Sediment/sedimentary basins

The features created by crustal movements may be mountain chains, like the Himalayas, where collision of continents causes extensive compression. Conversely, the depressions of the Red Sea and East African Rift Basin are formed by extensional plate movements. Both type of movements form large scale depressions into which sediments from the surrounding elevated areas ( highs ) are transported. These depressions are termed sedimentary basins (Fig. 2.3). The basin fill can attain a thickness of several kilometres. 

The Cenozoic portions of the Gulf Coast sedimentary basins are immature therefore, little cementing of the sediments has taken place. Poisson s ratio varies with depth for such sedimentary columns, reflecting the variation of properties through the column. At great depth (i.e., approaching 20,000 ft), Poisson s ratio approaches that of incompressible, plastic materials (i.e., 0.5) [35]. 

Paulen, R.C., 2009. Sampling techniques in the Western Canada Sedimentary Basin and the Cordillera. In R.C. Paulen I. McMartin (eds.), Application of Till and Stream Sediment Heavy Mineral and Geochemical Methods to Mineral Exploration in Western and Northern Canada, Geological Association of Canada, GAC Short Course Notes 18, 41-59. 

The large sedimentary basins trend NW and contain extensive deposits. Sedimentation occurred from the Neo-Proterozoic to Mesozoic. The Dos Parecis Basin (Siqueira 1989 Pedreira Bahia 2000) is comprised of marine and... 

Figure 42. Schematic sedimentary cross-section of a typical northwest Africa marginal sedimentary basin containing sepiolite-palygorskite bearing sediments (after the summary presented by Millot, 1964) K = Kaolinite ...

At pH = 6, which presumably occurred in the ancient Precambrian sedimentary basins, migration of iron could have been accomplished only in the form of Fe " at an Eh not lower than —0.10 and not higher than 0.0 to + 0.10 V. A lowering of Eh would have led to massive deposition-of pyrite, and an increase in deposition of Fe hydroxides. The actual conditions of chemogenic formation of cherty iron sediments consisting of siderite, iron... 

Formation of silicate or carbonate-silicate sediments begins at a ratio of activities of Fe " " Fe " = 10 to 10 " (ferric iron is absent) which corresponds to an Eh range of —0.025 to —0.085 V. In this same range, formation of complex hydroxide-carbonate-silicate iron sediments is possible. The relative amount of hydroxide in such sediments depends on the oxygen supply, and that of siderite on the carbonate capacity of the sedimentary basin. 

The original sediment had a complex composition which was determined by fluctuations in Eh, pH, Pqq, etc. in the sedimentary basin. Magnetite and hematite are believed to be primary sedimentary or diagenetic minerals, essentially unaltered in metamorphism (James, 1954 Huber, 1960 Garrels et al., 1973 Klein, 1973 Klein and Fink, 1976 Drever, 1974). 

Typical BIF are metamorphosed chemogenic cherty iron sediments, deposition of which was typical only of the Precambrian and ceased in subsequent geologic epochs. The formation of these rocks reflects a certain stage in the irreversible process of evolution of the Earth s crust, atmosphere, hydrosphere and biosphere. The period of intensive deposition apparently was preceded by a long period of accumulation of dissolved iron and silica in the waters of the original sedimentary basins. 

The principal sources of dissolved chloride in the more saline fluids of sedimentary basins include dissolved chloride buried at the time of sediment deposition, chloride derived by refluxing of subaerially evaporated surface brines, chloride derived from subsurface mineral dissolution, principally halite, and marine aerosols. The Cl-Br systematics of sedimentary brines provide useful constraints on interpreting the origin of chloride in these waters (Carpenter, 1978 Kharaka et al., 1987 Kesler et al., 1996). 

Since the Precambrian, the Sr/ Sr of seawater has fluctuated between —0.7070 and —0.7092 as the result of variations in the relative rates of input of Sr-enriched strontium from continental weathering and Sr-depleted strontium from mantle sources. Fluids in sedimentary basins containing Paleozoic strata typically have Sr/ Sr ratios in excess of seawater values that are contemporaneous or coeval with the deposi-tional age of the current host sediment. This is well illustrated by the data of Connolly et al. (1990) for the Alberta Basin, Canada. The enrichment is due to the release of strontium attending the alteration of silicates. Due to the significant increase of Sr/ Sr in seawater since the Jurassic, some formation waters in Cenozoic sedimentary basins actually have Sr/ Sr ratios lower than those of contemporaneous seawater due to the addition of strontium dissolved from older and deeper sedimentary sources... 

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