Data Report: Carbon and Carbonate Contents of the Cenomanian-Turonian Sediments from Hole 869B (Leg 143): Comparison with Other Deep Basins from Central and Northwestern Pacific Ocean

Abstract

Dark gray claystone and siltstone, correlated with a positive gamma-ray peak, were recovered around the Cenomanian/ Turonian boundary at Hole 869B. Organic carbon and calcium carbonate contents were measured on 22 samples chosen in the different lithologies, especially in dark-colored facies, from Cores 143-869B-37R to -34R. The organic carbon content is everywhere less than 0.2%, whereas calcium carbonate content ranges from 0% to 22%. The organic matter appears intensely reworked or strongly oxidized, and is related to type IV kerogen. Such low organic carbon contents seem common in the coeval sediments from basinal environments investigated by other DSDPand ODP drilling in central and northwestern Pacific Ocean. Only a thin redeposited carbonaceous level from Site 585 (East Mariana Basin) represents the deepest evidence of the Cenomanian-Turonian Oceanic Anoxic Event in the Pacific Ocean. A necessary condition of the oxygen-minimum-zone model proposed to explain the Cenomanian-Turonian Oceanic Anoxic Event is that basinal waters were oxygenated. These conditions are now further demonstrated in the deep basin flanking of the Pikinni-Wodejebato Ridge in the Marshall Islands.