Late Cenozoic paleo-oceanography
Hays, J . D., and N. D. Opdyke. 1967. Antarctic radiolaria, magnetic reversals, and climatic change. Science, 158: 1001.-1011. Heiberg, P. A. C. 1863. Conspectus criticus diatomacearum danicarum. Kjobenhavn. Wilhelm Priors Forlag. p. 50-52. Kanaya, T. 1971. Some aspects of pre-Quaternary diatoms
in the oceans. In: The Micropaleontology of Oceans
(Funnell and Reidel, eds.) Cambridge University Press. p. 545-565. Simonsen, R., and T. Kanaya. 1961. Notes on the marine species of the diatom genus Denticula Kutz. Internationale Revue der gesamten Hydrobiologie, 46:4. 498-513. Watkins, N. D., and J . P. Kennett. 1972. Regional sedimentary disconformatives and Upper Cenozoic changes in bottom water velocities between Australasia and Antarctica. Antarctic Research Series, 19: 273-293. Witt, 0. N. 1886. Ueber den Polierschiefer von ArchangelskKurojedowo im Gouv. Simbirsk. Verhandlungen der Rus-
sisch-Kaiserlichen Mineralogischen Gesellschaft. Series 2, 22: 137-177.
Late Cenozoic paleo-oceanography RICHARD H. FILLON Graduate School of Oceanography University of Rhode Island
During Cruises 27 and 32 of USNS Eltanin, 64 piston cores were taken from the continental shelf and slope within and just to the north of the Ross Sea. Paleomagnetic, paleontological, and sedimentological studies have been conducted on each core. A refined depth zonation consisting of five depth zones can be recognized on the basis of dead benthic foraminiferal assemblages (table). The division of benthic foraminiferal faunas in surface sediments within the Ross Sea into dominantly calcareous and dominantly arenaceous assemblages has been recognized by previous authors (Kennett, 1966; Thomas, 1968). So far, ages for 20 cores have been determined using paleomagnetic polarity patterns (Cox, 1969) and established radiolarian biostratigraphy (Opdyke et al., 1966; Hays and Opdyke, 1967). The age distribution of cores (fig.) offers an explanation for the foraminiferal faunal division in the Ross Sea. Calcareous benthic foraminiferal assemblages from Benthic foraminiferal de pth zonation in the Ross Sea.
Location
Depth range (meters) Type of fauna
Ross Sea (1) (2) (3) Slope north (4) of the Ross Sea (5)
0-550 dominantly calcareous 400-2000 " arenaceousa 550-3000 cccalcareous > 2200 arenaceous > 3000 " calcareous CC
a Arenaceous foraminifera in the Ross Sea construct their shells by cementing together sand grains and other noncalcareous particles.
September-October 1972
the continental shelf in the Ross Sea are restricted to sediment older than lower Matuyama (1.87 million years). Sediments bearing calcareous faunas are found exposed at the surface or separated by a disconformity from overlying Brunhes or late Matuyama sediments. The widespread erosion implied by the disconformity was caused probably by bottom current scour initiated by increased bottom-water velocities associated perhaps with a significant northward advance of the Ross Ice Shelf and with thicker pack ice formation in the Ross Sea. Previous evidence for a period of increased bottom-water velocity is presented by Watkins and Kennett (1971) who attribute an erosional disconformity in the southern ocean, south of Australia and Tasmania, to an increase in bottom-water production and velocities in post-Gilbert or post-Gauss time. In the Ross Sea, the change from calcareous to arenaceous faunas in post-Gauss time was probably effected by a rise in the calcium carbonate compensation depth caused by the increased production of undersaturated bottom water. Paralleling the faunal change was a sedimentological change. Gauss and lower Matuyama sediments are coarse, poorly sorted, and glacial marine, averaging about 30 percent sandsize and larger particles. Sediments above the disconformity contain generally less than 10 percent sand that is typically fine. Such a change in sedimentation could have been caused by a change in
Core logs showing paleomagnetic polarity (left) and benthic foraminiferal faunal type (right). Normal polarity intervals are portrayed in black, reversed polarity intervals in white. Dominantly arenaceous foraminiferal faunas are indicated by crosshatched bars, dominantly calcareous foraminiferal faunas by blank bars. Established paleomagnetic scales (Cox, 1969; Vine, 1968) are shown at the left of the diagram. Epoch boundaries delineated by heavy and light lines are according to Cox (1969) and Foster and Opdyke (1970), respectively. The cores are all plotted at a scale of 10 meters equals 1 million years. Arrows indicate range of uncertainty in dating short core segments.
199
the sediment transport capability of the Ross Ice Shelf. Today the ice shelf appears to be melting at the bottom over extensive areas (Swithinbank, 1970) so that much debris would probably be dropped before reaching the ice margin where calving takes place. A smaller, thinner ice shelf during the Gauss and early Matuyama, however, would have been less likely to lose mass by bottom melting (Thomas and Coslett, 1970), and thus greater amounts of icerafted material would have been delivered to the Ross Sea by calving and melting of icebergs. This assumed major change in the nature of the Ross Ice Shelf some time after the early Matuyama is consistent with the evidence of increased bottom water production at that time. It is probable, therefore, that cores obtained during the Ross Ice Shelf Project from beneath the ice shelf will reveal relatively coarse late Matuyama and Brunhes sediments. This research was supported by grant GA-28305 from the National Science Foundation. References Cox, A. 1969. Geomagnetic reversals. 245.
Science,
163: 237-
Foster, J . H., and N. D. Opdyke. 1970. Upper Miocene to Recent magnetic stratigraphy in deep-sea sediments. Journal of Geophysical Research, 75: 4465-4473. Hays, J . D., and N. D. Opdyke. 1967. Antarctic radiolaria, magnetic reversals, and climatic change. Science, 158(3804): 1001-1011. Kennett, J. P. 1966. Foraminiferal evidence of a shallow calcium carbonate solution boundary, Ross Sea, Antarctica. Science, 153(3732): 191-193. Opdyke, N. D., B. Glass, J . D. Hays, and J. Foster. 1966. Paleomagnetic study of antarctic deep sea cores. Science, 154(3747) : 349-357. Swithinbank, C. 1970. Ice movement in the McMurdo Sound area of Antarctica. In: International Symposium on Antarctic Glaciological Exploration. Belgium, International Association of Scientific Hydrology. Publication 86. p. 472487. Thomas, C. W. 1968. Antarctic ocean-floor fossils: their environments and possible significance as indicators of ice conditions. Pacific Science, 22(1): .45-51. Thomas, R. H., and P. H. Coslett. 1970. Bottom melting of ice shelves and the mass balance of Antarctica. Nature, 228(5266): 47-49. Vine, F. J . 1968. Magnetic anomalies associated with midocean ridges. In: The History of the Earth's Crust, E. A. Phinney, ed. Princeton University Press, p. 73-89. Watkins, N. D., and J. P. Kennett. 1971. Antarctic Bottom Water: major change in velocity during the Late Cenozoic between Australia and Antarctica. Science, 173(3999) 813-818.
78°
Paleomagnetic surveys of Amsterdam and St. Paul Islands, south Indian Ocean N. D. WATKINS Graduate School of Oceanography University of Rhode Island During January 1972, paleomagnetic surveys were made of the French-administered islands of Amsterdam and St. Paul (fig. 1) in the southeastern Indian Ocean. A total of 176 oriented cores were collected from 22 separate lavas on Amsterdam (fig. 2). On St. Paul, a total of 144 oriented cores were collected from 16 separate lavas (fig. 3). Preliminary results show that all lavas examined are normal polarity, consistent with an age of less than 0.7 million years. The data are being analysed in terms of geomagnetic secular variation models (Watkins et al., 1972) and variations in the nature of the earth's centered or offset axial dipole field (Watkins, 1972). The materials collected are also providing an opportunity to extend earlier geochemical studies (Girod et al., 1971; Gunn et al., 1971). Samples also have been provided to other laboratories for lead
2000
(AMSTERDAM
I 500
)
38°
j\0O
Fl
ST. PAUL
Figure 1 (right). Bathymetric chart of the Amsterdam—.-St. Paul Islands vicinity, southeast Indian Ocean.
200
ANTARCTIC JOURNAL
in the oceans. In: The Micropaleontology of Oceans
(Funnell and Reidel, eds.) Cambridge University Press. p. 545-565. Simonsen, R., and T. Kanaya. 1961. Notes on the marine species of the diatom genus Denticula Kutz. Internationale Revue der gesamten Hydrobiologie, 46:4. 498-513. Watkins, N. D., and J . P. Kennett. 1972. Regional sedimentary disconformatives and Upper Cenozoic changes in bottom water velocities between Australasia and Antarctica. Antarctic Research Series, 19: 273-293. Witt, 0. N. 1886. Ueber den Polierschiefer von ArchangelskKurojedowo im Gouv. Simbirsk. Verhandlungen der Rus-
sisch-Kaiserlichen Mineralogischen Gesellschaft. Series 2, 22: 137-177.
Late Cenozoic paleo-oceanography RICHARD H. FILLON Graduate School of Oceanography University of Rhode Island
During Cruises 27 and 32 of USNS Eltanin, 64 piston cores were taken from the continental shelf and slope within and just to the north of the Ross Sea. Paleomagnetic, paleontological, and sedimentological studies have been conducted on each core. A refined depth zonation consisting of five depth zones can be recognized on the basis of dead benthic foraminiferal assemblages (table). The division of benthic foraminiferal faunas in surface sediments within the Ross Sea into dominantly calcareous and dominantly arenaceous assemblages has been recognized by previous authors (Kennett, 1966; Thomas, 1968). So far, ages for 20 cores have been determined using paleomagnetic polarity patterns (Cox, 1969) and established radiolarian biostratigraphy (Opdyke et al., 1966; Hays and Opdyke, 1967). The age distribution of cores (fig.) offers an explanation for the foraminiferal faunal division in the Ross Sea. Calcareous benthic foraminiferal assemblages from Benthic foraminiferal de pth zonation in the Ross Sea.
Location
Depth range (meters) Type of fauna
Ross Sea (1) (2) (3) Slope north (4) of the Ross Sea (5)
0-550 dominantly calcareous 400-2000 " arenaceousa 550-3000 cccalcareous > 2200 arenaceous > 3000 " calcareous CC
a Arenaceous foraminifera in the Ross Sea construct their shells by cementing together sand grains and other noncalcareous particles.
September-October 1972
the continental shelf in the Ross Sea are restricted to sediment older than lower Matuyama (1.87 million years). Sediments bearing calcareous faunas are found exposed at the surface or separated by a disconformity from overlying Brunhes or late Matuyama sediments. The widespread erosion implied by the disconformity was caused probably by bottom current scour initiated by increased bottom-water velocities associated perhaps with a significant northward advance of the Ross Ice Shelf and with thicker pack ice formation in the Ross Sea. Previous evidence for a period of increased bottom-water velocity is presented by Watkins and Kennett (1971) who attribute an erosional disconformity in the southern ocean, south of Australia and Tasmania, to an increase in bottom-water production and velocities in post-Gilbert or post-Gauss time. In the Ross Sea, the change from calcareous to arenaceous faunas in post-Gauss time was probably effected by a rise in the calcium carbonate compensation depth caused by the increased production of undersaturated bottom water. Paralleling the faunal change was a sedimentological change. Gauss and lower Matuyama sediments are coarse, poorly sorted, and glacial marine, averaging about 30 percent sandsize and larger particles. Sediments above the disconformity contain generally less than 10 percent sand that is typically fine. Such a change in sedimentation could have been caused by a change in
Core logs showing paleomagnetic polarity (left) and benthic foraminiferal faunal type (right). Normal polarity intervals are portrayed in black, reversed polarity intervals in white. Dominantly arenaceous foraminiferal faunas are indicated by crosshatched bars, dominantly calcareous foraminiferal faunas by blank bars. Established paleomagnetic scales (Cox, 1969; Vine, 1968) are shown at the left of the diagram. Epoch boundaries delineated by heavy and light lines are according to Cox (1969) and Foster and Opdyke (1970), respectively. The cores are all plotted at a scale of 10 meters equals 1 million years. Arrows indicate range of uncertainty in dating short core segments.
199
the sediment transport capability of the Ross Ice Shelf. Today the ice shelf appears to be melting at the bottom over extensive areas (Swithinbank, 1970) so that much debris would probably be dropped before reaching the ice margin where calving takes place. A smaller, thinner ice shelf during the Gauss and early Matuyama, however, would have been less likely to lose mass by bottom melting (Thomas and Coslett, 1970), and thus greater amounts of icerafted material would have been delivered to the Ross Sea by calving and melting of icebergs. This assumed major change in the nature of the Ross Ice Shelf some time after the early Matuyama is consistent with the evidence of increased bottom water production at that time. It is probable, therefore, that cores obtained during the Ross Ice Shelf Project from beneath the ice shelf will reveal relatively coarse late Matuyama and Brunhes sediments. This research was supported by grant GA-28305 from the National Science Foundation. References Cox, A. 1969. Geomagnetic reversals. 245.
Science,
163: 237-
Foster, J . H., and N. D. Opdyke. 1970. Upper Miocene to Recent magnetic stratigraphy in deep-sea sediments. Journal of Geophysical Research, 75: 4465-4473. Hays, J . D., and N. D. Opdyke. 1967. Antarctic radiolaria, magnetic reversals, and climatic change. Science, 158(3804): 1001-1011. Kennett, J. P. 1966. Foraminiferal evidence of a shallow calcium carbonate solution boundary, Ross Sea, Antarctica. Science, 153(3732): 191-193. Opdyke, N. D., B. Glass, J . D. Hays, and J. Foster. 1966. Paleomagnetic study of antarctic deep sea cores. Science, 154(3747) : 349-357. Swithinbank, C. 1970. Ice movement in the McMurdo Sound area of Antarctica. In: International Symposium on Antarctic Glaciological Exploration. Belgium, International Association of Scientific Hydrology. Publication 86. p. 472487. Thomas, C. W. 1968. Antarctic ocean-floor fossils: their environments and possible significance as indicators of ice conditions. Pacific Science, 22(1): .45-51. Thomas, R. H., and P. H. Coslett. 1970. Bottom melting of ice shelves and the mass balance of Antarctica. Nature, 228(5266): 47-49. Vine, F. J . 1968. Magnetic anomalies associated with midocean ridges. In: The History of the Earth's Crust, E. A. Phinney, ed. Princeton University Press, p. 73-89. Watkins, N. D., and J. P. Kennett. 1971. Antarctic Bottom Water: major change in velocity during the Late Cenozoic between Australia and Antarctica. Science, 173(3999) 813-818.
78°
Paleomagnetic surveys of Amsterdam and St. Paul Islands, south Indian Ocean N. D. WATKINS Graduate School of Oceanography University of Rhode Island During January 1972, paleomagnetic surveys were made of the French-administered islands of Amsterdam and St. Paul (fig. 1) in the southeastern Indian Ocean. A total of 176 oriented cores were collected from 22 separate lavas on Amsterdam (fig. 2). On St. Paul, a total of 144 oriented cores were collected from 16 separate lavas (fig. 3). Preliminary results show that all lavas examined are normal polarity, consistent with an age of less than 0.7 million years. The data are being analysed in terms of geomagnetic secular variation models (Watkins et al., 1972) and variations in the nature of the earth's centered or offset axial dipole field (Watkins, 1972). The materials collected are also providing an opportunity to extend earlier geochemical studies (Girod et al., 1971; Gunn et al., 1971). Samples also have been provided to other laboratories for lead
2000
(AMSTERDAM
I 500
)
38°
j\0O
Fl
ST. PAUL
Figure 1 (right). Bathymetric chart of the Amsterdam—.-St. Paul Islands vicinity, southeast Indian Ocean.
200
ANTARCTIC JOURNAL
