Early Abiotic Dolomite Mineralization

Mg2+ ions can’t be forced into a calcite lattice structure to convert limestone to dolostone (Deelman 2011, Chapter 1 ,p. 1). Instead, Robert et al. (2013) propose the abiotic replacement process necessitates flushing limestone strata of burial fluids, activating high density carbonyl groups in buried strata, dewatering Mg2+ ions and precipitating dolomite on the surface of carboxyl group bonds. 

Abiotic dolostone formation is a cementation process at earth surface conditions. Since limestone particles can not be dissolve and converted to dolomite, the cement precipitation typically involves the inclusion of limestone particles Meyer 2017a). Included limestone particles reflect the corrosiveness of fluids that flushed the formation. The pattern of corrosion may also provide additional information about the diagenetic environment. Grains shrunk uniformly in size record phreatic environment. Grains with fitted and faced contact or mosaics of such contacts point to compaction of grains involving vadose processes (Meyer 2017b). vadose compaction requires uncemented grainstone depositional textures that permit grain movement. Active vadose environments are known to extend to depth of over 60 meters (Benvente, and Vadelllio, 2010) but only in telogenetic karst systems developed in indurated carbonates (Palmer et al., 1999). Vadose compaction requires grain movement possible only in eugenic karst systems . The presence of a mosaic of fitted and faced grains documents vadose compaction. Their appearance inside dolomite argues for dolomite precipitation concurrent with vadose diagenesis or shortly afterwards, but before burial sufficiently great for overburden to produce chemical compaction by pressure solution. Eogenic karst systems develop in peri-marine environments where the rocks are young and still undergoing diagenesis as a result of meteoric water passing through them. Dolomite development in an eogenic karst setting meets the requirements suggested by Roberts et al (2013); 1) meteoric water flushes out or displaces burial fluids as part of a freshwater - saltwater mixing zone, 2) Sea water providers an ample source of Mg2+ ions, 3) Organic matter concentrates at both the top and base of the meteoric lens (Palmer et al, 1999) a potential source of carboxyl groups.

The idea of very early Dolomite precipitation is not new, but was noted by Saller and Henderson (1988) in the course their study of platform dolostone from the Permian basin of west Texas.  Shinn et al in their study of Andros Island, Bahams were the first to report Recent dolomite from the supra tidal. Meyer (2017c) reported on a reworked dolomite intraclast from the Hobshan Reservoir in the U.A.E.

References

Benavente, J., and Vadillo, F. C., 2010, Air carbon dioxide contents in the vadose zone of a Mediterranean karst: Vadose Zone Journal, v. 9 no. 1, p. 126-136.

Deelman, J. C., 2011, Low-temperature formation of dolomite and magnesite, Eindhoven, the Netherlands, Compact Disc Publications, 515 p.:

Meyer, F. O., 2017a, Dolomite Fabric Tales from the Simsima Formation U.A.E.: LinkedIn.

Meyer F.O., 2017b, Dunham, R. J., 1969, Vadose Compaction on Cayo Arenas, Campeche Banks, in Company, S. O., ed.: Shell Bellair Research, Houston, LinkedIn.

Meyer F.O., 2017c. Dolomite intraclast. LinkedIn.

Palmer, A. N., Palmer, M. V., and Sasowsky, I. D., 1999, Karst modeling : proceedings of the symposium held February 24 through 27, 1999, Charlottesville, Virginia, Charles Town, W. Va., Karst Waters Institute, Special publication, v. 5, iii, 265 p. p.

Roberts, J. A., Kenward , P. A., Fowle , D. A., Goldstein , R. H., Gonzalez , L. A., and Moore , D. S., 2013, Surface chemistry allows for abiotic precipitation of dolomite at low temperature Proc. Natl. Acad. Sci. U.S.A. , v. 110, no. 36, p. 14540-14545.

Saller, A. H., and Henderson, N., 1988, Distribution of Porosity and Permeability in Platform Dolomites: Insight from the Permian of West Texas: American Association of Petroleum Geologists Bulletin, v. 82, no. 8, p. 1528-1550

Sinn, W. A., Ginsberg, R. N., and loyd, M., 1965, Recent supratidal dolomite from Andros Island Bahams, in Lloyd C. Pray, and Murray, R. C., eds., Dolomitization and Limestone Diagenesis: Tulsa, Oklahoma, p. 112-123.