Evolution and drowning of the late cretaceous Venezuelan carbonate platform

Abstract

A thick, oxic, rimmed carbonate platform (the Venezuelan carbonate platform, VCP) prograded in northern South America during the Aptian-Albian. Partial drowning of the VCP ( i.e., the Cogollo Group) occurred during the latest Aptian-earliest Albian along the Machiques trough. A definitive drowning of the VCP occurred during the latest Albian-earliest Cenomanian, when a rapid rise in sea level and intensive upwelling obliterated the platform and triggered the development of an oxygen minimum zone (OMZ). Pelagic, bituminous black limestone and shales (La Luna Formation) were deposited in a ramp setting, where anoxic sulfidic conditions prevailed immediately below the sediment-water interface. Changes in the ramp slopes are suggested for the Barquisimeto, Guajira, and Tachira regions. A maximum paleodepth (∼600 m) was reached during the Campanian with the deposition of glauconitic limestones of the Tres Esquinas Member of the Colón Formation (a regional condensed section). Anoxic post-oxic conditions are suggested for the sediment-water interface, whereas dysaerobia is suggested for the water column (for the Tres Esquinas Member). Shallower water conditions occurred from the latest Campanian to Maastrichtian. Hemipelagic limestones of the Socuy Member of the Colón Formation were deposited in the outer ramp, where the early (diagenetic) geochemical environment varied from anoxic post-oxic to anoxic sulfidic, while the water column was dysaerobic. Finally, increasing clastic input resulted in deposition of hemipelagic mudstones of the Colón Formation and establishment of aerobic conditions in the water column, compared to the early (diagenetic) geochemical environment, which remained anoxic post-oxic almost up to the end of the period.