Sedimentologic Expression of the Cretaceous Oceanic Anoxic Events along Eastern and Northern Colombia

摘要

The Cretaceous oceans witnessed several periods of de-oxygenation and acidification, known as oceanic anoxic events (OAEs), which resulted on the widespread occurrence of organic rich sedimentary successions of black shales. In tectonically active regions, their occurrence is not only controlled by changes on ocean chemistry, but also by regional tectonics. Perturbations on the marine C-cycle during the Cretaceous OAEs, resulted on global C-isotope anomalies on the marine records. Here, we use the Cisotope stratigraphy of several Cretaceous sedimentary successions from eastern and northern Colombia to investigate the lithological expression of the Cretaceous OAEs along these areas. The oldest Cretaceous OAEs, the Valanginian-Weissert and Barremian-Faraoni OAEs, were registered by shallow marine carbonate successions from the Rosablanca and the Palanz formations. The Uppermost carbonates from the Rosablanca Formation also registered the Early Aptian Selli OAE, which predates the middle Early Aptian OAEla registered by black shales from the La Paja Formation. The Faroni, Selli, and la OAEs were registered by deep marine organic-rich black shales from the Lutitas de Macanal and Fomeque formations. Shallowing upward carbonate successions from the Cogollo Group registered the Early Aptian OAEla, the Aptian-Albian OAElb, and middle Cenomanian OAE. The overlying La Luna Formation, which spans until the Santonian, displays basal black shales deposited during the Cenomanian-Turonian OAE (OAE2). The remarkable differences on sedimentary expression of the Cretaceous OAEs cannot be explained by changes on ocean chemistry alone. Local tectonics played an important role on the sedimentologic expression of the OAEs and controlled the occurrence of potential unconventional hydrocarbon resources.