L. Purton et M. Brasier, GASTROPOD CARBONATE DELTA-O-18 AND DELTA-C-13 VALUES RECORD STRONG SEASONAL PRODUCTIVITY AND STRATIFICATION SHIFTS DURING THE LATE EOCENE IN ENGLAND, Geology, 25(10), 1997, pp. 871-874
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.