Diagenesis and geochemistry of the Aptian dolomite (cretaceous) in the Razzak Oil Field, western Desert, Egypt

• Autores: Rifai I. Rifai, Mossbah M. Kolkas, Hanafy M. Holail, Khaled A. Khaled
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 21, Nº. 2, 2006, págs. 176-187
• Idioma: inglés
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• Resumen

  • Petrographic study of selected thin sections from the Aptian dolomites in the Razzak Oil Field, Egypt reveals three dolomite textures. These textures have been classified based on crystal size, shape, uniformity, and trace element distribution. These textures are as follows: 1) finely crystalline, planar-e dolomite, 2) medium to coarsely crystalline, non-planar dolomite, and 3) very coarsely crystalline, non-planar dolomite (saddle dolomite). Stable isotope analyses indicates that the Aptian dolomites formed in a marine environment and were later subjected to several diagenetic modifications that affected the original sediments. The finely crystalline, planar-e dolomite is penecontemporaneous in origin with d18O that ranges from -7.51 to -8.14%o VPDB and d13C that ranges from +0.39 to -1.27%o VPDB. The medium to coarsely crystalline, non-planar dolomite is a replacement type with a meteoric origin. In this non-planar dolomite, the d18O ranges from -7.99 to -8.82%o VPDB and the d13C ranges from -0.58 to -1.35%o VPDB. The void-filling (saddle dolomite) is the product of chemical compaction and is associated with the thermal sulfate reduction event. This saddle dolomite has d18O that ranges from -7.89 to -8.76%o VPDB and d13C that ranges from +1.41 to +2.42%o VPDB. The diagenetic parasequence of the Aptian Dolomite is recorded by: 1) deposition of the original sediments (lime mud); 2) dolomitization; 3) silicification, 4) pyritization, and 5) precipitation of saddle dolomites (pore-filling dolomite).