Cretaceous and Cenozoic calcareous nannofossil biostratigraphy of the NW inland basins of Colombia

Abstract

Calcareous nannofossils, a well-calibrated group of marine microfossils, are widely used to date and correlate Mesozoic and Cenozoic deposits. Despite their importance, relatively few studies have focused on these fossils in onshore deposits of South America. To address this gap, we analyzed calcareous nannofossils from several basins in the Caribbean, Pacific, and inter-Andean regions of Colombia, aiming to develop a regional framework for dating and correlating marine deposits. Our findings indicate that diagenesis significantly affects preservation of microfossils, and that nannofossil abundance is notably lower in coastal and deltaic deposits. Even so, we identified fourteen well-preserved assemblages that serve as key biostratigraphic markers, indicating ages from the Aptian (Cretaceous) to the Calabrian-Chibanian (Quaternary). By integrating these results with existing biostratigraphic data from foraminifera, palynomorphs, diatoms, and ammonites, we constructed a chronostratigraphic framework that compiles and summarizes biostratigraphic, sedimentary, and lithostratigraphic information. This regional perspective on the tropical basins of Colombia is critical for understanding the geological evolution of the Caribbean Sea and the eastern Pacific Ocean.