Miocene foraminifera from DSDP site 272, Ross Sea
Land, Antarctica. In T. Nagata (Ed.) Proceedings of the seminar lii on Dry Valley Drilling Project. Tokyo, Memoirs of the National Institute of Polar Research (Special Issue No. 13). D'Agostino, A. E. 1980. Foraminiferal systeniatics, hiostratigraphy, and palcoecology of DSL)P Site 273, Ross Sea, Antarctica. (Masters thesis, North-
ern Illinois University, DeKaib, Illinois.) D'Agostino, A. E., and P. Webb. 1980. Interpretation of mid-Miocene to Recent lithostratigraphy and biostratigraphy at DSDP site 273, Ross Sea. Antarctic Journal of the U.S., 15(5), 118-120. Harwood, D.M. 1986a. Diatoms. In P.J. Barrett (Ed.), Antarctic Cenozoic History from MSSTS-1 drillhole, McMurdo Sound. Bulletin in the Miscellaneous Series of the New Zealand Department of Scientific and Industrial Research, (No. 237). Harwood, D.M. 1986b. Diatom biostratigraphy and paleoecology with a Cenozoic history of Antarctic ice sheets. (Doctoral dissertation, Ohio State
University, Columbus, Ohio.) Hayes. D.E., L.A. Frakes, P.J. Barrett, D.A. Burns, P. Chen, A.B. Ford, A.G. Kaneps, F.M. Kemp, D.W. McCollum, D.J.W. Piper, R.E. Wall, and P.-N. Webb. 1975b. 8. Sites 270, 271, 272. In D.E. Hayes L.A.
Frakes et al. (Eds.), initial Reports of the Deep Sea Drilling Project
(Vol.28). Washington, D.C.: U.S. Government Printing Office. Ishman, S.E. 1985. Foraminiferal biostratigraphy and paleoecology of Dry Valley Drilling Project Cores 10 and 11, Taylor Valley, Antarctica. (Masters thesis, Ohio State University, Columbus, Ohio.) Leckie, R.M. 1980. Micropaleontology, biostratigraphy and paleoenvironmental studies of DSDP Site 270 (late Oligocene-Quaternary) Ross Sea, Antarctica. (Masters thesis, Northern Illinois University, DeKalb, Illinois.) Leckie, R.M., and P.-N. Webb. 1983. Late Oligocene-early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP Site 270. Geology, 11, 578-582. Leckie, R.M., and P.-N. Webb. 1985. Candeina antarctica n. sp. and the phylogenetic history and distribution of Candeina spp. in the Paleogene-early Neogene of the Southern Ocean. Journal of Foraminiferal Research, 15, 65-78.
Miocene foraminifera from DSDP site 272, Ross Sea D. MARK STEINHAUFF
Department of Geological Sciences University of Tennessee Knoxville, Tennessee 37996 PETER-N. WEBB
Department of Geology and Mineralogy
and Byrd Polar Research Center Ohio State University Columbus, Ohio 43210 DSDP site 272 provides one of the most southerly in situ middle Miocene glacial marine successions. The approximately 410 meters succession is subdivided into three subunits; an upper unit (2A), sandy silty claystone with sparse to common clasts; a middle unit (2B), diatom silty claystone and silty clay diatomite with rare clasts; and a lower unit (2C), a silty claystone with rare clasts (Hayes et al. 1975).
1987 REVIEW
Leckie, R.M., and P.-N. Webb. 1986. Late Paleogene and Early Neogene Foraminifers of Deep Sea Drilling Project Site 270, Ross Sea, Antarctica. In J. P. Kennett, C. von der Borch et al. (Eds.), initial Reports of the Deep Sea Drilling Project (Vol. 90). Washington, D.C.: U.S. Government Printing Office. McCollum, D.W. 1975. Diatom stratigraphy of the southern ocean. In D.E. Hayes, L.A. Frakes et al. (Eds.), initial Reports of the Deep Sea Drilling Project (Vol. 28). Washington, D.C.: U.S. Government Printing Office. Renz, M.E. 1985. Diatom biostratigraphic correlation of Deep Sea Drilling Project Sites 270 and 272, Ross Sea, Antarctica. (B.S. thesis, Ohio State University, Columbus, Ohio.) Savage, M.L. 1982. The glacial history of the Ross Sea region based on DSDP leg 28 sites 272 and 273. (Masters thesis, University of Georgia, Athens, Georgia.) Savage, ML., and RE Ciesielski. 1983. A revised history of glacial sedimentation in the Ross Sea region. In R. L. Oliver, P.R. James, and J.B. Jago, (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Steinhauff, D.M. 1985. Paleoecologic and stratigraphic analysis of Miocene foraminifera (Protozoa) from glacial-marine sediments, Ross Sea, Antarctica. (Masters thesis, Ohio State University, Columbus, Ohio.) Steinhauff, D.M., and P.-N. Webb. 1987. Miocene foraminifera from DSDP site 272, Ross Sea. Antarctic Journal of the U.S., 22(5). Weaver, EM., and A.M. Combos, Jr. 1981. Southern high latitude diatom biostratigraphy. In J.E. Warme, R.G. Douglas, and E.L. Winterer (Eds.) The Deep Sea Drilling Project: A decade of progress. Society of Economic Mineralogists and Paleontologists, (Special Publication No. 32). Webb, P.-N., 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.
Preliminary comments on foraminifera are provided in Hayes et al. (1975). Eighty-one samples from site 272 were investigated by Steinhauff (1985) in the course of a detailed study of foraminifera. Samples are distributed through subunits A and down into the upper part of subunit B (i.e., 23 to 179 meters subbottom). The lower parts of subunit B and all of subunit C are largely barren of foraminifera. Subunit A and uppermost subunit B yielded a total of 86 species of foraminifera; 8 agglutinated species, 72 calcareous benthic species, and 6 planktonic species. Dominant calcareous taxa include lslandiehla spp., Epistominella exigua (Brady), Glohocassidulina s uhglobosa (Brady), NonioneIla iridea Heron-Allen and Earland, and Melonis affinis (Reuss). Persistent low abundance forms include Euvigerina schwageri (Brady), Discorhis spp., Rosa/ma globularis d'Orbigny, Elphidium bartletti Cushman, Elphidium magel/anicum Heron-Allen and Earland, Trochoelphidiella uniforamina Leckie and Webb, Pullenia hulloides (d'Orbigny), Nonionella hradii (Chapman), Cihicides refulgens Montfort, and Anomalina hassensis Parr. Planktonics include species of Glohigerina, Gloho rota/ia, and Candeina. Candeina antarctica Leckie and Webb dominates the planktonic assemblage. The foraminifera of subunit 2A and uppermost subunit 2B of site 272 resemble assemblages in Lower to Middle Miocene subunit 2 of site 273 (D'Agostino 1980; D'Agostino and Webb 1980) and Lower Miocene subunit 2A (Epistominella-EiphidiumNonionella assemblage zone) of site 270 (Leckie and Webb 1980a, 125
1980b, 1983,1986; Webb in press). Savage (1982) and Savage and Ciesielski (1983) placed subunits 2A and 2B sediments in the Lower to Middle Miocene on the basis of diatom biostratigraphy. At site 272 a major decrease in foraminiferal abundance and diversity is noted between approximately 138 and 148 meters subbottom. This roughly corresponds to the subunit 2A/2B boundary and occurs at the level of a proposed 4-million-year hiatus which separates Lower and Middle Miocene sediments (Savage and Ciesielski 1983). Only sporadic occurrences of robust thick-walled forms such as Islandiella spp., Epistominella exigua (Brady), Globocassidulina suhglohosa (Brady), and Nonione!la iridea Heron-Allen and Earland occur below 147 meters (in subunit 2B) and much of the lower succession is barren of foraminifera. Absence of fauna is attributed to dissolution contemporaneous with deposition, or post-depositional diagenesis. Site 272 foraminiferal assemblages may have been subjected to glacial transport and redeposition and/or bottom current reworking. The wide size range of foraminifera at any stratigraphic level suggests size sorting is not a significant factor. This work was supported by National Science Foundation grant DPP 82-14174 to Peter-N. Webb; and Sigma Xi, American Association of Petroleum Geologists and Friends of Orton Hall (Ohio State University) grants to D. Mark Steinhauff. Thanks are extended to David Harwood for comments and suggestions during this laboratory study. References
D'Agostino, A.E. 1980.
Foraininiferal systematics, biostratigraphy and pal eoecology of DSt)P site 273, Ross Sea, Antarctica. (Masters thesis, North-
ern Illinois University, DeKalb, Illinois.)
The Wilkes Land continent-ocean crustal boundary STEPHEN L. EITTREIM U.S. Geological Survey Menlo Park, California 94025
Multichannel seismic data collected in 1984 on the east antarctic margin between 130° and 150° east have revealed the existence of a marginal rift basin that is proposed here to be the remnant of a Cretaceous rift valley similar to the present-day rift valleys of East Africa. A breakup unconformity that marks the change to a seafloor spreading regime in the rifting of Australia from Antarctica, overlaps the marginal rift basin and terminates at the oldest identified oceanic crust. Track lines of the 1984 U.S. Geological Survey investigation along which multichannel seismic, sonobuoy refraction, gravity and magnetics, 3.5- and 12-kilohertz echo sounding data were collected are shown in figure 1. Side-scan sonar data, 126
D'Agostino, A. E., and P.-N. Webb. 1980 Interpretation of mid-Miocene to Recent lithostratigraphy and biostratigraphy at osiiw site 273, Ross Sea. Antarctic Journal of the U.S., 15(5), 118-120. Hayes, D.E., L.A. Frakes, P.J. Barrett, D.A. Burns, P. Chen, A.B. Ford, A.G. Kaneps, E.M. Kemp, D.W. McCollum, D.J.W. Piper, R.E. Wall, and P.-N. Webb. 1975. 8. Sites 270, 271, 272. In D.E. Hayes, L.A. Frakes et al. (Eds.), Initial Reports of the Deep Sea Drilling Project (Vol.
28). Washington, D.C.: U.S. Government Printing Office. Leckie, R.M., and P.-N. Webb. 1980a. Foraminifera of DSDP 270 as indicators of the evolving Ross Sea in the late Oligocene/early Miocene. Antarctic Journal of the U.S., 15(5), 117-118. Leckie, R.M., and P.-N. Webb. 1980b. A provisional late Oligoceneearly Miocene foraminiferal zonation, Ross Sea continental shelf, Antarctica. Geological Society of America Abstracts with Program, 12, 469. Leckie, R.M., and P.-N. Webb. 1983. late Oligocene-early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP site 270. Geology, 11, 578-582. Leckie, R.M., and P.-N. Webb. 1986. Late Paleogene and Early Neogene foraminifers of Deep Sea Drilling Pro ject Site 270, Ross Sea, Antarctica. InJ.P. Kennett, C.C. von der Borch, et al., (Eds.), Initial Reports of the Deep Sea Drilling Project, (Vol. 90). Washington, D.C.: U.S. Government Printing Office. Savage, M . L. 1982. The glacial history of the Ross Sea region based on DSDP leg 28, sites 272 and 273. (Masters thesis, University of Georgia, Athens, Georgia.) Savage, ML., and P.F. Ciesielski. 1983. A revised history of glacial sedimentation in the Ross Sea region. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Steinhauff, D.M. 1985. Paleoecologic and st ratigraphic analysis of Miocene foraminifera (Protozoa) from glacial-marine sediments, Ross Sea, Antarctica.
(Masters thesis, Ohio State University, Columbus, Ohio.) Webb, P.-N. In press. Upper Oligocene-Holocene benthic foraminifera of the Ross Sea region. Revue de Paleohiologie.
sediment cores, and dredge samples were also collected in the area at the eastern edge of the map of figure 1. Reports on this data, including seismic records, most of which are processed through migration, are included in a volume of papers on the Wilkes Land margin (Eittreim and Hampton 1987). Four seismic sequences, A through ui, separated by the Unconformities T, Ki, and K2, have been recognized throughout most of the surveyed area (figure 2). The deepest sequence (D) consists of a block-faulted, moderate- to high-velocity layer with flat and parallel bedding. D is interpreted as a prerift sequence based on its block-faulted and parallel-bedded nature. The Beacon Supergroup (Barrett 1982), an antarctic lithologic unit of flat-bedded elastic sediments, with conformable sills of dolerite intrusions, may be represented in this sequence, with the dolerite sills seen as markedly high-amplitude reflecting horizons (Eittreim and Smith 1987). The top of this sequence is an erosional unconformity. C overlies this unconformity and is interpreted to be a synrift sequence that was deposited in basins produced during the crustal extension and subsidence associated with the extension of the Gondwana crust prior to the beginning of seafloor spreading at about 95 million years ago (Cande and Mutter 1982). Sequence C is topped by a breakup unconformity produced at the earliest generation of oceanic crust. C occurs only south of the edge of oceanic crust. The two remaining shallower sequences are interpreted as: B, a shelf or ANTARCTIC JOURNAL
ern Illinois University, DeKaib, Illinois.) D'Agostino, A. E., and P. Webb. 1980. Interpretation of mid-Miocene to Recent lithostratigraphy and biostratigraphy at DSDP site 273, Ross Sea. Antarctic Journal of the U.S., 15(5), 118-120. Harwood, D.M. 1986a. Diatoms. In P.J. Barrett (Ed.), Antarctic Cenozoic History from MSSTS-1 drillhole, McMurdo Sound. Bulletin in the Miscellaneous Series of the New Zealand Department of Scientific and Industrial Research, (No. 237). Harwood, D.M. 1986b. Diatom biostratigraphy and paleoecology with a Cenozoic history of Antarctic ice sheets. (Doctoral dissertation, Ohio State
University, Columbus, Ohio.) Hayes. D.E., L.A. Frakes, P.J. Barrett, D.A. Burns, P. Chen, A.B. Ford, A.G. Kaneps, F.M. Kemp, D.W. McCollum, D.J.W. Piper, R.E. Wall, and P.-N. Webb. 1975b. 8. Sites 270, 271, 272. In D.E. Hayes L.A.
Frakes et al. (Eds.), initial Reports of the Deep Sea Drilling Project
(Vol.28). Washington, D.C.: U.S. Government Printing Office. Ishman, S.E. 1985. Foraminiferal biostratigraphy and paleoecology of Dry Valley Drilling Project Cores 10 and 11, Taylor Valley, Antarctica. (Masters thesis, Ohio State University, Columbus, Ohio.) Leckie, R.M. 1980. Micropaleontology, biostratigraphy and paleoenvironmental studies of DSDP Site 270 (late Oligocene-Quaternary) Ross Sea, Antarctica. (Masters thesis, Northern Illinois University, DeKalb, Illinois.) Leckie, R.M., and P.-N. Webb. 1983. Late Oligocene-early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP Site 270. Geology, 11, 578-582. Leckie, R.M., and P.-N. Webb. 1985. Candeina antarctica n. sp. and the phylogenetic history and distribution of Candeina spp. in the Paleogene-early Neogene of the Southern Ocean. Journal of Foraminiferal Research, 15, 65-78.
Miocene foraminifera from DSDP site 272, Ross Sea D. MARK STEINHAUFF
Department of Geological Sciences University of Tennessee Knoxville, Tennessee 37996 PETER-N. WEBB
Department of Geology and Mineralogy
and Byrd Polar Research Center Ohio State University Columbus, Ohio 43210 DSDP site 272 provides one of the most southerly in situ middle Miocene glacial marine successions. The approximately 410 meters succession is subdivided into three subunits; an upper unit (2A), sandy silty claystone with sparse to common clasts; a middle unit (2B), diatom silty claystone and silty clay diatomite with rare clasts; and a lower unit (2C), a silty claystone with rare clasts (Hayes et al. 1975).
1987 REVIEW
Leckie, R.M., and P.-N. Webb. 1986. Late Paleogene and Early Neogene Foraminifers of Deep Sea Drilling Project Site 270, Ross Sea, Antarctica. In J. P. Kennett, C. von der Borch et al. (Eds.), initial Reports of the Deep Sea Drilling Project (Vol. 90). Washington, D.C.: U.S. Government Printing Office. McCollum, D.W. 1975. Diatom stratigraphy of the southern ocean. In D.E. Hayes, L.A. Frakes et al. (Eds.), initial Reports of the Deep Sea Drilling Project (Vol. 28). Washington, D.C.: U.S. Government Printing Office. Renz, M.E. 1985. Diatom biostratigraphic correlation of Deep Sea Drilling Project Sites 270 and 272, Ross Sea, Antarctica. (B.S. thesis, Ohio State University, Columbus, Ohio.) Savage, M.L. 1982. The glacial history of the Ross Sea region based on DSDP leg 28 sites 272 and 273. (Masters thesis, University of Georgia, Athens, Georgia.) Savage, ML., and RE Ciesielski. 1983. A revised history of glacial sedimentation in the Ross Sea region. In R. L. Oliver, P.R. James, and J.B. Jago, (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Steinhauff, D.M. 1985. Paleoecologic and stratigraphic analysis of Miocene foraminifera (Protozoa) from glacial-marine sediments, Ross Sea, Antarctica. (Masters thesis, Ohio State University, Columbus, Ohio.) Steinhauff, D.M., and P.-N. Webb. 1987. Miocene foraminifera from DSDP site 272, Ross Sea. Antarctic Journal of the U.S., 22(5). Weaver, EM., and A.M. Combos, Jr. 1981. Southern high latitude diatom biostratigraphy. In J.E. Warme, R.G. Douglas, and E.L. Winterer (Eds.) The Deep Sea Drilling Project: A decade of progress. Society of Economic Mineralogists and Paleontologists, (Special Publication No. 32). Webb, P.-N., 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.
Preliminary comments on foraminifera are provided in Hayes et al. (1975). Eighty-one samples from site 272 were investigated by Steinhauff (1985) in the course of a detailed study of foraminifera. Samples are distributed through subunits A and down into the upper part of subunit B (i.e., 23 to 179 meters subbottom). The lower parts of subunit B and all of subunit C are largely barren of foraminifera. Subunit A and uppermost subunit B yielded a total of 86 species of foraminifera; 8 agglutinated species, 72 calcareous benthic species, and 6 planktonic species. Dominant calcareous taxa include lslandiehla spp., Epistominella exigua (Brady), Glohocassidulina s uhglobosa (Brady), NonioneIla iridea Heron-Allen and Earland, and Melonis affinis (Reuss). Persistent low abundance forms include Euvigerina schwageri (Brady), Discorhis spp., Rosa/ma globularis d'Orbigny, Elphidium bartletti Cushman, Elphidium magel/anicum Heron-Allen and Earland, Trochoelphidiella uniforamina Leckie and Webb, Pullenia hulloides (d'Orbigny), Nonionella hradii (Chapman), Cihicides refulgens Montfort, and Anomalina hassensis Parr. Planktonics include species of Glohigerina, Gloho rota/ia, and Candeina. Candeina antarctica Leckie and Webb dominates the planktonic assemblage. The foraminifera of subunit 2A and uppermost subunit 2B of site 272 resemble assemblages in Lower to Middle Miocene subunit 2 of site 273 (D'Agostino 1980; D'Agostino and Webb 1980) and Lower Miocene subunit 2A (Epistominella-EiphidiumNonionella assemblage zone) of site 270 (Leckie and Webb 1980a, 125
1980b, 1983,1986; Webb in press). Savage (1982) and Savage and Ciesielski (1983) placed subunits 2A and 2B sediments in the Lower to Middle Miocene on the basis of diatom biostratigraphy. At site 272 a major decrease in foraminiferal abundance and diversity is noted between approximately 138 and 148 meters subbottom. This roughly corresponds to the subunit 2A/2B boundary and occurs at the level of a proposed 4-million-year hiatus which separates Lower and Middle Miocene sediments (Savage and Ciesielski 1983). Only sporadic occurrences of robust thick-walled forms such as Islandiella spp., Epistominella exigua (Brady), Globocassidulina suhglohosa (Brady), and Nonione!la iridea Heron-Allen and Earland occur below 147 meters (in subunit 2B) and much of the lower succession is barren of foraminifera. Absence of fauna is attributed to dissolution contemporaneous with deposition, or post-depositional diagenesis. Site 272 foraminiferal assemblages may have been subjected to glacial transport and redeposition and/or bottom current reworking. The wide size range of foraminifera at any stratigraphic level suggests size sorting is not a significant factor. This work was supported by National Science Foundation grant DPP 82-14174 to Peter-N. Webb; and Sigma Xi, American Association of Petroleum Geologists and Friends of Orton Hall (Ohio State University) grants to D. Mark Steinhauff. Thanks are extended to David Harwood for comments and suggestions during this laboratory study. References
D'Agostino, A.E. 1980.
Foraininiferal systematics, biostratigraphy and pal eoecology of DSt)P site 273, Ross Sea, Antarctica. (Masters thesis, North-
ern Illinois University, DeKalb, Illinois.)
The Wilkes Land continent-ocean crustal boundary STEPHEN L. EITTREIM U.S. Geological Survey Menlo Park, California 94025
Multichannel seismic data collected in 1984 on the east antarctic margin between 130° and 150° east have revealed the existence of a marginal rift basin that is proposed here to be the remnant of a Cretaceous rift valley similar to the present-day rift valleys of East Africa. A breakup unconformity that marks the change to a seafloor spreading regime in the rifting of Australia from Antarctica, overlaps the marginal rift basin and terminates at the oldest identified oceanic crust. Track lines of the 1984 U.S. Geological Survey investigation along which multichannel seismic, sonobuoy refraction, gravity and magnetics, 3.5- and 12-kilohertz echo sounding data were collected are shown in figure 1. Side-scan sonar data, 126
D'Agostino, A. E., and P.-N. Webb. 1980 Interpretation of mid-Miocene to Recent lithostratigraphy and biostratigraphy at osiiw site 273, Ross Sea. Antarctic Journal of the U.S., 15(5), 118-120. Hayes, D.E., L.A. Frakes, P.J. Barrett, D.A. Burns, P. Chen, A.B. Ford, A.G. Kaneps, E.M. Kemp, D.W. McCollum, D.J.W. Piper, R.E. Wall, and P.-N. Webb. 1975. 8. Sites 270, 271, 272. In D.E. Hayes, L.A. Frakes et al. (Eds.), Initial Reports of the Deep Sea Drilling Project (Vol.
28). Washington, D.C.: U.S. Government Printing Office. Leckie, R.M., and P.-N. Webb. 1980a. Foraminifera of DSDP 270 as indicators of the evolving Ross Sea in the late Oligocene/early Miocene. Antarctic Journal of the U.S., 15(5), 117-118. Leckie, R.M., and P.-N. Webb. 1980b. A provisional late Oligoceneearly Miocene foraminiferal zonation, Ross Sea continental shelf, Antarctica. Geological Society of America Abstracts with Program, 12, 469. Leckie, R.M., and P.-N. Webb. 1983. late Oligocene-early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP site 270. Geology, 11, 578-582. Leckie, R.M., and P.-N. Webb. 1986. Late Paleogene and Early Neogene foraminifers of Deep Sea Drilling Pro ject Site 270, Ross Sea, Antarctica. InJ.P. Kennett, C.C. von der Borch, et al., (Eds.), Initial Reports of the Deep Sea Drilling Project, (Vol. 90). Washington, D.C.: U.S. Government Printing Office. Savage, M . L. 1982. The glacial history of the Ross Sea region based on DSDP leg 28, sites 272 and 273. (Masters thesis, University of Georgia, Athens, Georgia.) Savage, ML., and P.F. Ciesielski. 1983. A revised history of glacial sedimentation in the Ross Sea region. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Steinhauff, D.M. 1985. Paleoecologic and st ratigraphic analysis of Miocene foraminifera (Protozoa) from glacial-marine sediments, Ross Sea, Antarctica.
(Masters thesis, Ohio State University, Columbus, Ohio.) Webb, P.-N. In press. Upper Oligocene-Holocene benthic foraminifera of the Ross Sea region. Revue de Paleohiologie.
sediment cores, and dredge samples were also collected in the area at the eastern edge of the map of figure 1. Reports on this data, including seismic records, most of which are processed through migration, are included in a volume of papers on the Wilkes Land margin (Eittreim and Hampton 1987). Four seismic sequences, A through ui, separated by the Unconformities T, Ki, and K2, have been recognized throughout most of the surveyed area (figure 2). The deepest sequence (D) consists of a block-faulted, moderate- to high-velocity layer with flat and parallel bedding. D is interpreted as a prerift sequence based on its block-faulted and parallel-bedded nature. The Beacon Supergroup (Barrett 1982), an antarctic lithologic unit of flat-bedded elastic sediments, with conformable sills of dolerite intrusions, may be represented in this sequence, with the dolerite sills seen as markedly high-amplitude reflecting horizons (Eittreim and Smith 1987). The top of this sequence is an erosional unconformity. C overlies this unconformity and is interpreted to be a synrift sequence that was deposited in basins produced during the crustal extension and subsidence associated with the extension of the Gondwana crust prior to the beginning of seafloor spreading at about 95 million years ago (Cande and Mutter 1982). Sequence C is topped by a breakup unconformity produced at the earliest generation of oceanic crust. C occurs only south of the edge of oceanic crust. The two remaining shallower sequences are interpreted as: B, a shelf or ANTARCTIC JOURNAL
