Sediment Distribution Characteristics And Sedimentary Environment Of Northern Bohai Bay

The study on sedimentary characteristics and provenances of marine deposits is an essential substance of marine geology,and it is also one of the key problems of studying modern sedimentation. The research of the sediment provenance and sedimentary environment is multi-faceted, including the analyses of grain size,detrital mineral,clay mineral,element geochemistry,isotope tracer and biological assemblage.This thesis reveals the sediment provenance and sedimentary environment by analyzing the parameters of grain size,heavy mineral and clay mineral.Based on the study of grain size,mineralogy and sediment dynamics,the thesis analyses sediment types,mineral compositions,transportation trends,sediment provenance and sedimentary environment of the surface sediments.And for the core sediments,the method of mineralogy and sedimentology is used to study the changes of sedimentary environment on time scale.Grain size analysis on surface samples shows that there are seven types of sediment in the study area according to Folk and Pejrup's sediment classification methods,which are sand,silty sand,muddy sand,sandy silt,sandy mud,silt and clay.The distribution of these sediment types indicates that the granularity approximately becomes finer from north to south.Sandy silt mainly distributes northwest of the study area and silt dominates southwest of this area.They are the most widely distributed sediment types and they account for about 80% of all the surface samples. Analyses on sediment environmental zones aside with parameters of grain size show that the distribution of sediments is chiefly controlled by environmental hydrodynamics and the provenance of sediments.Heavy mineral analysis shows that there are 25 kinds of heavy minerals found in the study area.The dominant are hornblende,epidote,garnet,biotite, authigenic pyrite,magnetite and ilmenite.The study area can be divided into 3 mineral provinces according to the Q-cluster analysis.Clay mineral analysis shows that illite is the dominant clay minerals in the study area.The amount of the four clay minerals in descending order is illite,smectite,chlorite and kaolinite.Their distributions are influenced by Haihe River and Yellow River.The study on the two sediment cores shows that the granularity is very fine and the main type of sediment is clay.The two cores can both be divided into two parts-the upper part and the lower part.From top to bottom it reflects the strengthening of hydrodynamic and the increase of sedimentation rate.Heavy mineral analysis indicates that there are a large amount of instable minerals and the mineral maturity is low which can reflect the short distance that the sediment transport as well as the poor sorting of sediment.