Multi-Proxy Study of Chicxulub Impact Breccias and Paleogene Carbonates in the Santa Elena Borehole, Yucatan, Mexico

Results of a joint paleomagnetic, petrographic, X-ray fluorescence, and stable isotope study of the impact breccias and Paleogene carbonate sediments in the Santa Elena borehole are used to investigate the impact effects and climatic and environmental changes in the Chicxulub crater and Yucatan platform, southern Gulf of Mexico. The Santa Elena borehole reached a depth of 504 m and was continuously cored, sampling the post-impact carbonate sediments and impact breccias. We analyze the section from ~230 m to ~340 m, corresponding to the upper breccias and Paleogene sediments, spanning the breccia-carbonate contact at 332 m depth. The lithological column from macroscopic and thin-section petrographic analyses comprises limestones, dolomitized limestones with thin clay layers, and breccias rich in melt and basement clasts within a melt- or carbonate-rich matrix. Magnetic polarities define a sequence of reverse to normal intervals within chrons 29r to 26r in the impact breccias and basal carbonates. Magnetic susceptibility shows high variable values in the breccias correlating with the clast contents and carbonate or melt-rich matrix. Low paramagnetic or diamagnetic susceptibilities characterize the carbonate sequence. Fe-Ti oxides are dominant magnetic carriers with pseudo-single and multidomain states. In the upper breccias, more complex magnetic mineralogy is observed, with hydrothermal alteration phases. The ∂13C values in the first 20 m interval range from 1.2 to 3.5 ‰ and ∂18O values range from -1.4 to -4.8 ‰. Isotopes show variation trends that correlate with the marine carbon and oxygen isotope patterns for the K-Pg boundary and early Paleocene records. Positive carbon isotopes suggest high productivity, with apparent recovery following the K-Pg extinction. Oxygen isotope values are negative, reflecting regional and local effects. Geochemical data define characteristic trends, with silica decreasing gradually from high values in the breccias, low contents between 320 to 247 m, with intervals of higher variability, particularly between 280 and 247 m, and then increased contents at 247-230 m. Ca shows the opposite trend with low values in the breccias, high in the Paleocene carbonates, and low in the PETM. Major oxides and trace elements show similar patterns, e.g., Fe, Ti, K, and Al, recording changing climatic and depositional conditions in the platform. Results are interpreted in terms of the paleoclimatic and paleoenvironmental evolution of the southern Gulf of Mexico at the Cretaceous-Paleogene boundary, Paleocene and Eocene, including analysis of post-impact processes, hydrothermal activity, platform sedimentation, and sea level changes.