Mega-lake formation in the eastern Hetao Basin, China, during marine isotope stages 7 and 5: A comparison of quartz and feldspar luminescence dating

Paleo-lacustrine sediments indicate that a mega-lake developed in the Hetao Basin (HTB), suggesting dramatic changes in the geomorphology and surface process of the Yellow River and surrounding regions. However, the formation time of the mega Hetao paleo-lake (HTPL) in the HTB remains unclear. In this study, a set of 7.6-m-thick lacustrine sediments in the middle of the HTB is dated by both quartz optically stimulated luminescence (OSL) and K-feldspar (KF) post-infrared infrared stimulated luminescence (p-IR IRSL, pIRIR). The results are as follows. 1) The quartz OSL ages do not increase with depth as the KF pIRIR ages displayed but are saturated at ca. 80-100 ka with the consequence of age underestimation. The influence of signal saturation may occur below 96 Gy (ca. 32 ka) in this region. Thus, the KF pIRIR ages are chosen for geomorphological evolution reconstruction. 2) These ages suggest the level of the HTPL exceeded 1033 m asl twice-at the early stages of MIS 7 (similar to 255-245 ka) and MIS 5 (similar to 130-120 ka). However, the exact scale of the HTPL and its relationship with the Jilantai paleo-lake is unclear. 3) This chronology suggests strong linkage between periodic formation of the HTPL and glacial-scale climatic change. We therefore propose an alternative hypothesis to interpret these processes: the Hobq dunefield expanded eastward to dam the narrow Jin-Shaan Gorge during the glacial periods when the flow of the Yellow River was weak. Then, in the beginning of the interglacial periods, the basin was filled by abruptly resumed runoff in response to increased glacial meltwater and precipitation on the northeastern Tibetan Plateau. Once the lake spilt out, the loose dune dam was quickly breached.