Marine-lacustrine systems during the Eocene in northern South America – Palynological evidence from Colombia

The Neotropics have experienced a series of marine incursions and the development of lacustrine systems at different intervals during the Cenozoic. One of these events occurred during the middle-late Eocene, an interval of time related to one of the most prolific oil reservoirs in Colombia, the Mirador Formation. Previous studies have identified marginal and marine environments during the late Eocene, especially in the Putumayo basin and the central Llanos foothills of Colombia. However, it is still not clear if the marine incursion is restricted to the late Eocene, or if the incursion started early. To investigate this, we analyzed a stratigraphic section located in the Llanos Foothills of Colombia. We studied the palynological content of 57 samples to stablish a temporal framework for the interval and to estimate the degree of marine, terrestrial and/or lacustrine influence during the deposition. The marine influence is especially marked during the middle Eocene and show a decreasing trend that finally reach values close to zero in the early Oligocene. Differences in the contribution of microforaminifera, dinoflagellate cysts, and freshwater algae are evident throughout the section. The corridor proposed to explain the marine incursion during the late Eocene, was active at least since the middle Eocene.