Chicxulub Post-Impact Sedimentary Sequence: Integrated Borehole Paleogene Carbonate Stratigraphy

Abstract:

The Chicxulub crater was formed by a bolide impact on the southern Gulf of Mexico at ~66 Ma ago that marked the Cretaceous/Paleogene (K/Pg) boundary, represented worldwide by the ejecta layer. The K/Pg boundary layer with its global distribution provides a high resolution marker, allowing high precision stratigraphic analyses in marine and continental sequences. Following crater formation, sedimentation re-established in the carbonate platform, filling the basin. Crater is located half on-land and half offshore, with the crater floor covered by sediments with variable thickness up to about 1 km. The target, impact and post-impact sequences have been drilled and cored, providing samples for stratigraphic, petrographic and physical-chemical laboratory studies. The post-impact stratigraphy has been analyzed in several studies at proximal, intermediate and distal outcrops and in the crater boreholes, using e.g., radiometric dating, micropaleontology, paleomagnetism, and strontium and stable isotope geochemistry. Emphasis has been given on the impact breccias-carbonates contact and the basal Paleocene sequence. Here we re-analyze the available data, revisiting the stratigraphy for the Santa Elena, Tekax, Peto and Yaxcopoil-1 boreholes using newly constructed detailed lithostratigraphic columns in the continuously cored boreholes. Additionally we extend the study to the Paleogene sequence in the Santa Elena and Yaxcopoil-1 boreholes using bulk carbon and oxygen isotopes, magnetic polarity, XRF core geochemistry and magnetic susceptibility stratigraphy. Results spanning chrons c29 to c24 constrain the K/Pg boundary, c29r-c29n polarity reversal and the Paleocene-Eocene thermal maximum, providing high resolution records. The basal Paleocene gap and age differences in an integrated stratigraphy are discussed and correlated to the GPTS scale and IODP marine isotope records. The extent and characteristics of crater structure and target/cover sediments have been imaged with terrestrial, marine and aerogeophysical surveys. We use the marine seismic sections for correlation of the geophysical logs and borehole stratigraphy, allowing lateral correlation across the crater and further constraining the sequence stratigraphy, platform evolution and impact effects.