Land ice studies___________________ Revised age for RISP ...
Land ice studies___________________ Revised age for RISP sediments and implications for the glacial history of Antarctica DAVIDA E. KELLOGG and THOMAS B. KELLOGG Department of Geological Sciences and Institute for Quaternary Studies University of Maine Orono, Maine 04469
Our purpose is to demonstrate the invalidity of the late middle Miocene age date for sediments obtained at Ross Ice Shelf Project (RIsP) site J-9 (82°22'S 168°38'W), proposed by Brady (1978) and Brady and Martin (1979) and adopted by Webb (1978, 1979a, 1979b), Webb and Brady (1978), and Webb, Ronan, Lipps, and DeLaca (1979). RISP cores 7 and 8, both of which were collected during the 1977-78 field season at site J-9, were sampled at a number of levels from top
to bottom. Diatoms were prepared and analyzed using standard methods. Although we concur with Brady and Martin (1979) that middle Miocene diatoms are present in the RISP sediments, we believe that these specimens are reworked because we also observed a number of species that are considerably younger in age, as shown in the table and figure. Younger species occur throughout both sedimentary units that occur in the RISP cores (see Webb 1978, 1979a) in all samples we have analyzed; their relative abundances are similar to those calculated for Holocene Ross Sea diatoms (Truesdale and Kellogg 1979), although they are often less abundant than the Miocene-aged forms. The younger species are usually small, delicate, weakly silicified forms that are easily overlooked when mixed with the larger, more striking Miocene forms. Stratigraphic ranges were established by McCollum (1975) for a large number of diatom species that occur in Deep Sea Drilling Project (DSDP) cores from the Ross Sea. He was able to calibrate the stratigraphic ranges with paleomagnetic stratigraphy for the past 4.5 million years, and
Stratigraphically important diatom species in sediment cores from Species
J-9
Remarks
Actinocyc/us ingens Rattray (1890) Asterompha/us parvulus Karsten (1905) Charcotla act/nochilus
RISP site
(Ehrenberg) Hustedt
(1958)
Dent/cu/a antarctica McCollum (1975) Dent/cu/a hustedt// Simonsen and Kanaya (1961) Dent/cu/a lauta Bally (1854) Eucamp/a antarct/ca (= E. ba/aust/um Castracane (1886]) Melosira sulcata (Ehrenberg) KUtzing (1844) Nitzsch/a /nterfr/g/dar/a McCollum (1975) Rh/zoso/en/a hebetata forma h/ama//s Gran (1904) Roux/a antarct/ca Heiden and Kolbe (1928) Sch/mper/e//a antarct/ca Karsten (1905) Stephanopyx/s turns (Greville and Am) Ralfs in Tha/ass/onema elegans Hustedt (1958) Thalass/osira grad/Is (Karsten) Hustedt (1958) Trinacria excavata Heiberg (1863) Trinacria p/leo/us (Ehrenberg) Grunow (1884)
Pritchard (1861)
Fairly common Very rare, as it is in Holocene Ross Sea sediments Stratigraphic range' is from Fenner (1977) Fairly common, but fragmented Brady (1978) also reported this species Brady and Martin (1979) also reported this species Brady and Martin (1979) also reported this species Rare Brady and Martin (1979) reported this species Rare to common Brady and Martin (1979) also reported this species Relatively rare and broken Stratigraphic range is from Fenner (1977) Rare Abundant Relatively abundant, but broken Fairly common Brady (1978) also reported this species Brady (1978) reported this species
'See the figure. 1980 REVIEW
61
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I
PLEISTOCENE Series / Epoch
Magnetic polarity
Gauss I Matuyama IunhesI Polarity epoch
PLIOCENE
a
0
Age (my)
-I
-I
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(II r -
he established diatom zones with tentative ages extending back into the lower Miocene. The figure displays the stratigraphic ranges of diatoms we encountered in lusi' cores, for all species for which such information is available (Fenner 1977; McCollum 1975). We encountered additional species for which no stratigraphic information is currently available from the Antarctic, although many are still extant. These include: Coscinodiscus radiatus (Ehrenberg) Kutzing (1849), Nitzschia cylindrus (Grunow) Hasle (1972), N. malemt erpretaria Schrader (1976), N. obliquecostata (van Heurck) Hasle (1972), N. sublineata (van Heurck) Hasle (1972), N. vanheurckii (Peragallo) Hasle (1972), Rhizosolenia bergonii Peragallo (1892), Stephanopyxis marginata Grunow (1884), S. superba (Greville) Grunow (1884), and Thalassionema nitzschioides Grunow in van Heurck (1881). Some of the species in the figure were also reported by Brady and Martin (1979) and Brady (1978), but they and Webb (1978, 1979a) specifically stated that no species younger than Miocene occur in the lusi' cores. If we assume that McCollum's (1975) stratigraphic ranges are correct, and neither we nor Brady doubt this, then we must conclude from the figure that Miocene, Pliocene, Pleistocene, and even late Pleistocene diatom species are present throughout iusi' cores 7 and 8. Because our examination of the cores at the Antarctic Core Facility in Tallahassee and our study of the core descriptions (Webb 1978, 1979a) show that these two cores are representative of the entire suite of RISP cores, this conclusion encompasses all RISP sediments. RISP diatom assemblages clearly are reworked. We hypothesize that other miocene microfossils in RISP cores are similarly reworked. These diatom analyses of RISP sediments support our previous work (Kellogg and Truesdale 1979; Kellogg, Osterman, and Stuiver 1979; Kellogg, Truesdale, and Osterman 1979). Both units in the RISP cores have sediment compositions and microfossil distributions almost identical to Unit B from the Ross Sea. We conclude that the ius p sediments and Unit B represent a basal till that was reworked and compacted by grounded west antarctic ice. The most recent advance, which occurred during the late Brunhes, probably represents a late Wisconsin advance of the West Antarctic Ice Sheet. The significance of our results extends far beyond merely confirming our previous work with Ross Sea sediments. The presence of late Pleistocene material throughout the sediment cores from site J-9 suggests that future acquisition of longer cores from beneath the Ross Ice Shelf may provide information on the history of Quaternary and Pliocene fluctuations of the West Antarctic Ice Sheet. In addition, it
1980 REviEw
throws considerable doubt on a recent hypothesis concerning Miocene paleogeographic evolution of the Ross Sea region (Webb 1979b; Webb and Brady 1978; Webb et al. 1979) as this hypothesis requires a middle Miocene age for RISP sediments. This research was supported by National Science Foundation grants DPP 77-21083 AOl and DPP 79-20112. References Brady, H. T. 1978. Miocene diatom flora from bottom cores at site J-9. Antarctic Journal of the U.S., 13(4), 123-124.
RISP
Brady, H. T., and Martin, H. 1979. Ross Sea region in the middle Miocene: A glimpse into the past. Science, 203, 437-438. Fenner, J. 1977. Cenozoic diatom biostratigraphy of the equatorial and southern Atlantic Ocean. In P. R. Supko, K. PerchNielson, et al., Initial reports of the Deep Sea Drilling Project, Vol. 39. Washington, D.C.: U.S. Government Printing Office. Kellogg, T. B., Osterman, L. E., and Stuiver, M. 1979. Late Quaternary sedimentology and benthic foraminiferal paleoecology of the Ross Sea, Antarctica. Journal of ForaminiferoJ Research, 9(4), 322-335. Kellogg, T. B., and Truesdale, R. S. 1979. Late Quaternary paleoecology and paleoclimatology of the Ross Sea: The diatom record. Marine Micropaleontology, 4(2), 137-158. Kellogg, T. B., Truesdale, R. S., and Osterman, L. E. 1979. Late Quaternary extent of the west antarctic ice sheet: New evidence from Ross Sea cores. Geology, 7(5), 249-253. McCollum, D. W. 1975. Diatom stratigraphy of the southern ocean. 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. Truesdale, R. S., and Kellogg, T. B. 1979. Ross Sea diatoms: Modem assemblage distributions and their relationship to ecologic, oceanographic, and sedimentary conditions. Marine Micropaleontology, 4(1), 13-31. Webb, P. N. 1978. Initial report on geological materials collected at R.isi' site 1-9 1977-1978 (RIsP Tech. Rep. 78-1). Lincoln: University of Nebraska. Webb, P. N. 1979. Initial report on geological materials collected at Ri site 1-9 1978-79 (RIsP Tech. Rep. 79-1). Lincoln: University of Nebraska. (a) Webb, P. N. 1979. Paleogeographic evolution of the Ross Sector during the Cenozoic. In T. Nagata (Ed.), Proceedings of the seminar III on Dry Valley Drilling Project, 1978. Memoirs of National Insti-
tute of Polar Research, Special Issue 13, 206-212. (b) Webb, P. N., and Brady, H. T. 1978. Cenozoic glaciomarine sediments at site J-9 southern Ross Ice Shelf. EQS, 59, 309.
Webb, P. N., Ronan, T. E., Jr., Lipps, J. H., and DeLaca, T.E. 1979. Miocene glaciomarine sediments from beneath the southern Ross Ice Shelf. Science, 203, 435-437.
63
Our purpose is to demonstrate the invalidity of the late middle Miocene age date for sediments obtained at Ross Ice Shelf Project (RIsP) site J-9 (82°22'S 168°38'W), proposed by Brady (1978) and Brady and Martin (1979) and adopted by Webb (1978, 1979a, 1979b), Webb and Brady (1978), and Webb, Ronan, Lipps, and DeLaca (1979). RISP cores 7 and 8, both of which were collected during the 1977-78 field season at site J-9, were sampled at a number of levels from top
to bottom. Diatoms were prepared and analyzed using standard methods. Although we concur with Brady and Martin (1979) that middle Miocene diatoms are present in the RISP sediments, we believe that these specimens are reworked because we also observed a number of species that are considerably younger in age, as shown in the table and figure. Younger species occur throughout both sedimentary units that occur in the RISP cores (see Webb 1978, 1979a) in all samples we have analyzed; their relative abundances are similar to those calculated for Holocene Ross Sea diatoms (Truesdale and Kellogg 1979), although they are often less abundant than the Miocene-aged forms. The younger species are usually small, delicate, weakly silicified forms that are easily overlooked when mixed with the larger, more striking Miocene forms. Stratigraphic ranges were established by McCollum (1975) for a large number of diatom species that occur in Deep Sea Drilling Project (DSDP) cores from the Ross Sea. He was able to calibrate the stratigraphic ranges with paleomagnetic stratigraphy for the past 4.5 million years, and
Stratigraphically important diatom species in sediment cores from Species
J-9
Remarks
Actinocyc/us ingens Rattray (1890) Asterompha/us parvulus Karsten (1905) Charcotla act/nochilus
RISP site
(Ehrenberg) Hustedt
(1958)
Dent/cu/a antarctica McCollum (1975) Dent/cu/a hustedt// Simonsen and Kanaya (1961) Dent/cu/a lauta Bally (1854) Eucamp/a antarct/ca (= E. ba/aust/um Castracane (1886]) Melosira sulcata (Ehrenberg) KUtzing (1844) Nitzsch/a /nterfr/g/dar/a McCollum (1975) Rh/zoso/en/a hebetata forma h/ama//s Gran (1904) Roux/a antarct/ca Heiden and Kolbe (1928) Sch/mper/e//a antarct/ca Karsten (1905) Stephanopyx/s turns (Greville and Am) Ralfs in Tha/ass/onema elegans Hustedt (1958) Thalass/osira grad/Is (Karsten) Hustedt (1958) Trinacria excavata Heiberg (1863) Trinacria p/leo/us (Ehrenberg) Grunow (1884)
Pritchard (1861)
Fairly common Very rare, as it is in Holocene Ross Sea sediments Stratigraphic range' is from Fenner (1977) Fairly common, but fragmented Brady (1978) also reported this species Brady and Martin (1979) also reported this species Brady and Martin (1979) also reported this species Rare Brady and Martin (1979) reported this species Rare to common Brady and Martin (1979) also reported this species Relatively rare and broken Stratigraphic range is from Fenner (1977) Rare Abundant Relatively abundant, but broken Fairly common Brady (1978) also reported this species Brady (1978) reported this species
'See the figure. 1980 REVIEW
61
I
a'
0
a
•-J
E
Cr
c;
T'
I I *
rL
N
6 ft— a
N
. •• o •
orb
CL
V; 3 ç5 0
—I
CL ^LOWIE^ R MIDDLE MIOCENE pa Tr F I
-a333
CL
a Ca
00
: '0
0 g— C
3 -. ..a
6. D..' — * -
• NO
2
2. C• P0
8
0
LATE (UPPER) MIOCENE
C
5' 5' •
! 2.!.a
xr
0 2 a
3
-
ID-1G0 UI (0
o 0
.i.,ons
grOcills
D. onforclice
M su/coto
T p/iso/us
-1
S. turns
h/.me/is
R. hb•toto forma
D. Icuto
D. /,usF.dtii
N. inNrr/g/dOrIO
A. ingens
r
E. onto,cIco
R. on1orcico
C. ocp,nech/Ius
A. porvulus
r
S. crnorcPicc
T •xCOvOtO
I
PLEISTOCENE Series / Epoch
Magnetic polarity
Gauss I Matuyama IunhesI Polarity epoch
PLIOCENE
a
0
Age (my)
-I
-I
0 Z
(II r -
he established diatom zones with tentative ages extending back into the lower Miocene. The figure displays the stratigraphic ranges of diatoms we encountered in lusi' cores, for all species for which such information is available (Fenner 1977; McCollum 1975). We encountered additional species for which no stratigraphic information is currently available from the Antarctic, although many are still extant. These include: Coscinodiscus radiatus (Ehrenberg) Kutzing (1849), Nitzschia cylindrus (Grunow) Hasle (1972), N. malemt erpretaria Schrader (1976), N. obliquecostata (van Heurck) Hasle (1972), N. sublineata (van Heurck) Hasle (1972), N. vanheurckii (Peragallo) Hasle (1972), Rhizosolenia bergonii Peragallo (1892), Stephanopyxis marginata Grunow (1884), S. superba (Greville) Grunow (1884), and Thalassionema nitzschioides Grunow in van Heurck (1881). Some of the species in the figure were also reported by Brady and Martin (1979) and Brady (1978), but they and Webb (1978, 1979a) specifically stated that no species younger than Miocene occur in the lusi' cores. If we assume that McCollum's (1975) stratigraphic ranges are correct, and neither we nor Brady doubt this, then we must conclude from the figure that Miocene, Pliocene, Pleistocene, and even late Pleistocene diatom species are present throughout iusi' cores 7 and 8. Because our examination of the cores at the Antarctic Core Facility in Tallahassee and our study of the core descriptions (Webb 1978, 1979a) show that these two cores are representative of the entire suite of RISP cores, this conclusion encompasses all RISP sediments. RISP diatom assemblages clearly are reworked. We hypothesize that other miocene microfossils in RISP cores are similarly reworked. These diatom analyses of RISP sediments support our previous work (Kellogg and Truesdale 1979; Kellogg, Osterman, and Stuiver 1979; Kellogg, Truesdale, and Osterman 1979). Both units in the RISP cores have sediment compositions and microfossil distributions almost identical to Unit B from the Ross Sea. We conclude that the ius p sediments and Unit B represent a basal till that was reworked and compacted by grounded west antarctic ice. The most recent advance, which occurred during the late Brunhes, probably represents a late Wisconsin advance of the West Antarctic Ice Sheet. The significance of our results extends far beyond merely confirming our previous work with Ross Sea sediments. The presence of late Pleistocene material throughout the sediment cores from site J-9 suggests that future acquisition of longer cores from beneath the Ross Ice Shelf may provide information on the history of Quaternary and Pliocene fluctuations of the West Antarctic Ice Sheet. In addition, it
1980 REviEw
throws considerable doubt on a recent hypothesis concerning Miocene paleogeographic evolution of the Ross Sea region (Webb 1979b; Webb and Brady 1978; Webb et al. 1979) as this hypothesis requires a middle Miocene age for RISP sediments. This research was supported by National Science Foundation grants DPP 77-21083 AOl and DPP 79-20112. References Brady, H. T. 1978. Miocene diatom flora from bottom cores at site J-9. Antarctic Journal of the U.S., 13(4), 123-124.
RISP
Brady, H. T., and Martin, H. 1979. Ross Sea region in the middle Miocene: A glimpse into the past. Science, 203, 437-438. Fenner, J. 1977. Cenozoic diatom biostratigraphy of the equatorial and southern Atlantic Ocean. In P. R. Supko, K. PerchNielson, et al., Initial reports of the Deep Sea Drilling Project, Vol. 39. Washington, D.C.: U.S. Government Printing Office. Kellogg, T. B., Osterman, L. E., and Stuiver, M. 1979. Late Quaternary sedimentology and benthic foraminiferal paleoecology of the Ross Sea, Antarctica. Journal of ForaminiferoJ Research, 9(4), 322-335. Kellogg, T. B., and Truesdale, R. S. 1979. Late Quaternary paleoecology and paleoclimatology of the Ross Sea: The diatom record. Marine Micropaleontology, 4(2), 137-158. Kellogg, T. B., Truesdale, R. S., and Osterman, L. E. 1979. Late Quaternary extent of the west antarctic ice sheet: New evidence from Ross Sea cores. Geology, 7(5), 249-253. McCollum, D. W. 1975. Diatom stratigraphy of the southern ocean. 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. Truesdale, R. S., and Kellogg, T. B. 1979. Ross Sea diatoms: Modem assemblage distributions and their relationship to ecologic, oceanographic, and sedimentary conditions. Marine Micropaleontology, 4(1), 13-31. Webb, P. N. 1978. Initial report on geological materials collected at R.isi' site 1-9 1977-1978 (RIsP Tech. Rep. 78-1). Lincoln: University of Nebraska. Webb, P. N. 1979. Initial report on geological materials collected at Ri site 1-9 1978-79 (RIsP Tech. Rep. 79-1). Lincoln: University of Nebraska. (a) Webb, P. N. 1979. Paleogeographic evolution of the Ross Sector during the Cenozoic. In T. Nagata (Ed.), Proceedings of the seminar III on Dry Valley Drilling Project, 1978. Memoirs of National Insti-
tute of Polar Research, Special Issue 13, 206-212. (b) Webb, P. N., and Brady, H. T. 1978. Cenozoic glaciomarine sediments at site J-9 southern Ross Ice Shelf. EQS, 59, 309.
Webb, P. N., Ronan, T. E., Jr., Lipps, J. H., and DeLaca, T.E. 1979. Miocene glaciomarine sediments from beneath the southern Ross Ice Shelf. Science, 203, 435-437.
63
