Ooids aragonitic

Suess, E., and Fiitterer, D. Aragonitic ooides Experimental precipitation from seawater in the presence of humic acid. Sedimentol. 19, 129-139 (1972). 

Before continuing, it is important to note that the solubility behavior of aragonite in seawater has proven rather strange, in that for equilibration periods of less than about a month, different solubility values can be obtained in an apparently reversible manner. This result points to some sort of short-term, solubility controlling surface phase and may have implications for processes such as ooid formation which is discussed in Chapter 5. 

Bathurst has presented a model that solves some of the problems associated with laminated aragonitic ooid formation. His suggestion involves a means for growing inorganic precipitates of tangentially oriented rods. His arguments also offer plausible explanations for limitations on ooid size and other characteristics. 

One of the difficulties in understanding typical aragonitic ooid formation is the fact that the aragonite needles, or battens, are arranged with their c crystallographic axes parallel to the solid surface. Bathurst (1974) observed that the... 

Their studies are remarkable in indicating that organic matter may be important for the formation of magnesian calcite radial ooids, but not aragonitic tangential ooids. This observation is contrary to general concensus on the formation of these two types of ooids. It may also offer a major clue to the formation of aragonitic and calcitic carbonate cements. 

Figure 10.17. Trend in relative percentage of originally calcite and aragonite ooid compositions during the Phanerozoic. (After Mackenzie and Agegian, 1989.)...

Tucker M.E. (1984) Calcitic, aragonitic and mixed calcitic-aragonitic ooids from the mid-Proterozoic Belt Supergroup, Montana. Sedimentology 31, 627-644. 

Wilkinson B.H., Bucznski C. and Owen R.M. (1984) Chemical control of carbonate phases implications from upper Pennsylvanian calcite-aragonite ooids of southeastern Kansas. J. Sediment. Petrol. 54, 932-947. 

Holland and Zimmermann, 2000). The latter authors do accept, however, that there is generally lower dolomite abundance in carbonate sediments deposited during the past 200 Myr. These qualihcations notwithstanding, a number of previously described parameters (Sr/Ca, Mg/ Ca, aragonite/calcite, possibly dolomite/calcite, and frequency of ooids and iron ores) appear to be related in some degree to sea-level stands, the latter at least in part a reflection of plate tectonic activity during the Phanerozoic. 

The amount of carbonate which is deposited in the oceans today is almost exclusively of biogenous origin. The long controversy whether chemical precipitation of lime occurs directly in the shallow waters of the tropical seas, such as the banks of the Bahamas and in the Persian Gulf (Fig. 1.5), during the formation of calcareous ooids and oozes of acicular aragonite, has been settled in preference of the concept of biomineralization (Fabricius 1977). The tiny aragonite... 

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