Field relations, regional correlations, and sedimentological observations show that the organic-rich Middle to Upper Devonian Marcellus to Dunkirk black shales (eastern United States), commonly interpreted to have been deposited in deep, quiet, and permanently anoxic basins, were instead deposited in relatively shallow settings that at times had moving currents and oxygenated bottom water that supported benthic life. Traditionally interpreted to downlap onto a deep basin floor, regional wireline-log correlations linked to outcrop studies show that these black shales instead onlap unconformities on a tectonic high to the west. The basic elements of the proposed model are present in a range of other occurrences around the world, and this shallow onlap model should be considered as a viable hypothesis for the origin of any black shale succession.

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