Paleoredox changes across the Paleocene-Eocene thermal maximum, Walvis Ridge (ODP Sites 1262, 1263, and 1266): Evidence from Mn and U enrichment factors

Abstract

An understanding of sediment redox conditions across the Paleocene?Eocene thermal maximum (PETM) (?55 Ma) is essential for evaluating changes in processes that control deep?sea oxygenation, as well as identifying the mechanisms responsible for driving the benthic foraminifera extinction. Sites cored on the flanks of Walvis Ridge (Ocean Drilling Program Leg 208, Sites 1262, 1266, and 1263) allow us to examine changes in bottom and pore water redox conditions across a ?2 km depth transect of deep?sea sediments of PETM age recovered from the South Atlantic. Here we present measurements of the concentrations of redox?sensitive trace metals manganese (Mn) and uranium (U) in bulk sediment as proxies for redox chemistry at the sediment?water interface and below. All three Walvis Ridge sites exhibit bulk Mn enrichment factors (EF) ranging between 4 and 12 prior to the warming, values at crustal averages (Mn EF = 1) during the warming interval, and a return to pre?event values during the recovery period. U enrichment factors across the PETM remains at crustal averages (U EF = 1) at Site 1262 (deep) and Site 1266 (intermediate depth). U enrichment factors at Site 1263 (shallow) peaked at 5 immediately prior to the PETM and dropped to values near crustal averages during and after the event. All sites were lower in dissolved oxygen content during the PETM. Before and after the PETM, the deep and intermediate sites were oxygenated, while the shallow site was suboxic. Our geochemical results indicate that oxygen concentrations did indeed drop during the PETM but not sufficiently to cause massive extinction of benthic foraminifera.