CARBONATE ISOTOPE CHEMOSTRATIGRAPHY OF THE LATE CRETACEOUS - EARLY TERTIARY FROM SEYMOUR ISLAND, ANTARCTICA

Seymour Island, in the James Ross Basin on the West Antarctic Peninsula, is the southernmost marine K-T boundary section in the world, and consequently provides valuable information on the latitudinal variability on the impact of the K-T event. Seymour Island has moved less than three degrees of latitude since deposition and has undergone minimal deformation (structural tilt ~5°) and diagenesis (most fossils preserve original aragonite). The Lopez de Bertodano formation is comprised of immature mud to sand deposited in a back-arc setting on the middle to inner shelf during the upper Maastrichtian and Danian. Carbon isotopic data is currently being generated from both aragonitic shell material and bulk rock samples to create a detailed chemostratigraphy. Recent identification of the magnetic chrons 31R/31N and 30N/29R on Seymour Island during ongoing paleomagnetic analysis at Caltech provides a firm basis for correlation with other K-T sections around the world as well as firm tie points for chemostratigraphy. Preliminary δ¹⁸O data from aragonitic (confirmed by XRD analysis) shells suggest that temperatures were considerably higher during the Maastrichtian and Danian than today (~10°C versus near 0°C), assuming minimal diagenetic alteration and a seawater δ¹⁸O composition of -1.0‰. These results are in broad agreement with previous studies and with preliminary results using the ‘clumped isotope in carbonate’ paleothermometer, which indicate seawater temperatures of ~12°C or lower.