Skeletal mineralogy

Figure 5.6. Influence of temperature on skeletal mineralogy for different categories (see text) of organisms. (After Lowenstam, 1954a.)...

Bischoff W.D. and Burke C.D. (1989) Phanerozoic carbonate skeletal mineralogy and atmospheric CO2. Proceed of the Chapman Confer, on the Gaia Hypothesis, Amer. Geophys. Union, Washington, D.C., (in press). 

Figure 25 Predominant skeletal mineralogy, calcite (shaded) versus aragonite + high-Mg calcite (blank), in Phanerozoic reefs. Mineralogy from Kiesshng (2002), Sr data from Steuber and Veizer (2002) and Lear et al. (2003)...

Paleozoic limestone (Webb et al. 2004). These kimberlites all have similar groundmass mineralogies consisting mainly of carbonate, spinel, and serpentine with lesser monticellite, mica, apatite, and perovskite (Kong et al. 1999) and they are all of volcaniclastic facies near ground surface. Varying thicknesses of clay and fine marine sediments of the Tyrell Sea ( 4000 - 12000 years BP) and 1 to 4 m of peat overlie kimberlites (Fraser et al. 2005). Bioherms composed of coral and skeletal remains of other marine organisms sometimes outcrop. 

In a further section, we emphasize the mineralogy and chemistry of carbonate skeletal grains, because of their abundance in Phanerozoic sediments, and their potential usefulness in paleoenvironmental interpretation. To provide the reader at this point with some idea of the complexity of skeletal carbonate grains, Tables 5.2 and 5.3 summarize the chemistry, mineralogy and structure of major... 

We will not attempt to cover the specific mechanisms and complex biochemistry of calcification in different organisms, which have been reviewed in numerous articles (e.g., Degens, 1976 Watabe, 1981 Chave, 1984 Lowenstam and Weiner, 1989). Instead we will concentrate on observations of how biogenic carbonates reflect environmental conditions. These observations can be divided into the major areas of mineralogy, stable isotope ratios, and trace component concentration. The stable isotope and trace component chemistries have received substantially more attention during the last 25 years than has mineralogy. Inorganic phases are also discussed in this section as a means of comparison with skeletal materials. 

Because of the general complexity of factors controlling mineralogy, stable isotope composition and the chemistry of skeletal carbonates, it has been found that the best approach is to use these parameters in combination, rather than relying on any one of them (e.g., Lowenstam, 1961 Schifano and Censi, 1986). This approach is especially necessary in cases where early diagenesis may have taken place. Because, as will be discussed later in this chapter, this process can take place nearly concurrently with skeletal deposition, considerable care must be taken in... 

Sandberg P.A. (1975) New interpretation of great salt lake ooids and of ancient non-skeletal carbonate mineralogy. Sedimentology 22, 497-538. 

Sandberg P.A. (1983) An oscillating trend in Phanerozoic non-skeletal carbonate mineralogy. Nature 305, 19-22. 

The above scenario is consistent with the observation that calcite was the dominant mineralogy of carbonate skeletal components in the early to mid-Paleozoic and the mid-Jurassic to mid-Tertiary (Figure 25), the times of high Sr/Ca and low Mg/Ca ratio (Figure 24). Aragonite mineralogy, however, dominated the mid-Carboniferous... 

There has been, and still is, much debate about the origins of these particles. Firstly, it is difficult to disprove the effects of microbial mediation in their formation. Thus we might regard the grains as non-skeletal, while accepting a possible microbial influence. Secondly, various geochemical and mineralogical studies have produced... 

Table 1.2 Major groups of marine organisms contributing to biogenic sediment formation and mineralogy of skeletal hard parts. Foraminifera and diatoms (underlined) are important groups of both plankton and benthos, x = common, (x) = rare (mainly after Fliigel 1978, 2004 and Milliman 1974).

Nemliher, J. (1999) Mineralogy of Phanerozoic skeletal and sedimentary apatites an XRD study. Dissertationes Geologicae Universitatis Tartuensis, 8, 1-47. 

Most skeletal carbonates have variably lower <5 Mg values than seawater, depending on taxon-specific processes, including the mineralogy precipitated (Figure 12.7). Unlike Ca isotopes, which show a small temperature-dependent... 

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