Environmental Controls on Green Bands in Marine Sediments

Abstract Widely observed banding in marine sediments is believed to be connected to oxygen‐sensitive diagenetic processes in shallow sediments. This study combines a spatial survey of distinctive banding in shallow sediments (<1 m below seafloor) with novel 1 million‐year long records of banding occurrence at International Ocean Discovery Program (IODP) Sites U1474 and U1313 to assess the link between sedimentary diagenetic band and bottom water oxygen across the middle to late Pleistocene. The spatial survey of banding in shallow sediments indicates that bands at active redox fronts are connected to high bottom‐water oxygen concentrations, while the stratigraphic survey shows numerous instances of the synchronous development of banding in both hemispheres during the glaciations of the Pleistocene in tandem with low bottom‐water oxygen events. A review of available evidence suggests that the diagenetic bands form due to rising bottom‐water oxygen concentrations, which trap reduced iron sourced from organic matter‐enriched deposits from a preceding low‐oxygen interval. Connections among Southern Ocean productivity, green‐band abundance, Mediterranean sapropel occurrence, and the 400‐kyr benthic δ 13 C cycle point to the possibility of long‐term variability in deep‐ocean oxygenation across the Pleistocene.