Response of the Cr isotope proxy to Cretaceous Ocean Anoxic Event 2 in a pelagic carbonate succession from the Western Interior Seaway

Chromium offers a redox sensitive isotopic proxy with potential for tracing past oxygen levels in the oceans. We explore this potential in a pelagic succession of marine carbonate sediment deposited during Cretaceous Ocean Anoxic Event 2 (OAE 2) in the Western Interior Seaway, Colorado (WIS), using the USGS Portland #1 Core. Reduction of Cr(VI) causes light isotopes of Cr to preferentially partition into Cr(III). Because Cr(VI) is the...