DSDP sites 511 and 512
Paleogene oxygen isotope records for the subantarctic South Atlantic Ocean: DSDP sites 511 and 512
which appeared to reflect global climatic events (Shackleton and Kennett 1975). One of the most profound of these events occurred during the early Oligocene when, according to Shackleton and Kennett (1975), the build-up of glacial ice on the antarctic continent reached a critical threshold and thus initiated antarctic bottom water circulation. Disagreement about the exact timing and significance of this event (Corliss 1981; Keigwin 1980; Miller and Curry 1983) led to the acquisition of a carbonate-bearing sequence across the Eocene/Oligocene boundary on the Falkland Plateau in the Atlantic sector of the southern ocean during DSDP leg 71. Site 511 lies at a water depth of 2,589 meters on the western margin of the Maurice Ewing Bank (51°00.28'S 46°58.30'W). Site 512 is located on the eastern margin of the bank at a water depth of 1,846 meters (49°52.194'S 40°50.713'W). Together, these sites provide an almost continuous sequence of carbonate sediments through the Eocene/ Oligocene boundary (figure). The planktonic foraminifers analyzed from site 511 were a mixed assemblage of Glohigernia angiporoides and Globigerina aff. linaperta in varying ratios for each sample. From site 512, Glohigernia angiporoides and Glohigerina linaperta were used. The benthic foraminifers from site 511 were a mixed assemblage of several different genera. The benthic foraminifers analyzed from site 512 were Cihicidoides parki. Each foraminiferal sample was analyzed by standard procedures (Williams, Sommer, and Bender 1977). Sh ..leton's (1974) equation was used to derive the isotopic paleotemperature scales shown in the figure, because it is considered to be more accurate at the low temperatures. These paleotemperatures are by no means absolute in view of the various assumptions that must be made regarding the isotopic composition of oceanic water and potential vital effects in the
JAY P. MUZA Department of Geology Florida State University Tallahassee, Florida 32306
DOUGLAS F. WILLIAMS Department of Geology University of South Carolina Columbia, South Carolina 29208
SHERWOOD W. WISE, JR. Department of Geology Florida State University Ta l lahassee, Florida 32306
The most successful attempts to obtain suitable Tertiary sections in the southern ocean have been carried out in the Pacific sector where Deep Sea Drilling Project (DSDP) leg 29 cored long Tertiary sequences on the Campbell Plateau and Macquarie Ridge (Kennett and Houtz 1975). Stable isotope studies of these sediments documented that the general deterioration of Cenozoic climates was punctuated by a number of sharp steps
SITE 511
SITE 512
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Oxygen isotope variations in benthic and planktonic foraminiferal records in the middle Eocene section of site 512 and late Eocene-early Oligocene section of site 511, leg 71, South Atlantic. Fairly stable isotopic values characterize the middle Eocene. A clear isotopic enrichment (inferred temperature drop) occurs in the earliest Oligocene section accompanied by a distinct decoupling between the benthic and planktonic records (Muza, Williams, and Wise in press).
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ANTARCTIC JOURNAL
foraminifera. Beginning in the middle Eocene (site 512), paleotemperatures derived from oxygen isotopes fluctuated in a narrow temperature range between 8°C and 12°C (figure) with no appreciable difference between bottom- and surface-water temperatures. For the late Eocene and earliest Oligocene of site 511, isotopic paleotemperatures from both planktonic and benthic foraminifers indicate relatively warm temperatures similar to those in the middle Eocene of site 512 (figure). From core 18-1 through core 17-1, latest Eocene surface- and bottom-water temperatures dropped from about 12.5°C to 8°C (figure). Between cores 16-1 and 12-1, early Oligocene surface-water isotopic temperatures remained at about 11°C, but bottom-water temperatures at the site dropped sharply from 11°C to less than 3°C, at least an 8°C temperature difference (figure). The drastic drop in bottom-water temperatures probably reflects the initial development of the present-day system of bottom waters known as the psychrosphere (Kennett and Shackleton 1976). The largest change in bottom-water temperature values occurred within the early Oligocene rather than across the Eocene/Oligocene boundary as suggested by Keigwin (1980). An expansion in the antarctic water mass could perhaps explain the sharp drop and divergence of bottom- and surface-water temperatures at site 511. The isotopic records at sites 511 and 512 can be correlated with the foraminiferal and radiolarian data which also suggest a cooling of surface- and bottom-waters at site 511 and 512 (Basov and Krasheninnikov in press; Krasheninnikov and Basov in press; Weaver in press). This research was supported by National Science Foundation grants DPP 80-23696 to Douglas F Williams and DPP 80-20382 to Sherwood W. Wise, Jr. The three authors did the field work for this study in 1981. References Basov, I. A. and V. A. Krasheninnikov. In press. Benthonic foraminifers of the Mesozoic and Cenozoic sediments of the southwestern Atlantic as an indicator of paleoenvironment, DSDP leg 71. In W. C. Ludwig, V. Krasheninnikov et al., Initial Reports of the Deep Sea Drilling
Diachronous niche expansion and morphological adaptation by Globorotalia truncatulinoides in Late Quaternary sediments R. BAXTER PHARR, JR., DOUGLAS F WILLIAMS, and NANCY HEALY-WILLIAMS Department of Geology University of South Carolina Columbia, South Carolina 29208
G. truncatulinoides is a rather unique planktonic foraminiferal species. It originally evolved in tropical-warm subtropical waters from its ancestor, Globorotalia tosaensis (Takayanagi and Saito) near the Plio-Pleistocene boundary. Over a million years 1983 REVIEW
Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Corliss, B. H. 1981. Deep Sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary. Marine Micropaleontology, 6, 367-384. Keigwin, L. D., Jr. 1980. Oxygen and carbon isotope analyses from Eocene/Oligocene boundary at DSDP site 277. Nature, 287, 722-725. Kennett, J . P., R. E. Houtz et al. 1975. Initial Reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Kennett, J . P., and N. J . Shackleton. 1976. Oxygen isotopic evidence for the development of the psychrosphere 38 m. yr. ago. Nature, 260, 513-515. Krasheninnikov, V. A. and I. A. Basov. In press. Cenozoic planktonic foraminifers of the Falkland Plateau and Argentine Basin, DSDI' leg 71. In W. J . Ludwig, V. Krashenjnnjkov et al., initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Miller, K. G., and W. B. Curry. 1982. Eocene to Oligocene benthic foraminiferal isotopic record in the Bay cf Biscay. Nature, 296, 347-350. Muza, J . P., D. F. Williams, and S. W. Wise, Jr. In press. Paleogene oxygen isotopic records for DSDP sites 511 and 512, subantarctic South Atlantic Ocean: Paleotemperatures and the Eocene/Oligocene Boundary Event. In W. J . Ludwig, V. Krasheninnikov et al. Initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Shackleton, N. J . 1974. Attainment of isotopic equilibrium between ocean water and the benthonic foraminifera genus LJvigerina: Isotopic changes in the ocean during the last glacial. Colloques Internat. Centre Nat. Recherche Sci., 219, 203-210. Shackleton, N. J., and J. P. Kennett. 1975. Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation: Oxygen and carbon isotope analyses in DSDP sites 277, 279 and 281, In J . P. Kennett, R. E. Houtz et al., Initial Reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Weaver, F. M. In press. Cenozoic radiolarians from the southwest Atlantic, Falkland Plateau region, DSDP leg 71. In W. J . Ludwig, V. Krasheninnikov et al., Initial Reports of the Deep Sea Drilling Project, Vol.
71. Washington, D.C.: U.S. Government Printing Office. Williams, D. F., M. A. Sommer, and M. L. Bender. 1977. Carbon isotopic compositions of Recent planktonic foraminifera of the Indian Ocean. Earth and Planetary Science Letters, 36, 391-403.
later, G. truncatulino ides diachronously expanded its biogeographic range into subantarctic and antarctic waters at approximately 0.5 to 0.2 million years ago, respectively (figure 1) (Kennett 1970; Vella and Watkins 1975; Williams 1976a). Apparently, the southern boundary of G. truncatulinoides' paleobiogeographic range prior to isotope stage 13 (approximately 0.5 million years ago) was restricted by the subtropical convergence (5TC), a major water mass boundary between subtropical and subantarctic regions and a potential barrier preventing the dispersal of peripheral populations. Determining how and why this expansion occurred has important implications for biostratigraphy as well as the paleobiology of foraminifera. In addition, documentation of an environmentally controlled morphological trend in Globorotalia truncatulinoides (Healy-Williams and Williams 1981; Kennett 1968; Takayanagi, Niitsuma, and Sakai 1968) has led to interest in determining the establishment of this trend in the fossil record. The present study attempts to determine, using Fourier shape analysis (Ehrlich and Weinberg 1970; Scott 1974, 1975), whether a specific morphotype or morphological adaptation within this species 147
which appeared to reflect global climatic events (Shackleton and Kennett 1975). One of the most profound of these events occurred during the early Oligocene when, according to Shackleton and Kennett (1975), the build-up of glacial ice on the antarctic continent reached a critical threshold and thus initiated antarctic bottom water circulation. Disagreement about the exact timing and significance of this event (Corliss 1981; Keigwin 1980; Miller and Curry 1983) led to the acquisition of a carbonate-bearing sequence across the Eocene/Oligocene boundary on the Falkland Plateau in the Atlantic sector of the southern ocean during DSDP leg 71. Site 511 lies at a water depth of 2,589 meters on the western margin of the Maurice Ewing Bank (51°00.28'S 46°58.30'W). Site 512 is located on the eastern margin of the bank at a water depth of 1,846 meters (49°52.194'S 40°50.713'W). Together, these sites provide an almost continuous sequence of carbonate sediments through the Eocene/ Oligocene boundary (figure). The planktonic foraminifers analyzed from site 511 were a mixed assemblage of Glohigernia angiporoides and Globigerina aff. linaperta in varying ratios for each sample. From site 512, Glohigernia angiporoides and Glohigerina linaperta were used. The benthic foraminifers from site 511 were a mixed assemblage of several different genera. The benthic foraminifers analyzed from site 512 were Cihicidoides parki. Each foraminiferal sample was analyzed by standard procedures (Williams, Sommer, and Bender 1977). Sh ..leton's (1974) equation was used to derive the isotopic paleotemperature scales shown in the figure, because it is considered to be more accurate at the low temperatures. These paleotemperatures are by no means absolute in view of the various assumptions that must be made regarding the isotopic composition of oceanic water and potential vital effects in the
JAY P. MUZA Department of Geology Florida State University Tallahassee, Florida 32306
DOUGLAS F. WILLIAMS Department of Geology University of South Carolina Columbia, South Carolina 29208
SHERWOOD W. WISE, JR. Department of Geology Florida State University Ta l lahassee, Florida 32306
The most successful attempts to obtain suitable Tertiary sections in the southern ocean have been carried out in the Pacific sector where Deep Sea Drilling Project (DSDP) leg 29 cored long Tertiary sequences on the Campbell Plateau and Macquarie Ridge (Kennett and Houtz 1975). Stable isotope studies of these sediments documented that the general deterioration of Cenozoic climates was punctuated by a number of sharp steps
SITE 511
SITE 512
-
ok
I I II I I
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I I I I I Ih.
\
\\
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MIDDLE EOCENE
0
-
II CD
LATE EARLY OLIGOCENE EOCENE
Oxygen isotope variations in benthic and planktonic foraminiferal records in the middle Eocene section of site 512 and late Eocene-early Oligocene section of site 511, leg 71, South Atlantic. Fairly stable isotopic values characterize the middle Eocene. A clear isotopic enrichment (inferred temperature drop) occurs in the earliest Oligocene section accompanied by a distinct decoupling between the benthic and planktonic records (Muza, Williams, and Wise in press).
146
ANTARCTIC JOURNAL
foraminifera. Beginning in the middle Eocene (site 512), paleotemperatures derived from oxygen isotopes fluctuated in a narrow temperature range between 8°C and 12°C (figure) with no appreciable difference between bottom- and surface-water temperatures. For the late Eocene and earliest Oligocene of site 511, isotopic paleotemperatures from both planktonic and benthic foraminifers indicate relatively warm temperatures similar to those in the middle Eocene of site 512 (figure). From core 18-1 through core 17-1, latest Eocene surface- and bottom-water temperatures dropped from about 12.5°C to 8°C (figure). Between cores 16-1 and 12-1, early Oligocene surface-water isotopic temperatures remained at about 11°C, but bottom-water temperatures at the site dropped sharply from 11°C to less than 3°C, at least an 8°C temperature difference (figure). The drastic drop in bottom-water temperatures probably reflects the initial development of the present-day system of bottom waters known as the psychrosphere (Kennett and Shackleton 1976). The largest change in bottom-water temperature values occurred within the early Oligocene rather than across the Eocene/Oligocene boundary as suggested by Keigwin (1980). An expansion in the antarctic water mass could perhaps explain the sharp drop and divergence of bottom- and surface-water temperatures at site 511. The isotopic records at sites 511 and 512 can be correlated with the foraminiferal and radiolarian data which also suggest a cooling of surface- and bottom-waters at site 511 and 512 (Basov and Krasheninnikov in press; Krasheninnikov and Basov in press; Weaver in press). This research was supported by National Science Foundation grants DPP 80-23696 to Douglas F Williams and DPP 80-20382 to Sherwood W. Wise, Jr. The three authors did the field work for this study in 1981. References Basov, I. A. and V. A. Krasheninnikov. In press. Benthonic foraminifers of the Mesozoic and Cenozoic sediments of the southwestern Atlantic as an indicator of paleoenvironment, DSDP leg 71. In W. C. Ludwig, V. Krasheninnikov et al., Initial Reports of the Deep Sea Drilling
Diachronous niche expansion and morphological adaptation by Globorotalia truncatulinoides in Late Quaternary sediments R. BAXTER PHARR, JR., DOUGLAS F WILLIAMS, and NANCY HEALY-WILLIAMS Department of Geology University of South Carolina Columbia, South Carolina 29208
G. truncatulinoides is a rather unique planktonic foraminiferal species. It originally evolved in tropical-warm subtropical waters from its ancestor, Globorotalia tosaensis (Takayanagi and Saito) near the Plio-Pleistocene boundary. Over a million years 1983 REVIEW
Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Corliss, B. H. 1981. Deep Sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary. Marine Micropaleontology, 6, 367-384. Keigwin, L. D., Jr. 1980. Oxygen and carbon isotope analyses from Eocene/Oligocene boundary at DSDP site 277. Nature, 287, 722-725. Kennett, J . P., R. E. Houtz et al. 1975. Initial Reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Kennett, J . P., and N. J . Shackleton. 1976. Oxygen isotopic evidence for the development of the psychrosphere 38 m. yr. ago. Nature, 260, 513-515. Krasheninnikov, V. A. and I. A. Basov. In press. Cenozoic planktonic foraminifers of the Falkland Plateau and Argentine Basin, DSDI' leg 71. In W. J . Ludwig, V. Krashenjnnjkov et al., initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Miller, K. G., and W. B. Curry. 1982. Eocene to Oligocene benthic foraminiferal isotopic record in the Bay cf Biscay. Nature, 296, 347-350. Muza, J . P., D. F. Williams, and S. W. Wise, Jr. In press. Paleogene oxygen isotopic records for DSDP sites 511 and 512, subantarctic South Atlantic Ocean: Paleotemperatures and the Eocene/Oligocene Boundary Event. In W. J . Ludwig, V. Krasheninnikov et al. Initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington, D.C.: U.S. Government Printing Office. Shackleton, N. J . 1974. Attainment of isotopic equilibrium between ocean water and the benthonic foraminifera genus LJvigerina: Isotopic changes in the ocean during the last glacial. Colloques Internat. Centre Nat. Recherche Sci., 219, 203-210. Shackleton, N. J., and J. P. Kennett. 1975. Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation: Oxygen and carbon isotope analyses in DSDP sites 277, 279 and 281, In J . P. Kennett, R. E. Houtz et al., Initial Reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Weaver, F. M. In press. Cenozoic radiolarians from the southwest Atlantic, Falkland Plateau region, DSDP leg 71. In W. J . Ludwig, V. Krasheninnikov et al., Initial Reports of the Deep Sea Drilling Project, Vol.
71. Washington, D.C.: U.S. Government Printing Office. Williams, D. F., M. A. Sommer, and M. L. Bender. 1977. Carbon isotopic compositions of Recent planktonic foraminifera of the Indian Ocean. Earth and Planetary Science Letters, 36, 391-403.
later, G. truncatulino ides diachronously expanded its biogeographic range into subantarctic and antarctic waters at approximately 0.5 to 0.2 million years ago, respectively (figure 1) (Kennett 1970; Vella and Watkins 1975; Williams 1976a). Apparently, the southern boundary of G. truncatulinoides' paleobiogeographic range prior to isotope stage 13 (approximately 0.5 million years ago) was restricted by the subtropical convergence (5TC), a major water mass boundary between subtropical and subantarctic regions and a potential barrier preventing the dispersal of peripheral populations. Determining how and why this expansion occurred has important implications for biostratigraphy as well as the paleobiology of foraminifera. In addition, documentation of an environmentally controlled morphological trend in Globorotalia truncatulinoides (Healy-Williams and Williams 1981; Kennett 1968; Takayanagi, Niitsuma, and Sakai 1968) has led to interest in determining the establishment of this trend in the fossil record. The present study attempts to determine, using Fourier shape analysis (Ehrlich and Weinberg 1970; Scott 1974, 1975), whether a specific morphotype or morphological adaptation within this species 147
