Non-Steady State Diagenesis

A second striking feature of the Amazon Fan sediments (gravity core GeoB 1514-6) is the occurrence of a pronounced maximum in magnetic susceptibility, located slightly above the zone of strong enrichment of iron sulfide minerals (Fig. 

As the total iron sulfides did not display a local maximum at the depth of the susceptibility peak, Kasten et al. (1998) suggested the presence of a specific iron sulfide with a high magnetic potential. X-ray diffraction analyses performed on sediment samples from this depth revealed the presence of the magnetic iron sulfide mineral. 

Effects of Sulfate Reduction on Sedimentary Solid Phases 

Sulfate reduction can also occur within discrete, organic-rich layers which can lead to a distinct overprint of the primary sediment composition within the organic-rich layers or in the sediment above and below. The non-steady state diagenetic processes occurring in and below the organic-rich layers (sapropels) of the Eastern Mediterranean have been studied by Passier et al. 

Downward progressing sulfidization fronts have also been reported to be initiated by transitions from limnic to brackish/marine conditions in the Baltic Sea (Bottcher and Lepland 2000 Neumann et al. 2005) and the Black Sea (Jorgensen et al. 2004 Neretin et al. 2004). In contrast to the example from the Eastern Mediterranean presented above, the sulfide driving the downward sulfidization in these sedimentary settings is derived primarily from AOM and from the increase in sulfate concentration in the water colunrn during the Holocene. At the sites on the western continental slope of the Black Sea investigated by Jorgensen et al. 

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Lasagna, A.C., and Holland, H.D. (1976) Mathematical aspects of non-steady state diagenesis. Geochim. Cosmochim. Acta 40, 257-266. 

Consequences of Non-steady-state Diagenesis and Impact of Euxinic Environments SULFUR ISOTOPE SYSTEMATICS OF MARINE SEDIMENTS. 7.1 Overview... 

The lock-in of a diagenetic front may be caused by non-steady state diagenesis due to a shift in, e.g. the rate of sediment deposition, the type of sediment or its organic content, the oxygen concentration of the bottom water, or the methane flux from below. As a result, the diagenetic front may be stationary within a sediment horizon for a prolonged period. 

For steady-state conditions this equation is set equal to 0, because at a given depth x, concentration does not change with time. Steady-state models are generally more amenable to mathematical solution than are non-steady-state models. Unfortunately, diagenesis in many shoal-water carbonate sediments is significantly influenced or even dominated by non-steady-state processes. 

Early diagenesis is typically described as a steady-state phenomenon however, unless very long-term geological timescales are considered, steady-state conditions are generally not common in shallow turbid environments such as estuaries. There are many factors that contribute to these non-steady-state conditions, such as variations in sedimentation rate, inputs of organic matter, chemistry of bottom waters and sediments, bioturbation rates, and resuspension (Lasagna and Holland, 1976). Consequently, numerous attempts... 

Raiswell, R. (1987) Non-steady state microbiological diagenesis and the origin of concretions and nodular limestones. In Diagenesis of Sedimentary Sequences (Ed. Marshall, J.D.). Spec. Publ. Geol. Soc. Lond., 36, 41-54. 

In the following Section 3.2, the laws of diffusion and the particularities of their application to sediment pore waters will be treated in more detail. In this context, the problem of steady state and non-steady state sitnations will have to be covered, since the simple examples described above have anticipated steady state situations. Moreover, as a further simplification, the examples of this section have by necessity neglected advection, bioirrigation, and biotnrba-tion. These processes will be discussed in detail in Section 3.6. Section 3.7 will then cover the investigations of the sediment s solid phase and thereby disclose the result of one or the other process of early diagenesis. 

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