PALYNOSTRATIGRAPHY OF THE MAASTRICHTIAN UMIR FORMATION, MIDDLE MAGDALENA VALLEY BASIN (MMVB), COLOMBIA -PRELIMINARY RESULTS-

The Middle Magdalena Valley Basin (MMVB) is one of the most important oil basins in Colombia. Current oil exploration focuses on areas with structural complexity and non-conventional reservoirs. The Umir formation is an effective regional seal in MMVB Petroleum System however, some of the recent new targets are located in the cross-stratified sandstones in the upper Umir. There is little known on this new reservoir in Central-Eastern MMVB because both of the complex structures and the presence of a large unconformity known as the Middle Magdalena Valley Unconformity (MMVU). Hence, the regional distribution of these oil-bearing sandstones is uncertain and exploratory risk is high. This research focuses on developing a biostratigraphic framework for the Maastrichtian Umir Formation using palynology. Palynology is the best micropaleontological proxy to be used because depositional conditions in Umir formation favored the preservation of abundant terrestrial (pollen and spores) and marine palynomorphs (dinoflagellate cysts and acritarchs). Major biostratigraphic events will be used to develop regional correlations, improve geological models, reduce the exploratory risk and serve as a key tool for on-site, real-time biostratigraphic control of exploratory wells. The study area is located on the western side of the Los Andes syncline, in Central Eastern MMVB. Ninety-nine samples for palynological content were selected from four cores covering a stratigraphic thickness of 2990 feet. The samples were processed in the Colombian Petroleum Institute (ICP) and standard palynological analyses are being conducted at Louisiana State University (LSU). Thus far, the palynological assemblage is characterized by the occurrence of Echimonocolpites protofranciscoi, Proteacidites dehaani, Buttinia andreevi, Echitriporites trianguliformis, Echitriporites suescae, Bacumorphomonocolpites taussae, Syndemicolpites typicus, Tetradites umirensis, Ulmoideipites krempii and Monocolpites grandispiniger. Six levels with abundant dinocysts and foram linings, showing a marked marine influence, have been recorded as well. The excellent recovery of terrestrial and marine palynomorphs shows potential to find new biostratigraphic events for the Maastrichtian biostratigraphy of Northern South America.