The Optically Stimulated Luminescence Chronology And Environmental Significance Of Paleolacustrine Sediments In The Hetao Basin

The Hetao Basin is located in the East Asian monsoon region,with abundant Quaternary lacustrine deposits that are crucial for researching the Yellow River system’s evolution and regional paleoenvironments.Despite previous extensive research,many unresolved issues remain,particularly regarding Hetao paleolake evolution and disappearance.To obtain reliable paleolimnological data,this study selected 7.6 m-thick lacustrine sedimentary strata in Heilai Gully,central Hetao Basin,for analysis using OSL and pIRIR dating methods.The study reconstructed the Hetao paleolake’s evolution process and surface area using grain size analysis,loss on ignition,and DEM,and explored its formation mechanism based on regional geomorphic processes.The primary findings are summarized below:（1）The equivalent dose（D_e）of lacustrine sediments determined by quartz OSL dating,is significantly underestimated due to the saturation of the quartz OSL signal at 96 Gy（32 ka）.The results of internal tests,such as luminescence characteristics and dose recovery test of K-feldspar,confirmed that the K-feldspar pIRIR₂₅₀ dating method could provide reliable ages for the research of lacustrine sediments in the Hetao Basin.（2）According to the chronologic and sedimentologic analysis,the paleolacustrine records in the HLG section demonstrated two stages of Hetao paleolake,which suggest the level of the Hetao paleolake exceeded 1033 m asl twice,i.e.,at the early stages of MIS 7（～255-245 ka）and MIS 5（～130-120 ka）.（3）The reconstructed development area of the Hetao paleolake is estimated to be at least1.447×10⁴ km²,based on modern geomorphic conditions.It is unclear whether the Hetao paleolake and Jilantai paleolake were interconnected.Additional sedimentological and K-feldspar dating evidence is required to confirm this hypothesis.（4）The development of the Hetao paleolake is not only driven by precipitation and tectonic forces but also controlled by the surface processes of aeolian-fluvial interactions.The Hetao Basin was closed because the northern end of the Jin-Shaan Gorge was dammed by the expanded Hobq Dunefield during the cold and arid glacial periods;Subsequently,the Hetao paleolake rapidly formed in response to the increased precipitation at the beginning of the interglacial periods.Once the lake spilt out,the loose dune dam was quickly breached.