Oxidation sediments

An analogous expression can be derived for 8 Mo x in terms of /ox (or/m). Such a model illustrates that changes in ocean redox, which affect the relative proportions ofand/ x, should result in changes in the isotopic composition of hydrogenous Mo in both euxinic and Mn-oxide sediments. Hence, measurements of 8 MOepx or 8 Mo x could yield information about changes in ocean redox through time. 

Local water column paleoredox. The offset between recent euxinic and suboxic sediments (Fig. 6) suggests that such data could provide an additional tool to differentiate between euxinic and suboxic conditions in ancient sediments. Such application requires independent constraint on 5 Mo, as might be obtained from analyses of coeval Mn oxide sediments. 

Schematic representation of manganese nodule end-member morphologies. The size of the arrows Indicates the proportion and direction of metal supply, (a) Typical situation In the open ocean with the nodules lying on an oxidized sediment substrate dominant mode of formation Is hydrogenous, (b) Typical situation In nearshore and freshwater environments with nodules lying on a sediment substrate that Is partly reducing In character. Dominant supply of metals Is via Interstitial waters from below the substrate surface. Source From Chester, R. (2003). Marine Geochemistry, 2nd ed. Blackwell, p. 425.

Petersen,W. Wallmann, K. Schroer, S. Schroeder, F. (1993) Studies on the adsorption of cadmium on hydrous iron (III) oxides in oxide sediments. Anal. Chim. Acta 273 323-327... 

Limnofix In situ Sediment Treatment (LIST) technology is offered by Limnofix, Inc., a Colder Associates Company. The technology allows for the in situ treatment of contaminated sediment in surface waters. LIST enhances bioremediation of organic contaminants oxidizes sediments to control odor, nutrient release, or sulfide toxicity and produces stable marine sediment surfaces via consolidation and flocculation. 

Neudorfer F, Meyer-Reil LA (1997) A microbial biosensor for the microscale measurement of bioavailable organic carbon in oxide sediments. Marine Ecology Progr Ser 147 295-309... 

Extraction of Sedimentary Constituents. The proportion of the total concentration of Fe, Mn and Zn removed from the estuarine sediments by the different extractants varied widely among sampling stations (Table II). Hydrochloric acid, acetic acid and ammonium oxalate removed a similar proportion of total Zn from all sediments. Concentrations of Zn well above detection limits were also fo-iind in the ammonia, hydroxyl-amine and ammonium acetate extracts. The quantity of Zn removed from oxidized sediments by the latter two extractants was significantly greater than reported in previous studies in which reduced sediments were extracted ( ). 

Proportion of total Zn, Fe and Mn removed from oxidized sediments by various extractants. The first value is the mean the values in parentheses represent the rai e of values observed. 

Figure 3. The hioavailability of zinc (Zurinm/Zuscdiment) to Macoma balthica as related to the ratio of hijdroxylamine—soluble iron/ammonium acetate-soluble manganese in oxidized sediments of San Francisco Bay (r = 0.77).

Iron oxide sediments are formed in the absence of or at low concentrations of active forms of silicic acid, carbonic acid, and sulfur in the waters. According to the data of investigations of the composition of recent ferric iron sediments, they consist mainly of amorphous hydroxides of Fe " " (Strakhov, 1947, 1960 Ostroumov, 1955 Volkov and Tikhomirova, 1966 ... 

Analysis of the stability of oxide sediments when there is a change in the oxidation-reduction environment during diagenesis (Fig. 58) also indicates... 

Reduction of oxide sediments is possible if the content of organic matter or free carbon is sufficient. The production of certain mineral forms depends on the activity of sulfur and pH. The formation of diagenetic magnetite is presumed only in neutral environments with low activity of sulfur and a slow rate of crystallization of the silicates. A rise in temperature (to 150-180°C) leads to the appearance of a magnetite stability field in silicate sediments. 

In the case of reduction by hydrogen, the appearance of hydrous silicates in the oxide sediments is possible ... 

In other districts, for instance in the KMA, reduction of oxide sediment to magnetite and siderite by organic matter probably was of great ore-forming importance (Plaksenko, 1966). Isotopic data on this district are still insufficient for definite conclusions in two out of three analyses (see Fig. 96) the S 0 of coexisting oxides are similar, and in one the magnetite oxygen is... 

A major constraint is an absolute requirement for anoxic conditions and the organisms are particularly active in sediments, aqueous basins and waterlogged soils where restricted water movement and oxidation of organic matter by aerobic organisms has led to a depletion of oxygen. Nevertheless, bacterial sulfate reduction may occur in oxidized sediments due to the presence of reduced microniches (Jorgensen, 1977a). 

Recent studies of sediments from Ramrail, Brahmanbaria in eastern Bangladesh by USGS/GSB (Foster et al., 2000) found 24 m of grey, reduced Holocene sediments overlying brown, oxidized sediments probably of Pleistocene age. The total As contents of the sediments were in the range 1-16 mg kg . A 5-10 cm thick Fe-rich layer had an As content of 264 mg kg and XANES spectra confirmed that most of this As was present as As(V). In... 

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