Abstract
Total organic carbon (TOC), total nitrogen (TN) and multi-biomarker indexes were analyzed for two sediment cores from the eastern coastal area of the Beibu Gulf (core 45, AMS 14C dated) and Qiongzhou Strait (core 29), South China Sea. The results showed that the TOC and TN content of the samples studied were 0.32–0.62% and 0.02–0.07%, respectively. The hydrocarbons in offshore sediments of Leizhou Peninsula were consisted of biogenic hydrocarbons and petrogenic hydrocarbons. The Core 29 sediments contain more terrigenous organic matter than that of sediments in core 45 due to the difference in hydrodynamic conditions. The composition and distribution of various lipid biomarkers indicate the presence of petrogenic hydrocarbons in the sediments of the whole profile of two sediment cores. There are multiple natural sources of hydrocarbons that could potentially contribute to the petroleum background through oil seeps and erosion of carbon-rich rock outcrops or bitumen deposits. Deep sourced hydrocarbon inputs from the submarine hydrocarbon seepage cannot be excluded. Further study is needed to resolve the specific sources for the petrogenic hydrocarbons and may be significant to petroleum exploration in the study area.
Highlights
Marine sediments act as the ultimate sink for organic carbon, incorporating organic matter (OM) into the geological carbon cycle (Dickens et al, 2004)
We evaluated the origins of OM using geochemical and biomarker indexes for two sediment cores from the Leizhou Peninsula’s coastal zone to explore the temporal changes of sources and sinks of OM in this area
Further research is needed to resolve the specific origin of the petrogenic hydrocarbon background in offshore area of Leizhou Peninsula
Summary
Marine sediments act as the ultimate sink for organic carbon, incorporating organic matter (OM) into the geological carbon cycle (Dickens et al, 2004). Coastal regions are areas where active interaction between land and ocean exists It plays a significant role in the global carbon cycle since about 80% of the global organic carbon buried in the shallow marine system, even though it only accounts for 7.6% of the total global ocean area (Hedges and Keil, 1995; Tesi et al, 2007). The sedimentary OM in the coastal area is a heterogeneous and complex mixture of organic compounds with different chemical characteristics, originating from various sources. Hydrocarbons from both natural and anthropogenic sources are very common in the marine environment (Bourbonniere and Meyers, 1996). Understanding the sources of hydrocarbons and chemical processes that affect the deposition and preservation of OM is necessary for a comprehensive examination of the global carbon cycle (Tesi et al, 2007)
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