Mississippi State University

Title: “Geochemistry of calcium carbonate minerals: tool for paleoenvironmental reconstruction, advantages and disadvantages”

Abstract: Marine and terrestrial carbonates contain important information about paleoenvironment including: i) composition of their growth media (i.e. oceans, fresh waters, springs) by preserving isotopic and elemental ratios of the fluid reservoirs; ii) conditions at which carbonates grew. For example 18O/16O and Mg/Ca in foraminifera are being used for paleotemperature and atmospheric precipitation studies; 11B/10B was proposed for reconstruction of oceanic pH values; multivalent elements (e.g. S, Mn, Fe) in marine carbonates has a potential to reflect concentration of O2 dissolved in seawater. These isotopic and chemical signatures of carbonate minerals relate to those in seawater through fractionation factors and partition coefficients, which are constant if thermodynamic equilibrium is maintained during mineral precipitation. However, the general assumption that precipitation of carbonates occurs at chemical equilibrium is not borne out by experimental results and studies of actual marine samples. Disequilibrium effects observed in experimental studies will be presented and discussed at the seminar.