Evaporite Mineral Evidence for the Dry–Wet Variations in the Mid-Pliocene Warm Period in the Qaidam Basin

Knowledge of dry–wet variations in arid Central Asia (ACA) during the mid-Pliocene warm period (mPWP; ~3.3–3.0 Ma) is instructive to understanding the future variations in this fragile ecosystem region. However, the dry–wet variations in ACA during the mPWP remain controversial. Here, we present high-resolution evaporite mineralogy records from the Gansen (GS) section of the western Qaidam Basin during 3.25–2.95 Ma. Based on the similar periodic variations between the calcite content and χfd/HIRM value-based precipitation records, we infer that the calcite content has the potential to reflect precipitation variations. The results suggest that the calcite content reveals dominant 20 kyr precessional cycles and strong 40 kyr non-obliquity cycles, consistent with the χfd/HIRM values from the GS section, further demonstrating that Qaidam precipitation was affected by the intensified East Asian summer monsoon during the mPWP. However, the occurrence of gypsum beds reveals that the Qaidam Basin still experienced relatively arid climatic conditions despite the increased precipitation during this warm interval. Furthermore, halite and gypsum records suggest that the degree of aridification was relatively moderate during 3.25–3.06 Ma but intensified during 3.06–2.95 Ma. For the intensified aridification, we infer that the further global cooling, which induced a relative decrease in water vapor, played an important role at ~3.06 Ma. Taking the mPWP as the reference, our findings indicate that under continued warming the East Asian summer monsoon will bring abundant water vapor to the inland basin and alleviate aridification in ACA. However, the increased precipitation will have difficulty reversing the aridification trend in the short term. This requires us to evaluate the warming and wetting trend in ACA from a dialectical perspective.