Abstract:
We present results of a stable isotope study of the carbonate sedimentary sequence recovered in the Santa Elena borehole (located 110 km from the crater center) of the UNAM Scientific Drilling Program, immediately above the impact breccia-carbonate contact at a depth of 332 m. Sixty samples spaced in a 17 m thick section representing the basal Tertiary sequence were analyzed for oxygen and carbon isotopes. The delta (super 13) C ranges from about 1.2 to 3.5 per mil, and the delta (super 18) O ranges from about -1.4 to -4.8 per mil. We correlate the isotopic records for bulk carbonate for the Paleocene with the DSDP Hole 577, assuming a tie point for the Cretaceous/Paleocene (K/T) boundary. The variation pattern in the Santa Elena borehole correlates well with the global pattern defined for marine carbonate sediments. In the Santa Elena borehole, delta (super 13) C values are slightly more positive; delta (super 13) C values reach approximately 3.5 per mil and there is a gradual increase from the Lower to the Middle Paleocene strata. The trend of delta (super 18) O values from Santa Elena borehole are also similar to delta (super 18) O DSDP Hole 577, however values in the Chicxulub Tertiary sequence are more negative; delta (super 13) C values reach ca. -4 per mil in the Lower Paleocene rocks. Paleomagnetic data for the study section document four geomagnetic polarity zones for the impact breccias and basal sedimentary sequence, which span from chron 29r (K/T boundary) to chron 28n. The combined stable isotope and magnetic polarity data provide a stratigraphic framework for the first 2.5 Ma after the K/T boundary, and permit inferences about the paleoceanographic conditions following the Chicxulub impact and into the Early Paleocene.