Petrology of organic matter in modern and late Quaternary deposits of the Equatorial Atlantic: climatic and oceanographic links

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• 作者：Wagner ; Thomas
• 关键词：organic facies ; modern deep sea deposits ; Quaternary deep sea deposits ; organic carbon isotopes ; C4 plants ; paleoclimate ; paleoceanography ; Equatorial Atlantic
• 刊名：International Journal of Coal Geology
• 出版年：1999
• 出版时间：March, 1999
• 年：1999
• 卷：39
• 期：1-3
• 页码：155-184
• 全文大小：5.24 M

文摘

Organic petrologic and geochemical analyses were performed on modern and Quaternary organic carbon-poor deep sea sediments from the Equatorial Atlantic. The study area covers depositional settings from the West African margin (ODP Site 959) through the Equatorial Divergence (ODP Site 663) to the pelagic Equatorial Atlantic. Response of organic matter (OM) deposition to Quaternary climatic cycles is discussed for ODP Sites 959 and 663. The results are finally compared to a concept established for fossil deep sea environments [Littke, R., Sachsenhofer, R.F., 1994. Organic petrology of deep sea sediments: a compilation of results from the Ocean Drilling Program and the Deep Sea Drilling Project, Energy and Fuels 8, 1498–1512.]. Organic geochemical results obtained from Equatorial Atlantic deep sea deposits provide new aspects on the distribution of sedimentary OM in response to continental distance, atmospheric and oceanographic circulation, and depositional processes controlling sedimentation under modern and past glacial–interglacial conditions. The inventory of macerals in deep sea deposits is limited due to mechanical breakdown of particles, degree of oxidation, and selective remineralization of labile (mostly marine) OM. Nevertheless, organic petrology has a great potential for paleoenvironmental studies, especially as a proxy to assess quantitative information on the relative abundance of marine vs. terrigenous OM. Discrepancies between quantitative data obtained from microscopic and isotopic (δ¹³C_org) analyses were observed depending on the stratigraphic level and depositional setting. Strongest offset between both records was found close to the continent and during glacial periods, suggesting a coupling with wind-born terrigenous OM from central Africa. Since African dust source areas are covered by C4 grass plants, supply of isotopically heavy OM is assumed to have caused the difference between microscopic and isotopic records.