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Abstract
The present work is a detailed petrographioal and geochemical study of the various lithologies of the Hammamat northern exposures at the type loca.lity”Wadi Hammamat” between latitudes 25°55’ and 26° 2t N. The Hammamat sediments represent an important stratigra phic unit in the basement oomplex of Egypt. This olastio sequence oo~sists of oonglomerates, sandstones (greywaokes) and siltstones. All of these sediments are immatu;re and poorly sorted.
Sampling ot the Hammamat major ooourrenoe at Wadi nUrn-Had” , ” El-Sh1hym1ya- Urn Hargel” and ”El-Sh1hym1ya Um Marha” was oarried out to represent the various root units of the Hanunamat sediments. The studied seotion orosses the major Ha.mmnrnat ooourrenoe in WSW-ENE dire ction. It measures about 2175 metres, and was divided into six units.
2- The Hnmrnamat conglomerates studied in the present work, usually occur as massive beds with regular and distinot bedding planes; and can be ditferentiated into two units. The upper one is oomparable to the Um-Had
conglomerate member of Noweir (1969), and reaches about 895 meters in thickness. It lies close to oore of the plunging synclinal fold of the major Hammamat occurrence. The lower unit measures about 240 metres in thickness,
and it seems to be gently affected by contact me~or phism, due to the intrusion of the Um-Had granitic pluton, hence the different ingredients of the rocks are oriented in a flattened manner. The feature is also accompanied
by the development of some minerals such as green biotite, clinochlore and magnetite.
The studied greywackes of the Hammamat sediments are represented by three units. They ocour as massive beds w~~h regu1ar and d~s~~o~ bedd~g p~es. Cross-bedd~g
and lamination are observed only in the upper part of the upper unit. The upper unit reaches about 180 metres in thiokness. This unit together with the upper sil tstone beds constitute the Um-Hassa greywaok~ member of Noweir(1969). They occupy the oore(1nlier) of the plunging syncline of the main occurrence of the Hammamat sediments. The upper greywack~ unit is ~hare.oter1zed
by red oolour in its upper part with subordinate oong lomerate, and a green colour in the lower part with subordinate greyish siltstone. The middle greywacke unit is grey in colour and reaohes about 410 met~. in thickness. It oomprises subordinate grey siltstone beds at the base. The lower ereywnoke unit measures about 190 metres in thickness. This ~~it together with the lower conglomerate unit represent the limbs (outlier)
of the plunging syncline. It seems to be more affeoted by oontact metamorphism due to the intrusion of the Urn-Had granitic pluton. The different ingredients of
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this rock unit are texturally affected with the deve lopment of some minerals such as green biotite, tremolite- actinolite, clinochlore and disseminated magnetite.