Sedimentary evolution of a foreland basin from the northeastern Qilian Mountains based on the integration of geomorphological and luminescence dating of alluvial conglomerates and fluvial terrace sediments

Abstract

Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains.