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[BPT25-03] Paleotemperature, productivity and shell size of Hedbergella delrioensis in the Cretaceous thermal maximum
Keywords:Cretaceous, planktic foraminifer, shell size, paleotemperature, productivity
On the other hand, size distribution within a modern planktic foraminiferal community, and intra-species size variation are known to respond to abiotic properties, such as temperature and salinity, and productivity (Bijma et al., 1990a, 1990b; Schmidt et al., 2004). However, the size distribution of the Cretaceous foraminifers has not been widely analyzed so far. We discuss the intra-species size variation of the mid-Cretaceous planktic foraminifer, Hedbergella delrioensis, and environmental qualities; paleotemperature, salinity and productivity.
Pelagic sediments used for this study were recovered in ODP Leg 207 at Demerara Rise, the equatorial Atlantic. Samples were washed through a sieve with 64μm opening. Approximately 100 individuals of H. delrioensis were picked from particles larger than 125 μm. The largest linear dimension of each individual was measured, and the stratigraphic variation of average size was described. Since TEX86 and carbon and oxygen isotope composition of planktic foraminifers have already been analyzed by Forster et al. (2007) and Moriya et al., (2007), stratigraphic variations of these proxies were discussed with the size distribution. Average size of H. delrioensis co-varies with the productivity estimated from the carbon isotope composition. Considering that the paleotemperature and salinity had been unchanged in the interval analyzed, it is expected that the size of H. delrioensis responded to the local productivity.
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