Alluvial stratigraphic sequences extensive photo mosaics from helicopter fly-bys at these sites, as well as at Mount Miller, Painted Cliffs, Mount Ropar, Lewis within the Permian Transantarctic Cliffs, Mount Dickerson, Barnes Peak, Bingley Glacier, Mount foreland basin, Donaldson, Mount Deakin, Kinsey Peak, and Mount Mills. Beardmore Glacier area, These photos aided in the three-dimensional reconstruction of Antarctica sedimentary bodies and stratigraphic packages. Rock samples collected for petrographic analysis are stored at the Byrd Polar Research Center and at the British Antarctic Survey. Coal, car- bonaceous shale, and samples containing fossil plants were for- JOHN L. ISBELL warded to E.L. Taylor, T.N. Taylor, and N.R. Cñneo for paleo- botanical and palynological analyses. Interpretations made in Byrd Polar Research Center this paper include data collected during the 1985-1986 field and season (Isbell 1990) and data reported by Barrett (1968). Department of Geological Sciences Ohio State University Sedimentologic and stratigraphic analyses of the Buckley For- Columbus, Ohio 43210 mation in the Beardmore Glacier region, support the hypoth- esis that the Permian strata were deposited within a foreland basin associated with the Gondwanide orogeny. Results sug- DAVID I.M. MACDONALD gest that tectonic loading along the paleo-Pacific margin of Ant- arctica controlled basin formation and sediment deposition. British Antarctic Survey The Buckley Formation in the Beardmore Glacier region, is Natural Environ,nent Research Council approximately 750 meters thick and consists of interstratified Cambridge CB3 0ET UK fluvial sandstone, siltstone, mudstone, and coal. Sandstone in the lower member of the Buckley Formation is quartzo-feld- spathic, and upper-member sandstone is volcaniclastic. During the austral summer of 1990-1991, we collected data The Buckley members define two major depositional se- from exposures of the Permian Buckley Formation in the Beard- quences. Disconformities bound each sequence along the cra- more Glacier region at Clarkson Peak, Mount Picciotto, Mount tonic margin of the basin (figure 2). These disconformities are Achernar, Mount Bowers, and Willey Point (figure 1). Data recognized within measured sections by abrupt upward stra- consist of detailed vertical logs, maps of lithofacies and sedi- tigraphic changes in sandstone composition, facies, and paleo- ment-body geometries, and paleocurrent orientations. We took current orientations and, at some sites, by well-developed in- traformational conglomerates at the base of sandstone bodies. Basinward, these surfaces become conformable and are marked by an abrupt shift in depositional patterns toward the orogenic 16 5 0EL... belt. Using data based on fluvial architecture, the large-scale r •() ^V distribution of sandstone bodies within fine-grained sedi- L on in C ments, and their mutual relationship (Allen 1978; Collinson ca Clarkson Pk.2" Cr 1986), we identify three major geographically distributed facies Mt. Miller patterns within the basin: • a thick succession of overlapping sandstone bodies along the A N I wc i "to orogenic basin margin, aD / • thick interstratified mudstone and sandstone along the basin axis, and o C.PtJ • a thin succession of overlapping sandstone bodies along the CZ • Mt. Picciotto cratonic basin margin. o \Painted Upward within each depositional sequence, the orogenic-mar- Cliffs gin sandstone expands basinward and the axial mudstone/ 4°S 840S •Mt. Ropar sandstone and cratonic-margin sandstone are displaced toward Mt. Achemar the craton. ? Mt. Dickerson Facies analysis reveals the occurrence of braided-stream de- 0 km 30 Lewis Cliffs L-. posits along basin margins. These grade basinward into low- 9 sinuosity, single-channel, and meandering-stream lithofacies. 1800 Barnes Pk Both braided- and meandering-stream lithofacies occur along the basin axis. Paleocurrent analysis suggests the rivers flowed e mt. "j t Donaidsor transversely across basin margins and longitudinally down the Areatu •V topographic basin axis. Upward within each depositional se- LJ\goow Mt. Deakin quence, the position of the longitudinal drainage axis shifted ANTARCTICA -I cratonward concurrent with displacement of depositional pat- (CKinsey terns within the basin. Mt. Bowers L Pk. Modeling by Heller, Angevine, and Paola (1988) and Flemings 1 650EJMt Mills I and Jordan (1989, 1990) have produced foreland-basin deposi- tional packages similar to those in the Beardmore Glacier area. Figure 1. Location map showing sites with Permian strata visited Flemings and Jordan (1990) suggested that abrupt shifts in dep- during the 1990-1991 field season in the Beardmore Glacier area. ositional patterns toward the orogenic belt occur during the (km denotes kilometer.) onset of thrust loading on an elastic lithosphere. Rapid subsi-

1991 REVIEW 13 CENTRAL TRANSANTARCTIC MOUNTAINS Basin Fill

Cratonic Permian-Triassic Disconformity Orogenic Margin Basin --.&----- Margin Upper Buckley Alluvial Stratigraphy "-.. .-.-a-" Member Disconformity ". T Base of Sequence 2 Lower Buckley Overlapping Channel Bodies Member IIsolated Channel Bodies Base of Sequence I

Figure 2. Diagrammatic interpretation of the Permian basin fill in the Beardmore Glacier area. Cross-section is east-west with the cratonic basin margin located along the present Polar Plateau side of the central Transantarctic Mountains.

dence during thrusting traps coarse-grained sediment next to Barrett, P.J. 1968. The post-glacial Permian and Triassic Beacon Rocks in the the orogenic belt (cf. Blair and Bilodeau 1988; Heller et al. 1988; Beardmore Glacier area, central Transantarctic Mountains, Antarctica. Paola 1988). Later, as subsidence decreases, progradation of a (Doctoral thesis, Ohio State University, Columbus, Ohio.) clastic wedge with cratonward displacement of depositional Blair, T.C., and WL. Bilodeau. 1988. Development of tectonic cyclo- patterns occurs. thems in rift, pull-apart, and foreland basins: Sedimentary response Combined paleocurrent, lithofacies, and petrologic analyses to episodic tectonism. Geology, 16, 517-520. Collinson, J.D. 1986. Alluvial sediments. In H.G. Reading (Ed.), Sedi- of the Permian Buckley Formation suggest that tectonic loading mentary environments and facies. Oxford: Blackwell Scientific Publica- controlled the deposition of major fluvial sequences. The se- tions. quences suggest that two loading events occurred during the Flemings, PB., and T.E. Jordan. 1989. A synthetic stratigraphic model Permian. of foreland basin development. Journal of Geophysical Research, 94, National Science Foundation grant DPP 89-17413 and the Brit- 3851-3866. ish Antarctic Survey provided financial support for this re- Flemings, PB., and T.E. Jordan. 1990. Stratigraphic modeling of fore- search. Antarctic Support Associates, Helicopters New Zea- land basins: Interpreting thrust deformation and lithosphere rheol- land Ltd., U.S. Navy Squadron VXE-6, and the National ogy. Geology, 18, 430-434. Science Foundation provided logistic support. Heller, EL., C.L. Angevine, and C. Paola. 1988. Two-phase strati- graphic model of foreland-basin sequences. Geology, 16, 501-504. Isbell, J.L. 1990. Fluvial sedimentology and basin analyses of the Permian Fairchild and Buckley Formations, Beardmore Glacier region, and the Weller References Coal Measures, southern Victoria Land, Antarctica. (Doctoral thesis, Ohio State University, Columbus, Ohio.) Allen, J.R.L. 1978. Studies in fluvial sedimentation: An exploratory Paola, C. 1988. Subsidence and gravel transport in alluvial basins. In quantitative model for the architecture of avulsion-controlled alluvial K.L. Kleinspehn and C. Paola (Eds.), New perspectives in basin analysis. suites. Sedimentary Geology, 21, 129-147 New York: Springer-Verlag.

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