Diagenesis recent sediments

Primary iron sulfides are encountered relatively rarely in Precambrian rocks, and it is not ruled out that they too were formed as a result of diagenetic transformations, as has occurred at the time of diagenesis of recent sediments (Strakhov, 1960 Berner, 1964a, b Stashchuk et al., 1964). 

Recent sediments of water basins. In recent basins iron sediments consist mainly of the iron hydroxides Fe(OH)3 or Fe203-nH20, but in very rare cases silicates and carbonates of Fe ", pyrite, and hydrotroilite enter into the composition of the sediment all together they constitute reactive (mobile) iron, which actively takes part in the diagenetic processes. A mixture of clastic minerals, which decompose negligibly and take practically no part in the processes of diagenesis, constitute another group. 

These tricyclic and tetracyclic series are absent from Recent sediments, suggesting that their formation from kerogen requires higher temperatures than those associated with diagenesis (Aquino Neto et al. 1983), assuming that the organisms that produce them still exist. 

Lee, C., Gagosian, R.B. and Farrington, J.W., 1977. Sterol diagenesis in Recent sediments from Buzzards Bay, Massachusetts. Geochim. Cosmochim. Acta, 41 985—992. 

Anderson, N. J. B. Rippey, 1988. Diagenesis of magnetic minerals in the recent sediments of a eutrophic lake. Limnol. Oceanogr. 33 1476-1492. 

Tessier et al. [82] pointed out the dependency between results and consistency of the sample, which is conditioned by the complexity of the microstructure of recent geological material. In this report we have already shown how complex conditions of both emergence and diagenesis of sediments affect the process in which various mineral phases can be found completely confined in other phases and hence become eco-chemically irrelevant, because they cannot participate in the processes of interaction with the surrounding (water) environment. This makes the above-mentioned model of Davies-Colley et al. [9] practically inappUcable, because it does not take into consideration this inactive phase. Here Ues one of the main causes of non-selectivity of sequential extraction - confined phases will be released only after their shell has been broken down (partially or completely) - therefore it is clear that in this manner a part of the carbonate, for example, can be found in the reducible phase , and a part of hydrous oxides in the organic phase , etc. 

These acids have an aliphatic group that contains one or more double carbon bonds, which determines the degree of unsaturation. More than half of the aliphatic carboxylic acids in most living organisms are unsaturated (Parker 1969). However, double carbon bonds are highly reactive sites and at burial of less than 1-m unsaturated carboxylic acids are typically absent in recent sediments (Rosenfield 1948 Parker and Leo 1965 Rhead et al. 1971). This loss of unsaturated carboxylic acids at low temperatures is considered to be related to bacterial activity within sediment pore waters (Johnson and Calder 1973). Some of these acids survive early diagenesis as... 

In the context of diagenesis in recent anoxic sediments, reduced carotenoids, steroids, and hopanoids have been identified, and it has been suggested that reduction by sulhde, produced for example, by the reduction of sulfate could play an important part (Hebting et al. 2006). The partial reduction of carotenoids by sulfide has been observed as a result of the addition of sulfide to selected allylic double bonds, followed by reductive desulfurization. This is supported by the finding that the thiol in allylic thiols could be reductively removed by sulhde to produce unsaturated products from free-radical reactions (Hebting et al. 2003). 

Once the radionuclides reach the sediments they are subject to several processes, prime among them being sedimentation, mixing, radioactive decay and production, and chemical diagenesis. This makes the distribution profiles of radionuclides observed in the sediment column a residuum of these multiple processes, rather than a reflection of their delivery pattern to the ocean floor. Therefore, the application of these nuclides as chrono-metric tracers of sedimentary processes requires a knowledge of the processes affecting their distribution and their relationship with time. Mathematical models describing some of these processes and their effects on the radionuclide profiles have been reviewed recently [8,9,10] and hence are not discussed in detail here. However, for the sake of completeness they are presented briefly below. 

Diagenesis Aloaline lake sediments (recent and old) e West regions of USA, East Africa (recent, Q,Tr> Gude (loss)... 

Wakeham, S.G., Schaffner, C., Giger, W., 1980. Polycyclic aromatic hydrocarbons in recent lake sediments—II. Compounds derived biogenic precursors during early diagenesis. Geochim. Cosmochim. Acta 44, 415-429. 

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