Characteristic And Source Analysis Of Surface Sediment In Wendeng Offshore Waters

This thesis is based on 97 surface sediment samples collected from Wendeng offshore waters in July to August,2013. According to size analysis and identification of detrital minerals to the sample, Study the types and distribution of surface sediments, characteristics of particle size and distribution of size parameters, distribution of heavy mineral content. Study heavy mineral assemblages combined with mathematical statistical methods such as correlation analysis and factor analysis. Discuss the source and its direction of the sediment in the study area combined with particle size trend analysis and characteristic index of heavy minerals, and comprehensively analyze affecting factors of sedimentary dynamic environment and its grain size and mineralogical response. Studies have shown that:(l)The grain size become finer from shore to the sea. Sediment types give priority to sand in coastal waters and estuaries, but to silt and mud in offshore waters. There are 9 types of surface sediment:gravelly sand (gS), sand (S), silty sand (zS), muddy sands (mS), clayey sand (cS), sandy silt (sZ), silt (Z), sandy mud (sM), mud(M).(2) 34 kinds of heavy minerals are identified from the sediment in the research area.They are hornblende, epidote, biotite, muscovite, weathered mica, ilmenite, magnetite, augite, chlorite, etc. The correlation coefficient between the various heavy minerals show, biotite, muscovite and weathered mica was a significant positive correlation. Ilmenite and magnetite was a significant positive correlation, biotite, muscovite and hornblende, epidote was significantly negatively correlated. Augite and diopside were positively correlated.(3)There are four kinds of heavy mineral assemblages in the study area. Namely I:hornblende, epidote combination, II:biotite, muscovite, weathered mica, chlorite combination, III:ilmenite, magnetite, hematite, zircon, garnet stone combinations, IV: augite, hypersthene, diopside, tourmaline combinations. According to the status quo of physical geography, grain size, heavy mineral distribution, the study area is divided into nine mineral zones combined with the results of mathematical statistics.(4) Analysis to the grain size trends of sediment in the study area indicate that the sediment transport from west to east in the western waters, from south to north in the southern waters, from east to west in the northeastern waters, and from southeast to northwest in west of bulwark. ZTR index is high in estuaries, both sides of the estuaries, southeast of Xishilan and southeast of the study area. It is gathering area of heavy mineral.Heavy mineral stability index is high in southeast of Xishilan and in the southeast of the study area, who are far away from the source. Comprehensive studies show that the source of the sediment in the study area include:materials from the river in north, materials transported along the coast from the headland in west, erosion materials outside of the breakwater of Zhangjiabu port in southeast, and materials from the outer waters in south.(5)The main factors of sedimentary dynamic environment are rivers, waves and tide. Shallow waters in the surf zone is mainly controlled by the waves. Characteristic from the shore to the sea is as follows:grain size of sediment become finer; the content of high density mineral decrease gradually, when small density mineral increase. Dominant mineral assemblages were epidote-hornblende-mica, hornblende-epidote-mica, hornblende-Mica-epidote from shore to sea. Estuary waters is controlled by waves and rivers, the isoline of grain size parameter is symmetrical based on river centerline. Affected by provenance, the content of ilmenite and magnetite is high. Slope deeper than the surf zone is affected by the tide and waves. Dominant mineral assemblage is mica-hornblende-epidote, sediment type is silt in the east and mud in the mid-west. A silty deposit had developmented from north to south in the middle of the muddy area, its content of ilmenite and magnetite is high. The depth become lighter in Xishilan, Dongshilan and Muzhushi. Affected by the waves, the particle size is coarser, density of sedment is higher compared with the surrounding waters. Dominated mineral assemblage is hornblende-epidote-mica. Waters in west of Zhangjiabu port is controlled by the tide, flow rate is large in dyke, particle size is coarse, content of high density mineral is high. Flow rate in the middle of the dyke is small, the particle size is fine, the content of low density mineral is high.Shallow sea plain deeper than 7.0m is controlled by the tide, the flow rate is much greater than in coastal waters. Compared with the middle waters, the average particle size is slightly coarse, contains less mica and other small density mineral, epidote and contains more ilmenite and other high density mineral.