Carbonate Diagenesis and Rifting in the Gulf of Suez

B. H. Purser, F. Orszag-Sperber, D. M. Aissaoui

Lower Miocene carbonates of the northwest Red Sea and Gulf of Suez have been deposited on a series of structural blocks where bathymetric relief, created by early rift tectonics, has strongly influenced both sedimentation and early diagenesis. Initial submarine cementation by fibrous calcite and aragonite strongly affects slope deposits, destroying most primary porosity. It was followed by several phases of regional dolomitization whose isotopic signatures suggest nonmarine influence. Undolomitized sediments are the exception. An intense dissolution is the principal agent determining petrophysical qualities of the series. Nonmarine sparitic cements are not important, indicating the dissolved carbonate has been flushed out of the system. Finally, large-scale sulfate replac ment affects dolomites adjacent to the middle Miocene primary evaporites. These secondary sulfates are associated with a zone of calcitized dolomite (dedolomite).

This diagenetic activity obviously reflects repeated changes in the composition of interstitial waters. Its exceptional intensity is explained by the contemporaneous basin relief; the presence of numerous subparallel blocks has resulted in the development of separate bodies of water relating to both meteoric influx and evaporation. Together with normal marine waters, these fluids of variable density have penetrated the intervening sedimentary platforms via the numerous slopes. It is clear that multiphased carbonate diagenesis is one of the many expressions of early rifting.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.