全新世长江泥沙堆积的时空分布及通量估算

利用长江中下游、河口及口外、浙-闽沿岸陆架6个主要沉积盆地的40个晚第四纪钻孔及其年代学数据和长江口外、陆架的浅地层剖面，计算了全新世不同阶段各沉积盆地的沉积速率，并进行了近7 000年来泥沙堆积通量的估算。研究发现全新世早期距今10 000年至8 000年间长江口下切古河谷是长江泥沙的主要堆积中心，沉积速率可高达15m/ka。随着海平面上升，全新世中期长江中下游也成为长江泥沙的重要沉积盆地，其中江汉盆地的沉积速率可达10m/ka。近2 000年来，口外、陆架的堆积呈明显增加趋势，反映长江中下游盆地和河口可容空间日益减小。根据沉积速率估算，距今7 000年来长江中下游堆积泥沙约13 074×108 t，同期水下三角洲和陆架的泥沙堆积量约为9 470×108 t。研究还发现全新世以来有两个异常低沉积速率时期：距今8000-7 000年期间上述各沉积盆地沉积速率均显著低，未见长江泥沙的沉积中心； 距今4 000-2 000 年期间长江口呈现低沉积速率。 这两次异常的原因推测与海平面、气候波动事件密切相关。

Spatial and temporal distribution of Changjiang sediments and estimation of sediment budget during the Holocene

The present study collected 40 sediment boreholes and their chronological data from the 6 major sedimentary basins of the Changjiang River and the seismic profiles from the Changjiang River mouth offshore and continental shelf, to calculate the sedimentation rates of each basin during various periods of the Holocene and to estimate the sediment budget during the last 7 000 years. The results demonstrate that the paleo incised valley of the Changjiang River mouth was the major depositional sink with a sedimentation rate of 15 m/ka during the Early Holocene of 10 000—8 000 a BP.The middle and lower Changjiang basins also became important depositional sinks with a sedimentation rate of 10 m/ka since the Middle Holocene due to the global sea level rise. The sedimentation rate increased obviously in the offshore and shelf area in the last 2000 years, indicating the decreasing of the capacity of sediment accumulation of the middle and lower Changjiang basins and the estuary. Calculation, according to the sedimentation rate, indicates that about 13074×108 ton sediments were deposited in the basins of middle and lower Changjiang and 9470×108 ton in the subaqueous delta and shelf areas during the last 7000 years. Our results also demonstrate that there were two periods of low sedimentation rates since the Holocene： 1)sedimentation was weak in all the basins during 8000—7000 a BP；  2)significant low sedimentation rate occurred in the estuarine area during 4000—2000 a BP. We suggest that these two periods  are related with the events of sea level and global climate changes.