Last ODP Legs Expand Black Shale Legacy of Scientific Ocean Drilling

Scientific ocean drilling has been central to our basic knowledge about Cretaceous black shales and to our growing understanding of the paleoceanographic and paleoclimatic processes that participated in their deposition. Spot-coring during early DSDP legs charted the geographical and temporal occurrence of black shales in the ocean basins. The concept of Oceanic Anoxic Events (OAE) is part of this legacy. Subsequent drilling recovered continuous sequences that have identified patterns of geographical and temporal differences in black shale sequences and have encouraged reconstructions of the paleoceanographic histories recorded by these differences. Sequences recovered by the last few ODP Legs have expanded this legacy and have opened new opportunities for improved understandings about black shales. Leg 198 recovered a classic section of TOC-rich (35 percent) early Aptian black shale from the Shatsky Rise that corresponds to OAE1a. Leg 207 recovered Cenomanian-Turonian (OAE2) and Coniacian-Santonian (OAE3) black shales, some containing nearly 30 percent TOC, from five sites on the Demerara Rise. Leg 210 recovered TOC-rich (4 percent) laminated black shales from the deep Newfoundland Margin that correspond to OAE1d and OAE2. The Demerara Rise sequences are particularly impressive in ranging in thickness from 56m to 93m and in having well-developed laminations and shale-limestone cycles. The five sites constitute a 1km paleodepth transect and record both high surface productivity and enhanced organic matter preservation under an intensified oxygen-minimum layer impinging on the Demerara Rise.