Sedimentary basins are commonly viewed as archives of ancient depositional environments and geochemical signals measured in these basins are frequently interpreted as proxies for ancient Earth-surface environments. However, in the course of the sedimentary basins life-cycle, sedimentary rocks can undergo alteration in diagenetic, epigenetic and metamorphic environments. When put in the correct context, these altered geochemical records are valuable sources of information that reflect the complex thermal, compositional, and deformational histories experienced by the sedimentary rocks. Additionally these measurements can serve as key observations in the study of the interactions among the Earth’s surface and internal processes.
In the talk, I will demonstrate how carbonate clumped isotope thermometry (a relatively new temperature-proxy) can be used to study the thermal history of the Colorado Plateau (southwestern N. America), and constrain the oxygen isotope composition of the Phanerozoic Ocean. Clumped and single isotope compositions of calcite and dolomite minerals collected from the Paleozoic sedimentary sequence at the Grand Canyon are consistent with isotopic alteration through open-system recrystallization and/or solid-state isotopic reordering at elevated burial temperatures. By comparing these values with modeled predictions of isotopic signal alteration, we constrain the peak burial temperatures and thermal gradient, and infer the total overburden and exhumation above the top Paleozoic datum at the Colorado Plateau. We also use our data to back-calculate the oxygen isotope composition of dolomite parental water and our results indicate that the oxygen isotope composition of seawater has remained stable throughout the Phanerozoic. This stability suggests that the fluxes of globally averaged oxygen isotope exchange, associated with weathering and hydrothermal alteration reactions, have remained proportional through time. This observation is consistent with the hypothesis that a steady-state balance exists between seafloor hydrothermal activity and surface weathering.
