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

The present study focuses on two Holocene sediment boreholes in Taihu Lake, sunk to examine the lake sediment including sedimentary texture and struct ure, microfossils, magnetic susceptibility and radiocarbon-dated Holocene s tratigraphy. Results demonstrate that the early Taihu Lake area consisted p rimarily of West Taihu Lake depression and a low floodplain in the East Tai hu Lake area. No hydraulic connection existed between the two sectors durin g the early Holocene when sea level stood at lower level. Core sediments, m icrofossil and magnetic evidence records that West Taihu Lake be.-an 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 fre shwater table in response to sea-level fluctuation progressively drowned th e entire lake, coalescing the two parts after 4600-3500 B.P. Our coring revealed that the lacustrine sediment began to form in West Taih u Lake as early as 11,000 years ago, while it happened much later (only aft er 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 simi lar to 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 similar to 6500 to 5500 B.P. Since then, sedimentation rates have dec elerated to a very low value (< 0.10 mm/year) in both West and East Taihu L akes. 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 5 500 B.P. and the rapid coastal progradation seaward. (C) 2001 Elsevier Scie nce B.V. All rights reserved.