Quaternary Subsidence and River Channel Migration in the Yangtze Delta Plain, Eastern China

Abstract

The Yangtze delta's fluvial channel system and overall depocenter configuration have been controlled largely by movement of active subsurface structures during most of the Quaternary. Data from numerous borings reveal marked variations in lithic distribution and thickness of Pleistocene and Holocene sequences across the delta plain. These stratigraphic differences record shifts in the Yangtze's depocenter through time and are in large part a direct response to the interaction of land motion with sea level variations and fluvial and oceanographic processes. Delta plain subsidence has progressed from north to south since early Quaternary time, and this has induced a southward shift of the Yangtze river channel from the early Pleistocene to the present.

During much of Quaternary time, the Yangtze river flowed across the northern part of the delta's plain. This is primarily the results of two factors: differential subsidence of the northern sector from the upper Tertiary to the late Pleistocene; and a "topographic barrier effect" produced by highlands which blocked the Yangtze from flowing to and across the southern sector of the plain. Thus, fluvial Quaternary deposits in the southern plain were not derived from the Yangtze river but from proximal highlands west of the southern delta plain. Stratal configuration, texture and composition serve to distinguish Yangtze river deposits concentrated in the north from the more proximal fluvial channel sediments in the south. Our investigation suggests that tectonically induced channel migration and southward shift of the Yangtze deltaic depocenter are continuing at present. These ongoing depositional changes related to differential subsidence have potentially serious ramifications for this low-lying, densely populated delta plain area. Hence, accurate measurements of land subsidence are needed throughout the plain, and particularly in the lower reaches of the Yangtze river.