Change from “Atlantic-type” to “Pacific-type” carbonate stratigraphy in the middle Pliocene Equatorial Pacific Ocean

Abstract

A paleomagnetically dated piston core from the Equatorial Pacific Ocean (V28-179) contains levels of highest carbonate percentage in association with lower δ 18 O values in early Pliocene sediments. This relationship is typical of the Atlantic during the Quaternary and is thus referred to as an “Atlantic-type” carbonate stratigraphy. The change from an “Atlantic-type” to a “Pacific-type” stratigraphy (high-carbonate glacial episodes) appears to have occurred during the earliest Gauss Magnetic Chron (3.18–3.41 Ma) of middle Pliocene age, and may be related to the development of Northern Hemisphere glaciation. Samples deposited prior to the development of Northern Hemisphere glaciation in V28-179 have a significant proportion of low-frequency ( > 400- ka period ) variance in both the benthic O 18 and carbonate spectra, and an “Atlantic-type” correlation. Both the oxygen-isotopic and the carbonate spectra of V28-179 have frequency-specific correlation (coherency) with the calculated Pliocene record of the eccentricity of Earth's orbit. Thus, orbital parameters may have affected Equatorial Pacific sedimentation in the Pliocene. The change from “Atlantic-type” to “Pacific-type” carbonate stratigraphy in the middle Pliocene may have been related to a change in the dominant frequency of variance of carbonate oscillations related to orbital parameters, and/or to intensification of Antarctic Bottom Water circulation during the middle Pliocene near the base of the Gauss Chron.