PALINOSTRATIGRAPHY OF THE PALEOGENE ESMERALDAS FORMATION, MIDDLE MAGDALENA VALLEY BASIN, COLOMBIA

Most of the oil production in Colombia comes from the Cenozoic continental stratigraphic record. The Middle Magdalena Valley, a traditional oil basin in Northern South America is a good example. The tectonic history of the basin by the uplifting of the Central and Eastern Cordilleras in the northern Andes created many structural complexities and stratigraphic asymmetry. The alluvial plains rocks of the Esmeraldas Formation are a very important reservoir of the basin. Because of the complex and continental nature of the basin, the lateral continuity of the Esmeraldas is not clearly understood. Additionally, there are very few reliable correlation elements. The Los Corros fossil horizon, a mollusk horizon located in the upper part of Esmeraldas, is the most traditional correlation component used to differentiate this unit. This is the only paleontological unit formally associated with the Esmeraldas. The age of this horizon, which is not continuous along the entire basin, is still debatable. These facts introduce uncertainty to existing stratigraphic models. Palynology is the best paleontological tool to use for correlation. Preliminary results of a composite outcrop section show that the lower part of the Esmeraldas has an inferred Middle Eocene age, mainly based on the First Appearance Datum (FAD) of Rhoipites guianensis and Cicatricosisporites dorogensis. The upper part (including Los Corros) has an inferred age between Late Eocene to earliest Oligocene, based on the Last Appearance Datum (LAD) of Racemonocolpites facilis and the presence of Retibrevitricolpites grandis. The results from this reference outcrop section will serve as reference points for accurate subsurface correlations and will be useful in the combination with non-paleontological tools. This will provide a better understanding of the lateral extent of the Esmeraldas and the development history of the basin.