ASPECTS OF CHERTIFICATION IN SOME LOWER EOCENE CARBONATE ROCKS IN EGYPT

Abstract

The origin of chert in the sedimentary succession of Egypt is less certain and much debatable. This study attempts to shed some light on the origin of bedded and nodular chert, the source of silica and the depositional environment of chert and carbonate host rocks.Mineralogical, petrographical and chemical examinations were carried out on some selected samples from the Lower Eocene Thebes Formation at three different localities; southwestern Sinai, Quseir-Safaga district and the Central Nile Valley.

Field observations have shown that the degree of chertification lS variable in the three studied areas. Generally, chertification effect is highly pronounced in the carbonate rocks of Gebel Duwi compared with the other two areas. However, chert occurs in various forms; nodular chert, bedded chert and quartz geodes. Both the nodular and bedded cherts are common in Gebel Duwi section whereas the latter is abundant in southwestern Sinai area. Meanwhile, the abundance of chert in the Central Nile Valley sections is less than both the Duwi and southwestern Sinai areas. Both the nodular and bedded cherts are present, but chert nodules are abundant at Gebel Shaghab whereas bedded cherts are common at Gebel Sheikh /sa.