Prehistoric and historic overbank floods in the Luoyang Basin along the Luohe River, middle Yellow River basin, China

Abstract

Paleohydrological investigations were carried out in the Luoyang Basin along the Luohe River in the middle reaches of the Yellow River basin. Three units of overbank flood deposits (OFD) were identified in a Holocene aeolian loess-soil profile on the south cliffy river bank at Taixuecun site (TXC). Analytical results including magnetic susceptibility, grain size distribution and geochemical elements indicate that these well-sorted overbank flood deposits were deposited from the suspended sediment load in floodwaters. We identified two episodes of prehistoric extraordinary overbank flooding that were dated to 6000–5500 and 4000–3800 yr BP using AMS 14C and OSL dating techniques with references to the already-known ages of the archaeological remains. Among of the two episodes, the overbank episode at 4000–3800 yr BP likely had a profound impact on the cultural development from the late Longshan Culture (4500–4000 yr BP) to the Erlitou Culture (3700–3500 yr BP) in the alluvial plain of the Luo River within the Luoyang Basin, providing geological evidence for the legends of ancient floods and their social impacts at ca. 4000 yr BP. In addition, an episode of historic overbank flood event was dated to 1800–1700 yr BP, i.e., from the Han to Wei dynasties, during which the ancient capital (Luoyang City) was subjected to frequent flooding. These aforementioned hydro-climatic events are considered to be regional expressions of known climatic events. The study adds our knowledge of the Holocene extraordinary overbank floods and their relationship with monsoonal climate change and human land-use practices, and the social impact of prehistoric environmental changes on human cultural development.