DISTRIBUTION OF MINERAL ASSEMBLAGES IN OFFSHORE SURFACE SEDIMENTS OF DALIAN BAY IN THE NORTHWESTERN NORTH YELLOW SEA AND THEIR PROVENANCE AND ENVIRONMENTAL IMPLICATIONS
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摘要: 对大连湾、大窑湾外近海表层沉积物进行了黏土矿物X射线衍射分析以及轻矿物的分离和鉴定,根据其组合分布特征,探讨了该区沉积物中黏土矿物和轻矿物的来源,并对沉积环境及其主控因素进行了初步分析。结果表明:研究区黏土矿物主要由伊利石(59%)、蒙皂石(20%)、绿泥石(16%)和高岭石(5%)组成,研究区西部伊利石较高,而东部绿泥石较高,蒙皂石有向湾内富集的趋势。轻矿物由斜长石(45%)、石英(34%)、钾长石(10%)、绿泥石(8%)、白云母(2%)和方解石(0.4%)组成,呈东西向条带状分布,与沉积物粒度分布特征较为一致。矿物分布受潮流、地形影响明显,研究区北部近岸水下岸坡区,水动力条件较强,沉积物粒度较粗,矿物组合以长石、石英富集为特征;向南水深增加,东部为一水下台地,矿物组合以白云母、绿泥石含量高为特征;研究区南部水深增加,又出现一水下岸坡,其下地形趋于平坦,因受出入渤海的潮流和进入渤海的黄海暖流的影响,水动力条件最强,沉积物粒度较粗,长石含量最高,轻矿物含量高。研究区潮流、地形对矿物组成、组合和含量具有控制作用。北部水下岸坡及以内近岸浅水区沉积物粒度较粗,轻矿物含量低,石英、长石含量高,物质主要来自沿岸侵蚀及周边河流注入。其外侧的水下台地上沉积物粒度较细,白云母、绿泥石含量高,主要为通过东部海域自西向东进入研究区的远源物质;离岸较远的深水岸坡之下,沉积物粒度最粗,轻矿物含量高,石英、长石含量富集,可能在潮流作用下接纳了较多的近岸和邻近区域的物质。Abstract: Based on X-ray diffraction analysis of clay mineral compositions in the offshore surface sediments of Dalian Bay and Dayao Bay, together with separation and identification on light minerals, the assemblages and distribution characteristics of these minerals were studied. Their sources and sedimentary environments were discussed. Four kinds of clay minerals (illite, smectite, chlorite and kaolinite) are identified, whose average contents are 59%, 20%, 16% and 5%, respectively. Illite is abundant in the west part of the study area, while chlorite in the east. Smectite content is higher in the bays. Light minerals mainly consist of plagioclase (with an average of 45%) and quartz (34%), followed by K-feldspar (10%), chlorite (8%), muscovite (2%) and calcite (0.4%). They are distributed bandedly from east to west, which is consistent with the distribution pattern of grain sizes. The mineral distribution is obviously controlled by local topography. The coastal shallow-water slope in the north of the study area is characterized by enrichment of plagioclase, quartz and K-feldspar, and lower weight percentage of light minerals, indicating strong hydrodynamic conditions and nearby source. With water depth increasing southward to a submarine platform, there are high contents of chlorite, muscovite, rich clay and silt in sediments, and lower contents of plagioclase, quartz and K-feldspar, indicating weakened hydrodynamic conditions and far sediment source. Calcite is a characteristic mineral of Yellow River sediments and mainly distributed in the western study area, which illustrates that sediments in the western study area are partly from the Yellow River. According to the distribution patterns of chlorite, muscovite and clay, fine grained sediment zone in the middle of the study area is transported from east to west. To the further south of the study area with the deepest water off another underwater slope, contents of plagioclase, quartz and K-feldspar are high, while those of chlorite and muscovite are low, implying strong hydrodynamic conditions induced by tide current which passes in to and out of Bohai Sea and Yellow Sea Warm Current (YSWC) that enters Bohai Sea. In addition, larger weight percentage of light minerals shows that the sediments are transported a relatively long distance from source area compared with coastal sediments.
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Key words:
- clay and light minerals /
- provenance and environmental implication /
- Dalian Bay /
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