HR: 1340h
AN: PP53B-1391    [Abstracts]
TI: Influence of Sedimentation Rate on Diagenetic Alteration of Geophysical Signals by Anaerobic Oxidation of Methane
AU: Riedinger, N
EM: nar@uni-bremen.de
AF: University of Bremen Department of Geosciences, P.O.B. 33 04 40, Bremen, 28334 Germany
AU: Pfeifer, K
EM: kpfeifer@uni-bremen.de
AF: University of Bremen Department of Geosciences, P.O.B. 33 04 40, Bremen, 28334 Germany
AU: * Kasten, S
EM: skasten@uni-bremen.de
AF: Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570 Germany
AU: Garming, L
EM: garming@uni-bremen.de
AF: University of Bremen Department of Geosciences, P.O.B. 33 04 40, Bremen, 28334 Germany
AU: Vogt, C
EM: cvogt@uni-bremen.de
AF: University of Bremen Department of Geosciences, P.O.B. 33 04 40, Bremen, 28334 Germany
AU: Hensen, C
EM: chensen@ifm-geomar.de
AF: Leibniz Institute for Marine Sciences IFM-GEOMAR / SFB 574 , Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: Geochemical and rock magnetic investigations of sediments from three sites on the continental margin off Argentina and Uruguay were carried out to study diagenetic processes driven by anaerobic oxidation of methane (AOM) focusing on iron minerals. The western Argentine Basin represents a suitable sedimentary environment to study non-steady state processes because it is characterized by highly dynamic sedimentary conditions such as gravity driven mass flow deposits. Mineralogical and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals. As a typical feature of these deposits distinct minima in magnetic susceptibilty are observed. Pore water data reveal that these 'susceptibility gaps' coincide with the current depth of the sulfate/methane transition (SMT) where hydrogen sulfide is generated by the process of AOM. The released hydrogen sulfide reacts with the abundant iron (hydr)oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility. Modelling of geochemical data showed that the magnetic record in this area is highly influenced by drastic changes in sedimentation rates (SR) which occurred during the transition from the last glacial to the Holocene. We assume that the strong decrease in SR encountered during this glacial/interglacial transition induced a fixation of the SMT at a specific depth. The stagnation is likely to have caused an enhanced diagenetic overprint of iron (hydr)oxides within a distinct sediment interval. This assumption was further substantiated by the numerical modelling in which the SR was decreased from 100 cm/kyr during glavial times to 5 cm/kyr in the Holocene and the methane flux from below was fixed to a constant value. To obtain the observed geochemical and geophysical patterns a time period of approximately 8,000 years is needed - closely correlating to the timing of the glacial/Holocene transition.
DE: 4842 Modeling
DE: 3022 Marine sediments--processes and transport
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1540 Rock and mineral magnetism
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting