Long-term development archive of the Yellow River since the Neogene in the central Jinshaan Gorge, China

Abstract

Formation and development of the middle Yellow River have been debated for a long time. In this study, we carried out detailed field investigation, sedimentological and stratigraphic analyses in the central Jinshaan Gorge area. Our field work reveals that six terraces have been well preserved in the central Jinshaan Gorge. Sedimentological features of the conglomerates on all terraces indicate that these terraces were abandoned by an ancient south-flowing river, that is, the Yellow River. Based on previous paleomagnetic study on the Weijiawa Red Clay section, the oldest conglomerate was abandoned 8.1 Ma and the Yellow River along the western piedmont of the Lüliang Mountain at least occurred at that time. Powder samples were collected from five aeolian sections and low field magnetic susceptibilities were measured in a bid to establish correlation with the known sections and constrain formation ages of the terraces. Our results demonstrate that the Yellow River had trenched a 3.5 km wide valley (T6) since it occurred in the Liulin area and then the river gradually incised 4 Ma which finally trenched another 5-km-wide paleovalley (T5). Aggradation in the 5-km-wide paleovalley initiated in the Pliocene under the control of climate and ceased in the early Pleistocene which resulted in deposition of the up to 58-m-thick conglomerate. Fluvial sediments on T2-T4 are directly covered by aeolian loess-paleosol sequence (LPS). The basal units of the LPSs on T2, T3 and T4 are S3, S14 and L21 based on field stratigraphic markers and magnetic susceptibilities. Formation ages of these three terraces are 0.34 Ma, 1.19 Ma and 1.5 Ma respectively in the light of the astronomical ages. Our analysis on the driving factors suggests that climate might play an important role in river evolution in the central Jinshaan Gorge.