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Two-stepping into the icehouse; east Antarctic weathering during progressive ice-sheet expansion at the Eocene-Oligocene transition

Howie D. Scher, Steven M. Bohaty, James C. Zachos and Margaret L. Delaney
Two-stepping into the icehouse; east Antarctic weathering during progressive ice-sheet expansion at the Eocene-Oligocene transition
Geology (Boulder) (April 2011) 39 (4): 383-386

Abstract

In conjunction with increasing benthic foraminiferal delta (super 18) O values at the Eocene-Oligocene transition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 mu m) appears abruptly alongside fossil fish teeth with continentally derived neodymium (Nd) isotope ratios (epsilon (sub Nd) ) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering flux, as inferred from two steps to less radiogenic epsilon (sub Nd) values, coincides with two steps in benthic foraminiferal delta (super 18) O values. These results indicate that two distinct surges of weathering were generated by East Antarctic ice growth during the EOT. Weathering by ice sheets during a precursor glaciation at 33.9 Ma did not produce significant IRD accumulation during the first epsilon (sub Nd) shift. Glacial weathering was sustained during a terrace interval between the two steps, probably by small high-elevation ice sheets. A large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions. Parallel changes in Antarctic weathering flux and deep-sea carbonate accumulation suggest that ice-sheet expansion during the EOT had a direct impact on the global carbon cycle; possible mechanisms include associated changes in silicate weathering on the East Antarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrant further investigation.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 39
Serial Issue: 4
Title: Two-stepping into the icehouse; east Antarctic weathering during progressive ice-sheet expansion at the Eocene-Oligocene transition
Affiliation: University of California, Santa Cruz, Ocean Sciences Department, Santa Cruz, CA, United States
Pages: 383-386
Published: 201104
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 39
Accession Number: 2011-038853
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2011123
Illustration Description: illus. incl. sketch map
S62°42'33" - S62°42'32", E82°47'14" - E82°47'15"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201122
Program Name: ODPOcean Drilling Program
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