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Organic and inorganic geochemical data (Rock-Eval, TOC, biomarker GC/MS, and mineral, major and trace element analyses) were used to characterize the palaeoceanographic and palaeoclimatic conditions that influenced the deposition of upper Albian to Maastrichtian rocks of western Venezuela. These data show that the late Albian to early Santonian was characterized by the accumulation and preservation of hydrogen-rich marine algal and foraminiferal organic matter, and was modulated, in part, by siliciclastic dilution (via eolian and fluvial/turbidite processes). The contemporaneous development of palaeobathymetric barriers surrounding the Maracaibo and Barinas/Apure Basins resulted in stagnation and poor circulation, and along with high evaporation rates, produced salinity stratification and entrapment of anoxic bottom waters. Bottom water oxygen levels increased from the late Santonian through the end of the Cretaceous as seasonal upwelling intensified, and stratified and entrapped anoxic bottom waters underwent frequent overturn and ventilation. These major changes in depositional patterns can now be identified and linked to regional or global oceanographic and climatic events. The depositional events that best demonstrate this link include: (1) late Albian to early Cenomanian drowning of the Maraca Formation carbonate platform (linked to the global mid-Cretaceous platform drowning event); (2) Cenomanian-Turonian drowning of the Guayacan Member (Capacho Formation) carbonate platform (southern Maracaibo Basin) and deposition of organic carbon-rich sediments (linked to the global Cenomanian-Turonian oceanic anoxic event); (3) depositions of Tres Esquinas Member (La Luna Formation) phosphates and glauconites in the Santonian to Campanian (linked to a regional increase in fluvially derived sediments); and (4) onset of delta progradation from Colombia into western Venezuela during the Campanian through Maastrichtian (linked to regional tectonic activity and cooling global climate). |
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