ton, B.C. Andersen, H.B. Conway, T.E. Lowell, M. Prentice, R. Campbell, lB., and G.G.C. Claridge. 1975. Morphology and age rela- Weed, and E. Vrba. This project was supported by National tionships of Antarctic soils. In R.P. Suggate and M.M. Cresswell Science Foundation grant DPP 83-19477. (Eds.), Quaternary studies. New Zealand Royal Society Bulletin, 13, 83-88. References Denton, G.H., J.G. Bockheim, R.H. Rutford, and B.G. Andersen. In press. Glacial history of the Ellsworth Mountains, West . In Bockheim, J.G. 1982. Properties of a chronosequence of ultraxerous C. Craddock, J. Splettstoesser, and G.E Webers (Eds.) Geology of the soils in the Trans-Antarctic Mountains. Geoderma, 28, 239-255. Ellsworth Mountains, West Antarctica. Geological Society of America Bockheim, J.G. 1979. Relative age and origin of soils in eastern Wright Memoir. , Antarctica. Soil Science, 128, 142-152. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the Trans- Bockheim, J. G., and S.C. Wilson. 1979. Pedology of the Darwin Antarctic Mountains, Antarctica. (Institute of Polar Studies Report No. area. Antarctic Journal of the U.S., 14(5), 58-59. 56.) Columbus: Ohio State University Press. Buntley, G.J., and F.C. Westin. 1965. A comparative study of develop- Mercer, J.H. 1972. Some observations on the glacial geology of the mental color in a chestnut-chernozem-brunizem climosequence. Soil area. In R.J. Adie (Ed.), Antarctic geology and Science Society of America Proceedings, 29, 579-582. geophysics. Oslo: Universitetsforlaget.

Pre-late Quaternary glaciation (Denton et al. 1984; Webb et al. 1984). This mode of glaciation contrasts markedly with relatively minor late Quaternary fluc- of the Beardmore Glacier region, tuations (Denton, Prentice, and Burckle in press). Such a Antarctica change in behavior presents a major opportunity to understand the controls of antarctic ice volume, an important component of the global climate system. During the 1985-1986

M. L. PRENTICE austral field season, we conducted studies in the Beardmore Glacier region (figure 1) to test hypotheses for pre-late Quatern- Institute for Quaternary Studies ary glaciation. Here we report some preliminary results. University of Maine We examined exposed highlands from the Orono, Maine 04469 north to the Queen Elizabeth Range (figure 1). Topographic and relief here is at least equal to the heights of the numerous 4,000- Department of Geological Sciences meter peaks (figure 2). We found a variety of mud-rich glacial Brown University deposits, unconsolidated to consolidated, in addition to those Providence, Rhode island 02912 previously described (Mercer 1972). We informally refer to all these deposits, which include the Sirius Formation, as "Sirius G.H. DENTON drift" because we consider formal stratigraphic subdivision premature. Institute for Quaternary Studies and Department of Geological Sciences Sirius Drift University of Maine Orono, Maine 04469 Basal till patches. Thin patches of Sirius basal till are scattered throughout the region between elevations of 150 and 4,115 T.V. LOWELL meters. Till patches were found at eleven localities above 3,000 meters. High-elevation till outcrops between 3,490 and 3,825 Department of Geology meters on Mount Falla; at 3,170, 3,215, 3,230, 3,370, and 4,015 University of Cincinnati meters on Mount Kirkpatrick; at 4,115 meters on Mount Mack- Cincinnati, Ohio 45221 ellar; from 3,140 to 3,292 meters on Markham Plateau; and at 3,538 and 3,660 meters on Flat Top (figure 2). The till is yellow to H.C. CONWAY gray, massive, and full of striated gravel. Consolidation is varia- ble. Sirius basal till on Mount Falla and on the highest surface in Department of Chemical and Process Engineering the northern Dominion Range contains far-traveled erratics of University of Canterbury, Private Bag Shackleton Limestone. Basal till on Markham Plateau contains Christchurch, New Zealand far-traveled erratics of granite and gneiss as well as Shackleton Limestone. Bedrock beneath many till patches exhibits striat- L.E. HEUSSER ions uniformly suggesting ice flow toward the northeast. High-elevation bedrock surfaces without till cover also exhibit Lamont-Doherty Geological Observatory well-preserved striations. Fifteen separate localities were found Columbia University above 3,000 meters. Examples occur on Mount Miller between Palisades, New York 10964 3,215 and 4,220 meters; on Grindley Plateau between 3,380 and 4,220 meters; and on Flat Top between 3,000 and 3,660 meters Massive fluctuations of the antarctic ice sheet have been infer- (figure 2). These striations likewise indicate northeasterly ice red for pre-late Quaternary time from continental evidence flow. High-elevation terrain lacks a dominant topographic grain

1986 REVIEW 95 / PLATEAU / IR Range "Z . . ^^ Im (,. Dominion 411 .1 W 4o 44

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Figure 1. Sketch map of the Beardmore Glacier region. ("Km" denotes "kilometer.) as occurs in the ice-free valleys region (Denton et al. 1984) and accretion at the margin of temperate ice below the coeval equi- glacial trimlines like those that occur in the Ellsworth Moun- librium line. Wedge elevations indicate that this paleoe- tains and northern Victoria Land (Denton et al. in press). Striat- quilibrium line occurs today as high as 2,500 meters. Sirius ed bedrock surfaces were found as low as 150 meters. waterlaid units suggest extensive summer melting. If our inter- The character of this Sirius till strongly suggests deposition pretations are correct, Sirius drift wedges represent a glacier from ice with a thawed bed. We infer that some patches, par- system that was far short of overriding the mountains. May- ticularly those at high elevations, were deposited beneath thick ewski (1975), on the other hand, inferred complete overriding of continental ice that completely overrode the mountains. This the from such deposits. We generally inference is based on the high elevation of the till patches, the agree with Mercer (1972) except for his proposal for consider- consistency of striation direction across a high-relief region, the able post-depositional glacial erosion of our ice-marginal drift. far-traveled erratics within Sirius till in the Dominion Range Rather, we interpret their wedge form as a primary feature and on Mount Falla and Markham Plateau, as well as the lack of reflecting deposition as lateral . high-elevation trimlines. Organic material was found at nine different localities within Ice-marginal drift. Sirius drift also occurs as thick wedges Sirius ice-marginal drift exposed in the northern Dominion alongside and at the confluence of major glacial troughs. Drift Range (Oliver Bluffs; Oliver 1964) (figure 2). The first locality wedges are commonly associated with bedrock cliffs. The was discovered on 3 December 1985. Wood fragments, amor- wedges are thickest directly adjacent to bedrock cliffs and pinch phous plant debris, and Nothofagus pollen, a temperate forest out away from the cliffs. Wedge crests parallel bedrock cliffs. genus of the Southern Hemisphere, are abundant. The excel- Examples occur on the north wall of the Beardmore trough at lent preservation and high concentration of the pollen as well as The Cloudmaker and Willey Point as well as atop Mount Sirius the absence of recycled palynomorphs as described by Truswell (figure 2). In the Dominion Range, several wedges, up to 150 and Drewry (1984) preclude significant reworking. These plant meters thick, parallel for 25 kilometers. macro- and microfossils corroborate the inference for warmer- The lithostratigraphy of Sirius drift wedges is complex. The than-present climate based on the form and lithologic character bottom portions are commonly rich in striated gravel and are of Sirius drift. basal till. Above this, many sedimentary units contain angular gravel with no glacial marks. These upper units are supra- and Dominion Drift en-glacial drift as well a colluvium. Waterlaid deposits from well-stratified sandy gravel to horizontally laminated sandy Small boulder belts parallel to modern ice margins overlie mud are also common in the wedges. Sirius drift throughout the Beardmore region. In the northern We infer from their form, distribution, and internal character Dominion Range, these lateral are well developed and that Sirius drift wedges were deposited subaerially by marginal stretch in unbroken sequence from the Beardmore Glacier at

96 ANTARCTIC JOURNAL 1,800 meters up to 2,500 meters in elevation (figure 2). This is meters thick here (figure 2). This would require the surface of significantly higher than such drift had previously been found the east antarctic ice sheet to have been much higher than today in this area (Mercer 1972; Mayewski 1975). These high moraines (figure 3). The high elevations of Sirius ice-marginal deposits uniformly exhibit much more soil development than those indicate that even minimum ice cover during this period of lower down (Denton, Anderson, and Conway Antarctic Journal, temperate glaciation may have been greater than today (figure this issue; Bockheim, Wilson, and Leide, Antarctic Journal, this 3). issue) and are named "Dominion drift." Similar moraines man- Age control on Beardmore region glacial deposits is poor. tle Sirius drift off the Walcott Névé near Gordon Valley. These Webb et al. (1984) reported late Oligocene diatoms in a sample Moraines consist of gravel, primarily boulders, and pods of silty of Sirius drift from Mount Sirius and rare Plio-Pleistocene di- till. We suggest that Dominion drift was deposited by ice with a atoms in a Sirius sample from the northern Dominion Range. frozen bed under a polar climate similar to todays. However, on the basis of diatoms in Sirius drift well outside the We infer from Sirius drift a long interval of temperate glacia- Beardmore region, Harwood (1985) proposed a late Pliocene tion during which thick continental ice with a thawed bed age for Sirius drift throughout the Transantarctic Mountains. completely overrode the mountains of the Beardmore region. Poor understanding of the uplift history of the Transantarctic Sirius glacial features were found from elevations of 150 to 4,220 Mountains coupled with these chronologic problems precludes meters. There are no trimlines above this to suggest that the estimation of Sirius ice sheet surface elevations. highest peaks (4,550 meters) projected through the ice sheet at Subsequent to Sirius temperate ice-sheet glaciation, Ant- maximum volume. If they reflect contemporaneous glaciation, arctica cooled and its ice cover assumed a polar character which Sirius glacial features suggest that Sirius ice was at least 4,000 it has retained to today. Mercer (1972) recognized a similar

AS QUEEN ALEXANDRA RANGE Kirkpatrick Grindley Plateau

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fl QUEEN ALEXANDRA RANGE QUEEN ELIZABETH RANGE r 5A" Elizabeth Mackellar Miller 4 R Markham St 4m tR Markham —I Rab/N Plateau / I o R 3 Clarkson Peak St/ Z 0 I-

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S 5 0 rm00 Figure 2. Schematic topographic profile with surf icial geology across the Beardmore Glacier region from the Dominion Range north to the Queen Elizabeth Range. Figure 1 shows the line of section. Selected nearby features were projected into this section. ("Km" denotes "kilometer:" "M x 10" indicates that the elevation measurements are expressed in thousands of meters.)

1986 REVIEW 97

TRANSANTARCTIC MTNS. V Scale: 1 6000,000

Kirkpatrick 0 100 250 • 500 KM Markham 4 Falls Titan Ice Dome \iominion cart,urtsevL3 I 3 I st Range Elev. D Mtna Sirius 44 Elev. I I 2M M2 Cloudmaker ..- (x103) EAST ANTARCTIC ICE SHEET 1

0 ROSS ICE SHELF 3 A Sirius basal till Dominion drift H1 Wood -1 FSTI ki Sirius ice-marginal Striated bedrock El drift surface

Figure 3. Schematic topographic profile with surf icial geology through the Beardmore Glacier trough from the Ross Ice Shelf to interior East Antarctica. Figure 1 shows the line of section. Selected nearby features were projected into section. Ice and bedrock profiles are from Drewry (1983). The dashed line depicts the highest surface of the Beardmore Glacier during deposition of the Beardmore Drift, probably in late 1031, Wisconsin time (Denton et al., Antarctic Journal, this issue). "Km denotes "kilometer." M x indicates that the elevation measurements are expressed in thousands of meters.)

change in glaciation style. The Dominion drift represents early Denton, G. H., M. Prentice, and L.H. Burckle. In press. Late Cenozoic polar glaciation. During Dominion glaciation, ice with a frozen history of the Antarctic Ice Sheet. In R.J. Tingey (Ed.), The geology of bed reached at least the 2,500-meter level in the northern Do- Antarctica. Cambridge: Oxford University Press. minion Range. Polar glaciation above this limit is not precluded Denton, G.H., B.G. Andersen, and H.B. Conway. 1986. Late Quatern- ary surface fluctuations of the Beardmore Glacier, Antarctica. Ant- because cold ice commonly leaves no record of its passage. arctic Journal of the U.S., 21(5). The Beardmore region provides the strongest evidence to Denton, G. H., M. Prentice, D. E. Kellogg, and T. B. Kellogg. 1984. Late date supporting the hypothesis (Denton et al. 1984) for com- Tertiary history of the Antarctic Ice Sheet: Evidence from the Dry plete overriding of the Transantarctic Mountains by thick conti- Valleys. Geology, 12, 263-267. nental ice in pre-Late Quaternary time. Further, the Beardmore Drewry, D.J. (Ed.) 1983. Antarctica: Glaciological and geophysical folio. data suggest that antarctic ice attained this massive volume Cambridge: Scott Polar Research Institute. under remarkably temperate conditions. The Beardmore record Harwood, D.M. 1985. Late Neogene climatic fluctuations in the south- also indicates that younger polar ice reached higher elevations ern high-latitudes: Implications of a warm Pliocene and deglaciated than previously thought. Antarctic continent. South African Journal of Science, 81, 239-241. We thank B. G. Andersen, J. G. Bockheim, J. E. Leide, and S. C. Mayewski, P.A. 1975. Glacial geology and late Cenozoic history of the Trans- antarctic Mountains, Antarctica. (Institute of Polar Studies, Report No. Wilson for their collaboration. D.H. Elliot and J.W. Collinson 56.) Columbus: Ohio State University Press. alerted us to important Sirius deposits. We are indebted to Mercer, J.H. 1972. Some observations on the glacial geology of the VXE-6 for their very-high-altitude helicopter support. Beardmore Glacier area. In R.J. Adie, (Ed.), Antarctic geology and This work was supported by National Science Foundation geophysics. Oslo: Universitetsforlaget. grants DPP 83-18808 and DPP 83-19477. Oliver, R.L. 1964. Geological observations at Plunket Point, Beardmore Glacier. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Hol- References land Publishing. Truswell, E.M., and D.J. Drewry. 1984. Distribution and provenance of Bockheim, J.G., S.W. Wilson, and J.E. Leide. 1986. Soil development in recycled palynomorphs in surficial sediments of the Ross Sea, Ant- the Beardmore Glacier region, Antarctica. Antarctic Journal of the U. S., arctica. Marine Geology, 59, 187-214. 21(5). Webb, P.-N., D.H. Harwood, J.H. McKelvey, and L.D. Stott. 1984. Bushnell, V. C. 1975. Antarctic map and folio series. New York: American Cenozoic marine sedimentation and ice-volume variation on the East Geographical Society. Antarctic craton. Geology, 12, 287-291.

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