Environment euxinic

Molybdenum isotope variations appear to be on the order of 3.5%o in Mo/ Mo ratios, where the largest fractionation is seen between aqueous Mo in seawater and that incorporated in Fe-Mn crusts and nodules on the seafloor (Chapter 12 Anbar 2004). This isotopic contrast is interpreted to reflect fractionation by Mo sorption to Mn oxide-rich sediments relative to aqueous Mo. The 5 Mo values for euxinic sediments in turn are distinct from those of Fe-Mn crusts, highlighting the isotopic contrasts between major repositories of Mo in surface and near-surface environments. As discussed by Anbar (2004) in Chapter 12, a major focus of research on Mo isotopes has been the potential use as a paleoredox indicator in marine systems. 

Euxinic An aquatic environment with stagnant and restricted circulation. Anaerobic water or sediments. 

Iron monosulfides comprise about 20% of the iron sulfide minerals in the noneuxinic sediment and about 50% in the euxinic sediment. Their greater preservation in the euxinic sediment, as in sediment from Walker Lake, is probably a result of insufficient elemental sulfur formation in this extremely reducing environment. Seasonally aerobic conditions at the sediment-water interface of the noneuxinic sediment would promote elemental sulfur formation from the oxidation of H2S that accumulates in pore water. 

Canheld D. E. (1989) Sulfate reduction and oxic respiration in marine sediments implications for organic carbon preservation in euxinic environments. Deep-Sea Res. 36(1), 121-138. 

Byers C. W. (1977) Biofacies patterns in euxinic basins a general model. In Deep-water Carbonate Environments. Special Publication, no. 25 (eds. H. E. Cook and P. Enos). Society Economic Paleontologists Minerologists, Tulsa, pp. 5-17. 

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

Dinorhopane (a.k.a. 28,30-bisnorhopane) and 25,28,30-trinorhopane (59) are often very prominent hydrocarbons in sediments from euxinic environments and their derived oils... 

Dinorhopane 25,28,30-trinorhopane TNH (59) Often prominent in sediments from euxinic environments. Grantham et al. (1980), Peters and Moldowan (1993)... 

It should be emphasised that most of the data in Table 6.1.3 are point measurements which are not necessarily representative of the overall rates of sulfate reduction in a particular environment. Nevertheless, Trudinger et al. (1972) and Rickard (1973) considered that the average rates in the Black Sea and other sediments may be typical of euxinic environments and concluded that they were of sufficient magnitude to account for synsedimentary sulfide ore deposition (see also. Temple, 1964). 

Schwarcz and Bumie (1973) reviewed sulfur isotope abundances in strata-bound sulfide deposits in clastic sediments not associated with volcanic rocks and concluded that two patterns were evident. One was a broad distribution ranging from arotmd the 5 S of sea water to values 25%o lower while the other was a narrow distribution around a 5 8 of —50%o with respect to oceanic sulfate. The former pattern was identified with shallow marine or brackish-water environments while the latter occurred in deep, euxinic basins. They explained the first distribution on the basis of Fig. 6.2.4a and assumed a closed system with an average 32/ 34 ratio of about 1.025. The second distribution pattern applied to deep basins and Schwarcz and Bumie (1973) concluded that the systems were fully open, in which case the isotopic selectivity was much larger as is the case in a number pf modem euxinic basins (e.g. Black Sea see pp. 338, 412). 

GEOCHEMISTRY OF HUMIC SUBSTANCES IN MARINE SEDIMENTS BLACK SEA (Euxinic environment)... 

ScH.l. Depositional environment schematic sulfur cycle in marine water body and upper water-sediment interface. The redox line (gray dashed perpendicular) is placed at S and relates only to the redox state of the sulfur, not the oxic or euxinic conditions. The black dashed line separates between sediment and water bodies. For the present paper, we would like to emphasize the major 8 ratio changes caused by the dissimilatory reduction of sulfate. For more detailed explanations on the formation of sulfur rich OM, see Aizenshtat et al. (1983, 1995, 2004) and Krein and Aizenshtat (1993, 1994). 

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