Taihu Lake, lower Yangtze drainage basin: evolution, sedimentation rate and the sea level

Abstract

The present study focuses on two Holocene sediment boreholes in Taihu Lake, sunk to examine the lake sediment including sedimentary texture and structure, microfossils, magnetic susceptibility and radiocarbon-dated Holocene stratigraphy. Results demonstrate that the early Taihu Lake area consisted primarily of West Taihu Lake depression and a low floodplain in the East Taihu Lake area. No hydraulic connection existed between the two sectors during the early Holocene when sea level stood at lower level. Core sediments, microfossil and magnetic evidence records that West Taihu Lake began to be inundated by brackish water prior to 6000 years ago, while East Taihu Lake still remained a freshwater setting. After 6000 B.P., a further rise in freshwater table in response to sea-level fluctuation progressively drowned the entire lake, coalescing the two parts after 4600–3500 B.P. Our coring revealed that the lacustrine sediment began to form in West Taihu Lake as early as 11,000 years ago, while it happened much later (only after 5700 B.P.) to form in East Taihu Lake. High sedimentation rates (0.42–0.35 mm/year) in lacustrine deposits of West Taihu Lake occurred between ~11,000 and 5000 B.P. In contrast, the high sedimentation rates (1.54 mm/year) in East Taihu Lake occurred only within a very short time period, from ~6500 to 5500 B.P. Since then, sedimentation rates have decelerated to a very low value (<0.10 mm/year) in both West and East Taihu Lakes. The low sedimentation rate of West and East Taihu Lake of the middle and late Holocene explains the deceleration of the sea-level rising after 5500 B.P. and the rapid coastal progradation seaward.