Constraining carbonate diagenesis using clumped isotope temperatures and U-Pb dating: A case study and implications for paleoelevation interpretations in western central Tibet

Carbonate rocks are susceptible to diagenesis, and the correct identification of diagenetic features and stages are primary tasks in paleoelevation and paleoclimate studies using carbonate proxies. In this study, we apply three key parameters that include stable isotopes, clumped isotope temperatures, and U-Pb ages to identify different diagenetic stages, i.e., eogenesis, mesogenesis, and telogenesis. We then adopt these criteria to explore the diagenetic history of the middle–late Eocene lacustrine carbonates in the Gerze area of western central Tibet, which have yielded contrasting interpretations of diagenetic stages and paleoelevation estimates. Petrographic observations and electron microprobe element mapping permitted the identification of different diagenetic features. The Gerze carbonates (4GZ section) contain distinct phases of micrite and vein/vug-fill calcite (sparite) with different stable oxygen isotope values of −4 to −6‰ and −10 to −14 ‰ (VPDB), respectively. The micrites are dominantly dolomite in composition and yield clumped isotope temperatures of 40–50 °C, which are interpreted to be the result of dolomitization during shallow burial. In contrast, the vein/vug-fill calcites exhibit lower clumped isotope temperatures of 20–30 °C and U-Pb ages of 3.0–3.3 Ma, indicating a late-stage telogenetic origin after exhumation to near the Earth's surface. Our documentation of different carbonate diagenetic stages sheds light on existing paleoelevation interpretations. We conclude that existing evidence remains inconclusive as to the paleoelevation of the Gerze area basin floors during the middle–late Eocene.