Dr. Jordan Wostbrock
Yale

Topic: Reconstructing paleoenvironments using triple oxygen isotope values

Academic host: Katie Snell

Abstract: The increase of d18O values in the rock record (where older samples have lower d18O values than modern) has been attributed to changing ocean temperature, an increase in the d18O value of the ocean water, or diagenesis obscuring paleoenvironmental information. Unlike conventional δ18O analysis where the formation water’s isotopic value is assumed, paired δ17O-δ18O measurements allow for the water’s isotopic composition to be calculated because there is only one unique solution for equilibrium fractionation using triple oxygen isotope values. This is particularly useful when measuring samples from the rock record, where the water is no longer present. These measurements are also useful for a definitive identification of diagenesis – samples that fall off the unique triple oxygen isotope equilibrium curve must have undergone some degree of diagenesis. A fluid-rock mixing model can be used to ‘see through’ alteration in samples such that the initial temperature of formation and the oxygen isotope value of the water in which the carbonate formed can be calculated. In this talk, I will present the first carbonate-water triple oxygen isotope equilibrium curve. I will then use the equilibrium curve to compare the triple oxygen isotope values of Phanerozoic brachiopods. Lastly, I will present results from carbonate concretions from the Late Cretaceous Western Interior Seaway that combines triple oxygen isotope measurements with carbonate clumped isotope measurements (D47 values) to better understand the diagenetic history of the carbonate concretions.