Abstract
Abstract Organic-rich black shales have been observed in Mesozoic strata penetrated by the Deep Sea Drilling Project (DSDP). These black shales represent a major carbon sink in the geologic record. Of paramount importance in establishing the origin of the black shales is the character and level of preservation of the organic matter. Within the North and South Atlantic sample suite, three types of organic matter were identified: well-preserved marine organic matter, moderately well preserved terrestrial material, and severely altered and/or recycled organic matter. The spatial and temporal distribution of the three types of organic matter suggest that the organic-rich shales are not of a single origin. These shales have developed as a result of high continental runoff from regions rich in sedimentary carbon and/or elevated terrestrial productivity, or high marine productivity and preservation in part due to rapid deposition by turbidity currents or mass slumping. A detailed analysis of individual and closely spaced DSDP sites further documents that anoxia was probably not the result of synchronous major expansions of anoxic bottom-water masses, but represents isolated occurrences.
Published Version
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