مشرف منتدى جيولوجيا البترول
عدد المساهمات : 108
تاريخ التسجيل : 20/03/2010
العمر : 31
|موضوع: REGIONAL TECTONIC SETTING 23rd نوفمبر 2010, 11:10 pm|| |
Regional Tectonic Setting During Precambrian period, the high grade poly-metamorphic and granitoids west of the Nile (Fig.4), are part of the pre-Pan-African, while the Basement east of the Nile comprises the Pan-African meta-volcanic, meta-sedimentary ophiolite and related granitoids assemblage of Nubian shield, but the rocks of the late Archean occur in a limited Basement Complex in the surrounding of Jebel Uweinat (Schandelmeier et. al., 1987). Thus, the Pan-African tectono-thermal event was dominated during the Precambrian.
During the late Proterozoic, the Central African Shear Zone was initiated and can be traced from Cameroon, through Central Africa, Chad, to North Kordofan in Central Sudan; and probably further into the Red Sea in NE Sudan Fig. (4); thus, representing one of the major shear zones of lithosphere weakness in Africa (Schandelmeier et. al., 1987).
The extensional tectonics related to the differential opening of the Atlantic and the Indian Ocean, lead to the formation of Central and Southern Sudanese rift basins; such as Southern Sudan rift, White Nile rift, Blue Nile rift, Atbara basin and Humar basin. These rift basins are considered as a part of the Central African rift system (Schull, 1988). During the Late Cretaceous the differentiation of the NE African plate increased, indicating the beginning of the Red Sea rifting.
Two pairs of E-W trending uplifts and troughs, which include: (1) The Third Cataract Arch/Selima-Toshka Trough and (2) the Gebel Uweinat-Bir Safsaf-Aswan Uplift/Kom Ombo graben (Thurmond et. al.,2004). These Two pairs of E-W trending uplifts and troughs have been active since Early-Mesozoic time; and led to the formation of the Nubian Swell in southern Egypt and northern Sudan(Thurmond et. al.,2004) Fig. (4).
In the North, and NW Sudan and SW Egypt, the Paleozoic-Mesozoic sediments consists mainly of fluvial strata intercalated with deltaic and shallow marine sequences, except the sediments of the Upper Carboniferous and Permotriassic to Lower Jurassic which consist of glacial and fluvial sediments, respectively (Klitzsch and Wycisk, 1987; Nafi, 1997; Nafi and Abdullatif, 2003; Nafi et al., 2005; Nafi and Abdullatif, 2007; Nafi et al., 2009; Nafi et al., 2010). A regional stratigraphic correlation across NE Africa is shown in Figure (5).
Klitzsch and Wycisk (1987) divided the so-called “Nubian Strata” of NW Sudan and SW Egypt to three cycles and more than 20 formations. Klitzsch and Squyres (1990) concluded that the term “Nubian Sandstone” is unjustified from both the sedimentological and stratigraphical points of view. This is because the term “Nubian” has been used in NE Africa to describe strata of different ages and environments. The subdivisions of these formations are based on stratigraphical and Paleontological evidences, fieldwork and fits logically in the regional framework.
I. The Lower cycle expands from Cambrian to early Carboniferous time and consists of Karkur Talh, Umm Ras, equivalent of Tadrat-sandstone of Libya and Wadi Malik formations.
II. The middle cycle expands from the late Carboniferous to early Jurassic time and consists of Northern Wadi Malik and Lakia formations.
III. The Upper cycle expands from late Jurassic to Tertiary time and consists of Gilf Kebir, Wadi Howar, Kababish, Wadi Milk and Jebel Abyad formations.