Late Cenozoic tectonic and glacial history of the ...
Late Cenozoic tectonic and glacial history of the Transantarctic Mountains P-N. WEBB, D.M. HARWOOD, B.C. MCKELVEY, M.C.G. MABIN, and J.H. MERCER Institute of Polar Studies
and
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
Numerous workers, including Katz (1977, 1982), have provided convincing evidence of near vertical, mostly normal, faulting of Precambrian/Paleozoic crystalline basement, Paleozoic/Mesozoic Beacon Supergroup and Jurassic Ferrar Dolerite rocks in the Transantarctic Mountains. Because there exists almost no stratigraphic record between the Jurassic and Pliocene, it has not been possible to describe this faulting more accurately than post-Jurassic. Mercer (1968, Plate 4; 1972, p. 429) and Elliot, Barrett, and Mayewski (1974) noted and illustrated faulting of the Sirius Formation, at that time considered to be early Pliocene or Miocene in age. Since we now place an age of less than 3 million years on the deposition of the glacigene Sirius Formation (Harwood 1983, Antarctic Journal, this issue; Webb et al. 1983, 1984, Antarctic Journal, this issue) any faulting of this unit assumes considerable significance in relating the neotectonic and glacial histories. Our interest in the tectonic-glacial history relationship is, in part, a response to Lester King's (1965) strictures that (p. 25) ". . prima faciae evidence of recent faulting has not been forthcoming"; and (p. 27) ". . . not one of these (hypothesized faults) have been shown to be modern in that it creates a recognizable scarp feature in the modern landscape." Barrett (1972) shows a northeast-southwest oriented syncline, with an axis extending from the Queen Elizabeth Range in the north, passing through the western Queen Alexandra Range, and ending in the Mill Glacier region between the Dominion and Supporters Range. This broad syncline (or crustal warping) involves deformation of basement crystalline rocks, Beacon Supergroup, and Ferrar Dolerite rocks. Barrett and Elliot (1973) and Elliot et al. (1974) provide isopach contours for the Kukri Erosion Surface (located at the contact between the basement complex and Beacon Supergroup). These delineate the form, relief, and distribution of the syncline. To the east (coastward) the Kukri Erosion Surface rises to more than 4,000 meters; to the west (inland) it rises to 2,000 meters. At the axis of the syncline the Kukri Erosion Surface lies at an elevation of about 0-500 meters. All known Sirius Formation localities in the area lie within the boundaries of this syncline or structurally controlled basin and exhibit a concentration at the 2,000-2,500-meter elevation level. Basal sediments of the Sirius Formation rest disconformably on a glaciated surface to which the name "Dominion Erosion Surface" is given. This erosion surface ranges from 1,200 to 4,000 meters elevation. Near the center of the basin (syncline) the Dominion Erosion Surface cuts deeply into the Beacon Supergroup and the overlying Pliocene Sirius Formation rests on Triassic sandstone or Jurassic dolerites. High on the flanks of 1986 REVIEW
the basin, the Dominion Erosion Surface intersects the Kukri Erosion Surface and the Sirius Formation is thin, absent, or reduced to a veneer of highly weathered rubble (Grindley 1967). The thickest successions of Sirius sediments are found near the basin center, e.g., Dominion Range. Water-laid glacio-lacustrine and fluvial sediments are also present at the basin center. On the western basin flanks, clast imbrication, and Dominion Erosion Surface striations and grooves are oriented at high angles to the basin axis. A variety of structural and glacial data point to the existence of a large, high-relief depression aligned approximately parallel to the major topography of the present Transantarctic Mountains. There is compelling evidence for massive ice over-riding during the Queen Maud Glaciation (to which the Sirius Formation has been coupled) of Mayewski (1975) and Mayewski and Goldthwait (1985) if the east antarctic ice sheet was forced to traverse the 3,000-4,500-meter ridge-line of the Transantarctic Mountains. A similar "giant-ice" scenario has been proposed by Denton et al. (1984) in the northern Transantarctic Mountains. We consider the possibility that synclinal upwarping and block uplift occurred during the latest Pliocene/Pleistocene, particularly at the coast. This would have the effect of raising the Dominion Erosion Surface and Sirius Formation remnants by perhaps 1,000 to 3,000 meters. Block elevation would raise the basin center (syncline axis) from near sea level to its present height of approximately 2,000 meters. The presence of glaciolacustrine and fluvioglacial sediments (Webb et al. in preparation) and the associated in situ to near in situ fossil wood, foliage, (Webb and Harwood, Antarctic Journal, this issue) and palynomorphs (Askin and Markgraf, Antarctic Journal, this issue) at basin center sites are more reasonably explained if they had originally been located nearer sea level. If topography was lower at the time of Sirius deposition (i.e., Queen Maud Glaciation), the Transantarctic Mountain threshold would also be less elevated, requiring a thinner east antarctic ice sheet, a less dramatic degree of over-riding and reduced expansion of late Pliocene/early Pleistocene ice across the Ross Sea. We term this the "dwarf-ice" hypothesis. The dwarf-ice scenario would produce drainage patterns similar to those of today with Sirius sedimentation within and across the Transantarctic Mountain topographic fabric. This appears to be the case (Webb et al. in preparation). In promoting the dwarf-ice hypothesis, we consider the possibility that, while synclinal warping was well developed before Sirius deposition, it continued to develop after deposition as well. Such late-stage neotectonic activity has found appeal with many workers, including King (1965) and Katz (1977, 1982) but compelling evidence has been lacking. The most obvious site for major faulting lies along the Transantarctic Mountain front. Barrett (1965) documents the largest known fault in this area, but temporal control is again lacking. Fission track and geophysical techniques would probably provide indication of neotectonic displacements. The Sirius Formation in the Dominion Range is heavily faulted. This area lies near the axis of the syncline (basin). The larger faults (one has a throw of 600 meters) are oriented parallel or subparallel to the syncline axis. Numerous small faults with displacements of tens of meters have orientations parallel, oblique, and normal-to-major faults. Normal faults dominate over reverse faults. Curvilinear fault planes mark the location of slump structures several kilometers across. Fault planes are steep, little modified, unweathered, and occasionally draped by Beardmore Glaciation deposits. Volcanics are apparently not associated with these fault fields. We conclude that major post99
Sirius faulting in the Dominion Range marks a rift-like structure near the axis of a major basin located immediately inland of the Transantarctic Mountain ridgeline. It is noteworthy that the Jurassic Kirkpatrick Basalts crop out along this synclinal axis, suggesting this lineament marks a zone of long-lived crustal weakness. A full understanding of neotectonic activity and the vertical limits of rock thresholds is desirable before setting limits on ice sheet dimensions and glacial-interglacial history. An unknown factor in consideration of Transantarctic Mountain structural deformation is the crustal history of the adjacent Wilkes-Pensacola basins. Thinner crust and shallow magnetic basement in this part of the east antarctic craton may point not only to rifting but also to some degree of crustal spreading and transformtranscurrent faulting as well. Davey (1981) directs a spreading axis across the Ross Sea and into the Nimrod Glacier area. This may continue into the Wilkes Basin, immediately inland of the Miller Range/Dominion Range area. The Dominion Range rift zone may be structurally related to deep crustal discontinuities in the western Wilkes Basin at about latitude 85°S. Detailed geophysical investigations are urgently needed to answer these problems. This work was supported by National Science Foundation grant DPP 84-20622. References Askin, R.A., and V. Markgraf. 1986. Palynomorphs from the Sirius Formation, Dominion Range, Antarctica. Antarctic Journal of the U.S., 21(5). Barrett, P.J. 1965. Geology of the area between the Axel Heiberg and Shackleton Glaciers, Queen Maud Range, Antarctica, Part 2- Beacon Group. New Zealand Journal of Geology and Geophysics, 8, 344-363. Barrett, P.J. 1972. Stratigraphy and petrology of the mainly fluviatile Permian and Triassic parts of the Beacon Supergroup, Beardmore Glacier Area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Barrett, P.J., and D.H. Elliot. 1973. Reconnaissance geological map of the Buckley Island Quadrangle, Transantarctic Mountains, Antarctica. (U.S.
Antarctic Research Program, Map A-3, U.S. Geological Survey.) Washington, D.C.: U.S. Government Printing Office. Davey, F.J. 1981. Geophysical studies in the Ross Sea region. Journal of the Royal Society of New Zealand, 11, 465-479. Denton, G. H., M. Prentice, D. E. Kellogg, and T. Kellogg. 1984. Late Tertiary history of the Antarctic ice sheet: Evidence from the Dry Valleys. Geology, 12, 263-267.
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Elliot, D.H., P.J. Barrett, and P.A. Mayewski. 1974. Reconnaissance geologic map of the Plunket Point Quadrangle, Transantarctic Mountains,
Antarctica. (U.S. Antarctic Research Program, Map A-4, U.S. Geological Survey.) Washington, D.C.: U.S. Government Printing Office. Grindley, G.W. 1967. The geology of the Miller Range, central Transantarctic Mountains, with notes on the glacial history and neotectonics of East Antarctica. New Zealand Journal of Geology and Geophysics, 10, 557-598. Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. Harwood, D.M. 1986. Diatoms of the Sirius Formation. Antarctic Journal of the U. S., 21(5). Katz, H.R. 1977. Post-Beacon tectonics in the region of Amundsen-Scott Glaciers, Queen Maud Range, Transantarctic Mountains. Abstract, Third Symposium on Antarctic Geology and Geophysics, August 1977, Madison. Katz, H.R. 1982. Post-Beacon tectonics in the region of Amundsen and Scott Glaciers, Queen Maud Range, Transantarctic Mountains. In C. Craddock (Ed.), Geoscience. Madison: University of Wisconsin Press. King, L.C. 1965. Geologic relationships between South Africa and Antarctica. Geological Society of South Africa, 68, 32. Mayewski, P. A. 1975. Glacial geology and the Late Cenozoic history of the Transantarctic Mountains, Antarctica. (Ohio State University, Institute of Polar Studies Report No. 56.) Columbus: Ohio State University Press. 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(4), 471-485. 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. Webb, P.-N., and D.M. Harwood. 1986. The terrestrial flora of the Sirius Formation: Its significance in interpreting Late Cenozoic glacial history. Antarctic Journal of the U.S. 21(5). Webb, P. D. M. Harwood, B. C. McKelvey, and L. D. Stott. 1983. Late Neogene and older Cenozoic microfossils in high elevation deposits of the Transantarctic Mountains: Evidence for marine sedimentation and ice volume variation on the east antarctic craton. Antarctic Journal of the U. S., 18(5), 96-97. Webb, P.-N., D.M. Harwood, B.C. McKelvey, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P. B. C. McKelvey, D. M. Harwood, M.C.G. Mabin, and J.H. Mercer. 1986. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S.,21(5).
ANTARCTIC JOURNAL
and
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
Numerous workers, including Katz (1977, 1982), have provided convincing evidence of near vertical, mostly normal, faulting of Precambrian/Paleozoic crystalline basement, Paleozoic/Mesozoic Beacon Supergroup and Jurassic Ferrar Dolerite rocks in the Transantarctic Mountains. Because there exists almost no stratigraphic record between the Jurassic and Pliocene, it has not been possible to describe this faulting more accurately than post-Jurassic. Mercer (1968, Plate 4; 1972, p. 429) and Elliot, Barrett, and Mayewski (1974) noted and illustrated faulting of the Sirius Formation, at that time considered to be early Pliocene or Miocene in age. Since we now place an age of less than 3 million years on the deposition of the glacigene Sirius Formation (Harwood 1983, Antarctic Journal, this issue; Webb et al. 1983, 1984, Antarctic Journal, this issue) any faulting of this unit assumes considerable significance in relating the neotectonic and glacial histories. Our interest in the tectonic-glacial history relationship is, in part, a response to Lester King's (1965) strictures that (p. 25) ". . prima faciae evidence of recent faulting has not been forthcoming"; and (p. 27) ". . . not one of these (hypothesized faults) have been shown to be modern in that it creates a recognizable scarp feature in the modern landscape." Barrett (1972) shows a northeast-southwest oriented syncline, with an axis extending from the Queen Elizabeth Range in the north, passing through the western Queen Alexandra Range, and ending in the Mill Glacier region between the Dominion and Supporters Range. This broad syncline (or crustal warping) involves deformation of basement crystalline rocks, Beacon Supergroup, and Ferrar Dolerite rocks. Barrett and Elliot (1973) and Elliot et al. (1974) provide isopach contours for the Kukri Erosion Surface (located at the contact between the basement complex and Beacon Supergroup). These delineate the form, relief, and distribution of the syncline. To the east (coastward) the Kukri Erosion Surface rises to more than 4,000 meters; to the west (inland) it rises to 2,000 meters. At the axis of the syncline the Kukri Erosion Surface lies at an elevation of about 0-500 meters. All known Sirius Formation localities in the area lie within the boundaries of this syncline or structurally controlled basin and exhibit a concentration at the 2,000-2,500-meter elevation level. Basal sediments of the Sirius Formation rest disconformably on a glaciated surface to which the name "Dominion Erosion Surface" is given. This erosion surface ranges from 1,200 to 4,000 meters elevation. Near the center of the basin (syncline) the Dominion Erosion Surface cuts deeply into the Beacon Supergroup and the overlying Pliocene Sirius Formation rests on Triassic sandstone or Jurassic dolerites. High on the flanks of 1986 REVIEW
the basin, the Dominion Erosion Surface intersects the Kukri Erosion Surface and the Sirius Formation is thin, absent, or reduced to a veneer of highly weathered rubble (Grindley 1967). The thickest successions of Sirius sediments are found near the basin center, e.g., Dominion Range. Water-laid glacio-lacustrine and fluvial sediments are also present at the basin center. On the western basin flanks, clast imbrication, and Dominion Erosion Surface striations and grooves are oriented at high angles to the basin axis. A variety of structural and glacial data point to the existence of a large, high-relief depression aligned approximately parallel to the major topography of the present Transantarctic Mountains. There is compelling evidence for massive ice over-riding during the Queen Maud Glaciation (to which the Sirius Formation has been coupled) of Mayewski (1975) and Mayewski and Goldthwait (1985) if the east antarctic ice sheet was forced to traverse the 3,000-4,500-meter ridge-line of the Transantarctic Mountains. A similar "giant-ice" scenario has been proposed by Denton et al. (1984) in the northern Transantarctic Mountains. We consider the possibility that synclinal upwarping and block uplift occurred during the latest Pliocene/Pleistocene, particularly at the coast. This would have the effect of raising the Dominion Erosion Surface and Sirius Formation remnants by perhaps 1,000 to 3,000 meters. Block elevation would raise the basin center (syncline axis) from near sea level to its present height of approximately 2,000 meters. The presence of glaciolacustrine and fluvioglacial sediments (Webb et al. in preparation) and the associated in situ to near in situ fossil wood, foliage, (Webb and Harwood, Antarctic Journal, this issue) and palynomorphs (Askin and Markgraf, Antarctic Journal, this issue) at basin center sites are more reasonably explained if they had originally been located nearer sea level. If topography was lower at the time of Sirius deposition (i.e., Queen Maud Glaciation), the Transantarctic Mountain threshold would also be less elevated, requiring a thinner east antarctic ice sheet, a less dramatic degree of over-riding and reduced expansion of late Pliocene/early Pleistocene ice across the Ross Sea. We term this the "dwarf-ice" hypothesis. The dwarf-ice scenario would produce drainage patterns similar to those of today with Sirius sedimentation within and across the Transantarctic Mountain topographic fabric. This appears to be the case (Webb et al. in preparation). In promoting the dwarf-ice hypothesis, we consider the possibility that, while synclinal warping was well developed before Sirius deposition, it continued to develop after deposition as well. Such late-stage neotectonic activity has found appeal with many workers, including King (1965) and Katz (1977, 1982) but compelling evidence has been lacking. The most obvious site for major faulting lies along the Transantarctic Mountain front. Barrett (1965) documents the largest known fault in this area, but temporal control is again lacking. Fission track and geophysical techniques would probably provide indication of neotectonic displacements. The Sirius Formation in the Dominion Range is heavily faulted. This area lies near the axis of the syncline (basin). The larger faults (one has a throw of 600 meters) are oriented parallel or subparallel to the syncline axis. Numerous small faults with displacements of tens of meters have orientations parallel, oblique, and normal-to-major faults. Normal faults dominate over reverse faults. Curvilinear fault planes mark the location of slump structures several kilometers across. Fault planes are steep, little modified, unweathered, and occasionally draped by Beardmore Glaciation deposits. Volcanics are apparently not associated with these fault fields. We conclude that major post99
Sirius faulting in the Dominion Range marks a rift-like structure near the axis of a major basin located immediately inland of the Transantarctic Mountain ridgeline. It is noteworthy that the Jurassic Kirkpatrick Basalts crop out along this synclinal axis, suggesting this lineament marks a zone of long-lived crustal weakness. A full understanding of neotectonic activity and the vertical limits of rock thresholds is desirable before setting limits on ice sheet dimensions and glacial-interglacial history. An unknown factor in consideration of Transantarctic Mountain structural deformation is the crustal history of the adjacent Wilkes-Pensacola basins. Thinner crust and shallow magnetic basement in this part of the east antarctic craton may point not only to rifting but also to some degree of crustal spreading and transformtranscurrent faulting as well. Davey (1981) directs a spreading axis across the Ross Sea and into the Nimrod Glacier area. This may continue into the Wilkes Basin, immediately inland of the Miller Range/Dominion Range area. The Dominion Range rift zone may be structurally related to deep crustal discontinuities in the western Wilkes Basin at about latitude 85°S. Detailed geophysical investigations are urgently needed to answer these problems. This work was supported by National Science Foundation grant DPP 84-20622. References Askin, R.A., and V. Markgraf. 1986. Palynomorphs from the Sirius Formation, Dominion Range, Antarctica. Antarctic Journal of the U.S., 21(5). Barrett, P.J. 1965. Geology of the area between the Axel Heiberg and Shackleton Glaciers, Queen Maud Range, Antarctica, Part 2- Beacon Group. New Zealand Journal of Geology and Geophysics, 8, 344-363. Barrett, P.J. 1972. Stratigraphy and petrology of the mainly fluviatile Permian and Triassic parts of the Beacon Supergroup, Beardmore Glacier Area. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Barrett, P.J., and D.H. Elliot. 1973. Reconnaissance geological map of the Buckley Island Quadrangle, Transantarctic Mountains, Antarctica. (U.S.
Antarctic Research Program, Map A-3, U.S. Geological Survey.) Washington, D.C.: U.S. Government Printing Office. Davey, F.J. 1981. Geophysical studies in the Ross Sea region. Journal of the Royal Society of New Zealand, 11, 465-479. Denton, G. H., M. Prentice, D. E. Kellogg, and T. Kellogg. 1984. Late Tertiary history of the Antarctic ice sheet: Evidence from the Dry Valleys. Geology, 12, 263-267.
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Elliot, D.H., P.J. Barrett, and P.A. Mayewski. 1974. Reconnaissance geologic map of the Plunket Point Quadrangle, Transantarctic Mountains,
Antarctica. (U.S. Antarctic Research Program, Map A-4, U.S. Geological Survey.) Washington, D.C.: U.S. Government Printing Office. Grindley, G.W. 1967. The geology of the Miller Range, central Transantarctic Mountains, with notes on the glacial history and neotectonics of East Antarctica. New Zealand Journal of Geology and Geophysics, 10, 557-598. Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. Harwood, D.M. 1986. Diatoms of the Sirius Formation. Antarctic Journal of the U. S., 21(5). Katz, H.R. 1977. Post-Beacon tectonics in the region of Amundsen-Scott Glaciers, Queen Maud Range, Transantarctic Mountains. Abstract, Third Symposium on Antarctic Geology and Geophysics, August 1977, Madison. Katz, H.R. 1982. Post-Beacon tectonics in the region of Amundsen and Scott Glaciers, Queen Maud Range, Transantarctic Mountains. In C. Craddock (Ed.), Geoscience. Madison: University of Wisconsin Press. King, L.C. 1965. Geologic relationships between South Africa and Antarctica. Geological Society of South Africa, 68, 32. Mayewski, P. A. 1975. Glacial geology and the Late Cenozoic history of the Transantarctic Mountains, Antarctica. (Ohio State University, Institute of Polar Studies Report No. 56.) Columbus: Ohio State University Press. 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(4), 471-485. 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. Webb, P.-N., and D.M. Harwood. 1986. The terrestrial flora of the Sirius Formation: Its significance in interpreting Late Cenozoic glacial history. Antarctic Journal of the U.S. 21(5). Webb, P. D. M. Harwood, B. C. McKelvey, and L. D. Stott. 1983. Late Neogene and older Cenozoic microfossils in high elevation deposits of the Transantarctic Mountains: Evidence for marine sedimentation and ice volume variation on the east antarctic craton. Antarctic Journal of the U. S., 18(5), 96-97. Webb, P.-N., D.M. Harwood, B.C. McKelvey, and L.D. Stott. 1984. Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P. B. C. McKelvey, D. M. Harwood, M.C.G. Mabin, and J.H. Mercer. 1986. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S.,21(5).
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