摘要
在岩心观察和沉积相研究基础上,对长江河口区H1孔末次冰期以来沉积物样品进行了粒度分析,讨论了沉积物粒度特征与水动力条件演化关系。分析表明,研究区末次冰期以来先后经历了河床、河漫滩、河口湾、浅海和三角洲等5种沉积环境。其中,河床相砂含量很高,平均粒径和环境敏感粒级最粗,分选变化较大,概率累积曲线主要为跳跃总体为主的两段式,频率分布曲线为单峰式且主峰粒径大;河漫滩沉积物整体粒度较细,以粉砂为主,分选较稳定,累积曲线仍以两段式为主,但悬浮总体比例较河床相高,环境敏感粒级更细;河口湾沉积物明显分异为粗细两类,分选波动较大,累积曲线主要为具过渡段的跳跃总体为主的两段式,双峰式粒度频率分布;浅海相平均粒径最细,分选性差但稳定,具悬浮一段式的累积曲线,粒度频率分布为单峰式且主峰粒径很小,环境敏感细粒组分分布宽泛;三角洲沉积物主要为砂和粉砂,分选性相对较好,累积曲线为跳跃总体为主的两段式,单峰式粒度频率分布但主峰粒径变化较大。总体上,H1孔沉积物的粒度特征能较好地反映研究区末次冰期以来沉积环境水动力条件"强—较弱—较强—弱—较强"的变化过程。
A drilling hole named The Bohole H1 was drilled at the Changjiang estuary for study of grainsize features of the deposits since last glacial and for interpretation of their dynamic conditions.Grain-size parameters are calculated and diagrams,such as So-Md diagram,C-M diagram,probability accumulation curves,frequency distribution curves and environmentally sensitive grain-size components used for interpretation of hydrodynamic conditions.The study suggests that the area experienced five types of sedimentary environment,i.e.fluvial channel,flood plain,estuary,shallow marine and delta since last glacial age.Fluvial channel sediments mainly consist of sandy deposits with coarser mean and unstable sorting coefficient.There are two segments in the probability accumulation curves dominated by saltation population and two peaks in the frequency distribution curves.The environmentally sensitive grain-size components are mainly composed of coarse deposits.The flood plain sediments have more silt and less sand which are,in general,fine and well sorted.In probability accumulation curves there are two segments.Suspension population is high.And the frequency distribution curves sometimes show two peaks.Environmentally sensitive grain-size is rather fine.The estuary sediments consist of sand and silt with fluctuated sorting coefficients.Saltation population dominates the probability accumulation curves with some transitional population as the subordinate.Frequency distribution curves show two peaks.Shallow marine sediments are mainly composed of muddy clay with little sand characterized by fine deposits of bad sorting.It mainly consists of suspension population and thus only one peak is observed in frequency distribution curves.The environmentally sensitive grain-size remains fine and distributed in a wide spectrum.Deltaic sediments,which have a coarser mean and good sorting coefficient,are mainly made of fine and silt sand,showing two segments in probability accumulation curves dominated by saltation population.The environmentally sensitive grain-size components are similar to those of the floodplain sediments.In conclusion,sediments grainsize characteristics of the Borehole H1 sediments taken from the Changjiang estuary since glacial age can well reflect the hydrodynamic condition variations.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2016年第6期185-198,共14页
Marine Geology & Quaternary Geology
基金
国家自然科学基金项目(41402092
41572112)
江苏省自然科学基金项目(BK20140604)
南京大学"内生金属矿床成矿机制研究国家重点实验室"自主研究基金项目(ZZKT-201321)
关键词
末次冰期
粒度特征
水动力条件
长江河口区
the Changjiang estuary
the last glacial age
sediments grain-size characteristics
hydrodynamic conditions
