Clumped Isotope Thermometry in Deeply Buried Sedimentary Carbonates: The Effects of Bond Reordering Kinetics and Recrystallization
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I utilize clumped isotope thermometry to explore the diagenetic and thermal histories of exhumed brachiopods, crinoids, cements, and host rock in the Palmarito Formation, Venezuela and the Bird Spring Formation, Nevada, USA. Carbonate components in the Palmarito Formation, which experienced ~4 km of burial, yield statistically indistinguishable clumped isotope temperatures (T(Δ_(47))s) ranging from 86 to 122 °C. Carbonate clumped isotope temperatures 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(Δ_(47))s (mean = 153 and 141 °C, respectively) and crinoids and host rock yielding significantly cooler T(Δ_(47))s (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, termed 'THRMs' (Thermal History Reordering Models), suggests that brachiopods in the Palmarito Formation experienced partial bond reordering without complete equilibration of clumped isotopes at maximum burial temperatures. In contrast, T(Δ_(47))s of brachiopods from the Bird Spring Formation completely equilibrated at maximum burial temperatures, and reflect blocking temperatures achieved during cooling. Relative to the brachiopod calcite, the 40-50 °C cooler clumped isotope temperatures measured in Bird Spring Formation crinoids and host rock can be explained by recrystallization and cementation during shallow burial and a greater inherent resistance to solid-state reordering.
Shenton, Brock Jay (2014). Clumped Isotope Thermometry in Deeply Buried Sedimentary Carbonates: The Effects of Bond Reordering Kinetics and Recrystallization. Master's thesis, Texas A & M University. Available electronically from