GASTROPOD CARBONATE DELTA-O-18 AND DELTA-C-13 VALUES RECORD STRONG SEASONAL PRODUCTIVITY AND STRATIFICATION SHIFTS DURING THE LATE EOCENE IN ENGLAND

High-resolution delta(18)O and delta(13)C measurements obtained from t he gastropod Clavilithes macrospira provide the most detailed record o f seasonal change in temperature (range similar to 14 degrees C, seawa ter chemistry, and bottom-water ventilation yet obtained from late Eoc ene strata (type Bartonian, ca. 40 Ma). The delta(18)O oscillations su ggest a line ar rate of long-term growth and rapid growth in spring-ea rly summer. Coherence analysis shows that delta(13)C patterns vary fro m being closely in phase with respect to annual delta(18)O oscillation s, to being antiphase, with a phase shift toward a spring, or more rar ely, an autumnal delta(18)C peak, These patterns are attributed to uns table seasonal productivity and/or the development of a seston-rich bo ttom layer, in which the delta(13)C gradients arising from seasonal eu trophication were perturbed by spring storms, Such episodes may have l ed to the decline and extinction of oligotrophic marine biota with pho tosymbionts, including Nummulites, in the late Eocene.