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An examination of benthic foraminiferal assemblages from Shatsky Rise, Central Pacific: can they be used to constrain the causes of the climate change across the Eocene-Oligocene Boundary?

Meaghan Julian

Texas A&M University, Department of Geology and Geophysics

College Station, TX

[email protected]

The transition from the hothouse climate of the Eocene to the icehouse climate of the Oligocene is one of the most pivotal transitions in Earth’s history. Geochemical data from benthic foraminifera have constrained the roles of ice buildup versus deep water cooling, but have reached different conclusions about their contributions. A large marine biotic turnover began to occur in the middle Eocene and continued into the early Oligocene; both microfossils and marine invertebrates suffered a large decline in diversity. A gradual step-wise turnover of benthic foraminifera, changing from Bulimina to Nuttallides dominated assemblages, has been noted at Maud Rise, which was affected by deep water bodies associated with formation of the Antarctic Circumpolar Current.

Benthic foraminiferal assemblages will be analyzed from 100 core samples, taken in 50 cm intervals, across the Eocene-Oligocene transition from ODP Sites 1209A and 1211A at Shatsky Rise (corresponding to depths of 113.83 to 138.18 mbsf and ages of 29.66 to 36.16 Ma for site 1209A; depths of 69.78 to 93.96 mbsf and ages of 28.8 to 38.0 Ma for site 1211A). Preliminary analysis of basal Eocene, Eocene-Oligocene transition, and upper Oligocene sediment yield results with Cibicidoides and Nuttallides as the most dominant genera across the transition, with Bulimina, Pleurostomella, and Nodosaria common secondary components in the assemblages. These results are similar to those of the Weddell Sea sediments because Bulimina decreases in abundance and Nuttallides is dominant throughout the transition.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid