 1977; Olson, 1979). Conditions that facilitated heterochroneity during the late Mesozoic and Cenozoic (namely, land and sea masses near at least one pole, and access through biogeographic dispersal pathways to low latitude areas) were also present during intervals of the late Paleozoic and early Mesozoic. In particular, assembly of Pangea would have been favorable for the distribution of terrestrial organisms that originated in southern Pangea (present-day Antarctica). Oceanic circulation along the Pangean shelf may have facilitated dispersal of marine organisms from high to low latitudes.
One example of possible heterochroneity is exhibited in freshwater crayfish (Babcock et al., 1996). Early crayfish or their burrows are present in high latitudes of the Antarctic sector of Pangea, but the next-youngest occurrences are in low-latitude areas of Laurasia (present-day western USA). Antarctic specimens predate their North American descendants by about 65 million years. Crayfish, one of the most important animals in modern freshwater ecosystems, probably evolved from marine lobsters in southern Pangea and then dispersed through freshwater systems of Pangea prior to its breakup. It is our impression that, with further study, other such late Paleozoic-early Mesozoic examples of high-latitude-to-low-latitude dispersal patterns will be documented.
More important than simply documenting disjunct times of evolution or migration in high and low latitudes, however, is developing an understanding of the mechanisms or pathways of biological innovation in high latitudes. Climatic forcing, oceanic circulation, availability of sunlight, and other factors must be considered in the search for answers to this interesting problem.
High Latitudes as a Source of Information Concerning the Change
From an "Icehouse" to a "Greenhouse" World
Data summarized by Fischer (1981, 1984a) suggest that eustatic sea level, world volcanism, continental aggregation/dispersal, and global climate fluctuate in a 300-million-year-long supercycle. The supercycles may extend back 2 Ga, and depending on the criteria used to identify the cycles, they may range from 300 to 500 million years in duration (Fischer, 1981, 1984a; Worsely et al., 1984; Veevers, 1990). Fischer (1981, 1984a) divided the climatic cycle into an "icehouse" and a "greenhouse" stage. Icehouse conditions are characterized by continental glaciation, low stands of eustatic sea level, cold oxygenated deep waters, strong oceanic circulation, distinct latitudinal climatic gradients, little volcanism, and the existence of a supercontinent. Greenhouse conditions are characterized by high stands of eustatic sea level, high rates of volcanism, warm sluggish oceans, oxygen-depleted deep waters, indistinct latitudinal climatic gradients, and times of continental dispersion. Fischer (1981, 1984a, 1984b) attempted to link plate motion, biotic evolution, mass extinction and biotic innovations to these cycles, and to the transition points separating icehouse and greenhouse states. Possible causes of the supercycle include: 1) changing concentrations of CO2 in the atmosphere, 2) venting of mantle CO2 during increased plate activity, 3) plate motion and changing continental configurations, 4) variations in the amount of solar energy received by the Earth due to orbital perturbations, 5) changes in the frequency and intensity of solar radiation, and 6) variations due to galactic rotation (Fischer, 1984a; Veevers, 1990; Hallam, 1994; Wopfner and Casshyap, 1997).
The last complete icehouse-to-greenhouse cycle began 320 Ma with the formation of Pangea in the Carboniferous. Depending on how the icehouse-to-greenhouse cycle is defined, the cycle either ended 35 Ma at the Eocene-Oligocene boundary (Fischer, 1984a), or has continued on to the present (Veevers, 1990) . Within the last cycle, Fischer (1984a) and Veevers (1990) noted that the icehouse-to-greenhouse transition occurred during the mid-Triassic, just prior to the initial breakup of Pangea. Although icehouse and greenhouse intervals, and the crossover points between the two conditions, are thought to reflect the Earth's prevailing climate at the time, the stages and their boundaries are often more closely linked to plate motion and predicted climate than to the actual climatic record (Hallam, 1994). Major anomalies within the last cycle include: 1) the termination of Gondwanan glaciation during the mid-Permian, which occurred near the predicted glacial peak within the icehouse state; 2) the apparent warm/ice-free conditions from the Late Permian to the Early Jurassic, which occurred during the last half of the icehouse state and the beginning of the greenhouse state; and 3) the glacial activity (indicated by the presence of ice rafted debris) extending from the Middle Jurassic to the Early Cretaceous, which occurred within the greenhouse state (cf., Frakes et al., 1992). Although the supercycle model is appealing, the examples cited above suggest that the causes and timing of the icehouse-to-greenhouse transition are more complicated than the model suggests.
Antarctica's unique position in high latitudes during the late Paleozoic and early Mesozoic makes it the ideal platform from which to collect a database from the sedimentary record documenting the change from an icehouse to a greenhouse world. Establishment of such a database is critical in developing an understanding of the mechanisms driving Earth's large-scale physical cycles; in interpreting the biota's response to such changes; and in predicting future changes to the Earth's physical, chemical, and biological systems. Questions that should be addressed include: 1) How extensive were glacial and interglacial events? 2) How quickly did the glacial-postglacial transition occur? 4) What caused the final collapse of the Gondwanan ice sheet? 4) Were uplands still covered by ice following the collapse of the Gondwanan ice sheet? 5) Were the post-glacial rocks deposited in a lacustrine or marine environment? 6) How extensive were the water bodies and what effect did they have on climate amelioration? 7) Do the Permian coal measures and Triassic fluvial rocks display cyclicity that can be linked to Milankovitch cycles? 8) What was the climate during coal measure time? and 9) Was the Triassic as warm as the fossils and rocks suggest?
Late Paleozoic and Early Mesozoic Paleogeography of Southernmost Pangea
Upper Paleozoic and lower Mesozoic sedimentary rocks of the central and southern Transantarctic Mountains contain the biotic, climatic, and tectonic records of southern Pangea. These rocks form a 2.5- to 3-km-thick (composite section) succession exposed from the Byrd Glacier to the Ohio Range. The rocks consist of: 1) 0- to 710-m-thick Devonian to Carboniferous(?) shallow marine and nonmarine rocks; 2) 0- to 440-m-thick Upper Carboniferous to Lower Permian glacial-marine and glacial-terrestrial rocks; 3) 350-m-thick Lower Permian marine, deltaic, fluvial, and lacustrine rocks; 4) 750-m-thick Upper Permian fluvial, lacustrine, and deltaic coal measures; and 5) 0- to 1100-m-thick Triassic fluvial rocks. Although the Byrd to Shackleton area consists of terrestrial rocks, and the Ohio Range consists predominantly of marine rocks (e.g., Elliot, 1975; Aitchison et al., 1988; Barrett, 1991; Barrett et al., 1986; Collinson et al., 1994; Isbell et al., 1997), fundamental questions concerning the nature and the distribution of these rocks remain because large areas exist where sedimentologic and stratigraphic investigations were last conducted prior to the advent of modern sedimentologic, stratigraphic, and plate tectonic concepts (e.g., 1958-62, Ohio Range, Long, 1964; 1962-63, Mt. Weaver, Minshew, 1967; 1963-64, Axel Heiberg Glacier, Barrett, 1965; 1964-65 Wisconsin Range, Minshew, 1967; 1970-71 Nilsen Plateau; Coates, 1985).
Upper Paleozoic and lower Mesozoic rocks are similar throughout the central and southern Transantarctic Mountains, which has led to the conclusion that these strata accumulated within a single, elongate, depositional basin (e.g., Collinson et al., 1994). This basin may have formed the central portion of a larger depositional basin that stretched from South America to Australia (Veevers et al., 1994). Hypotheses on the origin and evolution of the Antarctic basin include development as: 1) a passive-margin basin, 2) a rift basin, 3) a back-arc basin, 4) a cratonic basin, 5) an ice-loaded basin, and/or 6) a foreland basin (Barrett et al., 1986; Bradshaw and Webers, 1988; Collinson et al., 1994; Woolfe and Barrett, 1995; Isbell et al., 1997). Investigators apply different conditions to their paleogeographic interpretations depending on which basin model they adopt (cf. Collinson et al., 1994; Woolfe and Barrett, 1995; Isbell et al., 1997a, 1997b). These assumed conditions and the resultant paleogeographic models then serve as a foundation for constraining interpretations of tectonic activity, biotic ecology, and evolutionary pathways, as well as modeling climate in southern Pangea. Every effort should be made to provide a database for accurate basin interpretations, thus strengthening our understanding of Antarctic paleogeography.
Isbell et al. (1997a) recently questioned the single basin hypothesis for the Devonian to Early Permian rocks, suggesting that a complex paleogeography with deposition in multiple basins occurred. If their assumptions are correct, then the similarity of rocks within the central and southern Transantarctic Mountains may in part be the result of a high latitude position rather than accumulation within a single basin. Collinson et al. (1994) and Isbell et al. (1997b) summarized the data that suggest the occurrence of a latest Paleozoic and early Mesozoic foreland basin. This hypothesis is largely accepted by the scientific community; however, it has not been tested on rocks outside the area located between the Byrd and Shackleton Glaciers.
Although the upper Paleozoic and lower Mesozoic rocks are known in a general way, many of the details have not been fully ascertained. Sedimentologic, stratigraphic, and basin analysis studies of these rocks are not only important in determining the depositional history, but are critical in establishing a foundation from which the tectonic, biotic, and climatic histories of southern Pangea can be interpreted.
A sound biostratigraphic framework is the fundamental requirement for evaluation of the nature and rates of evolutionary and sedimentary processes, biotic distributional trends, tectonic and climatic changes, and subsequent biotic responses. Biostratigraphic control of the predominantly terrestrial Paleozoic-Mesozoic succession in the central to southern Transantarctic Mountains rests on the terrestrial fossil record, which for these rocks includes mainly plant and vertebrate fossils. Because they are abundantly and widely distributed through a variety of rock types, and include distinctive species with relatively rapid evolutionary change, plant microfossils (spores and pollen from land plants) make ideal biostratigraphic tools, and have provided the most precise means of correlation in the region (e.g., Kyle, 1977; Kyle and Schopf, 1982; Farabee et al., 1990). Key evolutionary or extinction events in the vertebrate and plant megafossil record also provide good biostratigraphic markers, although these fossils, in particular the vertebrates, are not preserved throughout the succession, and indeed may not have lived in the region during certain intervals. Plant microfossils are the only fossils that can potentially provide a continuous record.
The primary goal of palynological studies is to improve and refine the current biostratigraphic framework. An initial palynostratigraphic zonation was proposed for southern Victoria Land (Kyle, 1977) and extended to the central and southern Transantarctic Mountains (Kyle and Schopf, 1982). Subsequent additional assemblages (Farabee et al., 1989, 1990, 1991; Masood et al., 1994) have furnished data for parts of the succession in the Beardmore Glacier area, as has more recent ongoing work in the Shackleton Glacier area (e.g., Askin and Cully, in press; Askin, in prep.) and reconnaissance work on the Nimrod Glacier area (Askin and Isbell, in prep.). The palynostratigraphic framework still, however, includes gaps where palynological data are scarce or lacking, and there are some details on distributional trends throughout the Transantarctic Mountains that have yet to be obtained or clarified. Based on previous information, much of which is of a reconnaissance nature and lacking detailed biostratigraphic coverage, several areas and units have been identified that should fill these gaps in our current knowledge (see Table in H below).
The only major drawback with using spores and pollen for biostratigraphy is that they, like all organic matter, are progressively altered and eventually destroyed by oxidative and thermal effects. This has meant that syndepositional oxidation (associated with soil and redbed development in the lower Fremouw Formation, for example), and thermal metamorphism during Jurassic volcanism and emplacement of dolerite sills, has destroyed the fossil record in some areas or in some units, or made the microfossils very fragile and corroded, opaque black, and difficult to work with. Detailed sample collection from a wide geographic area, and in particular those areas outlined in the above-mentioned Table (and already proven to yield good to excellently preserved palynomorphs), should yield a complete palynological succession. Furthermore, well-preserved material from other unexpected sources (such as the recycled Middle and Upper Triassic palynomorphs from Sirius Group sediments in southern Victoria Land; Askin and Fleming, in prep.) can also provide an excellent record of species not previously encountered in in situ samples.
Use of Geologic and Biologic Evidence in the Calibration of
Physical Climate Models
The Central Transantarctic Mountains area has been in the southern polar region since the Late Carboniferous. The Lower Permian-to-Jurassic Gondwana sequence in the Central Transantarctic Mountains and the Mesozoic sedimentary sequences in the Antarctic Peninsula region suggest that climates were generally, but not always, much warmer than at present. These sequences document the end of a major Permo-Carboniferous glaciation and the transition in the Late Permian to relatively warm climates that appear to have persisted throughout the Mesozoic during the breakup of Pangea. Paleomagnetic pole models place the Central Transantarctic Mountains area at high latitudes throughout this long interval of time. However, paleontologic data appear to contradict global climate models that predict great annual extremes in the southern part of the Pangean supercontinent.
We suggest a cooperative scientific effort in compiling a comprehensive database that will be used to determine the climate history of Antarctica. Investigators should represent varied scientific disciplines and perspectives. Any data that might have some bearing on paleoclimates should be included. These data could be used to improve climate models and perhaps resolve the paradox of relatively warm climates in polar regions. In addition to filling gaps in the paleontological record, it is essential that existing and future data be compiled in a chronostratigraphic framework. Stratigraphic sequences have been correlated only to the series level, with a precision no better than several million years. Better time control will be required to document short term changes in paleoclimate. Questions include: Were polar paleoclimates really as mild as present data suggest? Were polar paleoclimates continuously warm or were they generally much cooler and punctuated by short warm periods? How did fauna and flora cope with darkness and cold during the polar winter? What were local conditions that may have ameliorated the climate?
A multidisciplinary approach is required to address the problems described above. Although individual projects must stand on their own merits, only collaboration among groups and a sense of esprit de corps will result in the resolution of the larger-scale problems. The table below lists the individual disciplines and what each discipline contributes to resolving the problems outlined in this document. All disciplines listed contribute to the development of a climatic database.
Evolution and paleoecology of high latitude faunas, including animals having non-mineralized skeletons, and their evolutionary innovations.
Evolution and paleoecology of high latitude invertebrate faunas and their evolutionary innovations.
Evolution and paleoecology of high latitude floras and their evolutionary innovations.
Application of data to climate models
Climatic signatures contained within paleosols, paleoecology of terrestrial faunas and floras.
Biostratigraphy/time control, evolution of high latitude floras and their reproductive evolutionary innovations.
Depositional, tectonic, and paleoecologic control; local and regional correlation of events.
Evolution of high latitude tetrapod faunas and their evolutionary innovations; paleoecology.
Rationale for Studies in the Central and Southern Transantarctic Mountains
Antarctica's Carboniferous-to-Triassic polar and near-polar position makes it the most significant continent on which to search for high-latitude, biologic and environmental signatures within the late Paleozoic and early Mesozoic rock record. Within Antarctica, the thickest and most complete Devonian to Upper Triassic rocks are exposed in the central and southern Transantarctic Mountains. There, composite exposures consist of a nearly complete 2.5- to 3-km-thick succession of rocks that consist of: 1) Devonian rocks deposited during a greenhouse state; 2) Upper Carboniferous to Lower Permian glacial rocks deposited during an icehouse state; 3) Lower Permian to upper Permian marine and terrestrial rocks deposited during an icehouse-to-greenhouse transition; and 4) Upper Permian to Jurassic terrestrial rocks deposited during a greenhouse state. Significant fossil faunas and floras contained in these rocks include: 1) a diverse Devonian marine fauna, 2) the oldest freshwater decapod fossils, 3) evidence for interglacial and postglacial faunal recolonization and diversification, 4) one of the southernmost fossil floras ever described, including the highest latitude fossil forests and Permian and Triassic silicified peat localities, 5) the southernmost Triassic and Jurassic tetrapod faunas, which includes the southernmost Lystrosaurus and Cynognathus faunas, the southernmost dinosaur and pterosaur faunas, and the oldest known allosaurid dinosaur. Within the central and southern Transantarctic Mountains, the Amundsen and Scott Glacier area separates Devonian to Lower Permian marine rocks in the Ohio and Wisconsin Ranges from nonmarine rocks exposed in the area between the Byrd and Amundsen Glaciers. Due to this regional segregation of rocks, a comparison of the biotic and environmental polar signature contained within both marine and nonmarine deposits can also be addressed. Because of the completeness of these rocks and their contained fossil faunas and floras, the central and southern Transantarctic Mountains are the single most important sites on Earth for addressing late Paleozoic and early Mesozoic biotic and environmental changes from a polar perspective.
Priorities -- Central and Southern Transantarctic Mountains
The table below lists areas in the central and southern Transantarctic Mountains where the objectives of this multidisciplinary work can best be addressed. The list is arranged from highest to lowest priority. The list also provides rationale for each area's ranking.
1. Beardmore Glacier
a. Thickest and most complete stratigraphic succession.
b. Best preserved Permian to Triassic fossil floras including silicified peat and fossil forests.
c. Best preserved Permian, Triassic, and potentially Jurassic palynofloras.
d. Diverse Triassic tetrapod faunas.
e. Jurassic dinosaur and fish faunas.
f. One of the best glacial to post-glacial transitions in Antarctica.
g. Diverse Permian to Jurassic ichnofauna.
h. Excellent Permian to Jurassic paleosols.
2. Amundsen/Scott Glacier
a. Thick succession of Permian and Triassic rocks.
b. The transition zone between marine and nonmarine environments.
c. Well preserved fossil forests.
d. Diverse Permian palynofloras
e. Diverse Permian to Jurassic ichnofauna.
f. Possible Permian tuff beds.
g. Possible Triassic tetrapod faunas.
3. Ohio to Wisconsin Range
a. A thick Devonian to Permian section .
b. Proximity to the Panthalassan Margin and may contain a distinct tectonic signature not seen elsewhere in CTM and STM.
c. Devonian to Upper Permian marine and deltaic rocks.
d. Glaciomarine to marine transition.
e. Diverse Devonian marine faunas.
f. Diverse Devonian to Permian palynofloras.
4. Byrd to Nimrod Glacier
a. Thick Devonian to Upper Permian rock succession.
b. Thickest Devonian section.
c. The best exposure of rocks in CTM and STM that were deposited on the cratonic side of the basin.
d. Best preserved Permian palynofloras owing to fewer dolerite sills.
e. Oldest silicified peat in Antarctica.
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Mesozoic-Cenozoic Tectonics of the
Central and Southern Transantarctic Mountains
Compiled by: David H. Elliot and Terry J. Wilson
Discussants: Robin Bell, Tom Fleming, Philip Kyle, B. Marsh, Ralph von Frese, and Philip Wannamaker
The Transantarctic Mountains (TAM) form one of Earth's major intraplate mountain belts (Dalziel and Elliot, 1982). The evolution of the TAM, stemming from the time of break-up of Gondwanaland, reflects regional- and global-scale processes. This starts with the initial fragmentation within the broader context of the Gondwana plate framework, and is recorded in the Ferrar tholeiites and their tectonic setting. The East-West Antarctic intraplate boundary was initiated at that time. Another aspect is development of that intraplate boundary and West Antarctic rifting, with accompanying inversion of the break-up rift to form the present mountain belt. Uplift of the range is also linked to the initiation, growth and fluctuations of the Antarctic icesheets. All these aspects have significance outside Antarctic earth sciences.
A comprehensive evaluation of the geodynamic evolution of the Transantarctic Mountains and associated West Antarctic Rift System, together with recommendations for research throughout that region, was presented in a recent workshop report (Wilson and Finn, 1996). This section deals with only part of that region, the central and southern Transantarctic Mountains, and identifies specific areas where particular problems might be addressed.
I. Ferrar Magmatic Province
The Ferrar tholeiites constitute the magmatic rocks in Antarctica associated with the initial rifting of Gondwanaland (Elliot, 1992). Recent zircon and baddeleyite dating (Encarnación et al., 1996) shows that the Ferrar is contemporaneous with a major part of the Karoo (Duncan et al., 1997), and preliminary dating of the Vestfjella lavas suggests their contemporaneity with the Ferrar. Further, 40Ar/39Ar dating and geochemical studies (Fleming et al., 1997) suggest that the Ferrar was derived from a single source which was most likely related in some manner to the inferred break-up plume centered in the region of Queen Maud Land and the adjacent coast of Africa (White and McKenzie, 1989; Storey, 1995). The Jurassic tholeiitic magmatism along the margin of the East Antarctic craton is an integral part of the break-up process.
The principal questions concerning the Ferrar relate to the petrogenetic processes, geochemical variability, transport of magmas for thousands of km and emplacement either in supracrustal rocks or at the surface, and the tectonic setting. Petrogenetic studies have been hampered by the fact that even the most mafic Ferrar rocks, with about 9% MgO, carry a significant crustal imprint. Therefore, unraveling the contributions of the asthenospheric mantle, lithospheric mantle, and crust, and the processes involved, has been problematic. Although a substantial body of data (Fleming et al., 1995 and references therein) exists for the extrusive rocks, the geochemical variability of Ferrar Dolerite sills and dikes (Fleming et al., 1997) are poorly documented outside Victoria Land. For instance, it is not known whether there are along-strike systematic changes, subtle or otherwise, in isotope and trace element compositions.
The source location is likely to have been in the Weddell Sea region (Fleming et al., 1997; Minor and Mukasa, 1997). Such a location implies magma transport for great distances, and in fact somewhat greater than those for the well-documented Mackenzie Dyke Swarm (Baragar et al., 1996). Magma transport was most likely at mid to upper crustal depths, with final dispersal and emplacement involving magma migration directly to the surface as well as supracrustal transport, as shown by the numerous sills within the Beacon sequence. The significance of the Dufek layered basic intrusion in the Ferrar magma system is unclear; it has been postulated to be the proximal source for all Ferrar magmas rather than a discrete and isolated plutonic body. The plumbing system for the Ferrar tholeiites is essentially unconstrained.
Structural studies on Ferrar dikes (Wilson, 1992, 1993) have demonstrated a stress field interpreted to indicate extension perpendicular to the trend of the Transantarctic Mountains. Petrologic, paleovolcanologic and other data suggest a rift setting into which the extrusive Ferrar rocks were erupted (Elliot, 1992, 1996; Elliot and Larsen, 1993; Hanson and Elliot, 1996). The regional extent of the surface expression of rifting is indicated by sparse and fragmentary supporting data from Victoria Land.
B. Key questions
Understanding of the Ferrar magmatic province requires information on:
1. Geochemical variability. What is the compositional variation of the Ferrar dolerites on a regional scale? Nd model ages of the crust vary along the length of the Transantarctic Mountains (Borg et al., 1990); is there a geochemical signature related to the crustal ages? Are there patterns of compositions that suggest local centers of emplacement or distinct phases of emplacement? Do any such patterns indicate magma transport effects or source region evolution (as has been suggested for the Mackenzie Dyke Swarm; Baragar et al., 1996)?
2. Regional magma budgets. Generalized estimates of volumes have been presented for the Dufek intrusion, Ferrar Dolerite and Kirkpatrick Basalt (Ford and Himmelberg, 1991; Kyle et al., 1981; Fleming et al., 1997). Within the limitations of the rock exposure, what are the volumes in the various sectors of the Transantarctic Mountains? Is there any regional pattern? Do the patterns reveal information about the plumbing system?
3. Regional plumbing system. The Ferrar Magmatic Province is over 4,000 km long; if not derived from a whole series of local mantle sources, then it implies transport even farther than the Mackenzie Dyke Swarm. How were Ferrar magmas transported through the crust over such long distances? Was a feeder dike swarm responsible for lateral transport or could magma have been transported via massive sills? Can consistent regional patterns of flow from the Weddell Sea region be established? What is the role of the Dufek intrusion in the plumbing system?
4. Local sources for supracrustal dispersal. Detailed studies in the Dry Valleys (Marsh, 1996) have documented vertical magma transport and lateral dispersal in a series of sills, as exemplified by the Basement Sill. Are there regions, other than the Dry Valleys, where evidence exists for rise of large volumes of magma through the basement rocks and emplacement supracrustally? Is there evidence for shallow depth magma chambers, such as suggested for the Butcher Ridge region (Behrendt et al., 1995) or might be inferred from layered dolerite intrusions such as the Warren Range? How do such centers link into a regional plumbing system?
5. The nature and extent of the rift topography and associated structural and tectonic features. The basaltic pyroclastic rocks underlying the flood basalts are probably the largest and most extensive basaltic phreatomagmatic field on earth. Are there features of this field of explosive volcanism that will further constrain the eruptive paleoenvironments? Are there any features indicating actual eruptive centers? Are there structural features, such as the monoclines observed in the Queen Alexandra Range, that will help constrain the location of rift valleys?
C. Study localities
Addressing these problems requires well-focused regional surveys and detailed studies in restricted areas. The outcrop pattern indicates that intensive studies will likely be most informative in the region from the Queen Alexandra Range to Nilsen Plateau, with those two areas as potentially the most rewarding.
1. The Queen Alexandra Range has the only complete and almost continuously exposed stratigraphic section from the basement to the Jurassic lavas. The estimated thickness of dolerite sills is more than 1,000 m and comprises at least six major sills. The section from the uppermost Beacon to the basalts is well exposed. The range in geochemistry of the sills and dikes in a single region can be addressed as well as lateral homogeneity and extent of individual sills. Magnetic anisotropy measurements and petrofabric studies may offer a way of establishing magma transport directions and thus possible locations of feeder systems. The relations between the Beacon Supergroup and the younger silicic and basaltic rocks is better exposed here than anywhere else in the whole of the Transantarctic Mountains. The inferred unconformities between the Beacon, the overlying Hanson Formation, and the Prebble Formation can be clarified and the possible geographic extent of Jurassic vertical tectonism addressed through sandstone petrology. Furthermore, more detailed studies of the paleovolcanology of the phreatomagmatic rocks of the Prebble Formation offer the possibility of developing the setting within which those rocks were erupted.
2. Nilsen Plateau has a section extending from basement granite to the Lower Triassic Fremouw Formation. A number of thick sills cut the Beacon rocks as well as the basement. These rocks include some of the few known Ferrar olivine dolerites and offer the possibility of extending the range of dolerite compositions to higher MgO contents.
3. The Shackleton Glacier region also has extensive exposures of sills. As in the Queen Alexandra Range, vertical and lateral variations in geochemistry can be addressed, as well as magma transport directions.
4. The Ohio Range region, from the Horlick Mountains to the Thiel Mountains, bridges the 1,000 km gap between the Dufek intrusion and the Nilsen Plateau, and thus may provide a key link between the Weddell Sea region and the Ross Sea sector of the Ferrar province. Although sills have very limited occurrence, they are important for assessing regional geochemical trends and plumbing system characteristics.
D. Geophysical approaches
Geophysical potential field methods offer a way to establish the existence of gabbroic bodies at shallow depth, the extent of Ferrar Dolerite sills beneath the polar ice sheet, and the existence of major dike swarms if at sufficiently shallow depth.
1. Gabbroic bodies. Shallow magma chambers may be an important part of the Ferrar plumbing system. Location of such bodies will aid in determining dispersal paths.
2. Lateral extent of Ferrar sills. Ferrar outcrops terminate at the Transantarctic Mountains Front, but originally they must have extended beyond that boundary; if still present, Ferrar rocks are most likely to be found in the deepest parts of the rifts in the Ross Embayment. On the other flank the Beacon Supergroup and Ferrar sills are thought to extend beneath the icesheet; magnetic data from south Victoria Land (ten Brink et al., 1997) suggest sub-glacial extension of the Ferrar for 200-300 km, and sub-glacial topography provides strong evidence for extension toward the South Pole from the Scott Glacier region (Drewry, 1972). Assuming that sills or their edge effects can be detected beneath increasing ice thickness, their regional extent beneath the icesheet would be important information for mapping distributions and assessing volumes.
3. Major dike swarms. The principal mode of long distance magma transport is through major dike swarms. These have not yet been identified but if magma was transported at shallow depths through dikes, then a regional linear anomaly pattern might be observed. The identification of such dike swarms would be significant for understanding the Ferrar plumbing system and magma dispersal.
II. Structure and History of the Transantarctic Mountains
The present mountain range forms one flank of a major intraplate boundary, separating the Precambrian craton margin with normal crustal thickness (40 km) from the thinned crust (20-30 km) of West Antarctica (Bentley, 1991). In this context, the Transantarctic Mountains are linked to the formation of the Weddell and Ross embayments and the Ellsworth-Whitmore block translations and rotations (Dalziel and Elliot, 1982; Grunow et al., 1991; DiVenere et al., 1994). Similarly, the mountains are part of a linked system of uplift and basin formation in West Antarctica and possibly on the craton but with vastly different characteristics. A variety of models have been proposed to explain these relationships (Fitzgerald et al., 1986; Stern and ten Brink, 1989; Fitzgerald and Baldwin, 1997), but no single model accounts for these Antarctic extensional provinces which are on the scale of the Colorado Plateau and the Basin and Range Province.
The basic architecture of the range is still poorly understood, and in the central and southern Transantarctic Mountains the only modern data have been collected in the Queen Alexandra Range region (Wilson, 1992,1993). Many of the faults have been inferred from stratigraphic and fission track studies. Offsets on individual faults range up to several hundred meters; the timing of movement is essentially unknown although faults on the Dominion Range at the head of the Beardmore Glacier have been interpreted to be younger than 3 Ma (McKelvey et al., 1991; Webb, 1990). There are only limited data on the structure of the TAM front; frontal faults are inferred but documented in few places. Faulting of Beacon strata in the Shackleton Glacier region, including the major offset at Cape Surprise (Barrett, 1965), is the only known occurrence outside south Victoria Land that can be directly associated with the TAM Front. Although it appears that Cenozoic frontal faults in south Victoria Land are oblique (Wilson, 1995), whether they are longitudinal or oblique on a regional scale is unknown. Faulting has also been recorded in the Scott Glacier region (Fitzgerald and Stump, 1997) but fault orientations and kinematics are unclear. Similarly the widely-inferred transverse segmentation of the mountain range is poorly documented. Significant offsets of the pre-Beacon erosion surface (Kukri and Maya Erosion Surfaces) are apparent only at the Byrd and Nimrod Glaciers, although probably present elsewhere. The transverse segmentation may be associated with significant differences in basement geology and history, for example the changes in basement lithologies across the Scott and Byrd glaciers, and thus be controlled by inheritance from the Ross Orogen.
b. Key questions
Understanding the basic architecture and evolution of the range requires information on:
1. Fault geometry and kinematics. What are the regional fault orientations and senses of movement? Do the faults form arrays that can be tracked along the mountain range? Are there transverse faults segmenting the range? How do any arrays relate to the basement and Gondwana geology? Do the fault arrays yield information on the kinematics? What kinematic episodes are recorded by the fault arrays? What is the structure of the "craton" margin of the mountains?
2. Timing. Can fault arrays be dated directly by association with Ferrar rocks and, at the head of the Scott Glacier, with Cenozoic volcanic centers? Can fault arrays be dated radiometrically by the secondary minerals on fault surfaces? Can the timing of faulting episodes be correlated with the uplift episodes? Are neotectonic faults cutting glacial deposits widespread on Cenozoic landscape surfaces?
B. Uplift history
The history of denudation, and by inference uplift, has been established by apatite fission-track dating. An Early Cretaceous episode has been documented in the Scott Glacier region (Fitzgerald and Stump, 1997) and is possibly linked to slightly older denudation in the Ellsworth Mountains (Fitzgerald and Stump, 1991). Late Cretaceous episodes are inferred for the Scott Glacier region and the Miller Range (Fitzgerald, 1994). The best documented episode started in the Eocene (55-50 Ma) and in addition to the Scott and Beardmore glacier regions, is known throughout Victoria Land (Fitzgerald, 1992; Fitzgerald and Gleadow, 1988). As much as 4 km of Miocene denudation has been demonstrated for the mountain front near the Beardmore Glacier (Fitzgerald, 1994). Fission track data indicate different histories of uplift for various segments of the Transantarctic Mountains and support inferences about tectonic segmentation. The products of denudation reside in flanking sedimentary basins, but even their existence is poorly documented.
b. Key questions
Understanding the uplift history and linkages to the associated sedimentary basins requires information on:
1. Timing. Can fission track dating and Ar/Ar dating of low temperature minerals provide better constraints on the onset of denudation episodes? Can they constrain the duration of such episodes?
2. Thermal structure. Can radiometric and fission track methods constrain the thermal structure at times of denudation? Can the thermal structure shed light on the processes of uplift?
3. Denudation processes. Sedimentary basins contain most of the record of denudation events and hence should be drilled, but are there landforms, and possibly remnant associated alluvial sequences, that can be tied to specific events?
4. Landscape evolution. Can exposed and subglacial landscape features document neotectonic uplift patterns? Do they demonstrate differential uplift between discrete segments of the mountains?
C. Study localities
These problems require an array of regional and focused studies. These include: determining the geometry and kinematics of frontal and transverse fault arrays; establishing any relationships between faulting and basement geology (inheritance); mapping the sub-ice extension of tectonic boundaries and structural trends; documenting neotectonic faulting and landscape surfaces; obtaining more detailed thermochronologic data on uplift history; and stratigraphic sampling of sub-ice basins.
1. The Scott Glacier region has the greatest exposure of basement rocks transverse to the range. This region has been investigated from the perspective of the evolution of the Ross orogen and the uplift history of the range. This region provides the opportunity to investigate Jurassic and younger structures, including variations along and across strike. This region also has the only known Cenozoic alkaline volcanic rocks outside Victoria Land. Although investigated from the petrological and age perspective, relationships to regional structure are not well documented. The region from Scott Glacier eastward is key to understanding links with rifts in the Weddell region, including motions of the Ellsworth-Whitmore block, and also to establishing the nature of the "southern" termination of the West Antarctic rift shoulder.
2. The Shackleton Glacier region has the most extensive array of offset Beacon strata in the whole of the Transantarctic Mountains. The Beacon rocks occur in back-tilted fault blocks with offsets of several hundred meters, and in the case of Cape Surprise as much as a cumulative 5,000 m. Analysis of structures in a transect across the range offer the possibility of documenting the frontal fault system in detail. Neotectonic structures have been reported on Bennett Platform and Roberts Massif and deserve detailed investigation.
3. The Nimrod Glacier region includes the only high-grade metamorphic terrain between the Shackleton Range and north Victoria Land, a wide variety of pre-Devonian basement strata, and the single greatest vertical offset of the Kukri/Maya Erosion Surface. The basement rocks provide the opportunity for structural analysis of faults in varying basement rock types, with respect to frontal faults and vertical faults parallel to the plateau margin, and with respect to a transverse system along the trend of the Nimrod Glacier.
4. The Byrd Glacier region appears to mark an accommodation zone where the frontal fault system steps eastward about 50 km. The nature of this zone can be addressed by structural studies adjacent to the Byrd Glacier.
5. The Mill Glacier region includes the Dominion Range where neotectonic faults with throws of several hundred meters have been reported. These and other structures cutting the extensive Cenozoic surfaces need to be analyzed in order to address questions of late Cenozoic uplift as well as faulting on the "inner" flank of the mountain range.
D. Geophysical approaches and targets
The gross characteristics of the sedimentary basins inferred to lie beneath the polar ice cap (the Wilkes-Pensacola Basin) and adjacent to the mountain front can be assessed by geophysical methods. Previous work has shown that there is no major basin beneath the Ross Ice Shelf immediately adjacent to the mountain front in the Nimrod-Beardmore sector and that if a recently active frontal fault system exists it lies offshore, not along the physiographic front (ten Brink et al., 1993). Recent work in south Victoria Land (ten Brink, et al., 1997) has lead to the conclusion that a significant thickness of sediment in the Wilkes Basin is not required by geophysical data.
b. Study localities
The regional magnetic and gravity structure of the range and adjacent sub-ice regions are known only from reconnaissance studies and satellite-derived potential field measurements (Bentley, 1991; Alsdorf et al., 1994). Magnetotelluric measurements provide a method of assessing the lithospheric contrasts between the Ross embayment and the East Antarctic craton. Transect and local detailed geophysical surveys are required to address these and other problems.
1. Scott Glacier region. The extent of bedrock outcrop transverse to the range makes this an ideal region for a transect from within the Ross Embayment, across the TAM and out into the Wilkes-Pensacola Basin. This will link up with ongoing surveys in the Ross Embayment and be part of a major crustal transect which will encompass sedimentary basins and the linked TAM uplift, the structure of the mountain range, the faulted or flexural nature of the "backside" margin, and the inferred Late Mesozoic-Cenozoic cratonic basins. Because of proximity to ongoing experiments, the Scott Glacier region is the place to conduct magnetotelluric surveys. Aeromagnetic mapping can be used to establish the regional extent of Cenozoic volcanism.
2. Shackleton Glacier region. The known frontal faulting suggests that a detailed grid from the mountain front out over the Ross Ice Shelf will define a significant segment of the frontal fault system and any associated sedimentary basin.
3. Nimrod-Beardmore segment. This is the only region between the Leverett and Skelton Glaciers where it is possible, with along-strike offsets, to conduct a surface traverse that crosses the range. It is an ideal location for a combined surface and aerogeophysical transect across the East-West Antarctic crustal boundary.
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Cenozoic History of the Transantarctic Mountains
I. Landscape Evolution
Key geomorphological and stratigraphic evidence for the evolution of the ice sheet occurs along the length of, and at nearly all elevations in, the Transantarctic Mountains. Therefore, the development of these two major physical features are intertwined and also linked to the evolution of polar climate in Antarctica.
The key linkage comes from the growing awareness that many of the landscapes of the Transantarctic Mountains are extraordinarily old, perhaps the most ancient on the planet. These macro-landscape elements consist of mountains, valleys, plateaus, escarpments, and buttes. The idea is that these features ceased to form actively once the freeze-dry conditions of the current polar desert were imposed on the continent. The only major erosion since that time may have been beneath outlet glaciers. There are now increasingly reliable data from the Royal Society and Dry Valleys blocks that polar desert conditions (and a virtual halt in denudation) date back at least to 17 million years ago. There are suggestions that such old landscapes also characterize northern Victoria Land and the Beardmore-Shackleton Glacier area. It should be emphasized that micro-landscapes can continue to be active in some places under polar conditions where contraction cracks form, where rock glaciers develop, and where salt weathering occurs. But these processes produce little denudation.
The major implication of this discovery is that old glacial deposits dating back at least into the early Miocene -and probably much earlier- are preserved both as unconformable erosional remnants on ancient high surfaces and as a conformable mantle on present-day valley floors and walls. The relative age relations of these deposits can be determined from a careful landscape analysis of the Transantarctic Mountains. An obvious example would be that the erosional remnants of basal Sirius till perched on high peaks and shoulders of the mountains are older than the valley wall remnants that occur much lower in the topography. To assign them all one age on the basis, for example, of their diatom content, does not make sense from the viewpoint of landscape analysis. Much more subtle differentiation can also come from detailed examination of glacial deposits and associated landscape elements. For example, some lower remnants occur on the older gentler parts of valley walls that, in turn, are cut by younger steep walls that again have remnant glacier deposits.
Any landscape analysis should be tied in closely with the structural geology, so that both the structural and landscape features can be put in a relative sequence. For example, the major frontal fault scarps in the Dry Valleys and Royal Society Range are rectilinear slopes with very old surface ages of at least middle to early Miocene. In contrast, there are relatively fresh but small fault scarps cut into the Miocene landscape of the foothills of the Royal Society Range. Also, there are fresh fault scarps cut into moraine sequences (including one scarp with a rotational slump block that still carries dislocated moraines) in the Meyer Desert near Beardmore Glacier. It would be a simple matter to determine the age of this young faulting from exposure dates of faulted and unfaulted moraines. Numerous such examples can be cited.
There has been another breakthrough. The means are now at hand to obtain minimum dates of the old landscapes. The first is to date with the 40Ar/39Ar technique individual feldspar crystals of airfall volcanic ash deposits on the old landscapes. The second is to exposure-date the dolerite surfaces on the old landscape by using the noble-gases (3Ne and 21Ne) accumulated in pyroxenes. Such exposure dates using noble gases now commonly extend well back into the Miocene. Hence a combination of landscape analysis and exposure-age dating can be applied along the length of the Transantarctic Mountains, thus linking geomorphic and tectonic development of the mountains at least for the Neogene. An additional benefit will automatically fall out of this approach. Namely, the Sirius outcrops will have a number of exposure dates that will immediately show whether all such deposits are truly Pliocene in age.
A new model being developed views the shape of a mountain range as involving the interaction of tectonic forces, climate, and denudation. Isostasy links the internal tectonic evolution to the external geomorphologic evolution. The geomorphologic development can accelerate or delay uplift. It can speed up or slow down tectonic processes. It is critically linked to climate. Hence there is a complex set of feedbacks among tectonics, climate and denudation. This approach can be initiated by extensive mapping of landscape elements in the Transantarctic Mountains. This would be especially important if the major geomorphologic elements dated well back into the Miocene. Along with apatite fission-track profiles, this would place severe age constraints on the timing of major denudation across the mountain front. The glacial landforms and Sirius outcrops can then be placed in the context of these landscape elements. The landscape surfaces (and hence timing of denudation) can be dated by exposure ages using noble gases in pyroxenes. Fission-track analyses can also constrain the timing of denudation. Long-term climate can be deduced from diagnostic periglacial features and from fossils on the landscape. The resulting analysis of landscape and climate can be linked with the results from sediment cores from basins in front of the Transantarctic Mountains. These data can then serve as input into tectonic models of rift settings to explore the role of processes which may explain the elevation of the Transantarctic Mountains. Such processes may involve asymmetric rifting associated with crustal Antarctica, and lateral heating from the thinned Ross Sea crust; flexural effects resulting from lithospheric necking; or uplift due to flexure as a result of differential denudation across the craton margin.
II. Cenozoic of the Transantarctic Mountains
Compiled by: Allan Ashworth
Discussants: Allan Ashworth, Rosie Askin, David Elliot, Ralph Harvey, David Harwood, Larry Krissek, Mark Kurz, Tom Lowell, Molly Miller, Greg Retallack, Gary Wilson, Peter Webb
Significant events in Antarcticas Cenozoic development are the establishment of a circumpolar oceanic circulation, the initiation of glaciation in the Oligocene, uplift and denudation of the Transantarctic Mountains (TAM), the establishment of a polar desert climate, and the virtual extinction of a biota. These events are probably linked in a complex feed back system but at this time critical pieces of evidence needed to build a process model are either missing or are controversial. For example, the initiation of a polar desert climate is interpreted to occur before 17 million Ma, at 9 Ma, or after 3 Ma. Oxygen isotope evidence from the oceans implied that large ice sheets had existed from the Middle Miocene until the present day without any major changes in ice volume (Shackleton and Kennett, 1975). The hypothesis for stability has been challenged in recent years by a hypothesis that the ice sheets have been more dynamic through most of the Neogene and that polar desert climate of today did not come into existence until after an episode of global warmth during the Pliocene. There have been a number of different reviews of the controversy, from various points-of-view (e.g. Denton et al., 1993; Van der Wateren and Hindmarsh, 1995; Kennett and Hodell, 1993). It is, nevertheless, difficult to reconcile the different conclusions that have been reached by a diverse group of researchers who have applied a variety of methods to the problem, including geomorphology, marine isotopes, radiometric dating, and biostratigraphy (Harwood and Webb, 1998; Miller and Mabin, 1998; Stroeven, et al., 1998). One reason for this difficulty is that key evidence has often been obtained from remote sites in the TAM (e.g. Beardmore Glacier) which few investigators have been able to visit. Another reason is that different methods have been applied to different field sites, making comparisons impossible. One major goal of future studies should be to provide access to the key sites in order to reconcile the different interpretations. What then are the differences between the two mutually exclusive hypotheses?
Stable v. Dynamic Ice Sheet Hypotheses
Briefly, proponents of the stable ice sheet hypothesis infer that surfaces and slopes of the Dry Valleys region have remained virtually unchanged for about 17 Ma, frozen in time by the ultra-cold and xeric polar desert climate (see Denton, these proceedings). They support their arguments with 40Ar/39Ar dating of volcanic ashes (Denton et al., 1993; Marchant et al., 1993; Sugden et al., 1995a; Sugden et al., 1995b; Marchant and Denton, 1996; Marchant et al., 1996). The argument for stability was bolstered with a report that glacier ice had survived 8.1 Ma (Sugden et al., 1995b), although such old fossil ice is difficult to reconcile with actual sublimation rates for the Dry Valleys (Van der Wateren and Hindmarsh, 1995). The marine record is also interpreted to represent relatively stable conditions since the Miocene, although apparently not as stable as the surfaces and landforms of the Dry Valleys just discussed. Oxygen isotopes from the Southern Ocean for the Pliocene warm episode are interpreted to represent sea surface temperatures about 3C warmer and sea level about 25 m higher as a result of melting of the ice sheets. Other lines of evidence cited for relative stability in the oceans around Antarctica during the Pliocene are the relative stability of 13C values, the continuation of deposition of ice rafted debris, and the inference that waters never became warm enough for Subantarctic planktonic assemblages to replace Antarctic ones (Kennett and Hodell, 1993).
Proponents of the dynamic ice sheets hypothesis have a very different interpretation. According to them, the Antarctic ice sheets were much smaller during the Pliocene warm interval. The outlet glaciers behaved more dynamically, discharging to the Ross Sea through fiords. During the warmest times, sea ways were open in the interior of Antarctica. At these times, glacier margins retreated far enough up the valleys to ground on land. At this time, a coastal Nothofagus-moorland mosaic vegetation colonized the Beardmore Valley (Askin and Markgraf, 1986; Mercer, 1986; Carlquist, 1987; Hill and Truswell, 1993; Hill et al., 1996; Francis and Hill, 1996).
The climate that supported these changes was warmer, wetter, and more variable than the cold, dry polar desert climate of today (Webb and Harwood, 1991; Webb et al., 1996). Just how much warmer is the subject of some debate. Studies based on growth rings in wood and on the mineralogical characteristics of paleosols from the Oliver Bluffs location (85S. lat. ) suggest a mean annual temperature of -15C which would be at about the physiological limits of plant growth (Francis and Hill, 1996; Retallack and Krull, 1997). Peat and marl deposits containing shells of freshwater snails and bivalves, and the tooth of a fish, imply a lake that did not freeze to the bottom. Seeds and pollen and spores of several species of vascular plants also occur in these deposits (Ashworth et al., 1995). The body parts of a weevil, including the head, imply a mean annual temperature in the estimated range of -5 to -9C (Ashworth et al, 1997). The stratigraphy at the Oliver Bluffs site represents a complex glaciation with several ice advances and retreats. The different paleoclimatic interpretations may be accommodated in a model with cooler interstadials and a warmer interglacial. There is now no doubt that the Sirius Group fossils are in situ and represent a much warmer and wetter climate than the present day. As this biota most probably represents the Antarctic biota before extinction, it can be inferred that the climate of Antarctica until this time in the Cenozoic was both warmer and wetter than it is today. The alternative hypothesis, that this fauna recolonized Antarctica during a warmer interval, is considered to be improbable. The really contentious issue is the age of the Sirius Group.
Age of the Sirius Group
Reworked marine diatoms in diamictites of the Sirius Group, exposed on the margins of the Beardmore Glacier, indicate a Late Pliocene age. The diatoms are believed to be from sediment sources in the Wilkes and Pensacola basins of interior Antarctica (Webb and Harwood, 1991). This estimate of a Pliocene age is supported by the occurrence in sediments off Cape Adare (DSDP Site 274) with a biostratigraphically restrained age of about 3 Ma of relatively high frequencies of the same species of Nothofagus pollen as that found at Oliver Bluffs. The most probable source for the pollen is considered to be Nothofagus growing on the coast of Antarctica adjacent to the Ross Embayment (Fleming and Barron, 1996; Mielke et al., 1997).
It has been suggested in several papers that the diatoms are younger than the wind blown contaminants and do not date the deposition of the Sirius deposits (Stroeven and Prentice, 1995; Burckle and Potter, 1996; Burckle et al., 1996; Kellogg and Kellogg, 1996). The source of the wind blown diatoms, however, is problematical. These studies made in the Dry Valleys, 900 km from the Beardmore Glacier, imply that the Sirius Group is older than the Pliocene but offer no alternative biostratigraphic or geochemically-based age estimates for the deposits in which the diatoms are reportedly windblown contaminants. One new method that holds considerable promise to establish the age of the Sirius Group deposits is surface exposure dating using cosmogenic nuclides (e.g., Kurz and Brook, 1994). Preliminary results from Sirius Group rocks yield ages that are considerably older than the Late Pleistocene (Brook et al., 1995; Ivy-Ochs et al., 1995; Bruno et al., 1997; Kurz and Ackert, 1997), but there are still no age data for the key outcrops that contain critical fossil evidence. In addition, there are some important issues relating to the assumptions of the method that must be addressed. For example, exposure to cosmic rays prior to deposition could yield exposure ages that are too old. Nevertheless, this method may provide age information on glacial deposits and landscape evolution as old as Miocene (Kurz and Ackert, 1997), and further data from the Sirius Group will undoubtedly help resolve the controversy.
The Pliocene was a time of higher global temperatures and sea levels. The USGS PRISM reconstructions show sea surface temperatures in the North Atlantic Ocean to be about 5-6C warmer and those in the South Atlantic Ocean to be about 3-4C warmer than the present interglacial (Dowsett et al., 1996). The biological response in the Arctic was that a coniferous forest with a rich insect fauna inhabited a region which today is a polar desert (Thompson and Fleming, 1996; Böcher, 1995). Significant melting of land-based ice caused a sea level rise estimated by the PRISM group to be about 35 m . The causes of Pliocene warmth are divided between a strong greenhouse-effect caused by higher CO2 levels and more energetic ocean heat transport system caused by different configurations of ocean basins. Crowley (1996) believes that the Pliocene climate, while not a perfect analog for the effects of future global warming, may be the best we have in the recent geological record. A long time ago, Mercer (1978) pointed out the inherent instability of the West Antarctic ice sheet with respect to global warming. More recently, the relationships between a trend towards higher temperatures and disintegration of the Wordie and northern Larsen ice shelves on the Antarctic Peninsula (Fahnestock, 1996; Rott et al., 1996) are cause for the British Antarctic Survey to include the possibility that the effects of global warming might already be occurring (http://www.nerc-bas.ac.uk/public/info/antwarm.html).
What then was the response of Antarctica to the warmer world of the Pliocene? Did the ice sheets undergo significant melting as proposed in the dynamic hypothesis or did they remain essentially unchanged as proposed in the stable hypothesis? This is a major paleoclimatic problem that needs to be resolved. Resolution will not come, however, until we have a better understanding of the Sirius Group deposits which occur in isolated outcrops throughout the Transantarctic Mountains.
Even in locations such as Mt. Feather and Mt. Fleming in the Dry Valleys, the Oliver Bluffs and Cloudmaker on the Beardmore Glacier, and Bennett Platform and Roberts Massif on the Shackleton Glacier, where Sirius Group deposits have been the subject of several studies, they are not well-known. There are no lithostratigraphic or biostratigraphic correlation's between outcrops in different drainage basins. It is assumed that the Sirius Group deposits are of the same age but there is no really hard evidence to support that conclusion. Basic questions regarding the source of the sediments and their mode of deposition are still contentious issues. To begin to answer some of the basic questions and to resolve the differences in interpretation associated with the Sirius Group, we prefer an integrated approach linking studies in stratigraphy, sedimentology, paleontology and palynology, paleopedology, and geochemistry. These studies need to be accompanied by structural and geomorphological studies supported by cosmogenic dating, that places the Sirius Group glaciations in context of tectonism and later Pleistocene glaciations.
Prominent Quaternary glacial deposits are also found through-out the TAM, and provide an important record of advance and retreat of the outlet glaciers that flow into the Ross Sea, connecting the East and West Antarctic ice sheets. During glacial maximum, the flow of these outlet glaciers may have been impeded by grounded ice in the Ross Sea (e.g., Mercer, 1968; Stuiver et al. 1981; Denton et al., 1989a). The evidence for extensive grounding in the Ross Sea (due to lower sea level during glacial maximum) comes from mapping and geochronology (primarily 14C) of the moraines (Stuiver et al., 1981; Denton et al., 1989a, 1989b, 1991). In this model, the marine ice sheets respond primarily to eustatic sea level, with lower sea level during the last glacial maximum resulting in thick, grounded, ice sheet in the Ross Sea. [An alternative hypothesis is that there was an extensive floating ice shelf and only localized grounded ice (e.g., Drewry, 1979; Colhoun et al., 1992)]. Because the Ross Ice shelf is an extension of the West Antarctic Ice Sheet, which is considered to be potentially unstable with respect to global warming (it is grounded below sea level), the history of the Ross Ice shelf is important not just to understanding sea level but also to the stability of the West Antarctic Ice Sheet (Mercer, 1978; Doake and Vaughan, 1991). Further understanding of the Quaternary deposits in the TAM is necessary to relate the behavior of the East and West Ice Sheets to global climate and sea level. The ultimate goal is to understand the relationships between the earlier Cenozoic glaciations and those of the Quaternary and to provide a comprehensive interpretation of the Cenozoic landscape evolution of the TAM.
1. To establish when the existing extreme cold and arid polar desert climate of Antarctica became established. Is this change part of a global climatic event?
2. To establish the relationship between climate change, uplift, and denudation in the Transantarctic Mountains.
3. To assess the effect of Cenozoic climate change to the configuration of the East and West Antarctic ice sheets and their effect on global sea level.
4. To assess whether the results of Cenozoic climate change in Antarctica are relevant to predicting the potential effects of global warming.
Specific Types of Studies
1. Stratigraphic and sedimentologic studies designed to determine the mode of deposition and source of Cenozoic glacial deposits
2. Paleontological and geochronological studies designed to improve age control for the Sirius Group.
3. Paleontological, palynological, geochemical, and paleopedological studies designed to improve paleoenvironmental and paleoclimatic interpretation for the Sirius Group.
4. Cosmogenic dating and geomorphological studies designed to provide age control for landscape evolution, especially Cenozoic glaciations.
5. Regional and global scale models of ice sheets and climate that utilize uplift, sea level, and paleoclimatic data from the field-based studies.
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Doake, C.S.M. and D.G. Vaughan. 1991. Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming. Nature, 350(6316), 328-330.
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Drewry, D.J. 1979. Late Wisconsin reconstruction for the Ross Sea region, Antarctica. J. Geol., 24, 231-244.
Fahnestock, M. 1996. An Ice Shelf Breakup. Science, 271, 775-776.
Fleming, R.F. and J.A. Barron. 1996 Evidence of Pliocene Nothofagus in Antarctica from Pliocene marine sedimentary deposits (DSDP Site 274). Mar. Micropaleont., 27, 227-236.
Francis, J.E. and R.E. Hill. 1996. Fossil plants from the Pliocene Sirius Group, Transantarctic Mountains: evidence for climate from growth rings and fossil leaves. Palaios, 11, 389-396.
Harwood, D.M. and P.-N. Webb. 1998. Glacial transport of diatoms in the Antarctic Sirius Group: Pliocene refrigerator. GSA Today, 8(4), 4-8.
Hill, R.S. and E.M. Truswell. 1993. Nothofagus fossils in the Sirius Group, Transantarctic Mountains: leaves and pollen and their climatic implications. In Kennett, J.P. and D.A. Warnke, (eds). The Antarctic Paleoenvironment: a Perspective on Global Change. Antarct. Res. Ser., 60, 67-73. American Geophysical Union, Washington, D. C.
Hill, R.S., D.M. Harwood, and P.-N. Webb. 1996. Nothofagus beardmorensis (Nothofagaceae), a new species based on leaves from the Pliocene Sirius Group, Transantarctic Mountains, Antarctica. Rev. Paleobot. Palynol., 94, 11-24.
Ivy-Ochs, S., C. Schlücter, P.W. Kubik, B. Dittrich-Hannen, and J. Beer. 1995. Minimum 10 Be exposure ages of early Pliocene for the Table Mountain plateau and the Sirius Group at Mount Fleming, Dry Valleys, Antarctica. Geology, 23, 1007-1010.
Kellogg, D.E. and D.B. Kellogg. 1996. Diatoms in South pole ice: Implications for eolian contamination of Sirius Group deposits. Geology , 24, 115- 118.
Kennett, J.P. and D.A. Hodell. 1993. Evidence for relative climatic stability of Antarctica during the early Pliocene: a marine perspective. Geograf. Annaler, 75 A, 205-220.
Kurz, M.D., and R.P. Ackert. 1997. Stability of the East Antarctic Ice Sheet?: New chronological evidence from Bennett Platform, Antarctica. EOS Trans. American Geophysical Union 78, S185.
Kurz, M.D., and E.J. Brook. 1994. Surface exposure dating with cosmogenic nuclides. In Beck, C. (ed.), Dating in Exposed and Surface Contexts, University of New Mexico Press, Albuquerque, 139-159.
Marchant, D.R. and G.H. Denton. 1996. Miocene and Pliocene paleoclimate of the Dry Valleys region, Southern Victoria land: a geomorphological approach. Mar. Micropaleont., 27, 253- 271.
Marchant, D.R., G.C. Swisher III, D.R. Lux, D.P. West, and G.H. Denton. 1993. Pliocene paleoclimate and East Antarctic ice-sheet history from surficial ash deposits. Science, 260, 667-670.
Marchant, D.R., G. H. Denton, C.W. Swisher III, and N. Potter Jr. 1996. Late Cenozoic Antarctic paleoclimate reconstructed from volcanic ashes in the Dry Valleys region of southern Victoria Land. Bull. Geol. Soc. Amer., 108, 181- 194.
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Miller, M. and M.C.G. Mabin. 1998. Antarctic Neogene landscapes: in the refrigerator or in the deep freeze? GSA Today, 8(4), 1-3,8.
Retallack, G.J., and E. Krull. 1997. Neogene paleosols and paleoclimate of the Sirius Group, Dominion Range, Antarctica. Geol. Soc. Amer. Abstr. Prog, A-213.
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Stroeven, A.P., L.H. Burckle, J. Klemen, and M.L. Prentice. 1998. Atmospheric transport of diatoms in the Antarctic Sirius Group: Pliocene deep freeze. GSA Today, 8(4), 1,4-5.
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Sugden, D.E., D.R. Marchant, N. Potter Jr., R.A. Souchez, G.H. Denton, C.C. Swisher III, and J-L. Tison. 1995b. Preservation of Miocene glacier ice in east Antarctica. Nature, 376, 412-414.
Thompson, R.S. and F.F. Fleming. 1996. Middle Pliocene vegetation: reconstructions, paleoclimatic inferences, and boundary conditions for climate modeling. Mar. Micropaleont., 27, 27- 50.
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Webb, P.-N D.M. Harwood, M.G.C. Mabin, and B.C. McKelvey. 1996 A marine and terrestrial Sirius Group
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APPENDIX B - ABSTRACTS
(In Alphabetical Order)
A Complete Weevil Head (Coleoptera: Curculionidae) From the
Meyer Desert Formation, Transantarctic Mountains
Department of Geosciences, North Dakota State University
Recent discoveries of fossils from the Meyer Desert Formation, Oliver Bluffs, Dominion Range, are causing a reevaluation of the paleoclimate indicated previously by Nothofagus wood. Francis and Hill concluded that narrow and distorted tree rings were representative of growth near the limit of plant growth at a mean annual temperature of about -12C. The most significant of the new fossils is a 3D, 1.5 mm long weevil head with the chitin preserving details of punctuation and microornament. This follows the earlier discovery of the tibia and femur of a listroderine weevil. The head is probably also that of a weevil in the subfamily Cylydrorhininae. The fossil beetle remains are associated in fluvial deposits with wood, leaves, and pollen of Nothofagus (southern beech), the seeds of several vascular plant species, and a fish tooth. The other new fossil is an ostracod with both valves still articulated. The ostracod occurs in a marl bed with complete shells of snails and fragmented shells of bivalves. The smooth carapace of the ostracod and the hingelines of the bivalves appear to be of freshwater types. The marl appears to be made up of broken, carbonate- coated plant stems, possibly Characeae. The stratigraphic and paleontologic relationships suggest a glacial margin at which a lake, unfrozen during the summer months, was bordered by vegetated moraines. The closest biogeographic affinity of the assemblage is southern South America, and a possible modern analog is the Magellanic Moorland of Tierra del Fuego. The climate of the Magellanic Moorland, however, is oceanic and it is improbable that the Pliocene climate of the interior of Antarctica was strongly oceanic. The fossil assemblage has characteristics of a treeline biota, and by comparison with the Canadian subarctic may represent a climate with a mean annual temperature in the estimated range of -5 to -9C, several degrees warmer than proposed by Francis and Hill. Compared to estimated mean annual temperature of the site today, corrected for about 1300m of postdepositional uplift, the mean annual temperature during the Pliocene would have been at least 15 to 19C warmer than today.
Are the different paleotemperature estimates for the Meyer Desert Formation really conflicting? Could the different paleotemperatures be part of a temperature spectrum in a glacial-interglacial-glacial cycle? Wood from the insect-bearing sediments will be examined by Francis and that question may be answered soon. The general stratigraphic relationships at the Oliver Bluffs, interbedded diamictites and laminated sediments, indicate multiple ice advances and retreats. Future research needs to focus on better defining glacial-interglacial cycles for the Sirius Group. In Step 1, glacial-interglacial cycles would be defined at the Oliver Bluffs by integrating stratigraphical, sedimentological, paleontological (including palynological), paleopedological, and geochemical studies. In Step 2, the search would continue in other glacial drainages (e.g. Reedy Glacier) for other Sirius Group fossil-bearing sediments for correlation with the glacial-interglacial cycles defined at the Oliver Bluffs type section.
Palynology of the Transantarctic Mountains Gondwana Succession
Rosemary A. Askin
Byrd Polar Research Center, The Ohio State University
Palynological studies in the Transantarctic Mountains Gondwana succession focus on improving and refining the current biostratigraphic framework. Spore and pollen assemblages recovered from this succession also provide information on vegetational composition and extinction, evolutionary and dispersal patterns, and have environmental, climatic and biogeographic implications.
Future palynological work in the central Transantarctic Mountains should fill gaps in the palynostratigraphy and extend the spatial coverage to best understand distributional trends. Areas least affected by thermal metamorphism associated with dolerite intrusion are of high priority. At present the Permian and basal Triassic units in particular are inadequately represented by well-preserved palynomorph assemblages. The Permian units and Permo-Triassic boundary beds are typically more severely affected by thermal metamorphism than the younger Triassic to Jurassic strata. Palynomorphs recently recovered from the Pagoda Formation on the upper Nimrod Glacier, along with previously reported Permian and well-preserved Triassic assemblages from scattered localities in the Beardmore Glacier area, suggest detailed collecting at selected sites in the upper Nimrod to upper Beardmore region will yield productive samples and thus a more detailed succession from earliest Permian to the Jurassic.
Palynology of Neogene Sediments in the Transantarctic Mountains
Rosemary A. Askin
Byrd Polar Research Center, The Ohio State University
Neogene sediments, including Sirius Group strata, will be examined for spores and pollen and any other plant remains derived from contemporaneous vegetation. Terrestrial vegetational history is intimately linked to climatic and tectonic history. If sufficient palynomorphs can be recovered from independently dated samples, this study will identify trends in vegetational composition, diversity, distribution and extinction patterns, in those areas where spores and pollen are preserved. Patterns of presence vs. absence, composition and diversity will be used to help interpret Antarctic climatic, cryospheric and tectonic evolution. If present, recycled palynomorphs from older sediments will help identify provenance of the sediments.
Examination of Neogene samples for palynomorphs will be part of an on-going palynological survey of Sirius Group and related Neogene sediments in the Transantarctic Mountains. The Oliver Bluffs locality in the Dominion Range, with its exceptional plant fossils, is our best known window on Antarctic Neogene terrestrial life. This remains a high priority locality for obtaining a more complete knowledge of vegetational composition and paleoenvironments. Rare, possibly contemporaneous, palynomorphs have also been obtained from Sirius Groups deposits near the Reedy Glacier. Outcrops of the Sirius Group are common and scattered throughout the Transantarctic Mountains. Any sample material of suitable fine-grained lithology obtained from colleagues will be gratefully accepted for this study.
Using Freshwater Decapod Crustaceans in the Central Transantarctic Mountains to Constrain Late Paleozoic-Early Mesozoic Paleoclimate and Interpret the Early Development of Freshwater Ecosystems
Loren E. Babcock1, Molly F. Miller2, John L. Isbell3, James W. Collinson1
1Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
2Geology Department, Vanderbilt University
3Department of Geosciences, University of Wisconsin-Milwaukee
Crayfish body and trace fossils were discovered at two localities in the Shackleton Glacier area during the 1996-97 Antarctic field season. A broken claw found by J.L. Isbell is from a small lacustrine deposit in the Lower Permian Pagoda Formation, and burrows found by M.F. Miller and J.W. Collinson are from floodplain deposits of the Lower Triassic Fremouw Formation. Discovery of the early Permian claw extends the fossil record of crayfish by ~65 million years, and demonstrates that decapod crustaceans had radiated into freshwater habitats by the late Paleozoic. The Early Triassic burrows, the oldest attributed to crayfish, have a morphology similar to modern crayfish burrows. They demonstrate that burrowing behavior was established early in the evolution of this group. The Antarctic crayfish fossils predate fossils of their low latitude descendants by up to 65 million years. This opens the intriguing possibility that high latitude areas may have been a source of biological innovation during the late Paleozoic-early Mesozoic, paralleling the pattern documented for late Mesozoic-Cenozoic biotas. However, considerably more data need to be assembled to test this hypothesis.
The new discoveries show that the earliest Permian crayfish were distributed in high paleolatitudes of southernmost Pangea, where they lived in freshwater lakes fed by glacial meltwater. Using modern crayfish as guides to temperature tolerance, summer temperatures of streams and lakes near the South Pole that supported the crayfish probably reached 10-20C during Permian-Triassic interglacial intervals. This evidence generally supports similar interpretations developed from studies of coeval plants and vertebrate animals.
Studying Transantarctic Mountain Structures With Aerogeophysics
From Outcrop to Lithospheric Scales
Lamont Doherty Earth Observatory, Columbia University
Aerogeophysics in Antarctica can be a powerful tool for studying geologic structures and clarifying lithospheric processes. Recently much aerogeophysical work has been focused on ice covered regions with few ties to well mapped geologic structures. Over the next two years several projects using aerogeophysics will target geologic problems in regions with outcrop. These include a high resolution aeromagnetic survey joint with the German program flown out of Skelton Neve (T. Wilson et al.), a detailed study of the Ford Ranges using gravity magnetic, radar and laser (Luyendyk and Siddoway) and a pair of 700 km long transects flown across the Transantarctic Mountains one from McMurdo to Dome C and a second crossing the Watson Escarpment and extending to the far side of Pole (Bell et al.).
Structures which can be mapped with aerogeophysics:
(1)Thickness and extent of sedimentary basins,
(2) Nature of bounding faults of sedimentary basins,
(3) Lineation of dyke swarms,
(4) Extent of Ferrar complex towards the Backside,
(5) Size and structural trend of batholiths.
Potential targets for future aerogeophysical work:
(1) Filling in ongoing work across Watson Escarpment at geologic scales,
(2) Linking CASERTZ work over ice which links Byrd Subglacial Basin, Interior Ross
Embayment and Whitmore Mountains with the Transantarctic Mountains Transect
(3) Use as a general tool for providing "regional" framework for geologic studies,
(4) Examine the boundary between the Whitmore Mountains, Thiel Mountains and the Ohio
A Focus on Late Paleozoic to Mesozoic Paleoclimate Interpretation
James W. Collinson
Byrd Polar Research Center, The Ohio State University
Late Paleozoic to Mesozoic paleoclimates, as suggested by the sedimentary and fossil record in the central Transantarctic Mountains, were warmer in the Late Permian to Early Jurassic than would be expected for a polar region with long periods of winter darkness. Paleontologic data appear to contradict global climate models that predict great annual extremes. I suggest a cooperative effort by investigators in various disciplines in compiling a database toward determining the climate history of Antarctica. Any data that might have some bearing on paleoclimates should be included. These data could be used to improve climate models and perhaps resolve the paradox of relatively warm climates in polar regions.
Landscape Analysis and Glacial History of the Transantarctic Mountains
George H. Denton
University of Maine
A particularly interesting problem involves the co-evolution of the Transantarctic Mountains and the East Antarctic Ice Sheet. The development of these two major physical features can be linked by applying a new model of how mountains develop to the Cenozoic history of the Transantarctic Mountains. Thus model views the shape of a mountain range as involving the complex interaction of tectonic forces, climate, and denudation. Isostasy links the internal tectonic evolution to the external geomorphic evolution. The geomorphologic development can accelerate or delay uplift. It can speed up or slow down tectonic processes. It is critically linked to climate. Hence there is a complex set of feedbacks among tectonics, climate, and denudation. This approach can be initiated by extensive mapping of landscape elements in the Transantarctic Mountains. The glacial landforms and Sirius outcrops can then be placed in the context of these landscape elements. The landscape surfaces (and hence timing of denudation) can be dated by exposure ages using noble gasses in pyroxenes. Fission track analyses can also constrain the timing of denudation. Long-term climate can be deduced from diagnostic periglacial features and from fossils on the landscape. The resulting analysis of landscape and climate can be linked with the results from sediment cores from basins in front of the Transantarctic Mountains. The overall results should clarify the history of uplift of the Transantarctic Mountains and of the development of the East Antarctic Ice Sheet.
A second problem involves the reconstruction and history of grounded ice in the Ross Embayment during the last glacial/interglacial hemicycle. These items affords background for investigations of the current behavior of the West Antarctic Ice Sheet. The lateral moraines beside outlet glaciers that pass through the Transantarctic Mountains can afford surface elevations for the grounded ice sheet at the mountain front. Exposure ages of maximum and recessional moraines can afford a chronology of the retreat of grounded ice from this margin of the Ross Embayment.
Chronology and Character of the Late Precambrian Tectonic and Thermal
Evolution of the Transantarctic Mountains
Donald J. DePaolo
Center for Isotope Geochemistry, Department of Geology and Geophysics
University of California
The SWEAT hypothesis of Moores (1991) and Dalziel (1991) represents an important step in global scale tectonics in that it is a bold attempt to extend to the Precambrian the principles of continental reconstruction which generated the original ideas about plate tectonics. Confirmation (or denial) of the SWEAT reconstruction, or any other description of Proterozoic continental evolution depends significantly on understanding the evolution of the Antarctic continental margin exposed in the Transantarctic Mountains (TM) (Goodge, 1995; Stump, 1992). As shown by Borg and DePaolo (1991, 1994), the current configuration of basement terranes in the TM is not compatible with the SWEAT reconstruction , but plausible rearrangements of the tectonic elements during the Late Proterozoic and earliest Paleozoic could make the reconstruction acceptable. Unfortunately, the Late Proterozoic and early Paleozoic evolution of the Antarctic margin is too poorly constrained to represent a suitable test of the hypothesis. One serious limitation is the paucity of reliable and precise radiometric ages for metamorphic and plutonic rocks, and the paucity of structural data tied to the radiometric timescale (cf. Goodge et al., 1993). I have been attempting to develop a systematic chronology of the metamorphism, deformation, and plutonism of the Transantarctic Mountains using the Sm-Nd mineral isochron method. Recent U-Pb zircon work by Encarnación and Grunow (1996) has also added significantly to the geochronological database.
The SWEAT reconstruction, and the existing isotopic mapping data, require that many parts of the TM basement did not reach their present positions relative to the East Antarctic Craton until Late Proterozoic time. New Sm-Nd and U-Pb geochronological data suggest, contrary to some previous reports, that there are no plutons older than about 540 Ma in the CTM south of Southern Victoria Land, and that even some of the foliated plutons are as young as 510 Ma. This suggests that Late Proterozoic basement rearrangement was by transform motion rather than being subduction-related. Evidence for Late Proterozoic tectonism is provided by 545-580 Ma ages of amphibolite in the Darwin-Byrd Glacier area (new Sm-Nd mineral data) and by published U-Pb data from the Miller Range (Goodge et al., 1993). Amphibolite from the Miller Range and from Spear Nunatak give much older Sm-Nd mineral ages of 780 and 885 Ma respectively. These ages suggest an earlier Proterozoic deformational history, the extent and nature of which is very poorly known.
To develop an adequate understanding of the Late Proterozoic and early Paleozoic tectonic history of the TM, it will be necessary to focus on the depositional, metamorphic, and deformational history of the pre-Granite Harbor rocks in the Byrd-Darwin Glacier area, the Central TM, and through to the Horlick Mountains. Further field studies need to be multidisciplinary, and distributed throughout a significant portion of the range. Structural, metamorphic, sedimentological, and geochronological studies are required, which to this point have mainly been carried out in the Miller Range.
Borg, S.G., and D.J. DePaolo. 1991. Crustal structure and tectonics of the Antarctic margin of Gondwana and implications for the tectonic development of southeastern Australia. Tectonophysics, 196, 339-358.
Borg, S.G., and D.J. DePaolo. 1994. Laurentia, Australia and Antarctica as a Late Proterozoic supercontinent: Constraints from isotopic mapping. Geology, 22, 307-310.
Dalziel, I.W.D. 1991. Pacific margins of Laurentia and East Antarctica - Australia as a conjugate rift pair: Evidence and implications for an Eocambrian supercontinent. Geology, 19, 185- 192.
Encarnación, J. and A. Grunow. 1996. Changing magmatic and tectonic styles along the paleo- Pacific margin of Gondwana and the onset of early Paleozoic magmatism in Antarctica. Tectonics, 15, 1325-1341.
Goodge, J.W., R.W. Walker, and V.L. Hansen. 1993. Neoproterozoic- Cambrian basement- involved orogenesis within the Antarctic margin of Gondwana: Geology, 21, 37-40.
Goodge, J.W. 1995. LIRA Workshop - Dallas, Texas - 20-23 October 1994, Ross Orogen: Crustal structure and plate tectonic significance. Terra Antartica, 2, 71-77.
Moores, E.M. 1991. Southwest U.S. - East Antarctic (SWEAT) connection: A hypothesis. Geology, 19, 425-428.
Stump, E. 1992. The Ross Orogen of the Transantarctic Mountains in light of the Laurentia- Gondwana split. GSA Today, 2, 25-31.
Petrological Problems in Antarctic Gondwana Geology
David H. Elliot
Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
The Transantarctic Mountains contain the Antarctic record of Gondwana evolution and break-up in the sedimentary rocks of the Beacon supergroup and the overlying and associated Jurassic igneous rocks.
The Permo-Triassic Victoria Group of the Beacon contains volcanic detritus derived from the active plate margin of Gondwanaland. This detritus occurs as epiclastic rock fragments and airfall debris; the heavy mineral suite may also contain components derived from the magmatic arc. The Victoria Group is overlain by a silicic volcanic sequence that is best known from the southern Queen Alexandra Range; this sequence, which is thought to be Early Jurassic based on vertebrate remains, appears to be bounded by unconformities. The silicic volcanic strata are overlain by the Middle Jurassic basaltic pyroclastic rocks of the Prebble Formation and the lavas of the Kirkpatrick Basalt. The Beacon strata, and to a much lesser extent the basement, are intruded by sills and dikes of the correlative Ferrar Dolerite. The basaltic rocks are related to break-up and are correlative, at least in part, with Karoo magmatism.
The first order problems are related to the Ferrar tholeiitic magmatism and include: a) the origin of the geochemical signature, b) whether there was a point or line source and consequently magma transport, distribution and emplacement, c) the relationship to the Karoo magmatism and other centers of contemporaneous activity such as in Patagonia, and d) the location and nature of the Ferrar rift system.
Second order problems include: a) the Permo-Triassic magmatic arc and its relationship to the Beacon depositional basin and its fill, b) the age and relationship of the silicic volcanic rocks to the Permo-Triassic and Middle Jurassic magmatism, c) the former spatial distribution of the Ferrar tholeiites and magma transport directions, and d) the relationship of silicic interbeds in the Kirkpatrick Basalt to the basaltic magmatism.
Testing the SWEAT Model and Understanding the Ross Orogeny
in the Central Transantarctic Mountains
Saint Louis University
The SWEAT model (Moores, 1991; Dalziel, 1991; Hoffman, 1991) which places Laurentia against East Antarctica and Australia in the Neoproterozoic continues to be a controversial and exciting subject. Although originally based on Grenville age 'piercing points' between Laurentia and Queen Maud Land, Antarctica, this connection is probably no longer valid because Queen Maud Land was not part of East Antarctica at ~1 Ga (Gose et al., 1996). There are now only two known locations in Antarctica that may still potentially be linked to Laurentia. One of these sites is in the central Transantarctic Mountains region at the Nimrod Glacier and it is here that there is a need to collect additional and new samples for geochronology, paleomagnetism and structural analysis. In collaboration with Anne Grunow and Timothy Paulsen (BPRC, The Ohio State University) the SWEAT hypothesis can be tested by providing tighter age constraints on the purported Rodinia rifting-related sedimentary and volcanic rocks and determining a paleolatitude and paleopole for the central Transantarctic Mountains at this time. There are presently no Neoproterozic paleopoles from East Antarctica that can be used to test the SWEAT theory. The Nimrod Glacier area offers the only paleomagnetically feasible Antarctic sampling location to test the SWEAT model. A new East Antarctic paleopole could also be compared with Australian and Indian paleopoles, potentially demonstrating East Gondwana's integrity. Following rifting, these supposed Neoproterozoic rocks are thought to have been deformed during the poorly understood Beardmore and Ross orogenies. In addition to testing the SWEAT hypothesis, we also propose to provide further structural and geochronologic data to constrain the timing and kinematics of this (these?) deformational event(s).
Studies of the Ferrar Magmatic Province in the
Central Transantarctic Mountains
Thomas H. Fleming
Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
Jurassic tholeiites of the Ferrar Group crop out in a linear belt that extends for more than 3000 km from northernmost Victoria Land to the Pensacola Mountains. Similar rocks are found in an extension of this belt in southern Australiasia. Recent geochronologic studies demonstrate that both the intrusive and extrusive phases of Ferrar magmatism were short lived and contemporaneous over much of this region. Chemically and isotopically, the Ferrar Province is notable for its enriched Sr and Nd isotopic compositions and crust-like trace element ratios. The Ferrar represents an extreme case of the development of these features in many continental flood basalts. In areas where they have been studied in detail, chemical and isotopic compositions show a remarkably consistent pattern of variation that is best described by a processes of fractional crystallization combined with crustal assimilation. Several outstanding questions remain to be addressed about the Ferrar Province. These include: 1) What is the geographic distribution of the mantle source(s) for the Ferrar ? Although temporally related to the breakup of Gondwanaland the distribution of Ferrar magmatism does not follow any well defined plate boundaries associated with breakup. Petrologic and structural studies, however, indicate a Jurassic tectonic rift system was developed within the Transantarctic Mountains. It has long been assumed that the mantle source for the Ferrar is a broad region lying beneath the present area of exposure and several localities have been inferred to represent major magmatic conduits. The chemical distinctiveness and short duration of Ferrar magmatism, on the other hand, suggest the possibility of more geographically restricted mantle source combined with large scale upper crustal transport of magma. These contrasting models are best addressed by geophysical studies aimed at identifying the feeder system and detailed field studies of magma flow patterns throughout the province. 2) What is the cause of the unique chemical and isotopic compositions of Ferrar rocks ? There has been long-standing debate whether the unique chemical features reflect the composition of their subcontinental mantle source(s) or an overprint due to interaction with the continental crust. The early history of magmatic evolution in the province is best addressed by examination of primitive dolerites which have been identified in several areas of the central Transantarctic Mountains. 3) How is Ferrar magmatism related to breakup of Gondwana and what are the relationships to compositionally distinct basaltic rocks of similar age that occur in Dronning Maud Land and southern Africa ?
Neoproterozoic to Early Paleozoic Tectonics in the Beardmore Glacier
Area of the Ross Orogen
John W. Goodge
Department of Geological Sciences, Southern Methodist University
The Transantarctic Mountains orogenic belt is recognized both for its early Paleozoic role in Gondwanaland amalgamation and its involvement in Jurassic to Neogene rifting and uplift. The pre-Devonian evolution of the Transantarctic Mountains has traditionally been viewed in terms of three orogenic cycles, culminating with the early Paleozoic Ross orogeny which imparted the principal structural fabric upon the present mountain belt. Critical to our understanding of the Ross orogen is the relationship between crystalline basement and sedimentary supracrustal assemblages, which together show evidence of protracted Ross tectonism during the latest Neoproterozoic and earliest Paleozoic (e.g., Kleinschmidt & Tessensohn, 1987; Flöttmann & Kleinschmidt, 1991; Goodge et al., 1991a, 1993b; Dallmeyer & Wright 1992; Rowell et al., 1992, 1993; Goodge & Dallmeyer, 1996). Recent discoveries have shown that what were once thought to comprise separate orogenic cycles are likely to be expressions of temporally diachronous and structurally partitioned Ross activity. For example, in the central Transantarctic Mountains, high-grade metamorphic rocks of the Nimrod Group experienced major dynamothermal activity that is not recorded in adjacent units. Although magmatic and depositional events in the Nimrod Group can be traced to the Archean, there is little discernible evidence for the so-called Nimrod orogeny. Rather, the principal metamorphic and structural features of the Nimrod Group are now recognized as a deep-crustal manifestation of the Ross orogeny.
Likewise, the younger orogenic record remains obscured by uncertain depositional, age and deformation relationships in widespread graywacke and carbonate units commonly assumed to be Neoproterozoic in age. These graywacke sequences were regionally deformed by Ross tectonism, but some evidence has been cited for an earlier deformation (so-called Beardmore orogeny). In the central Transantarctic Mountains, the Beardmore orogeny is based on apparently unconformable stratigraphic relations between the Beardmore Group and Lower Cambrian Byrd Group, and from two reported deformations in the Beardmore Group. However, because the Ross and Beardmore structures are nearly coaxial, because of great uncertainty in contact relations between key units, and because of poor internal biostratigraphic and age control in the Beardmore Group, the nature of the Beardmore orogeny remains uncertain. New structural and age relationships suggest that the Beardmore Group is relatively young (uppermost Neoproterozoic to lower Paleozoic) and only deformed during what is recognized as Ross activity (Goodge, in press).
Although conclusive evidence of pre-Ross tectonic activity appears lacking, there is much to be gained by more detailed study of the basement and supracrustal assemblages in the Transantarctic Mountains. Just as a deeper understanding of the Ross orogen emerged from studies of basement rocks in the Beardmore Glacier area beginning in 1985-86, a higher level of clarity is expected from detailed future studies of the supracrustal sequences in this important region. A key unit is the Beardmore Group, a thick assemblage of graywacke, carbonate and minor volcanic rocks that is traditionally correlated with similar siliciclastic sequences along the length of the Transantarctic Mountains. Important questions regarding the stratigraphy, sedimentology and deformation of the Beardmore Group include: what is its depositional setting? is it a parautochthonous marginal-basin assemblage or an allochthonous sequence? how many sequences are represented? what are their age(s)? what is their provenance? are they coeval with local shelf sequences? can they be correlated with other Neoproterozoic-lower Paleozoic graywacke sequences regionally? globally? what are the deformation patterns in these supracrustal rocks? is there evidence for multiple deformations during the Neoproterozoic and early Paleozoic? is there structural evidence for early extension, or just contraction? how do strain patterns relate to basement deformation? what is (are) the age(s) of deformation? what does deformation reveal about tectonic patterns along the incipient active margin of Gondwanaland?
Addressing these questions will help us to develop a more complete understanding of Ross orogenesis and evaluate the role of Ross margin activity with respect to Rodinia- and Gondwana-wide tectonic events.
The Neoproterozoic Legacy: The Influence of Precambrian Crustal
Structure on Tectonic Events in the Central Transantarctic Mountains
John W. Goodge1 and Carol A. Finn2
1Department of Geological Sciences, Southern Methodist University
2Mineral Resource Program, U.S. Geological Survey
Proposed research: Our research objectives are two-fold:
1. Map the character and structure of Precambrian to early Paleozoic crustal provinces in order to define the cratonic elements of Gondwana in the central Transantarctic Mountains (CTM). Geophysical mapping, coupled with outcrop studies in the well-exposed pre-Ross rocks along the CTM, will help to define Precambrian cratonic boundaries, the extent of Granite Harbour plutons, Jurassic and Cenozoic igneous rocks and regional structures, and sedimentary basins.
2. Trace the influence of Precambrian rift-related architecture on later tectonic events in order to establish the role of structural ancestry in the development of the Gondwana margin. Lithospheric structures formed during Neoproterozoic rifting may have controlled the geometry of the Ross orogen and early Paleozoic magmatism, as well as development of rift structures during the break-up of Gondwana and Cenozoic uplift of the TAM. Geologic mapping will place constraints on the style and reactivation history of observed structures. Geological and geophysical mapping can be shown to either cross-cut or parallel each other can establish the role of inherited structures in subsequent tectonic events.
We plan to carry out an integrated program involving geologic field mapping and airborne geophysical surveys. Field-based mapping studies will provide ground-truthing of geophysical data and allow us to collect materials for age dating and characterization of geophysical rock properties. Airborne acquisition of magnetic, gravity, bedrock-depth, and surface altimetry data using the SOAR aircraft will allow us to trace regional geologic units and structures beneath ice cover over a 200x700 km area extending over the polar plateau. Helicopter surveys will be used to collect high-resolution magnetic data at lower flight elevations to delineate small-scale structural features in areas over the CTM and foothills, and can be tuned to specific geologic targets.
Geographic area of study: CTM sector between the Mulock and Beardmore glaciers, with coverage in the mountains and across the adjacent polar plateau. These data will complement geological and geophysical studies farther north in Victoria Land. Areas of detailed study will focus on the major outlet glaciers and between the Nimrod and Beardmore glaciers.
Logistics: Logistics will involve a combination of remote geological field camps and airborne geophysical research. Remote field camps will require fixed-wing put-ins to establish 4-person field camps for 4-6 weeks duration. Camp moves may be required. Most field work can be accomplished by surface travel (snowmobile), but some helo support will be required. Airborne data acquisition will require use of the SOAR Twin Otter platform, to be operated out of McMurdo and/or remote field camps, as well as a helicopter-based magnetics platform, to be operated out of a remote field camp. The SOAR facility requires a large Jamesway, camp support for approximately 15-20 people, power, fuel and C-130 flights over a 2.5 month period. Helicopter magnetic surveys require fixed-wing put-ins to establish 10-person field camps, including science staff, science support, 2 pilots and a mechanic, with fuel depots and power.
Preferred field years: We anticipate 3 field seasons will be required to complete this project, tentatively beginning in austral 2001-2002 (principally using SOAR for geophysics, and helo support for surface geology), a second season in 2002-2003 (using SOAR for geophysics, and helo support for surface geology and initial geophysical data acquisition), and ending in 2003-2004 (detailed geology and geophysics studies with helicopter magnetics system).
Vertebrate Paleontology of the Jurassic and Triassic Sediments of the Central Transantarctic Mountains: Future Field Work
William R. Hammer
Jurassic - Falla Formation
Field objective: Further collect the Jurassic vertebrate site at Mt. Kirkpatrick and search additional exposures of the upper Falla Formation for new assemblages. The Beardmore Glacier area has the best potential for additional Jurassic vertebrates.
Rationale: The Jurassic fauna has only been collected from one site at Mt. Kirkpatrick and includes five or six taxa. Obviously many more taxa were part of this ecosystem and further collecting and study of this fauna is currently the most important vertebrate paleontological work to be accomplished in the Central Transantarctic Mountains. This fauna includes the only Jurassic dinosaurs from the Antarctic and the only dinosaurs of any type from the Antarctic mainland.
In addition, this assemblage represents one of only a few Early to Middle Jurassic faunas known from any of the southern continents, making it crucial to our understanding of earth history during this early period of diversification of the dinosaurs. Other reasons for further study include:
1. The fauna includes Cryolophosaurus, the oldest known allosauroid in the world (by some 40 million years). This suggests that the allosaurs, a fairly advanced group of theropods known otherwise from only the northern continents, originated much earlier than previously thought and, perhaps, in Gondwana. Additional specimens of Cryolophosaurus or related taxa from the Jurassic of Antarctica may further clarify the origin and evolution of the large theropod dinosaurs.
2. The fauna includes the highest paleolatitude pterosaur (flying reptile) known. Only the humerus of this animal has been collected to date, further specimens will clarify its relationship to other pterosaurs and indicate whether high latitude pterosaurs acquired any unique adaptations. Like the pterosaur, other Jurassic taxa from the upper Falla Formation are represented by few specimens. These include teeth of scavenging theropods and a tritylodont and a portion of the leg of a prosauropod. Additional specimens of these are needed to further understand their relationships to other members of their respective clades from other continents and whether they had any unique adaptations to deal with the paleolatitude.
3. As mentioned above, the number of Jurassic taxa collected is small. Additional collecting should add to the faunal list. This will give us a more complete view of the ecosystem and aid in making paleoclimate interpretations for the Jurassic of Antarctica. This is the highest paleolatitude fauna from the early part of the Jurassic known, if dwarf forms or (as mentioned above) unique adaptations are found among any of the animals, it might clarify how they dealt with annual polar darkness.
4. Additional taxa may also help establish a more precise age for the fauna. The Upper Falla Formation was previously identified as Late Triassic. The fauna itself appears to be Early Jurassic. However, it occurs in a sequence dominated by volcanic tuffs that may be genetically related to Middle Jurassic volcanism. In addition to more vertebrates, tuffs should also be collected for possible radiometric age dating.
Sedimentological and palynological studies of the upper Falla Formation could further elucidate the depositional setting and climate of the Antarctic Jurassic. If palynomorphs are found in the unit these could also aid in determining a precise age.
Jurassic - Lacustrine Interbeds
Almost thirty years since Jurassic fish were first collected from lacustrine interbeds within the Kirkpatrick Basalt at Storm Peak. These fish represented a new genus of actinopterygians. Additional collecting of these beds has not been an objective of any subsequent visits to the Beardmore Glacier area even though the potential for additional taxa of fish and perhaps flying vertebrates (pterosaurs or primitive birds) in these interbeds appears to be very good, if accessible exposures are available.
Triassic- Fremouw Formation and Lower Falla Formations
Additional vertebrate paleontological field work in the Middle Triassic upper Fremouw Formation is needed to resolve a number of issues regarding that period in Antarctic earth history:
1. Several taxa of synapsids from this unit show some relationships to both late Early Triassic genera of South Africa and Middle Triassic genera of South America. These animals are currently known only from jaw and maxillary fragments, additional collecting could produce more complete specimens that would clarify both the age of this fauna and its relationship to other Gondwana faunas. It is possible that it represents an age between the above mentioned assemblages. If that is the case, it could be a fauna of an age currently unknown from other parts of Gondwana.
2. Specimens of new taxa of very large capitosaur amphibians from the upper Fremouw Formation have unusual features, particularly in the dentition, compared to capitosaurs from other continents. It appears that these animals evolved independently in the Antarctic, probably because their restriction to a single drainage system inhibited their ability to migrate. The most intriguing new genus of these amphibians is represented by only the snout tip of a single skull, so further collection again could produced more complete specimens that would clarify its relationship to other capitosaurs.
3. Additional study of the upper Fremouw vertebrate fauna should be in conjunction with paleosol, palynomorph, and sedimentological studies on this unit to give a better understanding of the environmental setting and paleoclimate during the Triassic. Very little paleosol/palynomorph work has been accomplished in this part of the section.
Extensive collection of the lower Fremouw Formation during the past three decades has produced a diverse fauna of Early Triassic age. Study of this fauna suggests that the vertebrate taxa produced are somewhat facies controlled from locality to locality. The puzzling questions left to be answered about this fauna revolve mainly around paleoclimates and any paleontological objectives on this subject would have to be collaborative. Perhaps the most pressing need in the lower Fremouw is for further study of the paleosols, particularly in sections that include the vertebrates.
Finally, upper sections of the Fremouw Formation and the lower Falla Formation are very likely Late Triassic in age. Although vertebrates have not been found to date, it is important that these units are thoroughly searched wherever possible for vertebrate remains. The Late Triassic is a crucial period in vertebrate history, it is one of great change worldwide, and an Antarctic fauna of this age could add significantly to our understanding of global events at this time.
Reconnaissance for Meteorite Collection Sites Along the
Central-Southern Transantarctic Mountains
Ralph P. Harvey
Department of Geology, Case Western Reserve University
ANSMET (the Antarctic Search for Meteorites program) has a long history of field research along the Transantarctic Mountains. Meteorite collection sites typically are found where the flow of plateau ice to the sea is slowed, re-directed, or stopped, so that ablation rates exceed accumulation rates and deep, old ice is exposed. These sites, often identifiable by the deep blue color of the exposed ice, are found all along the plateau-side of the Transantarctics, most commonly in regions between and/or to the sides of major drainages. These sites are also often associated with outcrops of significant geological interest.
ANSMET field parties are typically put in to a single site for an entire season, where systematic searching will take place. However, dedicating a full field season to an icefield whose meteorite potential has not been fully explored can be a significant waste of logistical support. For this reason, ANSMET periodically conducts field seasons dedicated to reconnaissance, in an effort to survey several blue ice areas whose potential as good meteorite collection sites is apparent from the air, but have not been visited on the ground. These quick visits allows us to estimate the amount of fieldwork a site may require for systematically searching if they do yield specimens. Over the years we have found that such efforts are most efficient when small parties can be put in place by air, with a flexible flight schedule allowing adaptation to weather conditions and the searching circumstances associated each particular icefield.
Icefields that ANSMET hopes to examine from the ground are found all along the Transantarctics. Sites of potential interest north of the Beardmore Glacier and south of McMurdo include icefields along the Queen Alexandra Range, the Queen Elizabeth Range, the Miller Range, the Geologists Range, the Wilhoite and All Blacks Proterozoic, Meteorite Hills, the Brittania Range, Turnstile Ridge, Bates Proterozoic, and icefields at the headwaters of the Byrd glacier. Sites of interest south of the Beardmore Glacier include the Dominion Range, the Ottway Massif, the Scott icefalls, the Wisconsin Range, D'Angelo Bluffs, the Ohio Range, the Havola Escarpment, and others. Simply put, within helicopter range of an established camp virtually anywhere along the Transantarctics, there are several icefields of significant interest to ANSMET. Short (a few days) visits to these sites will allow ANSMET to identify and prioritize future visits, if called for, economically furthering our systematic collection efforts.
The Late Neogene Glacio-Climatic and Tectonic History of the
Reedy Glacier Area, Antarctica
(Collaborative Research Proposal)
David M. Harwood1 and Gary S. Wilson2
1 Department of Geology, University of Nebraska
2 Byrd Polar Research Center, The Ohio State University
A recent focus of the Antarctic earth sciences has been the nature of the ice sheet's response to Pliocene warming. Two contrasting hypotheses exist. One argues for persistent cold and modern glacial conditions for at least the last 15 million years. The other hypothesis suggests a dynamic record of the ice sheet through much of the Cenozoic, with the onset of modern conditions within the past 3 million years. The debate is also divided between data from the Dry Valleys region and other areas of Antarctica. The Sirius Group of terrestrial and marine (fjord) glacigene sediments provides information about the Neogene glacial and tectonic history of the Transantarctic Mountains. Sirius Group deposits in the Central Transantarctic Mountains record significant fluctuation in ice extent and a different thermal regime for the East Antarctic Ice Sheet and outlet glaciers. There, some deposits of the Sirius Group are up to 200m thick and cover more than 200 km2. In contrast, Sirius Group deposits in the Dry Valleys are patchy and generally less than 10m thick.
Sirius Group deposits of the Central Transantarctic Mountains, particularly that of the Beardmore Glacier region, demonstrate a time of relatively mild polar climate, with a lowland terrestrial landscape of streams and lakes, and a coastline of fjords and tidewater glaciers, covered by shrubby Nothofagus and other tundra-like vegetation supporting an insect population. In the 1994-95 Antarctic field season we visited a key deposit of the Sirius Group at Quartz Hills in the Reedy Glacier area, but logistical problems and poor weather limited the program to only 3 working days at this locality. Nevertheless, an excellent section of alternating glacial and "interglacial" units was described and samples collected for sedimentologic and micropaleontologic study, and some of the uppermost units originally interpreted to be lacustrine appear to be marine (see Wilson et al. abstract). We described less than 10% of the Sirius Group material at the Quartz Hills location and were only able to measure one partial section. Many other sections need describing and all sections including the one we initially described warrant further detailed study so that a three dimensional picture of the environment can be constructed, a chronology developed, and further knowledge can be gained of the Late Neogene fjord and lacustrine systems in the Transantarctic Mountains.
In the southern McMurdo Sound area, a collection of glacial erratics transported to coastal and ice sheet moraines is providing a picture of the Paleogene environment in Antarctica that is not currently available in outcrop. They are also providing some insight into more recent glacial transport processes and pathways. Between the Ross Ice Shelf and the Transantarctic Mountains at the mouth of the Reedy Glacier, an unexamined, but similar set of moraines exists, the Quonset Glacier Moraines. These moraines should be studied and examined in a similar approach to that taken with the McMurdo Sound Erratics project. Information derived from the erratics will add to the rapidly expanding paleoclimate and paleoenvironmental database from Cenozoic glaciogene sediments from the Transantarctic Mountains.
Earliest-Known Freshwater Decapods From Gondwana:
Permian-Triassic, Central Transantarctic Mountains
John L. Isbell1, Molly F. Miller2, Loren E. Babcock3, James W. Collinson3, and Stephen T. Hasiotis4
1Department of Geosciences, University of Wisconsin-Milwaukee
2Geology Department, Vanderbilt University
3Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
4Department of Geological Sciences, University of Colorado
Recently discoveries of Lower Permian body fossils and Lower Triassic trace fossils from the Shackleton Glacier area, Antarctica, represent the oldest fossils from Gondwana ascribed to crayfish or decapod crustaceans considered to be phylogenetically close relatives of crayfish. These fossils have important implications for the evolution of freshwater decapods, the evolution of early freshwater ecosystems, and for climate reconstruction during the late Paleozoic-early Mesozoic in high latitudes of Gondwana.
Lower Permian body fossils of a clawed crustacean from the Pagoda Formation (Lower Permian) of Mt. Butters, Antarctica, extends the fossil record of freshwater decapod crustaceans by ~65 million years, and confirms that decapods had radiated into freshwater habitats by the late Paleozoic. Preliminary work shows that the clawed crustacean has a closer resemblance to erymid and eryonid lobsters, both of which are marine, than to more advanced freshwater crayfish. Whether this new crustacean was ancestral to modern crayfish, or representative of a lineage that independently invaded the freshwater realm, is not resolved. The new clawed arthropod is found in glacio-lacustrine deposits in association with abundant conchostracan arthropods and sporadically abundant trace fossils representing the behavior of various animals. Some traces resemble those ascribed to the activity of insect larvae.
Burrows from the lower Fremouw Formation (Lower Triassic) of Kitching Ridge and Shenck Peak, Antarctica, are among the oldest apparently constructed by crayfish. Their morphology is similar to modern crayfish burrows, which demonstrates that burrowing behavior was established early in the evolution of this group. Burrows putatively constructed by crayfish are found in fluvial deposits, sometimes in association with large burrows resembling those from coeval deposits of South Africa that were constructed by vertebrate animals.
The new discoveries show that Permian freshwater decapods were distributed in high paleolatitudes of southernmost Pangea, where they lived in freshwater lakes fed by glacial meltwater. Triassic burrows attributed to crayfish were constructed in floodplain deposits of large braided stream valleys. Using modern crayfish as guides to temperature tolerance, summer temperatures of streams and lakes near the South Pole that supported the crayfish probably reached 10-20C during Permian-Triassic interglacial intervals.
Sedimentary Studies of the Sirius Group in the Transantarctic Mountains:
Interpreting Local vs. Long-Distance Provenance and Depositional Environments
Larry A. Krissek
Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
The Sirius Group is a glacigene sequence that outcrops at scattered, high altitude locations in the Transantarctic Mountains. The age(s?) and origin of this sequence are controversial, with implications for the timing and number of expansions in size of the East Antarctic Ice Sheet. Regardless of the controversy surrounding its age, however, the mineralogical and geochemical compositions of the Sirius Group deposits have not been examined in any systematic way; such examination should provide valuable information for mapping the variety of source rocks presently covered by glacial ice. Potential source rocks are hypothesized to include well-known lithologies exposed locally in the Transantarctic Mountains, poorly known lithologies exposed in East Antarctica, recycled Sirius Group materials, and (possibly) material derived from bedrock in the Ross Sea. The primary objective of detailed compositional analyses will be to distinguish these contributions, so that the sub-ice geology in East Antarctica can be mapped in more detail.
Field interpretation of Sirius Group outcrops, combined with more detailed compositional analyses of environmentally sensitive lithofacies (e.g., paleosols, lake deposits), can be used to interpret environmental conditions at the time of deposition. These reconstructions can then be used to test paleoenvironmental reconstructions previously developed on the basis of biotic components in the Sirius Group. At all stages in these analyses, care should be taken to identify and extract any pristine volcanic glass for subsequent dating, which may provide evidence constraining the timing of Sirius Group deposition.
At the present time, the Sirius Group "controversy" is based primarily on data from the Dry Valleys and the Beardmore Glacier region. Additional detailed fieldwork has been conducted in the areas of the Shackleton Glacier and the Reedy Glacier. In order to fully examine the potential range of Sirius Group compositions and depositional environments, future fieldwork should be focused on other areas, such as reported Sirius localities at the geographically widespread Wisconsin Range, Ohio Range, and Byrd/Darwin Glacier regions.
Quaternary to Miocene Glacial Deposits in the Transantarctic Mountains:
New Constraints From Cosmogenic Nuclides
Mark D. Kurz and Robert P. Ackert
Woods Hole Oceanographic Institution
Evidence for warmer climate, and a smaller East Antarctic Ice Sheet, has been inferred from Pliocene microfossil assemblages found in Sirius Group glacial deposits. The fossil evidence for warmer climate (such as well-preserved southern beech (Nothofagus) leaves and wood) is not in dispute, but the age of the deposits has been hotly debated. It is now possible to obtain minimum ages of Sirius Group deposits using measurement of cosmic ray-produced helium-3 from dolerite boulders, which are a common lithology within the Sirius Group. New surface exposure ages from glacially deposited Ferrar Dolerite boulders that overlie Sirius Group outcrops at Bennett Platform, adjacent to the Shackleton Glacier in the Queen Maude Mountains (85.25S at 1930 meters elevation) demonstrate the utility of this approach. The Bennett Platform ages, from helium-3 measurements in clinopyroxene mineral separates, range from 3.9 to 10.6 million years (Ma). These are the oldest reported terrestrial surface exposure ages and are significant in demonstrating the age range of the technique and the extremely low erosion rates of Antarctic surfaces. Based on existing diffusion data for clinopyroxene, diffusive loss is not expected to be significant. Exposure to cosmic rays prior to deposition could make the exposure ages older than the deposition age, but is not considered likely due to the cluster of ages at 8 Ma (the overall mean is 7.7 + 1.9 Ma) and that consistent results are obtained from different localities. Due to the potential effects of erosion and uplift, and because the boulders overlie the Sirius Group, the ages obtained probably represent minimum estimates. Therefore, these data provide strong evidence that the Sirius Group deposits at Bennett Platform are significantly older than Pliocene. However, few of the Sirius Group locations in the Transantarctic Mountains have been sampled for cosmogenic nuclides, and it is unclear if the results from Bennett Platform are representative. Cosmogenic nuclides can also provide key chronological constraints on the ages of well preserved Quaternary moraines, found throughout the Transantarctic Mountains, which are critical to ice sheet/climate reconstructions during the last few glacial cycles. New results from the Beardmore area demonstrate that cosmogenic nuclides will be useful to this endeavor.
A Plume Origin for the Ferrar Large Igneous Province (FLIP)
Philip R. Kyle
Department of Earth and Environmental Science, New Mexico Inst. of Mining and Technology
Significant new geochronological data on the Ferrar Large Igneous Province (FLIP) shows it was erupted extremely rapidly and was also contemporaneous with the Karoo rocks in southern Africa (Encarnación et al., 1996; Fleming et al., 1997) and the Chon Aike in South America. The FLIP is therefore an integral part of the major (mega) magmatic province associated with the breakup of Gondwana. Although the Karoo rocks have been associated with a mantle plume (White and McKenzie, 1989; Cox 1992) such a model has not been proposed for the Ferrar. The apparent linear distribution of the FLIP along the Transantarctic Mountains has been related to continental back-arc spreading (rifting) associated with subduction along the Pacific margin of Gondwanaland. (Elliot, 1974) Ford and Kistler (1980) suggested it was related to a failed continental rift. Cox (1988) has suggested that the FLIP was related to a "hot line" with a series of linked centers of magmatic activity.
We suggest that the large size of the Dufek Intrusion, and the volume of other FLIP rocks requires a mantle plume to provide such a large amount of magma. For simplicity sake we suggest the presence of a single megaplume and further contend that the Dufek is a fossil remnant of plume activity.
One of the fundamental questions of the FLIP is the origin of the unusual geochemical composition. In a reversal of opinion I now suggest the unusual geochemistry and elevated isotopic signatures result from upper crustal contamination; I no longer believe the magmas were derived from an enriched asthenospheric source (cf Kyle, 1980). I further suggest that the crustal contamination occurred in two stages. The first stage occurred by a complex assimilation fractional crystallization (AFC) process in and during the growth and evolution of the Dufek Intrusion. The second stage of contamination occurred during lateral flow of magmas as they were transported away from the Dufek Intrusion. Most studies of the FLIP agreed that a small degree of upper crustal contamination has occurred by an AFC process. We suggest that this occurred in sills and dikes as magma flowed outward from the Dufek intrusion. Upper crustal contamination is the simplest and I believe the best explanation for the FLIP geochemistry. Mantle reservoirs have been well characterized through the study of oceanic island basalts (Zindler and Hart, 1986; Hart et al., 1992) and there is no evidence of any mantle material with an isotopic signature like that of the Ferrar. In addition, if the Ferrar is plume-derived it requires upper crustal recycling down to the core/mantle boundary (D") or the 670 km discontinuity. Also, if we believe all the Jurassic magmatism was associated with a single plume, then major changes in its composition must have occurred over time. The interpretation of the isotopic chemistry of the FLIP has been driven partly by philosophical arguments (e.g. Kyle, 1980) and the lack of a workable mechanism to account for such a large volume of magma with such a uniformly enriched isotopic composition. This was constrained by thinking that magmas were emplaced predominantly in a vertical sense and that they could not be emplaced laterally over huge distances from a single body. The vertical emplacement mode requires numerous magma chambers to feed the FLIP. Clearly some geochemical arguments have been made for derivation of the FLIP from an enriched (asthenospheric) mantle source (e.g. Kyle et al., 1983, 1987; Hergt et al., 1989a, b, 1991; Molzahn et al., 1996) and this has almost become dogma with some research groups. However, recent studies of the Siberian traps have shown that the same geochemical data can be interpreted as a result of crustal contamination (Arndt et al., 1993; Wooden et al., 1993) or derivation from an enriched mantle source (Lightfoot et al., 1990, 1993).
In the early phases of the plume the resulting magmas did not reside in the crust for long periods and therefore suffered less crustal contamination. I suggest these early magmas were emplaced and erupted toward Dronning Maud Land, the Weddell Sea and southern Africa. Later, as the plume matured and the volume of magma increased, it was ponded in the crust as a large magma chamber (the Dufek Intrusion). Significant crustal doming must have accompanied the plume activity and formation of the Dufek magma chamber. Eruption of the Ferrar magmas from the Dufek intrusion was probably late in its development (this is shown by the similar isotopic compositions of the lavas, dolerites and the Dufek rocks) in which case the intrusion may have acted like a cistern, partially emptying after it was sufficiently full and perhaps topographically high enough. The development of the Dufek Intrusion must have had a significant heating effect on the crust and as the size increased it would have promoted crustal assimilation. Although high quality isotopic data have not been published on rocks from the Dufek Intrusion, the available analyses (Faure et al., 1972 ; Brewer et al., 1992; Kyle et al., 1981; Ford et al., 1986) show that it is isotopically similar to the dolerites and basalts. A progressive increase in isotopic ratios in the granophyres near the top of the intrusion are consistent with crustal assimilation.
Crustal contamination is the norm in most continental flood basalt provinces (Macdougall, 1988) and in many large mafic intrusions. In continental flood basalt provinces the volumes of individual lavas formed from contaminated magmas are usually small. Within a single continental flood basalt province there is always a wide range in isotopic compositions suggesting variable degrees of crustal contamination. The unique feature of the FLIP is the uniformity of the isotopic compositions and the large volumes of magma which were involved. Above I have proposed that the FLIP isotopic composition is a consequence of upper crustal contamination. Because all Ferrar rocks are so isotopically uniform we take this one step further and suggest the FLIP effectively represents only a single or perhaps two batches of magma for which we interpret the enriched isotopic signature as a fingerprint. Using this reasoning we therefore are drawn to conclude that all the FLIP was derived from one body (i.e. the Dufek intrusion) and could represent a short instant of time in its magmatic evolution (this is clearly borne out by the available dating).
Regional Continuity and Magmatic Structure of the Ferrar Dolerites
Johns Hopkins University
The Ferrar dolerites in the Dry Valleys region form an unusually complete magmatic system. Cored by a small, but exceedingly well formed, ultramafic layered intrusion at the Dais in Wright Valley, the sills form a Christmas tree-like magmatic structure. The lowermost (i.e., Basement) sill everywhere here (100 x 50 km) contains an ultramafic tongue of orthopyroxene phenocrysts that records the sequence of sill emplacement. The relation of one sill to another shows that the system was emplaced over a relatively short time of perhaps only thousands of years. Although the sills are each fairly thick (250-750 m), their solidification times are short relative to large ultramafic bodies. This has effectively quenched-in an unusually clear record of the overall magmatic process of emplacement, differentiation and layer formation. The N-S development of the system is still unclear, but it may have formed from a series of emplacement centers much like that inferred along ocean ridges. The exact style of regional emplacement is of fundamental importance to establish. The tracing of characteristic marker sills north and south from the Dry Valleys and the magmatic budget all along the Trans-Antarctic Mtns. must be ascertained.
Gondwana Sequence Records Evolution of Freshwater Fauna and High Latitude Fluvial and Lacustrine Ecosystems
Molly F. Miller
The Permian and Triassic sedimentary sequence in Central and Southern Transantarctic Mountains (CTM and STM) provides a unique glimpse of life and climatic conditions in high latitude stream, floodplain, and lacustrine settings and allows comparison both within diverse environments as conditions changed and between contemporaneous high latitude and tropical ecosystems. Because bottom-dwelling freshwater organisms are thought to have been proliferating during the late Paleozoic and early Mesozoic, the sequence potentially could yield important information about the development of freshwater communities. In addition, these faunas probably were sensitive to variations in salinity conditions, and the structures resulting from their activities (biogenic structures) may be used to interpret paleosalinities and constrain paleogeographic reconstructions.
Questions to be answered by further study of the sequence in the CTM and STM include, but are not limited to, the following:
1) How did Permian and Triassic infaunal activity in aquatic environments in high latitudes (e.g., CTM and STM) differ from that in equivalent environments at low latitudes? Is bioturbation intensity, a proxy for macrobenthic activity and (less reliably) for macro-benthic diversity, greater in CTM rocks deposited under cool, perhaps wet conditions than in equivalent rocks exposed in the western U.S. deposited under warmer, possibly seasonally arid conditions? What does this indicate about the early colonization of aquatic environments, and how does it compare with activity of modern animals in similar environments?
We presently have a data set consisting of thousands of semi-quantitative observations of bioturbation on bedding planes in the Shackleton Glacier area. Similar data will be collected from Permian and Triassic rocks of the western United States. However, for the comparison to be meaningful, we need to assess the within-high latitude variability in bioturbation in other areas of the CTM rather than rely solely on the Shackleton data.
2) Were crayfish present in the Permian and Triassic glacial lake, inland sea, and fluvial environments throughout the CTM and STM, and if so, how abundant were they? As the largest omnivores in modern aquatic systems, crayfish are important controllers of the energy flow through lake and river ecosystems. Discoveries of a crayfish body fossil and crayfish trace fossils in the Shackleton Glacier area suggests that they were present tens of millions of years earlier and at much higher latitudes than previously thought, implying that the structure and functioning of these ancient aquatic communities was surprisingly similar to those in similar modern ecosystems. Were they widespread in throughout the CTM and STM during the late Paleozoic and early Mesozoic, or were they confined to a small patch in the Shackleton area? Did they prefer some environments over others, and if so, what were the controlling factors? What does the distribution of crayfish indicated about the paleoclimate?
3) Do the trace fossils and extent of bioturbation differ significantly in Permian rocks of the CTM and STM? Gradations in trace fossil content and diversity from the Beardmore Glacier area to Ellsworth Mountains suggest a salinity gradient from fresh to near-normal marine salinity conditions. Can trends in amount of bioturbation and trace fossil content be used to constrain the location of significant salinity changes?
4) Were the dominant depositional processes and environments recorded by the post-glacial shale (Mackellar Formation and equivalents) the same throughout the CTM and STM? If not, how and why did they differ? What are the paleogeographical and paleoclimatic implications of differences in depositional regime?
Can Study of Wind-Blown Gravels in the Transantarctic Mountains Yield
Information Applicable to the Interpretation of Surficial Deposits
of Other Planets?
Molly F. Miller
Department of Geology, Vanderbilt University
During the 1995-96 field season, wind-blown gravel deposits were recognized in the Miers Dry Valley and Shackleton Glacier areas. During a storm in early November, transportation of gravel-sized particles was observed by Gary Wilson and members of his field party. Further investigation by Gary Wilson, Mike Wizevich, John Isbell, and Molly Miller revealed that at least some of the gravel transported during this event was deposited in low amplitude dunes. This observation lead to recognition and preliminary study of wind-blown gravel deposits in several locations in the Shackleton Glacier area by A. Ashworth, J. Isbell, M. Mabin and M. Miller. The particles are several centimeters in diameter and deposited in two and three dimensional dunes with wavelengths on the scale of meters and amplitudes on the scale of centimeters to decimeters. The gravel dunes may be concentrated in topographic lows where wind flow is constricted. The prevailing wisdom is that gravel particles are too large to be transported by wind and that wind-blown deposits are fine-grained (sand size and smaller). The only report of wind- blown gravel of which we are aware is by Howard Wiltshire and co-workers who experienced transportation of gravel during a storm in the southern Great Valley, California in 1977 and described the resulting deposits.
Studies by Malin in the 1980's of the interaction of wind and sediment in Antarctica focused on the mechanisms and rates of particle abrasion and the role of abrasion in determining weathering rate. Malin recently applied the results of these studies to interpretation of pictures of the surface of Mars taken by Sojouner, the Pathfinder's rover (Science News, 152, August 9, 1997, p. 84). It appears that sand-sized Martian sediment has been transported and deposited in dunes, and that larger particles are etched and grooves. However, the question of whether the coarse-grained particles have been displaced is not addressed. More complete understanding of the origin of the gravel deposits, the surficial texture of the gravel particles, and the distribution and abundance of the gravel deposits in the Transantarctic Mountains might constrain the conditions to which Martian (or other planetary) surficial sediments have been subjected.
Structural Kinematic Studies of the Transantarctic Mountains, Antarctica
Timothy Paulsen and Terry J. Wilson
Byrd Polar Research Center, The Ohio State University
Regional fault arrays typical of other extensional mountain belts in the world have yet to be mapped throughout the Transantarctic Mountains. Consequently, the kinematic development of the range remains problematic. Available data permit a variety of models for the kinematic development of the Transantarctic Mountains. Did the Transantarctic Mountains develop by orthogonal or oblique extensional processes? Did orthogonal and oblique extensional episodes occur at different times during TAM development? Each model predicts diagnostic fault geometries and kinematics and, thus, detailed mapping and fault kinematic analyses can distinguish which of these models best explains the kinematic development of the range.
Our current work integrating satellite-based mapping and previous field studies is providing a better picture of the regional structural architecture of the mountains, but little is known about the displacement patterns of the regional fault arrays found along the range. Obtaining field-based data on the slip-trajectories of mesoscopic and regional faults is critically needed in order to develop more robust kinematic models for the structural evolution of the mountain belt. Key targets for such structural analyses in the central and southern TAM include regions near the Byrd, Nimrod, and Scott Glaciers, where regional structures are suspected but little is known about the slip-trajectories of faults that occur in these regions. For example, our current work in the vicinity of Scott Glacier suggests the presence of two regional faults sets, one subparallel and another transverse to the mountain front. What role have the longitudinal and transverse structures played during mountain belt development? Do these faults reflect longitudinal normal and transfer faults that accommodate different rates, magnitudes, directions of extension and uplift within the mountains? Understanding the kinematic roles of these fault sets would help establish whether orthogonal extension or transcurrent motions occurred during rifting and uplift in this sector of the mountains.
Search for Impact Beds at the Permian-Triassic Boundary in Antarctica
Department of Geological Sciences, University of Oregon
The Permian-Triassic boundary was the time of the greatest of all mass extinctions in the history of life. This boundary was until recently difficult to locate in non-marine rocks, but now can be picked in Antarctica and Australia by a dramatic lightening in the carbon isotopic composition ( 13C) of organic matter (kerogen), supported by information from sequence stratigraphy, from palynology, from glossopterid fructifications and other paleobotanical evidence, from vertebrate biostratigraphy and from radiometric dating. There is already evidence of massive extinction of plants and animals on land at the same time as the well known decimation of marine life. Furthermore, there are breccia beds at the boundary in Antarctica and Australia that can be attributed to massive deforestation. These beds recently yielded shocked quartz, and the boundary breccias and coals also contain iridium anomalies. These new data together with discovery of a 500-km-diameter crater at the Permian-Triassic boundary in the offshore Canning Basin of western Australia provide new evidence for the role of extraterrestrial impact in the extinctions.
Unfortunately the boundary sections at Mt Crean (Victoria Land) and Graphite Peak (central Transantarctic Mountains) with breccias, shocked quartz and iridium anomalies have not yet yielded fallout layers like those known from the Cretaceous-Tertiary boundary. The breccia beds have the character of redeposited soil beds. There is a need to find more complete boundary sections, to sample them more thoroughly and to conduct more detailed sampling than has been possible so far.
Using Paleosols to Reassess Neogene Paleoclimates of the Sirius Group
Department of Geological Sciences, University of Oregon
The age and paleoclimate of the Sirius Group of the central Transantarctic Mountains have been controversial. Some see it as evidence of stability and others for instability of the East Antarctic ice cap during the Pliocene (3.5 Ma). At least three distinct pedotypes can be recognized among paleosols in the Sirius Group exposed in the Dominion Range Antarctica (85 6.8'S 166 43.2'E). The paleosols are similar to soils supporting cushion plant-lichen communities including the woody plant SalK arctica on beach ridges of Truelove Lowland, Devon Island, Canadian Arctic, where mean annual temperature (MAT) is - 16C, mean annual precipitation (MAP) is 130 mm and a growing season of 69-99 days has temperatures of 1.3-13.6C. Such an assessment is compatible with recent interpretation of Nothofagus fossils from Oliver Bluff as prostrate, dry tundra shrubs. Also comparable to the paleosols are soils of Enderby Land, Antarctica (MAT-11C, MAP 600 mm). The paleosols show no podzolization, lessivage or peat accumulation found under conditions of subantarctic tundra or southern Chilean moorland or woodland. They are like soils of frigid, glaciated climates.
These preliminary results underscore the need for further detailed characterization of the variety of paleosols found in the Sirius Group, not only in the Dominion Range but also in other parts of the Transantarctic Mountains and Victoria Land. Furthermore, the well- established chronofunctions for Antarctic soils and the relationships of many of the paleosols and soils within post-incisive flights of terraces opens the opportunity for dating of the various Sirius Group outcrops by means of soil development indicators.
Paleosols as Guides to Permian and Triassic Paleoclimates of Antarctica
Department of Geological Sciences, University of Oregon
Field, petrographic and chemical studies of a variety of early Triassic paleosols from Victoria Land and the central Transantarctic Mountains indicate a humid, forested paleoclimate(1300-1500 mm mean annual rainfall) in a temperature regime no cooler than cool temperate, similar to previously described early Triassic paleosols from near Sydney, Australia. The Antarctic and Australian paleosols are most similar to current soils in Pennsylvania, Tasmania and New Zealand, at much lower latitudes than their estimated Triassic paleolatitude of about 70S. In contrast, Permian and middle Triassic coal measures in Antarctica include patterns of cracking and doming compatible with interpretation as ice-disrupted string bogs (aapa mires and palsa mires), found at latitudes of 70N in Finland and Canada today. Although much has been made of anomalous Permian and Middle Triassic forests of Antarctica, the Early Triassic paleoclimate of the ice continent stands out as an especially prominent anomaly. Taken in conjunction with isotopic and paleobotanical evidence for a productivity crisis at the Permian-Triassic boundary, the Early Triassic anomalous polar warmth can now be regarded as a post- apocalyptic greenhouse.
These early Triassic paleosols show some striking differences from paleosols of other ages: particularly their lack of coal, abundant berthierine and exceedingly isotopically light carbon isotopic composition. These may be products of a greenhouse that included much methane. This issue could be addressed by petrographic and chemical studies and by depth functions for carbon isotopic composition within individual paleosols.
Late Neoproterozoic and Cambrian History
A.J. (Bert) Rowell
University of Kansas
The age of the oldest metasedimentary rocks and the timing of the principal episodes of deformation in the Transantarctic Mountains remain poorly constrained. Recent studies in the Pensacola Mountains, near the Weddell Sea terminus of the range demonstrate that not all of the metaturbidites and slates referred to the Beardmore Group are Precambrian and there is no compelling evidence for a Precambrian Beardmore orogeny in the area. U-Pb dating of detrital zircons of the Patuxent Formation from the western part of the region (the Patuxent Range, Rambo Nunatak, and the Schmidt Hills) are of Cambrian or younger age and contain detrital zircons from a ca. 500 Ma source. Farther to the east, in the eastern Neptune Range, rocks of similar lithology, presently also referred to the Patuxent Formation, are demonstrably older as they are overlain unconformably by the late Middle Cambrian Nelson Limestone. These metasediments have recently yielded detrital zircons of 561+/-2 Ma and thus they and their deformation are either of latest Neoproterozoic or, more probably, of Early Cambrian age. Their deformation is more intense than that of later episodes of folding, which were initially considered to be the total expression of the Ross orogeny (Storey et al., 1996).
In the Beardmore-Byrd sector of the Transantartic Mountains at least two episodes of deformation occurred. The main phase of folding is younger than the middle to ?upper Lower Cambrian Shackleton Limestone. Deformed clasts of this limestone occur in the unconformably overlying Douglas Conglomerate (Rees and Rowell, 1991). Because the Douglas Conglomerate is itself folded and cleaved, it is inferred to be substantially older than the Devonian Beacon Supergroup. A useful working hypothesis (Rowell et al., 1993) suggests that the Douglas Formation is Middle or Late Cambrian in its basal beds; that the main deformation of the Shackleton Limestone is of late Early Cambrian - early Middle Cambrian age and is an expression of the principal phase of the Ross orogeny; and that the youngest expressions of the Ross event, which folded the Douglas Conglomerate, are broadly contemporaneous with the post-Middle Cambrian events in the Weddell Sea sector of the range. The hypothesis is potentially testable by U-Pb isotopic dating of detrital zircons from the Douglas Conglomerate and by recovery of body fossils from some of its marine beds that so far have yielded only trace fossils.
Together with its probable continuation in Australia, the Transantarctic margin is the longest and best-preserved Cambrian active margin known. Understanding the timing of its deformation and magmatic activity is of potential global significance because they may share a common driver with other late Early Cambrian to Middle Cambrian global events, extinctions, and abrupt sea-level changes.
Potential Field Problems, Central Transantarctic Mountains
Department of Geology, Arizona State University
Relationship of the Byrd and Beardmore Groups, Nimrod Glacier Area
In the last decade the relationship of the Byrd and Beardmore Groups has become controversial In the original mapping by Laird et al. (1971) five localities were identified in which Early Cambrian Shackleton Limestone (Byrd Group) unconformably overlies Goldie Formation (Beardmore Group). The folding of the Beardmore Group was called the Beardmore orogeny (Grindley and McDougall, 1969), which has had long standing in the tectonic lexicon of the Ross orogenic belt, although the precise dating and the aerial extent of this event have remained elusive. Examination of a several of Laird's localities (excluding Cotton Plateau) by Rowell et al. (1986) led to the reinterpretation of these contacts as tectonic rather than unconformable. Stump et al. (1991) mapped the contact between Goldie Formation and Shackleton Limestone at Cotton Plateau concluding that it was in fact unconformable, and that Goldie Formation had been folded and eroded prior to deposition of the Shackleton Limestone, which was subsequently deformed during the Ross orogeny. However, Stump (1992) pointed out that a clayey zone at the contact had some earmarks of a fault pug. Except along its western margin of occurrence, the Goldie Formation has had only one generation of folding identified by any of the geologists who have mapped it. Most recently Goodge (1997) has argued that the term Beardmore orogeny should be altogether abandoned, since nowhere has he observed a second generation of folding in the Beardmore Group. To resolve the question of whether the Beardmore Group was deformed prior to the deposition of the Shackleton Limestone, a worthy project would be to examine each of the five known localities where the two units are in contact, and to undertake detailed mapping and structural analysis of the formations on both sides of the contacts, toward a resolution of the problem. Based presumably on air photo interpretation, Grindley and Laird (1969) have also mapped the contact between these two units in the catchment of the Hamilton Glacier, north of Mt. Markham, although no geologists have yet visited this area. Exploratory mapping of this area may also produce important information relevant to this problem.
Nature of the Byrd Glacier Discontinuity
In general, structural trends, formation boundaries, and plutonic bodies in the Ross orogenic belt are elongate subparallel to the Transantarctic Mountains throughout their 3500 km length. One notable exception to this generality occurs at Byrd Glacier. On the south side of Byrd Glacier, for nearly the entire width of the mountains the bedrock is composed of folded, unmetamorphosed Shackleton Limestone and associated clastic formations of the Byrd Group, which continue southward for more than 300 km. On the north side of Byrd Glacier, again for the entire width of the Transantarctic Mountains, are amphibolite-grade metamorphic rocks (Horney Formation) and intrusives that continue, albeit with variations, all the way to the end of the Transantarctic Mountains, more than 1,000 km to the north.
Determining the nature of this geological discontinuity is a fundamental question relating to the history of the Transantarctic Mountains. Is the discontinuity a relic of an irregular continental margin established at the time that Laurentia broke off from Gondwanaland, an irregularity that defined the basin of deposition of the carbonate shelf represented in the rocks of the Shackleton Limestone south of Byrd Glacier, but not north of it? Have the crystalline rocks north of Byrd Glacier acted as an abutment during folding of the Byrd Group? Or have the crystalline rocks north of Byrd Glacier been tectonically exhumed during extension from beneath the unmetamorphosed units to the south? Is the discontinuity due to strike-slip faulting parallel to Byrd Glacier, and if so was the movement pattern right-lateral or left-lateral? If strike slip faulting, did it occur before or after deposition of the Beacon Supergroup above the post-Ross erosion surface? Did the discontinuity have any effect on the pattern of Beacon sedimentation above the Kukri peneplain? Did brittle faulting associated with the Cenozoic uplift of the TAM produce patterns similar to those elsewhere in the TAM, or were they more locally controlled? Did the rocks north and south of Byrd Glacier follow a similar uplift/denudation history or were there appreciable differences? What is the regional geophysical signature of this discontinuity, and what does that imply about the geological history?
The scope of this problem will require a multidisciplinary approach to it solution, including field mapping and collection, airborne geophysical measurements, and laboratory analysis. Field mapping will include structural analysis of single and polyphase folding in the Byrd Group and Horney Formation, stratigraphic analysis of Beacon Supergroup, as well as analysis of Cenozoic, mesoscale faulting. Returned samples would be analyzed to determine pressure and temperature conditions of metamorphism on both sides of the discontinuity. Isotopic studies would indicate domains of lower crustal sources for the magmatic rocks in the area. The thermochronology of these rocks should be determined for the entire temperature range from magmatic crystallization to shallow unroofing using U/Pb, Ar/Ar, and fission-track techniques. The elevation of the post-Ross erosion surface should be accurately mapped to determine the present-day architecture of the mountains in this area. Depending on the antiquity of the discontinuity, the study offers the opportunity to document a classic example of geological inheritance, through a feature that may have regionally affected successive episodes of geological activity for more than a half billion years.
Central and Southern Transantarctic Mountains: Fossil Floras and Paleoclimate
Edith L. Taylor and Thomas N. Taylor
Department of Botany, University of Kansas
During the late Paleozoic and Mesozoic, Antarctica occupied a critical position in the center of Gondwana (Scotese, 1990), and is thus an important factor in understanding the distribution of past floras and migration routes into other continents. Moreover, the very high latitudes in which these organisms often existed provide a unique opportunity to investigate the influence of particular physical parameters on the biology and evolution of the organisms. Both the composition of individual floras and the structure of the plants within them provide an original data source that can, in some instances, be used as a climate proxy to assess such factors as available moisture, temperature, or growing season (e.g., Chaloner and Creber, 1990; Cùneo et al., 1991, 1993; Taylor et al., 1992). Unfortunately, our knowledge of particular floras in Antarctica and their relationships to those on other Gondwana continents (as well as those elsewhere in Antarctica) is still in the formative stages. Systematic collections of both plant and animal fossils have only recently been undertaken in Antarctica. To gain the maximum amount of information from field collections, they must be done in concert with detailed sedimentological, paleoecologic, and biostratigraphic studies. The cooperative program that focused on the Seymour Island area is an excellent model for this type of approach (see Feldman and Woodburne, 1988 and papers cited therein).
Preliminary work has clearly demonstrated that there are several areas in Antarctica that have the potential to yield important information about past biotas and the physical factors that affected their evolution and distribution. One such area, based on the exquisite preservation and the diversity of the fossil plants found there, is the Beardmore Glacier region. Studies in our laboratory have focused on this area for some years, but have recently been extended to include collections made in the Shackleton Glacier region during the 1995-1996 field season. Exceptionally well-preserved fossil plants and permineralized wood were also found at these sites (e.g., Taylor et al., 1997). These megafossil plant collections from the central Transantarctic Mountains are expanding our knowledge of the diversity, distribution and adaptations of Permian and Triassic floras from Antarctica.
Fossil plants have been reported from a number of additional sites in the central and southern Transantarctic Mountains, but most of these have never been systematically studied. Some of these sites are: the Starshot Glacier region (M. Rees, pers. comm.), Mt. Weaver in the Queen Maud Mountains (Darrah, 1936; Doumani and Minshew, 1965) the Ohio Range (Cridland, 1963; Long 1965; Schopf, 1967, 1968), Mill Glacier (Townrow, 1967), the Law Glacier (Lambrecht et al., 1973), and the Horlick Mountains (Schopf, 1962, 1968; Long, 1964; Minshew, 1966).
Our component of the Transantarctic Mountains cooperative research activity will include the collection of megafossil plant material from known sites (e. g., Beardmore and Shackleton Glacier areas), which have yielded permineralized trunks and peat, as well as exquisitely preserved compressions. In addition, we propose to explore a number of promising sites that have been noted by other Antarctic research teams. The data that we collect on diversity and distribution of Permian and Triassic floras in the Transantarctic Mountains, as well as paleoclimate information from fossil tree rings and permineralized plants, complement other existing Antarctic research programs. Finally, the exceptional preservation of these Permian and Triassic floras (and Jurassic material where available) offers the rare chance to study plant and floral evolution at high paleolatitudes.
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Scotese, C.R. (chair of Paleomap Project). 1990. Atlas of Phanerozoic plate tectonics reconstructions, International Lithosphere Program (IUGG-IUGS). Paleomap Project Techn. Rept. 10-90-1, 53 figs.
Taylor, E.L., T.N. Taylor and N.R. Cùneo. 1992. The present is not the key to the past: A polar forest from the Permian of Antarctica. Science , 257, 1675-1677.
Taylor, E.L., T.N. Taylor and J. Isbell. 1997. Evidence of Permian forests from the Shackleton Glacier area, Antarctica. Amer. J. Bot., 84 (6, supplement), 143 pages.
Townrow, J.A. 1967. Fossil plants from the Allan and Carapace Nunataks and from the Upper Mill and Shackleton Glaciers, Antarctica. New Zealand J. Geol. Geophys., 10, 456-473.
Crustal Structure of the Central and Southern Transantarctic Mountains
Ralph von Frese
Department of Geological Sciences and Byrd Polar Research Center , The Ohio State University
The Transantarctic Mountains (TAM) form a major transcontinental range over 2500 km long with elevations up to 4500 m, which separates East Antarctica from the Ross Ice Shelf and Sea, and West Antarctica. The crustal structure of this range reflects significant details concerning the interaction and tectonic histories of East and West Antarctica, and the uplift of the mountains which has occurred during the inception, growth, and fluctuations of the present ice sheet. However, despite their considerable geologic significance, relatively little is known concerning the tectonic evolution and crustal attributes of the TAM. The geographic limits and crustal properties of the central and southern TAM in particular are very poorly known at present. Fixed- and rotary-wing gravity and magnetic surveys can provide important constraints on the crustal structure of the TAM to help decipher their tectonic setting, structural limits, and uplift history. These surveys also will contribute important new data to international efforts to produce digital magnetic and gravity anomaly databases for the Antarctic. Gravity and magnetic data obtained within the 7-degree hole about the South Pole are especially critical for augmenting the lack of satellite coverage, and hence for updating global models of the Earth's gravity and magnetic fields.
Structure and Thermal State of the Antarctic Crust From Deep
Resistivity (Magnetotelluric) Surveying
Philip E. Wannamaker and John A. Stodt
University of Utah/EGI
A new window has been opened on deep thermal and fluid state of the Antarctic lithosphere with the ability now to acquire high-quality magnetotelluric (MT) measurements over the thick polar ice sheet. MT makes use of naturally- occuring electromagnetic (EM) waves in the frequency range 1 KHz to 0.001 Hz, or even lower, as source fields for imaging electrical resistivity structure of the earth's interior. Electrical structure of the deep crust and upper mantle in turn provides useful bounds on fluid and melt fraction, and can thereby distinguish mechanisms of uplift and topographic compensation. This has been born out in previous studies of the U.S. Southern Sierras, Great Basin to Colorado Plateau transition, and the New Zealand South Island.
The principal challenge for obtaining high-quality MT data in Antarctica is the extremely high (0.5 M-ohm or greater) contact impedance of the firn for making the sensitive electric field measurement. This has been overcome with an original electrometer design using ultra low noise components and provision to calibrate the effects of the contact. Example soundings and an interpretation of a profile from the Central West Antarctic (CWA) geophysical campaign are described by Wannamaker et al. (1986) and will be reviewed briefly. A newly funded project by the NSF/OPP will attempt to acquire a followup profile at South Pole station. This effort will test the cratonic nature of this area of East Antarctica test the efficacy of MT under the more severe temperatures of South Pole, and provide a crustal baseline for possible deep mantle resistivity sounding (100- 1000 km depth range).
A successful South Pole project will help demonstrate feasibility of the method throughout Antarctica. Hence, there will be the exciting possibility of contributing to a multi- technique study of the tectonic transition across the central and southern Trans Antarctic Mountains from Late Cenozoic extension and magmatism to stable but uplifted shield conditions. Ideally, MT profiling in Antarctica should have a crew of four or five fit and experienced people equipped with a towable central recording hut, generator, tracked vehicle (Tucker or Sprite), snowmobiles and Nansen sleds. Weather needs to be calm - winds over 12 knots cause serious measurement noise. Surveying rates under good conditions are about 4 km per day. This assumes logistical support for meals, structures, etc., which otherwise would reduce productivity.
Wannamaker, P.E., J.A. Stodt, and S.L. Olsen. 1996. Dormant state of rifting below the Byrd subglacial basin, West Antarctica, implied by magnetotelluric (MT) profiling. Geophys. Res. Lett., 23, 2983-2986.
Wannamaker, P.E., J.M. Johnston, J.A. Stodt and J.R. Booker. 1997. Anatomy of the Southern Cordilleran Hingeline, Utah and Nevada, from deep resistivity profiling. Geophysics, 62, 1069-1086.
The Late Phanerozoic Terrestrial Realm
Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University
The terrestrial record of late Phanerozoic (the last 100 m.y., or Late Cretaceous-Cenozoic) Antarctica is the most poorly understood of all major continental landmasses, even after forty years of intensive investigation since the International Geophysical Year (1957-58) . It is sobering that we have probably documented no more than about 15 percent of late Phanerozoic time in the Antarctic terrestrial realm. Conclusions and hypotheses based on proxy data from Deep Sea Drilling Project and Ocean Drilling Program investigations provide generalized views of events on Antarctica at different points in the Cretaceous and Cenozoic but these are unable to contribute high resolution detail or portray events in specific regions of the continent.
It is often observed that Gondwana fragmented and dispersed during the late Phanerozoic, leaving Antarctica isolated in a high latitude location and surrounded by a major ocean system; that a hothouse (greenhouse) world evolved into an icehouse world during the same interval of time; and that geosphere-hydrosphere-atmosphere events in the southern high latitudes were major factors in global evolution from a non-glacial to a bi-polar (cryospheric) Earth. This scenario seems reasonable, but Antarctic data sensu stricto has played little direct role in arriving at currently accepted doctrine.
The presence of two large ice sheets are the principal reasons why we are at an impasse as far as the terrestrial record is concerned. We must now ask ourselves two major questions. First, should we accept the fact that long-time-scale global change can and should be resolved, at all temporal levels, via a bigger and better proxy (usually paleoceanographic) records. Second, if the answer to this question is NO, then what actions do we propose to take to improve the proximal (continental) record. If the decision is made to redouble our efforts in building a more complete late Phanerozoic terrestrial data base, then we must urgently reassess our science strategies and also count the cost of the major technological and logistic efforts that will be required.
Available Terrestrial Data
Most existing terrestrial data are documented at points along the margins of the continent. Late Cretaceous and Paleogene data are best developed along the Pacific and Atlantic margins of the Antarctic Peninsula; and most Neogene data derive from the Amery Graben-Prince Charles Mountains and Transantarctic Mountains regions of East Antarctica, and Marie Byrd Land. Little or no information is available from outcrops in the interior of West or East Antarctica, although some indirect information comes from material transported to the continent margins. A rough estimate suggests the total terrestrial data base is representative of no more than 15 percent of the area of West and East Antarctica. No one will seriously suggest that late Phanerozoic terrestrial history and its impact at the global level can be argued from such a restricted geographic sample. It is fortuitous, however, that in this relatively small area there is a close association of sedimentary and datable volcanic rocks and so what we have had to work with is quite well time-constrained.
I now suggest and comment on priorities one might include in a future long-time-scale terrestrial science plan. This discussion assumes that new programs of scientific drilling are necessary and will lead to the successful recovery of geological materials which provide significantly improved temporal and geographic data point coverage for the last 100 m.y. It is suggested that each topic discussed below be categorized in terms of macro-temporal (5 to 10 m.y.), meso-temporal (0 .1 m.y. to 1 m.y.), and micro-temporal (1 yr to 10,000 yr) scales.
Standard chronostratigraphy, biochronostratigraphy, & magneto-chronostratigraphy - The best known terrestrial localities occur at the continental margins, usually in passive and compressional tectonic environments, and with sedimentary successions having a close association with volcanic and marine sediments. These areas will continue to be essential in refining terrestrial histories in marginal environments, and in providing linkages to high resolution deep sea data bases. Standard isotope dating procedures and marine biostratigraphy will continue to provide temporal resolutions at the million year scale. However, it is unlikely that the amount of time accounted for in these areas will be increased substantially.
Terrestrial successions from the tectonically stable continental interior will be more difficult to date by conventional methods. Opportunities for refined time control will arise if interdigitating terrestrial and marine successions and infra-cratonic volcanic provinces are encountered. Ash shower penetration across the interior montane and basinal regions might provide additional time control for pre-glacial or deglacial episodes on the continent. Wherever possible these and other methods should be used to provide time-constraints of major erosional, weathering and depositional phases; and in assessing the duration of high latitude geosphere processes.
Paleotopography and geomorphology - Present knowledge of sub-ice sheet topography relies on a combination of geophysical techniques, glacio-isostatic adjustment estimations, and hypsometric contouring. Time-slice physiographic contouring procedures should be devised at macro-temporal scales (i.e. 10 m.y. intervals of time). More refined paleotopographic controls might be possible for some intervals of time by the use of accurately dated elevational datums provided by paleontological, eustatic and other data. Improved paleotopographic analysis will allow a pinpointing of both upland topography and the lowland drainage patterns which acted as major sediment transport conduits to infra and peri-cratonic freshwater and marine deltas. Factors to be considered here include: evolving deep crustal tectonic history, glacial and non-glacial erosion phases and associated crustal adjustments, ice volume changes and associated glacio-isostasy, characterization of the terrestrial hydrosphere and cryosphere through time, environmental diversity (i.e. fluvial, lacustrine, cold and warm deserts, etc.), weathering and pedogenic development, and landscape evolution.
Terrestrial stratigraphic record - Formal lithostratigraphy (i.e. groups, formations, and members) should be proposed, disconformities highlighted, with both constrained by age control wherever possible. Sub-ice sheet drillhole data should be coupled with acoustic and other geophysical surveys in attempts to understand the thickness and extent of the probable very extensive sub-ice sheet sedimentary basins. Physical property measurements would be undertaken on all core material and drillholes subjected to geophysical logging.
Terrestrial-marine stratigraphic interfaces and relationships - Because of the very extensive coastal zone around Antarctica and the probability of marine advances and retreats across the continental margin and into the continental interior (produced by glacial-deglacial cycles, eustatic oscillations, and tectonic emergence and subsidence), there exists the probability of very complex but meaningful terrestrial-marine succession relationships. This provides a unique opportunity to examine a number of significant regional and global problems. These include ice history-sea level history, mass transport of sediment to the continental shelf basins, maritime paleoclimate, and evolving littoral distribution patterns.
Biosphere - Plate tectonic events, involving the fragmentation of the Gondwana supercontinent, the northward flight of the component fragments, and the geographic isolation of Antarctica in a polar setting , make for a unique late Phanerozoic terrestrial biospheric history. The fate of the greenhouse biological isolates and their icehouse (cryosphere) successors is of central importance in assessing global change in the southern high latitudes. Current terrestrial data bases provide a wealth of information on the paleobotanical record for West and East Antarctica, but the invertebrate and vertebrate paleozoological record is surprisingly meager. A concerted effort should be maintained to build on current paleontological data bases through systematic and assemblage studies. Equally important are contributions these floras and faunas make to understanding biogeographic range (provinces) across the continent, and the significance this holds in the tracing paleoenvironment and paleoclimate shifts. Attempts should be made to portray provincial range oscillation at the macro-temporal (5-10 m.y.) and meso-temporal (1 m.y.) scales. Such studies will provide indicators, by geographic and topographic region, of the magnitude and rapidity of climate change, events surrounding the greenhouse to icehouse transition, patterns of evolution, migration, biotic thresholds, refugia, extinctions, and the emergence of the modern Antarctic biota after the demise of the Paleoaustral elements. Studies of taxa at the micro-temporal scale (1 y. to 10,000 yrs), particularly floral elements from the Neogene, provide essential data on survivorship, adaptation, propagation, seasonality, and decadal macro- and microclimate.
Paleoclimate - The documentation of paleoclimate over the past 100 m. yrs., at several levels of temporal resolution, demands synthesis of all available data sets. Firstly, specific data sets are not universally applicable through the entire late Phanerozoic. Secondly, specific data sets are not equally well preserved through all 100 m.y. We must then, use any and all available information that can be gleaned from geosphere, hydrosphere, cryosphere, atmosphere and biosphere sources. The following factors constitute high priority objectives: variability, periodicity, frequency and amplitude in climate; seasonal and multi-season records including temperature extremes and averages, duration of major climate phases, thermal thresholds, lower atmosphere temperature gradients between terrestrial and marine environments, recognition of the active phases of water (ice, water, rain, snow, cloud, vapor, etc.), the recognition of catastrophic change (floods), and comparisons between different terrestrial Paleoaustral regions and between the Paleoaustral region and lower latitudes.
1. Prepare a prioritized list of terrestrial thematic and topic objectives, accompanied by justifications, and technical requirements for task execution.
2. Match terrestrial science objectives against relevant data sets, and categorize elements of each data set in terms of its/their ability to solve problems at various temporal scales.
3. Consider whether science priority listings test prevailing assumptions and hypotheses.
4. Discuss where and how future conventional outcrop field geology might contribute
further to science objectives enumerated above.
5. Review/preview future priorities in geophysical surveying of regions presently veiled by
the West and East Antarctic ice sheets; with emphasis on detailed sub-ice sheet
contouring, mapping of sub-ice sheet crustal geology and structure, and the delineation
of extent and thickness of late Phanerozoic sedimentary basins. These programs should
be coupled with site surveys as preparation for deep stratigraphic drilling beneath ice
sheets, ice streams and glaciers.
6. Plan future sub-ice deep stratigraphic drilling "legs." Future drilling should have a wide
geographic distribution. The basic geology for vast areas of the Antarctic interior is
unknown and so all regional geological activities should maintain a prominent
reconnaissance survey element in their planning. Regional geophysical surveys are an
essential component in this reconnaissance program. This level of investigation will
serve as preparation for future more specialized drillhole based studies.
7. Because studies of late Phanerozoic history over such a large area are likely to have a
strong regional flavor, it is suggested that site selection be planned to test the existence
of discrete major pre-glacial, glacial, and deglacial drainage systems which probably
entered the Southern Ocean at many points around the continent. Close ties should be
maintained with those planning future Ocean Drilling Program activity in the peri-
Antarctic region. It is recommended that onshore-offshore drilling arrays be expressed
as multi-sector longitudinal transects. Obvious candidates for this type of exploration
include the Wilkes and Pensacola subglacial basins, Aurora subglacial basin, and Amery
8. There already exists sufficient background information in some areas to allow selection
of sub-ice drilling sites. Major "trunk" drainage systems occur at many locations around
the periphery of Antarctica and in some instances these extend for hundreds of
kilometers into the continent. Results from outcrop geology and earlier stratigraphic
drilling projects confirm that these drainage systems have existed through much of the
Cenozoic, and that they preserve both terrestrial and marine strata associations. Data
from this category of physiographic environment would address many of the priority
issues enumerated above, particularly those concerning glacial histories, sea level
oscillations, tectonism, and terrestrial-marine linkages. It is recommended that ~300 km
long deep drilling transects be planned along one or more of the major "trunk drainage
systems," for example, the Reedy, Shackleton, Beardmore, Byrd, Skelton, and David
and Amery glaciers. Drilling transects through the Transantarctic Mountains should
include "pinning" sites in the interior subglacial basins and in the marine rift basins
seaward of the TAM Front.
Late Neogene Sirius Group Strata in Reedy Valley:
A Multiple Resolution Record of Climate, Ice Sheet and Sea Level Events
Gary S. Wilson1, David M. Harwood2, Richard H. Levy2 and Rosemary A. Askin1
1 Byrd Polar Research Center, The Ohio State University
2 Department of Geology, University of Nebraska
Late Neogene Sirius Group strata from Tillite Spur and Quartz Hills in the Reedy Glacier area demonstrate the variability in Sirius Group facies and the spatial relationship between Sirius Group strata deposited at high and low paleo-altitudes. The Tillite Spur and Quartz Hills formations (Pliocene) of the Sirius Group are formally defined here.
The Tillite Spur Formation type section crops out on the edge of the Wisconsin Plateau overlooking Tillite Spur. It comprises a 32 m sequence of alternating coarse gray conglomeratic and muddy olive-brown diamictite units. The Quartz Hills Formation type section crops out above the western margin of the Reedy Glacier in a pre-existing cirque towards the southern end of the Quartz Hills. It comprises a greater than 100 m sequence of alternating massive diamictites and varve-like interbedded sandstone and laminated mudstone sequences.
Lithostratigraphy, sedimentology and paleontology indicate three orders of glacial/interglacial variability in these strata: 1) Recycled marine microfloras, in glacial diamictites of both the Tillite Spur and Quartz Hills formations, indicate Cenozoic cyclical (m.y. scale) reduction in the East Antarctic ice sheet and co-occurring marine incursions into the Antarctic cratonic interior; 2) an advancing and retreating paleo-Reedy Glacier producing an alternating glacial interglacial sequence (10-100 k.y. scale) in both the Tillite Spur and Quartz Hills formations; 3) high resolution varve-like stratification (annual-k.y. scale) in interglacial strata of the Quartz Hills Formation. The Tillite Spur and Quartz Hills formations are interpreted to be high paleo-altitude and low paleo-altitude end-members, respectively, of the Sirius Group. Quartz Hills Formation sediments were deposited close to sea level and have subsequently been rapidly uplifted along with the Queen Maud Mountains of the Transantarctic Mountains (> 500 m/m.y.) to their present elevation at ca. 1500 m. above sea level.
APPENDIX C - PARTICIPANT LIST
APPENDIX C - PARTICIPANT LIST
Sam Creasey (email@example.com)