摘要
大河特大洪水会对河口地区沉积环境产生显著影响,然而当前有关河口三角洲古洪水沉积特征的认识存在较大争议,有待通过现代洪水沉积研究深入揭示河口三角州洪水沉积特征。本文于2020年长江流域性特大洪水发生期间,在长江水下三角洲采集了16根短柱样,在实验室进行了粒度和有机地球化学指标(TOC、TN)分析。结果表明短柱中洪水期间产生的沉积层厚度为3~21 cm,上部洪水沉积层TOC含量平均值为0.59%,TN含量平均值为0.077%,与下部常态沉积层相比均有所增加。洪水层沉积物的平均粒径(13.23μm)比其下部常态沉积物平均粒径(13.87μm)略微偏细。代表洪水事件沉积的粒度端元组分EM1和研究区以往钻孔中洪水沉积粒度结果的对比表明,2020年长江口洪水沉积相对底部常态沉积粒度偏细,但比以往研究区钻孔中的洪水沉积粒径偏粗,这与传统古洪水沉积以粗颗粒组分为主的认识存在不同,这应该是流域内大坝建设对沉积物的圈闭作用、中下游河道侵蚀作用和水下三角洲受海洋动力侵蚀作用共同导致。该研究对于河口地区长时间尺度古洪水事件序列的重建以及极端水文事件沉积记录解译具有重要的科学意义。
Catastrophic floods in large rivers exert significant influences on the sedimentary environment in the estuarine region.However,viewpoints of sedimentary characteristics of the paleoflood in the estuarine delta is controversial.Therefore,it is necessary to understand the sedimentary characteristics of modern flood.The whole Changjiang River basin suffered from a catastrophic flood in 2020.Sixteen sediment cores in the Changjiang subaqueous delta were collected during the flood period.Grain size and organic index(TOC,TN)were measured.The result indicates that the flood layers is 3~21 cm thick,the average TOC and TN is 0.59%and 0.077%,respectively,which is higher than that of lower part deposit.The mean grain size of the flood layers(13.23μm)is finer than that of the lower part deposits(13.87μm).The end-member modelling analysis indicated that the finest populations(EM1)were originated from the 2020 flooding.Comparing the EMs of 2020 flood deposits with grain size characteristics of flood deposits in previous studies,we found that the 2020 flood sediments were finer than the lower part non-flood deposits,but coarser than the previous flood sediments,which is different from the common view that the paleoflood deposits are characterized by coarser sediments.We believed that this difference was due to(1)human activities(e.g.dam construction)in the river basin,by which more coarse sediment were trapped within the dam;(2)the weakened erosion in middle and lower reaches of river channels;and(3)the subaqueous delta by ocean dynamic erosion.This study is beneficial for the reconstruction of long-term paleoflood events sequences and the interpretation of extreme event deposition in the estuarine region.
作者
李明宸
闫粟
公力维
王雪晨
耿润玉
徐润喆
周亮
汪亚平
沈治雄
LI Mingchen;YAN Su;GONG Liwei;WANG Xuechen;GENG Runyu;XU Runzhe;ZHOU Liang;WANG Yaping;SHEN Zhixiong(School of Geography,Geomatics and Planning,Jiangsu Normal University,Xuzhou 221116,China;State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200241,China)
出处
《海洋地质与第四纪地质》
北大核心
2025年第2期31-42,共12页
Marine Geology & Quaternary Geology
基金
国家自然科学基金项目“海南岛南部海岸风暴巨砾沉积揭示的风暴强度”(41706096),“长江流域两千年以来入海水沙通量变化及其对河口-陆架泥质沉积体系发育和演化的影响”(41776048),“海岸风暴频率-强度关系的沉积记录分析”(41530962),“The magnitude and frequency of extreme late Holocene flooding in the middle Yangtze River and their climatic and anthropogenic forcing”(42250610211)
上海市教育委员会科研创新项目“长江三角洲蓝图重绘的基础科学问题研究”(2019-01-07-00-05-E00027)
江苏省研究生科研与实践创新计划项目“长江口历史水道变迁和特大洪水事件的沉积记录”(KYCX22_2787)
江苏省高等学校大学生创新创业训练计划“长江水下三角洲历史特大水文事件沉积的识别”(202110320121Y)。
关键词
特大洪水
沉积特征
人类活动
长江水下三角洲
extreme flood
sedimentary characteristic
human activities
Changjiang River subaqueous delta
