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Late Quaternary Sedimentation and Early Diagenesis in the Equatorial Atlantic Ocean : Magnetic and Geochemical Indices.

Lookup NU author(s): Professor Thomas Wagner


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This is an interdisciplinary and synoptic study of Equatorial Atlantic sediment formation in the Late Quaternary aimed at untangling the interlaced signatures of terrigenous and biogenies deposition and early diagenesis. It is based on a stratigraphic network of 16 gravity core records arranged along one meridional and three zonal transects (4°N, 0° and 4°S) crossing the Amazon and Sahara plumes as well as the Equatorial Divergence high productivity region. All newly introduced sediment sequences are collectively dated by their coherent CaCO3 content profiles and two available δ18O age models. To infer proxy records indicative of individual fluxes and processes, we analyse environmental magnetic parameters describing magnetite concentration, magnetic grain sizes and magnetic mineralogy along with CaCO3, Corg, Fe, Mn, Ba and color data. Diagenetically affected layers are identified by a newly introduced Fe/κ index. Reach and climatic variability of the major regional sedimentation systems is delimited from lithological patterns and glacial/interglacial accumulation rate averages. The most prominent regional trends are the N-S decrease in terrigenous accumulation and the Equatorial Divergence high in glacial Corg accumulation, which decays much faster south- than northwards. Glacial enrichments in Corg and proportional depletions in CaCO3 content appear to reflect sedimentary carbonate diagenesis more than lysoclinal oscillations and dominate temporal lithology changes. Suboxic iron mineral reduction is low at Ceará Rise and Sierra Leone Rise, but more intense on both flanks of the Mid-Atlantic ridge, where it occurs within organic rich layers deposited during oxygen isotope stages 6, 10 and 12, in particular at the terminations. To the equator, these zones reflect a full precessional rhythm with individual diagenesis peaks merging into broader magnetite-depleted zones. Rock magnetic and geochemical data show, that the depths of the Fe3+/Fe2+ redox boundary in the Equatorial Atlantic are not indicative of average productivity and were frequently shifted in the past. They are now located just above the topmost preserved productivity pulse. At 4°N, this organically enriched layer coincides with glacial stage 6, at 0° with glacial stage 2. Subsequent oxic and suboxic degradation of organic material entails stratigraphically coincident carbonate and magnetite losses opening new analytical perspectives.

Publication metadata

Author(s): Funk JA, von Dobeneck T, Wagner T, Kasten S

Editor(s): Wefer G; Mulitza S; Rathmeyer V

Publication type: Book Chapter

Publication status: Published

Book Title: The South Atlantic in the Late Quaternary: Reconstruction of Material Budget and Current Systems

Year: 2004

Pages: 461-497

Publisher: Springer

Place Published: Berlin

Library holdings: Search Newcastle University Library for this item

ISBN: 3540210288