Elemental and Oxygen Isotope Composition of Early Jurassic Belemnites: Salinity vs. Temperature Signals

摘要

Well preserved calcitic belemnite samples from the Basque-Cantabrian basin of northern Spain have been analyzed to improve our current understanding of the chemistry of seawater as an index of paleoceanographic changes during the Early Jurassic, a period punctuated by times of oceanic anoxia and global mass extinctions. Because the oxygen-isotope composition of calcite depends not only on temperature but also on salinity, we present here a combination of Sr/Ca, Mg/Ca, and 18O analyses that helped us to evaluate both effects separately. Comparison between the temporal records and cross plots of these geochemical parameters shows a good correlation of Mg/Ca with 18O and a weak correlation of Sr/Ca with 18O.