Abstract
Black shales and bituminous limestones were widely deposited in northwestern South America during the maximum transgression of late Cretaceous seas. These Cenomanian to Santonian (Campanian) anoxic sediments are distributed in two main subprovinces. Thick chert and phosphorite accumulated in the Trough Subprovince, landward of a possibly partially emergent Cordillera Central (Colombia). Only minor intercalations of chert were deposited in the Platform Subprovince, lying northward in the Maracaibo Basin (northwestern Venezuela). Faunal evidence (depauperate benthic fauna, planktic foraminiferal assemblages, high-dominance clupeoid fish assemblages) and sedimentological evidence suggest anoxic condition prevailed throughout the region, probably the result of dynamic upwelling in the Trough Subprovince, but the reflection of a “global” anoxic event within the Platform Subprovince.
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