High Resolution Secular Variation in Oxygen, Carbon, Strontium Isotopic Composition

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This research will document the magnitude, rates and relative timing of change among numerous isotopic (18O, 13C, 87Sr/86Sr) and elemental (Li/A1) tracers through the Devono-Carboniferous interval. This period in Earth's history, which is marked by a dramatic shift in 18O and 13C of marine carbonates records either a dramatic decrease in global surface temperature of 30-40 degree, or an enrichment in 18O composition of seawater. Paired analysis of chemical tracers will be performed on non-biological marine carbonates from Devono-Carboniferous reefal sequences of the Dinant Synclinorium (Belgium) - Waulsortian Sequence of Ireland and the time equivalent succession of the Alberta Basin to test the hypothesis that a shift in ocean 18O composition was caused by an increase in 18O flux associated with enhanced hydrothermal alteration at submarine spreading ridges. Analysis of 87Sr/86Sr variation will provide insight on relative contributions from mantle versus crustal sources; Li/Al ratios will record the increasing versus decreasing dominance of high temperature, hydrothermal alteration versus low temperature submarine weathering of mantle-derived basalts. Specific goals of the research include: (1) evaluation of correlations, in time and magnitude, of variation among chemical tracers to determine whether they are responding to a common geologic process; (2) determination of empirical time constants of change in chemistry to constrain the magnitude of elemental fluxes into an out of the ocean; and (3) quantitative modelling, based on empirical relationships, to assess the role of seawater cycling through mid- ocean ridge basalt in defining the 18O composition of the paleocean.