Astrobiochronological calibration of an early Oligocene succession from the Colombian Caribe: Tectonostratigraphic implications

The Colombian Caribbean is an active margin characterized by constant and intense tectonic activity since the Cretaceous. Nonetheless, recent studies have reported a period of relative stability during the early Oligocene for some Caribbean basins. We have studied the biostratigraphic and well-log record of a 143-m sedimentary succession from the ANH San Jacinto-1 well in the Sinú-San Jacinto Basin. We present the first astrobiochronological age model constructed for the early Oligocene (32-28 Ma) based on the integrated use of planktonic foraminifer biostratigraphy and the gamma-ray record (GR). Rhythmic GR alternations, associated with changes in clay/organic matter concentration, exhibit a regular pattern of 1:2:5:20 and are correlated in amplitude and intensity with orbital cycles, being the eccentricity-related alternations, the most prominent signal imprinted in the GR record. The correlation with the astronomical target curves allowed us to establish a robust age model for the early Oligocene, which will be instrumental for defining future high-resolution correlations in the Colombian Caribbean basins. Orbitally driven GR patterns indicate that changes in sediment yield are associated with seasonal climatic changes, revealing that during eccentricity maxima (likely precession minima), enhanced humid climate conditions existed in the Caribbean area. At the same time, reduced precipitations persisted over eccentricity minima (likely precession maxima). The GR record amplitude also suggests that at times of reduced precession-driven Equatorial insolation, the obliquity exerted a larger control over the clay-rich sediment input, likely via enhanced humid conditions.