Evolution of deep-sea sediments across the Paleocene-Eocene and Eocene-Oligocene boundaries

Abstract

The composition and distribution of deep-sea sediments is the result of a multitude of climatic, biotic and oceanic conditions relating to biogeochemical cycles and environmental change. Here we utilize the extensive sediment archives of the International Ocean Discovery Program (IODP) and its predecessors to construct maps of deep-sea sediment type across two critical but contrasting boundaries in the Paleogene, one characterised by an interval of extreme warmth (Paleocene/Eocene) and the other by global cooling (Eocene/Oligocene). Ocean sediment distribution shows significant divergence both between the latest Paleocene and Paleocene Eocene Thermal Maximum (PETM), across the Eocene-Oligocene Transition (EOT), and in comparison to modern sediment distributions. Carbonate sedimentation in the latest Paleocene extends to high southern latitudes. Disappearance of carbonate sediments at the PETM is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon-cycle perturbation. Biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early Paleogene ocean. In the Southern Ocean, we attribute the low in biosiliceous burial, to the warm deep water temperatures which would have impacted biogenic silica preservation. In the late Eocene, our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial Pacific. Enhanced biosiliceous deposits in the late Eocene equatorial Pacific and South Atlantic are due to increased productivity and the spin-up of the oceans. Our compilation documents the enhanced global carbonate sedimentation in the early Oligocene, confirming that the drop in the carbonate compensation depth was global.