EARLY TO MIDDLE MIOCENE MARINE PALYNOLOGY OF THE COLOMBIAN CARIBBEAN MARGIN: BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC IMPLICATIONS

Dinoflagellate cysts and acritarchs are widely used to date and reconstruct paleoenvironments in shallow to marginal marine sequences, especially in the Neogene of temperate latitudes. However, little is known about tropical regions. Here, we present an early to middle Miocene assemblage of dinocysts and acritarchs from the Cosinetas-1 Well, northern Colombia. The abundance of Spiniferites ramosus and Operculodinium centrocarpum, along with the presence of Lingulodinium machaerophorum, Spiniferites mirabilis, Polysphaeridium zoharyi, Selenopemphix nephroides and Tuberculodinium vancampoae, indicates an accumulation in warm and shallow marine environments. The peridinioid versus gonyaulacoid (P/G) ratio suggests low nutrient availability in the Cocinetas Basin during the early Neogene. In contrast, modern shallow waters along the Guajira Peninsula are productive except in the eastern part where coastal upwelling is perturbed by warm water inflow from the Lake Maracaibo. In addition, the biostratigraphic range proposed for Achomosphaera alcicornu in equatorial latitudes is constrained to the Rupelian according to Williams et al. (2004); however, the continuous presence of A. alcicornu in the Cosinetas-1 Well extends its last appearance datum in the tropical Americas to at least the early Miocene.