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Abstract

The deposition of organic carbon–rich sediments during the Late Cretaceous in northern South America was controlled by global and local oceanographic, climatic, and tectonic variables. Key in establishing “source rock” depositional systems across the region were eustatic sea-level rise, warming global sea-surface temperatures, the formation of low-latitude saline bottom waters, and a relatively constant supply of fine-grained hemipelagic sediment (mostly derived from the south and east). Specific paleobathymetric conditions enhanced the development of stagnant water masses from the proto-Caribbean plate to Suriname. Organic-matter preservation was aided by the presence of these water masses across the region. Primary productivity was elevated above “normal” marine levels only in the protocentral Caribbean and along the ancestral Costa Rica/Panama island arc, or during seasonal upwelling in northern South America.

Cooler, wetter climatic conditions that began in the late Santonian also were modified by regional and local variables. The development of new intermediate/bottom-water masses, increased polar heat transport caused by improved deep-ocean circulation, and fluctuations in volcanogenic CO2 provided a background effect for local variables such as bathymetry and topography. The development of oxygenated high-latitude water masses provided a means for ventilation of stagnant, low-oxygen bottom waters across northern South America and the central Caribbean. Stronger seasonal upwelling (increased wind stress caused by better polar heat transport, and northward movement of the South American Plate into the zone of northward Ekman transport), more frequent fluvial outflow and deltaic deposition, and the submergence of key paleobathymetric barriers aided ventilation and subsequently diminished organic-matter preservation. Most of these variables had a positive impact on primary productivity and caused rapid changes in the diversity of planktonic foraminifera through the end of the Cretaceous.

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