Compositional variations of dolomite from a chain of ephemeral lakes in Coorong region, south Australia
Detailed x-ray diffraction (XRD) analyses of samples containing more than 80% dolomite demonstrate that all dolomite types have ordering reflections; however, the degree of ordering between individual samples is highly variable. XRD patterns from Type 1 dolomite indicate that the dolomites has a/sub 0/ and c/sub 0/ unit cell dimensions close to ideal dolomite, but slightly expanded in the c/sub 0/ direction. Type 2 dolomite is expanded in the c/sub 0/ direction and contracted in the a/sub 0/ direction (relative to ideal dolomite) and is magnesium rich. Type 3 dolomite is greatly expanded in both a/sub 0/ and c/sub 0/ directions and is calcium rich. Transmission electron microscopy reveals that Type 3 dolomite has a relatively homogeneous microstructure, Type 2 dolomite has a heterogeneous microstructure, and Type 1 dolomite is intermediate. Type 1 dolomite is characterized by a mean /delta//sup 18/O of +6.3 /per thousand/ PDB (stand. dev. /plus minus/ 0.3 /per thousand/), and mean /delta//sup 13/C of /minus/0.5 /per thousand/ PDB (stand. dev. /plus minus/ 0.8 /per thousand/). Type 2 dolomite has a mean /delta//sup 18/O of + 7.2 /per thousand/ PDB (stand. dev. /plus minus/0.6/per thousand/) and mean /delta//sup 13/C of +3.52/per thousand/ PDB (stand. dev. /plus minus/0.8 /per thousand/). No data are available on Type 3 isotopes. The mineral associations of each dolomite type, combined with the above data, suggest that variations in the composition of dolomite in these lakes is strongly dependent on the magnesium-calcium ratio of the precipitating fluid.
- Research Organization:
- Univ. of Texas, Austin (USA)
- OSTI ID:
- 6015078
- Report Number(s):
- CONF-880301-
- Journal Information:
- AAPG Bull.; (United States), Vol. 72:2; Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20-23 Mar 1988
- Country of Publication:
- United States
- Language:
- English
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