Abstract
Black shales possessing high concentrations of organic carbon1 were deposited in many parts of the proto South Atlantic Ocean during the Cretaceous period2. The way such sediments accumulated is not fully understood, but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter. Thin, centimetre-thick layers of black shales are commonly interbedded with thicker layers of organic carbon-deficient, green claystones, as found in strata of Aptian to Coniacian age, at Deep Sea Drilling Project (DSDP) Site 530, in the southern Angola Basin3 and elsewhere. These differences in carbon content and colour reflect the conditions of deposition, and possibly variations in the supply of organic matter4,5. We have compared, using organic geochemical methods the compositions of organic matter in three pairs of closely-bedded black and green Cenomanian claystones obtained from Site 530. Kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones.
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Meyers, P., Leenheer, M., Kawka, O. et al. Enhanced preservation of marine-derived organic matter in Cenomanian black shales from the southern Angola Basin. Nature 312, 356–359 (1984). https://doi.org/10.1038/312356a0
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DOI: https://doi.org/10.1038/312356a0
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