Sediment accumulation and diagenesis in the late quaterary equatorial Atlantic Ocean

an environmental magnetic and geochemical perspective

Zusammenfassung

Nonsteady-state Diagenesis, Equatorial Atlantic, Rock-magnetic and Geochemical Multiproxy Approach, XRF Core Scanner, Fe Redox, Magnetite Dissolution. - This thesis investigates 25 Late Quaternary sediment records from the central Equatorial Atlantic by rock magnetic, geochemical and stratigraphical methods. The work was performed in the framework of the Collaborative Research Center 261 ‘The South Atlantic in the Late Quaternary: Reconstruction of Material Budgets and Current Systems’ funded by the Deutsche Forschungsgemeinschaft. The main objective was to analyze and distinguish terrigenous and diagenetic proxysignatures, in particular of rock magnetic parameters. All cores were correlated and dated on basis of their carbonate, iron and rock magnetic records. Magnetite coarsening and partial depletion was observed in glacial organic-rich layers, most intensely during oxygen isotope stages 6, 10 and 12. Non-magnetic and magnetic iron mineral enrichments were found below and at former and active Fe(II) / Fe(III) redox boundaries. Various new proxies quantifying magnetite reduction (ratio of Fe to magnetic susceptibility, ratio of non-ferrimagnetic to total magnetic susceptibility) and authigenesis (ratio of Fe to magnetic susceptibility) were established and found to be highly sensitive indicators of past redox conditions. Comparing these signals with the organic carbon records, it was shown, that rock magnetic, carbon and carbonate records in most parts ...
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