Sediment chemical

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Runnells, D. D., 1969, Diagenesis, chemical sediments, and the mixing of natural waters. Journal of Sedimentary Petrology 39, 1188-1201. 

Only a few evaporites have been found that are more than 800 miUion years old, indicating that most of the salt formed prior to this period has been recycled via uplift and weathering. No evaporites of Archean age have as yet been discovered. The oldest known chemical sediments were deposited 3.45 bybp in what is now western Australia. They appear to have precipitated as shallow-water carbonates. This suggests that sulfate concentrations during the Archean were much lower than present day, probably because of limited oxygenation of the atmosphere and ocean. 

JOHANNESSON, K.H., HAWKINS JR., D.L. Cortes, A., 2006. Do Archean chemical sediments record ancient seawater rare earth element patterns Geochimica et Cosmochmica Acta, 70, 871-890. 

Bodies of Water and the Chemical Sediments ,— The chemistry of the deposition of salts from sea-water has already been made the subject of special research, and van t Hoff s results in this field are already familiar. The deposition of calcium carbonate awaits a similar thorough study. Allied questions are the formation of dolomite, the deposition of various salts from inclosed bodies of water, the deposition of phosphate rocks, the precipitation of colloidal suspensions of clay and other substances, and the origin of the great deposits of sedimentary iron ore. 

One of the most sensitive tracers recording the composition of ancient sea water is the isotopic composition of chemical sediments precipitated from sea water. The following discussion concentrates on the stable isotope composition of oxygen, carbon, and sulfur, but in recent years other isotope systems have been included such as Ca (De La Rocha and De Paolo 2000 Schmitt et al. 2003 Fantle and de Paolo 2005 Farkas et al. 2007) and B (Lemarchand et al. 2000, 2002 Joachimski et al. 2005) and Li (Hoefs and Sywall 1997). One of the fundamental questions in all these approaches is which kind of sample provides the necessary information, in the sense that it represents the ocean water composition at its time of formation and has not been modified subsequently by diagenetic reactions. 

The sample locations are shown on the map in Figure 1. Euromonding (Port of Rotterdam) and the North Sea Canal (Port of Amsterdam) are well-known polluted areas. The sites in the North Sea are situated at the end of the estuarine harbour areas, except for Noordwijk (site 6), which is a t5 ical coastal location. Two relatively clean sites, the Oesterput in the Eastern Scheldt estuary (site 14) and Ussehneer near Enkhuizen (site 12), were also sampled and used as saltwater and freshwater reference sites respectively. In the Port of Rotterdam transect the salinity gradient is continuous whilst in the Port of Amsterdam transect the salinity gradient is interrupted and more complex due to canalisation. The numbers of the sampling sites correspond with the site numbers reported previously for the results of the chemical sediment and flounder liver analyses (De Boer 2001). The transects were sampled from 19 to 26 September 1996. 

This thesis focuses on the applicability of in vitro and in vivo bioassays and bioindicators as tools for evaluating the effects of complex chemical sediment contaminants in the process of deciding whether dredged harbour sediments can be safely disposed of at sea. To this end three objectives have been defined ... 

Models for the formation of Precambrian sediments suggest that the chemical sediments (such as cherts) of the Isua supracrustal belt have formed as shallow water deposits. This is in agreement with structures locally preserved in the metacherts of the sequence. After deposition, the supracrustals were folded and metamorphosed. Finally, the metamorphism reached lower amphibolite facies and in consequence, most of the primary minerals became recrystallized. As a result all chert now appears as quartzite. But apparently metacherts, magnetite iron formation and quartz carbonate rocks have retained their major element chemistry largely unaltered during metamorphism (Nutman et al., 1984) 119). 

Opal is a common mineral in chemical sediments, as deposits around hot springs, replacing fossils such as wood, or as secondary vein-filling. Most opal is common opal, without the internal play of colors that makes some opal precious. Common opal is usually light colored, and has a distinctive waxy luster. 

Chemical sediments precipitate out of a solution, usually water, as it evaporates. These include hot spring deposits, salts that crystallize around the shores of lakes and bays, and solution cavern deposits. 

Organization for Economic Cooperation and Development (2004a) OECD Guidelines for the Testing of Chemicals, Sediment-water chironomid toxicity test using spiked water, OECD 219, adopted 13 April 2004. 

The pollutants thus transported include fertilizers, pesticides, oil, grease, other organic and inorganic industrial chemicals, sediments, salts, acid mine drainage, nutrients, radionuclides, microorganisms, and noxious gases. 

Weaver C. E. and Beck R. C. (1977) Miocene of the SE United States a Model for Chemical Sedimentation in a Peri-marine Environment, Developments in Sedimentology, Elsevier, Amsterdam, vol. 22, 234p. 

Perry E. C. and Ahmad S. N. (1983) Oxygen isotope geochemistry of Proterozoic chemical sediments. GSA Memoir 161, 253 —263. 

Figure 9 Relative proportions of lithological types within intracratonic to transform hasins and the averages for geological periods. Based on the North American cross-sections in Cook and Bally (1975). An independent compilation hy Berry and Wilkinson (1994) from the same source, hut based on different criteria, yielded comparable temporal patterns. CCL coarse elastics FCL fine elastics CS chemical sediments. A global review based on the Ronov (1982) database also yields comparable patterns (after Veizer and Ernst, 1996).

The previous discussion dealt with the solid earth component of the exogenic cycle, a system that is recycled on 10 -10 yr timescales. In contrast, the ocean, atmosphere, and life are recycled at much faster rates and the continuity of the past record is lost rapidly. For quantitative evaluations we have to rely therefore on proxy signals embedded in marine (bio)chemical sediments. 

Other contributions in this Treatise (Volumes 6-8) deal with the lithological and chemical aspects of evolution of specific types of (bio)-chemical sediments, such as cherts, phosphorites, hydrocarbons, and evaporites, and we will therefore concentrate on the most ubiquitous category, the carbonate rocks (see also Section 7.15.12). This carrier phase also contains the largest number of chemical and isotopic tracers. 

Krumbein, W.C. and Garrels, R.M., 1952. Origin and classification of chemical sediments in terms of pH and oxidation reduction potentials. J. Geol., 60 1—33. 

Goudie, A.S. Pye, K. (Eds) (1983a) Chemical Sediments and Geomorphology. London Academic Press. 

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