Glacial geology of Spike Cape, McMurdo Sound
valleys and other areas to the east of the Transantarctic Mountains divide may have a source in sedimentary basins in East Antarctica. Correlation of glacial deposits by their constituent microfossils should be approached with caution in light of evidence for reworking of marine sediments from East Antarctica. The presence of similar microfossil assemblages in glacial deposits does not imply coeval deposition but more likely reflects an earlier marine event "upstream" from these deposits. This research was supported by National Science Foundation grant DPP 83-15553 and DPP 84-20622.
References Denton, G.H., M.L. Prentice, D.E. Kellogg, andT.B. Kellogg. 1984. Late Tertiary history of the Antarctic ice sheet: Evidence from the Dry Valleys. Geology, 12, 263-267. Drewry, D.J. 1980. Pleistocene bimodal response of Antarctic ice. Nature, 287, 214-216. Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100.
Glacial geology of Spike Cape, McMurdo Sound M.C.G. MABIN Institute of Polar Studies Ohio State University Columbus, Ohio 43210
Spike Cape is a small ice-free area on the western side of McMurdo Sound, 15 kilometers northwest of Marble Point. A promontory rises to about 150 meters above sea level and is connected by a tombolo with two low knolls rising to 25 meters above sea level. These form a small peninsula that extends northeast for 1.25 kilometers. Bedrock is microdiorite gneiss (Gunn and Warren 1962) that has been smoothed and streamlined by glacial action. A thin mantle of glacial deposits now covers most of the area and at lower elevations, the bedrock and till has been further modified by marine processes (Nichols 1968). The surficial geology is shown in the figure. Differences in composition and weathering allow three till sheets to be identified: knoll till, promontory till, and piedmont till. Knoll till caps the two low knolls near Spike Cape. It consists of poorly sorted sand to boulder-sized material. Most is locally derived gneiss, but erratic rock types are common including granodiorite, granite, and scoriaceous basalts of the McMurdo Volcanic Group. The till and exposed bedrock are noticeably weathered. Quartz-rich veins stand up to 8 centimeters above the gneiss country-rock, and cavernous weathering has re88
Harwood, D.M. 1986. Diatom biostratigraphy and paleoecology with a Cenozoic history of antarctic ice sheets. (Doctoral dissertation, Ohio State University, Columbus, Ohio.) Ishman, S.E. 1985. Foraminiferal hiostratigraphy and paleoecology of Dry Valley Drilling Project cores 10 and ii, Taylor Valley, Antarctic. (Masters Thesis, Ohio State University.) Mayewski, PA., and R. P. Goldthwait. 1985. Glacial events in the Transantarctic Mountains: A record of the East Antarctic ice sheet. In M.D. Turner and J.F. Splettstoesser (Eds.), Geology of the Transantarctic Mountains. (Antarctic Research Series, Vol. 36.) Washington, D.C.: American Geophysical Union. Webb, P.-N. 1974. Micropaleontology, paleoecology and correlation of the Pecten gravels, Wright Valley, Antarctica and a description of Trochoelphidiella onyxi n.gen., n.sp. Journal of Foraminiferal Research, 185-199. Webb, P.-N., D.M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P.-N., B.C. McKelvey, D.M. Harwood, M.C.G. Mabin, and J.H. Mercer. In preparation. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S.
Webb, P. and j.H. Wrenn. 1982. Upper Cenozoic micropaleontology and biostratigraphy of eastern Taylor Valley, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press.
moved over 30 centimeters of material from some of the granodiorite and granite boulders. Many of the cobbles and boulders have had their exposed surfaces rounded by exfoliation and grain-disintegration processes. A soil profile has begun to develop in the till which is oxidized a red-brown color to a depth of 25 centimeters. Promotory till mantles the steep slopes near the Wilson Piedmont Glacier. It has similar characteristics as the knoll till, except that no McMurdo volcanic clasts were found. The piedmont till occurs on the generally flat area at the top of the promontory, in front of a recently retreated portion of the Wilson Piedmont Glacier. It consists of boulders and cobbles scattered over the gneiss bedrock. It is composed mainly of gneissic rocks with occasional granodiorite and granite erratics; however, no McMurdo volcanic clasts were seen. The rocks are all unweathered and some boulders can be seen precariously perched on smaller rock fragments. Striations were found on the surface of a dark fine-grained dyke that intrudes the gneiss (figure). The dyke is 2.5 meters wide and extends east-northeast for about 400 meters from the glacier margin. Two contrasting sets of striations commonly occur, and cross-cutting relationships allow relative age differentiation and sense of movement to be determined. The most common set trends between 65° and 80° (approximately eastnortheast) and is preserved on rock faces oriented toward the Wilson Piedmont Glacier. The second set trends at 320°-140° (northwest to southeast) and is preserved on small facets oriented away from the Wilson Piedmont Glacier. The formation of the east-northeast trending set has obliterated most of the northwest-to-southeast trending set, the latter being preserved only on protected lee-side rock facets. Thus, the east-northeast set is interpreted as the youngest, formed by an expanded Wilson Piedmont Glacier. The sense of ice-flow direction for the older set cannot be directly determined, although they are oriented perpendicular to the present general flow of the ANTARCTIC JOURNAL
163030'E
Spike Cape
::• ioi . .. hi I-I : 141
Co
MC
17&.
CL
>< striation trends
9'S-
' Spot elevations (m) Elevated marine features
o N
Li Piedmont till
Promontory till
-
Knoll till 0 500 Meters
Surf icial geology of Spike Cape.
Wilson Piedmont Glacier and, therefore, were probably not formed by it. A northwest flow of ice in McMurdo Sound seems likely. Striations were also noted on Cape Dunlop, a rocky promontory 7.5 kilometers north of Spike Cape. Here, a younger set trends eastward, and an older set is oriented northwest to southeast. Thus, these ice-flow directions are considered to have regional significance in this part of McMurdo Sound. A variety of elevated marine features is preserved at Spike Cape (figure). These have been briefly described by Nichols (1968) and include beach ridges, ice-push ridges, tombolos, and wave-washed bedrock surfaces. They have been formed by wave action reworking the knoll and promontory till sheets. Isostatic rebound has elevated the oldest beach ridges to 17 meters above sea level. As noted by Nichols (1968) the beach ridge deposits are clearly less weathered than the knoll and promontory tills, indicating the area had been deglaciated for a considerable time before the highest beach ridge began to form. The absolute ages of these deposits has not been determined because no datable materials were found. However, other work done in the McMurdo Sound area allows some limits on their age to be suggested. Stuiver et al. (1981) have reconstructed a history of the McMurdo Sound area during the last glaciation
1986 REVIEW
(approximately 18,000 years ago) that shows Spike Cape covered by some 700 meters of ice. Thus, the deposits at Spike Cape were probably formed during and since that time and, therefore, provide useful information on the nature of the last glaciation. The east-northeast trending striations and piedmont till are clearly very young and are believed to have been formed during a recent small advance of this portion of the Wilson Piedmont Glacier. The older striations and till sheets are more difficult to interpret because their relative age relationships and provenance of the deposits is difficult to determine or correlate with the existing model of the glaciation of McMurdo Sound. The knoll and promontory tills are more weathered than is characteristic for deposits of last glaciation age in nearby Wright Valley (Bockheim 1978); however, this is probably due to more rapid weathering occurring in this maritime setting. The presence of erratic clasts in the tills indicates deposition by nonlocal glacier ice. McMurdo volcanic rocks outcrop to the south and east of Spike Cape, thus ice that deposited on the knoll till probably came from this general sector. However, the apparent lack of these rocks in the promontory till is problematic. This configuration may reflect differences in age of the tills and differences in flow regimes at the times of deposition. A generally northward flow of ice through McMurdo Sound is also indicated by the northwest trending striations at both Spike Cape and Dunlop Island. However, this is not consistent with the Stuiver et al. (1981, p. 336) reconstruction which shows ice flowing southwest across the region. Further work on ice-free areas in this part of McMurdo Sound is needed to refine the glacial history. This research was supported by National Science Foundation grant DPP 84-20622 to P.-N. Webb and J.H. Mercer, Ohio State University. Assistance was also provided by a New Zealand University Grants Committee grant to R.M. Kirk, Canterbury University, the New Zealand Antarctic Research Programme, and Glen Lauder.
References Bockeim, J.G. 1978. Soil weathering sequences in Wright Valley. Antarctic Journal of the U.S., 13(4), 36-39. Gunn, B.M., and C. Warren. 1962. Geology of Victoria Land between the Mawson and Mulock glaciers, Antarctica. Bulletin New Zealand Geological Survey, (No. 71). Wellington: New Zealand Department of Scientific and Industrial Research. Nichols, R.L. 1968. Coastal geomorphology, McMurdo Sound, Antarctica. Journal of Glaciology, 7(51), 449-478. 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 The last great ice sheets. New York: Wiley.
89
References Denton, G.H., M.L. Prentice, D.E. Kellogg, andT.B. Kellogg. 1984. Late Tertiary history of the Antarctic ice sheet: Evidence from the Dry Valleys. Geology, 12, 263-267. Drewry, D.J. 1980. Pleistocene bimodal response of Antarctic ice. Nature, 287, 214-216. Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100.
Glacial geology of Spike Cape, McMurdo Sound M.C.G. MABIN Institute of Polar Studies Ohio State University Columbus, Ohio 43210
Spike Cape is a small ice-free area on the western side of McMurdo Sound, 15 kilometers northwest of Marble Point. A promontory rises to about 150 meters above sea level and is connected by a tombolo with two low knolls rising to 25 meters above sea level. These form a small peninsula that extends northeast for 1.25 kilometers. Bedrock is microdiorite gneiss (Gunn and Warren 1962) that has been smoothed and streamlined by glacial action. A thin mantle of glacial deposits now covers most of the area and at lower elevations, the bedrock and till has been further modified by marine processes (Nichols 1968). The surficial geology is shown in the figure. Differences in composition and weathering allow three till sheets to be identified: knoll till, promontory till, and piedmont till. Knoll till caps the two low knolls near Spike Cape. It consists of poorly sorted sand to boulder-sized material. Most is locally derived gneiss, but erratic rock types are common including granodiorite, granite, and scoriaceous basalts of the McMurdo Volcanic Group. The till and exposed bedrock are noticeably weathered. Quartz-rich veins stand up to 8 centimeters above the gneiss country-rock, and cavernous weathering has re88
Harwood, D.M. 1986. Diatom biostratigraphy and paleoecology with a Cenozoic history of antarctic ice sheets. (Doctoral dissertation, Ohio State University, Columbus, Ohio.) Ishman, S.E. 1985. Foraminiferal hiostratigraphy and paleoecology of Dry Valley Drilling Project cores 10 and ii, Taylor Valley, Antarctic. (Masters Thesis, Ohio State University.) Mayewski, PA., and R. P. Goldthwait. 1985. Glacial events in the Transantarctic Mountains: A record of the East Antarctic ice sheet. In M.D. Turner and J.F. Splettstoesser (Eds.), Geology of the Transantarctic Mountains. (Antarctic Research Series, Vol. 36.) Washington, D.C.: American Geophysical Union. Webb, P.-N. 1974. Micropaleontology, paleoecology and correlation of the Pecten gravels, Wright Valley, Antarctica and a description of Trochoelphidiella onyxi n.gen., n.sp. Journal of Foraminiferal Research, 185-199. Webb, P.-N., D.M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P.-N., B.C. McKelvey, D.M. Harwood, M.C.G. Mabin, and J.H. Mercer. In preparation. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S.
Webb, P. and j.H. Wrenn. 1982. Upper Cenozoic micropaleontology and biostratigraphy of eastern Taylor Valley, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press.
moved over 30 centimeters of material from some of the granodiorite and granite boulders. Many of the cobbles and boulders have had their exposed surfaces rounded by exfoliation and grain-disintegration processes. A soil profile has begun to develop in the till which is oxidized a red-brown color to a depth of 25 centimeters. Promotory till mantles the steep slopes near the Wilson Piedmont Glacier. It has similar characteristics as the knoll till, except that no McMurdo volcanic clasts were found. The piedmont till occurs on the generally flat area at the top of the promontory, in front of a recently retreated portion of the Wilson Piedmont Glacier. It consists of boulders and cobbles scattered over the gneiss bedrock. It is composed mainly of gneissic rocks with occasional granodiorite and granite erratics; however, no McMurdo volcanic clasts were seen. The rocks are all unweathered and some boulders can be seen precariously perched on smaller rock fragments. Striations were found on the surface of a dark fine-grained dyke that intrudes the gneiss (figure). The dyke is 2.5 meters wide and extends east-northeast for about 400 meters from the glacier margin. Two contrasting sets of striations commonly occur, and cross-cutting relationships allow relative age differentiation and sense of movement to be determined. The most common set trends between 65° and 80° (approximately eastnortheast) and is preserved on rock faces oriented toward the Wilson Piedmont Glacier. The second set trends at 320°-140° (northwest to southeast) and is preserved on small facets oriented away from the Wilson Piedmont Glacier. The formation of the east-northeast trending set has obliterated most of the northwest-to-southeast trending set, the latter being preserved only on protected lee-side rock facets. Thus, the east-northeast set is interpreted as the youngest, formed by an expanded Wilson Piedmont Glacier. The sense of ice-flow direction for the older set cannot be directly determined, although they are oriented perpendicular to the present general flow of the ANTARCTIC JOURNAL
163030'E
Spike Cape
::• ioi . .. hi I-I : 141
Co
MC
17&.
CL
>< striation trends
9'S-
' Spot elevations (m) Elevated marine features
o N
Li Piedmont till
Promontory till
-
Knoll till 0 500 Meters
Surf icial geology of Spike Cape.
Wilson Piedmont Glacier and, therefore, were probably not formed by it. A northwest flow of ice in McMurdo Sound seems likely. Striations were also noted on Cape Dunlop, a rocky promontory 7.5 kilometers north of Spike Cape. Here, a younger set trends eastward, and an older set is oriented northwest to southeast. Thus, these ice-flow directions are considered to have regional significance in this part of McMurdo Sound. A variety of elevated marine features is preserved at Spike Cape (figure). These have been briefly described by Nichols (1968) and include beach ridges, ice-push ridges, tombolos, and wave-washed bedrock surfaces. They have been formed by wave action reworking the knoll and promontory till sheets. Isostatic rebound has elevated the oldest beach ridges to 17 meters above sea level. As noted by Nichols (1968) the beach ridge deposits are clearly less weathered than the knoll and promontory tills, indicating the area had been deglaciated for a considerable time before the highest beach ridge began to form. The absolute ages of these deposits has not been determined because no datable materials were found. However, other work done in the McMurdo Sound area allows some limits on their age to be suggested. Stuiver et al. (1981) have reconstructed a history of the McMurdo Sound area during the last glaciation
1986 REVIEW
(approximately 18,000 years ago) that shows Spike Cape covered by some 700 meters of ice. Thus, the deposits at Spike Cape were probably formed during and since that time and, therefore, provide useful information on the nature of the last glaciation. The east-northeast trending striations and piedmont till are clearly very young and are believed to have been formed during a recent small advance of this portion of the Wilson Piedmont Glacier. The older striations and till sheets are more difficult to interpret because their relative age relationships and provenance of the deposits is difficult to determine or correlate with the existing model of the glaciation of McMurdo Sound. The knoll and promontory tills are more weathered than is characteristic for deposits of last glaciation age in nearby Wright Valley (Bockheim 1978); however, this is probably due to more rapid weathering occurring in this maritime setting. The presence of erratic clasts in the tills indicates deposition by nonlocal glacier ice. McMurdo volcanic rocks outcrop to the south and east of Spike Cape, thus ice that deposited on the knoll till probably came from this general sector. However, the apparent lack of these rocks in the promontory till is problematic. This configuration may reflect differences in age of the tills and differences in flow regimes at the times of deposition. A generally northward flow of ice through McMurdo Sound is also indicated by the northwest trending striations at both Spike Cape and Dunlop Island. However, this is not consistent with the Stuiver et al. (1981, p. 336) reconstruction which shows ice flowing southwest across the region. Further work on ice-free areas in this part of McMurdo Sound is needed to refine the glacial history. This research was supported by National Science Foundation grant DPP 84-20622 to P.-N. Webb and J.H. Mercer, Ohio State University. Assistance was also provided by a New Zealand University Grants Committee grant to R.M. Kirk, Canterbury University, the New Zealand Antarctic Research Programme, and Glen Lauder.
References Bockeim, J.G. 1978. Soil weathering sequences in Wright Valley. Antarctic Journal of the U.S., 13(4), 36-39. Gunn, B.M., and C. Warren. 1962. Geology of Victoria Land between the Mawson and Mulock glaciers, Antarctica. Bulletin New Zealand Geological Survey, (No. 71). Wellington: New Zealand Department of Scientific and Industrial Research. Nichols, R.L. 1968. Coastal geomorphology, McMurdo Sound, Antarctica. Journal of Glaciology, 7(51), 449-478. 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 The last great ice sheets. New York: Wiley.
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