崇明东滩DT孔沉积特征及其环境意义

崇明东滩是典型的河口型沙岛边缘的潮滩地貌,2007年在崇明岛东滩采集了深50m的DT孔岩芯,对崇明东滩DT孔沉积物粒度组成及粒度参数特征分析,并参照该孔沉积物环境磁学参数和有孔虫组合特征,详细阐述了崇明东滩DT孔13.0kaB.P.以来的沉积特征,将DT孔划分出7个沉积层次: 该孔沉积水动力强弱变化,自层1→层7依次按较弱→较强→较强→最弱→最强→较强→较弱规律演变; 该孔沉积环境自层1→层3为还原环境,层4→层7为氧化环境,且氧化性自下而上逐渐增强。通过对该孔沉积环境综合分析,并与长江口北支CY孔及南汇鹤鸣孔(Hm)沉积环境进行对比分析,得出崇明东滩DT孔所反映的长江口沉积环境演变规律,自层1至层7依次为: 滨海沼泽-浅海→河口湾→三角洲前缘→前三角洲→河口沙坝→潮汐水道→潮滩。

SEDIMENT CHARACTERISTICS OF CORE DT FROM THE EAST END OF CHONGMING DONGTAN, CHANGJIANG RIVER ESTUARY AND ITS ENVIRONMENTAL IMPLICATION

The estuary of the Changjiang River is a kind of branching estuaries affected by the actions of tidal current.Chongming Dongtan is a geomorphology of tidal flat at the typical estuaine sand island edge.The samples acquired from the core DT(31° 32'N,121° 57'E) with the depth about 50m,located in the Changjiang River estuary in Chongming Dongtan wetland,in the year of 2007.Together got 215 samples for environmental magnetism,364 pieces of sample for particle size analysis,and 171 samples for foraminifera's analysis.With the analysis of the granularity and grain parameter size of the sediments of core DT in Chongming Dongtan,the sedimentary characteristics is elaborated since 13.0kaB.P.,refering to the characteristics of environmental magnetism,foraminiferal assemblages and its analysis parameters.With the regular pulses of hydrodynamic force reflected by the sedimentary characteristics,the core DT is divided into 7 sedimentary layers: layer 1(50~40m),layer 2(40~35m),layer 3(35~27m),layer 4(27~17m),layer 5(17~6m),layer 6(6~2m)and layer 7(2m~0).The regular pulses' changes in accordance with the sequence from layer 1 to layer 7 is weaker→stronger→stronger→weakest→strongest→stronger→weaker.According to the characteristics of its colors changed from the bottom up,the sedimentary environment taking turns from layer 1 to layer 3 is a reducing environment,while the sedimentary environment from layer 4 to layer 7 is an oxidation environment,and the oxidation from the bottom up gradually enhanced.Based on the comprehensive analysis of sedimentary environment of the core DT,and with the comparative analysis of core CY(in the North branch of Changjiang River estuary)and core Hm(in Nanhui district)at the same time,obtained the law of sedimentary environment evolution in the core DT of Chongming Dongtan,which reflected the sedimentary environmental evolution in the Changjiang River estuary.The law of sedimentary environment evolution is that seashore swamp-shallow sea→river estuary→delta front→pro delta→mouth bar→tidal channel→tidal flat from layer 1 to layer 7,from the Dongtan of Chongming,the Changjiang estuary.The rate of deposition from layer 1 to layer 5 is increasing gradually,though the rate of deposition from layer 5 to layer 7 is also increasing in general,layer 6 belows layer 5.