【摘要】 基于现代黄河水下三角洲浅地层剖面资料和GYDY钻孔的岩性、磁性、地层年代与古生物数据,将研究区26.2m以浅地层自上而下划分为6个沉积单元,分别对应DU 1~6。在高分辨率粒度测试的基础上,根据沉积物粒径组分、粒度参数、粒度资料图解和结构散点图等分析手段,分析了各沉积单元的粒度分布规律及对应的动力沉积环境,并探讨了研究区晚更新世末期(约36.2cal.ka B.P.)以来的动力环境演化。结果表明:DU 6沉积单元为献县海侵层,形成于浅海陆架沉积环境,水动力环境强度弱,沉积作用以静水悬浮沉积为主;DU 5沉积单元形成于末次盛冰期,动力强度大,动力环境变化复杂,粒度图解显示其整段或局部可能接收风营力改造,接受风成沉积物补给的可能性较大;DU 4沉积单元冰后期约13.3~8.5ka B.P.,为河口沉积层,以中等到弱沉积动力为主,动力环境变化复杂;DU 3沉积单元为狭义黄骅海侵层,形成于受多种营力作用的滨海环境,沉积环境较稳定;DU 1和DU 2沉积单元属现代黄河三角洲沉积层,形成于较弱到中等动力强度三角洲环境,其中DU 2沉积单元可能受到黄河1855年铜瓦厢改道入渤初期尾间大幅度摆动的影响,粒度特征变化复杂。各沉积单元的粒度特征的变化规律与海侵-海退层序基本一致,是冰期-间冰期旋回海陆变迁过程中多营力共同作用的结果。研究区古气候变化仅在本区暴露于陆的末次盛冰期与冰后期早期对相应沉积单元粒度分布有一定影响。更多还原

【Abstract】 Core GYDY(38°3’39.0 "N,119°9’15.97" E) was retrieved from waters approximately 45 km northwest of the modern Yellow River mouth,western coast of the Bohai Sea,with the water depth of 10.55 m.The depth of the core was 40.02 m,but we focused on the 0 ~ 26.2m segment because(1) it represented the Latest Pleistocene strata and(2) it was well-sampled with a average recovery of 82.17%.Magnetic susceptibility was measured using a MS2 C magnetometer.The data obtained at 1cm intervals.The core was then split and sub-sampled with 2~5cm intervals(6~16m and 22~23m were sampled 2cm intervals and the rest core samples were sampled 5cm intervals).Total624 samples were measured using a Mastersizer-2000 laser particle size analyzer for grain size.The AMS C chronology was built using 11 samples(peat and plant debris) downcore at Beta Analytic Inc.(Table 1).To reconstruct the depostional environment since the Latest Pleitocene,Phyolith analysis from Core GYDY,benthic foraminifera and ostracods analyses from two adjuacent cores,about 650 km high-resolution seismic profiles collected at the modern Yellow River subaqueous delta and previous studies of the sea level history in the Bohai Sea were analyzed in this study.The Late Pleistocene(since 36.17 cal.ka B.P.,during MIS 3) succession in Core GYDY was divided into six depositional units,DU 1 through 6 downcore.DU 6 corresponds to neritic facies in Xianxian transgression period;DU 4 and DU 5 correspond to second terrestrial facies in LGM and the early post-LGM;DU 3 is coastal/neritic facies in the Huanghua transgression;DU 1 and DU 2 is modem Yellow River Delta sediments deposited since 1855 A.D.Data of lithology,grain size,frequency distribution curves,probability accumulation curves,distribution curves between sorting coefficient and median diameter(σ_i-M_i figure),and distribution curves between 1%grain diameter and median diameter(C- M figure) in Core GYDY,were used to interpret the downcore grain size distribution and the evolution of the sediment-dynamic environment since the Late Pleistocene.The result showed that DU 6 generated at a weak-dynamic neritic setting.Probability accumulation curves and C-M figure indicated that the sediments of DU 6 came from the lenitic suspended solids.DU 5 was formed during the LGM with mutable strong dynamics.The grain size characteristic,especially the probability curves which assemble the standard Visher curves of eolian sediment,indicated a partial or a whole eolian desert environment of the western Bohai Sea area.Grain size data in DU 4 resembles that of DU 1 and DU 2,revealing that it was formed at a fickle estuarine setting with weak-medium environmental dynamics.DU 3 was formed at a stable littoral environment with the influences of different kinds of dynamics.Sediments in DU 1~2 were formed at the deltaic setting with weak-medium dynamics.In terms of the rechanneling of the modern Yellow River courses since 1855 A.D.,the grain size characteristics in sediments of DU 2 varied intricately.The analysis of the sea level history since LGM indicated that downcore grain size distribution and the evolution of the sediment-dynamic environment in Core GYDY was a result of the sea level variations which contributed to alternative marine/terrestrial settings in the research area.However,the evolution of paleo-climate was proved to influence little on the grain size characteristics in Core GYDY.They had merely contributed to the variations of the grain size on sediments when the study area exposed subearially since the LGM.更多还原