(Permian) Mackellar Formation, Beardmore Glacier area
Depositional setting of the (Permian) Mackellar Formation, Beardmore Glacier area M.F. MILLER and R.S. FRISCH Department of Geology Vanderbilt University Nashville, Tennessee 37235
The Permian Mackellar Formation in the central Transantarctic Mountains represents a transition between glacial and fluvial deposition (see table). Interpretation of the environments in which the Mackellar Formation was deposited, includ ing the salinity and oxygen conditions, is important because it can lead to a better understanding of the processes acting after a major period of glaciation as well as to a clearer picture of the Permian paleogeography of this sector of Gondwana. A Permian postglacial sequence is ubiquitous and consistently 100 to 200 meters thick throughout the central and southern Transantarctic Mountains (e.g., La Prade 1970; Elliot 1975; Bradshaw, Newman, and Aitchison 1984). It is absent to the north of the Beardmore area, thinning markedly in the Nimrod Glacier area (Grindley 1963; Laird, Mansergh, and Chappell 1971), but it is much thicker (1,000 meters) in the Ellsworth Mountains (Collinson and Vavra 1982). Extensive stratigraphic study of the Mackellar Formation in the Beardmore Glacier area by Barrett (1969) provided the background for this project, which involved measurement, sampling, and observation of the Mackellar Formation at 12 outcrops in the Beardmore Glacier area between November 1985 and January 1986. In the Beardmore Glacier area, the Mackellar Formation abruptly, but conformably, overlies the Pagoda Formation. It consists of about 75 meters of shale, siltstone, and sandstone,
most of which is interbedded. Dolerite commonly intrudes the unit. Emphasis of the field work in this study was to define the nature and lateral continuity of the interbeds and to describe the sedimentary structures within them. Coarsening upward cycles about 5 meters thick are common in the Mackellar Formation but are not correlative from outcrop to outcrop. Thick sandstones typically occur at the top of the formation, where the contact with the overlying Fairchild Formation is gradational. Paleocurrent analysis based on 183 measurements of ripple lamination, ripple marks, trough axes, and parting lineation indicate flow toward the south (see figure). No body fossils were found in the Mackellar Formation. Biogenic structures, including a few types of simple horizontal to oblique traces, are ubiquitous but not abundant in ripple-laminated siltstone and sandstone. At a few localities, burrowing was sufficiently intense to destroy small-scale sedimentary lamination, but trace diversity remains low. The Mackellar Formation represents the initial stage of filling of a starved post-glacial basin. Interbedding indicates intermittent pulses of sediment-laden water into a stagnant basin. Fluctuations from high- to low-flow regime and vice versa, as shown by sequences of plane beds, with parting lineation followed upward by ripple lamination and plane beds reflect fluctuations in current velocity. Climbing ripple lamination and soft sedi-
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Stratigraphic units, rock types, and inferred depositional environments of Devonian (Alexandra Formation) and Permian (all other units) part of Beacon supergroup, Beardmore Glacier area
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Depositional Unit Rock type environment Author Buckley Sandstone, shale Fluvial Barrett 1969 Formation coal glaciolacustrine Collinson and Isbell, Antarctic Journal,
this issue Fairchild Sandstone Fluvial Barrett 1969 Formation (low sinuosity) Collinson and Isbell,
83°
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KILOMETERS 0 20 40 BO
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Antarctic Journal,
this issue Mackellar Shale, sandstone Lacustrine/marine Barrett 1969 Formation siltstone deltaic Lindsay 1970 Pagoda Diamictite, Glacial, glacio- Lindsay 1970 Formation sandstone, shale fluvial, Miller and Waugh, glaciolacustrine Antarctic Journal,
this issue
Alexandra Formation 1986 REVIEW
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4
4 INS
Map of the Beardmore region showing paleocurrent directions from the Mackellar Formation in 10 outcrops, using combined data of ripple crests, ripple lamination, climbing ripples, parting lineation, scour marks, and trough axes. 37
ment deformation features were formed during episodic rapid sedimentation and slumping events. Pinchout of the Mackellar just north of the Nimrod Glacier and southward-directed paleocurrents suggest that the edge of the basin was to the north. Lack of broadly correlative units and the abundance of discontinuous sand beds reflects deposition in a temporally and laterally complex mosaic of deltaic subenvironments. Gradual coarsening upward to sandstones of the Fairchild Formation represents basin filling and establishment of fluvial environments. Was the Mackellar Formation deposited under marine conditions as were portions of the correlative Polarstar Formation (Ellsworth Mountains; Collinson and Vavra 1982) and Discovery Ridge Formation (Ohio Range; Bradshaw, Newman, and Aitchison 1984), or was it deposited under brackish to freshwater conditions (Barrett and Faure 1973)? Low diversity and abundance of trace fossils and paucity of bioturbation may be characteristic of Paleozoic brackish and nonmarine facies; this and the absence of the Permian Eurydesma body-fossil fauna suggests deposition in brackish to freshwater environments. However, low faunal diversity and absence of shelled bottom fauna might also be caused by low-oxygen conditions and rapid sedimentation, both of which were prevalent in the Mackellar basin. Thus, although it appears that the starved post-glacial Mackellar basin was filled with sediments which were derived from the north and deposited in and adjacent to relatively small-scale distributaries, the relationship between this basin and the Pacific Ocean remains problematic. Planned additional work, including study of the trace fossils, analyses of sequences of bedding types, petrographic analyses of sandstone and shales, and organic geochemical analyses of shales may clarify provenance and depositional environments and allow more accurate paleogeographic reconstructions. We would like to thank the other members of the nine-person Vanderbilt University and Ohio State University team (studying the Permo-Triassic sequence in the Beardmore Glacier area) including J.M.G. Miller and B.J. Waugh (Vanderbilt) and J.W.
Fission-track tectonic studies of the Transantarctic Mountains, Beardmore Glacier area P.G. FITZGERALD Antarctic Research Centre Victoria University Private Bag, Wellington, New Zealand
and Department of Geology University of Melbourne Parkville, Victoria, 3052, Australia
The Transantarctic Mountains are a major transcontinental range stretching for some 4,000 kilometers, varying from 38
Collinson, L.A. Krissek, T. C. Homer, B. Lord, and J. Isbell, for their assistance. This research was supported by National Science Foundation grant DPP 84-18445. References Barrett, P.J. 1969. Stratigra pity and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. (Ohio State University Research Foundation, Institute of Polar Studies, Report 34.) Columbus: Ohio State University Press. Barrett, P.J., and C. Faure. 1973. Strontium isotope compositions of nonmarine carbonate rocks from the Beacon Supergroup of the Transantarctic Mountains. Journal of Sedimentary Petrology, 43(2), 447-457. Bradshaw, MA., J . Newman, and J.C. Aitchison. 1984. Preliminary geological results of the 1983-84 Ohio Range Expedition. New Zealand Antarctic Record, 5(3), 1-17. Collinson, J.W., and J . Isbell. 1986. Permo-Triassic sedimentology of the Beardmore Glacier area. Antarctic Journal of the U.S., 21(5). Collinson, J.W., and C.L. Vavra. 1982. Sedimentology of the Polarstar Formation (Permian), Ellsworth Mountains, Antarctica. Geological Society of America, (Abstracts with Programs), 14(7), 466. Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell, (Ed.), Gondwana geology. Canberra: Australian National University Press. Grindley, G.W. 1963. The geology of the Queen Alexandra Range, Beardmore Glacier, Ross Dependency, Antarctica; with notes on the correlation of Gondwana sequences. New Zealand Journal of Geology and Geophysics, 6(3), 307-347. Laird, MG., G.D. Mansergh, and J.M.A. Chappell. 1971. Geology of the Central Nimrod Glacier area, Antarctica. New Zealand Journal of Geology and Geophysics, 14(3), 427-468. La Prade, K.E. 1970. Permian-Triassic Beacon Group of the Shackleton Glacier area, Queen Maud Range, Transantarctic Mountains, Antarctica. Geological Society of America Bulletin, 81(4), 1403-1410. Lindsay, J.F. 1970. Depositional environment of Paleozoic glacial rocks in the Central Transantarctic Mountains. Geological Society of America Bulletin, 81(4), 1149-1171. 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).
200-400 kilometers in width, and having elevations up to 4,500 meters. The uplift and formation of the Transantarctic Mountains have always been something of an enigma, but recent apatite fission-track analysis is providing important new informtion not only about their uplift history but also about the implications of that uplift history for the glacial history of Antarctica as a whole. The main field objective of this project was to collect samples for fission-track analysis to determine the timing and rate of uplift of the Transantarctic Mountains and measure relative vertical displacements across faults within the range. As part of the 1985-1986 Beardmore Glacier field camp, two general areas were selected for study: the coastal region around the mouth of the Beardmore Glacier and further inland in the Miller and Queen Elizabeth Ranges. Fieldwork was done on foot from two helicopter-supported satellite camps as well as by close support on day trips out of Beardmore camp during the period from 23 November to 16 December 1985. The two-person field party consisted of Paul Fitzgerald and Ken Woolfe, also of Victoria University. ANTARCTIC JOURNAL
The Permian Mackellar Formation in the central Transantarctic Mountains represents a transition between glacial and fluvial deposition (see table). Interpretation of the environments in which the Mackellar Formation was deposited, includ ing the salinity and oxygen conditions, is important because it can lead to a better understanding of the processes acting after a major period of glaciation as well as to a clearer picture of the Permian paleogeography of this sector of Gondwana. A Permian postglacial sequence is ubiquitous and consistently 100 to 200 meters thick throughout the central and southern Transantarctic Mountains (e.g., La Prade 1970; Elliot 1975; Bradshaw, Newman, and Aitchison 1984). It is absent to the north of the Beardmore area, thinning markedly in the Nimrod Glacier area (Grindley 1963; Laird, Mansergh, and Chappell 1971), but it is much thicker (1,000 meters) in the Ellsworth Mountains (Collinson and Vavra 1982). Extensive stratigraphic study of the Mackellar Formation in the Beardmore Glacier area by Barrett (1969) provided the background for this project, which involved measurement, sampling, and observation of the Mackellar Formation at 12 outcrops in the Beardmore Glacier area between November 1985 and January 1986. In the Beardmore Glacier area, the Mackellar Formation abruptly, but conformably, overlies the Pagoda Formation. It consists of about 75 meters of shale, siltstone, and sandstone,
most of which is interbedded. Dolerite commonly intrudes the unit. Emphasis of the field work in this study was to define the nature and lateral continuity of the interbeds and to describe the sedimentary structures within them. Coarsening upward cycles about 5 meters thick are common in the Mackellar Formation but are not correlative from outcrop to outcrop. Thick sandstones typically occur at the top of the formation, where the contact with the overlying Fairchild Formation is gradational. Paleocurrent analysis based on 183 measurements of ripple lamination, ripple marks, trough axes, and parting lineation indicate flow toward the south (see figure). No body fossils were found in the Mackellar Formation. Biogenic structures, including a few types of simple horizontal to oblique traces, are ubiquitous but not abundant in ripple-laminated siltstone and sandstone. At a few localities, burrowing was sufficiently intense to destroy small-scale sedimentary lamination, but trace diversity remains low. The Mackellar Formation represents the initial stage of filling of a starved post-glacial basin. Interbedding indicates intermittent pulses of sediment-laden water into a stagnant basin. Fluctuations from high- to low-flow regime and vice versa, as shown by sequences of plane beds, with parting lineation followed upward by ripple lamination and plane beds reflect fluctuations in current velocity. Climbing ripple lamination and soft sedi-
#1" 'IC;..
3 LA Ci E
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0 .7
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Stratigraphic units, rock types, and inferred depositional environments of Devonian (Alexandra Formation) and Permian (all other units) part of Beacon supergroup, Beardmore Glacier area
V C
84°
Depositional Unit Rock type environment Author Buckley Sandstone, shale Fluvial Barrett 1969 Formation coal glaciolacustrine Collinson and Isbell, Antarctic Journal,
this issue Fairchild Sandstone Fluvial Barrett 1969 Formation (low sinuosity) Collinson and Isbell,
83°
cc
KILOMETERS 0 20 40 BO
cc
* AM
Antarctic Journal,
this issue Mackellar Shale, sandstone Lacustrine/marine Barrett 1969 Formation siltstone deltaic Lindsay 1970 Pagoda Diamictite, Glacial, glacio- Lindsay 1970 Formation sandstone, shale fluvial, Miller and Waugh, glaciolacustrine Antarctic Journal,
this issue
Alexandra Formation 1986 REVIEW
Ilk
C'
so
OCEAN
,
4
4 INS
Map of the Beardmore region showing paleocurrent directions from the Mackellar Formation in 10 outcrops, using combined data of ripple crests, ripple lamination, climbing ripples, parting lineation, scour marks, and trough axes. 37
ment deformation features were formed during episodic rapid sedimentation and slumping events. Pinchout of the Mackellar just north of the Nimrod Glacier and southward-directed paleocurrents suggest that the edge of the basin was to the north. Lack of broadly correlative units and the abundance of discontinuous sand beds reflects deposition in a temporally and laterally complex mosaic of deltaic subenvironments. Gradual coarsening upward to sandstones of the Fairchild Formation represents basin filling and establishment of fluvial environments. Was the Mackellar Formation deposited under marine conditions as were portions of the correlative Polarstar Formation (Ellsworth Mountains; Collinson and Vavra 1982) and Discovery Ridge Formation (Ohio Range; Bradshaw, Newman, and Aitchison 1984), or was it deposited under brackish to freshwater conditions (Barrett and Faure 1973)? Low diversity and abundance of trace fossils and paucity of bioturbation may be characteristic of Paleozoic brackish and nonmarine facies; this and the absence of the Permian Eurydesma body-fossil fauna suggests deposition in brackish to freshwater environments. However, low faunal diversity and absence of shelled bottom fauna might also be caused by low-oxygen conditions and rapid sedimentation, both of which were prevalent in the Mackellar basin. Thus, although it appears that the starved post-glacial Mackellar basin was filled with sediments which were derived from the north and deposited in and adjacent to relatively small-scale distributaries, the relationship between this basin and the Pacific Ocean remains problematic. Planned additional work, including study of the trace fossils, analyses of sequences of bedding types, petrographic analyses of sandstone and shales, and organic geochemical analyses of shales may clarify provenance and depositional environments and allow more accurate paleogeographic reconstructions. We would like to thank the other members of the nine-person Vanderbilt University and Ohio State University team (studying the Permo-Triassic sequence in the Beardmore Glacier area) including J.M.G. Miller and B.J. Waugh (Vanderbilt) and J.W.
Fission-track tectonic studies of the Transantarctic Mountains, Beardmore Glacier area P.G. FITZGERALD Antarctic Research Centre Victoria University Private Bag, Wellington, New Zealand
and Department of Geology University of Melbourne Parkville, Victoria, 3052, Australia
The Transantarctic Mountains are a major transcontinental range stretching for some 4,000 kilometers, varying from 38
Collinson, L.A. Krissek, T. C. Homer, B. Lord, and J. Isbell, for their assistance. This research was supported by National Science Foundation grant DPP 84-18445. References Barrett, P.J. 1969. Stratigra pity and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. (Ohio State University Research Foundation, Institute of Polar Studies, Report 34.) Columbus: Ohio State University Press. Barrett, P.J., and C. Faure. 1973. Strontium isotope compositions of nonmarine carbonate rocks from the Beacon Supergroup of the Transantarctic Mountains. Journal of Sedimentary Petrology, 43(2), 447-457. Bradshaw, MA., J . Newman, and J.C. Aitchison. 1984. Preliminary geological results of the 1983-84 Ohio Range Expedition. New Zealand Antarctic Record, 5(3), 1-17. Collinson, J.W., and J . Isbell. 1986. Permo-Triassic sedimentology of the Beardmore Glacier area. Antarctic Journal of the U.S., 21(5). Collinson, J.W., and C.L. Vavra. 1982. Sedimentology of the Polarstar Formation (Permian), Ellsworth Mountains, Antarctica. Geological Society of America, (Abstracts with Programs), 14(7), 466. Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell, (Ed.), Gondwana geology. Canberra: Australian National University Press. Grindley, G.W. 1963. The geology of the Queen Alexandra Range, Beardmore Glacier, Ross Dependency, Antarctica; with notes on the correlation of Gondwana sequences. New Zealand Journal of Geology and Geophysics, 6(3), 307-347. Laird, MG., G.D. Mansergh, and J.M.A. Chappell. 1971. Geology of the Central Nimrod Glacier area, Antarctica. New Zealand Journal of Geology and Geophysics, 14(3), 427-468. La Prade, K.E. 1970. Permian-Triassic Beacon Group of the Shackleton Glacier area, Queen Maud Range, Transantarctic Mountains, Antarctica. Geological Society of America Bulletin, 81(4), 1403-1410. Lindsay, J.F. 1970. Depositional environment of Paleozoic glacial rocks in the Central Transantarctic Mountains. Geological Society of America Bulletin, 81(4), 1149-1171. 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).
200-400 kilometers in width, and having elevations up to 4,500 meters. The uplift and formation of the Transantarctic Mountains have always been something of an enigma, but recent apatite fission-track analysis is providing important new informtion not only about their uplift history but also about the implications of that uplift history for the glacial history of Antarctica as a whole. The main field objective of this project was to collect samples for fission-track analysis to determine the timing and rate of uplift of the Transantarctic Mountains and measure relative vertical displacements across faults within the range. As part of the 1985-1986 Beardmore Glacier field camp, two general areas were selected for study: the coastal region around the mouth of the Beardmore Glacier and further inland in the Miller and Queen Elizabeth Ranges. Fieldwork was done on foot from two helicopter-supported satellite camps as well as by close support on day trips out of Beardmore camp during the period from 23 November to 16 December 1985. The two-person field party consisted of Paul Fitzgerald and Ken Woolfe, also of Victoria University. ANTARCTIC JOURNAL
