Oxidation Fronts in Pelagic Sediments: Diagenetic Formation of Metal-Rich Layers

Abstract

The periodic deposition of distal turbidites at a site on the Madeira Abyssal Plain causes the development of a nonsteady-state diagenetic system in which an oxidation front migrates downward into the sediment. Data presented here show that iron, manganese, and particulate organic carbon are oxidized at this front by oxidants (molecular oxygen and nitrate) diffusing from above. A numerical model of systems of this type predicts the formation of iron-rich layers under certain nonsteady-state conditions. The layers predicted by the model are closely comparable in thickness and general morphology to iron-rich layers found in certain ocean sediments, the origin of which has been until now unexplained.

Linking diagenetic alteration of amino acids and bulk organic matter reactivity

“…A remarkable feature of the distal MAP turbidites is their homogeneity upon emplacement (Prahl et al 1989). Postdepositional exposure to oxygen (and nitrate) under pelagic conditions for about 10-20 kyr caused carbon removal in the uppermost section due to a downward-progressing oxidation front (Wilson et al 1986). The lowermost section of the initially homogeneous sediments has survived postoxic conditions without significant degradation for about 140 kyr (Weaver and Kuijpers 1983;Cowie et al 1995;Prahl et al 1997).…”

“…K-values of samples 7-13 (North Sea) and 18-20 (Eastern Mediterranean) are based on the ratio of the amount of CO 2 generated during sediment-water slurry incubations and organic carbon contents. Other k-values are based on modeling degradation experiments (phytoplankton) (Middelburg 1989) and solid-phase organic carbon profiles; MAP turbidites (Wilson et al 1986), Saanich inlet sediments (Cowie et al 1992), Dabob Bay sediments (Cowie and Hedges 1992), and Eastern Mediterranean sediments (Jung et al 1997). No data are available for samples 3-6 and 25-28. nonprotein amino acids and hexosamines are sensitive indicators for intermediate to extensively degraded materials (DI Ͻ 0.5).…”

Modeling vertical excursions of the redox boundary in sediments: Application to deep basins of the Arctic Ocean

“…The depth of oxygen penetration varies temporally in lacustrine (Carignan and Lean 1991), estuarine (Benoit et al in press), and marine sediments (Wilson et al 1986;Gobeil et al 1997). The most common causes are variations in temperature, bottom-water oxygen concentration, and the flux of degradable organic matter to the sediment surface.…”

“…Estimates based on the magnitudes of the upward fluxes of dissolved Mn suggest that such peaks could accumulate following a redox-boundary migration on the time scale of 10 3 -10 4 yr, possibly in a Glacial-Holocene transition (Mangini et al 2001; Burdige in press). Wilson et al (1986) proposed that peaks in the profiles of other redox-sensitive elements, which were depth correlated with those of Mn, had a similar origin. Formation of such peaks in response to redox boundary migrations on decadal or seasonal time scales has not yet been subjected to quantitative analysis.…”

Occurrence of thin, metal-rich layers in deep-sea sediments: a geochemical characterization of copper remobilization

“…By their nature, these remarkably homogenous turbidites are extremely suited to study the effects of oxidation and the subsequent diagenetic alterations (e.g. WILSON et al, 1986;PRAHL et al, 1989;THOMSON et al, 1989). Oxidation of the top of these turbidites caused drastic colour changes of the sediment, mostly from brown-pale green (oxidized) to dark green (reduced) (MIDDELBURG and DE LANGE, 1988).…”