Eocene biogeochronology and magnetostratigraphic revision of ODP Hole 762C, Exmouth Plateau (northwest Australian Shelf)

Abstract

We present a chronostratigraphic model for the Eocene from ODP Leg 122 Hole 762C (northwest Australian shelf), integrating calcareous nannofossil data with previously published planktonic foraminiferal data, magnetostratigraphy and stable isotopic data. This ~240m thick interval extends from magnetic polarity Chron C25r to Chron C15r, and nannofossil zones CP6/7 to CP16a (NP7/8-NP21). Examination of the calcareous nannofossil biostratigraphy showed several potential hiatuses within this stratigraphic section at Hole 762C. The presence of these hiatuses was supported by cross-correlation of planktonic foraminiferal P-zones, magnetostratigraphic reversals and δ13C and δ18O isotopic excursions. These biostratigraphic and isotopic data were used to re-evaluate the original magnetostratigraphy, and this revised framework was integrated into a new age model. The original depositional model from Leg 122 proposed a continuous section with relatively low sedimentation rates in the Lutetian and basal Ypresian (< 1.0cm/ky); however, our results suggest that sedimentation rates were relatively high but that the section is interrupted by four hiatuses, each ~1-2 myr in duration. This new age model allowed revision of sedimentation rates at Hole 762C. These revised rates are used to estimate the ages of calcareous nannofossil bioevents, which are compared to several additional, globally distributed localities.