Summary of sediment descriptions of piston cores
sedimentary clasts. Sediments across the America-Antarctic Ridge (core 4) are composed of Quaternary diatomaceous ooze occasionally rich in volcanic ash. Farther to the east, and approaching the Weddell basin, sediments are pelagic clays and muds (cores 5 through 8). Only core 8 has a Quaternary basal sediment, while basal sediments of cores 5 through 7 predate middle Pliocene. This is similar to the situation farther east in sediments south of the Atlantic-Indian Ridge, where buried disconformities also have been documented (Ledbetter and Ciesielski 1981). Other cores on the northern part of the Weddell basin (cores 56 and 49) are composed of Quaternary pelagic clay overlain by ash-bearing diatomaceous ooze (core 49). Sediments in the Weddell abyssal plain proper are mostly barren of microfossils; thus, basal ages of the cores in this area cannot be determined. Sediments in the western part of the abyssal plain (traverse A—A'; cores 55, 52, and 40) generally are composed of pelagic clay bearing minor amounts of sand and silt (core 40). Similarly, pelagic clay is found on the northern part of traverse D—D' (core 47a), as well as in cores 48 and 47 (Kaharoeddin et al. 1980). However, in the vicinity of the Islas Orcadas Seamounts (traverse D—D'; cores 45 through 42) the primary sediment is sand, with minor amounts of clay, an occurrence that probably can be attributed to local factors. Core 50, which is composed of interbedded clay and sand (Kaharoeddin et al. 1980), shows the effect of both general and local sedimentation patterns. In the eastern part of the abyssal plain along traverse E—E' (cores 9 through 12) the pelagic clay is interbedded with silt and mud. Cores on the continental margin can be divided into two groups: those on the continental rise and those on the continental terrace. The continental rise cores include cores 25 through 33 (traverse B—B') and cores 24 and 22 (traverse F—F'). In general, these cores consist of mud and interbedded sandy mud, characterized by an abundance of sedimentary clasts and pebbles and also showing evidence of unconformities separating the lower Miocene and younger sediments. Core 22 is an exception to this pattern, as it consists primarily of marly for-
aminiferal ooze, a lithology that is indicative of a local high productivity coupled with a favorable carbonate compensation depth. Core 24 penetrates lower Oligocene sediments and is composed of diatomaceous mud. The unconformities along the continental margin have been documented by Ledbetter and Ciesielski (1981) for sediments from cruise 12-77 of ARA Islas Orcadas. Cores 39 and 14, which were recovered from the lower continental rise, are composed of clay and mud having an abundance of sedimentary clasts and pebbles. Their composition indicates that these two cores are the product of both abyssal plain and continental margin sedimentary processes. They contain several unconformities, and their basal ages are early Miocene. Continental terrace cores, which include cores 32 through 28 (traverse B—B') and cores 20 through 16 (traverse F—F'), consist mostly of sand, mud, and a mixture of the two, except core 18, which is composed largely of pebbles. Although basal sediments of these cores are mostly barren, they are all believed to be Quaternary in age; this assumption is based on the basal ages of cores 32 and 28. We wish to acknowledge Dennis Cassidy for his help in several phases of this work, including photography of the figures. Rosemarie Raymond drafted the figures. This work has been supported by National Science Foundation contract c-1059.
Summary of sediment descriptions of ARA Islas Orcadas cruise 16 piston cores
Bank, the Georgia Basin, and the Islas Orcadas Rise and to trace the flow of antarctic deep water in the southwest Atlantic Ocean between the Mid-Atlantic Ridge and the America-Antarctic Ridge (Wise et al. 1978). A total of 69 piston cores were recovered, of which 68 were received at the Antarctic Research Facility (figure 1). This article presents a summary of the descriptions of these cores, based on the more detailed sediment descriptions prepared by Kaharoeddin and associates (1982). Although the locations of all cores are shown in figure 1, limitations of space make it necessary to omit the lithologic logs of 20 cores from the graphic summary presented in figures 2 and 3. (The omitted cores are 23, 24, 27, 34, 37, 41, 44, 50, 51, 57, 65, 67, 70, 83, 104, 105, 106, 111, 114, and 117.) Discussion of basal ages of the cores is based on the work of Jones and associates (1979). Of the 32 piston cores taken on the Maurice Ewing Bank, only 18 recovered undisturbed (by flow-in) sediments greater than 100 centimeters in length. All 32 of these cores are relatively
F. AMRISAR KAHAROEDDIN, R. SHELTON GRAVES, and CYNTHIA L. HUMI'HREYS
Antarctic Marine Geology Research Facility Department of Geology Florida State university Tallahassee, Florida 32306
The primary goals of the coring program aboard cruise 16-78 of ARA Islas Orcadas (Sherwood W. Wise, Jr., chief scientist) were to survey older (pre-Pliocene) sediments of the Maurice Ewing 1982 REVIEW
References Ciesielski, P. F., and Jones, S. C. 1979. Sediment ages of ARA Islas Orcadas cruise 15 piston cores. Antarctic Journal of the U.S., 14(5), 148-151. Kaharoeddin, F A., Eggers, M. R., Goldstein, E. H., Graves, R. S., Watkins, D. K., Bergen, J . A., and Jones, S. C. 1980. ARA Islas Orcadas cruise 1578 sediment descriptions (Contribution 48). Tallahassee: Florida State University, Department of Geology, Sedimentology Research Laboratory. Ledbetter, M. T., and Ciesielski, P. F. 1981. Bottom-current erosion in the South Atlantic sector of the southern ocean. Antarctic Journal of the U.S., 16(5),110-112.
135
7OW
CO.
5O
'V 40
45
55
4,
48W 46
44
42
40'W
Figure 1. Locations of piston cores recovered aboard cruise 16-78 of
short, with their undisturbed portions ranging from 20 to 520 centimeters. Three of the cores (23, 24, 51) for which lithologic logs are not shown in figure 2 penetrated only Quaternary sediments consisting of foraminiferal sand or sandy foraminiferal ooze. Core 27, also not shown, is similar to core 29; it consists of pelagic clay containing some zeolites. (These cores are very similar to Islas Orcadas piston core 0775-50, which has been dated by Ciesielski and Wise, 1977, as Eocene in age.) Other cores in this area not shown in figure 2 (cores 34, 37, 41, 44, and 50) are similar in lithology to one or more of their companion cores whose logs are shown. Most of the pre-Pliocene sediments on the Maurice Ewing Bank range in age from late Miocene to late Paleocene and consist of nannofossil ooze occasionally containing common to abundant diatoms and/or radiolarians. Exceptions to this are core 20 (diatomaceous mud), core 25 (glauconitic, sandy diatomaceous ooze), core 26 (muddy diatomaceous ooze), core 28 (diatomaceous sand), and core 19 (intermixed diatomaceous ooze and glauconitic, sandy siliceous ooze). Numerous unconformities can be seen in these cores. A detailed discussion of the 136
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Islas Orcadas.
unconformities in Neogene sediments in this area can be found in Ciesielski and others (1982). On the western flank of the northeast Georgia Rise, two cores (55 and 56) penetrated lower Pliocene sediments; however, they consist of differing lithologies. When combined, these two cores provide an excellent Pliocene record (Wise et al. 1978). Evidence of unconformities can be seen in the top parts of these cores. One core not shown in figure 2, core 57, is composed primarily of Quaternary foraminiferal diatomaceous ooze overlain by a sandy or muddy diatomaceous ooze. Cores 103 through 109 were taken on the Islas Orcadas Rise (cores 104-106 are not shown in figure 3). In general, the Islas Orcadas Rise cores are short, but they penetrated pre-Quaternary sediments. In core 104, only the top 37 centimeters is undisturbed by flow-in, although its total length is 662 centimeters. Nevertheless, this core is valuable for stratigraphic work, because the interval between 36 and 37 centimeters consists of a lower Oligocene nannofossil ooze overlain by a sandy, muddy diatomaceous ooze. Cores 105 (220 centimeters) and 106 (47 centimeters) are lithologically similar to the upper part of core ANTARCTIC JOURNAL
!IIlIi
31 32 33 30 29 28
8 19 20 21 22 25 26
3091 m 2771m 2465m 2012m 2182m 2557m
2345m 2725 m 2498m 2262m 2420m 2573m 2703
100Z
- G.
B'
B
A'
A
.
50cm
- ' :-,--r 85cm (105cm) j--
•I00
:G
(527cm)
200
Ocm
"-G
140 cm
144cm
78cm
19 6 cm
-200
230 Cm
G.
-300
=--
317 cm
-
(447 cm
307cm -::--:
t
(509cm) --'-:
339 cm (530 cm)
372 cm
-400
400
447 cm
460 cm
(563 cm)
(570 cm)
500
-500
C' D
C 36 35
38
45
43
39
47
46
2622m 2429m 1595 m 1840 m 1706 m 1624 m 1693 m 1529 m 1598 0cm-
52
49
48
100-
I
. p
Z=Z 200 ''
(281 cm)
--
ZP
-ioo --
159cm
C
_.L L—aLUA
zZ :0= Z=?:: Z=z -'-
229 cm (500 cm (309cm)
E
1
-zoo
(1762cm) -'- -,
188 cm
215 cm
KEY NANNOFOSSIL OOZE
SAND
FORAMINIFERAL OOZE
MUDDY SAND
CALCAREOUS OOZE
PEBBLES
DIATOMACEOUS OOZE
VOLCANIC ASH
MUDDY, DIATOMACEOUS OOZE
LAPILLI
280 cm
—300
1=
Jr
RADIOLARIAN OOZE Z1
LI1
492 cm
FG 7G
GL AU CON IT E
PELAGIC CLAY
Fuo
SEDIMENTARY CLASTS
r 520 cm
MUD
400
CHERT
SILICEOUS OOZE
EGE
500-
-
:t
- ^Z_ Mct=
Z 400-
73 cm (532 cm)
=0cm
-q-0 :-'---
300-
56
m 1708 m 3936 m 2533m 2374m
53cm (99 cm)
-- 74cm :-'- -
55
D'
ZEOLITES
DIATOMACEOUS MUD
MANGANESE NODULES
GRADATIONAL CONTACT
SHARP CONTACT
500
777 cm L..800
Figure 2. Simplified lithologic logs of cores from the Maurice Ewing Bank and the Georgia Basin. Numbers above log are core number and water depth; number at base of log is core length; number at base in parentheses is actual core length, including flow-in portion (not shown). 1982 REVIEW
137
E
El F
F
116 115 112 109 108 107 103 76 73 68 66 64 63 0cm
5044m 5047m 4374m 2999m 2772m 2986m 3028m 3312m 3877m 4422m 4422m 45(5m 4389m
200
200
(1089cm)
400
401 cm 444 cm
600
-'487cm (1036cm)
-
400
--
- 695cm 740cm (1030cm) 1148 cm)
800
600
-z 659Cm 697cm
2- -800 (838 _= cm 843cm (1086cm) 11000
1120cm
1106cm
(1700cm)
(174 1cm)
1361cm (1780cm)
400
1600
1600
1686cm (1761cm)
G G' 80 81 84 87 89 90 91 98 96 3102m 3464m 3952m 3738m 4285m 4545m 3954m 4631 m 4177m
KEY
ocrnfl
NANNOFOSSIL OOZE
FM
FORAMINIFERAL OOZE CALCAREOUS OOZE DIATOMACEOUS OOZE MUDDY. DIATOMACEOUS OOZE
4
DIATOMACEOUS MUD PELAGIC CLAY
11167 cm) 600-
SAND
535 cm (1715cm)
-
P7- 71 VOLCANIC ASH
rs-1—
800 -
1000_i - I
PEBBLES
LAPILLI
R—M
SEDIMENTARY CLASTS
845cm
MANGANESE NODULES SHARP CONTACT
(1761cm)
GRADATIONAL CONTACT
1049cm EEi
1094cm (1735cm) 1146cm
1172cm (1207cm) 400
1386 cm (1717cm)
Figure 3. Simplified lithologic logs of cores in the southwestern sector of the Atlantic Ocean, between the Mid-Atlantic Ridge and the AmericaAntarctic Ridge. Numbers above log are core number and water depth; number at base of log is core length; number at base in parentheses is actual core length, including flow-in portion (not shown).
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ANTARCTIC JOURNAL
103, permitting stratigraphic correlation. Core 109 contains nannofossil ooze of middle to late Miocene age and is unconformably overlain by Quaternary diatomaceous and muddy diatomaceous oozes. The remaining cores shown in figure 3 are Quaternary in age. Predictable changes in lithology are found in the progression from north to south along traverses E-E', F-F, and C-C'. In the deeper part of the Argentine Basin, the sediment consists of pelagic clay (cores 117, 116, and 115). Farther south are primarily diatomaceous ooze and muddy diatomaceous ooze (cores 114, 112, and 111). Less deep, and in the vicinity of the Mid-Atlantic Ridge, are to be found a calcareous diatomaceous ooze (core 76) and a unit of nannofossil ooze (core 80). Although the rest of the cores are primarily diatomaceous ooze, local variations do occur. For example, the sediments of cores 89, 90, and 91, near the America-Antarctic Ridge, contain volcanic ash, lapilli, pebbles, and sedimentary clasts. Unconformities can be observed in several cores. We wish to acknowledge the assistance and advice of Dennis Cassidy in the preparation of this article. Steve KnUttel helped in preparing the figures, which were drafted by Rosemarie Raymond and photographed by Dennis Cassidy. Funding for
Biostratigraphic correlations and regional erosion shown by the
radiolarian Cycladophora davisiana and the diatoms Eucampia balaustium and Hemidiscus karstenll R. SHELTON GRAVES Antarctic Research Facility Department of Geology Florida State University Tallahassee, Florida 32306
To conduct sedimentological studies of upper Brunhes southern ocean sediments, it is necessary to use high-resolution biostratigraphic schemes. Three biostratigraphically useful species for the interval 195,000 years before present to recent are the radiolarian Cycladophora davisiana and the diatoms Eucampia balaustium and Hemidiscus karstenii. This article describes their utility in biostratigraphic work with USNS Eltanin piston cores from the southeast Indian Ocean (for core locations, see table). The last-abundant-appearance datum (LAAD) of Hemidiscus karstenii has been dated at 195,000 years before present (Burckle, Clarke, and Shackleton 1978). This datum is of marginal utility in the present study, however. Although the datum was well established in cores E49-3, E49-24 (although somewhat stratigraphically high), and E50-9, in cores E50-10, E50-16, and E49-16, the maximum abundance of Hemidiscus karstenii is less than 4 percent. In these situations, extreme care must be exercised in 1982 REVIEW
this work has been provided by National Science Foundation contract c-1059.
References Ciesielski, P. F., and Wise, S. W., Jr. 1977. Basal sediment ages of Islas Orcadas cruise 7 piston cores. Antarctic Journal of the U.S., 12(4), 70-72. Ciesielski, P. F., Ledbetter, M. T., and Ellwood, B. B. 1982. The development of antarctic glaciation and the Neogene paleoenvironment of the Maurice Ewing Bank. Marine Geology, 46, 1-51. Jones, S. C., Wise, S. W., Jr., DeFelice, DR., Hattner, J. G., Mostajo, E. L., Gombos, A. M., and Weaver, F. M. 1979. Basal sediment ages of ARA Islas Orcadas cruise 16 piston cores. Antarctic Journal of the U.S., 14(5),151-153.
Kaharoeddin, F. A., Graves, R. S., Bergen, J. A., Eggers, M. R., Harwood, D. M., Humphreys, C. L., Goldstein, E. H., Jones, S. C., and Watkins, D. K. 1982. ARA Islas Orcadas cruise 1678 sediment descriptions (Contribution 50). Tallahassee: Florida State University, Department of Geology, Sedimentology Research Laboratory. Wise, S. W., Jr., Jones, S. C., Ciesielski, P. F., Georgi, D. T., Woodroffe, D. S., and Jacobs, S. S. 1978. Islas Orcadas cruise 16. Antarctic Journal of the U. S., 13(4), 92-94.
interpretation, because faulty slide preparation, erroneous counting, and so forth may result in a "LAAD" being indicated when in fact one is not present. In cores E50-6 and E50-12, no LAAD of Hemidiscus karstenii could be detected. A stratigraphy based on the relative abundances of the radiolarian Cycladophora davisiana, one that can be correlated with the oxygen isotope stratigraphy for the last 150,000 years, was proposed by Hays and associates (1976). Their stratigraphy was extended to 500,000 years before present by Williams and Keany (1978). These and other studies (Morley and Hays 1979; Weaver 1979) show low abundances of this radiolarian in recent sediments, followed by an acme estimated to be at 18,000 years before present (Hays et al. 1976). From this acme (interval b), abundances of C. davisiana generally decrease in older sediments to interval e3, estimated to be at 125,000 years before present (Hays et al. 1976). In the present study, the C. davisiana stratigraphy is well developed in four cores—E49-3, E49-24, E50-9, and E49-16 (figure
Piston core locations Piston core number Latitude (S)
Longitude (E)
E49-3 E49-16 E49-24 E50-6
45006.4' 5026.0' 470593 48001.6'
10954.9 9010.6' 9502.2' 10514.6'
E50-9 E50-10 E50-12 E50-16
5201.3' 53058.7' 57057.2' 6102.6'
105000.6' 104056.2' 105001.0' 11448.8'
139
aminiferal ooze, a lithology that is indicative of a local high productivity coupled with a favorable carbonate compensation depth. Core 24 penetrates lower Oligocene sediments and is composed of diatomaceous mud. The unconformities along the continental margin have been documented by Ledbetter and Ciesielski (1981) for sediments from cruise 12-77 of ARA Islas Orcadas. Cores 39 and 14, which were recovered from the lower continental rise, are composed of clay and mud having an abundance of sedimentary clasts and pebbles. Their composition indicates that these two cores are the product of both abyssal plain and continental margin sedimentary processes. They contain several unconformities, and their basal ages are early Miocene. Continental terrace cores, which include cores 32 through 28 (traverse B—B') and cores 20 through 16 (traverse F—F'), consist mostly of sand, mud, and a mixture of the two, except core 18, which is composed largely of pebbles. Although basal sediments of these cores are mostly barren, they are all believed to be Quaternary in age; this assumption is based on the basal ages of cores 32 and 28. We wish to acknowledge Dennis Cassidy for his help in several phases of this work, including photography of the figures. Rosemarie Raymond drafted the figures. This work has been supported by National Science Foundation contract c-1059.
Summary of sediment descriptions of ARA Islas Orcadas cruise 16 piston cores
Bank, the Georgia Basin, and the Islas Orcadas Rise and to trace the flow of antarctic deep water in the southwest Atlantic Ocean between the Mid-Atlantic Ridge and the America-Antarctic Ridge (Wise et al. 1978). A total of 69 piston cores were recovered, of which 68 were received at the Antarctic Research Facility (figure 1). This article presents a summary of the descriptions of these cores, based on the more detailed sediment descriptions prepared by Kaharoeddin and associates (1982). Although the locations of all cores are shown in figure 1, limitations of space make it necessary to omit the lithologic logs of 20 cores from the graphic summary presented in figures 2 and 3. (The omitted cores are 23, 24, 27, 34, 37, 41, 44, 50, 51, 57, 65, 67, 70, 83, 104, 105, 106, 111, 114, and 117.) Discussion of basal ages of the cores is based on the work of Jones and associates (1979). Of the 32 piston cores taken on the Maurice Ewing Bank, only 18 recovered undisturbed (by flow-in) sediments greater than 100 centimeters in length. All 32 of these cores are relatively
F. AMRISAR KAHAROEDDIN, R. SHELTON GRAVES, and CYNTHIA L. HUMI'HREYS
Antarctic Marine Geology Research Facility Department of Geology Florida State university Tallahassee, Florida 32306
The primary goals of the coring program aboard cruise 16-78 of ARA Islas Orcadas (Sherwood W. Wise, Jr., chief scientist) were to survey older (pre-Pliocene) sediments of the Maurice Ewing 1982 REVIEW
References Ciesielski, P. F., and Jones, S. C. 1979. Sediment ages of ARA Islas Orcadas cruise 15 piston cores. Antarctic Journal of the U.S., 14(5), 148-151. Kaharoeddin, F A., Eggers, M. R., Goldstein, E. H., Graves, R. S., Watkins, D. K., Bergen, J . A., and Jones, S. C. 1980. ARA Islas Orcadas cruise 1578 sediment descriptions (Contribution 48). Tallahassee: Florida State University, Department of Geology, Sedimentology Research Laboratory. Ledbetter, M. T., and Ciesielski, P. F. 1981. Bottom-current erosion in the South Atlantic sector of the southern ocean. Antarctic Journal of the U.S., 16(5),110-112.
135
7OW
CO.
5O
'V 40
45
55
4,
48W 46
44
42
40'W
Figure 1. Locations of piston cores recovered aboard cruise 16-78 of
short, with their undisturbed portions ranging from 20 to 520 centimeters. Three of the cores (23, 24, 51) for which lithologic logs are not shown in figure 2 penetrated only Quaternary sediments consisting of foraminiferal sand or sandy foraminiferal ooze. Core 27, also not shown, is similar to core 29; it consists of pelagic clay containing some zeolites. (These cores are very similar to Islas Orcadas piston core 0775-50, which has been dated by Ciesielski and Wise, 1977, as Eocene in age.) Other cores in this area not shown in figure 2 (cores 34, 37, 41, 44, and 50) are similar in lithology to one or more of their companion cores whose logs are shown. Most of the pre-Pliocene sediments on the Maurice Ewing Bank range in age from late Miocene to late Paleocene and consist of nannofossil ooze occasionally containing common to abundant diatoms and/or radiolarians. Exceptions to this are core 20 (diatomaceous mud), core 25 (glauconitic, sandy diatomaceous ooze), core 26 (muddy diatomaceous ooze), core 28 (diatomaceous sand), and core 19 (intermixed diatomaceous ooze and glauconitic, sandy siliceous ooze). Numerous unconformities can be seen in these cores. A detailed discussion of the 136
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Islas Orcadas.
unconformities in Neogene sediments in this area can be found in Ciesielski and others (1982). On the western flank of the northeast Georgia Rise, two cores (55 and 56) penetrated lower Pliocene sediments; however, they consist of differing lithologies. When combined, these two cores provide an excellent Pliocene record (Wise et al. 1978). Evidence of unconformities can be seen in the top parts of these cores. One core not shown in figure 2, core 57, is composed primarily of Quaternary foraminiferal diatomaceous ooze overlain by a sandy or muddy diatomaceous ooze. Cores 103 through 109 were taken on the Islas Orcadas Rise (cores 104-106 are not shown in figure 3). In general, the Islas Orcadas Rise cores are short, but they penetrated pre-Quaternary sediments. In core 104, only the top 37 centimeters is undisturbed by flow-in, although its total length is 662 centimeters. Nevertheless, this core is valuable for stratigraphic work, because the interval between 36 and 37 centimeters consists of a lower Oligocene nannofossil ooze overlain by a sandy, muddy diatomaceous ooze. Cores 105 (220 centimeters) and 106 (47 centimeters) are lithologically similar to the upper part of core ANTARCTIC JOURNAL
!IIlIi
31 32 33 30 29 28
8 19 20 21 22 25 26
3091 m 2771m 2465m 2012m 2182m 2557m
2345m 2725 m 2498m 2262m 2420m 2573m 2703
100Z
- G.
B'
B
A'
A
.
50cm
- ' :-,--r 85cm (105cm) j--
•I00
:G
(527cm)
200
Ocm
"-G
140 cm
144cm
78cm
19 6 cm
-200
230 Cm
G.
-300
=--
317 cm
-
(447 cm
307cm -::--:
t
(509cm) --'-:
339 cm (530 cm)
372 cm
-400
400
447 cm
460 cm
(563 cm)
(570 cm)
500
-500
C' D
C 36 35
38
45
43
39
47
46
2622m 2429m 1595 m 1840 m 1706 m 1624 m 1693 m 1529 m 1598 0cm-
52
49
48
100-
I
. p
Z=Z 200 ''
(281 cm)
--
ZP
-ioo --
159cm
C
_.L L—aLUA
zZ :0= Z=?:: Z=z -'-
229 cm (500 cm (309cm)
E
1
-zoo
(1762cm) -'- -,
188 cm
215 cm
KEY NANNOFOSSIL OOZE
SAND
FORAMINIFERAL OOZE
MUDDY SAND
CALCAREOUS OOZE
PEBBLES
DIATOMACEOUS OOZE
VOLCANIC ASH
MUDDY, DIATOMACEOUS OOZE
LAPILLI
280 cm
—300
1=
Jr
RADIOLARIAN OOZE Z1
LI1
492 cm
FG 7G
GL AU CON IT E
PELAGIC CLAY
Fuo
SEDIMENTARY CLASTS
r 520 cm
MUD
400
CHERT
SILICEOUS OOZE
EGE
500-
-
:t
- ^Z_ Mct=
Z 400-
73 cm (532 cm)
=0cm
-q-0 :-'---
300-
56
m 1708 m 3936 m 2533m 2374m
53cm (99 cm)
-- 74cm :-'- -
55
D'
ZEOLITES
DIATOMACEOUS MUD
MANGANESE NODULES
GRADATIONAL CONTACT
SHARP CONTACT
500
777 cm L..800
Figure 2. Simplified lithologic logs of cores from the Maurice Ewing Bank and the Georgia Basin. Numbers above log are core number and water depth; number at base of log is core length; number at base in parentheses is actual core length, including flow-in portion (not shown). 1982 REVIEW
137
E
El F
F
116 115 112 109 108 107 103 76 73 68 66 64 63 0cm
5044m 5047m 4374m 2999m 2772m 2986m 3028m 3312m 3877m 4422m 4422m 45(5m 4389m
200
200
(1089cm)
400
401 cm 444 cm
600
-'487cm (1036cm)
-
400
--
- 695cm 740cm (1030cm) 1148 cm)
800
600
-z 659Cm 697cm
2- -800 (838 _= cm 843cm (1086cm) 11000
1120cm
1106cm
(1700cm)
(174 1cm)
1361cm (1780cm)
400
1600
1600
1686cm (1761cm)
G G' 80 81 84 87 89 90 91 98 96 3102m 3464m 3952m 3738m 4285m 4545m 3954m 4631 m 4177m
KEY
ocrnfl
NANNOFOSSIL OOZE
FM
FORAMINIFERAL OOZE CALCAREOUS OOZE DIATOMACEOUS OOZE MUDDY. DIATOMACEOUS OOZE
4
DIATOMACEOUS MUD PELAGIC CLAY
11167 cm) 600-
SAND
535 cm (1715cm)
-
P7- 71 VOLCANIC ASH
rs-1—
800 -
1000_i - I
PEBBLES
LAPILLI
R—M
SEDIMENTARY CLASTS
845cm
MANGANESE NODULES SHARP CONTACT
(1761cm)
GRADATIONAL CONTACT
1049cm EEi
1094cm (1735cm) 1146cm
1172cm (1207cm) 400
1386 cm (1717cm)
Figure 3. Simplified lithologic logs of cores in the southwestern sector of the Atlantic Ocean, between the Mid-Atlantic Ridge and the AmericaAntarctic Ridge. Numbers above log are core number and water depth; number at base of log is core length; number at base in parentheses is actual core length, including flow-in portion (not shown).
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103, permitting stratigraphic correlation. Core 109 contains nannofossil ooze of middle to late Miocene age and is unconformably overlain by Quaternary diatomaceous and muddy diatomaceous oozes. The remaining cores shown in figure 3 are Quaternary in age. Predictable changes in lithology are found in the progression from north to south along traverses E-E', F-F, and C-C'. In the deeper part of the Argentine Basin, the sediment consists of pelagic clay (cores 117, 116, and 115). Farther south are primarily diatomaceous ooze and muddy diatomaceous ooze (cores 114, 112, and 111). Less deep, and in the vicinity of the Mid-Atlantic Ridge, are to be found a calcareous diatomaceous ooze (core 76) and a unit of nannofossil ooze (core 80). Although the rest of the cores are primarily diatomaceous ooze, local variations do occur. For example, the sediments of cores 89, 90, and 91, near the America-Antarctic Ridge, contain volcanic ash, lapilli, pebbles, and sedimentary clasts. Unconformities can be observed in several cores. We wish to acknowledge the assistance and advice of Dennis Cassidy in the preparation of this article. Steve KnUttel helped in preparing the figures, which were drafted by Rosemarie Raymond and photographed by Dennis Cassidy. Funding for
Biostratigraphic correlations and regional erosion shown by the
radiolarian Cycladophora davisiana and the diatoms Eucampia balaustium and Hemidiscus karstenll R. SHELTON GRAVES Antarctic Research Facility Department of Geology Florida State University Tallahassee, Florida 32306
To conduct sedimentological studies of upper Brunhes southern ocean sediments, it is necessary to use high-resolution biostratigraphic schemes. Three biostratigraphically useful species for the interval 195,000 years before present to recent are the radiolarian Cycladophora davisiana and the diatoms Eucampia balaustium and Hemidiscus karstenii. This article describes their utility in biostratigraphic work with USNS Eltanin piston cores from the southeast Indian Ocean (for core locations, see table). The last-abundant-appearance datum (LAAD) of Hemidiscus karstenii has been dated at 195,000 years before present (Burckle, Clarke, and Shackleton 1978). This datum is of marginal utility in the present study, however. Although the datum was well established in cores E49-3, E49-24 (although somewhat stratigraphically high), and E50-9, in cores E50-10, E50-16, and E49-16, the maximum abundance of Hemidiscus karstenii is less than 4 percent. In these situations, extreme care must be exercised in 1982 REVIEW
this work has been provided by National Science Foundation contract c-1059.
References Ciesielski, P. F., and Wise, S. W., Jr. 1977. Basal sediment ages of Islas Orcadas cruise 7 piston cores. Antarctic Journal of the U.S., 12(4), 70-72. Ciesielski, P. F., Ledbetter, M. T., and Ellwood, B. B. 1982. The development of antarctic glaciation and the Neogene paleoenvironment of the Maurice Ewing Bank. Marine Geology, 46, 1-51. Jones, S. C., Wise, S. W., Jr., DeFelice, DR., Hattner, J. G., Mostajo, E. L., Gombos, A. M., and Weaver, F. M. 1979. Basal sediment ages of ARA Islas Orcadas cruise 16 piston cores. Antarctic Journal of the U.S., 14(5),151-153.
Kaharoeddin, F. A., Graves, R. S., Bergen, J. A., Eggers, M. R., Harwood, D. M., Humphreys, C. L., Goldstein, E. H., Jones, S. C., and Watkins, D. K. 1982. ARA Islas Orcadas cruise 1678 sediment descriptions (Contribution 50). Tallahassee: Florida State University, Department of Geology, Sedimentology Research Laboratory. Wise, S. W., Jr., Jones, S. C., Ciesielski, P. F., Georgi, D. T., Woodroffe, D. S., and Jacobs, S. S. 1978. Islas Orcadas cruise 16. Antarctic Journal of the U. S., 13(4), 92-94.
interpretation, because faulty slide preparation, erroneous counting, and so forth may result in a "LAAD" being indicated when in fact one is not present. In cores E50-6 and E50-12, no LAAD of Hemidiscus karstenii could be detected. A stratigraphy based on the relative abundances of the radiolarian Cycladophora davisiana, one that can be correlated with the oxygen isotope stratigraphy for the last 150,000 years, was proposed by Hays and associates (1976). Their stratigraphy was extended to 500,000 years before present by Williams and Keany (1978). These and other studies (Morley and Hays 1979; Weaver 1979) show low abundances of this radiolarian in recent sediments, followed by an acme estimated to be at 18,000 years before present (Hays et al. 1976). From this acme (interval b), abundances of C. davisiana generally decrease in older sediments to interval e3, estimated to be at 125,000 years before present (Hays et al. 1976). In the present study, the C. davisiana stratigraphy is well developed in four cores—E49-3, E49-24, E50-9, and E49-16 (figure
Piston core locations Piston core number Latitude (S)
Longitude (E)
E49-3 E49-16 E49-24 E50-6
45006.4' 5026.0' 470593 48001.6'
10954.9 9010.6' 9502.2' 10514.6'
E50-9 E50-10 E50-12 E50-16
5201.3' 53058.7' 57057.2' 6102.6'
105000.6' 104056.2' 105001.0' 11448.8'
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