Palaeoecology, palaeogeography and depositional environments of Upper Cretaceous rocks of western Venezuela

The end of the Early Cretaceous in northern South America was marked by regional palaeoceanographic change. In western Venezuela, this change was highlighted near the end of the Albian by drowning of the Maraca Formation shallow-water carbonate platform. Regional marine transgression continued during the Cenomanian and Turonian in western Venezuela with drowning of the more southerly Guayacan Member (Capacho and Escandalosa formations) carbonate platform. Deposition of organic carbon-rich intervals of the La Luna and Navay formations occurred unconformably on Maraca Formation and Guayacan Member shallow-water carbonates and continued through the early Santonian. During this interval, the Maracaibo and Barinas/Apure basins were characterized by low-oxygen or anoxic bottom-water conditions away from the basin margins. Deposition of organic carbon-lean upper La Luna and Navay formation strata show that bottom-water oxygen content increased from the late Santonian through the end of the Cretaceous. The siliceous and phosphatic late Santonian to early Maastrichtian Tres Esquinas Member, and the glauconitic late Campanian to early Maastrichtian Socuy Member (both of the La Luna Formation) represent the final phase of La Luna deposition in the Maracaibo Basin. Tectonic uplift in eastern Colombia during the Campanian and Maastrichtian caused progradation of the Colَn, Mito Juan, and Burgüita Formation deltas, and eventual infilling of the Maracaibo and Barinas/Apure basins.