Diagenetic evolution of the middle eocene carbonates (mokattam formation)‎, Eastern Cairo-Suez District, Egypt

الملخص EN

The exposed carbonate rocks of the Mokattam Formation in Gebels Shabrawet, Geneifa and Abu Treifiya are made up of dolosparite, pelbiosparite and dolobiomicrite.

Their original compositional and textural characteristics are greatly modified by cementation, neomorphism, dissolution, compaction, dolomitization, dedolomitization and silicification.

Both aggrading and degrading neomorphism were occasionally recorded.

Dissolution and leaching of the primary aragonitic and calcitic components of allochems and matrix resulted in the development of fabric- and non-fabric-selective porosity.

The intensity of selective and pervasive dolomitization varies throughout each of the measured sections in the studied areas.

Evidently, the diagenetic history of the studied Mokattam carbonates commenced with the eogenetic phase which witnessed an initial stage of cementation with calcite, degrading neomorphism a development of fabric-selective porosity in the marine phreatic environment.

The early cementation inhibited the effect of burial compaction during mesogenesis.

The telogenetic phase, on the other hand, involved the processes of cementation with calcite and silica, aggrading neomorphism and dedolomitization under phreatic meteoric condition.

The meteoric vadose zone, on the other hand, was the site of dissolution and leaching.

Also, the telogenetic phase involved extensive dolomitization especially in the northern part of the studied area.

It occurred in mixed marine-meteoric environments characterized by frequent intermittent intrusion of freshwater lenses during subaerial exposure, either by tectonism or drop of sea level.

Also, it is likely that dolomitization was controlled by fracturing which played an important role in flow of the dolomitizing fluid.

Generally, the relative abundance of the various diagenetic features in the studied Mokattam carbonates indicated that the diagenetic processes that occurred during telogenesis were much more effective than those occurred during mesogenesis and eogenesis.