Geochemistry carbonate

Ishibashi, J., Wakita, H., Nojiri, Y, Grimand, D., Jean-Baptisto, P, Game, T., Auzende, J.M. and Urabe, T. (1994b) Helium and carbon geochemistry of hydrothermal fluids from the North Fuji Basin Spreading ridge. Southern Pacific. Earth Planet. Sci. Lett., 128, 183-197. 

Despite the vast amount of work on 14C dating which has already been accomplished and despite the fact that it is the best developed method available today, numerous difficulties still exist with its application. First, carbonate geochemistry which helped control 14C concentrations in the past is not simple to reconstruct. Carbonate minerals are commonly in a state of near equilibrium with groundwater, and only slight changes in water temperature or chemistry will promote either dissolution or precipitation of carbonate ions. In this way, the proportion of modern carbon in the water can be changed and some isotope... 

Morse, J. W., and F. J. Mackenzie (1990), Geochemistry of Sedimentary Carbonates, Elsevier, Amsterdam. (Comprehensive treatment of carbonate geochemistry, covering the range from electrolyte chemistry of carbon-containing waters to the global cycles of carbon.)... 

The coordination chemistry of sea water represents a new and useful approach to understanding the chemical properties of sea water. The coordination chemistry of sea water differs from contemporary coordination chemistry in the following respects most complexes involve pretransition metals, most complexes are labile, the ligands are simpler (water, hydroxide, chloride, carbonate, sulfate), and time and space are important parameters. Principles of coordination chemistry are applied to contemporary research in marine science in four areas analysis of constituents of natural waters, the nature of metallic species in the oceans, the Red Tide problem, and carbonate geochemistry. 

In theory, it should be possible to deal with all carbonate geochemistry in seawater simply by knowing what the appropriate activity coefficients are and how salinity, temperature, and pressure affect them. In practice, we are only now beginning to approach the treatment of activity coefficients under this varying set of conditions with sufficient accuracy to be useful for most problems of interest. That is why "apparent" and stoichiometric equilibrium constants, which do not involve the use of activity coefficients, have been in widespread use in the study of marine carbonate chemistry for over 20 years. The stoichiometric constants, usually designated as K. involve only the use of concentrations, whereas expressions for apparent equilibrium constants contain both concentrations and aH+ derived from "apparent pH". These constants are usually designated as K Examples of these different types of constants are ... 

Natural carbonate minerals do not form from pure solutions where the only components are water, calcium, and the carbonic acid system species. Because of the general phenomenon known as coprecipitation, at least trace amounts of all components present in the solution from which a carbonate mineral forms can be incorporated into the solid. Natural carbonates contain such coprecipitates in concentrations ranging from trace (e.g., heavy metals), to minor (e.g., Sr), to major (e.g., Mg). When the concentration of the coprecipitate reaches major (>1%) concentrations, it can significantly alter the chemical properties of the carbonate mineral, such as its solubility. The most important example of this mineral property in marine sediments is the magnesian calcites, which commonly contain in excess of 12 mole % Mg. The fact that natural carbonate minerals contain coprecipitates whose concentrations reflect the composition of the solution and conditions, such as temperature, under which their formation took place, means that there is potentially a large amount of information which can be obtained from the study of carbonate mineral composition. This type of information allied with stable isotope ratio data, which are influenced by many of the same environmental factors, has become a major area of study in carbonate geochemistry. 

Over the last 30 years the study of the stable isotope composition of carbonates has been one of the more active areas of research in carbonate geochemistry. These studies have particular application to later discussion of carbonate diagenesis and historical geochemistry of carbonate rocks. Many of the same considerations involved in understanding elemental distribution coefficients apply to the fractionation of stable isotopes. Consequently, we have included a discussion of the chemical principals associated with isotope behavior in this chapter. Only a relatively brief summary of these basic chemical considerations will be presented here, because recent books and extensive reviews are available on this topic (e.g., Arthur et al., 1983 Hoefs, 1987). Also, our discussion will be restricted to carbon and oxygen isotopes, because these isotopes are by far the most important for the study of carbonate geochemistry. The principles, however, apply to other stable isotopes (e.g., sulfur). 

One of the most controversial areas of carbonate geochemistry has been the relation between calcium carbonate accumulation in deep sea sediments and the saturation state of the overlying water. The CCD, FL, R0, and ACD have been carefully mapped in many areas. However, with the exception of complete dissolution at the CCD and ACD, the extent of dissolution that has occurred in most sediments is difficult to determine. Consequently, it is generally not possible to make reasonably precise plots of percent dissolution versus depth. In addition, the analytical chemistry of the carbonate system (e.g., GEOSECS data) and constants used to calculate the saturation states of seawater have been a source of almost constant contention (see earlier discussions). Even our own calculations have resulted in differences for the saturation depth in the Atlantic of close to 1 km (e.g., Morse and Berner, 1979 this book). 

The 1960 s can be viewed as the "golden age" of sedimentary carbonate geochemistry. This "golden age" was in no small part due to the "gold" which started to flow rapidly and relatively easily into university research. There was an... 

It is hard to say why the study of sedimentary carbonate geochemistry started the 1960 s with such vigor and ended the decade in such a chaotic manner. The tumultuous nature of the times, sudden infusion of previously undreamed of levels of funding, and rapid addition of new investigators to the field certainly were all part of it. However, it also seems probable that frustration with the unexpected complexities of the chemical behavior of carbonates and failure to arrive at solutions of basic problems also contributed substantially to the chaotic state of the field as the 1960 s ended. These were the wild adolescent years of the field. 

We feel that it is worthwhile to attempt to view the current status of carbonate geochemistry in light of the fundamental problems that were largely defined 20 to 30 years ago. Although one frequently encounters the attitude that so much as been done in the field of carbonate mineral geochemistry relative to other mineral systems that all the major problems have been solved, it is our opinion that this assertion is far from the truth. On the contrary, many of the most important problems are largely unresolved in spite of this mammoth effort. 

Goodell H.G. and Garman R.K. (1969) Carbonate geochemistry of Superior deep test well, Andros Island, Bahamas. Am. Assoc. Petrol. Geol. Bull. 53, 513-536. 

Thrailkill J. and Robl T.L. (1981) Carbonate geochemistry of vadose water recharging limestone aquifers. J. Hydrology 54, 195-208. 

Jacobson A. D., Blum J. D., and Walter L. M. (2002) Reconciling the elemental and Sr isotope composition of Himalayan weathering fluxes insights from the carbonate geochemistry of stream waters. Geochim. Cosmochim. Acta 66, 3417-3429. 

The chemistry of the carbonic acid system in seawater has been one of the more intensely studied areas of carbonate geochemistry. This is because a very precise and detailed knowledge of this system is necessary to understand carbon dioxide cycling and the deposition of carbonate sediments in the marine environment. A major concept applicable to problems dealing with the behavior of carbonic acid and carbonate minerals in seawater is the idea of a constant ionic medium. This concept is based on the observation that the salt in seawater has almost constant composition, i.e., the ratios of the major ions are the same from place to place in the ocean (Marcet s principle). Possible exceptions can include seawater in evaporative lagoons, pores of marine sediments, and near river mouths. Consequently, the major ion composition of seawater can generally be determined from its salinity. It has been possible, therefore, to develop equations in which the influence of seawater composition on carbonate equilibria is described simply in terms of salinity. 

Ronov A. B. (1976) Global carbon geochemistry, volcanism, carbonate accumulation, and life. Geokhimiya 8, 1252-1257 Geochem. Int. 13, 175-196. 

Morse, J. W. Mackenzie, F. T. 1998. Hadean ocean carbonate geochemistry. Aquatic Geochemistry, 4, 301-319. 

Frisia, S., Borsato, A., Fairchild, I.J., McDermott, F. Selmo, E.M. (2002) Ara-gonite-calcite relationships in speleothems (Grotte de Clamouse, France) environment, fabrics, and carbonate geochemistry. Journal of Sedimentary Research 72, 687-699. 

CARBONATE GEOCHEMISTRY OF VADOSE WATER RECHARGING LIMESTONE AQUIFERS... 

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