The research focused on integrating sedimentologic, stratigraphic, palynologic, paleomagnetic and ichnologic data from Permian and Triassic strata in the Darwin Glacier (DG) and southern Victoria Land (SVL) regions to constrain paleoenvironmental, tectonic, biotic, and paleogeographic histories of southern Pangea and provide a polar view of the world ... during an 'icehouse' to 'greenhouse' transition. Detailed work on the glacial and post-glacial rocks indicates that this area and the Transantarctic Mountains were not located near the center of an enormous Carboniferous to Early Permian ice sheet as depicted in popular paleogeographic reconstructions. Weathering profiles and soft-sediment deformation along the pre-glacial (pre-Permian) unconformity suggest an absence of ice cover during the Carboniferous; otherwise, these features would have been destroyed by multiple glacial cycles. The occurrence of glaciotectonite, foliated diamictite, massive and stratified diamictite, thrust sheets, sandstone, and lonestone-bearing shales in SVL, DG, and CTM indicate that Permian sedimentation occurred in ice marginal, periglacial, and/or glaciomarine settings. No evidence was found that indicates late Paleozoic deposition in the Transantarctic Mountains took place beneath kilometers of ice near a glacial spreading center. Although these findings do not negate Carboniferous glaciation in Antarctica, results indicate that Gondwana glaciation, and therefore, changes to other glacially-driven systems (i.e., glacio-eustatic fluctuations, paleoclimate), were much smaller than previously hypothesized in paleogeographic and paleoclimatic reconstructions. Previous reports also indicate that the Permian-Triassic transition in this region was conformable and contains signatures of an impact event at the boundary possibly related to the P-T mass extinction. In SVL, Lower to lower Upper Permian rocks are unconformably overlain by Lower Triassic rocks, thus negating the occurrence of a conformable Permian-Triassic succession. Work on the grant is continuing. Samples and data are currently stored at the UWM and at Ohio State University, but will be transferred to the Antarctic Rock Repository at the conclusion of the project.
Additional findings of this project include:
1) Glacial rocks of the Darwin Formation are Early Permian rather than Upper Carboniferous to Permian as previously believed.
2) Devonian and Lower Permian strata of the Darwin Glacier region are similar to strata on the south side of the Byrd Glacier, which suggests that the sedimentary basin in the central Transantarctic Mountains (previously believed to have ended at the Byrd Glacier) extended into at least the Darwin Glacier region.
3) Glacial and coal measures rocks in the Darwin Glacier region and in southern Victoria Land are similar suggesting that the central Transantarctic Mountain glacial and post glacial basin extended as far north as the Mackay Glacier.
4) Permian glacial deposits in the Darwin Glacier region were deposited as sediment gravity flows and as rain-out of material from ice shelves and icebergs into a glacially influenced marine/lacustrine setting, suggesting that the Darwin region was situated near the ice front of a dynamic, wet-based ice sheet during the Early Permian.
5) Glacimarine/glacilacustrine deposits in the Darwin and southern Victoria Land areas suggest that previous interpretations of glaci-terrestrial conditions in the central Transantarctic Mountains may not be accurate.
6) Subglacial groundwater during the Permian glaciation played an important role in deformation of the underlying Devonian sandstones.
7) Rapid withdrawal of the ice sheet from the depositional basin occurred in the Darwin and southern Victoria Land regions during the Early Permian.
8) One of the first described sub-glacial deformation till deposits (Lower Permian Darwin and Metschel formations) from the rock record was described from rocks exposed at Mt. Metschel, which will aid in determining controls on formation and preservation of deforming bed conditions and deposits.
9) Large topographic relief occurred during deposition of Permian glacial and coal measures rocks.
10) The temporal and geographic extent of Gondwana glacial deposits does not support the hypothesis that Upper Carboniferous coal-bearing deposits in the northern hemisphere resulted from glacioeustatic fluctuations in sea level.
11) The depositional basin during deposition of the Weller Coal Measures was quite large and extending farther to the west than previously believed.
12) The occurrence of lonestones within lacustrine beds of the Misthound and Weller coal measures suggests that glaciers were located along basin margins long after they withdrew from the depositional basin during the Early Permian.
13) Rocks in the Weller Coal Measures were found to consist of fluvial, lacustrine and deltaic deposits rather than being entirely fluvial as previously believed.
14) Although no palynomorphs could be recovered from the Ellis Formation, Vertebraria roots were found that indicate a Permian age for this unit, which was previously thought to be unfossiliferous and of questionable Permian or Triassic age.
15) Good assemblages of palynomorphs indicating Early Permian age have been recovered from the Darwin Formation from several sites, most on Colosseum Ridge.
16) Paleomagnetic analysis of Permian silicified peat and fossil wood from Mt. Henderson and near Mt. Ellis in the Darwin Glacier region yielded extremely weak magnetizations and it was not possible to determine paleopole positions. A few samples yielded Jurassic-like magnetizations probably due to remagnetization by nearby Ferrar dolerite sills.
17) Collections of silicified peat and wood were made in the second season from Mt. Crean, Mt. Robison, Allan Hills, and Mt. Fleming in southern Victoria Land. Triassic silicified wood was also collected at Allan Hills in southern Victoria Land. It is hoped that the Allan Hills and Mt. Crean localities, in particular, are little affected by dolerite intrusion.
18) Petrographic and paleocurrent analyses suggest that Lower Permian strata were deposited in an extensional basin that was linked to depositional basins farther to the south in the central Transantarctic Mountains.
19) During the Late Permian, southern Victoria Land was characterized by erosion and appears to have been located on a peripheral bulge associated with a developing foreland basin.
20) Southern Victoria Land was incorporated into the foreland basin during the Triassic.
Analyses of the rocks are continuing. Results of the work are now appearing in the literature.
Dept. of Geosciences
Univ. of Wisconsin-Milwaukee
PO Box 413
Province or State:
Journal Publications and Theses:
Askin, R.A., Isbell, J.L. and Lenaker, P.A., in prep. The palynological record from Permian glacial and postglacial strata in the Darwin Mountains, Antarctica.
Woolfe, K. L., in prep., Sedimentology of the Weller Coal Measures at Maya Mountain, southern Victoria Land, Antarctica: ... unpublished M.S. thesis, Department of Geosciences, University of Wisconsin-Milwaukee.
Isbell, J. L., Lenaker, P.A., and Askin, R.A., In review Stratigraphic and palaeogeographic implications of glacitectonic deformation within Permian strata, Southern Victoria Land and Darwin Glacier regions, Antarctica: Sedimentology.
Askins, R.A. and Isbell, J.L., in review, Early Permian spores and pollen from the Pagoda Formation, Nimrod Glacier area, central Transantarctic Mountains: Paleobotany and Palynology.
Isbell, J.L., In revision, Formation and evolution of the Transantarctic basin during the late Paleozoic: Central Transantarctic Mountains, Antarctica: Geological Society of America Bulletin.
Isbell, J.L., Lenaker, P.A., Askin, R.A., Miller, M.F., and Babcock, L.E., 2003, Reevaluation of the timing and extent of late Paleozoic glaciation in Gondwana: Role of the Transantarctic Mountains: Geology, v. 31, p. 977-980.
Isbell, J. L., Miller, M. F., Wolfe, K. L., and Lenaker, P.A., 2003, Timing of late Paleozoic glaciation in Gondwana: was glaciation responsible for the development of northern hemisphere cyclothems - in Chan, M. A., and Archer, A. A., editors, Sedimentary Giants- Extreme Depositional Environments: Geological Society of America Special Paper 370, p. 5-24
Lenaker, P. A., 2002, Sedimentology of Permian glacial deposits in the Darwin Glacier region, Antarctica: unpublished M.S. thesis, Department of Geosciences, University of Wisconsin-Milwaukee, 173 p.
Babcock, L. E., Isbell, J. L., Miller, M. F., Hasiotis, S. T., 2002, New late Paleozoic Conchostracan (Crustacea: Branchiopoda) from the Shackleton Glacier area, Antarctica: age and paleoenvironmental implications: Journal of Paleontology, v.76 (1), p. 70-75.
Isbell, J. L., Miller, M. F., Babcock, L. E., Hasiotis, S. T., 2001, Ice-marginal environment and ecosystem prior to initial advance of the late Palaeozoic ice sheet in the Mt. Butters area of the central Transantarctic Mountains, Antarctica: Sedimentology, v. 48 (5), p. 953-970.
Miller, M. F., Babcock, L. E., Hasiotis, S. T., and Isbell, J. L., 2001, Tetrapod and large burrows of uncertain origin in Triassic high latitude flood plain deposits: Palaios, v.16 (3), p. 218-232.
Isbell, John L., Koch, Zelenda J., Lenaker, Paul A., and Askin, Rosemary A., in press, Gondwana glaciation in the Darwin and central Transantarctic Mountains, Antarctica: evidence against an immense late Paleozoic ice sheet centered over Antarctica, Geological Society of America, Annual Meeting, November, 2004, Abstracts with Programs, 36(6).
Isbell, John, Koch, Zelenda, Lenaker, Paul, and Askin, Rosemary, 2004, Gondwana glaciation in Antarctica: Are the strata glacial-terrestrial or glacial-basinal in origin and were they deposited by ice sheets or mountain glaciers?: 32nd International Geological Congress (IGC), August 20 to 28, 2004, Florence, Italy.
Miller, Molly F. and Isbell, John L., 2004, Biogenic Structures Elucidate Gondwana Glacial and Post-glacial History in the Transantarctic Mountains: 32nd International Geological Congress (IGC), August 20 to 28, 2004, Florence, Italy.
Mumpy, Andrew J., Kean, William F., Isbell, John L., and Jol, Harry, 2003, Sedimentology of a modern braid bar in the Wisconsin River near Spring Green, Wisconsin: analysis using ground-penetrating radar: Geological Society of America, Annual Meeting, November, 2003, Abstracts with Programs, 35(6), p.218.
Isbell, J. L., Lenaker, P.A., and Askin, R.A., 2003, When did Gondwana glaciation occur in Antarctica, and how large were the glaciers? The stratigraphic and paleogeographic implications of glaciotectonic deformation within Permian strata, southern Victoria Land and Darwin Glacier regions, Antarctica: Geological Society of America, North-Central Section Annual Meeting, March, 2003, Abstracts with Programs, 35(2), p.52.
Flaig, Peter P., Knepprath, Nichole Elizabeth, Borosund, Miriam N., Isbell, John L., and Miller, Molly F, 2003 Sandstone composition and tectonic setting of the Lower Permian Weller Coal Measures, Southern Victoria Land, Antarctica: Geological Society of America, North-Central Section Annual Meeting, March, 2003, Abstracts with Programs, 35(2), p.45.
Mumpy, Andrew J., Kean, William F., Isbell, John L., and Jol, Harry M., 2003, Sedimentology of a modern braid bar in the Wisconsin River near Spring Green, Wisconsin: analysis using ground penetrating radar: Geological Society of America, North-Central Section Annual Meeting, March, 2003, Abstracts with Programs, 35(2), p.55.
Borosund, Miriam N., Miller, Molly F., and Isbell, John L, 2003, Sandstone composition and feldspar weathering, Weller Coal Measures (Permian), Transantarctic Mountains, Antarctica: Geological Society of America, Joint annual meeting of the South-Central Section and Southeastern Section, March, 2003, Abstracts with Programs, 35(1), p.18.
Holmes, Allison, Miller, Molly F., and Isbell, John L, 2003, Composition and feldspar alteration in Pleistocene glacial sands, Wind River Range, Wyoming Geological Society of America, Joint annual meeting of the South-Central Section and Southeastern Section, March, 2003, Abstracts with Programs, 35(1), p.18.
Isbell, J. L., Miller, M. F., Wolfe, K. L, and Lenaker, P. A., 2002, Did waxing and waning of Gondwanan glaciers cause upper Paleozoic cyclothems?: Annual meeting of Southeastern/North-Central Section of the Geological Society of America, GSA Abstracts with Programs Vol. 34, No. 2, p. 10.
Miller, M. F., Isbell, J. L.a nd Wolfe, K. L., 2002, Environmental distribution of bottom-dwelling animals in a Permian freshwater system, Antarctica: Geological Society of America, National Convention, Denver, Colorado, October, 2002, Abstracts with Programs, 34(6), p. 212.
Henderson, S. S., Miller, M. F., Isbell, J. L., and Mabin, M.C.G., 2002, Coarse,wind blown gravel deposits, Bennett Platform, Antarctica: constraining wind velocities during transport: Annual meeting of Southeastern/North-Central Section of the Geological Society of America, GSA Abstracts with Programs Vol. 34, No. 2, p. 9.
Isbell, J. L., Lenaker, P. A., and Wolfe, K. L., 2001, Climbing macroforms and their potential relationship to rising base levels: Permian Misthound Coal Measures and Triassic Fremouw Formation, Antarctica, and the Pine Creek Sandstone Member of the Breathitt Group, Kentucky, U.S.A.: 7th International Conference on Fluvial Sedimentology, Lincoln, Nebraska, U.S.A., August 5-10, 2001, Program and Abstracts, p. 135.
Isbell, J. L., Miller, M. F., Wolfe, K. L., and Lenaker, P. A., 2001, Timing of late Paleozoic glaciation in Gondwana: Was glaciation responsible for the creation of accommodation space associated with the development of northern hemisphere cyclothems and incised fluvial valleys?: 7th International Conference on Fluvial Sedimentology, Lincoln, Nebraska, U.S.A., August 5-10, 2001, Program and Abstracts, p. 136.
Isbell, J.L. and Miller, M. F., 2001, Timing and possible causes of late Paleozoic ice sheet(s) advance and retreat cycles: GSA and Geological Society of London Global Meeting-Earth System Processes, Edinburgh, Scotland, June 24-28, 2001.
Isbell, J.L. and Miller, M. F., 2000 Possible Effects of Basins on the Growth, Waxing and Waning, and Decay of the Late Paleozoic Ice Sheet(s) in Gondwanaland: AAPG National Convention, Denver.
Miller, M.F., McDowell, T.A., Shyr, Y., Kemp, N.R., Isbell, J.L., 2000, Bioturbation in Freshwater vs. Marine Deposits: AAPG National Convention, Denver.