长江三角洲北翼如东县兵房钻孔粒度特征与沉积环境——缅怀恩师施雅风院士

将长江三角洲北翼如东县兵房孔(BF10)岩芯自下而上分为5个阶段(A,B,C,D和E段),对岩芯的岩性、沉积物粒度参数、频率分布曲线、概率累计曲线以及分选系数-中值粒径(σi-d(0.5))图和C-M图进行分析,结合已有文献资料和测年数据,研究表明: 阶段A以粉砂和砂为主,分选中等以上占96%,概率累计曲线为三段式,以推移和跃移搬运为主,包含递变悬浮和均匀悬浮两个区域,水动力强度中等,属浅海环境; 阶段B以砂为主,分选中等以上占96%,分选好的比例有所增加,概率累计曲线为三段式,以推移和跃移搬运为主,包含悬浮和滚动区、递变悬浮区,水动力强度中等,也属浅海环境; 阶段C以粉砂和砂为主,分选中等以上比例超过86%,概率累计曲线为四段式,以推移和跃移组分为主,存在悬浮和滚动区、递变悬浮区、均匀悬浮区,该段沉积环境和水动力条件复杂,属于滨海环境; 阶段D以砂为主,分选中等以上占95%,概率累计曲线为三段式,以推移和跃移组分为主,包含递变悬浮区和均匀悬浮区,水动力减弱,属受海洋作用控制的海湾环境; 阶段E以粉砂为主,分选极好比例超过85%,概率累计曲线为三段式,以推移和跃移搬运为主,属均匀悬浮区,沉积水动力最弱,该段为粒径向上变细的潮坪环境。

THE GRAIN SIZE CHARACTERISTICS AND DEPOSIT ENVIRONMENTS OF BF10 CORE IN THE NORTH WING OF CHANGJIANG DELTA:IN MEMORY OF MY TEACHER SHI YAFENG

Core BF10( 32°15’31.6″N, 121°17’33.4″E) is nearby Bingfang middle school in Dayu town of Rudong County,Nantong area of the north flank of Changjiang Delta.The depth of Core BF10 was 30m,but we just got 20m sediments for the core with thick sand layer and a loose state.Two of the dating data was measured by National Isotope Centre,Institute of Geological and Nuclear Sciences Ltd(GNS Science),844±20aB.P.in 5.4m and 4508±25aB.P.in 23m,respectively.The other 2 dating data was measured by Acceleration Mass Spectrometry Lab.and School of Archaeology and Museology of Peking University,870±25aB.P.in 7.5m and 1060±25aB.P.in 8m,respectively.The materials of dating are shell and the dating data are mainly help to identify deposit environments.Changjiang Delta region can be subdivided into 3 basic areas by Late Quaternary stratigraphical framework,which are the main delta,southern and northern flanks respectively.In the northern flank there exists stiff mud as a basement of the postglacial transgressive sedimentary cycle,which belongs to the paleosol in genesis and is exposed for a long term.The postglacial transgressive sedimentary cycle basically consists of sandy deposits of littoral,shallow marine and littoral facies in the front zone of the northern flank.According to the dating data of AMS 14C,it is suggested that Core BF10 mainly reflects the deposit environments since the largest transgression in Holocene.The analysis of Core BF10 is helping to understand the interaction between river and sea,between land and sea,between human and environments,and is conducive to recognize the environment evolution of Nantong area.Data of lithology,grain sizes,frequency distribution curves,probability accumulation curves,distribution curves between sorting coefficient and median diameter(σi-d(0.5)figure),and distribution curves between 1% grain diameter and median diameter(C-M figure)of the Core BF10,are used to interpret the deposit environments.Combined with the existing literatures and dating data,Core BF10 is divided into 5 parts from bottom to up: shallow marine I,shallow marine II,littoral,gulf and tidal flat.Shallow marine I sediments,which mainly consist of silt and sand,96% and more of beyond medium sorting coefficient,show 3 parts in probability accumulation curves.The transport is mainly of scrolling and saltation,with C-M figure showing contain gradients and uniform suspension,medium strength of hydrodynamic.Shallow marine II sediments,which mainly consist of sand,96% and more of beyond medium sorting coefficient with the proportion of fine increased,show 3 parts in probability accumulation curves and the transport is mainly of scrolling and saltation,with the C-M figure showing contain suspension and scrolling,gradients suspension,medium strength of hydrodynamic.Littoral environments sediments,which mainly consist of silt and sand,86% and more of beyond medium sorting coefficient,show 4 parts in probability accumulation curves,in which saltation consist of 2 parts and the transport is mainly of scrolling and saltation,with the C-M figure showing contain suspension and scrolling,gradients and uniform suspension,as well as complexity of deposit environments and hydrodynamic.Gulf environments sediments are mainly made up of sand with 95% and more of beyond medium sorting coefficient,and show 3 parts in probability accumulation curves.Transport is mainly of scrolling and saltation,with the C-M figure showing contain gradients and uniform suspension,and strength of hydrodynamic decreased.Tidal flat sediments,which mainly consist of silt,85% and more of beyond fine sorting coefficient,show 3 parts in probability accumulation curves.Transport is mainly of scrolling and saltation,with C-M figure showing contain uniform suspension,and the least strength of hydrodynamic in the 5 parts.