A dataset on dolomite abundance, geochemistry, and U-Pb dating from a Triassic evaporative platform in the Sichuan Basin, SW China

Table 1 presents 20 XRD analyses documenting the mineral compositions of the Middle Triassic borehole interval. Within the evaporite-dominated interval, the volume fractions of evaporite and dolomite range between 70–90% and 5–15%, respectively. Table 2 summarizes the isotopic results (δ26Mg, δ44Ca, δ34S, 87Sr/86Sr) for the same interval. Carbonates show a rough anti-correlation between δ26Mg and δ44Ca isotopic compositions. δ26Mg exhibits an upward increasing trend stratigraphically (‒2.31‰ to ‒1.21‰; n=28), while δ44Ca shows a corresponding decreasing trend (‒1.28‰ to ‒0.28‰; n=13). Anhydrite samples (n=10) display a narrow δ34S isotopic range of 29.3‰ to 26.2‰, averaging 27.8 ± 1.2 ‰. Carbonate (n=12) exhibit 87Sr/86Sr ratios within a tight range of ~0.70825 to 0.70855. Table 3 provides U-Pb dating results for eight dolomites: two dates are from the Middle Triassic and six are from the Lower Triassic borehole samples. All dolomites yielded relative high-quality isochrons, with minor uncertainties (3.1 to 11.7%, average at ~6.5%) and limited scatter in data points (low MSWD values of 0.25 to 1.1, average at 0.82). Lower Triassic dolomites (n=6) yield U-Pb ages ranging from 209 to 237 Ma, averaging 224 ± 13 Ma, which aligns with the older U-Pb age (226 ± 14 Ma) of the Middle Triassic dolomite. One Middle Triassic dolomite date provides a significantly younger age of 94 ± 11 Ma. The reconstructed 238U/206Pb values for all dolomites range from 0.9 to 10.7, with an average of 4.7.