Eocene-Oligocene paleoceanographic changes in the stratotype section, Massignano, Italy: Clues from rock magnetism and stable isotopes

Abstract

We have conducted high-resolution paleomagnetic and rock magnetic studies, in addition to stable isotope analyses of the Massignano sedimentary section, which is the Global Stratotype Section and Point (GSSP) for the Eocene-Oligocene boundary. Our research builds upon the many past studies of the Massignano section in seeking to understand the timing and nature of the paleoenvironmental variations that occurred during the transition for the Earth's climate system from greenhouse to icehouse. The new paleomagnetic results provide a refined magnetostratigraphy of the section and new age for the Eocene-Oligocene boundary at 33.7 Ma. Abrupt and large alternations in magnetic, concentration, composition, and grain sizes that occur in the high-resolution rock magnetic record are interpreted to be the result of rapid bimodal shifts in deep-sea circulation that affect sediment sources or transport. We speculate that currents flowing through the gateway between the Atlantic and Indo-Pacific Oceans may have turned on and off as the gateway was progressively closing, resulting in the deposition of two different assemblages of magnetic minerals at Massignano. Finally, stable isotope (δ18O and δ 13C) data collected on ostracod valves also suggest significant changes in sea bottom circulation in the Neo-Tethys Ocean at and about 2 m.y. before the Eocene-Oligocene boundary. Copyright 2007 by the American Geophysical Union.