Geochemical and isotopic study of sediment from unit I ...
tions have occurred recently in the southwestern section of the island. Drainage through the inlet and into Port Foster must have removed most of the ash before it could settle and accumulate. A single sedimentary facies has been designated in the region of Bransfield Strait surrounding Deception Island. Winds and currents are probably most responsible for the removal of the finer sediment from the exterior slopes of the land. The distribution of pyroclastics (particularly ash) originating from Deception Island is extensive, ranging as far as King George Island approximately 120 kilometers to the northeast (Baker and McReath, 1971). This research was supported by National Science Foundation grant GV-3 1162. References Baker, P. E., and I. McReath. 1971. 1970 volcanic eruption at Deception Island. Nature ('Physical Science), 231(18): 5-9. Finger, K. L. 1975. Benthic foraminifera from Deception Island. Antarctic Journal of the U.S., X(4): 134-135. Finger, K. L. 1976. Recent benthic foraminifera from pyroclastic substrates: a biofacies analysis of Deception Island, South Shetland Islands, Antarctica. Ph.D. dissertation. Davis, University of California. 165p. Folk, R. L. 1954. The distinction between grain size and mineral composition in sedimentary-rock nomenclature. Journal of Geology, 62(4): 344-359. Lipps, J . H., and T. F. DeLaca. 1974. Foraminiferal ecology, Antarctica Peninsula. Antarctic Journal of the U.S., IX(4): 111113.
Geochemical and isotopic study of sediment from unit I, DSDP site 270, Ross Sea GUNTER FAURE and JANE L. BOGER Institute of Polar Studies The Ohio State University Columbus, Ohio 43210
As part of a study of the chemical composition and strontium isotopic composition of sediment deposited in the Ross Sea (Faure and Bannigan, 1975; Shaffer and Faure, in press), we analyzed samples from unit 1 of Deep Sea Drilling Project (DSDP) site 270 (Hayes et al., 1975). The site is located at 77°26.48'S. 178°30.19'W. This unit exSeptember 1976
tends to about 20 meters below the bottom and consists of unconsolidated silty clay of late Pliocene to Recent age. The upper 20 centimeters of unit 1 is a soupy, diatomaceous, silty clay (labeled subunit 1A) that makes a sharp contact with somewhat more compacted sand-silt-clay sediment (subunit 1B). Hayes et al. (1975) report finding rare specimens of the foraminifer Miliammina arenacea at the top of core 1 (suggesting a Brunhes age) and Globocassidulina biora in the core catcher of core 3 (suggesting a Gauss age). The samples we analyzed are from unit lB. The table gives the analytical results. Figure 1 demonstrates that the strontium-87/ strontium-86 ratios of the noncarbonate fractions of the sediment increase linearly with the reciprocals of the strontium concentration. This relationship indicates that the sediment is a mixture of two components having differing strontium-87/strontium-86 ratios and strontium concentrations. Faure and Bannigan (1975) identified these components as volcanogenic detritus (low strontium-87/strontium-86, high strontium content) and weathering products of older sialic rocks (high strontium-87/ strontium-86, low strontium content). Although the linear correlation of the data points is substantial (correlation coefficient r = +0.85), no further quantitative interpretation will be attempted at this time. Figure 2 contains depth profiles of the parameters listed in the table on the basis of which unit lB is subdivided as shown. Unit lB 1 (extending to 1.35 meters below the bottom) has low concentrations of coarse particles (15.8 percent) and low concentrations of strontium (110.4 parts per million), rubidium (114.3 parts per million), and calcium oxide (1.18 percent). It has a high Si0 2 content (77.3 percent) and a strontium-87/strontium-86 ratio of 0.7241. Unit 111 2 is of unknown thickness (due to loss of core) and has higher concentrations of coarse fraction (22.4 percent), strontium (130.6 parts per million), rubidium (124.5 parts per million), and calcium oxide (1.25 percent). Its Si02 content is low (73.3 percent), and its strontium-87/ strontium-86 ratio is 0.7219. The third subunit (1113 ), occurring at the base of unit 1B, has intermediate concentrations of coarse sediment (18.1 percent), strontium (115.4 parts per million), and Si02 (75.3 percent). It has a somewhat elevated concentration of rubidium (127.4 parts per million) and calcium oxide (1.26 percent), and its strontium87/strontium-86 ratio is 0.7249. The proposed subdivision of the unconsolidated sediments at DSDP site 270 may be useful in correlating sediment layers among piston cores collected elsewhere in the Ross Sea from USNS Eltanin. Moreover, such studies provide baseline data for interpretation of sediment cores to be recovered from beneath the Ross Ice Shelf. 163
Analytical data for sediment from unit 1B, DSDP site 270, Ross Sea. Strontium Rubidium Coarse fraction +100 mesh Strontium-87 (parts per (parts per Calcium oxide Si02 Sample (percent) Strontium-86 million) million) (percent) (percent) 1-1, 110-112 14.1 1-1, 129-130 17.4 1-1, 148-149 22.0 1-2, 20- 21 23.5 1-2, 43- 44 22.9 1-2, 60- 61 23.2 1-2, 82- 83 22.0 1-2, 112-113 20.7 3-1, 101-102 22.4 3-1, 119-120 16.4 3-1, 141-142 15.4
0.7265 0.7217 0.7210 0.7228 0.7224 0.7210 0.7221 0.7222 0.7246 0.7251 0.7252
99.3 121.5 130.7 130.8 133.9 135.4 125.9 127.2 116.2 116.2 113.9
106.0 122.6 128.7 126.2 123.0 126.9 120.1 122.3 129.2 128.5 124.6
1.13 1.23 1.26 1.33 1.26 1.24 1.22 1.22 1.23 1.26 1.29
80.0 74.6 72.1 72.8 72.8 74.5 73.6 74.2 74.1 75.0 76.7
Concentrations of the +100 mesh fractions refer to the total sediment. All other measurements were made on the - 100 mesh fractions after removal of carbonate phases by leaching with 2N HCl. The concentrations of strontium, rubidium, calcium oxide, and Si02 were determined by X-ray fluorescence using calibrations based on rock standards of the U.S. Geological Survey (Reynolds, 1963).
87
Sr
86 Sr 'ø-S
0.726 • •
• I 0.724 •-0
•1E/.
0.722
87
Sr - 2.427 0.7032 1 Sr
867 -
0.720
6
/
0
9 10 1/Sr,ppni -1
164
II 1t.I I A I V
Figure 1. Linear correlation of strontium-87/strontium86 ratios and the reciprocals of the strontium concentrations of noncarbonate sediment. The line was fitted by least-squares regression after shifting the c+rrntIi im trntntrntinfln of three samples by 2; shown.
ANTARCTIC JOURNAL
Coarse Fraction +100 Mesh, % 10 15 20 25
Sr ppm 110
Rb ppm
120 130
110
140
CaO
120
1301.1 1.2
Si0 1.3 72
74
76
2 78
80
Strat, Units
• S
S •
S
• 4)
.1-i
4) E
S
S
• •
• S
•
S S
.
S 4) 0
4)3 7
No Sediment Recovered
Li
S
• •
S
.
S S .
7
S •
• I
1
3
I
Figure 2. Depth variation of chemical parameters on the basis of which unit lB is subdivided as indicated. Analytical data are explained briefly In the table.
This research was supported by National Science Foundation grant DPP 72-00459. The Deep Sea Drilling Project provided the sediment samples.
Recent deep-sea benthic foraminiferal distributions in the southeast Indian Ocean
References
BRUCE H. CoRLIss Graduate School of Oceanography University of Rhode Island Kingston, Rhode Island 02881
Faure, G., and J . L. Bannigan. 1975. Geochemistry and mineralogy of DSDP core 270, Ross Sea. Antarctic Journal of the U.S., X(5): 256-257. The distribution of deep-sea benthic foraminiHayes, D. E., et al. 1975. Initial Reports of the Deep Sea Drilling fera has been examined from Recent surface sediProject, 28. Washington, D.C., U.S. Government Printing Ofments from USNS Eltanin trigger cores in the fice. 10 17p. Reynolds, R. C. 1963. Matrix corrections in trace element analy- southeast Indian Ocean between 250 to 50°S. and sis by X-ray fluorescence. American Mineralogy, 48: 1133- 80° to 120°E. to evaluate possible relationships 1143. with water masses. Two abyssal water masses are Shaffer, N. R., and G. Faure. In press. Regional variation of 87 Sr/ 86 Sr ratios and mineral compositions of sediment from present in the area with Antarctic Bottom Water the Ross Sea, Antarctica. Geological Society of America Bulle- (AABW) found south of the Southeast Indian Ridge tin, 87(10). and Indian Bottom Water found astride the west-
September 1976
165
Geochemical and isotopic study of sediment from unit I, DSDP site 270, Ross Sea GUNTER FAURE and JANE L. BOGER Institute of Polar Studies The Ohio State University Columbus, Ohio 43210
As part of a study of the chemical composition and strontium isotopic composition of sediment deposited in the Ross Sea (Faure and Bannigan, 1975; Shaffer and Faure, in press), we analyzed samples from unit 1 of Deep Sea Drilling Project (DSDP) site 270 (Hayes et al., 1975). The site is located at 77°26.48'S. 178°30.19'W. This unit exSeptember 1976
tends to about 20 meters below the bottom and consists of unconsolidated silty clay of late Pliocene to Recent age. The upper 20 centimeters of unit 1 is a soupy, diatomaceous, silty clay (labeled subunit 1A) that makes a sharp contact with somewhat more compacted sand-silt-clay sediment (subunit 1B). Hayes et al. (1975) report finding rare specimens of the foraminifer Miliammina arenacea at the top of core 1 (suggesting a Brunhes age) and Globocassidulina biora in the core catcher of core 3 (suggesting a Gauss age). The samples we analyzed are from unit lB. The table gives the analytical results. Figure 1 demonstrates that the strontium-87/ strontium-86 ratios of the noncarbonate fractions of the sediment increase linearly with the reciprocals of the strontium concentration. This relationship indicates that the sediment is a mixture of two components having differing strontium-87/strontium-86 ratios and strontium concentrations. Faure and Bannigan (1975) identified these components as volcanogenic detritus (low strontium-87/strontium-86, high strontium content) and weathering products of older sialic rocks (high strontium-87/ strontium-86, low strontium content). Although the linear correlation of the data points is substantial (correlation coefficient r = +0.85), no further quantitative interpretation will be attempted at this time. Figure 2 contains depth profiles of the parameters listed in the table on the basis of which unit lB is subdivided as shown. Unit lB 1 (extending to 1.35 meters below the bottom) has low concentrations of coarse particles (15.8 percent) and low concentrations of strontium (110.4 parts per million), rubidium (114.3 parts per million), and calcium oxide (1.18 percent). It has a high Si0 2 content (77.3 percent) and a strontium-87/strontium-86 ratio of 0.7241. Unit 111 2 is of unknown thickness (due to loss of core) and has higher concentrations of coarse fraction (22.4 percent), strontium (130.6 parts per million), rubidium (124.5 parts per million), and calcium oxide (1.25 percent). Its Si02 content is low (73.3 percent), and its strontium-87/ strontium-86 ratio is 0.7219. The third subunit (1113 ), occurring at the base of unit 1B, has intermediate concentrations of coarse sediment (18.1 percent), strontium (115.4 parts per million), and Si02 (75.3 percent). It has a somewhat elevated concentration of rubidium (127.4 parts per million) and calcium oxide (1.26 percent), and its strontium87/strontium-86 ratio is 0.7249. The proposed subdivision of the unconsolidated sediments at DSDP site 270 may be useful in correlating sediment layers among piston cores collected elsewhere in the Ross Sea from USNS Eltanin. Moreover, such studies provide baseline data for interpretation of sediment cores to be recovered from beneath the Ross Ice Shelf. 163
Analytical data for sediment from unit 1B, DSDP site 270, Ross Sea. Strontium Rubidium Coarse fraction +100 mesh Strontium-87 (parts per (parts per Calcium oxide Si02 Sample (percent) Strontium-86 million) million) (percent) (percent) 1-1, 110-112 14.1 1-1, 129-130 17.4 1-1, 148-149 22.0 1-2, 20- 21 23.5 1-2, 43- 44 22.9 1-2, 60- 61 23.2 1-2, 82- 83 22.0 1-2, 112-113 20.7 3-1, 101-102 22.4 3-1, 119-120 16.4 3-1, 141-142 15.4
0.7265 0.7217 0.7210 0.7228 0.7224 0.7210 0.7221 0.7222 0.7246 0.7251 0.7252
99.3 121.5 130.7 130.8 133.9 135.4 125.9 127.2 116.2 116.2 113.9
106.0 122.6 128.7 126.2 123.0 126.9 120.1 122.3 129.2 128.5 124.6
1.13 1.23 1.26 1.33 1.26 1.24 1.22 1.22 1.23 1.26 1.29
80.0 74.6 72.1 72.8 72.8 74.5 73.6 74.2 74.1 75.0 76.7
Concentrations of the +100 mesh fractions refer to the total sediment. All other measurements were made on the - 100 mesh fractions after removal of carbonate phases by leaching with 2N HCl. The concentrations of strontium, rubidium, calcium oxide, and Si02 were determined by X-ray fluorescence using calibrations based on rock standards of the U.S. Geological Survey (Reynolds, 1963).
87
Sr
86 Sr 'ø-S
0.726 • •
• I 0.724 •-0
•1E/.
0.722
87
Sr - 2.427 0.7032 1 Sr
867 -
0.720
6
/
0
9 10 1/Sr,ppni -1
164
II 1t.I I A I V
Figure 1. Linear correlation of strontium-87/strontium86 ratios and the reciprocals of the strontium concentrations of noncarbonate sediment. The line was fitted by least-squares regression after shifting the c+rrntIi im trntntrntinfln of three samples by 2; shown.
ANTARCTIC JOURNAL
Coarse Fraction +100 Mesh, % 10 15 20 25
Sr ppm 110
Rb ppm
120 130
110
140
CaO
120
1301.1 1.2
Si0 1.3 72
74
76
2 78
80
Strat, Units
• S
S •
S
• 4)
.1-i
4) E
S
S
• •
• S
•
S S
.
S 4) 0
4)3 7
No Sediment Recovered
Li
S
• •
S
.
S S .
7
S •
• I
1
3
I
Figure 2. Depth variation of chemical parameters on the basis of which unit lB is subdivided as indicated. Analytical data are explained briefly In the table.
This research was supported by National Science Foundation grant DPP 72-00459. The Deep Sea Drilling Project provided the sediment samples.
Recent deep-sea benthic foraminiferal distributions in the southeast Indian Ocean
References
BRUCE H. CoRLIss Graduate School of Oceanography University of Rhode Island Kingston, Rhode Island 02881
Faure, G., and J . L. Bannigan. 1975. Geochemistry and mineralogy of DSDP core 270, Ross Sea. Antarctic Journal of the U.S., X(5): 256-257. The distribution of deep-sea benthic foraminiHayes, D. E., et al. 1975. Initial Reports of the Deep Sea Drilling fera has been examined from Recent surface sediProject, 28. Washington, D.C., U.S. Government Printing Ofments from USNS Eltanin trigger cores in the fice. 10 17p. Reynolds, R. C. 1963. Matrix corrections in trace element analy- southeast Indian Ocean between 250 to 50°S. and sis by X-ray fluorescence. American Mineralogy, 48: 1133- 80° to 120°E. to evaluate possible relationships 1143. with water masses. Two abyssal water masses are Shaffer, N. R., and G. Faure. In press. Regional variation of 87 Sr/ 86 Sr ratios and mineral compositions of sediment from present in the area with Antarctic Bottom Water the Ross Sea, Antarctica. Geological Society of America Bulle- (AABW) found south of the Southeast Indian Ridge tin, 87(10). and Indian Bottom Water found astride the west-
September 1976
165
