Geochemical Characteristics of Hydrocarbons in the Core Sediments from the South Yellow Sea and Its Implication for the Sedimentary Environment

Key words: 
• aliphatic hydrocarbons /
• core sediments /
• molecular compositional patterns /
• source /
• sedimentary environment /
• The south Yellow Sea /
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Abstract: The vertical variation, composition and sources of sedimentary organic matter and aliphatic hydrocarbons of the core sediments from the south Yellow Sea were exactly evaluated and characterized in terms of the molecular composition of the hydrocarbon compounds and its implication for the sedimentary environment. The results show that there exited a good positive correlation between the total organic carbon and total nitrogen, while the occurrence inorganic nitrogen and its potential influence on the SOM identification is poor, which could be related with the low riverine input of the terrigenous materials in the study area. The long chain nalkanes show a high abundance in the 0～10 cm section with eventoodd predominance of the C2535 nalkanes and a higher Pr/Ph ratio (>1.0), indicating a relatively oxidative sedimentary environment. This condition is unfavorable for the preservation of marine organic matter, and in turn, exhibiting a more contribution from the terrigenous organic matter at this interval, while the compositional patterns of hopanes and steranes suggested the presence of a more mature constituents in the upper sections. The sedimentary setting exchanged from the oxidative condition to the anoxic ones with the increasing depth at the 10～20 cm section. Below the 20 cm layer, the sedimentary environment is more characterized of anoxic condition with a low maturation of the buried organic matter. The alkanes in those downsections showed a bimodal with the even carbon preference of the C1222 nalkanes, which could be derived from marine bacteria, fungi and yeast species. By comparing with the sedimentary records in Bohai Sea which were more related to the variation of the historical fluvial input and human actions, while for the Yellow Sea, the molecular compositional patterns of the typical hydrocarbon compounds indicate the important role of the sedimentary condition and microbial biodegradation for the burial and preservation of organic matter in the core sediments.