晚更新世以来杭州湾沉积物黏土矿物特征及其古环境意义

通过对杭州湾南岸HZW1907长84 m及甬江口YJ19-02长9 m柱状样进行粒度分析、X射线衍射（XRD）分析，研究了沉积物粒度变化、黏土矿物特征，探讨杭州湾地区晚更新世以来源区风化程度、水动力条件变化、物质来源及环境演变情况。根据岩性粒度特征及黏土矿物变化规律，将HZW1907柱状样划分为4个沉积阶段：阶段1（0~26 m）、阶段2（26~49 m）、阶段3（49~70 m）、阶段4（70~84 m）。阶段4和3处于晚更新世至早全新世，沉积物以粉砂、砂质粉砂、粉砂质砂为主，处于湖泊河床相、泛滥平原相沉积，水动力条件较强。阶段4黏土矿物组合较复杂，高岭石、蒙皂石占比异常高，阶段3以伊利石—绿泥石—高岭石—蒙皂石组合类型为主，2个阶段沉积物受钱塘江物质输入影响巨大，同时部分受长江物质影响，气候环境由温暖湿润转为温凉偏湿，源区经历较强风化过程。阶段2和1沉积物主要由粉砂组成，粒度较细，水动力条件较弱，处于近岸潮坪相及河口湾相沉积，黏土矿物组合类型均以伊利石—绿泥石—高岭石—蒙皂石为主，指示全新世（约10.8 ka BP）以来杭州湾沉积物主要受长江物质输入影响，经历温凉偏湿—冷凉干燥的环境，源区风化程度较弱。甬江口YJ19-02柱状样沉积物类型为粉砂及砂质粉砂，水动力条件较弱，黏土矿物组合类型为伊利石—绿泥石—高岭石—蒙皂石，沉积物主要由长江物质输入，处于相对稳定、偏寒冷干燥的环境，源区风化过程较弱。柱状沉积物粒度、黏土矿物在垂向上的变化及组合特征为研究区及邻区沉积物的物质来源及古环境状况提供了有效指示。

Characteristics of clay minerals in sediments of Hangzhou Bay since the Late Pleistocene and their paleoenvironmental significance

The grain-size variation and clay mineral characteristics of sediments in the cores of HZW1907 (84 m) near the south bank of the Hangzhou Bay and YJ19-02 (9 m) near the Yongjiang Estuary are studied by grain-size measurement and X-ray diffraction (XRD) analysis, in order to investigate the weathering degree, hydrodynamic variation, material source and sedimentary environmental evolution of the Hangzhou Bay since the Late Pleistocene. According to the grain-size characteristics and clay mineral changes, the HZW1907 core can be divided into four sedimentary stages, i.e., stage 1 (0~26 m), stage 2 (26~49 m), stage 3 (49~70 m) and stage 4 (70~84 m). The sediments from stage 4 and stage 3 were formed at the Late Pleistocene-Early Holocene, composed of are mainly silt, sandy silt and silty sand, which indicated that they were formed under the lake -riverbed phase facies and floodplain facie, with strong hydrodynamic conditions. The clay mineral assemblages in stage 4 were more complex, having abnormally rich kaolinite and smectite. The clay mineral assemblage type of the stage 3 was mainly composed of illite-chlorite-kaolinite-smectite. The sediments from the above two stages were greatly affected by the source of the Qiantang River, and by the source of the Yangtze River partly. It appeared that the climate environment changed from warm and humid to less warm and wet, and the source area experienced strong weathering. The sediments from the stage 2 and stage 1 were mainly composed of fine-grain silt, with weak hydrodynamic conditions, and were located in near-shore tidal flats facies and estuarine facies. The dominant type of their clay mineral assemblage was illite-chlorite-kaolinite-smectite, indicating that the Hangzhou Bay were mainly affected by the materials of the Yangtze River since the Holocene (ca. 10.8 ka BP), and experienced the environmental changes from mild and slightly dry to cold and dry conditions. The weathering degree in the source area was relatively weak. The sediments of the core YJ19-02 were silt and sandy silt, and had clay mineral assemblage of illite-chlorite-kaolinite-smectite, indicating the weak hydrodynamic conditions. The sediments were mainly from the Yangtze River, indicating a relatively stable, cold and dry sedimentary environment, and the source area underwent weak weathering. The vertical variation and assemblage characteristics of grain-sizes and clay minerals in sediments of the cores provide effective indicators for the material source and paleoenvironment in the study area and adjacent area.