Expedition 342 summary

Abstract

Integrated Ocean Drilling Program Expedition 342 was designed to recover Paleogene sedimentary sequences with unusually high deposition rates across a wide range of water depths. The drilling area is positioned to capture sedimentary and geochemical records of ocean chemistry and overturning circulation beneath the flow of the Deep Western Boundary Current in the northwest Atlantic Ocean. The expedition was primarily targeted at reconstructing the Paleogene carbonate compensation depth (CCD) in the North Atlantic for reference to recently obtained high-fidelity records of the CCD in the equatorial Pacific. We find evidence of carbonate deposition events following the Cretaceous/Paleogene (K/Pg) boundary mass extinction, the Paleocene/Eocene Thermal Maximum, and the Eocene–Oligocene transition (EOT). These deposition events may reflect the rebalancing of ocean alkalinity after mass extinctions or abrupt global climate change. Expedition 342 recovered sequences with sedimentation rates high enough to enable studies of the dynamics of past abrupt climate change, including both transitions into “greenhouse” and “icehouse” climate states, the full magnitudes of hyperthermal events, and rates of change in the CCD. An unexpected finding was the recovery of a number of Cretaceous “critical boundaries.” These include the K/Pg boundary, the Campanian–Coniacian interval, the Cenomanian/Turonian boundary and Oceanic Anoxic Event (OAE) 2, and the Albian/Cenomanian boundary OAE 1d.