Ooids

After 3 hours, replace the separating-funnel by a reflux condenser, and the thermometer by a stopper. Add 11 g. of zinc dust in small portions by rapid removal of the stopper at such a rate that the liquid is first brought to the boil (usually about 2 portions of 2 g. each) and is then maintained gently boiling. A ooid too rapid addition of the zinc, otherwise the reaction will become too vigorous, and rapid immersion of the flask in ice-water will be necessary to control the effervescence. 

Chung GS, Swart PK (1990) The concentrahon of ttranium in freshwater vadose and phreatic cements in a Holocene ooid clay a method of identifying ancient water tables. J Sediment Petrol 60 735-746 Cliff RA, Spotl C (2001) U-Pb dahng of speleothems from the Spannagel Cave, Austria. XI EUG... 

Calcitic ooids Nodules of calcite that are less than 2 mm in diameter. They are commonly found in and on the sediments of shallow tropical seas. 

Calcitic oolite A pavement of calcitic ooids formed by continuing precipitation of calcium carbonate between the calcitic ooids. 

Often iron stones have an oolithic texture, i.e. they consist of perfectly rounded bodies, the so-called ooids. Iron oxide ooids are mm to cm in size, hardened and showing concentric Fe accumulations (Plate 15.1), which suggest cyclic precipitation of the Fe oxide. Ghemical point analysis by the electron microprobe indicates enrichment of Ti, P and V in the Fe oxides, whereas Si and Al concentrations are very low (Fig. 15.5). The mode of Fe ooid formation and in particular the need for some mechanical action to produce the perfect rounding has been a matter for discussion for a long time. In principle, both terrestrial and marine formation is possible and it... 

Fig. 15.5 Element distribution across two Fe oxide ooids. The position of the two ooids is also indicated (Schwarz, 1992 with permission).

Gehring, A.U. (1985) A microchemical study of iron ooids. Eclogae Geol. Helv. 78 451-457 Gehring, A.U. Karthein, R. Reller, A. (1990) Activated state in the lepidocrocite structure during thermal treatment. Naturwissenschaf-ten 77 177-179... 

Plate 15.1 I ron oxide ooids in a silty matrix from an iron oolite -a thin section. Fula, Sudan (Schwarz, 1992 Courtesy T. Schwarz). 

Arsenious ooid forms many salts, of which the following arc examples —... 

Dissolves in hot solution of potassio hydrate. By the addition of an ooid to the liquid, n salt, said to have the composition... 

Oxide of Tin—SaOj—may be prepared by treating the metal with nitric acid. In its most concentrated form the ooid does not immediately aot, but will violently effervesce with heat upon the addition of a few drops of wator. The peroxide of tin remains in tho form of a white insoluble powder, and is purified by washing with boiling distilled water, and drying at a dull-red beat.. ... 

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. 

Both classifications are based on the depositional texture of the limestone Folk s emphasis is on the similarity of carbonate sedimentation to that of sandstones, resulting in a scheme employing as variables the lime mud spar cement ratio and allochem composition. Allochems may be intraclasts, ooids, fossils or... 

We will not attempt to review the occurrence and general characteristics of odlites here, because this has been done by several authors (e.g., Milliman, 1974 Bathurst, 1975 Fabricius, 1977 Simone, 1981) however, to quote Cayeux (as translated by Bathurst, 1975), "it is remarkable that so large a body of writing should contain so small a measure of achievement." Instead, we will concentrate on the major hypotheses for ooid formation and summarize the chemical characteristics of odids and experimental studies aimed at determining their processes of formation. 

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... 

Experimental studies of ooid formation During the past 20 years relatively few experimental studies have been carried out on the formation of ooids. Most of these studies have emphasized the role of organic matter. The primary reason for this emphasis is the observation of abundant protein matrices in obids (e.g.,... 

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