Paleoenvironmental inferences based on benthic foraminifera from the Uitpa Formation (Guajira, Colombia)

Abstract

The Uitpa Formation is a lithostratigraphic unit that crops out in the Guajira peninsula, northeastern Colombia in the Cocinas Basin. This formation consists mainly of marly and argillaceous mudstones of gray to light brown color, intercalated with sandstone and calcarenite beds. The lower contact with de Siamana Formation is unconformable, and at the top the contact with the Jimol Formation is conformable at Uitpa. These units contain an abundant and diverse fauna of planktic and benthic foraminifera that has not been studied in detail yet. In this research, two outcrop sections from the upper Guajira containing the Uitpa Formation were analyzed: the Pisuuluu hill and Jososuwou creek sections. Planktic foraminifera were extracted and taxonomically classified, allowing to assign an age of Chattian (Late Oligocene) (planktic foraminifera biozones O6 - O7). This investigation presents for the first time in Colombia a paleoenvironmental reconstruction integrating various methodologies using quantitative and qualitative analyses in benthic foraminifera. From these analyses an outer neritic to upper bathyal paleodepth was inferred, with environments characterized by high organic matter inputs in eutrophic conditions for both sections. Oxygenation levels were higher in the Pisuuluu hill section, represented by high diversity heterogeneous assemblages, while for the Jososuwou creek section oxygenation was very low producing stressed environments and low diversity homogeneous assemblages.