Sediment near-surface

Photolysis calculated t,/2 = 22 h for direct sunlight photolysis of 50% conversion at 40°N latitude of midday in midsummer in near surface water, t,/2 = 180 d in 5-m deep inland water and t,/2 = 190 d in inland water with a suspended sediment concentration of 20 mg/L partitioning (Zepp Schlotzhauer 1979) t,/2 = 180 d under summer sunlight in surface water (Mill Mabey 1985) direct photolysis t,/2 = 11.14 h (predicted- QSPR) in atmospheric aerosol (Chen et al. 2001). 

Air t1/2 = 6 h with a steady-state concn of tropospheric ozone of 2 x 10-9 M in clean air (Butkovic et al. 1983) t/2 = 2.01-20.1 h, based on photooxidation half-life in air (Howard et al. 1991) calculated atmospheric lifetime of 11 h based on gas-phase OH reactions (Brubaker Hites 1998). Surface water computed near-surface of a water body, tl/2 = 8.4 h for direct photochemical transformation at latitude 40°N, midday, midsummer with tl/2 = 59 d (no sediment-water partitioning), t,/2 = 69 d (with sediment-water partitioning) on direct photolysis in a 5-m deep inland water body (Zepp Schlotzhauer 1979) t,/2 = 0.44 s in presence of 10 M ozone at pH 7 (Butkovic et al. 1983) calculated t,/2 = 59 d under sunlight for summer at 40°N latitude (Mill Mabey 1985) t,/2 = 3-25 h, based on aqueous photolysis half-life (Howard et al. 1991) ... 

Surface water computed t,/2 = 0.13 h at near-surface of a water body, for direct photochemical transformation, and t,/2 = 0.79 d for direct photolysis in a 5-m deep inland water body with no sediment-water partitioning, t,/2 = 1.2 d with sediment-water partitioning to top cm bottom sediment and t,/2 = 10 h for photosensitized oxygenation with singlet oxygen at near-surface natural water, 40°N, midday, midsummer (Zepp Schlotzhauer 1979) ... 

Surface water photolysis t,2 = 4.4 h near surface water, t,/2 = 13 d and 68 d in 5-m deep water body without and with sediment-water partitioning in full summer day, 40°N photosensitized oxygenation t,/2 = 2.6 h at near surface water, 40°N, midday, midsummer (Zepp Schlotzhauer 1979) t,/2 4.4-13 h, based on photolysis half-life in water (Howard et al. 1991) ... 

Six sulphide species were observed in the non-ferromagnetic heavy mineral concentrates (NFM-HMCs) of bedrock samples arsenopyrite pyrite > chalcopyrite > bismuthinite = molybdenite = cobaltite. Chalcopyrite, pyrite and bismuthinite do survive in near-surface till but only in minor amounts (<8 grains/sample). Although the Co-rich composition of arsenopyrite is possibly the strongest vector to Au-rich polymetallic mineralization in the study area, sandsized arsenopyrite is absent in C-horizon tills, suggesting that arsenopyrite more readily oxidizes than chalcopyrite and pyrite in till, and therefore is an impractical indicator mineral to detect mineralization using surficial sediments at NICO. 

Schumacher, D. 1996. Hydrocarbon-induced alteration of soils and sediments. In Schumacher, D. Abrams, M.A. (eds.), Hydrocarbon migration and its near-surface expression AAPG Memoir, 66, 71-89. 

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. 

Lithium isotope studies of sediments and sedimentary rocks have thus far concentrated on marine clastic and carbonate material. No systematic description of the effects of diagenetic processes on sediments has been made. Clay rich sediments are important to Li budgets in near-surface systems, as they concentrate Li relative to marine carbonates, which are among... 

Bulk carbonate samples have been analyzed in several studies. You and Chan (1996) determined the compositions of a pair of carbonate-rich sediment samples from ODP Site 851. The near-surface sample had 5 Li = +6.2, whereas a sample from 196 m below the sea floor was +32.0. Carbonate-rich oozes from Hoefs and Sywall (1997) from the time period 81-9... 

Hagiwara (2000) completed a reconnaissance survey of Se isotope variation in marine sediments and sedimentary rocks (Table 4). The most important observation was a lack of strong enrichment in lighter isotopes in most shale samples and three Black Sea sediments. It appears that near-surface alteration has altered Se isotope ratios in some cases. All of the Phosphoria formation samples were probably altered by deep groundwater or hydrothermal... 

No information concerning the transport and partitioning of 1,2-diphenylhydrazine in the environment was located in the literature. In water, 1,2-diphenylhydrazine is not expected to volatilize because of its rapid oxidation in aerated water (near-surface water) to azobenzene and its low calculated Henry s Law constant (9.42 x 10 atm-m mof) (Lyman et al. 1982). The calculated log Koc (2.76) suggests that 1,2-diphenylhydrazine may sorb to sediments or suspended particles. This is based on the analysis of Kenaga (1980), who stated that chemicals with a K°<= <100 tend to be mobile in soil, while those with a K°<= >L000 tend to sorb. In soil, 1,2-diphenylhydrazine is not expected to leach to groundwater, based on its physical and chemical properties (i.e.. 1,2-diphenylhydrazine reacts rapidly under environmental conditions and, based on its K°c will not rapidly leach downward in the soil column). 

Soil organic matter is found wherever organic matter is decomposed, mainly in the near surface. However soil organic matter may also be transported as suspended particles into deeper layers of the vadose zone or via surface- and groundwaterforming sediments. Although these components form a minor part of the total solid phase, they are of major importance in defining the surface properties of the solid phase and have a great impact on the chemical behavior. 

A total of 80 soil samples and 30 stream sediment samples were collected in the vicinity of known mineralization and analyzed for 36 elements in four size fractions. Orientation results indicate that soil samples should be collected from the near-surface soil horizon on a 100 by 200 m grid pattern, and sieved to the coarse, -8+35 mesh fraction prior to analysis. Stream sediment samples should be collected at a sample density of approximately 1 sample per 1 km and sieved to the fine, -150 mesh fraction. As expected, copper and molybdenum show the strongest response to copper-molybdenum mineralization at both Pico Prieto and Venado in addition, the following elements are also associated with mineralization at Tameapa Au, Ag, Pb, Zn, V, W, Ni, As, Sb, Bi, Se, Sr, and Ba. 

Alteration assemblages may include primary chlorite, illite, smectites, and/or kaolinite, and various primary and secondary iron oxides, carbonates, and sulfides (Fig.1), any one of which may serve as indicators of fluid composition. Lithologic geochemical surveys rely on an understanding of these patterns to vector towards uranium deposits. The interpretation of hydromorphic geochemical surveys, including lake and stream sediment, and soil, depends on the mobility of uranium and associated elements in the surface and near surface environment. 

On the other hand, the concentration of positive ions, including H2O, near sediment particle surfaces would be expected to be enhanced relative to the bulk solution concentrations. From this consideration, we would predict that acid-catalyzed hydrolysis reactions should occur at enhanced rates for sorbed molecules. 

The forms of SiC found in sediments and sedimentary rocks are quite varied but those which could be suspected of near surface origin are generally as follows quartz, chalcedony, opal, amorphous gels and ionic forms in solution. Natural occurrences indicate that the solid forms of silica precipitate which has crystallized after the time of initial deposition (Siever, 1962). 

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