Geology and evolutionary stages of the Late Precambrian Hammamat sediments at Gebel Um Tawat, North Eastern Desert, Egypt

Abstract

The Um Tawat Late Precambrian immature molasse-type Hammamat sedimentary rocks, located in the Northern part of the Eastern Desert of Egypt, were deposited at the late stage evolution of the Pan-African Orogeny. The Um Tawat molasse sediments are mainly derived from Dokhan volcanics and rest unconformably on these volcanics. They are intruded by the younger granites of Sala’at El-Belih granites and Gebel Gattar batholith. Hammamat sediments consist of repeated cycles of conglomerates, sandstones, siltstones, and minor mudstones deposited in an inter-mountainous basin by braided stream and alluvial fan regime constituting a stratigraphic section of about 500 m thick. Petrographically, the conglomerates are of polymictic type. Sandstone could be termed arkosic greywacke and shows ripple marks and in some places cross bedding. Siltstone is characterized by clear lamination and graded bedding. Mudstone is characterized by very fine grains of silt and clay size particles. The evolutionary stages of the study area is divided into five stages: (1) compressional regime resulted in the formation of the metavolcanics and metagabbro-diorite complex; (2) tension and relaxation crustal regime and uplift of the old basement forming G. Dokhan; (3) relaxation period, weathering, and erosion processes of the Dokhan volcanics formed the Hammamat molasse-type sediments; (4) tensional regime or weak rift-like processes led to the eruption of the younger granites and (5) regional compressional deformation subjected to the Hammamat sediments. This phase form G. Um Tawat and forming one regional open anticline fold whose fold axis is trending N47°E–S47°W and plunges 5° toward SW.