Geochemical Characteristics And Its Significance Of Hydrocarbon From The Seabed Sediment In Central South Yellow Sea

Hydrocarbons, one of the important components in marine sediment, can provide an insight into the origin and depositional environment of fossil organic matter as its stablity in situ through the geologic time. In this paper, based on the program of petroleum resources survey in South Yellow Sea (GZH00800503 - 090), the saturated hydrocarbons and aromatics in surface sediment samples have been analysied by gas chromatography (GC-FID) and chromatography - mass spectrometry (GC-MS). All samples were colected in the central area of Yellow Sea during July to October 2009. To identify their sources and the carbon cycle of estuary– shelf, and also the impact of human activities on the marine environment, we studed geochemical characteristics of the n-alkanes, isoprenoid hydrocarbons, steranes, terpane and PAHs from seabed samples in the Central Yellow Sea.According to the characteristics of n-alkane molecules and gas chromatographic (GC-FID) profiles, the alkane in the Central South Yellow Sea sediment were classified into three types: typeâ… , the number of peaks in the low carbon, and the UCM is not obvious; for typeâ…¡, the number of peaks sited in the high carbon, and the UCM is obvious; for typeâ…¢, the number of peaks sited in the high carbon, and the UCM is not obvious. The n-alkane distribution showed that the organic matter in the Central South Yellow Sea sediments are mainly from terrigenous higher plant orangic matter. The first source is from the ancient Yellow River, which had transported massive amount of terrigenous sediments from Chinese mainland. The second source for the terrigenous material is from the Yangtze River. The marine biological contribution is last. In this study, It indicates a strong input of continental higher plants that the CPI and OEP are greater than 1, and the rotio (nC₂₁ + nC₂₂)/(nC₂₈ + nC₂₉),ΣnC₂₁-/ΣnC22- is less than 1. The CPI of organic matter from the Yangtze River significantly higher than that of the organic matter from the Yellow River, it shows the difference between the two valleys ecological environment. The Pr/Ph values in middle-low carbon number n-alkanes showed strong anoxic environment, it permits the contribution of marine Marine algae is existed. In addition, the higher levels squalane showed in GC-FID profiles indicated methane bacteria contributed to sedimentary organic matter.High abundance of hopane and sterane in sediment indicates that fossil fuels or petroleum pollution exist in the sediments from South Yellow Sea. In this study area, hopanes has a obvious characteristic: the mean of Tm/Ts is 0.61 that is characterized by immature - low maturity, but the hopane isomer reflects the higher maturity, and the mean of 22S / (22S +22R) (dihomohopane) is 0.66; The patterns of steranes (C29> C27> C28) and high maturity, compared with coal thermal simulation results, we could included that steranes terpane area comes mainly from incomplete combustion of coal and other products of higher plants, and atmospheric long-range transport and bacterial action to "improve" the hopane and sterane methane maturity.The concentration of total PAHs in surface sediments ranged from 246.90 ng/g- 10818.12 ng/g, and the average concentration is 2544.64 ng/g. The analysis of PAH distribution suggested combustion as the main input for these compounds, such as the low rotio of LMW/HMW, Flu/Pyr and MP/P.Perylene, a geochemicaly derived PAH, was found highly aboundant in the areas. The content of perylene is 6.40% - 88.85%. Principal component analysis (PCA) showed that the amount of perylene is influrence by river input. It represents diagenesis and rapid accumulation of terrigenous material.The distribution parterns of peroleum biomarkers (terpanes, steranes, MPI1, MPI2) and high abundance UCM (