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

Organic petrologic and geochemical analyses were performed on modem and Qua ternary 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 pela gic Equatorial Atlantic. Response of organic matter (OM) deposition to Quat ernary climatic cycles is discussed for ODP Sites 959 and 663. The results are finally compared to a concept established for fossil deep sea environme nts [Littke, R., Sachsenhofer, R.F., 1994. Organic petrology of deep sea se diments: a compilation of results from the Ocean Drilling Program and the D eep Sea Drilling Project, Energy and Fuels 8, 1498-1512.]. Organic geochemi cal results obtained from Equatorial Atlantic deep sea deposits provide new aspects on the distribution of sedimentary OM in response to continental d istance, atmospheric and oceanographic circulation, and depositional proces ses controlling sedimentation under modern and past glacial-interglacial co nditions. The inventory of macerals in deep sea deposits is limited due to mechanical breakdown of particles, degree of oxidation, and selective remin eralization of labile (mostly marine) OM. Nevertheless, organic petrology h as 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 micro scopic and isotopic (delta(13)C(org)) analyses were observed depending on t he stratigraphic level and depositional setting. Strongest offset between b oth records was found close to the continent and during glacial periods, su ggesting a coupling with wind-born terrigenous OM from central Africa. Sinc e African dust source areas are covered by C4 grass plants, supply of isoto pically heavy OM is assumed to have caused the difference between microscop ic and isotopic records. (C) 1999 Elsevier Science B.V. All rights reserved .