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Abstract

Two problems complicate the rigorous use of isotopic data to delineate the origin and diagenesis of dolomitized limestones. First, the re-lationship between δ , δodolomite . and temperature is imperfectly known, and may, in fact, depend in part on the crystal structure (composition and degree of order) of a particular dolomite under consideration. And second, the initial dolomitization of a sediment or limestone appears to be nearly open system because of the large volume of water necessary to import sufficient magnesium to cause massive dolomitization (at least 800 pore volumes of seawater, for example). But many dolomitized rocks, particularly older ones, have undergone one or more recry-stallizations to more stable dolomite phases, and these replacement reactions are certainly not open-system. The problem of interpreting recrystallization(s) in partly closed systems is not yet solved.

The relationship between the isotopic composition of dolomite, temperature and the isotopic composition of water has been determined experimentally by a variety of investigators using a variety of techniques Using standard notation,

All equations have been corrected to be consistent with Friedman 18 and O'Neil (1977). These relations are plotted for δwater =0 ‰ in Figure4–1. Given a dolomite analysis, and assuming open system reaction, the range in uncertainty in temperature (given or assuming a is about and the range in uncertainty in water (given or assuming a temperature) is about 4 o/oo. The difference (ti) between a co-existing calcite and dolomite ranges from about 3 o/oo to 6 o/oo at Using natural examples, mostly from

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