Multi-Method Luminescence Dating of Old Fluvial Sediments from Northern Tian Shan, China

At the eastern tip of Anjihai anticline on the northern piedmont of Tian Shan (northwest China), deformed fluvial deposits have recorded active folding since the Pleistocene, but the absence of accurate ages makes it difficult to evaluate the anticline's shortening rate. Geological studies ascribed the fluvial strata to the early Pleistocene, which poses potential challenges for luminescence dating. In this study, multi-methods luminescence dating was applied to a fluvial sand sample taken from the sandy bed of the deformed basal strata. Single grain post-Infrared Infrared Stimulated Luminescence (pIRIR) and multiple-aliquot-regenerative (MAR) dose along with multiple-elevated-temperature pIRIR (MET-pIRIR) procedures were applied to determine the paleodose of the sample. The methodological uncertainties, such as thermal transfer and initial sensitivity change, were treated by increasing the test dose and performing dose recovery test. With consideration of the potential partial bleaching and anomalous fading, various statistical metrics were applied to the D_e values determined by using the single grain pIRIR₂₂₅, single grain pIRIR₂₉₀ and MAR-MET-pIRIR₂₉₀ signals. The minimum age model (MAM) D_e values are 11% – 17% lower than the central age model (CAM) D_e values in general, and the MAM D_e values determined by the single grain pIRIR procedures are underestimated by more than 40% when compared with those determined by MAR-MET-pIRIR₂₉₀ procedure. The MAM MAR-MET-pIRIR₂₉₀ D_e of 811 ± 44 Gy results in a burial age of 284 ka for the basal deformed fluvial strata, which is much younger than the proposed early Pleistocene age.