Geologic evidence for pre-late Quaternary east antarctic glaciation of ...
References
Austin, K.G. In preparation. Stratigraphy, sedimentology, and chronology of minor moraines, lower Taylor Valley, Antarctica. (Masters Thesis, University of Maine, Orono, Maine.) Dansgaard, W., S.J. Johnsen, H.B. Clausen, D. Dahl-Jensen, N. Gundestrup, C.V. Hammer, and H. Oeschger. 1984. North Atlantic climatic oscillations revealed by deep Greenland ice cores. American Geophysical Union Monograph, 29, 288 - 298.
Geologic evidence for pre-late Quaternary east antarctic glaciation of central and eastern Wright Valley M.L. PRENTICE Institute for Quaternary Studies University of Maine Orono, Maine 04469
and Department of Geological Sciences Brown University Providence, Rhode Island 02912
S.C. WILSON and J.G. BOCKHEIM Department of Soil Science University of Wisconsin Madison, Wisconsin 53706
G. H. DENTON Institute for Quaternary Studies
and Department of Geological Sciences University of Maine Orono, Maine 04469
Geologic evidence within central and eastern Wright Valley has important implications for the prelate Quaternary glacial history of Antarctica (Denton et al. 1984; Prentice 1985). We continued our investigations of this area for 4 weeks during the 1984 - 1985 austral summer. Our primary objective is to reconstruct paleo-ice dynamics in Wright Valley as a test of the overriding ice model of Denton et al. (1984). Here we report some of our findings. Peleus basal till outcrops discontinuously within the valley up to an elevation of 1,150 meters near Bartley Glacier and records extensive Neogene glaciation (figure) (Denton et al. 1984). Texturally, the till is a very poorly sorted, pebbly, muddy sand. Based on analysis of 43 samples, the average gravel, sand, and mud percentages are 27, 43, and 30, respectively. The till is 1985 REVIEW
Denton, G. H., R. L. Armstrong, and M. Stuiver. 1971. The late Cenozoic glacial history of Antarctica. In K.K. Turekian (Ed.), The Late Cenozoic glacial ages. New Haven, Conn.: Yale University Press. Oeschger, H., J. Beer, U. Siegenthaler, B. Stauffer, W. Dansgaard, and C.C. Langway. 1984. Late glacial climate history from ice cores. American Geophysical Union Monograph, 29, 299 - 306. Stauffer, B., H. Hofer, H. Oeschger, J. Schwander, and U. Siegenthaler. 1984. Atmospheric CO21 concentration during the last glaciation. Annals of Glaciology, 5, 160 - 164. Stuiver, M., G. H. Denton, T. J. Hughes, and J. L. Fastook. 1981. History of the marine ice sheet in West Antarctica during the last glaciation: A working hypothesis. In G.H. Denton, and T.J. Hughes (Eds.), The last great ice sheets. New York: Wiley-Interscience.
moderately to highly compact and fissile. It is typically not stratified. Approximately 5 percent of the gravel clasts are striated. Examination of 38 samples yielded a few unidentifiable nonmarine and marine diatoms as well as shell fragments. Lithologies of Peleus gravel, constituting a total volume of 41,000 cubic centimeters, as well as glacial erosional features, strongly suggest that the depositing ice mass flowed from the west (Prentice 1982). Critical data for this are the presence of Vida granite in till at localities east of its easternmost valley outcrop and abundance of Ferrar dolerite at locations with little Ferrar outcrop to the east but considerable exposure to the west. The lack of meta-sediments from the Asgard Formation, a unit which outcrops extensively east of Bartley Glacier (McKelvey and Webb 1962), constitutes further support of a westerly source for Peleus ice. Stoss-lee molding of striated bedrock beneath Peleus till as well as striated boulders in Peleus till also indicate eastward ice flow. Prentice (1985) inferred that Peleus ice not only filled Wright Valley but also engulfed much of the adjacent mountain ranges. The discovery of Peleus till on the north valley wall north of Goodspeed Glacier about 900 meters above the valley floor constitutes further evidence for this (figure). Because Peleus ice flowed from the west, it must have been thicker than this to the west (up-glacier), over most of Wright Valley. Hence, recent evidence is consistent with ice thicknesses proposed in the model of Denton et al. (1984) and, further, suggests that thick ice has flowed eastward in addition to northeastward, as proposed in the same model. Peleus till directly overlies bedrock, mud-rich waterlaid diamicton and, at Prospect Mesa, the pecten-bearing gravels. The latter deposits suggest a maximum age of middle Pliocene to mid-middle Miocene for the Peleus (Denton et al. 1984). Alpine drift older than 2.0 million years as well as colluvium overlie Peleus till (Denton et al. 1984). Soils derived from Peleus drift contain a well-developed desert pavement overlying an oxidized zone that is seldom thicker than 25 centimeters and always exhibits pulverulence. Pseudomorphs or "ghosts" are usually restricted to the oxidized zone. A weakly to strongly cemented salt pan commonly occurs below a depth of 7 centimeters and averages 8 centimeters in thickness. Abundant soluble salts provide coherence to depths of 80 centimeters or more. Based on our model of increasing soil development in coarse sandy soils with age (Bockheim 1979), we would expect soils 61
Peleus till outcrop within Wright Valley. (Symbols are: EA, east antarctic ice sheet; Rs, Ross Sea; AR, Asgard Range; OR, Olympus Range; WL, Wright Lower Glacier; wu, Wright Upper Glacier; BP, Bull Pass; Lv, Lake Vanda; B, Bartley Glacier; M, Meserve Glacier; G, Goodspeed Glacier; +, mountain peak. Black areas depict Peleus outcrop. Numbers are elevations in meters.)
derived from Peleus drift to be more mature than those of the oldest overlying deposits. However, Peleus soils examined to date are morphologically and chemically less well developed than the most mature soils developed in superposed deposits (Bockheim 1978). We are investigating this problem. Denton et al. (1984) inferred that isolated gravel-rich ripples in the mountains adjacent to Wright Valley and elsewhere record thick overriding ice. Trains of isolated ripples also occur on Peleus till, colluvium, older alpine drift, and bedrock within Wright Valley and may be closely related to those in the mountains. In cross-section, these ripples are commonly 15 centimeters high at their crests, between 1 and 3 meters long, and asymmetric both up- and downslope. The symmetry index (stoss-side length divided by lee-side length) for 250 measured profiles on 81 ripples varies between 0.4 and 6.0. Internally, the ripples consist of moderately to poorly sorted pebbly sand exhibiting little stratification. Intermediate axes of the largest clasts on the ripples average 17 centimeters in length. With respect to the foregoing, these ripples differ significantly from obvious wind ripples on the modern floodplain. For example, all wind ripples that we measured had a symmetry index greater than or equal to 2.0. In map view, however, both groups of valley ripples trend northwest-southeast. Therefore, eolian as well as glacial origins for the ripples are being investigated. Soil development in the ripples is minimal. Slightly more than half of the 21 ripples examined for soil development contain ghosts; nearly all show some accumulations of soluble salts beneath clasts. However, only two ripples displayed free salts in the matrix. Consequently, electrical conductivities are typically
62
low. If these ripples record ice sheet overriding like their mountain counterparts may, the soil's data suggest that this glaciation is much younger than the Peleus glaciation. This is corroborated by the mature soils in both colluvium and alpine drift which separate Peleus till from the ripples in many locations. This work was supported by National Science Foundation grants DPP 83-18808 and DPP 83-19477. We thank N. Potter, B. Hess, H. Conway, R. Ackert, and R. Weed for their assistance.
References Bockheim, J.G. 1978. Soil weathering sequences in Wright Valley. Antarctic Journal of the U.S., 13, 36 - 39. Bockheim, J.G. 1979. Relative age and origin of soils in eastern Wright Valley. Soil Science, 128, 142 - 152. Denton, G. H., M. L. Prentice, D. E. Kellogg, and T.B. Kellogg. 1984. Late Tertiary history of the Antarctic Ice Sheet: Evidence from the Dry Valleys. Geology, 12, 263 - 267. McKelvey, B.C., and P.N. Webb. 1962. Geological investigations in southern Victoria Land, Antarctica: Part 3—Geolog y of Wright Valley. New Zealand Journal of Geology and Geophysics, 5, 143 - 162. Prentice, M. L. 1982. Surficial geology and stratigraphy in central Wright Valley, Antarctica: Implications for Antarctic Tertiary glacial history. (Masters Thesis, University of Maine, Orono, Maine.) Prentice, M.L. 1985. Peleus glaciation of Wright Valley, Antarctica. South African Journal of Science, 81, 241 - 243.
ANTARCTIC JOURNAL
Austin, K.G. In preparation. Stratigraphy, sedimentology, and chronology of minor moraines, lower Taylor Valley, Antarctica. (Masters Thesis, University of Maine, Orono, Maine.) Dansgaard, W., S.J. Johnsen, H.B. Clausen, D. Dahl-Jensen, N. Gundestrup, C.V. Hammer, and H. Oeschger. 1984. North Atlantic climatic oscillations revealed by deep Greenland ice cores. American Geophysical Union Monograph, 29, 288 - 298.
Geologic evidence for pre-late Quaternary east antarctic glaciation of central and eastern Wright Valley M.L. PRENTICE Institute for Quaternary Studies University of Maine Orono, Maine 04469
and Department of Geological Sciences Brown University Providence, Rhode Island 02912
S.C. WILSON and J.G. BOCKHEIM Department of Soil Science University of Wisconsin Madison, Wisconsin 53706
G. H. DENTON Institute for Quaternary Studies
and Department of Geological Sciences University of Maine Orono, Maine 04469
Geologic evidence within central and eastern Wright Valley has important implications for the prelate Quaternary glacial history of Antarctica (Denton et al. 1984; Prentice 1985). We continued our investigations of this area for 4 weeks during the 1984 - 1985 austral summer. Our primary objective is to reconstruct paleo-ice dynamics in Wright Valley as a test of the overriding ice model of Denton et al. (1984). Here we report some of our findings. Peleus basal till outcrops discontinuously within the valley up to an elevation of 1,150 meters near Bartley Glacier and records extensive Neogene glaciation (figure) (Denton et al. 1984). Texturally, the till is a very poorly sorted, pebbly, muddy sand. Based on analysis of 43 samples, the average gravel, sand, and mud percentages are 27, 43, and 30, respectively. The till is 1985 REVIEW
Denton, G. H., R. L. Armstrong, and M. Stuiver. 1971. The late Cenozoic glacial history of Antarctica. In K.K. Turekian (Ed.), The Late Cenozoic glacial ages. New Haven, Conn.: Yale University Press. Oeschger, H., J. Beer, U. Siegenthaler, B. Stauffer, W. Dansgaard, and C.C. Langway. 1984. Late glacial climate history from ice cores. American Geophysical Union Monograph, 29, 299 - 306. Stauffer, B., H. Hofer, H. Oeschger, J. Schwander, and U. Siegenthaler. 1984. Atmospheric CO21 concentration during the last glaciation. Annals of Glaciology, 5, 160 - 164. Stuiver, M., G. H. Denton, T. J. Hughes, and J. L. Fastook. 1981. History of the marine ice sheet in West Antarctica during the last glaciation: A working hypothesis. In G.H. Denton, and T.J. Hughes (Eds.), The last great ice sheets. New York: Wiley-Interscience.
moderately to highly compact and fissile. It is typically not stratified. Approximately 5 percent of the gravel clasts are striated. Examination of 38 samples yielded a few unidentifiable nonmarine and marine diatoms as well as shell fragments. Lithologies of Peleus gravel, constituting a total volume of 41,000 cubic centimeters, as well as glacial erosional features, strongly suggest that the depositing ice mass flowed from the west (Prentice 1982). Critical data for this are the presence of Vida granite in till at localities east of its easternmost valley outcrop and abundance of Ferrar dolerite at locations with little Ferrar outcrop to the east but considerable exposure to the west. The lack of meta-sediments from the Asgard Formation, a unit which outcrops extensively east of Bartley Glacier (McKelvey and Webb 1962), constitutes further support of a westerly source for Peleus ice. Stoss-lee molding of striated bedrock beneath Peleus till as well as striated boulders in Peleus till also indicate eastward ice flow. Prentice (1985) inferred that Peleus ice not only filled Wright Valley but also engulfed much of the adjacent mountain ranges. The discovery of Peleus till on the north valley wall north of Goodspeed Glacier about 900 meters above the valley floor constitutes further evidence for this (figure). Because Peleus ice flowed from the west, it must have been thicker than this to the west (up-glacier), over most of Wright Valley. Hence, recent evidence is consistent with ice thicknesses proposed in the model of Denton et al. (1984) and, further, suggests that thick ice has flowed eastward in addition to northeastward, as proposed in the same model. Peleus till directly overlies bedrock, mud-rich waterlaid diamicton and, at Prospect Mesa, the pecten-bearing gravels. The latter deposits suggest a maximum age of middle Pliocene to mid-middle Miocene for the Peleus (Denton et al. 1984). Alpine drift older than 2.0 million years as well as colluvium overlie Peleus till (Denton et al. 1984). Soils derived from Peleus drift contain a well-developed desert pavement overlying an oxidized zone that is seldom thicker than 25 centimeters and always exhibits pulverulence. Pseudomorphs or "ghosts" are usually restricted to the oxidized zone. A weakly to strongly cemented salt pan commonly occurs below a depth of 7 centimeters and averages 8 centimeters in thickness. Abundant soluble salts provide coherence to depths of 80 centimeters or more. Based on our model of increasing soil development in coarse sandy soils with age (Bockheim 1979), we would expect soils 61
Peleus till outcrop within Wright Valley. (Symbols are: EA, east antarctic ice sheet; Rs, Ross Sea; AR, Asgard Range; OR, Olympus Range; WL, Wright Lower Glacier; wu, Wright Upper Glacier; BP, Bull Pass; Lv, Lake Vanda; B, Bartley Glacier; M, Meserve Glacier; G, Goodspeed Glacier; +, mountain peak. Black areas depict Peleus outcrop. Numbers are elevations in meters.)
derived from Peleus drift to be more mature than those of the oldest overlying deposits. However, Peleus soils examined to date are morphologically and chemically less well developed than the most mature soils developed in superposed deposits (Bockheim 1978). We are investigating this problem. Denton et al. (1984) inferred that isolated gravel-rich ripples in the mountains adjacent to Wright Valley and elsewhere record thick overriding ice. Trains of isolated ripples also occur on Peleus till, colluvium, older alpine drift, and bedrock within Wright Valley and may be closely related to those in the mountains. In cross-section, these ripples are commonly 15 centimeters high at their crests, between 1 and 3 meters long, and asymmetric both up- and downslope. The symmetry index (stoss-side length divided by lee-side length) for 250 measured profiles on 81 ripples varies between 0.4 and 6.0. Internally, the ripples consist of moderately to poorly sorted pebbly sand exhibiting little stratification. Intermediate axes of the largest clasts on the ripples average 17 centimeters in length. With respect to the foregoing, these ripples differ significantly from obvious wind ripples on the modern floodplain. For example, all wind ripples that we measured had a symmetry index greater than or equal to 2.0. In map view, however, both groups of valley ripples trend northwest-southeast. Therefore, eolian as well as glacial origins for the ripples are being investigated. Soil development in the ripples is minimal. Slightly more than half of the 21 ripples examined for soil development contain ghosts; nearly all show some accumulations of soluble salts beneath clasts. However, only two ripples displayed free salts in the matrix. Consequently, electrical conductivities are typically
62
low. If these ripples record ice sheet overriding like their mountain counterparts may, the soil's data suggest that this glaciation is much younger than the Peleus glaciation. This is corroborated by the mature soils in both colluvium and alpine drift which separate Peleus till from the ripples in many locations. This work was supported by National Science Foundation grants DPP 83-18808 and DPP 83-19477. We thank N. Potter, B. Hess, H. Conway, R. Ackert, and R. Weed for their assistance.
References Bockheim, J.G. 1978. Soil weathering sequences in Wright Valley. Antarctic Journal of the U.S., 13, 36 - 39. Bockheim, J.G. 1979. Relative age and origin of soils in eastern Wright Valley. Soil Science, 128, 142 - 152. Denton, G. H., M. L. Prentice, D. E. Kellogg, and T.B. Kellogg. 1984. Late Tertiary history of the Antarctic Ice Sheet: Evidence from the Dry Valleys. Geology, 12, 263 - 267. McKelvey, B.C., and P.N. Webb. 1962. Geological investigations in southern Victoria Land, Antarctica: Part 3—Geolog y of Wright Valley. New Zealand Journal of Geology and Geophysics, 5, 143 - 162. Prentice, M. L. 1982. Surficial geology and stratigraphy in central Wright Valley, Antarctica: Implications for Antarctic Tertiary glacial history. (Masters Thesis, University of Maine, Orono, Maine.) Prentice, M.L. 1985. Peleus glaciation of Wright Valley, Antarctica. South African Journal of Science, 81, 241 - 243.
ANTARCTIC JOURNAL
