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zone between Miocene carbonate and anhydrite beds, Gemsa borehole No. 1, Gulf of Suez,
Egypt
Gamal M. Attia
Geology Dept., Fac. Sciences, Menoufia Univ. Egypt. |
A
diagenetic carbonate zone between carbonate and evaporite beds is developed in the Middle
Miocene Gemsa borehole No. 1, Gulf of Suez, Egypt, and exhibits several interesting
petrographic, chemical and isotopic features. These features suggest that the original
sediments had undergone recognizable alteration. The zone mostly contains calcite,
dolomite, aragonite and celestite.
Petrographically and by scanning microscope, the zone lies between two main rock types,
dolomitic limestone with fibrous aragonite cement and dolostone, and evaporites. The zone
develops two diagenetic variably altered types namely, diagenetic carbonate after sulfate
and other different diagenetic carbonates related to pressure solution crystallization and
crack-fillings.
Isotopically, the highly negative oxygen and carbon values obtained from the unaltered
aragonite reveal generally that appreciable amounts of calcite formed diagenetically were
derived from combination influx of sea water with a contribution of fresh water coming
into a restricted environment.
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