Summary of sediment descriptions of piston cores
Summary of sediment descriptions of ARA Is/as Orcadas cruise 15 piston cores R. SHELTON GRAVES, F. AMRISAR KAHAROEDDIN,
aiid CYNTHIA L. l-IUMI'HREYS Antarctic Marine Geology Research Facility Department of Geology Florida State University Tallahassee, Florida 32306
Cruise 15-78 of ARA Islas Orcadas (John L. LaBrecque, chief scientist) collected a total of 51 liner-encased piston cores (figure 1). This article presents a summary of the descriptions of 46 of these cores, along six traverses, in the form of graphic lithologic logs (figures 2 and 3). Limitations of space make it necessary to 50'W
40'
WON
omit the graphic logs of five cores (20, 27, 47, 48, 50), the lithologies of which are similar to those of other cores in their vicinities. These lithologic logs represent very generalized descriptions of the cores; detailed sediment descriptions can be found in Kaharoeddin and others (1980). Basal sediment ages referred to in this article are based on the work of Ciesielski and Jones (1979). Cores 64, 63, and 62, in the Scotia Sea, consist generally of Quaternary diatomaceous muds. The two northernmost cores (64 and 63), despite being close to one another, obviously represent different sedimentary regimes. Evidence for this is provided by the abundance of pebbles and sedimentary clasts found in core 63. Farther south, core 61 is composed of early Pliocene mud and diatomaceous mud. Approaching the escarpment north of the South Orkney Islands one finds Eocene to Oligocene pelagic clays (core 59). West of the South Sandwich Islands the predominant sediment is Quaternary volcanic ash (core 2), overlain by interbedded diatomaceous and muddy diatomaceous oozes containing 20'
50'S
55'
60'
65'
70'
71'
70'
72'S
72'S
20'W 18o 16o 14' 12' 10'W
Figure 1. Locations of piston cores retrieved aboard
132
ARA
Islas Orcadas cruise 15-78. ANTARCTIC JOURNAL
A'
A
64 63 62 61 59 56 55 52 40 39 0cm -
3420m 3091 m 3420m 3438m 2707m 4512 m 4353m 4649m 4481m 4334m
-200
200-
400- 351
cm
497cm : --
600-
800-
- 0cm
515 cm
-400
515 cm (796cm)
568cm
-600
-800 814cm
1000-
-bOO 1070 cm
B'
B
25 38 37 36 35 26 34 33 32 31 30 29 28 4440m 4301 m 3681 m 2751 m 2350m 2242m 1865 m 1536 m 1061 m 810m 530m 380m 530m
: S
TOE
400 o ---
a 64 a
==
a'.
486 cm
600
242cm
241 cm 2Ocm 400
i0
-- - 521 cm :-:-- ----
:-_ -
--
hi
L--1
600
0
800 --
:::::: - - :--- --802 cm -0-.- -
1000 :--: 1013 cm 1200
943cm (1139cm)
ci- 955cm 0 (1135cm) 1143cm
768 cm (1045cm)
800
000
11200
Figure 2. Simplified lithologic logs along traverses A—A' and B—B' (see figure 1). 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
133
C
C' D
D'
2 4 5 6 7 8 49 47A 45 44 43 42 41 0cm -
3246m 4217 3968m 4283m 5214m 5130m 4718 4855m 4898m 4857m 4812m 4746m 4631 - 0cm = —
= I
88 cm
I
000 - -
-.
200 0
_J
— = 0
400-
-200
0
'96 m
0=
360cm
--
-- -
471cm
500 cm
556 cm
600-
400
-600 641 cm
800-
-800
788 cm 848 cm 896 cm
1000-
953 cm
900 cm
940 cm
E 8 9 10 II 12 14
E'
5130 m 5201 m 5128 m 4987m 4806m 4256m
-1000
F
F' 24 22 19 18 16
4078m 2820m 1339m 1039m 366m
r-T-1 V I
-. -# -;___ -'- -------
131 cm
--
249 cm
140cm
;T
KEY MARLY FORAMINIFERAL OOZE 357 cm 400-
362cm
-.
397cm
DIATOMACEOUS OOZE MUDDY, DIATOMACEOUS OOZE
—
600-
512cm
499 cm
PELAGIC CLAY MUD DIATOMACEOUS MUD
SILT 800-
O-0 SAND
896cm
SANDY SILT MUDDY SAND
PEBBLES
SEDIMENTARY CLASTS
LAPILLI
VOLCANIC ASH
SHARP -- -- GRADATIONAL CONTACT CONTACT
000-
1068cm
3. Simplified lithologic logs along traverses C-C', D-D', E-E', and F- -F. Numbers above log are core number and water depth; number at of log is core length. ANTARCTIC JOURNAL
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
aiid CYNTHIA L. l-IUMI'HREYS Antarctic Marine Geology Research Facility Department of Geology Florida State University Tallahassee, Florida 32306
Cruise 15-78 of ARA Islas Orcadas (John L. LaBrecque, chief scientist) collected a total of 51 liner-encased piston cores (figure 1). This article presents a summary of the descriptions of 46 of these cores, along six traverses, in the form of graphic lithologic logs (figures 2 and 3). Limitations of space make it necessary to 50'W
40'
WON
omit the graphic logs of five cores (20, 27, 47, 48, 50), the lithologies of which are similar to those of other cores in their vicinities. These lithologic logs represent very generalized descriptions of the cores; detailed sediment descriptions can be found in Kaharoeddin and others (1980). Basal sediment ages referred to in this article are based on the work of Ciesielski and Jones (1979). Cores 64, 63, and 62, in the Scotia Sea, consist generally of Quaternary diatomaceous muds. The two northernmost cores (64 and 63), despite being close to one another, obviously represent different sedimentary regimes. Evidence for this is provided by the abundance of pebbles and sedimentary clasts found in core 63. Farther south, core 61 is composed of early Pliocene mud and diatomaceous mud. Approaching the escarpment north of the South Orkney Islands one finds Eocene to Oligocene pelagic clays (core 59). West of the South Sandwich Islands the predominant sediment is Quaternary volcanic ash (core 2), overlain by interbedded diatomaceous and muddy diatomaceous oozes containing 20'
50'S
55'
60'
65'
70'
71'
70'
72'S
72'S
20'W 18o 16o 14' 12' 10'W
Figure 1. Locations of piston cores retrieved aboard
132
ARA
Islas Orcadas cruise 15-78. ANTARCTIC JOURNAL
A'
A
64 63 62 61 59 56 55 52 40 39 0cm -
3420m 3091 m 3420m 3438m 2707m 4512 m 4353m 4649m 4481m 4334m
-200
200-
400- 351
cm
497cm : --
600-
800-
- 0cm
515 cm
-400
515 cm (796cm)
568cm
-600
-800 814cm
1000-
-bOO 1070 cm
B'
B
25 38 37 36 35 26 34 33 32 31 30 29 28 4440m 4301 m 3681 m 2751 m 2350m 2242m 1865 m 1536 m 1061 m 810m 530m 380m 530m
: S
TOE
400 o ---
a 64 a
==
a'.
486 cm
600
242cm
241 cm 2Ocm 400
i0
-- - 521 cm :-:-- ----
:-_ -
--
hi
L--1
600
0
800 --
:::::: - - :--- --802 cm -0-.- -
1000 :--: 1013 cm 1200
943cm (1139cm)
ci- 955cm 0 (1135cm) 1143cm
768 cm (1045cm)
800
000
11200
Figure 2. Simplified lithologic logs along traverses A—A' and B—B' (see figure 1). 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
133
C
C' D
D'
2 4 5 6 7 8 49 47A 45 44 43 42 41 0cm -
3246m 4217 3968m 4283m 5214m 5130m 4718 4855m 4898m 4857m 4812m 4746m 4631 - 0cm = —
= I
88 cm
I
000 - -
-.
200 0
_J
— = 0
400-
-200
0
'96 m
0=
360cm
--
-- -
471cm
500 cm
556 cm
600-
400
-600 641 cm
800-
-800
788 cm 848 cm 896 cm
1000-
953 cm
900 cm
940 cm
E 8 9 10 II 12 14
E'
5130 m 5201 m 5128 m 4987m 4806m 4256m
-1000
F
F' 24 22 19 18 16
4078m 2820m 1339m 1039m 366m
r-T-1 V I
-. -# -;___ -'- -------
131 cm
--
249 cm
140cm
;T
KEY MARLY FORAMINIFERAL OOZE 357 cm 400-
362cm
-.
397cm
DIATOMACEOUS OOZE MUDDY, DIATOMACEOUS OOZE
—
600-
512cm
499 cm
PELAGIC CLAY MUD DIATOMACEOUS MUD
SILT 800-
O-0 SAND
896cm
SANDY SILT MUDDY SAND
PEBBLES
SEDIMENTARY CLASTS
LAPILLI
VOLCANIC ASH
SHARP -- -- GRADATIONAL CONTACT CONTACT
000-
1068cm
3. Simplified lithologic logs along traverses C-C', D-D', E-E', and F- -F. Numbers above log are core number and water depth; number at of log is core length. ANTARCTIC JOURNAL
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
