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Magnetobiostratigraphic chronology of the Eocene–Oligocene transition in the CIROS-1 core, Victoria Land margin, Antarctica: Implications for Antarctic glacial history

Magnetobiostratigraphic chronology of the Eocene–Oligocene transition in the CIROS-1 core, Victoria Land margin, Antarctica: Implications for Antarctic glacial history
Magnetobiostratigraphic chronology of the Eocene–Oligocene transition in the CIROS-1 core, Victoria Land margin, Antarctica: Implications for Antarctic glacial history
In 1986, cores were obtained to a depth of 702 m (with 98% recovery) from the CIROS-1 drill hole beneath the Ross Sea on the Victoria Land margin. Glaciogene sediments identified near the base of the hole mark the earliest known record of Antarctic glaciation. Initial biostratigraphic analysis indicated that the lower 336 m of the core is early Oligocene in age, and that the upper 366 m is of late Oligocene–early Miocene age. Recently, the chronology of the CIROS-1 core has been questioned. We developed a magnetostratigraphy for the lower 400 m of the CIROS-1 core to clarify the chronology. Our magnetobiostratigraphic results indicate that the base of the CIROS-1 core is early-late Eocene in age (corresponding to Chron C16r; ca. 36.5 Ma). We identify the Eocene-Oligocene boundary at about 410–420 m, within a 20-m-thick, poorly stratified, bioturbated sandy mudstone. This makes the CIROS-1 core the highest latitude site (77.1°S) from which this datum event has been recognized. At 366 m, a 4 m.y. hiatus, which lies immediately beneath fluvial sediments, accounts for most of Chrons C11 and C12. We recognize three major climatic episodes in the CIROS-1 core: (1) the late Eocene (34.5–36.5 Ma, 430–702 m), when relatively warm conditions dominated and there were high sedimentation rates and some glacial activity; (2) the late Eocene–early Oligocene boundary interval (28.5–34.5 Ma, 340–430 m), which was a transition from relatively warm to cooler conditions that coincided with glacial intensification, sea-level fall, and subaerial erosion of the shelf; and; (3) the late Oligocene – early Miocene (22–28.5 Ma, 50–340 m), when large-scale glaciation dominated the region and glaciers grounded across the continental shelf. From correlation with global oxygen isotope and sea-level records, we infer that the Antarctic climate and surrounding oceans cooled after separation of Australia and Antarctica and development of deep-water circulation between them. This marked the onset of the Eocene–Oligocene transition at ca. 34.5 Ma. A major East Antarctic ice sheet did not develop until the early-late Oligocene boundary, toward the end of the Eocene–Oligocene transition (ca. 28.5 Ma). Outlet glaciers did not breach the Transantarctic Mountains and ground across the Ross Sea Shelf until 0.5 m.y. later (ca. 28 Ma).
0016-7606
35-47
Wilson, Gary S.
6dad8d23-23a6-4b25-bc69-1ea7ad428b3b
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Verosub, Kenneth L.
396d0f22-35c1-42b9-8581-96fbb6df597d
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5
Sagnotti, Leonardo
7c810d6f-8a83-4e71-9b56-194a54a59513
Wilson, Gary S.
6dad8d23-23a6-4b25-bc69-1ea7ad428b3b
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Verosub, Kenneth L.
396d0f22-35c1-42b9-8581-96fbb6df597d
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5
Sagnotti, Leonardo
7c810d6f-8a83-4e71-9b56-194a54a59513

Wilson, Gary S., Roberts, Andrew P., Verosub, Kenneth L., Florindo, Fabio and Sagnotti, Leonardo (1998) Magnetobiostratigraphic chronology of the Eocene–Oligocene transition in the CIROS-1 core, Victoria Land margin, Antarctica: Implications for Antarctic glacial history. Geological Society of America Bulletin, 110 (1), 35-47.

Record type: Article

Abstract

In 1986, cores were obtained to a depth of 702 m (with 98% recovery) from the CIROS-1 drill hole beneath the Ross Sea on the Victoria Land margin. Glaciogene sediments identified near the base of the hole mark the earliest known record of Antarctic glaciation. Initial biostratigraphic analysis indicated that the lower 336 m of the core is early Oligocene in age, and that the upper 366 m is of late Oligocene–early Miocene age. Recently, the chronology of the CIROS-1 core has been questioned. We developed a magnetostratigraphy for the lower 400 m of the CIROS-1 core to clarify the chronology. Our magnetobiostratigraphic results indicate that the base of the CIROS-1 core is early-late Eocene in age (corresponding to Chron C16r; ca. 36.5 Ma). We identify the Eocene-Oligocene boundary at about 410–420 m, within a 20-m-thick, poorly stratified, bioturbated sandy mudstone. This makes the CIROS-1 core the highest latitude site (77.1°S) from which this datum event has been recognized. At 366 m, a 4 m.y. hiatus, which lies immediately beneath fluvial sediments, accounts for most of Chrons C11 and C12. We recognize three major climatic episodes in the CIROS-1 core: (1) the late Eocene (34.5–36.5 Ma, 430–702 m), when relatively warm conditions dominated and there were high sedimentation rates and some glacial activity; (2) the late Eocene–early Oligocene boundary interval (28.5–34.5 Ma, 340–430 m), which was a transition from relatively warm to cooler conditions that coincided with glacial intensification, sea-level fall, and subaerial erosion of the shelf; and; (3) the late Oligocene – early Miocene (22–28.5 Ma, 50–340 m), when large-scale glaciation dominated the region and glaciers grounded across the continental shelf. From correlation with global oxygen isotope and sea-level records, we infer that the Antarctic climate and surrounding oceans cooled after separation of Australia and Antarctica and development of deep-water circulation between them. This marked the onset of the Eocene–Oligocene transition at ca. 34.5 Ma. A major East Antarctic ice sheet did not develop until the early-late Oligocene boundary, toward the end of the Eocene–Oligocene transition (ca. 28.5 Ma). Outlet glaciers did not breach the Transantarctic Mountains and ground across the Ross Sea Shelf until 0.5 m.y. later (ca. 28 Ma).

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Published date: January 1998

Identifiers

Local EPrints ID: 66113
URI: http://eprints.soton.ac.uk/id/eprint/66113
ISSN: 0016-7606
PURE UUID: 59615d08-59e0-4e6c-9126-ee190b4cfbcf

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Date deposited: 30 Apr 2009
Last modified: 08 Nov 2021 16:33

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Contributors

Author: Gary S. Wilson
Author: Andrew P. Roberts
Author: Kenneth L. Verosub
Author: Fabio Florindo
Author: Leonardo Sagnotti

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