PEKAR, STEPHEN F., KENNETH G. MILLER, MICHELLE KOMINZ, and WRIGHT, JAMES, D.
Dept. Geological Sciences, Rutgers University, Piscataway, New Jersey 08855-1179

Abstract: Extracting an Eustatic Record From Western Equatorial Pacific d¹⁸O Records and Onshore New Jersey Oligocene Sequence Stratigraphy

Attempts at estimating the amplitudes of eustatic changes for the Oligocene have been controversial. For example, a "mid" Oligocene eustatic fall of >100 m has been estimated by Exxon Production Research, versus ~35 m indicated by d¹⁸O records. We address discrepancies among Oligocene eustatic estimates in two regions most sensitive to eustatic change: western equatorial Pacific (ODP Site 803D) and onshore New Jersey (ODP Legs 150X and 174AX).

The d¹⁸O records from Site 803D provide an indirect proxy for glacioeustasy. In this study, monospecific planktonic and monogeneric benthic foraminiferal samples were used, ranging in age from 34.1 to 29.5 Ma. The planktonic d¹⁸O records covary with the benthic foraminiferal d¹⁸O events Oil (33.5 Ma), Oi1a (32.8 Ma), Oi1b (31.7 Ma), and Oi2 (30.1 Ma).

New Jersey onshore records provide a more direct proxy for relative sea level changes. From these sites, we developed a benthic foraminiferal paleoslope model for multiple time slices, providing water depth estimates. Using these water depth variations in backstripping, we estimated eustatic changes from 34.0 to 23.0 Ma.

A comparison of the Site 803 d¹⁸O records with the eustatic estimates from New Jersey show excellent agreement. At the Oi1b d¹⁸O event, there is a 0.5 ^o/oo increase in the planktonic foraminiferal d¹⁸O records. Ascribing the entire d¹⁸O signal to ice yields a 45 m eustatic decrease. This compares well with the estimated eustatic fall of 42 m from the New Jersey data. Three other major planktonic foraminiferal d¹⁸O increases at Oi1a, Oi1b, and Oi2 show similar correlations.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas