V11A-4693:
Clumped isotope thermometry in deeply buried sedimentary carbonates: The effects of C-O bond reordering and recrystallization
Monday, 15 December 2014
Brock Shenton1, Ethan L Grossman1, Benjamin H Passey2, Gregory A Henkes2, Juan Carlos Laya1 and Alberto Perez-Huerta3, (1)Texas A & M University, Department of Geology and Geophysics, College Station, TX, United States, (2)Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD, United States, (3)University of Alabama, Department of Geological Sciences, Tuscaloosa, AL, United States
Abstract:
Constraining the thermal histories of sedimentary basins is fundamental to a range of geologic applications including tectonics, petroleum system analysis, and the genesis of ore deposits. Carbonate rocks can serve as archives of basin thermal histories through solid-state reordering of their 13C-18O, or ‘clumped isotope’, bonds at elevated burial temperatures. Here we present one of the first applied studies of carbonate clumped isotope reordering to explore the diagenetic and thermal histories of exhumed brachiopods, crinoids, cements, and host rock in the Permian Palmarito Formation, Venezuela and the Carboniferous Bird Spring Formation, Nevada, USA. Carbonate components in the Palmarito Formation, buried to ~4 km depth, yield statistically indistinguishable clumped isotope temperatures (T(∆47)) ranging from 86 to 122 °C. Clumped isotope temperatures of components in the more deeply buried Bird Spring Formation (>5 km), range from ~100 to 165 °C and differ by component type, with brachiopods and pore-filling cements yielding the highest T(∆47) (mean = 153 and 141 °C, respectively) and crinoids and host rock yielding significantly cooler T(∆47) (mean = 103 and 114 °C). New high-resolution thermal histories are coupled with kinetic models to predict the extent of solid-state C–O bond reordering during burial and exhumation for both sites. Application of these models suggests that brachiopods in the Palmarito Formation experienced partial bond reordering without complete equilibration of clumped isotopes at maximum burial temperature. In contrast, clumped isotope bonds of brachiopods from the Bird Spring Formation appear to have completely equilibrated at maximum burial temperature, and now reflect blocking temperatures ‘locked-in’ during cooling. The 40–50 °C cooler clumped isotope temperatures measured in Bird Spring Formation crinoids and host rock can be explained by both recrystallization and cementation during shallow burial and a greater inherent resistance to solid-state reordering than brachiopods.
