晚更新世以来杭州湾沉积地球化学特征对源–汇过程的启示  

Implications of sedimentary geochemical characteristics for source-sink processes in Hangzhou Bay since the Late Pleistocene

作　　者：高秦 厉子龙[1] 陈燕婷 曾志杰 Piotrowski A M 杨师航 郭增卿 崔锦梅 GAO Qin;LI Zilong;CHEN Yanting;ZENG Zhijie;Piotrowski A M;YANG Shihang;GUO Zengqing;CUI Jinmei(Institute of Marine Geology and Resources,Ocean College,Zhejiang University,Zhoushan 316021,Zhejiang,China;Department of Earth Sciences,University of Cambridge,Cambridge CB23EQ,UK;Second Institute of Oceanography,Ministry of Natural Resources,Hangzhou 310012,Zhejiang,China;POWERCHINA HUADONG Engineering Co.,Ltd,Hangzhou 310014,Zhejiang,China;Zhejiang Engineering Survey and Design Institute Group Co.,Ltd,Ningbo 315000,Zhejiang,China)

机构地区：[1]浙江大学海洋学院海洋地质与资源研究所,浙江舟山316021 [2]剑桥大学地球科学系,英国剑桥CB23EQ [3]自然资源部第二海洋研究所,浙江杭州310012 [4]浙江华东建设工程有限公司,浙江杭州310014 [5]浙江省工程勘察设计院集团有限公司,浙江宁波315000

出　　处：《地球化学》2024年第3期454-478,共25页Geochimica

基　　金：浙江大学教育基金“世界顶尖大学合作计划”项目(100000-11320)资助。

摘　　要：长江将大量泥沙排入东海,对杭州湾的沉积演变产生重大影响,但长江型碎屑对杭州湾不同时期、不同位置的贡献差异缺乏研究。通过分析杭州湾舟山海域水下钻孔(HZW1907孔)沉积物中有机、无机元素地球化学特征,对杭州湾沉积过程中的水体古盐度、源区风化过程、沉积物组成与来源和长江–杭州湾–东海陆架沉积系统进行研究,并基于稀土元素组成的两端元混合模型,定量探讨长江泥沙对杭州湾不同位置沉积的贡献程度差异。结果表明,杭州湾湾口从晚更新世以来,经历了冰期的下切河谷深切、河谷充填和河谷埋藏3个阶段演化过程,相应发育了河床相(约33.9~23.7kaBP)、河漫滩相(约23.7~12.0kaBP)、古河口湾相(约12.0~9.0 ka BP)、浅海相(约9.0~4.0 ka BP)和现代河口湾相(约4.0 ka BP至今);沉积物的Ga/Rb和K_(2)O/Al_(2)O_(3)关系揭示了中国东部在33.9 ka BP以来经历了冷干–暖湿的气候变化;TS和TOC的变化反映了淡水–不稳定淡水、海水混合–稳定海水的沉积水体演替,与东海陆架一致。晚更新世期间,杭州湾地区发育的河床相、河漫滩相沉积物源区主要来自钱塘江流域,显示长英质火成岩的特征;全新世以来的古河口湾相、浅海相和现代河口湾相沉积物为钱塘江型碎屑与长江型碎屑的混合,显示中基性火成岩的特征,湾口受到长江物质的影响更强。以长江和钱塘江流域(Gd/Yb)_(UCC)为端元的模拟结果显示,杭州湾湾口与湾顶受到长江物质影响差异较大,古河口湾相时期,长江供给杭州湾湾口沉积物约78%,湾顶约39%;浅海相时期,长江供给杭州湾地区超过80%的碎屑,湾口、湾顶无明显差别;现代河口湾相时期,长江供给湾口沉积物约76%,湾顶约22%。该模拟方法在长江向杭州湾输送的碎屑分析中具有定量化的作用,并有望适用于其他沿海陆架河流系统。The Yangtze River discharges a large amount of sediment into the East China Sea and has a significant impact on the sedimentary evolution of Hangzhou Bay.The differences in the impacts of the Yangtze-type fragment on the sediments of Hangzhou Bay in spatiotemporal distribution have not been well studied.Based on the previous studies,samples from the borehole HZW1907 which is near the Zhoushan sea area,were systematically analyzed for the particle size,foraminifera,14C dating,and geochemical characteristics of organic and inorganic elements in core sediments.This study focuses on the sedimentary process,paleosalinity,weathering process,geochemical composition of the sediments,and the depositional system of the Yangtze River-Hangzhou Bay-East China Sea shelf.Based on the two-unit mixing model of rare earth element composition,the spatiotemporal distribution of the Yangtze River sediment to Hangzhou Bay,in particular,is quantitatively discussed.The results show that the estuary area of Hangzhou Bay has experienced three stages of evolution:incised valley cutting,valley filling,and valley burial in the glacial period since the Late Pleistocene,and the corresponding development of riverbed facies(between about 33.9 ka BP to 23.7 ka BP),flood plain facies(about 23.7 ka BP to 12.0 ka BP),ancient estuary facies(about 12.0 ka BP to 9.0 ka BP),shallow sea facies(about 9.0 ka BP to 4.0 ka BP),and modern estuary facies(about 4.0 ka BP to present).The relationship between Ga/Rb and K2O/Al2O3 in the sediments reveals that Eastern China has experienced cold-dry to warm-wet climate change since 33.9 ka BP.The contents of TS and TOC reflect that the sedimentary environment changed from fresh water to unstable brackish water,and finally into seawater environment,which is contemporaneously consistent with the continental shelf of the East China Sea.During the Late Pleistocene,bedding facies and flood plain facies developed in the Hangzhou Bay area,and the clasts,which show the geochemical characteristics of felsic igneous rocks,mai

关 键 词：源汇过程 元素地球化学 混合模型 杭州湾 长江三角洲–陆架–河口体系 

分 类 号：P534.631[天文地球—第四纪地质学] P595[天文地球—古生物学与地层学] P736.41[天文地球—地质学]