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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

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), pp. 35-47.

Record type: Article


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


Local EPrints ID: 66113
ISSN: 0016-7606
PURE UUID: 59615d08-59e0-4e6c-9126-ee190b4cfbcf

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Date deposited: 30 Apr 2009
Last modified: 19 Jul 2017 00:27

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

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