Dolomite concrete

The soils from the morama bean-growing sites in Botswana were characterized by brown sand with no dolomite or limestone concretions on the surface or in the soil profile. Of all the sites in Botswana, only Ghanzi was characterized by white sand with dolomite or limestone concretions in the soil profile. Nonmorama soils from Namibia (Sandveld Site 4) were very fine white sands that appeared wet, waterlogged, and clayish, while those from Botswana soils (Groote Laagte Site 2 and Makgobokgobo Site 2) were generally brown sands with no limestone or dolomite concretions in the profile. 

Sandveld Site 1 Brown fine aeolian sand with limestone/dolomite concretions on top and subsurface layers Sandveld Site 2 Brown fine aeolian sand with no limestone/dolomite concretions... 

Sandveld Site 4 White water-logged very fine sand with limestone/ dolomite concretions in profile but not on surface layer. Appeared a bit clayish... 

Brown fine aeolian sand with no limestone/dolomite concretions... 

White fine aeolian sand with limestone/dolomite concretions in soil profile... 

Lawrence, M.J.F. (1991) Early diagenetic dolomite concretions in the late Cretaceous Herring Formation, eastern Marlborough, New Zealand. Sediment. GeoL, 75, 125-140. 

Hennessy, j. Knauth, L.P. (1985) Isotopic variations in dolomite concretions from the Monterey Formation, California. J. sediment. Petrol, 55, 120-130. 

Croal LR, Johnson CM, Beard BL, Newman DK (2004) Iron isotope fractionation by anoxygenic Fe(II)-phototrophic bacteria. Geochim Cosmochim Acta 68 1227-1242 Curtis CD, Coleman ML, Love LG (1986) Pore water evolution during sediment burial from isotopic and mineral chemistry of calcite, dolomite and siderite concretions. Geochim Cosmochim Acta 50 2321-2334... 

Destructive expansion occurs in concretes made with some aggregates containing dolomite, which reacts with OH" ions in the so-called dcdolomi-tization reaction ... 

Underclay and overburden sediments are typically clays with about 80% clay and 20% silt and muds with about 50% clay and 50% silt. The most distinct chemical variation in the overburden is the compact siderite- and dolomite-cemented concretion zone, 4.5 m above the base of the Kinneman Creek lignite. 

D 3.04 Concretion zone Siderite, dolomite, quartz Mica-illite, kaolinite, plagioclase... 

Dolomite rock cement and concrete evaporative brines. 

Bicarbonate ion is usually the chief anion in freshwaters. In and on silicate rocks, the HCOj concentration is usually 50 to 200 mg/L, whereas in groundwaters that contact a few percent carbonate materials up to pure limestone and dolomite, bicarbonate levels are usually in the range of 200 to 400 ppm. Seawater contains 140 mg/L HCOj. Carbonate alkalinity (CO3 ) rarely exceeds 10 mg/L. Why The presence of caustic alkalinity (free OH ) at pH s above 10 usually indicates artificial contamination of a water by, for example, Ca(OH)2 (portlandite) from the setting of concrete at newly completed wells. Cg concentrations can reach 1000 ppm as HCO3 in sodium carbonate-bicarbonate brines found in evaporative, closed basin lakes. 

Unlike calcite and dolomite, siderite rarely forms as an extensive pore-filling cement, but rather as discrete fine crystals, spherules and nodules scattered in the host sediments. Nevertheless, Baker et al. (1996) found that early diagenetic siderite concretions (0.5-2 mm) form up to 30% of Triassic sandstones and mudstones from eastern Australia. Laterally continuous siderite-cemented offshore shelf sandstone sheets (15 cm thick) occur in Upper Cretaceous sequences from Canada (McKay et ai, 1995). 

Curtis, C.D. Coleman, M.L. (1986) Controls on the precipitation of early diagenetic calcite, dolomite and siderite concretions in complex depositional sequences. In Roles of Organic Matter in Sediment Diagenesis (Ed. Gautier, D.L.), Spec. Publ. Soc. Econ. Paleont. Miner., Tulsa, 38, 23-33. 

Sources of Ca are very uncertain. No detrital carbonate (apart from the trivial volume of detrital dolomite described above) survives in the sandstones (including the early concretions). Carbonate... 

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