Calcite carbon enrichment

Note that the curve for this relation falls between the aragonite-bicarbonate and calcite-bicarbonate enrichment factors of Rubinson and Clayton, consistent with the fact that the calcium carbonate was a mixture of aragonite and calcite. 

Concerning calcium carbonate polymorphs calcite and aragonite, the experiments of Romanek et al. (1992) at low T (10 to 40 °C) seem to indicate that the enrichment factor of in the solid phase for CaC03-C02 partitioning is reduced by about two units in the aragonite polymorph with respect to the calcite counterpart, r being equal (e.g., at T = 10 °C, 1000 In a 13 for calcite-C02 and 11 for... 

Fig. 3.17. Carbon isotopic enrichment factors for aragonitic (dots) and calcitic (circles) foraminifera and inorganic precipitates as a function of temperature. Shown are the inorganic precipitate data of Baertschi (1957)- circle with dot Emrich et al. (1970)- large dots and Rubinson and Clayton (1969) revised - see text aragonite - solid diamond, calcite - hollow diamond. (After Grossman, 1984.)...

Figure 10. Comparison of the C-isotopic evolution at 25°C during dissolution of limestone (typically with = -4 to +2%o average. = 0%o, Deines et al., 1973) by soil waters initially equilibrated with CO2 derived from a Cs-type vegetation source of = -24%o (a) and a C4-type vegetation source of = -12%o (b) under open (solid line) and closed (dashed line) system conditions (after Salomons and Mook, 1986 and Deines et al., 1974). The lines and curves in each figure represent solution paths for different conditions of initial CO2 partial pressure (PCO2) conditions until equilibrium with calcite (i.e. saturation) is reached. The tick marks on the lines represent the C-isotope composition of the solution at that point of on evolutionary trajectory. Note that carbonate dissolution under closed system conditions leads to higher 5 C values (%o PDB) at saturation than open system dissolution, the lower the initial PCO2 value, the greater the degree of C enrichment at saturation.

The band of buff-colored, translucent pallisade calcite from 11 mm to 32 mm. Zone C, is relatively event-free, with only a few minor dissolution horizons or detrital drapes (not visible with the naked eye) representing short-term local flood events but not longterm glacial advance flooding. The isotopes show parallel oscillations and are somewhat more enriched than the upper zones of the sample. The oxygen isotopic values lie close to those of modern calcite in the cave, suggesting a moderately cool, wet climate similar to that of today. The oscillations in the carbon isotopic values follow the simple pattern of... 

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