The volcanic rocks of Bahariya Oasis, Egypt U. A. R.

Abstract

The types of volcanic rocks in this region can be divided into three main varieties, mainly an amygdaloidal basalt which is the oldest extruded lava followed by the intruded dolerite. Later another period of volcanicity took place and the olivine basalt porphyry was extruded covering the amygdaloidal basalt in Gebel Hafhuf and the small basalt hill nearby, and helped to cover and preserve in these two hills the layer of amygdaloidal basalt below it, while in Gebel Maesera and Mandisha where this basalt porphyry was not represented caused the lower layer of amygdaloidal basalt to be also absent and probably leached. As to the age of these volcanic rocks there is no doubt that it is post-cretaceous. The Eocene being not represented in this part of the oasis leads the writer to conclude that the volcanic rocks are probably of Oligocene age specially that this period of Tertiary volcanicity was recorded in Egypt (Tosson 1954 andRittmann 1954). The eruption was at several steps and took a long period. The variation in types of rock and alteration indicate that the formation of the volcanic rocks in this area took place at several times and more or less during long periods of volcanicity.