ated surfaces suggest deposition from wet-based terrestrial gist Range and the All Black Nunataks and at Mount Cerberus glaciers. and Turbidite Hill. Sandstones contain abundant silicified Black shales of the overlying Mackellar Formation are in logs, some of which are contained within large deformed sharp contact with diamictite and sandstone of the Pagoda mudstone clasts. The presence of mudstone clast suggest Formation. Lonestones are extremely rare in these shales and slumping of cutbanks into the adjacent channel. The associ- were observed only in the lower 1.5 m. Two coarsening-upward ated logs were probably transported only a few hundred sequences occur within rocks of the Mackellar Formation. meters or less. Silicified peat and logs in the Nimrod-Byrd These sequences consist of basal shales that grade upward into area occur lower in the Buckley Formation than similar fossils interstratified cross-laminated sandstone (0.01-0.1 m thick) in the Beardmore Glacier region. These fossils may be the old- and shale (0.1-0.5 m thick); the shale in turn grades into hori- est silicified Permian plant material in the central zontally and cross laminated sandstone (1-10 m thick). Sand- Transantarctic Mountains. stone at the top of the lower sequences is in sharp contact with We are grateful to Nicholas Rowe, Shaun Norman, and black shale of the overlying sequence. The second sequence Mike Roberts for their help in the field. Dr. Rowe collected coarsens upward into medium-grained sandstone of the most of the plant fossils reported in this paper. These fossils Fairchild Formation. Shales in the Mackellar were deposited are being examined at the paleobotanical laboratory at the from suspension in a basinal setting. Sandstones were intro- Ohio State University. Logistics in Antarctica were provided duced into this environment as underfiow currents in front of a by Antarctic Support Associates, the U.S. Navy Squadron VXE- prograding deltaic system. The sharp lower contact of the 6, Ken Bork Air Ltd., and the National Science Foundation. Mackellar Formation is a flooding surface and suggests rapid This research was supported by National Science Foundation destruction of the late Paleozoic ice sheets followed by flooding grant OPP 91-18495. of the depositional basin. The sharp contact separating the two coarsening-upward sequences is also a flooding surface and due to its widespread distribution across the Byrd-Nimrod area References indicates a rapid rise in basinal water levels. Barrett, P.J., and B.P. Kohn. 1975. Changing sediment transport direc- Basal medium-grained sandstones of the 150-rn-thick tions from Devonian to Triassic in the Beacon Supergroup of Fairchild Formation contain dipping foreset beds 1-5 rn thick south Victoria Land, Antarctica. In K.S.W. Campbell (Ed.), Gond- These foresets dip at 4-16 0 and grade downward into fine- wana geology. Canberra: Australian National University Press. grained sandstone that interfingers with shale in the underlying Bradshaw, M.A., F.J. Harmsen, and M.P. Kirkbride. 1990. Preliminary Mackellar Formation. Upward, the Fairchild is characterized by results of the 1988-1989 expedition to the Darwin Glacier area. New Zealand Antarctic Record, 10(1), 28-48. sandstone filled channel-form structures. Deltaic sedimenta- Collinson, J.W., J.L. Isbell, D.H. Elliot, M.F. Miller, and J.M.G. Miller. tion characterizes the lower Fairchild, whereas rocks in the In press. Transantarctic Basin. In J.J. Veevers (Ed.), Paleo -Pacific upper portions of the unit were deposited by braided streams. margin of Gondwana (Geological Society of America Memoir). The 250(+) -m-thick Buckley Formation consists predomi- New York: Geological Society of America. nantly of coarse-grained sandstone (5-40 m thick) interstrati- Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell (Ed.), Gondwana geology. Canberra: Australian National Univer- fled with shale (0.5-5 rn thick) and coal (0.05-0.3 m thick) sity Press. beds. The sandstones occur as sheets, which contain numer- Grindley, G.W., and M.G. Laird. 1969. Sheet 15, Shackleton Coast geo- ous downstream accreting macroforms surfaces and sand- logic map of Antarctica, 1:1,000,000. In Antarctic Map Folio Series, stone-filled channel structures. The Buckley was deposited Plate XfV Folio 12—Geology. New York: American Geographical within a braided stream depositional system. Society. Compression, impression, silicified peat, and silicified Laird, M.G., G.D. Mansergh, and J.M.A. Chappell. 1971. Geology of the central Nimrod Glacier area, Antarctica. New Zealand Journal of logs were collected from the Buckley Formation in the Geolo- Geology and Geophysics, 14(3), 427-468.

Geodynamic links between the Transantarctic Mountains and Tethys RASOUL B. SoRIulArn and EDMUND STUMP, Department of Geology, Arizona State University, Tempe, Arizona 85287-1404

he Transantarctic Mountains, extending for approximately antarctic crust, with the mountains forming the shoulder of a T3,500 kilometers, constitute a major morphotectonic rift system on the east antarctic side (e.g., Fitzgerald et al. 1986; boundary between the Precambrian craton of East Antarctica Stern and ten Brink 1989). Therefore, the Transantarctic and the continental "collage" of West Antarctica (figure 1; Mountains do not represent an "orogen" resulting from con- Elliot 1985, pp. 39-61). The genesis of the Transantarctic vergence of tectonic plates but, rather, a "taphrogen" related Mountains has been attributed to an extensional regime in the to fault-block uplifts of a thinning crust.

ANTARCTIC JOURNAL - REVIEW 1994 36

(Africa-South America) and East Gondwanaland (Antarctica- (Sbrkneykmnds India-Australia) resulting in the widening of the Weddell Sea. S Shetland Islands (We have followed the review by Lawyer et al. 1991, pp. Sea Weddell 2 IV Maud L OARarcfica 533-539, and references therein for the timing of breakup of Peninsula - - / Gondwanaland). Africa separated from Antarctica around 150 Larson / Enderby /#ct,ner -?- eos million years ago. Initiation of a rapid phase of uplift- \ Ice Shelf -, hackIeton exhumation in the Ellsworth Mountains of West Antarctica Ale shortly before 140 million years ago, as shown by fission-track data, probably records tectonism of the region related to this Sea

901W 1>0 Po .^ S breakup (Fitzgerald and Stump 1991). This was followed by rift-volcanism between Africa and Th.won WEST % ANTARCTICA South America approximately 130 million years ago, a rift that Amurlen Made ultimately led to the opening of the South Atlantic Ocean. Geometrically, the Transantarctic Mountains lie online with

Ice shelf edge S- Ross Sea the South Atlantic Mid-Ocean Ridge. Sufficient separation Ice surface elevation in km Vlsi between West and East Gondwanaland possibly prevented 2000m bathyrnetric contour Basin Extent of s bglac at features this sea-floor spreading from extending to the locus of the Generalized area of rock exposure 70 + _. Transantarctic Mountains. Nevertheless, the Transantarctic Transantarcf IC Mountains 0- km Mountains seem to have been affected by the same line of Ellsworth Mountains - - 1000 mites tension. The continuous uplift-exhumation as documented Figure 1. A physiographic map of Antarctica (modified after Elliot by fission-track data in the Ellsworth Mountains may be a 1985, 39-61). (m denotes meter.) pp. record of this extensional event, and we suspect that the Early The Transantarctic Mountains taphrogeny is geodynami- Cretaceous phase of rift-block uplifts was widely spread in the cally related to major plate reorganizations surrounding Transantarctic Mountains. Antarctica. With this view, we suggest here a scenario for the The fragmentation of Gondwanaland seems to have fol- formation of the Transantarctic Mountains in light of the lowed a clockwise (west-east) direction (Behrendt, LeMa- breakup of Gondwanaland and the opening and closure of surier, and Cooper 1992, pp. 315-322) so that after Africa, the the Mesozoic Tethyan Ocean(s) lying between Gondwanaland next continent to break away was India approximately 120 and the northern supercontinent of Laurasia (figure 2). million years ago. Australia separated from Antarctica proba- SengOr et al. (1988, pp. 119-181) have argued that the first bly around 95 million years ago. Separation of these conti- fragments to break away from Gondwanaland were those of nental blocks from the northerly margin of the east antarctic the Cimmerian continent (notably Tibetan, Iranian, and Turk- craton marked phases of uplift-exhumation in the ish plateaus) during Permian times. Evidence for this rifting is Transantarctic Mountains margin of East Antarctica as preserved in, for example, the Panjal Traps of the Himalaya (northern margin of the Indian plate) (Gansser 1964). The drift- ing Cimmerian continental blocks closed Paleo-Tethys, which then lay between Gond- wanaland and Laurasia and sub- sequently collided with the Eurasian plate during Late Juras- sic times. It is of note that the clo- sure of Paleo-Tethys was coeval with widespread alkaline/tholei- itic magmatism in Gondwana- land (e.g., the Ferrar dolerites of approximately 180 million years ago in the Transantarctic Moun- tains; Kyle, Elliot, and Sutter Laurasia Gondwana-land ftflflj Cimmerian Continent Exotic Blocks 1981, pp. 283-287). The magma- E tism in Gondwanaland ushered Palaeo-Tethayan sutures Atlantic sutures - Non-Tethayan sutures - Neo-Tethyan sutures in other episodes of fragmenta- (Circum-Pacific) (Alpine-Himalayan) tion in Gondwanaland (figure 3). Figure 2. A first-order paleogeographic/paleotectonic sketch map of the Earth showing elements of the The first drift took place be- Tethyan belt (Cimmeride continent), Laurasia, and dispersed fragments of Gondwanaland (modified after tween West Gondwanaland Sengoretal. 1988, pp. 119-181).

ANTARCTIC JOURNAL - REVIEW 1994 37 Figure 3. Reconstruction of Gondwanaland (modified after Lawyer and Scotese 1987, pp. 17-23) showing the approximate tim- ing of breakup and paleogeologic relations between Antarctica and other tectonic plates derived from Gondwanaland. EM (Ellsworth Mountains), M (Madagascar), MBL (Marie Byrd Land), NNZ (North New Zealand), SNZ (South New Zealand), I (Tasmania), TI (Thurston Island block), and WM (Whitmore Mountains). (Ma denotes millions of years ago.)

revealed by apatite fission-track ages of rocks in the Scott Fitzgerald, P.G. 1994. Thermochronologic constraints on post-Pale- Glacier Area (Mount Griffith: 115 million years ago; Fission ozoic tectonic evolution of the central Transantarctic Moun- Wall: 80 million years ago) (Stump and Fitzgerald 1992) and tains, Antarctica. Tectonics, 13(4), 818-836. Fitzgerald, P.G., M. Sandiford, P.J. Barret, and A.J.W. Gleadow. 1986. the Beardmore Glacier Area (Moody Nuntak: 115 million Asymmetric extension associated with uplift and subsidence in years ago) (Fitzgerald 1994). the Transantarctic mountains and Ross embayment. Earth and Drift of the Africa-Arabia-India cratons during Creta- Planetary Science Letters, 81, 67-78. ceous was accomplished at the expense of Neo-Tethys, which Fitzgerald, P.G., and E. Stump. 1991. Early Cretaceous uplift in the was consumed beneath the Eurasian plate. The closure of Ellsworth mountains of West Antarctica. Science, 254, 92-94. Gansser, A. 1964. Geology of the Himalayas. London: Interscience. Neo-Tethys and initial continental collision occurred in Pale- Gleadow, A.J.W., and P.G. Fitzgerald. 1987. Uplift history and struc- ocene times (e.g., Searle et al. 1987). This was coeval with the ture of the Transantarctic Mountains: New evidence from fission major phase of uplift-exhumation at 55±5 million years ago track dating of basement apatites in the Dry Valley area, south- throughout the Transantarctic Mountains as revealed by fis- ern Victoria Land. Earth and Planetary Science Letters, 82(1/2), sion-track data (e.g., Gleadow and Fitzgerald 1987). 1-14. Kyle, P.R., D.H. Elliot, and J.F. Sutter. 1981. Jurassic Ferrar Group In this short article, we have documented several coeval tholeiites from the Transantarctic Mountains, Antarctica, and events in the tectonic evolution of the Transantarctic Moun- their relationship to the initial fragmentation of Gondwana. In tains and the opening and closing of Paleo- and Neo-Tethys. M.M. Cresswell and P. Vella (Eds.), Gondwana Five. Rotterdam: This is a new perspective on the geological problems of the A.A. Balkema. Transantarctic Mountains because most studies have viewed Lawyer, L.A., J.Y. Royer, D.T. Sandwell, and C.R. Scotese. 1991. Evo- lution of the antarctic continental margin. In M.R.A. Thomson, the Transantarctic Mountains in light of Pacific tectonic evo- J.A. Cramer, and J.W. Thomson (Eds.), Geological evolution of lution. Although our scenario is a first step and needs to be Antarctica. Cambridge: Cambridge University Press. critically assessed and refined, it does point to possible geody- Lawyer, L.A., and C.R. Scotese. 1987. A revised reconstruction of namic links between the Transantarctic Mountain margin of Gondwanaland. In G.D. McKenzie (Ed.), Gondwana Six: Struc- the east antarctic craton and the tectonic history of Tethys ture, Tectonics, and Geophysics. Washington, D.C.: American Geophysical Union. through the breakup and northward dispersion of Gond- Searle, M.P., B.F. Windley, M.P. Coward, D.J.W. Cooper, A.J. Rex, wanaland fragments surrounding Antarctica. D. Rex, L. Tingdong, X. Xuchang, M.Q. Jan, V.C. Thakur, and S. This research was supported by National Science Foun- Kumar. 1987. The closing of Tethys and the tectonics of the dation grant OPP 91-17441. Himalaya. Geological Society of America Bulletin, 98(6), 678-701. Sengor, A.M.C., D. Altiner, A. Cm, T. Ustaömer, and K.J. Hsü. 1988. References Origin and assembly of the Tethyside orogenic collage at the expense of Gondwana Land. In M.G. Audley-Charles and A. Hal- Behrendt, J.C., W. LeMasurier, and A.K. Cooper. 1992. The west lam (Eds.), Gondwana and Tethys (Special Publication No. 37). antarctic rift system—A propogating rift "captured" by mantle London: Geological Society. plume? In Y. Yoshida, K. Kaminuma, and K. Shiraishi (Eds.), Stern, T.A., and U.S. ten Brink. 1989. Flexural uplift of the Recent progress in antarctic earth science. Tokyo: Terra Scientific. Transantarctic Mountains. Journal of Geophysical Research, Elliot, D.H. 1985. Physical geography—Geological evolution. In W.N. 94B(8), 10315-10330. Bonner and D.W.H. Walton (Eds.), Key environments, Antarctica. Stump, E., and P.G. Fitzgerald. 1992. Episodic uplift of the Oxford: Pergammon Press. Transantarctic Mountains. Geology, 20(2), 161-164.

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