Growth of the antarctic ice sheets and the Neogene paleoenvironment ...
Growth of the antarctic ice sheets and the Neogene paleoenvironment of the Maurice Ewing Bank PAUL F. CIE5IEL5KI, MICHAEL T. LEDBETrER, and BROOKS B. ELLw00D University of Georgia Athens, Georgia 30602
A micropaleontologic, magnetostratigraphic, and sedimentologic analysis of 56 piston cores was the basis of a geologic study of the late Miocene to Recent depositional and erosional history of the intermediate-depth Maurice Ewing Bank (Ciesielski, Ledbetter, and Ellwood in press) located at the eastern extremity of the Falkland (Malvinas) Plateau, southwest Atlantic Ocean (see Ciesielski and Wise 1977 for location map). This article presents the major conclusions of this study. 1. A review of regional oceanographic data indicates that oceanic circulation over the Falkland Platform is dominated by the Pacific water masses of the Antarctic Circumpolar Current (ACC), with current velocities generally inferred to be 10-20 centimeters per second. The direction and relative intensity of ACC bottom water flow over the Falkland Platform was inferrred independently on the basis of a regional study of bottom photographs, nephelometer profiles, direct measurements of current, and surface sediment distribution (Ciesielski 1978). 2. Fluctuations through time in the position of the Polar Front and in the intensity of the ACC probably have been the dominant influence on the depositional history of the Maurice Ewing Bank since the initiation of the ACC flow over the bank during the Miocene. 3. A detailed analysis of the late Miocene-Recent geologic history of the Maurice Ewing Bank reveals a depositional and erosional history, summarized in the following paragraphs, which may be correlated with globally significant paleoceanographic events and episodes (figure 1). The Maurice Ewing Bank suffered a major erosional event during the late Miocene which exposed most CretaceousMiocene sediment, now near the surface, and shaped the present configuration of the bank. This erosional event occurred during the late Miocene to early Pliocene (-7.2-4.7 million years ago), with the major phase of erosion probably occurring between middle magnetostratigraphic Chron 7 and late Chron 6 (-7.4-6.2 million years ago). A widespread resumption of deposition on the Maurice Ewing Bank occurred from 4.5 to 3.9 million years ago due to a decrease in ACC velocity associated with an early Pliocene amelioration of climate (figure 2). Limited deposition and widespread erosion and/or nondeposition over most of the bank approximately 4.0-3.2 million years ago occurred due to an intensification of the ACC during the late Gilbert and early Gauss magnetostratigraphic chrons. A renewal of widespread deposition occurred as bottom current velocities decreased throughout much of late Gauss time between 2.8 and 2.43 million years ago, and more limited deposition occurred during the earliest Matuyama Chron (2.48-2.2 million years ago). 114
A regional disconformity was formed between sediments of approximately 2.0-1.0 million years in age by intensified ACC flow which is inferred to have occurred during the late Matuyama Chron (1.2 to approximately 1.0 million years ago). The disconformity is thought to be temporally correlative with the greatest Patagonian glaciation (Mercer 1976) in nearby southern Argentina. Between approximately 1.0 and 0.7 million years ago the bank was blanketed with a coarse, erosion-resistant layer of ice-rafted detritus which armored the older sediment, thereby protecting it from subsequent major erosion. Sedimentation on the Maurice Ewing Bank was intermittent during the Brunhes Chron (720,000 years ago to Present) and finally culminated with the deposition of a veneer of carbonate ooze during the last 200,000 years. This is the first record of carbonate deposition on the bank since late Miocene time and probably marks a southward shift of the Polar Front to its present position over the bank. 4. The Miocene sedimentary record of the Maurice Ewing Bank and other paleoenvironmental evidence from the circumantarctic region suggests several things about conditions prior to the late Miocene. First, extensive ice shelves were not present along the antarctic margins. Second, no grounded ice sheet was present in West Antarctica. Instead, present-day West Antarctica was occupied by an archipelago and West Antarctic Sea (figure 3). Finally, most ice-rafted detritus was deposited close to the antarctic continent (e.g., Ross Sea), with more limited deposition as far as 56°S. Ice-rafting was by small bergs principally from tidewater glaciers and small ice shelves. 5. Extensive ice shelves formed in the Ross and Weddell Seas during the late Miocene in response to expansion of the east antarctic ice sheet and further reductions in ocean and atmospheric temperatures. 6. With the formation of the Ross and Weddell ice shelves, or shortly after, an immense ice shelf covered the former West Antarctic Sea. Formation of this ice shelf was accompanied by a significant increase in the velocity of oceanic circumpolar circulation, resulting in widespread late Miocene erosion of deep-sea sediments. 7. During the late Miocene, the west antarctic ice shelf rapidly thickened by basal and surface accretion until it grounded below sea level to form the west antarctic ice sheet. 8. Formation of the west antarctic ice shelf and subsequent formation of the west antarctic ice sheet, with floating and partially grounded extensions (ice shelves) in the Ross and Weddell embayments, led to the first major production of antarctic bottom water (AABw) with characteristics similar to those of the present-day AABW. 9. The late Miocene change in the character and volume of AABW permanently altered rates of global abyssal circulation and the temperature of abyssal water. Late Miocene changes in oceanic carbonate compensation depth levels and an apparent permanent shift in the oceanic 13C/12C composition may be attributed to this major change in abyssal circulation. 10. Antarctica was more extensively glaciated during most of the Pliocene-Quaternary than at any time during the Miocene. F. McCoy assisted in providing core samples from the Lamont-Doherty Geological Observatory Core Laboratory. Support for their collection and curatorial facilities is provided by National Science Foundation grant OCE 76-18049 and Office of Naval Research grant N000 14075-C-021. D. S. Cassidy proANTARCTIc JOURNAL
PALEOCLIMATIC, PALEOCEANOGRAPHIC, AND PALEOGLACIAL Events
Episodes
a-
Age (m.y.)*
GREATEST PATNX,IIN4 GLICIATION (?RCEL
(Is &
I
1976)
I
I
i
F
;
21
SIGNIFICANT INCREASE IN MoRTH ATL*TIC ICE-RAFTING REw,mEL 1972) liCREASE IN mAeNITLIx OF GLACIATIONS (SI4ACKLEm & romxE, l977) COMING BEGINS IN U ZEALAND OUTTHEWS & üpris, 1%6) Sami PACIFIC OwKE, 197) ie Sczms€sT !p Im OCEAN (Si.ciq.m & Karr, 117e) CcxuNS TREND BEGINSON
C MmIER Pi (V&picrr & VELLA, 1979
I
INITIATION OF It)RTH ATIJ#T1C ICE-RAFTING (BEROGREN, 1q12) -
(9Iq11ON & )'EWNE, 1977) Fowrioii OF PAies ICE sr (s(N & RLAZ)CHISHIN, 17R) PATAGONIAN GLACIATION MERCER ET AL., 1975) *flW) DISPIJC84MT OF GLACIAL IRINE/SILICEGL5 OOZE BOI.NRY (1'AVER, INIATION OF NOFTiERA FlISPIIC GLACIATION
ru
III) io 91, !(B (mis PAPER) 1AJCJ1 PCRflWRE) MIGRATION OF Fku Fqo,i,- (LLDIIG, IASNI1sIIIqJ, ET AL., IN PRESS) ICE OOVERW ARCTIC OCEAN P'ARGoLIS & I4'J, 1980) FIRST AaA(T
FIRST I)
0
o 91'S.,
SITE 328, PkVINAS f*JTER JRSIN (ftwKER ET AL., 1977; THIS PAPER) FIRST WIOFSPREAD DEPOSITION OF PLIOCENE SEDIMENT BEGINS ON PFB (mis PAPER) Ui
SEA-LEVEL LCBERING AT BLIND RIVER, N.Z. ( V p,IErr, 1%5) SEA-LEVEL LI)RINS (71Th), SPAIN (Rm & Hw, 1q76) )U2TION IN SURFACE WATER STABILITY AND (bIrIT &
-
C SHIFT AT BLiNn RIVER, N.Z, - 6
KBIETT, 1979) AND 13C SHIFT IN PACIFIC (KEIONIN & 5+4cKLEnl, 1980) FIRST I)
rn 9;OS, SITE 266 (HAVES, FRAKES El AL., 1975; THIS PAPER) -
FIRST PEBBLE-SIZE III) FIRST S-SIZE
TO
91'S, 9B (mis PAPER)
I) io 91's, IEB (THIS ppp€p )
8 -.
10
I i
I
I LATE MIOCENE GLACIAL CONDITIONS IN ANTARCTICA • WEST ANTARCTIC ICE SHEET ESTABLISHED • ErrENSIVE ICE SHELVES FOIED IN ROSS & WEEIELL FISAWENTS • ICE-RAFTINS TO LON LATIThES OF &BmENN (EN • PRCIXETION OF LARGE VELIJES OF THAN TODAY • ANTARCTIC ICE LESS EXTENSIVE • MOST ICE ABOVE SEA-LEVEL ON EAST ANTARCTICA
• No WEST ANTARCTIC ICE SHEET WEST ANTARmc. SEA & ARCHIPELO OCCIPIED PRESENT TKiY WEsT ANTARCTICA
• No 12 Fiisr I)
TO 9PS, SITE 267 (HAYES & FRAKES, 1975)
-
EXTENSIVE ICE SHELVES
• ICE RAFTING BY SI'#LL. BERGS FROM OUTLET CtKIERS & ShALL ICE SHELVES
14
Figure 1. Compilation of major late Miocene to mid-Pleistocene (1.0 million years ago) paleocilmatic, paleoglaclal, and paleoceanographic events (left column) and episodes (right column). Also presented is a summary of late Miocene glacial conditions (lower right corner) prior to (below diagonal lines) and after (above diagonal lines) establishment of the west antarctic ice sheet. For comparison purposes all ages are quoted according to a single magnetostratigraphic time scale of LaBrecque, Kent, and Cande (1977) with the revised potassium-argon (K-Ar) constants of Mankinen and Dalrymple (1979). (Figure is taken from Clesielski, Ledbetter, and Ellwood in press. All references to "this paper" in the figure refer to that publication.)
1981 REVIEW
115
M A U R I C E E W I N G BANK
>.
O4__j w X ( 03.4 zE E
ARA ISLAS ORCADAS PISTON CORES
A (west)
U)
w I 2 Ix
A' B (west)
B'
7-51 7-52 7-50 7-55 7-53 7-54 7-49 7-48 7-47 7-46 7-45 7-44 7-43 7-40 11-9 11-10 11-12 11-13
0.72 - P0.91
4 2 4 - 164
GEM
4. ..G
244 2.92 to 3.18
_1343
Iw -I 0
3.44 395 4.04 4.21 435 4.43 4.52 4.71
XW
LATE EALT(') LATE LATE LATE LATE LATE EARLY LATE MIOCENE EOCENE MIOCENE MIOCENE MIOCENE MIOCENE MIOCENE MIOCENE PALEOCENE
ALEOMAGNETI CORRELATION FORAMINIFERAL OOZE
CAWAMAN/ EARLY
EARLY MIDDLE LATE LATE
E31141
RM
ma
I-1 FcyG-1 CALCAREOUS OOZE RADIOLARIAN OOZE MUD
[j NANNOFOSSIL OOZE DIATOMACEOUS OOZE SILICEOUS OOZE
SAND
MANGANESE NODULE A. CHERT -. ABRUPT CONTACT
PM PELAGIC CLAY SEDIMENTARY CLASTS GLAUCONITE
GRAVEL, PEBBLES, GRANULES
- - - GRADATIONAL CONTACT
Figure 2. Lithologies of the Pliocene-Recent sediments of Islas Orcadas piston cores recovered from the Maurice Ewing Bank. Gaps in the lithologic columns represent disconformities. Ages of core sequences below the regional upper Miocene disconformity (lower part of figure) are given above the lithologic columns showing the upper few meters of sediment below the disconformity. Ages of pre-Pliocene portions of piston cores taken from CiesieIski and Wise (1972).
vided samples from the Antarctic Marine Geology Research Facility Core Library at Florida State University. Support for this collection and curatorial facility is provided by National Science Foundation grant OPP 74-20109. Partial financial support for this study was provided by National Science Foundation grants ON' 74-20109 and DPP 77-19360 to S. W. Wise and DPP 79-05111 to M. T. Ledbetter and by the Institute for Polar Studies of Ohio State University. References Adams, C. G., Benson, R. H., Kidd, R. B., Ryan, W. B. F., and Wright, R. C. 1977. The Messinian salinity crisis and evidence of late Miocene eustatic changes in the world ocean. Nature, 269, 383-386. Anderson, J . B. 1972. The marine geology of the Weddell Sea (Contribution 35). Tallahassee: Florida State University, Sedimentological Research Laboratory. Barrett, P. J . 1975. Textural characteristics of Cenozoic preglacial and glacial sediments of site 270, Ross Sea, Antarctica. In D. E. Hayes, L. A. Frakes et al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Berggren, W. A. 1972. Late Pliocene-Pleistocene glaciation. In A. S. Laughton et al., Initial reports of the Deep Sea Drilling Project, Vol. 12. Washington, D.C.: U.S. Government Printing Office. 116
Berggren, W. A., and Haq, B. U. 1976. The Andalusian stage (late Miocene): Biostratigraphy, biochronology and paleoecology. Palaeogeography, Palaeoclimatology, Palaeoecology, 20, 67-129. Brady, H. T. In press. Late Neogene history of Taylor and Wright Valleys and McMurdo Sound, derived from diatom biostratigraphy and paleoecology of DVDP cores. In C. C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Ciesielski, P. F. 1978. The Maurice Ewing Bank of the Malvinas (Falkland) Plateau: Depositional and erosional history and its paleoenvironmental implications. Unpublished doctoral dissertation, Florida State University. Ciesielski, P. F., Ledbetter, M. T., and Ellwood, B. B. In press. The development of antarctic glaciation and the Neogene paleoenvironment of the Maurice Ewing Bank. Marine Geology. Ciesielski, P. F., and Weaver, F. M. 1974. Early Pliocene temperature changes in the antarctic seas. Geology, 2, 511--515. Ciesielski, P. F., and Wise, S. W. 1977. Geologic history of the Maurice Ewing Bank of the Falkland Plateau (southwest Atlantic sector of the southern ocean) based on piston and drill cores. Marine Geology, 25, 175-207. Fillon, R. H. 1975. Late Cenozoic paleo-oceanography of the Ross Sea, Antarctica. Geological Society of America Bulletin, 86, 839-845. Fleck, R. J., Mercer, J . H., Nairn, A. E. M., and Peterson, D. N. 1972. Chronology of late Pliocene and early Pleistocene glacial and magnetic events in southern Argentina. Earth and Planetary Science Letters, 16, 15-22. ANTARCTIC JOURNAL
EAST ANTARCTICA
0 1500 kilometers
.' WEDDEN SEA I
.:.
Ice cov:ring land
CE
SHELF
I •12(
El Ice shelf -I Ice grounded r.LLJ below sea level Figure 3. 3. (a) Antarctica prior to the late Miocene, with the west antarctic ice sheet/shelf absent, thus exposing an island archipelago in the West Antarctic Sea; (b) Antarctica since the late Miocene with ice sheets in East and West Antarctica and ice shelves in the Ross and Weddell embayments; (c) enlargement of present-day West Antarctica showing the extent of ice shelves and portions of the west antarctic ice sheet grounded below sea level (after Mercer 1978).
Hayes, D. E., and Frakes, L. A. 1975. General synthesis, Deep Sea Drilling Project leg 28. In D. E. Hayes, L. A. Frakes et al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hayes, D. E., Frakes, L. A. et al. 1975. Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hays, J . D., and Opdyke, N. D. 1967. Antarctic radiolaria, magnetic reversals, and climate changes. Science, 158, 1001-1011. Keany, J . 1978. Paleoclimatic trends in early and middle Pliocene deepsea sediments of the antarctic. Marine Micropaleontology, 3, 35-49. Keigwin, L. D., and Shackleton, N. J . 1980. Uppermost Miocene carbon isotope stratigraphy of a piston core in the equatorial Pacific. Nature, 284, 613-614. Kennett, J . P. 1965. Faunal succession in two upper Miocene-lower Pliocene sections, Marlborough, New Zealand. Transactions Royal Society of New Zealand, 3, 197-213. Kennett, J . P., Houtz, R. E. et al. 1977. Cenozoic paleoceanography in the southwest Pacific Ocean, antarctic glaciation and the development of the circum -antarctic current. 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. Kennett, J . P., and Vella, P. 1975. Late Cenozoic planktonic forami-
1981 REVIEW
nifera and paleoceanography at DSDP site 284 in the cool subtropical South Pacific. 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. Kvasov, D. D., and Blazhchishin, A. I. 1978. The key to sources of the Pliocene and Pleistocene glaciation is at the bottom of the Barents Sea. Nature, 273, 138-140. LaBrecque, J . L., Kent, D. V., and Cande, S. C. 1977. Revised magnetic polarity time scale for Late Cretaceous and Cenozoic and Cenozoic time, Geology, 5, 330-335. Ledbetter, M. T., Williams, D. F., and Ellwood, B. B. 1978. Late Pliocene climate and south-west Atlantic abyssal circulation. Nature, 272, 237-239. 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. Ludwig, W. J . , Krasheninnikov, V. et al. 1980. Tertiary and Cretaceous paleoenvironments in the southwest Atlantic Ocean: Preliminary results of Deep Sea Drilling Project Key 71. Geological Society of America Bulletin, 91, 655-664. Mankinen, E. A., and Dalrymple, G. B. 1979. Revised geomagnetic polarity time scale for the interval 0-5 m.y. B.P.Journal of Geophysical Research, 84, 615-626. Margolis, S. V., and Herman, Y. 1980. Northern Hemisphere sea-ice and glacial development in the late Cenozoic. Nature, 286, 145-149. Matthews, W. H., and Curtis, C. H. 1966. Date of the Pliocene-Pleistocene boundary in New Zealand. Nature, 212, 979-980. Mercer, J . H. 1976. Glacial history of southernmost South America. Quaternary Research, 6, 125-166. Mercer, J . H. 1978. West antarctic ice sheet and CO 2 greenhouse effect: A threat of disaster, Nature, 271, 321-325. Mercer, J . H. 1979. Late Miocene to earliest Pliocene glaciation in southern Argentina. Geological Society of America, Abstracts with Programs, 11, 478. Mercer, J . H., Fleck, R. J . , Mankinen, E. A., and Sander, W. 1975. Southern Patagonia: Glacial events between 4 MY and 1 MY. In R. P. Suggate and M. M. Cresswell (Eds.), Quaternary Studies (Bulletin 13). Wellington: Royal Society of New Zealand. Plafker, G., Bartsch-Winkler, S., and Ovenshine, A. T. 1977. In P. F. Barker et al., Initial reports of the Deep Sea Drilling Project, Vol. 36. Washington, D.C.: U.S. Government Printing Office. Shackleton, N. J . , and Kennett, J. P. 1975. Late Cenozoic oxygen and carbon isotopic changes at DSDP site 284: Implications for glacial history of the Northern Hemisphere and Antarctica. 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. (a) Shackleton, N. J., and Kennett, J . P. 1975. Paleotemperature history of the Cenozoic and the initiation of antarctic glaciation: Oxygen and carbon isotope analysis 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. (b) Shackleton, N. J . , and Opdyke, N. D. 1977. Oxygen isotope and paleomagnetic evidence for early Northern Hemisphere glaciation. Nature, 270, 216-219. Tucholke, B. E., and Carpenter, C. B. 1977. Sediment distribution and Cenozoic sedimentation patterns on the Agulhas Plateau. Geological Society of America Bulletin, 88, 1337-1346. Weaver, F. M. 1973. Pliocene paleoclimatic and paleoglacial history of East Antarctica recorded in deep-sea piston cores (Contribution 36). Tallahassee: Florida State University, Sedimentological Research Laboratory.
117
A micropaleontologic, magnetostratigraphic, and sedimentologic analysis of 56 piston cores was the basis of a geologic study of the late Miocene to Recent depositional and erosional history of the intermediate-depth Maurice Ewing Bank (Ciesielski, Ledbetter, and Ellwood in press) located at the eastern extremity of the Falkland (Malvinas) Plateau, southwest Atlantic Ocean (see Ciesielski and Wise 1977 for location map). This article presents the major conclusions of this study. 1. A review of regional oceanographic data indicates that oceanic circulation over the Falkland Platform is dominated by the Pacific water masses of the Antarctic Circumpolar Current (ACC), with current velocities generally inferred to be 10-20 centimeters per second. The direction and relative intensity of ACC bottom water flow over the Falkland Platform was inferrred independently on the basis of a regional study of bottom photographs, nephelometer profiles, direct measurements of current, and surface sediment distribution (Ciesielski 1978). 2. Fluctuations through time in the position of the Polar Front and in the intensity of the ACC probably have been the dominant influence on the depositional history of the Maurice Ewing Bank since the initiation of the ACC flow over the bank during the Miocene. 3. A detailed analysis of the late Miocene-Recent geologic history of the Maurice Ewing Bank reveals a depositional and erosional history, summarized in the following paragraphs, which may be correlated with globally significant paleoceanographic events and episodes (figure 1). The Maurice Ewing Bank suffered a major erosional event during the late Miocene which exposed most CretaceousMiocene sediment, now near the surface, and shaped the present configuration of the bank. This erosional event occurred during the late Miocene to early Pliocene (-7.2-4.7 million years ago), with the major phase of erosion probably occurring between middle magnetostratigraphic Chron 7 and late Chron 6 (-7.4-6.2 million years ago). A widespread resumption of deposition on the Maurice Ewing Bank occurred from 4.5 to 3.9 million years ago due to a decrease in ACC velocity associated with an early Pliocene amelioration of climate (figure 2). Limited deposition and widespread erosion and/or nondeposition over most of the bank approximately 4.0-3.2 million years ago occurred due to an intensification of the ACC during the late Gilbert and early Gauss magnetostratigraphic chrons. A renewal of widespread deposition occurred as bottom current velocities decreased throughout much of late Gauss time between 2.8 and 2.43 million years ago, and more limited deposition occurred during the earliest Matuyama Chron (2.48-2.2 million years ago). 114
A regional disconformity was formed between sediments of approximately 2.0-1.0 million years in age by intensified ACC flow which is inferred to have occurred during the late Matuyama Chron (1.2 to approximately 1.0 million years ago). The disconformity is thought to be temporally correlative with the greatest Patagonian glaciation (Mercer 1976) in nearby southern Argentina. Between approximately 1.0 and 0.7 million years ago the bank was blanketed with a coarse, erosion-resistant layer of ice-rafted detritus which armored the older sediment, thereby protecting it from subsequent major erosion. Sedimentation on the Maurice Ewing Bank was intermittent during the Brunhes Chron (720,000 years ago to Present) and finally culminated with the deposition of a veneer of carbonate ooze during the last 200,000 years. This is the first record of carbonate deposition on the bank since late Miocene time and probably marks a southward shift of the Polar Front to its present position over the bank. 4. The Miocene sedimentary record of the Maurice Ewing Bank and other paleoenvironmental evidence from the circumantarctic region suggests several things about conditions prior to the late Miocene. First, extensive ice shelves were not present along the antarctic margins. Second, no grounded ice sheet was present in West Antarctica. Instead, present-day West Antarctica was occupied by an archipelago and West Antarctic Sea (figure 3). Finally, most ice-rafted detritus was deposited close to the antarctic continent (e.g., Ross Sea), with more limited deposition as far as 56°S. Ice-rafting was by small bergs principally from tidewater glaciers and small ice shelves. 5. Extensive ice shelves formed in the Ross and Weddell Seas during the late Miocene in response to expansion of the east antarctic ice sheet and further reductions in ocean and atmospheric temperatures. 6. With the formation of the Ross and Weddell ice shelves, or shortly after, an immense ice shelf covered the former West Antarctic Sea. Formation of this ice shelf was accompanied by a significant increase in the velocity of oceanic circumpolar circulation, resulting in widespread late Miocene erosion of deep-sea sediments. 7. During the late Miocene, the west antarctic ice shelf rapidly thickened by basal and surface accretion until it grounded below sea level to form the west antarctic ice sheet. 8. Formation of the west antarctic ice shelf and subsequent formation of the west antarctic ice sheet, with floating and partially grounded extensions (ice shelves) in the Ross and Weddell embayments, led to the first major production of antarctic bottom water (AABw) with characteristics similar to those of the present-day AABW. 9. The late Miocene change in the character and volume of AABW permanently altered rates of global abyssal circulation and the temperature of abyssal water. Late Miocene changes in oceanic carbonate compensation depth levels and an apparent permanent shift in the oceanic 13C/12C composition may be attributed to this major change in abyssal circulation. 10. Antarctica was more extensively glaciated during most of the Pliocene-Quaternary than at any time during the Miocene. F. McCoy assisted in providing core samples from the Lamont-Doherty Geological Observatory Core Laboratory. Support for their collection and curatorial facilities is provided by National Science Foundation grant OCE 76-18049 and Office of Naval Research grant N000 14075-C-021. D. S. Cassidy proANTARCTIc JOURNAL
PALEOCLIMATIC, PALEOCEANOGRAPHIC, AND PALEOGLACIAL Events
Episodes
a-
Age (m.y.)*
GREATEST PATNX,IIN4 GLICIATION (?RCEL
(Is &
I
1976)
I
I
i
F
;
21
SIGNIFICANT INCREASE IN MoRTH ATL*TIC ICE-RAFTING REw,mEL 1972) liCREASE IN mAeNITLIx OF GLACIATIONS (SI4ACKLEm & romxE, l977) COMING BEGINS IN U ZEALAND OUTTHEWS & üpris, 1%6) Sami PACIFIC OwKE, 197) ie Sczms€sT !p Im OCEAN (Si.ciq.m & Karr, 117e) CcxuNS TREND BEGINSON
C MmIER Pi (V&picrr & VELLA, 1979
I
INITIATION OF It)RTH ATIJ#T1C ICE-RAFTING (BEROGREN, 1q12) -
(9Iq11ON & )'EWNE, 1977) Fowrioii OF PAies ICE sr (s(N & RLAZ)CHISHIN, 17R) PATAGONIAN GLACIATION MERCER ET AL., 1975) *flW) DISPIJC84MT OF GLACIAL IRINE/SILICEGL5 OOZE BOI.NRY (1'AVER, INIATION OF NOFTiERA FlISPIIC GLACIATION
ru
III) io 91, !(B (mis PAPER) 1AJCJ1 PCRflWRE) MIGRATION OF Fku Fqo,i,- (LLDIIG, IASNI1sIIIqJ, ET AL., IN PRESS) ICE OOVERW ARCTIC OCEAN P'ARGoLIS & I4'J, 1980) FIRST AaA(T
FIRST I)
0
o 91'S.,
SITE 328, PkVINAS f*JTER JRSIN (ftwKER ET AL., 1977; THIS PAPER) FIRST WIOFSPREAD DEPOSITION OF PLIOCENE SEDIMENT BEGINS ON PFB (mis PAPER) Ui
SEA-LEVEL LCBERING AT BLIND RIVER, N.Z. ( V p,IErr, 1%5) SEA-LEVEL LI)RINS (71Th), SPAIN (Rm & Hw, 1q76) )U2TION IN SURFACE WATER STABILITY AND (bIrIT &
-
C SHIFT AT BLiNn RIVER, N.Z, - 6
KBIETT, 1979) AND 13C SHIFT IN PACIFIC (KEIONIN & 5+4cKLEnl, 1980) FIRST I)
rn 9;OS, SITE 266 (HAVES, FRAKES El AL., 1975; THIS PAPER) -
FIRST PEBBLE-SIZE III) FIRST S-SIZE
TO
91'S, 9B (mis PAPER)
I) io 91's, IEB (THIS ppp€p )
8 -.
10
I i
I
I LATE MIOCENE GLACIAL CONDITIONS IN ANTARCTICA • WEST ANTARCTIC ICE SHEET ESTABLISHED • ErrENSIVE ICE SHELVES FOIED IN ROSS & WEEIELL FISAWENTS • ICE-RAFTINS TO LON LATIThES OF &BmENN (EN • PRCIXETION OF LARGE VELIJES OF THAN TODAY • ANTARCTIC ICE LESS EXTENSIVE • MOST ICE ABOVE SEA-LEVEL ON EAST ANTARCTICA
• No WEST ANTARCTIC ICE SHEET WEST ANTARmc. SEA & ARCHIPELO OCCIPIED PRESENT TKiY WEsT ANTARCTICA
• No 12 Fiisr I)
TO 9PS, SITE 267 (HAYES & FRAKES, 1975)
-
EXTENSIVE ICE SHELVES
• ICE RAFTING BY SI'#LL. BERGS FROM OUTLET CtKIERS & ShALL ICE SHELVES
14
Figure 1. Compilation of major late Miocene to mid-Pleistocene (1.0 million years ago) paleocilmatic, paleoglaclal, and paleoceanographic events (left column) and episodes (right column). Also presented is a summary of late Miocene glacial conditions (lower right corner) prior to (below diagonal lines) and after (above diagonal lines) establishment of the west antarctic ice sheet. For comparison purposes all ages are quoted according to a single magnetostratigraphic time scale of LaBrecque, Kent, and Cande (1977) with the revised potassium-argon (K-Ar) constants of Mankinen and Dalrymple (1979). (Figure is taken from Clesielski, Ledbetter, and Ellwood in press. All references to "this paper" in the figure refer to that publication.)
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115
M A U R I C E E W I N G BANK
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Figure 2. Lithologies of the Pliocene-Recent sediments of Islas Orcadas piston cores recovered from the Maurice Ewing Bank. Gaps in the lithologic columns represent disconformities. Ages of core sequences below the regional upper Miocene disconformity (lower part of figure) are given above the lithologic columns showing the upper few meters of sediment below the disconformity. Ages of pre-Pliocene portions of piston cores taken from CiesieIski and Wise (1972).
vided samples from the Antarctic Marine Geology Research Facility Core Library at Florida State University. Support for this collection and curatorial facility is provided by National Science Foundation grant OPP 74-20109. Partial financial support for this study was provided by National Science Foundation grants ON' 74-20109 and DPP 77-19360 to S. W. Wise and DPP 79-05111 to M. T. Ledbetter and by the Institute for Polar Studies of Ohio State University. References Adams, C. G., Benson, R. H., Kidd, R. B., Ryan, W. B. F., and Wright, R. C. 1977. The Messinian salinity crisis and evidence of late Miocene eustatic changes in the world ocean. Nature, 269, 383-386. Anderson, J . B. 1972. The marine geology of the Weddell Sea (Contribution 35). Tallahassee: Florida State University, Sedimentological Research Laboratory. Barrett, P. J . 1975. Textural characteristics of Cenozoic preglacial and glacial sediments of site 270, Ross Sea, Antarctica. In D. E. Hayes, L. A. Frakes et al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Berggren, W. A. 1972. Late Pliocene-Pleistocene glaciation. In A. S. Laughton et al., Initial reports of the Deep Sea Drilling Project, Vol. 12. Washington, D.C.: U.S. Government Printing Office. 116
Berggren, W. A., and Haq, B. U. 1976. The Andalusian stage (late Miocene): Biostratigraphy, biochronology and paleoecology. Palaeogeography, Palaeoclimatology, Palaeoecology, 20, 67-129. Brady, H. T. In press. Late Neogene history of Taylor and Wright Valleys and McMurdo Sound, derived from diatom biostratigraphy and paleoecology of DVDP cores. In C. C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Ciesielski, P. F. 1978. The Maurice Ewing Bank of the Malvinas (Falkland) Plateau: Depositional and erosional history and its paleoenvironmental implications. Unpublished doctoral dissertation, Florida State University. Ciesielski, P. F., Ledbetter, M. T., and Ellwood, B. B. In press. The development of antarctic glaciation and the Neogene paleoenvironment of the Maurice Ewing Bank. Marine Geology. Ciesielski, P. F., and Weaver, F. M. 1974. Early Pliocene temperature changes in the antarctic seas. Geology, 2, 511--515. Ciesielski, P. F., and Wise, S. W. 1977. Geologic history of the Maurice Ewing Bank of the Falkland Plateau (southwest Atlantic sector of the southern ocean) based on piston and drill cores. Marine Geology, 25, 175-207. Fillon, R. H. 1975. Late Cenozoic paleo-oceanography of the Ross Sea, Antarctica. Geological Society of America Bulletin, 86, 839-845. Fleck, R. J., Mercer, J . H., Nairn, A. E. M., and Peterson, D. N. 1972. Chronology of late Pliocene and early Pleistocene glacial and magnetic events in southern Argentina. Earth and Planetary Science Letters, 16, 15-22. ANTARCTIC JOURNAL
EAST ANTARCTICA
0 1500 kilometers
.' WEDDEN SEA I
.:.
Ice cov:ring land
CE
SHELF
I •12(
El Ice shelf -I Ice grounded r.LLJ below sea level Figure 3. 3. (a) Antarctica prior to the late Miocene, with the west antarctic ice sheet/shelf absent, thus exposing an island archipelago in the West Antarctic Sea; (b) Antarctica since the late Miocene with ice sheets in East and West Antarctica and ice shelves in the Ross and Weddell embayments; (c) enlargement of present-day West Antarctica showing the extent of ice shelves and portions of the west antarctic ice sheet grounded below sea level (after Mercer 1978).
Hayes, D. E., and Frakes, L. A. 1975. General synthesis, Deep Sea Drilling Project leg 28. In D. E. Hayes, L. A. Frakes et al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hayes, D. E., Frakes, L. A. et al. 1975. Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hays, J . D., and Opdyke, N. D. 1967. Antarctic radiolaria, magnetic reversals, and climate changes. Science, 158, 1001-1011. Keany, J . 1978. Paleoclimatic trends in early and middle Pliocene deepsea sediments of the antarctic. Marine Micropaleontology, 3, 35-49. Keigwin, L. D., and Shackleton, N. J . 1980. Uppermost Miocene carbon isotope stratigraphy of a piston core in the equatorial Pacific. Nature, 284, 613-614. Kennett, J . P. 1965. Faunal succession in two upper Miocene-lower Pliocene sections, Marlborough, New Zealand. Transactions Royal Society of New Zealand, 3, 197-213. Kennett, J . P., Houtz, R. E. et al. 1977. Cenozoic paleoceanography in the southwest Pacific Ocean, antarctic glaciation and the development of the circum -antarctic current. 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. Kennett, J . P., and Vella, P. 1975. Late Cenozoic planktonic forami-
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nifera and paleoceanography at DSDP site 284 in the cool subtropical South Pacific. 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. Kvasov, D. D., and Blazhchishin, A. I. 1978. The key to sources of the Pliocene and Pleistocene glaciation is at the bottom of the Barents Sea. Nature, 273, 138-140. LaBrecque, J . L., Kent, D. V., and Cande, S. C. 1977. Revised magnetic polarity time scale for Late Cretaceous and Cenozoic and Cenozoic time, Geology, 5, 330-335. Ledbetter, M. T., Williams, D. F., and Ellwood, B. B. 1978. Late Pliocene climate and south-west Atlantic abyssal circulation. Nature, 272, 237-239. 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. Ludwig, W. J . , Krasheninnikov, V. et al. 1980. Tertiary and Cretaceous paleoenvironments in the southwest Atlantic Ocean: Preliminary results of Deep Sea Drilling Project Key 71. Geological Society of America Bulletin, 91, 655-664. Mankinen, E. A., and Dalrymple, G. B. 1979. Revised geomagnetic polarity time scale for the interval 0-5 m.y. B.P.Journal of Geophysical Research, 84, 615-626. Margolis, S. V., and Herman, Y. 1980. Northern Hemisphere sea-ice and glacial development in the late Cenozoic. Nature, 286, 145-149. Matthews, W. H., and Curtis, C. H. 1966. Date of the Pliocene-Pleistocene boundary in New Zealand. Nature, 212, 979-980. Mercer, J . H. 1976. Glacial history of southernmost South America. Quaternary Research, 6, 125-166. Mercer, J . H. 1978. West antarctic ice sheet and CO 2 greenhouse effect: A threat of disaster, Nature, 271, 321-325. Mercer, J . H. 1979. Late Miocene to earliest Pliocene glaciation in southern Argentina. Geological Society of America, Abstracts with Programs, 11, 478. Mercer, J . H., Fleck, R. J . , Mankinen, E. A., and Sander, W. 1975. Southern Patagonia: Glacial events between 4 MY and 1 MY. In R. P. Suggate and M. M. Cresswell (Eds.), Quaternary Studies (Bulletin 13). Wellington: Royal Society of New Zealand. Plafker, G., Bartsch-Winkler, S., and Ovenshine, A. T. 1977. In P. F. Barker et al., Initial reports of the Deep Sea Drilling Project, Vol. 36. Washington, D.C.: U.S. Government Printing Office. Shackleton, N. J . , and Kennett, J. P. 1975. Late Cenozoic oxygen and carbon isotopic changes at DSDP site 284: Implications for glacial history of the Northern Hemisphere and Antarctica. 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. (a) Shackleton, N. J., and Kennett, J . P. 1975. Paleotemperature history of the Cenozoic and the initiation of antarctic glaciation: Oxygen and carbon isotope analysis 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. (b) Shackleton, N. J . , and Opdyke, N. D. 1977. Oxygen isotope and paleomagnetic evidence for early Northern Hemisphere glaciation. Nature, 270, 216-219. Tucholke, B. E., and Carpenter, C. B. 1977. Sediment distribution and Cenozoic sedimentation patterns on the Agulhas Plateau. Geological Society of America Bulletin, 88, 1337-1346. Weaver, F. M. 1973. Pliocene paleoclimatic and paleoglacial history of East Antarctica recorded in deep-sea piston cores (Contribution 36). Tallahassee: Florida State University, Sedimentological Research Laboratory.
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