Ichnology of a tropical delta and associated strandplain: the Oligocene–Miocene Ciénaga de Oro Formation of Colombia

The Oligocene-Miocene Ciénaga de Oro Formation, located in the San Jacinto Fold Belt Basin (SJFB) of northwestern Colombia, records a complex interplay of fluvial, wave, and tidal (Fwt) processes. This study integrates sedimentologic and ichnologic data to reconstruct depositional environments and corresponding paleoecologic conditions. Two facies associations were identified: FA1 (deltaic), including distributary channels, interdistributary bays, lagoons, marshes, and delta front deposits; and FA2 (strandplain), comprising backshore, foreshore, and shoreface deposits. The succession reflects a deltaic system, varying laterally to a strandplain. Ichnologic analysis reveals archetypal ichnofacies, such as the Skolithos Ichnofacies in the high-energy shoreface, the Rosselia Ichnofacies in the delta front, and the Teichichnus Ichnofacies in the interdistributary bays and lagoons. These trace fossils indicate varying stress factors, including high sedimentation rates, alternating hydrodynamic energy conditions, elevated water turbidity, and salinity fluctuations, which influenced benthic communities. The stratal stacking pattern is progradational and aggradational, indicating that deposition occurred in a highstand systems tract (HST). This study provides a depositional model for mixed influence deltaic (Fwt) and strandplain systems in a tropical area, enhancing our understanding of the Oligocene-Miocene evolution of the SJFB and offering insights applicable to similar systems in low-latitude settings.