Late Miocene paieociimatoiogy In the subantarctic water ...
Daiziel, I. W. D., Elliot, D. H., Thomson, J. W., Thomson, M. R. A., Wells, N.A., and Zinsmeister, W. J. 1977. Geologic studies in the South Orkney Islands: R/V Hero cruise 77-1, January 1977. Antarctic Journal of the U.S., 12(4), 98-101. Forsythe, R. D. 1978. Geologic reconnaissance of the pre-Late Jurassic basement: Patagonian Andes. Antarctic Journal of the U.S., 13(4),10-12.
Forsythe, R. D., and Allen, R. B. In press. The basement of Peninsula Staines, X11 2 Region, Province of Ultima Esperanza. Revista de Geologia de Chile. Forsythe, R. D., and Mpodozis, C. 1979. El Archipielago Madre de Dios, Patagonia occidental, Magallanes: Rasgos generales de la estratigrafia y estructura del "basamento" pre-Jurassico superior. Revista Geologia de Chile, 7, 13-29.
Late Miocene paieociimatoiogy In the subantarctic water mass, southwest Pacific
the northern edge of the subantarctic water mass (Sub- tropical Convergence) appears to have been relatively stable during much of the Miocene, with a distinct northward expansion during the late Miocene (Kennett, Houtz et al. 1975). Today, the Subtropical Convergence is much farther to the south than in the Late Miocene (figure 1). Faunal TOM S. LouiTr and JAMES P. KENNEYr migrations from the south and north (e.g. Neogloboquadrina pachyderma) (Kennett and Vella 1975) and the formation of Graduate School of Oceanography assemblages unique to subantarctic water appear to have University of Rhode Island occurred in response to climatic variation (Kennett 1978). Kingston, Rhode Island 02881 For example, between the Middle and Late Miocene ages there was a reduction in diversity of planktonic forarninifera in the subantarctic (from 13 to 15 species to 8 to The Late Miocene paleoclimatic history of the sub9 species), perhaps in response to increasing refrigeration in antarctic water mass based on quantitative microthe Late Miocene (Kennett 1978). Planktonic foraminiferal paleontology and stable isotope studies was obtained from populations within the subantarctic water show recogtwo sedimentary sequences in the southwest Pacific: (1) nizable species assemblage changes, thus providing an exDeep Sea Drilling Project (DsDP) site 281 located on the cellent record of climatic variation in the Late Cenozoic age. South Tasman Rise (1,600-meter water depth) and (2) the Planktonic foraminiferal studies at site 281 and Blind Blind River section in the South Island of New Zealand River within the subantarctic water mass show climatic and (figure 1). Both sequences were covered by subantarctic oceanographic changes that are in agreement with the water during the Late Miocene. overall picture of the Late Miocene age as a period of inThe subantarctic water mass is transitional between antcreasing refrigeration. Increasing abundances of sinistrally arctic waters to the south and cool subtropical waters to the coiling N. pachyderma, increasing abundances of N. pachynorth. Micropaleontological evidence suggests that the sub- - derma, decreasing numbers of G. bulloides, and decreasing antarctic water mass formed in the Early to Middle Miocene diversity within planktonic foraminiferal assemblages in age (Burns 1977; Edwards and Perch-Nielsen 1975; and Kenthe Kapitean Stage all culminate in a latest Miocene surface nett 1978). However, the boundary between the antarctic water "cooling event" at both site 281 and Blind River and subantarctic water masses (the Polar Front) shifted (figure 2). Faunal parameters from the subantarctic water both north and south during the Neogene. The position of mass appear to be far more sensitive to surface water temperature changes than do similar faunal parameters reS35 corded by Kennett and Vella (1975) at DSDP site 284 in the cool subtropical water mass to the north. ___...< / BLIND RIVER 40-1 Benthonic foraminiferal oxygen isotopic data from site -OSOP 284 \1I NEW 281 and Blind River (figure 3) and other circum-Pacific cores ZEALAND 45 suggest that ice volume, after an initial buildup in the MidSOUTH SUBTROPICAL TASMAN dle Miocene age at approximately 14 million years (Shack50 RISE OSDP 281 CAMPBELL CONVERGENCE leton and Kennett 1975), remained relatively constant PLATEAU throughout the Late Miocene age, with several distinct events indicative of warmer or less glacial conditions. The 55 planktonic foraminiferal oxygen isotopic record parallels POLAR FRON the faunal climatic record for subantarctic surface waters, 60thus adding to the theory that the latest Miocene age (KapiJ - - — ESTIMATED BQADARY LATE MIOCENE tean) was a time of increased refrigeration but not necesSU8MATAPCTIC WATER 79955 (KEverr. 966; KENNETT ACA WATKINS. 1974; sarily of increased ice volume. SAP6cETTA, 1978) 65 The Late Miocene benthonic foraminiferal carbon isoPRESENT DAY BQJNDARY SUBNTMACT IC WATER MASS topic records from site 281 and Blind River both show a (s.1972) permanent decrease in 5 13C (carbon 13) at the base of the ANTARCTICA Kapitean (figure 3). Loutit and Kennett (1979) dated this E130 140 150 160 170 180 170 W160 carbon shift at 6.2 to 6.3 ± 0.1 million years. Keigwin and Figure 1. Location of DSDP Site 281, on the South Tasman Shackleton (1980) also dated a similar shift, in piston core Rise; on the Challenger Plateau and the Blind River section, RC12-66, at 6.2 ± 0.1 million years. The carbon shift apNew Zealand. pears to represent some permanent and important change CF
CF
1980 REviEw
111
Figure 2. Shannon Wiener diversity index, percent frequency N. pachyderms, age and New Zealand Stage correlations for Blind River and Site 281. Low diversity index values and high frequencies of N. pachyderms indicate cool surface water temperatures.
in the paleooceanographic and geochemical state of the oceans. Bender and Keigwin (1979) have speculated that the shift may reflect either a global decrease in upwelling rate or a change in abyssal circulation patterns. Whatever the cause, the carbon shift is an extremely valuable timestratigraphic marker within the Pacific and Indian Oceans. Regional biostratigraphic zonations can now be correlated with the ö'3C and paleomagnetic records, and radiometric ages can be assigned to biostratigraphic events. It can be concluded that the Late Miocene age was a time of considerable climatic and oceanographic change in the subantarctic water mass. The major historical events at Blind River in chronological order are: (1) A latest Miocene (Kapitean Stage) surface water cooling event 6.2 million years ago. An apparent change in the stability of the paleoclimatic record also occurred at that time, from warmer, relatively stable conditions in the Tongaporutuan to greater surface water temperature oscillations during the Kapitean and earliest Pliocene ages (Kennett and Watkins 1974). (2) A dramatic permanent shift in the state of the oceans, indicated by the ö' 3C record, 6.3 to 6.2 ± 0.1 million years ago Lbutit and Kennett 1979). (3) A distinct shallowing of water depths, suggested by benthonic foraminiferal species assemblage changes (Kennett 1966), 6.1 million years ago. The 112
history at site 281 is remarkably similar to the Blind River section, with one exception: Faunal evidence at site 281 shows that a major surface water cooling event occurred at least 100,000 years before the carbon shift, whereas at Blind River the first major surface cooling event appears to have occurred simultaneously with the carbon shift. However, the sampling interval at Blind River is not close enough to allow accurate dating of the cooling event, which may have begun as early as 6.4 million years ago. Finally, it appears that the planktonic foraminiferal paleoclimatic indicators obtained from the subantarctic water mass provide a very sensitive record of relative temperature change with which we can study Late Cenozoic climate and oceanographic changes. This work was supported by National Science Foundation grant DPP 78-08512 to J. P. Kennett. We would like to thank T. C. Moore, Jr., and L. D. Keigwin, Jr., for providing helpful comments throughout the course of this project. References Bender, M. L., and Keigwin, L. D., Jr. 1979. Speculations about the Upper Miocene change in abyssal Pacific dissolved bicarbonate ' 3C. Earth and Planetary Science Letters, 45, 383-393. ANTARCTIC JOURNAL
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Loutit, T. S., and Kennett, J . P. 1979. Application of carbon isotope stratigraphy to Late Miocene shallow marine sediments, New Zealand. Science, 204, 1196-1199. MacDougall, I., Saemundsson, K., Johannesson, H., Watkins, N. 0., Kristjansson, L. 1977. Extension of the geomagnetic polarity time scale to G.S.M.Y.: K-Ar dating, geological and paleomagnetic study of a 3,500-M lava succession in western Iceland. Geological Society of America Bulletin, 88, 1-15.
USCGC Glacier JOHN B. ANDERSON
Deep Freeze 80 and DENNIS D. KURTZ
Department of Geology Rice University Houston, Texas 77001
On 19 December 1979 the USCGC Glacier left Auckland, New Zealand, to conduct marine geologic investigations in the valley glacial-marine sedimentary environments bordering the Transantarctic Mountains. The objectives were: (1) to occupy closely spaced geologic stations along the Pennell Coast, in Terra Nova Bay, and in McMurdo Sound; (2) to conduct a reconnaissance study of other portions of the western Ross Sea; (3) to conduct bathymetric surveys in uncharted waters; (4) to sample ice-rafted detritus from icebergs and floating ice; and (5) to chart the current positions of ice tongues and glacier termini using the ship's radar. During the cruise, a series of seamounts and a possible southern extension of the Balleny Fracture Zone from the Balleny Islands to Cape Adare were discovered. Later efforts focused on delineating these features in greater detail. Marine geologic operations were conducted along with additional ship duties as part of Deep Freeze 80 until 11 February 1980, when the Glacier departed the Ross Sea. Geologic Observations. This cruise marks the first detailed geologic survey of any portion of the antarctic valley glacial-marine sedimentary environment. Closely spaced piston cores and bottom-grab samples were obtained at 66 stations off the Pennell Coast between 163°E and 171°E (figures 1 and 2) and at 41 stations in and around Terra Nova Bay (figures 1 and 3). In addition, 24 more widely spaced stations were occupied as part of a general survey of the western Ross Sea (figure 1). Sixty-two stations were taken in McMurdo Sound and the Ross Island area (figure 1). In all, 193 stations were occupied; 167 piston cores and 133 bottom-grab samples were collected at 171 piston coring stations and 22 bottom-grab stations. Preliminary bathymetric maps of the Pennell Coast (figure 2) and the Terra Nova Bay area (figure 3) were constructed on board ship using available existing data and bathymetric data acquired during Deep Freeze 80. The continental shelf off the Pennell Coast averages 250 meters deep but is dissected by several northward-trending canyons. Each of these canyons represents the seaward extension of major glacial valleys, and some exceed 1,000 meters 114
Sancetta, C. 1978. Neogene Pacific microfossils and paleooceanography, Marine Micropaleontology, 3, 347-376. Shackleton, N. J . , and Kennett, J. P. 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 (Eds.), Initial reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office.
•29 17OE1 1127 .30 1126 25 23 31 24 21 22 19 0 166 70*S 35 36 33 40 L0 / ".42 12 3 11 - ' 4) 5; _ 0169 I55 63 65 t'53 l6Ot17 1591151 10 el _JjT2SL\ 11)7) ''';C( 156 J .-,.J,U_ 67— ;4v9j1 ', 0172 )46 I48/ 0 NO RECOVERY
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Figure 1. Deep Freeze 80 station locations In the northwestern and southwestern Ross Sea. ANTARCTIC JOURNAL
Forsythe, R. D., and Allen, R. B. In press. The basement of Peninsula Staines, X11 2 Region, Province of Ultima Esperanza. Revista de Geologia de Chile. Forsythe, R. D., and Mpodozis, C. 1979. El Archipielago Madre de Dios, Patagonia occidental, Magallanes: Rasgos generales de la estratigrafia y estructura del "basamento" pre-Jurassico superior. Revista Geologia de Chile, 7, 13-29.
Late Miocene paieociimatoiogy In the subantarctic water mass, southwest Pacific
the northern edge of the subantarctic water mass (Sub- tropical Convergence) appears to have been relatively stable during much of the Miocene, with a distinct northward expansion during the late Miocene (Kennett, Houtz et al. 1975). Today, the Subtropical Convergence is much farther to the south than in the Late Miocene (figure 1). Faunal TOM S. LouiTr and JAMES P. KENNEYr migrations from the south and north (e.g. Neogloboquadrina pachyderma) (Kennett and Vella 1975) and the formation of Graduate School of Oceanography assemblages unique to subantarctic water appear to have University of Rhode Island occurred in response to climatic variation (Kennett 1978). Kingston, Rhode Island 02881 For example, between the Middle and Late Miocene ages there was a reduction in diversity of planktonic forarninifera in the subantarctic (from 13 to 15 species to 8 to The Late Miocene paleoclimatic history of the sub9 species), perhaps in response to increasing refrigeration in antarctic water mass based on quantitative microthe Late Miocene (Kennett 1978). Planktonic foraminiferal paleontology and stable isotope studies was obtained from populations within the subantarctic water show recogtwo sedimentary sequences in the southwest Pacific: (1) nizable species assemblage changes, thus providing an exDeep Sea Drilling Project (DsDP) site 281 located on the cellent record of climatic variation in the Late Cenozoic age. South Tasman Rise (1,600-meter water depth) and (2) the Planktonic foraminiferal studies at site 281 and Blind Blind River section in the South Island of New Zealand River within the subantarctic water mass show climatic and (figure 1). Both sequences were covered by subantarctic oceanographic changes that are in agreement with the water during the Late Miocene. overall picture of the Late Miocene age as a period of inThe subantarctic water mass is transitional between antcreasing refrigeration. Increasing abundances of sinistrally arctic waters to the south and cool subtropical waters to the coiling N. pachyderma, increasing abundances of N. pachynorth. Micropaleontological evidence suggests that the sub- - derma, decreasing numbers of G. bulloides, and decreasing antarctic water mass formed in the Early to Middle Miocene diversity within planktonic foraminiferal assemblages in age (Burns 1977; Edwards and Perch-Nielsen 1975; and Kenthe Kapitean Stage all culminate in a latest Miocene surface nett 1978). However, the boundary between the antarctic water "cooling event" at both site 281 and Blind River and subantarctic water masses (the Polar Front) shifted (figure 2). Faunal parameters from the subantarctic water both north and south during the Neogene. The position of mass appear to be far more sensitive to surface water temperature changes than do similar faunal parameters reS35 corded by Kennett and Vella (1975) at DSDP site 284 in the cool subtropical water mass to the north. ___...< / BLIND RIVER 40-1 Benthonic foraminiferal oxygen isotopic data from site -OSOP 284 \1I NEW 281 and Blind River (figure 3) and other circum-Pacific cores ZEALAND 45 suggest that ice volume, after an initial buildup in the MidSOUTH SUBTROPICAL TASMAN dle Miocene age at approximately 14 million years (Shack50 RISE OSDP 281 CAMPBELL CONVERGENCE leton and Kennett 1975), remained relatively constant PLATEAU throughout the Late Miocene age, with several distinct events indicative of warmer or less glacial conditions. The 55 planktonic foraminiferal oxygen isotopic record parallels POLAR FRON the faunal climatic record for subantarctic surface waters, 60thus adding to the theory that the latest Miocene age (KapiJ - - — ESTIMATED BQADARY LATE MIOCENE tean) was a time of increased refrigeration but not necesSU8MATAPCTIC WATER 79955 (KEverr. 966; KENNETT ACA WATKINS. 1974; sarily of increased ice volume. SAP6cETTA, 1978) 65 The Late Miocene benthonic foraminiferal carbon isoPRESENT DAY BQJNDARY SUBNTMACT IC WATER MASS topic records from site 281 and Blind River both show a (s.1972) permanent decrease in 5 13C (carbon 13) at the base of the ANTARCTICA Kapitean (figure 3). Loutit and Kennett (1979) dated this E130 140 150 160 170 180 170 W160 carbon shift at 6.2 to 6.3 ± 0.1 million years. Keigwin and Figure 1. Location of DSDP Site 281, on the South Tasman Shackleton (1980) also dated a similar shift, in piston core Rise; on the Challenger Plateau and the Blind River section, RC12-66, at 6.2 ± 0.1 million years. The carbon shift apNew Zealand. pears to represent some permanent and important change CF
CF
1980 REviEw
111
Figure 2. Shannon Wiener diversity index, percent frequency N. pachyderms, age and New Zealand Stage correlations for Blind River and Site 281. Low diversity index values and high frequencies of N. pachyderms indicate cool surface water temperatures.
in the paleooceanographic and geochemical state of the oceans. Bender and Keigwin (1979) have speculated that the shift may reflect either a global decrease in upwelling rate or a change in abyssal circulation patterns. Whatever the cause, the carbon shift is an extremely valuable timestratigraphic marker within the Pacific and Indian Oceans. Regional biostratigraphic zonations can now be correlated with the ö'3C and paleomagnetic records, and radiometric ages can be assigned to biostratigraphic events. It can be concluded that the Late Miocene age was a time of considerable climatic and oceanographic change in the subantarctic water mass. The major historical events at Blind River in chronological order are: (1) A latest Miocene (Kapitean Stage) surface water cooling event 6.2 million years ago. An apparent change in the stability of the paleoclimatic record also occurred at that time, from warmer, relatively stable conditions in the Tongaporutuan to greater surface water temperature oscillations during the Kapitean and earliest Pliocene ages (Kennett and Watkins 1974). (2) A dramatic permanent shift in the state of the oceans, indicated by the ö' 3C record, 6.3 to 6.2 ± 0.1 million years ago Lbutit and Kennett 1979). (3) A distinct shallowing of water depths, suggested by benthonic foraminiferal species assemblage changes (Kennett 1966), 6.1 million years ago. The 112
history at site 281 is remarkably similar to the Blind River section, with one exception: Faunal evidence at site 281 shows that a major surface water cooling event occurred at least 100,000 years before the carbon shift, whereas at Blind River the first major surface cooling event appears to have occurred simultaneously with the carbon shift. However, the sampling interval at Blind River is not close enough to allow accurate dating of the cooling event, which may have begun as early as 6.4 million years ago. Finally, it appears that the planktonic foraminiferal paleoclimatic indicators obtained from the subantarctic water mass provide a very sensitive record of relative temperature change with which we can study Late Cenozoic climate and oceanographic changes. This work was supported by National Science Foundation grant DPP 78-08512 to J. P. Kennett. We would like to thank T. C. Moore, Jr., and L. D. Keigwin, Jr., for providing helpful comments throughout the course of this project. References Bender, M. L., and Keigwin, L. D., Jr. 1979. Speculations about the Upper Miocene change in abyssal Pacific dissolved bicarbonate ' 3C. Earth and Planetary Science Letters, 45, 383-393. ANTARCTIC JOURNAL
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Loutit, T. S., and Kennett, J . P. 1979. Application of carbon isotope stratigraphy to Late Miocene shallow marine sediments, New Zealand. Science, 204, 1196-1199. MacDougall, I., Saemundsson, K., Johannesson, H., Watkins, N. 0., Kristjansson, L. 1977. Extension of the geomagnetic polarity time scale to G.S.M.Y.: K-Ar dating, geological and paleomagnetic study of a 3,500-M lava succession in western Iceland. Geological Society of America Bulletin, 88, 1-15.
USCGC Glacier JOHN B. ANDERSON
Deep Freeze 80 and DENNIS D. KURTZ
Department of Geology Rice University Houston, Texas 77001
On 19 December 1979 the USCGC Glacier left Auckland, New Zealand, to conduct marine geologic investigations in the valley glacial-marine sedimentary environments bordering the Transantarctic Mountains. The objectives were: (1) to occupy closely spaced geologic stations along the Pennell Coast, in Terra Nova Bay, and in McMurdo Sound; (2) to conduct a reconnaissance study of other portions of the western Ross Sea; (3) to conduct bathymetric surveys in uncharted waters; (4) to sample ice-rafted detritus from icebergs and floating ice; and (5) to chart the current positions of ice tongues and glacier termini using the ship's radar. During the cruise, a series of seamounts and a possible southern extension of the Balleny Fracture Zone from the Balleny Islands to Cape Adare were discovered. Later efforts focused on delineating these features in greater detail. Marine geologic operations were conducted along with additional ship duties as part of Deep Freeze 80 until 11 February 1980, when the Glacier departed the Ross Sea. Geologic Observations. This cruise marks the first detailed geologic survey of any portion of the antarctic valley glacial-marine sedimentary environment. Closely spaced piston cores and bottom-grab samples were obtained at 66 stations off the Pennell Coast between 163°E and 171°E (figures 1 and 2) and at 41 stations in and around Terra Nova Bay (figures 1 and 3). In addition, 24 more widely spaced stations were occupied as part of a general survey of the western Ross Sea (figure 1). Sixty-two stations were taken in McMurdo Sound and the Ross Island area (figure 1). In all, 193 stations were occupied; 167 piston cores and 133 bottom-grab samples were collected at 171 piston coring stations and 22 bottom-grab stations. Preliminary bathymetric maps of the Pennell Coast (figure 2) and the Terra Nova Bay area (figure 3) were constructed on board ship using available existing data and bathymetric data acquired during Deep Freeze 80. The continental shelf off the Pennell Coast averages 250 meters deep but is dissected by several northward-trending canyons. Each of these canyons represents the seaward extension of major glacial valleys, and some exceed 1,000 meters 114
Sancetta, C. 1978. Neogene Pacific microfossils and paleooceanography, Marine Micropaleontology, 3, 347-376. Shackleton, N. J . , and Kennett, J. P. 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 (Eds.), Initial reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office.
•29 17OE1 1127 .30 1126 25 23 31 24 21 22 19 0 166 70*S 35 36 33 40 L0 / ".42 12 3 11 - ' 4) 5; _ 0169 I55 63 65 t'53 l6Ot17 1591151 10 el _JjT2SL\ 11)7) ''';C( 156 J .-,.J,U_ 67— ;4v9j1 ', 0172 )46 I48/ 0 NO RECOVERY
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Figure 1. Deep Freeze 80 station locations In the northwestern and southwestern Ross Sea. ANTARCTIC JOURNAL
