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Tectonic and Environmental Factors Controlling the Distribution of Sedimentary Facies During the Cretaceous Oceanic Anoxic Events in an Epicontinental Sea: The Colombian Case

Abstract

The evolution of Cretaceous sedimentary basins in Colombia seems to have been related to the re-activation of former tectonic structures and associated to the development of proto-Caribbean and Gulf of Mexico basins. Timing of the opening of this sedimentary basin has remained difficult due to the lack of a high-resolution age controls of the sedimentary record. It has also affected our ability to identify and predict the occurrence of economically important oil and gas generating rocks and reservoirs. Here we use detailed C-, O- and Sr- chemostratigraphy and published bioestratigraphic information and U-Pb detrital zircon ages to precisely date several carbonate and black shale successions in several Colombia Cretaceous basins. Our multiproxy approach allows suggesting the opening of a major north to south epicontinental seaway, similar to the modern Black Sea; and limited by the ancestral Central Cordillera-Santa Marta massif of Colombia (to the west) and the Guyana Shield (to the east). Variations in depositional systems allow suggesting a consistent deepening of the sedimentary environments towards the south and the central part of the Colombia seaway. Our multi-pronged approach also allows identifying the occurrence of several of the Cretaceous Oceanic Anoxic Events (OAEs) in carbonate units from the northern part of this paleo-seaway, i.e. Weissert-OAE-(Palanz and Rosablanca Formations), Faraoni-(Rosablanca Formation), AOE1a-(Paja and Fomeque Formations, Cogollo Group), OAE1c-(Cogollo Group), OAE2-(Cogollo Group), OAE3-(La Luna Formation). These events are preserved in highly euxinic - organic rich “black shales” successions deposited along the deepest part of the seaway at the Middle Magdalena Valley and Cundinamarca Basin; Weiser-OAE-(Lutitas de Macanal Formation), OAE1a-(Paja Formation, Fomeque Formation), OAE1C-(San Gil Formation). Regional changes in depositional settings and sedimentary facies preserving the different Cretaceous OAEs was likely the result of the combined action of regional changes in paleogeography and tectonic regimes and changes in the physicochemical conditions of the Cretaceous seawater along the Colombian epicontinental seaway. Our results highlight the need of using multi-proxies to investigate the occurrence of conventional and unconventional oil and gas prospectus along the Colombian epicontinental seaway and the proto-Caribbean.