Late Cretaceous calcareous nannofossil assemblages from Colombia: Biostratigraphic contributions to northwestern South American Basins

The Upper Cretaceous deposits of northwestern Colombia accumulated in two regions with distinct tectonic settings. eastern deposits, consisting Turonian–Maastrichtian rocks from the Magdalena Valley (UMV) and Cesar-Rancheria basins, were deposited by an epicontinental sea that partially covered South American Plate. In contrast, western which comprise a series highly faulted folded Coniacian–Maastrichtian Sinú-San Jacinto Folded Belt (SSJFB), Gorgonilla Island, Western Cordillera, influenced seaway connecting Pacific Ocean proto-Caribbean Sea near collision zone between Caribbean Plates. We conducted biostratigraphic analysis 119 rock samples these deposits. Although some well-preserved microfossils found Cesar-Ranchería Basin, most exhibited poor to moderate preservation nannofossils. Biostratigraphic markers identified Basin Quadrum gartneri, Micula concava, staurophora, Lithastrinus septenarius, grillii, Arkhangelskiella cymbiformis, Uniplanarius trifidus, sissinghii, Reinhardtites anthophorus. Lithraphidites cf. L. praequadratus, acme Kamptnerius magnificus. Based on taxa, stratigraphic sections sometime UC7 (CC11) UC20 (CC26) biozones, is equivalent age range early Turonian upper Maastrichtian. Key taxa outcrops more limited, yielding only trifidus are indicative biozones UC15d–UC17 (CC22–CC23). This signifies sedimentation late Campanian Our results correlate well previous models reveal undistinguished Campanian–lower Maastrichtian can be correlated last marine UMV. calcareous nannofossils displayed best preservation, low-latitude absent this locality, making regional correlations challenging. hypothesize formed during Maastrichtian, but changes oceanic water conditions affected productivity markers.