Sirius Formation basal contacts in the Beardmore Glacier region
We wish to express our sincere appreciation to the other members of the Vanderbilt/Ohio State University research team, our fellow scientists from the Beardmore South camp, and the civilian and military support personnel for their efforts on our behalf. This work is supported by National Science Foundation grant DPP 84-18354. References
Barrett, P.J. 1969. Stratigraphy and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. institute of Polar Studies Report, Vol. 34. Columbus: Ohio State University Press. Berner, R.A., and R. Raiswell. 1984. C/S method for distinguishing freshwater from marine sedimentary rocks. Geology, 12, 365-368. Cody, R.D. 1971. Adsorption and the reliability of trace elements as environment indicators for shales. Journal of Sedimentary Petrology, 41, 461-471.
Collinson, J.W., and J.L. Isbell. 1986. Permian-Triassic sedimentology of the Beardmore Glacier region. Antarctic Journal of the U.S., 21(5).
Sirius Formation basal contacts in the Beardmore Glacier region M.C.G. MABIN Institute of Polar Studies Ohio State University Columbus, Ohio 43210
Sirius Formation outcrops examined in the Beardmore Glacier region during the 1985-1986 season are described by Webb et al. (in preparation). The disconformity between the basal Sirius Formation and underlying rocks was examined at five localities. The morphology of the underlying surface exhibits varying degrees of ice moulding on a variety of rock types, as reported from other sites (Mayewski and Goldthwait 1985). It is referred to by Webb et al. (Antarctic Journal, this issue; in preparation) as the "Dominion erosion surface." At two locations, Mount Sirius and Plunket Point, it is extensively exposed and easily accessible. Surveys of the contact were made using a theodolite and electronic distance meter. At the type locality, Mount Sirius (84°08'S 163°15'E), 85 meters of diamictite rest on a platform of columnar jointed dolerite, which is approximately 2,200 meters above sea level and 400 meters above the surrounding Bowden Névé. In plan view, the platform is L-shaped, one limb extending north for 1.3 kilometers, the other east for 0.9 kilometer. Width varies from 125 to 500 meters, and it covers an area of 4 hectares. The platform edge varies between 2,179 and 2,226 meters above sea level. It has two sets of undulations: one set is 20 meters deep and 300 meters apart, and the other set is superimposed on the 32
1975. Clay distributions in recent estuarine sediments. Clays and Clay Mineralogy, 23, 39-44. Fan, P.F. 1976. Recent silts of the Santa Clara River drainage basin,
Edzwald, J.K., and C.R. O'Melia.
southern California: A mineralogical investigation of their origin and
evolution. Journal of Sedimentary Petrology, 46, 802-812. Keller, W.D. 1970. Environmental aspects of clay minerals. Journal of Sedimentary Petrology. 40, 788-813. Lindsay, J.F. 1969. Stratigraphy and sedimentation of lower Beacon rocks in the central Transantarctic Mountains. Institute of Polar Studies Report, Vol. 33. Columbus: Ohio State University Press. Miller, M.F. 1984. Distribution of biogenic structures in Paleozoic nonmarine and marine margin sequences: An actualistic model. Journal of Paleontology, 58, 550-570. Miller, M.F., and R.S. Frisch. 1986. Depositional setting of the (Permian) Mackellar Formation, Beardmore Glacier area. Antarctic Journal of the U. S., 21(5). Miller, J.M.G., and B.J. Waugh. 1986. Sedimentology of the Pagoda Formation (Permian), Beardmore Glacier area. Antarctic Journal of the U. S., 21(5). Nesbitt, H.W., and G.M. Young. 1982. Early Proterozoic climates and
plate motions inferred from major element chemistry of lutites.
Nature, 299, 715-717.
first at ito 5 meters deep and 20 to 30 meters apart. These forms probably represent glacial whaleback features. Overall, the platform dips approximately 2° to the northwest. Where naturally exposed, it is weathered, in places into small, irregularly shaped tors up to 40 centimeters high and 25 centimeters across. Removal of the overlying compacted diamictite reveals a fresh, heavily striated surface. Striation directions measured at six localities along the eastern side of the platform trended between 22° and 105°, with the predominant ice-flow direction being to the east-northeast, as reported by McKelvey et al. (1984) and Mercer (1972). On the western side of the platform, striations are similarly oriented, and there are crescentic gouges up to 35 centimeters across, convex in an east-northeast direction (Harwood personal communication). Also exposed on this western edge is a P-form feature 2 meters across and 0.5 meter deep, eroded into the dolerite (Harwood personal communication). This meandering channel is exposed for 5 meters and is oriented southeastward. It indicates the presence of subglacial meltwater beneath the ice that overrode the platform. Sirius Formation deposits are well exposed in the Dominion Range in cliffs on the east side of the Beardmore Glacier, between 2.2 and 3.9 kilometers southwest of Plunket Point (85°06'S 166°56'E) (Oliver 1964; Mercer 1972). The diamictite rests on an undulating surface of columnar-jointed dolerite at about 1,750 meters above sea level and 15 to 95 meters above the glacier. The undulations vary from 3 to 36 meters high and 80 to 300 meters apart and are interpreted as whaleback features. Striations on the dolerite trend between 355° and 25°, the variations representing diverging and converging or north-northeast flowing ice over and around the whalebacks. Other glacial erosion features include minor plucking on the downglacier (northern) sides of the whalebacks, lunate fractures up to 8 centimeters across, and small grooves. A fault has displaced both the dolerite and overlying Sirius Formation diamictite. The northern side is upthrown 55 meters, and the fault trace can be followed south for 2.1 kilometers. ANTARCTIC JOURNAL
Extensive exposures of Sirius Formation occur in the upthrown face of a major fault scarp that runs north-south along the Dominion Range, 7 kilometers west of the Mill Glacier (Elliot, Barrett, and Mayewski 1974). The basal contact is intermittently exposed between 5.5 and 11.2 kilometers south of the Beardmore Glacier, at between 1,850 and 2,500 meters above sea level. In the south, two small exposures of diamictite rest in shallow depressions on dolerite at about 800 and 620 meters above the glacier. North of these, a 3.6-kilometer succession of Sirius Formation rests in a broad depression at 350 to 400 meters above the glacier. It is cut mainly in sandstone and mudstone of the Triassic Fremouw Formation (Elliot et al. 1974) and is buttressed at either end by dolerite. The northernmost basal contact exposed here is much lower, at only 50 meters above the glacier, and is a sloping platform cut across dolerite and Fremouw Formation sediments (Mayewski and Goldthwait 1985, figure 5). In all these exposures, the basal contact is difficult to reach due to precipitous slopes. However, four sited were reached and striations were observed trending between 25° and 65°. A thick exposure of Sirius Formation deposits is located in the lower Beardmore Valley, near The Cloudmaker (84°23'S 1690 14'E). Diamictite rests on a steeply sloping platform at about 1,060 meters above sea level and 80 meters above the Beardmore Glacier. It is cut in nearly vertically dipping metasediments of the Goldie Formation (Grindley, McGregor, and Walcott 1964), and dips 15° to 20° to the south. In profile, it appears to represent the lower part of a glacial valley-side, the floor of which would have been near the present glacier surface. These cross-cutting sets of striations are visible on the platform beneath the diamictite. They trend at 325°, 40°, and 80°. The former two sets are consistent with ice-flow trending in the general direction of the present valley. The 80° set is oriented perpendicular to the present valley system and probably reflects local perturbations in the basal ice-flow regime. The basal contacts of the Sirius Formation, and the indicated ice-flow directions from the Dominion Range, Plunket Point, and The Cloudmaker, appear to indicate a glacial system that was flowing through, and at times over, a landscape similar to the present. A small outcrop of Sirius Formation was found near Orr Peak (83°30'S 157°48'E) in the Miller Range (Webb et al. in preparation). It differs from those described above, because it does not rest on a glacially polished surface. The base of the exposure is at about 2,100 meters above sea level, 150 meters above the adjacent Marsh Glacier, and rests on gently dipping schist and marble of the Miller Formation (Grindley, McGregor, and Walcott 1964). The contact is sharp and horizontal and is underlain by up to 0.5 meter of weathered fragments of Miller Formation rocks. This material may represent the lower part of a truncated soil profile or slope deposits derived from adjacent hillsides. It is probably analogous to the Early Horlick Drift at Tillite Spur in the Reedy Glacier area described by Mercer (1968), which was interpreted as a pre-Sirius glaciation deposit. The geomorphology of the Miller Range is dominated by three glacial
1986 REVIEW
planation surfaces (Grindley 1967). Deposition of the Sirius Formation probably pre-dates the cutting of these surfaces, because they would be unlikely to have survived the scale of weathering implied by the deposits underlying the diamictite at Orr peak. The basal contacts of the Sirius Formation described here range from those showing extensive glacial erosion to surfaces largely unmodified by overriding ice. They range in elevation through some 1,500 meters, and indicate glaciation of a relatively high-relief landscape in a configuration similar to the present day. It is also likely that they are of different ages, and some may have been formed during several different ice advances prior to the commencement of deposition of the Sirius Formation. I thank Dan Greene, Chuck McGrosky, and Steve Munsell for willing assistance in the field. The Cloudmaker exposure was kindly shown to me by George Denton. This work was supported by National Science Foundation grant DPP 84-20622 to the Institute of Polar Studies, and an Ohio State University postdoctoral fellowship. References Elliot, DEL, P.J. Barrett, and P.A. Mayewski. 1974. Reconnaissance geologic map of the Plunket Point Quadrangle, Transantarctic Mountains, Antarctica. (U.S. Geological Survey Map A-4,1:250,000.) Washington,
D.C.: U.S. Government Printing Office. Grindley, G.W. 1967. The geomorphology of the Miller Range, Transantarctic Mountains, with notes on, the glacial history and neotectonics of East Antarctica. New Zealand Journal of Geology and Geophysics, 10,
557-598. Grindley, G.W., V.R. McGregor, and R.I. Walcott. 1964. Outline of the geology of the Nimrod-Beardmore-Axel Heiberg Glaciers region, Ross Dependency. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Holland Publishing House. Harwood, D.M. 1986. Personal communication. 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 Central Transantarctic Mountains. (Antarctic Research Series, Vol. 36.) Washington, D.C.: American Geophysical Union. Mercer, J.H. 1968. Glacial geology of the Reedy Glacier area, Antarctica. Geological Society of America Bulletin, 79, 471-486. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. McKelvey, B.C., J.H. Mercer, D.M. Harwood, and L.D. Stott. 1984. The Sirius Formation: Further considerations. Antarctic Journal of the U.S., 19(5), 42-43. Oliver, R.L. 1964. Geological observations at Plunket Point, Beardmore Glacier. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Ho!land Publishing House. Webb, P. D. M. Harwood, B. C. McKelvey, M.C.G. Mabin, and J. H. Mercer. 1986. Late Cenozoic tectonic and glacial history of the Transantarctic Mountains. Antarctic Journal of the U.S., 21(5). Webb, P.-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. Mercer. In preparation. Sirius Formation of the Miller Range-Dominion Range, central Transantarctic Mountains.
33
Barrett, P.J. 1969. Stratigraphy and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. institute of Polar Studies Report, Vol. 34. Columbus: Ohio State University Press. Berner, R.A., and R. Raiswell. 1984. C/S method for distinguishing freshwater from marine sedimentary rocks. Geology, 12, 365-368. Cody, R.D. 1971. Adsorption and the reliability of trace elements as environment indicators for shales. Journal of Sedimentary Petrology, 41, 461-471.
Collinson, J.W., and J.L. Isbell. 1986. Permian-Triassic sedimentology of the Beardmore Glacier region. Antarctic Journal of the U.S., 21(5).
Sirius Formation basal contacts in the Beardmore Glacier region M.C.G. MABIN Institute of Polar Studies Ohio State University Columbus, Ohio 43210
Sirius Formation outcrops examined in the Beardmore Glacier region during the 1985-1986 season are described by Webb et al. (in preparation). The disconformity between the basal Sirius Formation and underlying rocks was examined at five localities. The morphology of the underlying surface exhibits varying degrees of ice moulding on a variety of rock types, as reported from other sites (Mayewski and Goldthwait 1985). It is referred to by Webb et al. (Antarctic Journal, this issue; in preparation) as the "Dominion erosion surface." At two locations, Mount Sirius and Plunket Point, it is extensively exposed and easily accessible. Surveys of the contact were made using a theodolite and electronic distance meter. At the type locality, Mount Sirius (84°08'S 163°15'E), 85 meters of diamictite rest on a platform of columnar jointed dolerite, which is approximately 2,200 meters above sea level and 400 meters above the surrounding Bowden Névé. In plan view, the platform is L-shaped, one limb extending north for 1.3 kilometers, the other east for 0.9 kilometer. Width varies from 125 to 500 meters, and it covers an area of 4 hectares. The platform edge varies between 2,179 and 2,226 meters above sea level. It has two sets of undulations: one set is 20 meters deep and 300 meters apart, and the other set is superimposed on the 32
1975. Clay distributions in recent estuarine sediments. Clays and Clay Mineralogy, 23, 39-44. Fan, P.F. 1976. Recent silts of the Santa Clara River drainage basin,
Edzwald, J.K., and C.R. O'Melia.
southern California: A mineralogical investigation of their origin and
evolution. Journal of Sedimentary Petrology, 46, 802-812. Keller, W.D. 1970. Environmental aspects of clay minerals. Journal of Sedimentary Petrology. 40, 788-813. Lindsay, J.F. 1969. Stratigraphy and sedimentation of lower Beacon rocks in the central Transantarctic Mountains. Institute of Polar Studies Report, Vol. 33. Columbus: Ohio State University Press. Miller, M.F. 1984. Distribution of biogenic structures in Paleozoic nonmarine and marine margin sequences: An actualistic model. Journal of Paleontology, 58, 550-570. Miller, M.F., and R.S. Frisch. 1986. Depositional setting of the (Permian) Mackellar Formation, Beardmore Glacier area. Antarctic Journal of the U. S., 21(5). Miller, J.M.G., and B.J. Waugh. 1986. Sedimentology of the Pagoda Formation (Permian), Beardmore Glacier area. Antarctic Journal of the U. S., 21(5). Nesbitt, H.W., and G.M. Young. 1982. Early Proterozoic climates and
plate motions inferred from major element chemistry of lutites.
Nature, 299, 715-717.
first at ito 5 meters deep and 20 to 30 meters apart. These forms probably represent glacial whaleback features. Overall, the platform dips approximately 2° to the northwest. Where naturally exposed, it is weathered, in places into small, irregularly shaped tors up to 40 centimeters high and 25 centimeters across. Removal of the overlying compacted diamictite reveals a fresh, heavily striated surface. Striation directions measured at six localities along the eastern side of the platform trended between 22° and 105°, with the predominant ice-flow direction being to the east-northeast, as reported by McKelvey et al. (1984) and Mercer (1972). On the western side of the platform, striations are similarly oriented, and there are crescentic gouges up to 35 centimeters across, convex in an east-northeast direction (Harwood personal communication). Also exposed on this western edge is a P-form feature 2 meters across and 0.5 meter deep, eroded into the dolerite (Harwood personal communication). This meandering channel is exposed for 5 meters and is oriented southeastward. It indicates the presence of subglacial meltwater beneath the ice that overrode the platform. Sirius Formation deposits are well exposed in the Dominion Range in cliffs on the east side of the Beardmore Glacier, between 2.2 and 3.9 kilometers southwest of Plunket Point (85°06'S 166°56'E) (Oliver 1964; Mercer 1972). The diamictite rests on an undulating surface of columnar-jointed dolerite at about 1,750 meters above sea level and 15 to 95 meters above the glacier. The undulations vary from 3 to 36 meters high and 80 to 300 meters apart and are interpreted as whaleback features. Striations on the dolerite trend between 355° and 25°, the variations representing diverging and converging or north-northeast flowing ice over and around the whalebacks. Other glacial erosion features include minor plucking on the downglacier (northern) sides of the whalebacks, lunate fractures up to 8 centimeters across, and small grooves. A fault has displaced both the dolerite and overlying Sirius Formation diamictite. The northern side is upthrown 55 meters, and the fault trace can be followed south for 2.1 kilometers. ANTARCTIC JOURNAL
Extensive exposures of Sirius Formation occur in the upthrown face of a major fault scarp that runs north-south along the Dominion Range, 7 kilometers west of the Mill Glacier (Elliot, Barrett, and Mayewski 1974). The basal contact is intermittently exposed between 5.5 and 11.2 kilometers south of the Beardmore Glacier, at between 1,850 and 2,500 meters above sea level. In the south, two small exposures of diamictite rest in shallow depressions on dolerite at about 800 and 620 meters above the glacier. North of these, a 3.6-kilometer succession of Sirius Formation rests in a broad depression at 350 to 400 meters above the glacier. It is cut mainly in sandstone and mudstone of the Triassic Fremouw Formation (Elliot et al. 1974) and is buttressed at either end by dolerite. The northernmost basal contact exposed here is much lower, at only 50 meters above the glacier, and is a sloping platform cut across dolerite and Fremouw Formation sediments (Mayewski and Goldthwait 1985, figure 5). In all these exposures, the basal contact is difficult to reach due to precipitous slopes. However, four sited were reached and striations were observed trending between 25° and 65°. A thick exposure of Sirius Formation deposits is located in the lower Beardmore Valley, near The Cloudmaker (84°23'S 1690 14'E). Diamictite rests on a steeply sloping platform at about 1,060 meters above sea level and 80 meters above the Beardmore Glacier. It is cut in nearly vertically dipping metasediments of the Goldie Formation (Grindley, McGregor, and Walcott 1964), and dips 15° to 20° to the south. In profile, it appears to represent the lower part of a glacial valley-side, the floor of which would have been near the present glacier surface. These cross-cutting sets of striations are visible on the platform beneath the diamictite. They trend at 325°, 40°, and 80°. The former two sets are consistent with ice-flow trending in the general direction of the present valley. The 80° set is oriented perpendicular to the present valley system and probably reflects local perturbations in the basal ice-flow regime. The basal contacts of the Sirius Formation, and the indicated ice-flow directions from the Dominion Range, Plunket Point, and The Cloudmaker, appear to indicate a glacial system that was flowing through, and at times over, a landscape similar to the present. A small outcrop of Sirius Formation was found near Orr Peak (83°30'S 157°48'E) in the Miller Range (Webb et al. in preparation). It differs from those described above, because it does not rest on a glacially polished surface. The base of the exposure is at about 2,100 meters above sea level, 150 meters above the adjacent Marsh Glacier, and rests on gently dipping schist and marble of the Miller Formation (Grindley, McGregor, and Walcott 1964). The contact is sharp and horizontal and is underlain by up to 0.5 meter of weathered fragments of Miller Formation rocks. This material may represent the lower part of a truncated soil profile or slope deposits derived from adjacent hillsides. It is probably analogous to the Early Horlick Drift at Tillite Spur in the Reedy Glacier area described by Mercer (1968), which was interpreted as a pre-Sirius glaciation deposit. The geomorphology of the Miller Range is dominated by three glacial
1986 REVIEW
planation surfaces (Grindley 1967). Deposition of the Sirius Formation probably pre-dates the cutting of these surfaces, because they would be unlikely to have survived the scale of weathering implied by the deposits underlying the diamictite at Orr peak. The basal contacts of the Sirius Formation described here range from those showing extensive glacial erosion to surfaces largely unmodified by overriding ice. They range in elevation through some 1,500 meters, and indicate glaciation of a relatively high-relief landscape in a configuration similar to the present day. It is also likely that they are of different ages, and some may have been formed during several different ice advances prior to the commencement of deposition of the Sirius Formation. I thank Dan Greene, Chuck McGrosky, and Steve Munsell for willing assistance in the field. The Cloudmaker exposure was kindly shown to me by George Denton. This work was supported by National Science Foundation grant DPP 84-20622 to the Institute of Polar Studies, and an Ohio State University postdoctoral fellowship. References Elliot, DEL, P.J. Barrett, and P.A. Mayewski. 1974. Reconnaissance geologic map of the Plunket Point Quadrangle, Transantarctic Mountains, Antarctica. (U.S. Geological Survey Map A-4,1:250,000.) Washington,
D.C.: U.S. Government Printing Office. Grindley, G.W. 1967. The geomorphology of the Miller Range, Transantarctic Mountains, with notes on, the glacial history and neotectonics of East Antarctica. New Zealand Journal of Geology and Geophysics, 10,
557-598. Grindley, G.W., V.R. McGregor, and R.I. Walcott. 1964. Outline of the geology of the Nimrod-Beardmore-Axel Heiberg Glaciers region, Ross Dependency. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Holland Publishing House. Harwood, D.M. 1986. Personal communication. 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 Central Transantarctic Mountains. (Antarctic Research Series, Vol. 36.) Washington, D.C.: American Geophysical Union. Mercer, J.H. 1968. Glacial geology of the Reedy Glacier area, Antarctica. Geological Society of America Bulletin, 79, 471-486. Mercer, J.H. 1972. Some observations on the glacial geology of the Beardmore Glacier area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. McKelvey, B.C., J.H. Mercer, D.M. Harwood, and L.D. Stott. 1984. The Sirius Formation: Further considerations. Antarctic Journal of the U.S., 19(5), 42-43. Oliver, R.L. 1964. Geological observations at Plunket Point, Beardmore Glacier. In R.J. Adie (Ed.), Antarctic geology. Amsterdam: North-Ho!land Publishing House. Webb, P. D. M. Harwood, B. C. McKelvey, M.C.G. Mabin, and J. H. Mercer. 1986. Late Cenozoic tectonic and glacial history of the Transantarctic Mountains. Antarctic Journal of the U.S., 21(5). Webb, P.-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. Mercer. In preparation. Sirius Formation of the Miller Range-Dominion Range, central Transantarctic Mountains.
33
