known. The framework modes and their sources suggest depo- sitional setting. Fifth International Syinposiu in on Antarctic Earth Sciences sition in a foreland basin but do not preclude accumulation in a Abstracts. pull-apart basin. Resolution of basin type is hindered because Rees, MN., and A.J. Rowell. In press. The pre-Devonian Paleozoic sequences are fragmentary, folded, and sheared, thus obscur- clastics of the central Transantarctic Mountains: Stratigraphy and ing stratigraphic relationships and thicknesses. In addition, depositional settings. Volume of the Fifth International Symposium on Antarctic Earth Sciences. basin type has not been clarified by lithofacies analysis because Cambridge, U.K. Rees, MN., A.J. Rowell, B.R. Pratt, and P. Braddock. 1985. The Byrd the lithofacies imply development of alluvial fans and fan deltas Group of the Holyoake Range, central Transantarctic Mountains. in lacustrine and marine environments (Rees and Rowell in Antarctic Journal of the U.S., 20(5), 3-5. press) and all such associations are common to both basin types. Rowell, A.J., and M.N. Rees. In press. Setting and significance of the This work was supported in part by National Science Founda- Shackleton Limestone, central Transantarctic Mountains. Volume of tion grant DPP 85-18157 to the University of Nevada Las Vegas. the Fifth International Symposium on Antarctic Earth Sciences. Cambridge, U.K. References Rowell, A.J., M.N. Rees, and P. Braddock. 1986. Pre-Devonian Pal- eozoic rocks of the central Transantarctic Mountains. Antarctic Journal of the U.S., 21(5), 48-50. Burgess, C.J., and W. Lammerink. 1979. Geology of the Shackleton Rowell, A.J., M.N. Rees, R.A. Cooper, and B.R. Pratt. In press. Early Limestone (Cambrian) in the Byrd Glacier area. New Zealand Antarctic Paleozoic history of the central Transantarctic Mountains: Evidence Record, 2, 12-16. from the Holyoake Range, Antarctica. New Zealand Journal of Geology Dickinson, W. R., and C. A. Suczek. 1979. Plate tectonics and sandstone and Geophysics. compositions. American Association of Pet roleu in Geologists Bulletin, 63, Skinner, D.N.B. 1964. A summary of the geology of the region between 2164-2182. Byrd and Starshot glaciers, south Victoria Land. In R.J. Adie (Ed.), Dickinson, W.R., L.S. Beard, G.R. Brakenridge, J.L. Erjavec, R.C. Fer- Antarctic geology. Amsterdam: North Holland. guson, K.F. Inman, R.A. Knepp, F.A. Lindberg, and P.T. Ryberg. Skinner, D.N.B. 1965. Petrographic criteria of the rock units between 1983. Provenance of North American Phanerozoic sandstones in the Byrd and Starshot glaciers, south Victoria Land, Antarctica. New relation to tectonic setting. Geological Society of America Bulletin, 94, Zealand Journal of Geology and Geophysics. 8, 292-303. 222-235. Stump, E., M.R. Sheridan, S.G. Borg, P.H. Lowry, and P.V. Colbert. Rees, M.N., and A.J. Rowell. 1987. The pre-Devonian Paleozoic Doug- 1979. Geological investigations in the Scott Glacier and Byrd Glacier las Conglomerate of the Transantarctic Mountains: Origin and depo- areas. Antarctic Journal of the U.S., 14(5), 39-40.

Paleoenvironmental studies of Diatoms within these sediments are compared with modern floras in sediment from Lake Vanda in Wright Valley and nu- nonmarine diatoms in Quaternary merous meltwater streams and ponds distributed throughout antarctic sediments Wright Valley, lower Taylor Valley, Cape Chocolate, Ross Island, Brown Peninsula, and on the McMurdo Ice Shelf around East Dailey Island. Modern diatom assemblages within these sam- ples, as well as those reported in the literature, provide an REED P. SCHERER analog for ecologic interpretation of fossil assemblages and their sedimentary environments. Older nonmarine diatom flo- Department of Geology and Mineralogy ras from upper Pliocene/Pleistocene sediments from DVDP-15 and and CIROS2 drill cores in McMurdo Sound and Ferrar Fjord Byrd Polar Research Center are also under study. A paleoecologic model is being con- Ohio State University structed based in part on these results. Columbus, Ohio 43210-1293 Discontinuous outcrops of lacustrine and deltaic sediments are scattered along valley walls and dry basins of southern Victoria Land (Debenham 1921; Speden 1960; Péwé 1960; Kel- Nonmarine sediments from ice-free areas of southern Vic- logg et al. 1980). These generally represent only high stands of toria Land contain a largely unexploited paleoclimatic resource. previous lake levels, and thus do not contain continuous strat- Diatom assemblages within lacustrine sediment sequences are igraphic successions. A high-resolution Late Quaternary pal- being used to evaluate Quaternary paleoenvironments in the eoclimatic signal, based on diatom, sedimentologic and chemi- McMurdo Sound region. In the first phase of the study, begun cal analyses, may be extracted from the near-continuous during the 1986-1987 field season, lacustrine and associated sediment records underlying certain modern lakes. The only deltaic sediments were sampled at outcrops in lower Taylor available record of this kind is the upper 4 meters of DVDP-4A in Valley, the Cape Chocolate region, Wright Valley, Brown Penin- Lake Vanda. Although badly disturbed by drilling, this succes- sula, East Dailey Island, and Ross Island. Results from two sion showed evidence of major changes in sedimentation, in- sequences near Cape Chocolate and one in lower Taylor Valley cluding periodic evaporite deposition (Brady 1981). Continuous are reported here. These samples were processed for diatom sedimentary records underlying modern lakes need to be ex- analysis using a method (Scherer in preparation) which allows the establishment of absolute abundance (diatoms per gram of dry sediment). This relationship allows comparison of diatom "DVDP" denotes Dry Valley Drilling Project and "CIROS" denotes productivity and sediment input. Cenozoic Investigations of the Ross Sea.

1987 REVIEW 35 tracted using methods that preserve stratigraphy and sedimen- tary structures. Kellogg et al. (1980) studied diatom fossils from Late Wiscon- sin nonmarine perched deltas in Taylor Valley and defined six diatom assemblages. They used these assemblages to evaluate lake-level history but were unable to draw specific pal- eoecologic conclusions due to a paucity of modern ecologic data. Kellogg et al. (1980) reported nine diatom taxa as endemic to southern Victoria Land, including six species which they described as new. These findings conflict with the results of a recent algal monograph (Seaburg et al. 1979) which reports no nonmarine diatom taxa as endemic to southern Victoria Land. For this study, diatoms were identified using the taxonomic assignments of Kellogg et al. (1980). Some taxonomic revision to accomodate the above discrepancy will ultimately be necessary. Certain diatoms are cosmopolitan in antarctic nonmarine aq- ueous environments (e.g., Navicula multicopsis and varieties, Navicula quciternaria, Navicula shackleton i, Nitzschia westii), de- spite widely differing ionic concentrations between various a-c: Melosira charcotii Peragello, Salmon Creek, Cape Chocolate. Conrad bodies of water. However, it is the distribution of ecologically (2000 x) d-f: Chrysomonad cyst, Ochromonas miniscula (?), Lake Vanda, Wright Valley. (2000 x) restricted taxa that permit assemblage differentiation and pal- eoecologic interpretation. Many extant species range back at least into the Pliocene (Brady 1981) suggesting that a pal- Glacier. Small, discontinuous outcrops of similar material are eoecologic model based on ecologically restricted nonmarine scattered throughout the vicinity. Advances of the Hobbs diatoms from modern environments has potential for applica- Glacier since 1903 have apparently destroyed similar deltaic tion to pre-Quaternary sediments. The following is a descrip- sediments (Denton and Hughes 1981). The sediments collected tive analysis and comparison of sediments studied, with pal- from the outcrop contain an average of 1.2 million diatoms per eoecological notes. gram, based on six samples. The diverse nonmarine as- Salmon Stream, Cape Chocolate. Lacustrine sediments near semblage is dominated by Navicula ccntenta, Navicula gibbula, Salmon Stream in the Cape Chocolate region were described by and Hantzschia amphioxys. Marine fragments are uncommon. Speden (1960) and discussed by Miagkov, Nedeshava, and Melosira charcotii is absent from this sequence. Riaboba (1976) and Kellogg et al. (1980). Our recent field studies Commonwealth Glacier, Taylor Valley. A 4-meter-thick exposure brought to light some new observations. A thick succession of of lacustrine and associated deltaic sequences crops out at the finely laminated, moderately calcareous sediments on the north snout of Commonwealth Glacier. The sequence has evidence of shore of Salmon Stream, near the snout of Salmon Glacier, has high sedimentation rates and rapid shifts in sedimentary regi- been overridden by subsequent glacial activity. The lacustrine me, including several distinct units and a variety of soft sedi- succession is overlain by a compact tillite and stratigraphy is ment deformational structures. Nonmarine diatoms occur in disrupted by numerous small thrust faults. Five samples from low concentrations in this succession. Low nonmarine diatom this sequence were studied. Samples are rich in nonmarine abundance reflects high sediment input rather than low pro- diatoms, averaging 6.5 million valves per gram. Marine diatom ductivity. Despite the differing character of sediment units, the fragments are rare in this sequence. The diatom assemblage is diatom assemblages in the samples studied are fairly consistent dominated (65-75 percent) by a small centric diatom, Melosira in absolute abundance and taxonomic compositions. Non- charcotii (figure a—c). This diatom is known from intertidal pools marine diatom abundance in four samples from the lighter along the Antarctic Peninsula and associated islands (Peragallo colored units averages only 200,000 per gram. 1921; Frenguelli and Orlando 1958) but has not been previously Contrary to the observations of Kellogg et al. (1980), who reported from the Ross Sea sector of the antarctic. Specimens of report an absence of Nitzschia westii in Commonwealth Glacier M. charcotii are common in meltpools on the McMurdo Ice Shelf lacustrine sediments, N. westii is common in all samples studied today, especially near tidal cracks, but were not found in iso- from this outcrop. Reworked nonmarine diatom-rich sediment lated inland waters or under exclusively marine conditions. The clasts from older deposits are present in this succession. The published ecology for M. charcotii and the distribution of this clasts contain abundant Navicula shackletoni and common Melo- diatom in the McMurdo Sound region suggests an association sira charcotii. The occurrence of these clasts and common marine with tidally influenced ice-shelf conditions and other marine- diatom fragments indicates significant sediment transport and proximal, brackish water environments. Melosira charcotii is also redeposition. common in Pleistocene nonmarine intervals recovered from Lake Vanda, Wright Valley. Recent sediment from the anoxic DVDP-15 and CIROS-2 drill cores in McMurdo Sound. These basin of Lake Vanda was evaluated using the same methods as intervals, up to approximately 80 meters thick, contain an ex- above. This sample has about 3 million nonmarine diatoms per clusively nonmarine diatom flora, as reported by Brady (1978, gram of sediment. Species composition is unlike the diatom 1981, 1982) and Harwood (1986), respectively. The sediments of assemblages present in outcrop or modern meltpool samples. Salmon Stream and McMurdo Sound drill cores could reflect While several cosmopolitan diatoms are present, most notably nonmarine conditions at the ice edge during advance or retreat Navicula multicopsis and varieties, the dominant diatom is Pin- of grounded Ross Sea ice in McMurdo Sound. nularia cymatopleura. Several forms are present which were not Hobbs Glacier, Cape Chocolate. A 3-meter-thick outcrop of finely observed in outcrop samples or in modern shallow meltpools. laminated, (average of 0.8 millimeters per laminade) highly These included Amphora delicatissima, which has been reported calcareous sediments is located adjacent to the snout of Hobbs from Lake Miers (Baker 1967).

36 ANTARCTIC JOURNAL A small (5-8 micron) siliceous cyst formed by a planktonic References chrysophyte (Ochromonas niiniscula?) (figure, d-f) makes the Baker, A. N. 1967. Algae from Lake Miers, a solar-heated Antarctic lake. greatest contribution to the siliceous microflora in this sedi- New Zealand Journal of Botany, 5, 453-468. ment. The sample contains more than three times as many of Brady, H.T. 1977. Freshwater lakes in Pleistocene McMurdo Sound. these chrysomonad cysts as diatoms, amounting to 10 million Antarctic Journal of the U.S., 12(4), 117-118. cysts per gram, making them an important ecological marker. Brady, H.T. 1981. The significance of fossil marine and non-marine The distribution of this algal species has been previously de- diatoms in DVDP cores. in L.D. McGinnis (Ed.), Dry Valley Drilling scribed as abundant in Lake Vanda but rare in Taylor Valley Project. Antarctic Research Series, Vol. 33, Washington, D.C.: American lakes (Seaburg et al. 1979). The cysts are found in very low Geophysical Union. abundance in other nonmarine sediments, despite wide dis- Brady, H.T. 1982. Late Cenozoic history of Taylor and Wright Valleys and McMurdo Sound inferred from diatoms in Dry Valley Drilling tribution. Chrysomonad cysts have been found forming under Project cores. In C. Craddock (Ed.), Antarctic geoscience. Madison: winter ice in Scandinavian lakes (Cronberg 1973), suggesting University of Wisconsin Press. that cyst formation provides a survival strategy during winter Cronberg, G. 1973. Development of cysts in Malloinonas eoa examined and perhaps other times of environmental stress. Abundant by scanning electron microscopy. Hydrohiologia, 43, 29-38. occurrence of this fossil in a sediment sequence may suggest Debenham, F. 1921. Recent and local deposits of McMurdo region. conditions similar to Lake Vanda today, i.e., thick, clear ice and British Antarctic Expedition "Terra Nova," 1910. Natural History Report, deep, chemically and thermally stratified water. Oxygenated Geology, 1(3), 63-100. shallow antarctic lake floors are host to a complex community of Denton, G. H., and T.J. Hughes. 1981. The last great ice sheets. New York: mat-forming filimentous blue-green algae, which accumulate Wiley. stromatolitic laminations (Parker et al. 1981). Benthic diatom Frenguelli, J., and H. Orlando. 1958. Diatoms and silicoflagellates of the floras are found in association with these algal mats. By con- South American sector of the Antarctic. Buenos Aires: Instituto Antartico Argentino. (In Spanish) trast, the microfossil assemblage in sediments from the deep Harwood, D.M. 1986. Diatom hiostratigraphy and paleoecology with a anoxic basin of Lake Vanda is dominated by planktonic forms, Cenozoic history of antarctic ice sheets. (Doctoral dissertation, Columbus: reflecting productivity in the water column under the ice but a Ohio State University.) relatively inactive benthic community. These assemblage dif- Kellogg, D.E., M. Stuiver, T.B. Kellogg, and G.H. Denton. 1980. Non- ferences may be useful in reconstructing past lake conditions. marine diatoms from Late Wisconsin perched deltas in Taylor Valley, These results are very encouraging, but further work is Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, 30, needed. Detailed ecologic and distributional studies on the 157-189. modern diatom floras will refine the paleoenvironmental Miagkov, SM., G.N. Nedeshava, and E.I. Riabova. 1976. McMurdo model. To apply this model best, long, undisturbed cores Sound sea level changes in the last 50,000 years. Antarctic Journal of the should be extracted from the bottom of several modern dry U.S., 11(5), 233-235. Parker, B.C., G.M. Simmons, Jr., F.G. Love, R.A. Wharton, Jr., and K.G. valley lakes. Continuous sedimentary successions and the lack Seaburg. 1981. Modern stromatolites in Antarctic dry valley lakes. of bioturbation make these records attractive for high resolution Bioscience, 31, 656-661. paleoclimatic studies. The record spanning the last few 1,000 Peragallo, M. 1921. Freshwater and saltwater diatoms. In J . Charcot years maybe compared with the antarctic ice-core record. Long- (ed.), Botanique. Paris: Second French Antarctic Expedition er time-scale lacustrine successions may contain trends for com- 1908-1910. (in French) parison with nearshore antarctic marine core records. These Péwé, T. 1960. Multiple glaciation in the McMurdo Sound region, Ant- sedimentary successions have the potential for providing an arctica: A progressive report. Journal of Geology, 68, 489-514. excellent record of terrestrial Quaternary climate change in Scherer, R.P. In preparation. An absolute abundance method for quan- Antarctica. titative analysis of diatoms or other fine sand and silt-sized sedimen- This research was supported by National Science Foundation tary particles. Micropaleontology. Seaburg, K.G., B.C. Parker, G.W. Prescott, and L.A. Witford. 1979. The grant DPP 85-17625 to Peter-Noel Webb. Lake Vanda sediment algae of Southern Victorialand, Antarctica. Bihliothecza Phycologica, material was collected under National Science Foundation grant Vol. 34. Valduz: J. Cramer. DPP 85-16465 to William Green and was generously provided for Spederi, I. 1960. Post-glacial terraces near Cape Chocolate, McMurdo this study. Peter Webb and Dave Harwood made helpful com- Sound, Antarctica. New Zealand Journal of Geology and Geophysics, 3, ments regarding the manuscript. 203-217.

1987 REVIEW 37