Carbonate cementation controlling factors

Factors controlling the mineralogy and chemical composition of carbonate cements in the marine environment have also been extensively investigated. Bathurst (e.g., 1975 1987) summarized many of the observations (e.g., Glover and... 

Factors that control the geochemistry, abundance and distribution of carbonate cements are of prime importance in the understanding and prediction of porosity-permeability variations and in tracing the geochemical evolution of pore waters during the burial of sandstones and associated sediments. Moreover, the stable isotopic composition of nearsurface, eogenetic carbonates (e.g. in soil profiles) provides important clues to the palaeoclimatic conditions (e.g. Ceding, 1984). 

Anions are another factor controlling the stoichiometric efficiency of organic acids. In the case where carbonic acid acts as a solvent for carbonate cement the carbonate ions in solution result from the solvent (acid) as well as from the mineral dissolved. In contrast to this, for acetic acid as the solvent, at least half of the carbonate ions produced during dissolution will be substituted by acetate anions calcium acetate and not merely calcium carbonate alone is also a product of the dissolution. Calcium acetate is three times more soluble in water than calcium carbonate (Table 4.5). This actually favours the stay of the calcium ions in solution, hindering their precipitation in the form of calcium carbonate. Thus, the higher solubility of the salts of a... 

Let us now consider the problem from the standpoint of calcite precipitation kinetics. At saturation states encountered in most natural waters, the calcite reaction rate is controlled by surface reaction kinetics, not diffusion. In a relatively chemically pure system the rate of precipitation can be approximated by a third order reaction with respect to disequilibrium [( 2-l)3, see Chapter 2]. This high order means that the change in reaction rate is not simply proportional to the extent of disequilibrium. For example, if a water is initially in equilibrium with aragonite ( 2c=1.5) when it enters a rock body, and is close to equilibrium with respect to calcite ( 2C = 1.01), when it exits, the difference in precipitation rates between the two points will be over a factor of 100,000 The extent of cement or porosity formation across the length of the carbonate rock body will directly reflect these... 

The timing of the dolomitization of carbonate rock bodies and emplacement of dolomite cements has been one of the more controversial aspects of the "dolomite problem." Most of the basic factors controlling dolomite formation, where were discussed in Chapters 6 and 7, also apply to dolomite formation during the later stages of diagenesis. However, the extended periods of time, the solution compositions likely to be encountered, and the elevated temperature and pressure that occur during deep burial provide highly favorable conditions for dolomite formation. 

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