Late Cretaceous calcareous nannofossil assemblages from Colombia: Biostratigraphic contributions to northwestern South American Basins
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MicropaleontologyCaribbean nannofossilsLa luna seaEastern equatorial Pacific nannofossils
E. Angulo-Pardo et al. Late Cretaceous calcareous nannofossil assemblages from Colombia: Biostratigraphic contributions to northwestern South American Basins. Journal of South American Earth Sciences 127 (2023) 104315. [https://doi.org/10.1016/j.jsames.2023.104315]
SponsorshipANH en las cuencas de Sinú-San Jacinto y Cordillera FP44842-494-2017; Instituto de Investigaciones en Estratigrafía; Ministerio de Ciencia, Tecnología e Innovación MINCyT; Agencia Nacional de Hidrocarburos ANH
The Upper Cretaceous deposits of northwestern Colombia accumulated in two regions with distinct tectonic settings. The eastern deposits, consisting of Turonian–Maastrichtian rocks from the Upper Magdalena Valley (UMV) and the Cesar-Rancheria basins, were deposited by an epicontinental sea that partially covered the South American Plate. In contrast, the western deposits, which comprise a series of highly faulted and folded Coniacian–Maastrichtian deposits in the Sinú-San Jacinto Folded Belt (SSJFB), Gorgonilla Island, and Western Cordillera, were influenced by a seaway connecting the eastern Pacific Ocean with the proto-Caribbean Sea and were deposited near the collision zone between the Caribbean and South American Plates. We conducted a biostratigraphic analysis of 119 rock samples from these deposits. Although some well-preserved microfossils were found in the Cesar-Ranchería Basin, most samples exhibited poor to moderate preservation of nannofossils. Biostratigraphic markers identified in the Upper Magdalena Valley Basin were Quadrum gartneri, Micula concava, Micula staurophora, Lithastrinus septenarius, Lithastrinus grillii, Arkhangelskiella cymbiformis, Uniplanarius trifidus, Uniplanarius sissinghii, and Reinhardtites anthophorus. In the Cesar-Rancheria Basin, the markers identified were Arkhangelskiella cymbiformis, Lithraphidites cf. L. praequadratus, and an acme of Kamptnerius magnificus. Based on these taxa, the eastern stratigraphic sections accumulated sometime between UC7 (CC11) and UC20 (CC26) biozones, which is equivalent to an age range of early Turonian to upper Maastrichtian. Key biostratigraphic taxa from the western outcrops were more limited, yielding only Uniplanarius trifidus and Uniplanarius sissinghii, which are indicative of biozones UC15d–UC17 (CC22–CC23). This signifies a sedimentation age sometime from late Campanian to early Maastrichtian. Our results correlate well with previous age models and reveal that undistinguished upper Campanian–lower Maastrichtian deposits of the collision zone can be correlated with the last marine deposits of the epicontinental sea in the UMV. Although calcareous nannofossils from the Cesar-Rancheria Basin displayed the best preservation, low-latitude biostratigraphic markers were absent in this locality, making regional correlations challenging. We hypothesize that these deposits formed during the Maastrichtian, but changes in oceanic water conditions of the proto-Caribbean Sea affected productivity and preservation of biostratigraphic markers.