Lithostratigraphic analysis of the La Loma Formation and depositional model of the intermontane Cesar Sub-Basin (Colombia) during the Eocene: Exploring potential for CO2 storage

The Cesar-Ranchería Basin in Colombia presents significant knowledge gaps concerning its Eocene stratigraphy, impeding a comprehensive understanding of its geological evolution and regional correlations. This study focuses on characterizing the La Loma Formation (Eocene) using well log data, petrographic analysis, and X-ray diffraction to delineate its depositional environment and sediment provenance. The La Loma Formation comprises sandstones, conglomerates, and interbedded siltstones within the central La Loma syncline. Petrographic analysis of 100 thin sections identifies two distinct sedimentary environments: fluvial fans and a fluvial system. The Santander Massif and Serranía de Perijá are identified as primary source areas for La Loma Formation sediments. In the lower section of the La Loma Formation, sedimentary contributions primarily originated from the Santander Massif (Eastern Cordillera), indicating uplift during the early Eocene. This geological event potentially redirected drainage towards the Lower Magdalena Valley Basin and connected the Cesar Sub-basin with the Middle Magdalena Valley Basin. Conversely, the upper section of the La Loma Formation reveals a mixed sediment contribution from the Santander Massif, Serranía de Perijá, and Sierra Nevada de Santa Marta. This variation suggests significant environmental shifts and tectonic reconfigurations during the Eocene, influencing connectivity between the Middle Magdalena Valley Basin, the Lower Magdalena Valley Basin, and the Cesar Sub-basin. This lithostratigraphic analysis enhances our understanding of the La Loma Formation's role in regional stratigraphy and basin evolution within the Cesar-Ranchería Basin. Moreover, the study explores the formation's potential for carbon dioxide (CO 2 ) storage, emphasizing its geological stability, adequate porosity, and potential as a natural sealant, crucial for long-term CO 2 storage and climate change mitigation strategies. • Detailed analysis of La Loma Formation using well logs and petrographic data. • Identification of fluvial fans and systems within La Loma Formation. • Santander Massif and Serranía de Perijá identified as primary sediment contributors. • Early Eocene uplift in Santander Massif redirected drainage patterns. • La Loma Formation shows promise for CO 2 storage with favorable porosity and sealing characteristics.