杭州湾近期环境演变与沉积速率

本文追述了杭州湾4万年来的沉积环境演变,论述了近期湾内沉积环境的差异,以及不同时间尺度的沉积速率。从钻孔样品的综合分析得知,4万年来杭州湾和东海大陆架一样亦二经沧桑。陆海变迁不仅在岩性组合、微体古生物诸方面留下确凿证据,而且有确切地貌部位样品~(14)C测年印证。杭州湾3～5m厚的沉积结构特征,显示出其各沉积区环境的明显差异和数百年来的继承性。从全新世沉积层的厚度与年代推算,8000～9000a来其沉积速率一般平均为0.11～0.25cm/a;其口门段中北部细粒沉积物区(锋面活动区),近百年来的沉积速率(~(210)Pb)为1.0～1.2cm/a;有机农药以及风暴层比对的沉积速率与其吻合。

Geological development and sedimen tary rate in recent Hangzhou Bay

This paper reviews the geological development of the Hangzhou Bay since 40, 000 a B.P., and describes the differances of sedimentologic setting inside recent Hangzhou Bay. The sedimentary rates refer to different time scales are also discussed.Analysis of the Pleistocene and Holocene cores suggests that the sea has reached the Hangzhou Bay twice during last 40, 000 a, just as those found in the continental shelf of the East China Sea.Environment changing between land and sea is marked by both sedimentation types and their micropaleontologic images, and dated by 14C from certain samples. There are obviously differences in every sedimentary provinces of recent Hangzhou Bay.This feature has being carried on for hundreds years as the sedimentary structures in the short cores with depth of 3- 5 m recorded. The sedimentary rate for the last 8 000-9 000 years is ca.0.11-0.25 cm / a due to the estimation by thickness of Holocene deposits. While in the sedimentary apron along the plume front of Hangzhou Bay, the sedimentary rates for last hundred years ranges from 1-1.2cm/ a as marked with 210Pb, organochlorine pesticides and storm deposits.