Marine geology and geophysics
Marine geology and geophysics Glacial erosion on the George V/Adélie continental margin, East Antarctica E.W. DOMACK* Department of Geology University of Wisconsin Eau Claire, Wisconsin 54701
Evidence for preglacial sedimentary sequences adjacent to and on the continental shelf of East Antarctica between 1400 and \
¼ 4-. \ Al \ \_. \ 500
150°E is presently limited. Geophysical surveys of the interior (Steed and Drewry 1982) as well as portions of the continental shelf (Eittreim et al. 1984; Sato et al. 1984) have demonstrated the existence, if not the age, of several hundred meters of sedimentary section. Surficial sediments on the continental shelf contain reworked palynomorphs of Permian to early Tertiary age which indicate that similar-age sedimentary rocks may exist in the vicinity (Truswell 1983-a). The only in situ occurrence of preglacial strata on the continental shelf comes from a lower Cretaceous siltstone recovered during austral summer 1978 1979—or Deep Freeze 79 (DF-79)—from the seaward flank of the Mertz-Ninnis Trough (Domack, Fairchild, and Anderson 1980) (figure 1). Presented herein are additional data from this and other austral summer 1978 - 1979 cores which suggest that
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DISTRIBUTION OF CORED SEDIMENTS GEORGE V - ADELIE CONTINENTAL SHELF
NINNIS GLACIER
(DEPTH IN METERS) Figure 1. Bathymetry and core location on George V/Adélie continental margin. The George V basin has been formally named the Mertz-NlnnlS Trough or Valley as listed in the Gazetteer of Undersea Features (Defense Mapping Agency 1982). 76
ANTARCTIC JOURNAL
up to 2,000 meters of preglacial section may have existed at one time within the present area of the Mertz-Ninnis Trough (formerly referred to as the George V Basin). Sedimentary rocks occur as erratics in most of the piston cores from the continental shelf. These cores consist of glacial and glacial-marine diamictons. Specifically, several clasts of dark-brown, indurated shale were recovered from core DF-79-37. Organic material is abundant within these shales and, upon processing, palynomorphs were concentrated (figure 2). All of the identified spores are of Early Cretaceous age according to the palynostratigraphy of Burger (1980). Therefore, glacial erosion has cut into Lower Cretaceous section somewhere in the vicinity of core DF-79-37. Further, more than one cycle of glacial erosion and deposition is indicated, because the shale clasts were covered with a well-indurated coating resembling till matrix in mineralogy and texture. The well-indurated nature of these shale clasts is in contrast to the almost unlithified character of the Lower Cretaceous siltstone recovered nearby (i.e., DF-79-38).
Vitrinite reflectance data were obtained from the in situ Lower Cretaceous sediment in DF-79-3 (figure 3). The data show that vitrinite macerals within the siltstone were derived from contemporaneous coaly material and some material from an older, thermally more mature, sedimentary unit. The reflectance value of the indigenous vitrinite (mean reflectance equals .51) can be used to access the thermal history and hence depth of burial of the Lower Cretaceous siltstone in DF-79-38. Continental reconstructions and analysis of seafloor magnetic anomalies place Antarctica and Australia in a late rift stage during the Early Cretaceous (Sproll and Dietz 1969; Cande and Mutter 1982). Therefore, a reasonable estimate of depth/temperature relationships for the George V continental margin can be obtained from the Mesozoic sequence which has been drilled in the Otway Basin, Australia (figure 3). The data of Middleton and Falvey (1983) (figure 3) suggest that the vitrinite in DF-79-38 experienced temperatures equivalent to those found at a depth of 1,500 to 2,200 meters within the Otway Basin. Shallower burial depths could be inferred for DF-79-38 if a substantially
:
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2
3
.*.
Yp\
0
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Figure 2. Photomicrographs (x 750) of spores isolated from shale clasts found in core DF-79-37. 1. Microcachryidites antarcticus, (Cookson 1947). 2/3. Lycopodiumsporites nodosus, (Dettman 1963). 4. Cicatricosisporites cf.C. australiensis, (Cookson 1947). 5. Classopollis cf.C. chateaunovi, (Reyre 1970). 6. Cyathidites australis, (Couper 1953). Stratigraphic distribution for the above according to Burger (1980) and Truswell (1983-b): Late Jurassic to Miocene (1), Late Jurassic to Middle Albian (2, 3, 5, 6), Neocomian to Middle Albian (4).
1985 REVIEW
77
greater geothermal gradient is assumed. However, there is no reason to expect this, because spreading of Australia and Antarctica away from the South East Indian Ridge appears to have been symmetrical (Heezen et al. 1977).
Anderson (Rice University). Gratitude is extended to Dennis Cassidy at Florida State University for his help in providing samples.
References
Mean Vitrinite Reflectance, R0 0
Voluta .1 Pecten1ADF7938-0 0 0
-
Burger, D. 1980. Palynological studies in the Lower Cretaceous of the Surat Basin, Australia. Australian Bureau of Mineral Resources, Bulletin,
189, 106. Cande, S. C., and J. Mutter. 1982. A revised identification of the oldest sea-floor spreading anomalies between Australia and Antarctica. Earth and Planetary Science Letters, 58, 151 - 160. Cookson, I. 1947. Plant microfossils from the lignites of Kerguelen Archipelago. British, Australian, New Zealand Antarctic Research Expedition, 1929 - 1931, (Report A-2). Adelaide: BANZAR Expedition
Committee. Couper, R.A. 1953. Upper Mesozoic and Cainozoic spores and pollen
-
C)
b 0
grains from New Zealand. New Zealand Geological Survey Paleontological Bulletin, (Wellington), 22, 77. Defense Mapping Agency. 1982. Gazetteer of undersea features. Wash-
I-
- c
ington, D.C.: U.S. Government Printing Office. Dettman, M.R. 1963. Upper Mesozoic microfloras from Southeastern Australia. Proceedings of the Royal Society of Victoria, 77, 148. Domack, E.W., W.W. Fairchild, and J.B. Anderson. 1980. Lower Cretaceous sediment from the East Antarctic Continental Shelf. Nature, 287, 625 - 626. Eittreim, S.L., A.K. Cooper, and others. 1984. Marine geological and
.c a. w
geophysical investigations of the antarctic continental margin 1984. (U.S. o 0 o
I
0.0 .2 .4 .6 .8 1.0 1.2 1.4 Figure 3. Comparison of reflectance (Ro) vs. depth for sediments from wells in the Otway Basin, S. Australia (from Middleton and Falvey 1983). A mean Roof .51 for sample DF-79-38 corresponds to a depth of 1,500 to 2,200 meters assuming the geothermal history defined by the South Australian data. Error bars are standard deviations and where large (i.e., Voluta-1) indicate possible reworking of older vitrinite (Middleton personal communication). A histogram of vitrinite reflectance for core DF-79-38 is available, upon request, from the author.
If the above assumptions are valid and DF-79-38 indeed represents an in situ submarine outcrop, then a significant preglacial sedimentary sequence (now partially eroded) exists on the George V continental shelf. The abundance of Lower Cretaceous erratics within glacial sediments, and the predominance of similar age palynomorphs in nearby surface sediments (Truswell 1983-a), suggests that the majority of the sedimentary basin consists of Lower Cretaceous strata. This stratigraphy is similar to several basins of the Southeast Australian continental shelf, including the Otway (Falvey and Mutter 1981). The trend of the Mertz-Ninnis Trough marks the landward boundary of the sedimentary basin (here termed the George V Basin) as Precambrian granite crops out along the coast (Mawson 1942). It is likely that similar troughs found along the east antarctic margin may mark the landward boundaries of preglacial sedimentary basins. This work was supported originally by National Science Foundation grants DPP 77-26407 and DPP 80-80242 to John B. 78
Geological Survey Circular 935.) Washington, D.C.: U.S. Government Printing Office. Falvey, D.A., and J.C. Mutter. 1981. Regional plate tectonics and the evolution of Australia's passive margins. BMR Journal of Australian Geology and Geophysics, 6, 1 - 29. Heezen, B.C., R.P. Lynde, Jr., and D.J. Fornari. 1977. Geologic map of the Indian Ocean. In J.R. Heirtzler, H.M. Bolli, T.A. Davies, J.B. Saunders, and J. G. Sciater (Eds.), Indian Ocean geology and biostratigraphy. Washington, D.C.: American Geophysical Union.
Mawson, D. 1942. Geographical narrative and cartography, Australasian Antarctic Expedition 1911 -1914. Scientific Reports, (Series A.), 1, 1-364. Middleton, M.F. 1983. Personal communication. Middleton, M. F., and D.A. Falvey. 1983. Maturation modeling in Otway Basin, Australia. American Association of Petroleum Geologists Bulletin,
67, 271 - 279. Reyre, Y. 1970. Stereoscan observations on the pollen genus Classopollis, Pflug, 1953. Paleontology, 13(2), 303 - 322. Sato, S., N. Asakura, T. Saki, N. Oikawa, and Y. Kaneda. 1984. Preliminary results of geological and geophysical surveys in the Ross Sea and on the Dumont D'Urville Sea, off Antarctica. National Institute of Polar Research, (Memoir), 33, 66 - 92. Sproll, W. P., and R. S. Deitz. 1969. Morphological continental drift fit of Australia and Antarctica. Nature, 222, 345 - 348. Steed, R.H.N., and D.J. Drewry. 1982. Radio-echo sounding investigations of Wilkes Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Truswell, E.M. 1983-a. Geological implications of recycled palynomorphs in continental shelf sediments around Antarctica. In R. L. Oliver, P.R. James, andJ.B. Jago (Eds.), Antarctic Earth science. Canberra: Australian Academy of Science. Truswell, E.M. 1983-b. Recycled Cretaceous and Tertiary pollen and spores in antarctic marine sediments: A catalogue. Palaeontographica Abteilung B, 186, 121 - 174.
* Present address: Department of Geology, Hamilton College, Clinton, New York 13323. ANTARCTIC JOURNAL
Evidence for preglacial sedimentary sequences adjacent to and on the continental shelf of East Antarctica between 1400 and \
¼ 4-. \ Al \ \_. \ 500
150°E is presently limited. Geophysical surveys of the interior (Steed and Drewry 1982) as well as portions of the continental shelf (Eittreim et al. 1984; Sato et al. 1984) have demonstrated the existence, if not the age, of several hundred meters of sedimentary section. Surficial sediments on the continental shelf contain reworked palynomorphs of Permian to early Tertiary age which indicate that similar-age sedimentary rocks may exist in the vicinity (Truswell 1983-a). The only in situ occurrence of preglacial strata on the continental shelf comes from a lower Cretaceous siltstone recovered during austral summer 1978 1979—or Deep Freeze 79 (DF-79)—from the seaward flank of the Mertz-Ninnis Trough (Domack, Fairchild, and Anderson 1980) (figure 1). Presented herein are additional data from this and other austral summer 1978 - 1979 cores which suggest that
/7
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300
A
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300 11-
7)
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900 -
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1
309
320
500
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34
DIAMICTONS MUDDY , SANDY
m36
MERTZ
loo,
GLACIER
MASSIVE
SILICEOUS MUDS
)\ \ I I I \\I 01
A\ S.,.--'
\\
\
%' S.__
S.
1
•
\
SANDS & MUDDY SANDS
A NON PEBBLY
A PEBBLY
SILTSTONE BRECCIA
0
DISTRIBUTION OF CORED SEDIMENTS GEORGE V - ADELIE CONTINENTAL SHELF
NINNIS GLACIER
(DEPTH IN METERS) Figure 1. Bathymetry and core location on George V/Adélie continental margin. The George V basin has been formally named the Mertz-NlnnlS Trough or Valley as listed in the Gazetteer of Undersea Features (Defense Mapping Agency 1982). 76
ANTARCTIC JOURNAL
up to 2,000 meters of preglacial section may have existed at one time within the present area of the Mertz-Ninnis Trough (formerly referred to as the George V Basin). Sedimentary rocks occur as erratics in most of the piston cores from the continental shelf. These cores consist of glacial and glacial-marine diamictons. Specifically, several clasts of dark-brown, indurated shale were recovered from core DF-79-37. Organic material is abundant within these shales and, upon processing, palynomorphs were concentrated (figure 2). All of the identified spores are of Early Cretaceous age according to the palynostratigraphy of Burger (1980). Therefore, glacial erosion has cut into Lower Cretaceous section somewhere in the vicinity of core DF-79-37. Further, more than one cycle of glacial erosion and deposition is indicated, because the shale clasts were covered with a well-indurated coating resembling till matrix in mineralogy and texture. The well-indurated nature of these shale clasts is in contrast to the almost unlithified character of the Lower Cretaceous siltstone recovered nearby (i.e., DF-79-38).
Vitrinite reflectance data were obtained from the in situ Lower Cretaceous sediment in DF-79-3 (figure 3). The data show that vitrinite macerals within the siltstone were derived from contemporaneous coaly material and some material from an older, thermally more mature, sedimentary unit. The reflectance value of the indigenous vitrinite (mean reflectance equals .51) can be used to access the thermal history and hence depth of burial of the Lower Cretaceous siltstone in DF-79-38. Continental reconstructions and analysis of seafloor magnetic anomalies place Antarctica and Australia in a late rift stage during the Early Cretaceous (Sproll and Dietz 1969; Cande and Mutter 1982). Therefore, a reasonable estimate of depth/temperature relationships for the George V continental margin can be obtained from the Mesozoic sequence which has been drilled in the Otway Basin, Australia (figure 3). The data of Middleton and Falvey (1983) (figure 3) suggest that the vitrinite in DF-79-38 experienced temperatures equivalent to those found at a depth of 1,500 to 2,200 meters within the Otway Basin. Shallower burial depths could be inferred for DF-79-38 if a substantially
:
,p
2
3
.*.
Yp\
0
tot
*
\\>
rA..1
5
1
Figure 2. Photomicrographs (x 750) of spores isolated from shale clasts found in core DF-79-37. 1. Microcachryidites antarcticus, (Cookson 1947). 2/3. Lycopodiumsporites nodosus, (Dettman 1963). 4. Cicatricosisporites cf.C. australiensis, (Cookson 1947). 5. Classopollis cf.C. chateaunovi, (Reyre 1970). 6. Cyathidites australis, (Couper 1953). Stratigraphic distribution for the above according to Burger (1980) and Truswell (1983-b): Late Jurassic to Miocene (1), Late Jurassic to Middle Albian (2, 3, 5, 6), Neocomian to Middle Albian (4).
1985 REVIEW
77
greater geothermal gradient is assumed. However, there is no reason to expect this, because spreading of Australia and Antarctica away from the South East Indian Ridge appears to have been symmetrical (Heezen et al. 1977).
Anderson (Rice University). Gratitude is extended to Dennis Cassidy at Florida State University for his help in providing samples.
References
Mean Vitrinite Reflectance, R0 0
Voluta .1 Pecten1ADF7938-0 0 0
-
Burger, D. 1980. Palynological studies in the Lower Cretaceous of the Surat Basin, Australia. Australian Bureau of Mineral Resources, Bulletin,
189, 106. Cande, S. C., and J. Mutter. 1982. A revised identification of the oldest sea-floor spreading anomalies between Australia and Antarctica. Earth and Planetary Science Letters, 58, 151 - 160. Cookson, I. 1947. Plant microfossils from the lignites of Kerguelen Archipelago. British, Australian, New Zealand Antarctic Research Expedition, 1929 - 1931, (Report A-2). Adelaide: BANZAR Expedition
Committee. Couper, R.A. 1953. Upper Mesozoic and Cainozoic spores and pollen
-
C)
b 0
grains from New Zealand. New Zealand Geological Survey Paleontological Bulletin, (Wellington), 22, 77. Defense Mapping Agency. 1982. Gazetteer of undersea features. Wash-
I-
- c
ington, D.C.: U.S. Government Printing Office. Dettman, M.R. 1963. Upper Mesozoic microfloras from Southeastern Australia. Proceedings of the Royal Society of Victoria, 77, 148. Domack, E.W., W.W. Fairchild, and J.B. Anderson. 1980. Lower Cretaceous sediment from the East Antarctic Continental Shelf. Nature, 287, 625 - 626. Eittreim, S.L., A.K. Cooper, and others. 1984. Marine geological and
.c a. w
geophysical investigations of the antarctic continental margin 1984. (U.S. o 0 o
I
0.0 .2 .4 .6 .8 1.0 1.2 1.4 Figure 3. Comparison of reflectance (Ro) vs. depth for sediments from wells in the Otway Basin, S. Australia (from Middleton and Falvey 1983). A mean Roof .51 for sample DF-79-38 corresponds to a depth of 1,500 to 2,200 meters assuming the geothermal history defined by the South Australian data. Error bars are standard deviations and where large (i.e., Voluta-1) indicate possible reworking of older vitrinite (Middleton personal communication). A histogram of vitrinite reflectance for core DF-79-38 is available, upon request, from the author.
If the above assumptions are valid and DF-79-38 indeed represents an in situ submarine outcrop, then a significant preglacial sedimentary sequence (now partially eroded) exists on the George V continental shelf. The abundance of Lower Cretaceous erratics within glacial sediments, and the predominance of similar age palynomorphs in nearby surface sediments (Truswell 1983-a), suggests that the majority of the sedimentary basin consists of Lower Cretaceous strata. This stratigraphy is similar to several basins of the Southeast Australian continental shelf, including the Otway (Falvey and Mutter 1981). The trend of the Mertz-Ninnis Trough marks the landward boundary of the sedimentary basin (here termed the George V Basin) as Precambrian granite crops out along the coast (Mawson 1942). It is likely that similar troughs found along the east antarctic margin may mark the landward boundaries of preglacial sedimentary basins. This work was supported originally by National Science Foundation grants DPP 77-26407 and DPP 80-80242 to John B. 78
Geological Survey Circular 935.) Washington, D.C.: U.S. Government Printing Office. Falvey, D.A., and J.C. Mutter. 1981. Regional plate tectonics and the evolution of Australia's passive margins. BMR Journal of Australian Geology and Geophysics, 6, 1 - 29. Heezen, B.C., R.P. Lynde, Jr., and D.J. Fornari. 1977. Geologic map of the Indian Ocean. In J.R. Heirtzler, H.M. Bolli, T.A. Davies, J.B. Saunders, and J. G. Sciater (Eds.), Indian Ocean geology and biostratigraphy. Washington, D.C.: American Geophysical Union.
Mawson, D. 1942. Geographical narrative and cartography, Australasian Antarctic Expedition 1911 -1914. Scientific Reports, (Series A.), 1, 1-364. Middleton, M.F. 1983. Personal communication. Middleton, M. F., and D.A. Falvey. 1983. Maturation modeling in Otway Basin, Australia. American Association of Petroleum Geologists Bulletin,
67, 271 - 279. Reyre, Y. 1970. Stereoscan observations on the pollen genus Classopollis, Pflug, 1953. Paleontology, 13(2), 303 - 322. Sato, S., N. Asakura, T. Saki, N. Oikawa, and Y. Kaneda. 1984. Preliminary results of geological and geophysical surveys in the Ross Sea and on the Dumont D'Urville Sea, off Antarctica. National Institute of Polar Research, (Memoir), 33, 66 - 92. Sproll, W. P., and R. S. Deitz. 1969. Morphological continental drift fit of Australia and Antarctica. Nature, 222, 345 - 348. Steed, R.H.N., and D.J. Drewry. 1982. Radio-echo sounding investigations of Wilkes Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Truswell, E.M. 1983-a. Geological implications of recycled palynomorphs in continental shelf sediments around Antarctica. In R. L. Oliver, P.R. James, andJ.B. Jago (Eds.), Antarctic Earth science. Canberra: Australian Academy of Science. Truswell, E.M. 1983-b. Recycled Cretaceous and Tertiary pollen and spores in antarctic marine sediments: A catalogue. Palaeontographica Abteilung B, 186, 121 - 174.
* Present address: Department of Geology, Hamilton College, Clinton, New York 13323. ANTARCTIC JOURNAL
