Regional Stratigraphic Framework of the Paleocene in the Cesar Sub-Basin of Colombia

Alejandro Mora, Alberto García, and Ricardo Triana
Drummond Ltd. Colombia, Bogotá, Colombia

Besides from carrying out coal exploration and exploitation activities, Drummond Ltd. is currently exploring for hydrocarbons and coal-bed gas in the Cesar Sub-basin of northern Colombia. The integration of exploration data recently acquired by Drummond, with the available data from previous hydrocarbon exploration campaigns, allowed erecting the regional stratigraphic framework of the Paleocene in the Cesar Sub-basin.

Detailed core-calibrated well correlations with palynologic and petrographic control made possible recognizing major base-level changes and identifying third-order stratigraphic sequences within the Late Maastrichtian-Paleocene succession. The interpretation of well logs and cores shows the progradation of the Barco fluvio-estuarine facies over the Molino fine-grained offshore facies, followed by the aggradation to progradation that characterizes the Cuervos Formation, in which a thick coal-bearing succession that is mined by Drummond was deposited. As the stacking patterns show, the thick and laterally continuous coals which are being mined were deposited within the middle highstand systems tract of the main third-order sequence that was recognized in this study.

Petrographically, the Late Maastrichtian-Paleocene succession shows a notorious change in the source area as indicated by the increase of metamorphic and sedimentary lithic fragments towards the top of the Barco-Cuervos Formations, evidencing the progressive unroofing of mixed sedimentary and metamorphic terranes. The Paleocene-Eocene boundary is marked by a notorious change in depositional environments that was probably caused by strong uplift pulses of the Central Cordillera and/or the Sierra Nevada de Santa Marta. These pulses allowed the deposition of coarse-grained fluvial and alluvial fan Eocene deposits that are preserved in the La Loma Syncline.