Dinoflagellates from the Upper Campanian - Maastrichtian of Colombia and western Venezuela: Biostratigraphic and sequence stratigraphic implications

Dinoflagellate biostratigraphy of the Upper Campanian-Danian was studied in five surface sections from Colombia and one from western Venezuela (Rio Loro section). The Rio Molino section is in northern Colombia, the Chiguata Creek and Tausa sections are in the central part of the Eastern Cordillera, La Buitrera Creek section is in the western flank of the Eastern Cordillera, and the Aico Creek Section is in the Upper Magdalena Valley. At least twenty-two biostratigraphically significant events were identified in the upper Campanian and Maastrichtlan of the studied sections. In absence of calcareous macro- and microfossils the Campanian/Maastrichtian boundary was identified based on the highest occurrence of Trichodinium castanea and near the lowest occurrence of Phelodinium tricuspe, Yolkinigymnium lanceolatum and Hafniasphaera fluens. Several third-order coarsening upward cycles were recognized within the overall shallowing upward pattern displayed in the six sections. Dinoflagellates tend to be more abundant at the base of these cycles and peridinoid cysts dominate the dinoflagellate assemblage in most samples. During the upper Campanian carbonate sediments accumulated in northern Colombia (Socuy Limestones), while high paleo-productivity conditions generated biosiliceous sediments and condensed phosphorites in the Eastern Cordillera and the Upper Magdalena Valley (Plaeners Formation and Lidita Superior). These become younger to the east. Continuous, cyclic progradation from the east and south during the upper Campanian accumulated coarse-grained siliciclastics in proximal settings where sandstones are interbedded with porcelanites and cherts (Chiguata and Tausa sections). In more distal environments, micritic limestones and dark mudstones from the Buscavida Formation represent coeval sediments (La Buitrera Creek and Alco Creek sections). An expanded section of mudstones and sandstones from Los Pinos and Tierna Formations was recognized in the Chiguata Creek section relative to the Aico, La Buitrera, Rio Molino and Tausa sections. The K/T boundary is present in the Venezuelan section but coincides with an 11.5 m unexposed interval separating uppermost Maastrichtian dinoflagellate events below from Danian dinoflagellates above.