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Late Quaternary changes in terrigenous organic matter supply on the Congo Deep Sea Fan (ODP Site 1075): Implications for African paleoclimate

Lookup NU author(s): Professor Thomas Wagner


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Late Quaternary sections (about 1 Ma) from the Congo deep sea fan (ODP-Leg 175, Site 1075) are used to reconstruct the terrigenous organic matter supply into the easternmost equatorial Atlantic. Variations in quantity and quality of the riverine organic matter reflect the interaction between the paleoclimatic development within the continental catchment area and the paleoceanographic conditions in the Congo river plume. To characterize the delivery of organic matter from terrigenous and marine sources we used elemental and bulk carbon isotopic analysis, Rock-Eval pyrolysis, lignin chemistry, and organic petrology. High-amplitude fluctuations occurring about every 15-25 ka reveal a mainly precessional control on organic sedimentation. Results from Rock-Eval pyrolysis indicate a mixed kerogen type-III/II as anticipated in front of a major river. Fluctuations in Tmax from Rock-Eval Pyrolysis demonstrate pronounced cyclic changes in delivery of low and high mature organic matter. Organic petrological observations confirm the existence of abundant terrigenous plant tissues, both non-oxidized (vitrinite) and oxidized (inertinite). Charcoal-like organic matter (fusinite) is attributed to periods of increased bushfires in the continental hinterland and implies more arid climatic conditions. Results from ratios of specific phenolic lignin components suggest that terrigenous organic matter in late Quaternary sections of Site 1075 mainly derives from non-woody angiosperm tissue, i.e. grasses or leaves. Correlation between the amount of specific lignin phenols (l) and the bulk d13Corg signature fosters the conclusion that an appreciable amount of the terrigenous organic fraction derives from C4 plant matter and may cause an underestimation of the terrigenous proportion of bulk organic matter when deduced from the bulk carbon isotopic signature alone.

Publication metadata

Author(s): Holtvoeth J, Wagner T, Schubert C, Horsfield B, Mann U

Publication type: Article

Publication status: Published

Journal: GeoMarine Letters

Year: 2001

Volume: 21

Issue: 1

Pages: 23-33

ISSN (print): 0276-0460

ISSN (electronic): 1432-1157

Publisher: Springer