Anthropogenic origins of a late Holocene, basin-wide unconformity in the middle reaches of the Yellow River, the Luoyang Basin, Henan Province, China

We evaluate the relative importance of climate change, fluvial dynamics, and anthropogenic environmental modification in forming the Holocene sedimentary record of the Luoyang Basin, a tributary drainage basin of the Yellow River, located in western Henan Province, China. Our 2011 fieldwork south of the Erlitou site in the Luoyang Basin indicates that an unconformity dating to ca. AD 1100 is roughly coincident with a major southward shift in the lower course of the Yellow River. In AD 1128, the governor of Kaifeng breached the dikes of the Yellow River to impede an advancing army, causing the Yellow River to flow south out to the Yellow Sea. We argue that the dike breach not only changed the fluvial dynamics of the Yellow River but also switched the rivers in the Luoyang Basin from an aggrading to an incising system. The resumption of sedimentation in the Luoyang Basin is roughly coincident with the next major shift of the Yellow River's main course northward to the Bohai Sea in AD 1855. The unconformity found in the Luoyang Basin may be a legacy of historically contingent human agency rather than climatic shifts or gradual environmental modification.