The Surface Sediment In Buha Estuary Region And Its Comparative Sedimentology Significance

Qinghai Lake is the largest inland brackish water lake in China.As the salinity is between 0.13%¹.21%and pH in 9.12-9.85,the water belonging to carbonate water.The sediments of Buha River estuary in the northwest of Qinghai Lake were studied,witch collected from river,prodelta,lakeshore,shallow lake and semi-deep lake in Buha estuary region,were analyzed in aspects of Major element and trace element analysis,whole-rock composition analysis?XRD?,total organic carbon?TOC?and examination of the kerogen.The study finds that the sediments of Buha River estuary sediments are mainly made of mud,silt,fine sand and transitional type composition.The sediments is generally has low clay mineral content.The main types of kerogen in the sediments were?₁ and?₂,and most of organic matter come from terrigenous organisms while a small quantity of organic matter come from aquatic organisms.TOC in Buha River estuary sediments is in the range of 0.02%to 4.29%.TOC in the sediments of semi-deep lake and prodelta is usually higher than that in other environmental sediments,and the samples collected from semi-deep lake generally have high TOC content while the quality of organic matter is better than that of the other places.Moreover,organic matter has a significant effect on the enrichment of some trace elements.There is a significant positive correlation of trace elements and TOC in the sediments,such as boron,cobalt,nickel,zinc,gallium,rubidium,cesium,lead,uranium.The enrichment ability and strength of organic matter to trace elements are controlled by the contact time of sediment and water,and so the correlation between trace elements and TOC has obvious difference in different sedimentary environments.TOC in sediments of fluvial,delta plain,prodelta,shallow lake and semi-deep lake environment is higher,while is lower in sediments lakeshore environment.Boron was the most sensitive to the change of organic carbon content,and the content of boron in the intermittent exposure of lakeshore also showed a significant positive correlation with TOC.Boron is an effective index that can reflect the hydrocarbon source rocks original organic carbon content.According to the excellent linear relationship between the boron concentration and TOC in the sediments of Buha River estuary,a formula for the quantitative calculation of the original organic carbon content via the content of boron in the source rock was established.The formula is suitable for the reconstruction of the total organic carbon in the terrestrial brackish water and salt water of environment.