Continuing paleoenvironmental studies of Eltanin deep ...
Continuing paleoenvironmental studies of Eltanin deep sea sedimentary cores JAMES P. KENNETT
Graduate School of Oceanography University of Rhode Island In progress are biostratigraphic studies of Eltanin cores generally taken in the southern Indian Ocean during Cruises 40 to 50. Paleontological ages will be integrated with paleomagnetic stratigraphy determined by Dr. N. D. Watkins, University of Rhode Island. The primary objective is to determine general sedimentary patterns within the Late Cenozoic and to assess the effects of bottom erosion by bottom waters associated with the ctrcumantarctic current, as was done for the region south of Australia and New Zealand (Watkins and Kennett, 1971, 1972). The history of bottom water activity in the southern Indian Ocean is important in relation to other areas. Evidence exists that bottom water velocities increased dramatically during the Pliocene (Watkins & Kennett, 1971, 1972; Fillon, 1972). This may be related to the increased development of antarctic glaciation that also is reflected by greatly increased biogenic productivity associated with the Antarctic Convergence (Kennett et al., 1973) and with the initiation of widespread glaciation in the northern hemisphere (Berggren, 1972). It was found that fluctuations in the important antarctic radiolarian, A ntarctissa strelk o vi Petrushevskaya, closely are related to fluctuations in other temperature sensitive species in subantarctic cores (Keany, in press). Increased frequencies of this species reflect cooler climatic episodes. Establishment of frequency fluctuations in A. strelkovi, relative to other radiolaria, is a valuable rapid method for determining paleoclimatic curves for high latitude cores, that often are devoid of planktonic foraminifera. Planktonic foraminiferal assemblages of 32 surface sediment samples from high latitudes of the South Pacific have been subjected to a multivariate statistical classification method called principal coordinates analysis" (Malmgren and Kennett, 1973). On the basis of the presence or absence of 18 species of planktonic foraminifera, and of the frequency and coiling direction of the cold water species Globigerina pachyderma, the samples wçre clustered into 5 groups: one represents the subtropical, two the subantarctic, and two the antarctic water mass. This assemblage grouping method is suitable for investigations of past climatic changes (Malmgren & Kennett, 1973). This work is supported by National Science Foundation grant GV-28305. September-October 1973
References Berggren, W. A. 1972. Late Pliocene-Pleistocene glaciation. In: Laughton, A. S., W. A. Berggren et al., 1972. Initial Reports of the Deep Sea Drilling Project, XII: 953-963. Washington, D.C., U.S. Government Printing Office. Fillon, R. H. 1972. Evidence from the Ross Sea for widespread submarine erosion. Nature Physical Sciences, 283: 40-42. Keany, J . In preparation. New radiolarian paleoclimatic index in the Plio- Pleistoceneof the southern ocean. Kennett, J . P., R. E. Houtz, P. B. Andrews, A. R. Edwards, V. A. Gostin, M. Hajos, M. Hampton, D. G. Jenkins, S. V. Margolis, A. T. Ovenshine and K. Perch-Nielson. 1973. Deep Sea Drilling Project, leg 29 in the roaring forties. Geotimes, 18(7): 14-17. Malmgren, B. A., and J . P. Kennett. In press. Recent planktonic foraminiferal distribution in high latitudes of the South Pacific: multivariate statistical analysis. Paleo Geography, Paleo Climatology, and Paleo Ecology. 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: 813-818. Watkins, N. D., and J . P. Kennett. 1972. Regional sedimentary disconformities and Upper Cenozoic changes in bottom water velocities between Australia and Antarctica. Antarctic Re. search Series, 19: 273-293.
Sediment accumulation rates in the Tasman Sea J . K. OSMOND
Florida State University, Tallahassee J.
K.
COCHRAN*
Yale University The pattern of sediment accumulation rates in the Tasman Sea has been studied by applying the non-destructive gamma ray spectrometric method to 22 cores from Eltanin Cruises 16, 26, 34, 36, 38, and 39. The decrease in the 1.76 million electron volts gamma peak of BI-214 down through the first several meters of the cores is due to decay of one of its predecessors in the U-238 decay series, Th-230, with a half-life of 75,000 years. Two problems associated with this method proved not to be serious in determining Tasman Sea sedimentation rates: (a) evaluation of that component of the BI-214 activity in equilibrium with uranium; (b) recognition of diminished Bi-214 activity near core tops, due to migration and loss of Ra-226, intermediate between Th-230 and Bi-214. * Formerly of Florida State University, Tallahassee.
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Graduate School of Oceanography University of Rhode Island In progress are biostratigraphic studies of Eltanin cores generally taken in the southern Indian Ocean during Cruises 40 to 50. Paleontological ages will be integrated with paleomagnetic stratigraphy determined by Dr. N. D. Watkins, University of Rhode Island. The primary objective is to determine general sedimentary patterns within the Late Cenozoic and to assess the effects of bottom erosion by bottom waters associated with the ctrcumantarctic current, as was done for the region south of Australia and New Zealand (Watkins and Kennett, 1971, 1972). The history of bottom water activity in the southern Indian Ocean is important in relation to other areas. Evidence exists that bottom water velocities increased dramatically during the Pliocene (Watkins & Kennett, 1971, 1972; Fillon, 1972). This may be related to the increased development of antarctic glaciation that also is reflected by greatly increased biogenic productivity associated with the Antarctic Convergence (Kennett et al., 1973) and with the initiation of widespread glaciation in the northern hemisphere (Berggren, 1972). It was found that fluctuations in the important antarctic radiolarian, A ntarctissa strelk o vi Petrushevskaya, closely are related to fluctuations in other temperature sensitive species in subantarctic cores (Keany, in press). Increased frequencies of this species reflect cooler climatic episodes. Establishment of frequency fluctuations in A. strelkovi, relative to other radiolaria, is a valuable rapid method for determining paleoclimatic curves for high latitude cores, that often are devoid of planktonic foraminifera. Planktonic foraminiferal assemblages of 32 surface sediment samples from high latitudes of the South Pacific have been subjected to a multivariate statistical classification method called principal coordinates analysis" (Malmgren and Kennett, 1973). On the basis of the presence or absence of 18 species of planktonic foraminifera, and of the frequency and coiling direction of the cold water species Globigerina pachyderma, the samples wçre clustered into 5 groups: one represents the subtropical, two the subantarctic, and two the antarctic water mass. This assemblage grouping method is suitable for investigations of past climatic changes (Malmgren & Kennett, 1973). This work is supported by National Science Foundation grant GV-28305. September-October 1973
References Berggren, W. A. 1972. Late Pliocene-Pleistocene glaciation. In: Laughton, A. S., W. A. Berggren et al., 1972. Initial Reports of the Deep Sea Drilling Project, XII: 953-963. Washington, D.C., U.S. Government Printing Office. Fillon, R. H. 1972. Evidence from the Ross Sea for widespread submarine erosion. Nature Physical Sciences, 283: 40-42. Keany, J . In preparation. New radiolarian paleoclimatic index in the Plio- Pleistoceneof the southern ocean. Kennett, J . P., R. E. Houtz, P. B. Andrews, A. R. Edwards, V. A. Gostin, M. Hajos, M. Hampton, D. G. Jenkins, S. V. Margolis, A. T. Ovenshine and K. Perch-Nielson. 1973. Deep Sea Drilling Project, leg 29 in the roaring forties. Geotimes, 18(7): 14-17. Malmgren, B. A., and J . P. Kennett. In press. Recent planktonic foraminiferal distribution in high latitudes of the South Pacific: multivariate statistical analysis. Paleo Geography, Paleo Climatology, and Paleo Ecology. 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: 813-818. Watkins, N. D., and J . P. Kennett. 1972. Regional sedimentary disconformities and Upper Cenozoic changes in bottom water velocities between Australia and Antarctica. Antarctic Re. search Series, 19: 273-293.
Sediment accumulation rates in the Tasman Sea J . K. OSMOND
Florida State University, Tallahassee J.
K.
COCHRAN*
Yale University The pattern of sediment accumulation rates in the Tasman Sea has been studied by applying the non-destructive gamma ray spectrometric method to 22 cores from Eltanin Cruises 16, 26, 34, 36, 38, and 39. The decrease in the 1.76 million electron volts gamma peak of BI-214 down through the first several meters of the cores is due to decay of one of its predecessors in the U-238 decay series, Th-230, with a half-life of 75,000 years. Two problems associated with this method proved not to be serious in determining Tasman Sea sedimentation rates: (a) evaluation of that component of the BI-214 activity in equilibrium with uranium; (b) recognition of diminished Bi-214 activity near core tops, due to migration and loss of Ra-226, intermediate between Th-230 and Bi-214. * Formerly of Florida State University, Tallahassee.
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