Burial estimates constrained by clumped isotope thermometry: example of the Lower Cretaceous Qishn Formation (Haushi-Huqf High, Oman)

Abstract

Abstract Accurate determination of the thermal history of sedimentary basins is critical to constrain the timing of diagenetic processes. Here, clumped isotope palaeothermometry is used to estimate minimum burial depth of the Lower Cretaceous Qishn Formation in east central Oman. Fossil oysters were collected in a soft argillaceous unit, thin-sectioned, and studied under petrographical and cathodoluminescence microscopy, revealing a variable state of shell preservations with early silica replacement of carbonate and late-stage calcite cementation. Clumped isotopes values varied from 0.602 to 0.666‰, with the best-preserved oyster shell yielding a temperature of 37 ± 4°C and a calculated oxygen isotope ratio in seawater (δ 18 O seawater ) compatible with Cretaceous seawater having experienced moderate evaporation (1.0–1.5‰ VSMOW). The new minimum estimates for the burial depth of the Qishn Formation is 1.0–1.2 km, based on the temperature difference between the well-preserved oyster and the partially neomorphosed oyster recording the highest burial temperature (63 ± 4°C). This is in excess of what was predicted by previous studies (<400 m), but compatible with conodonts alteration index temperatures (<80°C). This study highlights the potential of clumped isotopes as a quantitative tool to estimate temperature and burial depth in fine-grained carbonate succession where fluid inclusions are absent, and offers a new tool to constrain the thermal histories of sedimentary basins.