Southern ocean Pliocene paleotemperatures based on ...
tributed tentatively to opposite preferred coiling senses in sexual and asexual generations (Thiede, 1971). This suggested explanation by Thiede is only one of the possible explanations in the case of N. pachyderma. This work was performed at the Graduate School of Oceanography, University of Rhode Island, during the tenure of a Fu!lbright-Hays Travel Grant, and it was supported by Victoria University of Wellington, and by National Science Foundation grant GV-28305.
References Be, A. W. H., and D. S. Tolderlund. 1971. Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian Oceans, In: Micro paleontology of Oceans (B. M. Funnell and W. R. Reidel, eds.). London, Cambridge University Press. 105-149. Collen, J. D., and P. Vella. 1973 Pliocene planktonic foraminifera, southern North Island, New Zealand. Journal of For. a,ninif era Research, 3: 13-29, plates 1-7. Gordon, A. L. 1972. Introduction to the physical oceanography of the southeast Indian Ocean. Antarctic Research Series, 19: 3.9 Kennetta J. P. 1968. Paleo-oceanographic aspects of the for. aminiferal zonation in the Upper Miocene-Lower Pliocene of New Zealand. Giornale di Geologia, 35(2): 143-156. Ruddiman, W. F., D. S. Tolderlund, and A. W. H. Be. 1970. Foraminiferal evidence of a modern warming of the North Atlantic Ocean. Deep Sea Research, 17: 141-155. Thiede, J. 1971. Variations in coiling ratios of Holocene planktonic foraminifera. Deep Sea Research, 18: 823-831.
Southern ocean Pliocene paleotemperatures based on silicoflagellates from deep sea cores PAUL F. CIESIELSKI
and FRED M. WEAVER
Department of Geology Florida State University A majority of detailed paleoclimatic analyses of sediments taken from the southern ocean have been concerned with the more easily recoverable Pleistocene-aged samples. Not much research has been completed on Middle and Lower Pliocene sediments due to the general paucity of older and continuous piston core sections of this age. Hays and Opdyke (1967) and Bandy et al. (1971) were the first to study the paleoclimatic history of the Antarctic as recorded during the Gauss and Gilbert magnetic epochs. These investigations revealed warm water radiolarians and diatoms characteristic of sub-tropical and tropical water masses at or below Gilbert event 'c". Bandy et al. (1971) also defined a cooling trend that occurs between Gilbert 'c' and "a" magnetic events, September-October 1973
with water temperatures decreasing from 20 0 to 5°C. Weaver (1973) completed a regional study of the Pliocene paleoclimatic history of the southern ocean, utilizing the latitudinal migration of sedimentary regimes adjacent to the coast of East Antarctica. He defines six intervals of climatic warming and cooling that occur throughout the Upper Gilbert and Gauss magnetic epochs. The most commonly utilized methods in paleoclimatological analysis have been coiling ratio studies of planktonic foraminifera, and studies of the ratios of cold and warm water radiolarian species through time. The applicability of these methods for paleoclimatic studies of Pliocene-aged sedimentary cores is limited because of (1) a relatively shallow carbonate compensation depth during the Pliocene (Weaver, 1973), and (2) the lack of longranging radiolarians of known paleoecology in Plioceneaged sediments of the southern ocean. Mandra and Mandra (1969) developed and demonstrated the reliability of a relatively new paleoecological temperature curve methodology that is dependent upon the silicoflagellate abundance of the genera Dictyocha and Distephanus. Jendrzejewski and Zarillo (1971) also showed the usefulness of silicoflagellates for interpreting paleoclimatic fluctuations in Pleistocene cores. Kennett (1972) illustrates that these fluctuations correspond well to those he defined by using planktonic foraminifera. A detailed micropaleontological study is complete for the abundances of the silicoflagellate genera Dictyocha and Distephanus found in two Lower Gauss and Upper Gilbert antarctic deep sea cores, E 38-8 (latitude 61048' S., longitude 149 1 54'E.) and E 50-28 (latitude 62054'S., longitude 150 0 41'E.) (figs. 1 and 2). Utilization of the silicoflagellate temperature curve, based upon Dictyocha/ Distephanus ratios delineates a general cooling trend between 4.0 and 3.7 million years before present (figs. 1 and 2). This Upper Gilbert cooling trend records a significant climatic deterioration within the southern ocean with surface water temperatures fluctuating from those commonly associated with waters north of the modern position of the subtropical convergence (>12° C.), to those found associated with antarctic waters (- WCO O SW 0 _i OF- 0 J
I4
LLJ
0
II
z
Iz LU _J
LU ---
0 0
3-
II
CL
IJ
SILICEOUS OOZE MUD SAND MOTTLED SPECIES ABUNDANCES 1 >02% 12-5% 5-10% 1>10%
1
Figure 1. Lithology and paleomagnetic stratigraphy of Eltanin core 50-28, showing abundances of selected radiolarians and silicoflagellates, Dictyocha/Distephanus ratios and a silicoflagel late temperature curve. Two different varieties of Distephanus speculum forma vanans, described by Gran and Braarud (1935), are distinguished from one another in the figure by subscripts 1 and 2 which refer respectively to figures 68B and 68A of Gran and Braarud (1935, p. 390). The presence of tropical collosphaerids within Lower Gilbert age sediments led Bandy et al. (1971) to speculate that surface water temperatures might have approached 20°C. at this time. E 50-28 and E-38-8 both contain collosphaerids below Gilbert event "a" near the base of each core, but their relative abundances are low when compared to the entire radiolarian fauna. Since silicoflagellate temperatures below Gilbert event "a" correspond to the lowest subtropical and subantarctic water mass temperatures, the presence of collosphaerids in these cores may indicate their previous environmental adaptation to colder surface waters during the Pliocene, as suggested by Kennett and Brunner (1973). From 3.7 million years before present to the Mammoth 296
event (B) within the Gauss normal epoch, surface water temperatures of the southern ocean south of Australia remained within a range similar to those found within this region today, except for one interval near the GaussGilbert boundary where silicoflagellate temperatures reflect subantarctic conditions (fig. 1). Dr. Norman D. Watkins, University of Rhode Island, is gratefully acknowledged for his continuing generosity in supplying unpublished paleomagnetic data. References Bandy, 0. L., R. E. Ca:ey, and R. C. Wright. 1971. Late NeoANTARCTIC JOURNAL
E 38-8 SILICOFLAGELLATES
WATER MASSES
DK:TY0CHA I DI STE S
RATIO Z
A A
Figure 2. Lithology and paleomagnetic stratigraphy of Eltanirt core 38-8, showing abundances of selected radiolarians and silicoflagellates, Dictyocha/Disfephanus ratios and a silicoflagellate temperature curve. Two different varieties of Distephanus speculum forma varians, described by Gran and Braarud (1935), are distinguished from one another in the figure by subscripts 1 and 2, which refer respectively to figures 68B and 68A of Gran and Braarud (1935, p. 390).
IIII uj LJ
ir
0
MI
8 8
SILICOFLASELLATE TEMPERATURE CURVEINC IAFTERMANDRA19721
B
RADIOLARIANS
3
0 25 50 75 10 5 10 15 20
Hi i
III
I
SILICEOUS OOZE MUD EI SAND MOTTLED SPECIES ABUNDANCES >0-2% 2-5% 5-10T', 1>106
gene planktonic zonation, magnetic reversals, and radiometric dates, Antarctic to the tropics. Antarctic Research Series, 15: 1-26. Gran, H. H., and T. Braarud. 1935. A quantitative study of the phytoplankton in the Bay of Fundy and the Gulf of Maine (including observations of hydrography, chemistry, and turbidity). Journal of the Biological Board of Canada, 1(5): 279.467. Hays, J . D.. and N. D. Opdyke. 1967. Antarctic radiolaria, magnetic reversals, and climate change. Science, 158: 10011011. Jendrzejewski, J . P., and G. A. Zarillo. 1971. Late Pleistocene paleotemperatures: si I icoflagel late and foraminiferal frequency changes in a subantarctic deep sea core. Antarctic Journal of the U.S, VT(S): 178-179. Kennett, J . P. 1972. The climatic and glacial record in Cenozoic sediments of the southern ocean. In: Palaeoecology of Africa. the surrounding islands and Antarctic (E. M. van Zinderen Bakker Sr., ed.). Cape Town, Balkema. VI: 59-78. Kennett, J . P., and C. A. Brunner. 1973. Antarctic Late Cenozoic glaciation: evidence for initiation of ice rafting and inferred bottom water activity. Geological Society of America. Bulletin, 84(6): 2043-2052. Mandra, Y. T., and H. Mandra. 1969. Silicoflagellates: a new tool for the study of antarctic Tertiary climates. Antarctic Journal of the U.S., TV(S): 172-174. Weaver, F. M. 1973. Pliocene paleoclimatic and paleoglacial history of East Antarctica recorded in deep sea piston cores. Sedimentology Research Laboratory, Department of Geology, Florida Stale University. Contribution, 36. 142 p. September-October 1973
Cretaceous and Paleogene cores from the Kerguelen Plateau, southern ocean F. AMRISAR KAI-IAROEDDIN, FRED M. WEAVER, SHERWOOD W. WISE, JR.
and
Department of Geology Florida State University, Tallahassee Although Pilo/Pleistocene sediments have been recovered from over 3,000 Eltanin cores, cores penetrating southern ocean sediments older than Miocene are so rare that they can be labeled 'flukes." The consistent recovery of older cores from the eastern flank of the Kerguelen Plateau, during the last phase of the Eltanin coring program, therefore is a noteworthy technical achievement and a subject of scientific interest. Cores taken on Eltanin Cruise 47, under the supervision of Weaver, include one containing Eocene chalk ooze. This core's age is in agreement with the presumed minimum age of the Plateau that is bounded on its eastern flank by magnetic anomaly 17 (McKenzie and Sclater, 1971). A primary 297
References Be, A. W. H., and D. S. Tolderlund. 1971. Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian Oceans, In: Micro paleontology of Oceans (B. M. Funnell and W. R. Reidel, eds.). London, Cambridge University Press. 105-149. Collen, J. D., and P. Vella. 1973 Pliocene planktonic foraminifera, southern North Island, New Zealand. Journal of For. a,ninif era Research, 3: 13-29, plates 1-7. Gordon, A. L. 1972. Introduction to the physical oceanography of the southeast Indian Ocean. Antarctic Research Series, 19: 3.9 Kennetta J. P. 1968. Paleo-oceanographic aspects of the for. aminiferal zonation in the Upper Miocene-Lower Pliocene of New Zealand. Giornale di Geologia, 35(2): 143-156. Ruddiman, W. F., D. S. Tolderlund, and A. W. H. Be. 1970. Foraminiferal evidence of a modern warming of the North Atlantic Ocean. Deep Sea Research, 17: 141-155. Thiede, J. 1971. Variations in coiling ratios of Holocene planktonic foraminifera. Deep Sea Research, 18: 823-831.
Southern ocean Pliocene paleotemperatures based on silicoflagellates from deep sea cores PAUL F. CIESIELSKI
and FRED M. WEAVER
Department of Geology Florida State University A majority of detailed paleoclimatic analyses of sediments taken from the southern ocean have been concerned with the more easily recoverable Pleistocene-aged samples. Not much research has been completed on Middle and Lower Pliocene sediments due to the general paucity of older and continuous piston core sections of this age. Hays and Opdyke (1967) and Bandy et al. (1971) were the first to study the paleoclimatic history of the Antarctic as recorded during the Gauss and Gilbert magnetic epochs. These investigations revealed warm water radiolarians and diatoms characteristic of sub-tropical and tropical water masses at or below Gilbert event 'c". Bandy et al. (1971) also defined a cooling trend that occurs between Gilbert 'c' and "a" magnetic events, September-October 1973
with water temperatures decreasing from 20 0 to 5°C. Weaver (1973) completed a regional study of the Pliocene paleoclimatic history of the southern ocean, utilizing the latitudinal migration of sedimentary regimes adjacent to the coast of East Antarctica. He defines six intervals of climatic warming and cooling that occur throughout the Upper Gilbert and Gauss magnetic epochs. The most commonly utilized methods in paleoclimatological analysis have been coiling ratio studies of planktonic foraminifera, and studies of the ratios of cold and warm water radiolarian species through time. The applicability of these methods for paleoclimatic studies of Pliocene-aged sedimentary cores is limited because of (1) a relatively shallow carbonate compensation depth during the Pliocene (Weaver, 1973), and (2) the lack of longranging radiolarians of known paleoecology in Plioceneaged sediments of the southern ocean. Mandra and Mandra (1969) developed and demonstrated the reliability of a relatively new paleoecological temperature curve methodology that is dependent upon the silicoflagellate abundance of the genera Dictyocha and Distephanus. Jendrzejewski and Zarillo (1971) also showed the usefulness of silicoflagellates for interpreting paleoclimatic fluctuations in Pleistocene cores. Kennett (1972) illustrates that these fluctuations correspond well to those he defined by using planktonic foraminifera. A detailed micropaleontological study is complete for the abundances of the silicoflagellate genera Dictyocha and Distephanus found in two Lower Gauss and Upper Gilbert antarctic deep sea cores, E 38-8 (latitude 61048' S., longitude 149 1 54'E.) and E 50-28 (latitude 62054'S., longitude 150 0 41'E.) (figs. 1 and 2). Utilization of the silicoflagellate temperature curve, based upon Dictyocha/ Distephanus ratios delineates a general cooling trend between 4.0 and 3.7 million years before present (figs. 1 and 2). This Upper Gilbert cooling trend records a significant climatic deterioration within the southern ocean with surface water temperatures fluctuating from those commonly associated with waters north of the modern position of the subtropical convergence (>12° C.), to those found associated with antarctic waters (- WCO O SW 0 _i OF- 0 J
I4
LLJ
0
II
z
Iz LU _J
LU ---
0 0
3-
II
CL
IJ
SILICEOUS OOZE MUD SAND MOTTLED SPECIES ABUNDANCES 1 >02% 12-5% 5-10% 1>10%
1
Figure 1. Lithology and paleomagnetic stratigraphy of Eltanin core 50-28, showing abundances of selected radiolarians and silicoflagellates, Dictyocha/Distephanus ratios and a silicoflagel late temperature curve. Two different varieties of Distephanus speculum forma vanans, described by Gran and Braarud (1935), are distinguished from one another in the figure by subscripts 1 and 2 which refer respectively to figures 68B and 68A of Gran and Braarud (1935, p. 390). The presence of tropical collosphaerids within Lower Gilbert age sediments led Bandy et al. (1971) to speculate that surface water temperatures might have approached 20°C. at this time. E 50-28 and E-38-8 both contain collosphaerids below Gilbert event "a" near the base of each core, but their relative abundances are low when compared to the entire radiolarian fauna. Since silicoflagellate temperatures below Gilbert event "a" correspond to the lowest subtropical and subantarctic water mass temperatures, the presence of collosphaerids in these cores may indicate their previous environmental adaptation to colder surface waters during the Pliocene, as suggested by Kennett and Brunner (1973). From 3.7 million years before present to the Mammoth 296
event (B) within the Gauss normal epoch, surface water temperatures of the southern ocean south of Australia remained within a range similar to those found within this region today, except for one interval near the GaussGilbert boundary where silicoflagellate temperatures reflect subantarctic conditions (fig. 1). Dr. Norman D. Watkins, University of Rhode Island, is gratefully acknowledged for his continuing generosity in supplying unpublished paleomagnetic data. References Bandy, 0. L., R. E. Ca:ey, and R. C. Wright. 1971. Late NeoANTARCTIC JOURNAL
E 38-8 SILICOFLAGELLATES
WATER MASSES
DK:TY0CHA I DI STE S
RATIO Z
A A
Figure 2. Lithology and paleomagnetic stratigraphy of Eltanirt core 38-8, showing abundances of selected radiolarians and silicoflagellates, Dictyocha/Disfephanus ratios and a silicoflagellate temperature curve. Two different varieties of Distephanus speculum forma varians, described by Gran and Braarud (1935), are distinguished from one another in the figure by subscripts 1 and 2, which refer respectively to figures 68B and 68A of Gran and Braarud (1935, p. 390).
IIII uj LJ
ir
0
MI
8 8
SILICOFLASELLATE TEMPERATURE CURVEINC IAFTERMANDRA19721
B
RADIOLARIANS
3
0 25 50 75 10 5 10 15 20
Hi i
III
I
SILICEOUS OOZE MUD EI SAND MOTTLED SPECIES ABUNDANCES >0-2% 2-5% 5-10T', 1>106
gene planktonic zonation, magnetic reversals, and radiometric dates, Antarctic to the tropics. Antarctic Research Series, 15: 1-26. Gran, H. H., and T. Braarud. 1935. A quantitative study of the phytoplankton in the Bay of Fundy and the Gulf of Maine (including observations of hydrography, chemistry, and turbidity). Journal of the Biological Board of Canada, 1(5): 279.467. Hays, J . D.. and N. D. Opdyke. 1967. Antarctic radiolaria, magnetic reversals, and climate change. Science, 158: 10011011. Jendrzejewski, J . P., and G. A. Zarillo. 1971. Late Pleistocene paleotemperatures: si I icoflagel late and foraminiferal frequency changes in a subantarctic deep sea core. Antarctic Journal of the U.S, VT(S): 178-179. Kennett, J . P. 1972. The climatic and glacial record in Cenozoic sediments of the southern ocean. In: Palaeoecology of Africa. the surrounding islands and Antarctic (E. M. van Zinderen Bakker Sr., ed.). Cape Town, Balkema. VI: 59-78. Kennett, J . P., and C. A. Brunner. 1973. Antarctic Late Cenozoic glaciation: evidence for initiation of ice rafting and inferred bottom water activity. Geological Society of America. Bulletin, 84(6): 2043-2052. Mandra, Y. T., and H. Mandra. 1969. Silicoflagellates: a new tool for the study of antarctic Tertiary climates. Antarctic Journal of the U.S., TV(S): 172-174. Weaver, F. M. 1973. Pliocene paleoclimatic and paleoglacial history of East Antarctica recorded in deep sea piston cores. Sedimentology Research Laboratory, Department of Geology, Florida Stale University. Contribution, 36. 142 p. September-October 1973
Cretaceous and Paleogene cores from the Kerguelen Plateau, southern ocean F. AMRISAR KAI-IAROEDDIN, FRED M. WEAVER, SHERWOOD W. WISE, JR.
and
Department of Geology Florida State University, Tallahassee Although Pilo/Pleistocene sediments have been recovered from over 3,000 Eltanin cores, cores penetrating southern ocean sediments older than Miocene are so rare that they can be labeled 'flukes." The consistent recovery of older cores from the eastern flank of the Kerguelen Plateau, during the last phase of the Eltanin coring program, therefore is a noteworthy technical achievement and a subject of scientific interest. Cores taken on Eltanin Cruise 47, under the supervision of Weaver, include one containing Eocene chalk ooze. This core's age is in agreement with the presumed minimum age of the Plateau that is bounded on its eastern flank by magnetic anomaly 17 (McKenzie and Sclater, 1971). A primary 297
