Disentangling Primary Climatic Signals from Burial Diagenetic Overprints in Tibetan Paleosols Using Clumped and Triple Oxygen Isotopes

Paleosol carbonate nodules may preserve environmental information despite later burial alteration, yet disentangling original signals from diagenetic overprints remains a central challenge. Here we apply paired clumped and triple oxygen isotope analyses (Δ47–Δ’17O) to microsampled Eocene paleosol carbonates from the Gonjo Basin, southeastern Tibet. Intra-nodule TΔ47 values of 9–58 °C define a spectrum of microscale thermal heterogeneity, spanning lower-temperature to more strongly burial-modified domains. In contrast, carbonate Δ’17O does not vary systematically with TΔ47 (R2 < 0.6), whereas reconstructed diagenetic-water compositions (δ18Ow and Δ’17Ow) covary with TΔ47, suggesting progressive fluid–rock exchange during burial. Together with petrographic and geochemical observations, these data are most consistent with fluid-limited, rock-buffered recrystallization at low-water–rock ratios, with modeled solutions for most micritic domains falling at W/R < 0.05. Reconstructed Δ’17Ow values of diagenetic fluids range from −77 to −27 per meg, consistent with interaction with isotopically evolved meteoric waters and plausibly reflecting prior evaporative modification, although alternative fluid histories cannot be fully excluded. Rather than fully erasing environmental information, burial recrystallization in these carbonates appears to preserve a quantifiable record of fluid–rock interaction and hydroclimatic conditions. Our results show that paired Δ47–Δ’17O approach can help distinguish lower-temperature domains from more strongly burial-modified domains and trace diagenetic fluid evolution in ancient terrestrial carbonates.