Abstract The Sirt Basin is one of the youngest sedimentary basins in Libya and covers an area of approximately 600.000 km² in north central Libya. It is located on the northern margin of the African plate, with approximate coordinates 14°00`- 20°00`E and 28°00`-31°00`N. The Late Jurassic-Early Cretaceous as Sarir Sandstone in the Sirt Basin evolved as a consequence of the interplay between global eustasy and regional tectonics. As Sarir Sandstone of the eastern Sirt Basin is composed mainly of sandstones and shales resting unconformably on a basement complex of igneous and metamorphic rocks. It is unconformably overlain by the Upper Cretaceous sediments of Maragh, Lidam and Etel formations. It has been subdivided into three members. The upper member consists mainly of sandstones with intercalations of siltstones and shales of variable thickness. The middle member consists of shale and silty shale. The basal part of the formation, which rests directly on the crystalline basement represents the lower member. It is comprised of sandstone with subordinate intercalations of siltstones and shale. Two main facies have been recognized on the basis of lithological features and types of stratifications: which consist mainly of shale and intercalation of silt and sand. The Middle Shale Member consists mainly of shallow lake deposits, containing black shale facies. Continental Fluvial Deposits represent most of the cored interval and it belongs to the Upper as Sarir Sandstone. These facies have been subdivided into braided and meandering lithofacies: The braided depositional system, has been recognized in three different intervals of the studied cores; classified as subfacies (1), subfacies (2) and subfacies (3). The meandering depositional system, represents three sub-environments including point bars, abandoned channels and over-bank deposits. The reservoir characteristics of these sediments are studied on the basis of porosity, permeability and reservoir zonation. The reservoir quality of As Sarir Formation is largely controlled by primary sedimentary features associations, which were shaped by the depositional environments. Meandering Lithofacies are formed from continuous sand successions and show good porosities, up to 18.51%, and permeabilities up to 125.5mD. The Braided Lithofacies also show good reservoir quality, but the effective porosity and permeability are lower, because of associated shales. The most important diagenetic features responsible for a reduction in reservoir quality are those resulting from compaction, cementation, and the diagenesis of clay minerals.
صلاح الدين محمد الوحيشي (2014)

Abstract Seven geological sections have been examined and sampled with emphasis on sedimentological & diagenetic processes within Abu Ghaylan Formation and the contact relationships with the underlying Abu Shaybah and overlying Kiklah Formations. Based on current detailed field loggings and microscope investigations, 10 facies are recognized within Abu Ghaylan Formation. The lowermost succession characterised by an overall transition from continental fluvially dominated deposits of the Abu Shaybah Formation into transitional to marginal marine, tidal flat deposits of the Abu Ghaylan Formation upward. The transitional nature of this lowermost part succession is demonstrated by interbeddings of claystone, sandstone and fossiliferous facies arranging in coarsening up cycle, in which most probably deposited in estuary / beach environment.The Abu Ghaylan Formation generally wedges laterally eastward and exposes intermittently east of Wadi Ghan area resulting of syngenetic uplift of Wadi Ghan area followed by erosion (ElHinnawy & Cheshitev, 1975). A slightly earlier uplift and greater erosion in a westward sloping basin of deposition near the close of the Early Jurassic and Early Cretaceous times is suggested by Fatmi & Sbeta (1991). The current study reveals that several exposure surfaces are demonstrated within Abu Ghaylan Formation suggesting uplifting and erosion episodes interrupted Abu Ghaylan Formation, where a restricted distribution of Abu Ghaylan may suggest a local tectonic overprint.Although the overall impression is that the base beds of Kiklah Formation starts with sandstone and red clay beds as channel infill deposits above Abu Ghaylan carbonate unit with surface of unconformity, however, based on current close investigation, a sequence characterized by interbeddings of carbonate and greenish clay overlying Abu Ghaylan Formation with surface of unconformity and gradationally overlain by sandstone beds should be introduced as separate unit attributes to Kiklah Formation.The current study emphasizes and supports a solution collapse origin for the breccias and introduces better insight into architecture and geomorphology of the breccias bodies that are exposed in the area of study. The dissolution of evaporites is considered responsible for all breccias development in this stratigraphic interval. According to the occurrence mode of breccias, the breccias intervals have been divided into two main parts; a lower section of strata that contains collapsed paleocaves and an upper section of strata that is deformed to varying degrees due to the collapse and compaction of the section of paleocave-bearing strata. The sharp flat base, inverse grading, V-shaped/ sag structures and irregular undulating top of brecciated bodies are recognized within Abu Ghaylan Formation and typically characterize solution collapse processes. Based on field study and architecture relationships, five distinctive karst facies are recognized in the area of study.The early diagenetic genetically related processes probably interrupted the deposition of Abu Ghaylan Formation is a most possible assumption for the origin and timing of breccias formation.
أحمد أبوبكر الحلو (2015)

Abstract The basaltic Intrusions of the Central Jabal Nafūsah Foothills which extend from NW Wādi Zāret to NE Wādi Ghān Dām are part of the latest stage of Gharyān Volcanic Province (GVP). These intrusions are classified on basis of their shape and mechanism of emplacement into four kinds of volcanic bodies. These are; sheets (dykes and a sill), dykes associated with volcaniclasts, volcanic cone and lava mounds. Generally, the dyke emplacements are restricted only to the area between Wādi Zāret to Abū Ghaylān, while the other forms extend from Rās al Mazūl Dome to Wādi Ghān Dam. The more differentiated rocks are restricted to the area between Rās al Mazūl Dome and Wādi Ghān. Farther west towards Wādi Zāret, ultramafic xenoliths and magnesium-number increase, suggesting closer proximity to the source. The rocks are essentially alkaline with within Intraplate signatures. They straddle the composition from picrites, basanites, alkali basalts through hawaiites, mugearite to benmoreites with a compositional gap between the last two types. Generally, the phenocrysts are represented by foresteritic olivine, Cadiopsidic pyroxene, magnesiotaramitic amphibole, plagioclase, K-feldspar and titanomagnetite. The chemical composition of the mafic minerals indicates that they are high pressure phenocryst phases. The most primitive picrites satisfied the criteria of primary mantle melts. The rocks are generally, enriched in LILE suggesting an enriched mantle source. The studied rocks were grouped into five groups based on incompatible trace element ratios; Group-A includes picrite, basanites and hawaiites, and Group-B includes picrite (Z-3), basanites , alkali basalts, and hawaiites, while Group-C is formed of hawaiites, Group-D is composed of mugearite and Group-E is made up of benmoreites. Picrites and basanites of these rock have high Mg-number (>0.64), high Cr and Ni contents and strong light rare earth element enrichment, but systematic depletion in Rb, K and Ba relative to trace elements of similar compatibility in anhydrous mantle. Alkali basalts and more differentiated magmatic rocks have lower Mg-number and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe–Ti oxide, amphibole and plagioclase. The variation in the concentrations of major, trace, rare earth elements, and incompatible element ratios in the rock samples demonstrate the heterogeneous character of their source region. Such heterogeneity can be interpreted by the involvement of a heterogeneous mantle reservoir to different degrees of partial melting. The REE data require residual spinel stability peridotite field in the source and constrain the melting process of Group-C and Group-D to 2% to 3.5% degrees of melting respectively, Group-A and Group-B both to 5% degree of partial melting while Group-E to 10% degree of partial melting of spinel lherzolite xenoliths of Al Ourban area. Mass balance modelling of the major suggests two possible FC scenarios; Derivation of basanites and hawaiites of group-A from G-3 picritic parental magma. Derivation of Group-D and Group-E was also possible from these basanites. Derivation of basanites of Group-B from Z-3 picrite parental magma and simultaneous derivation of G-4 and QJ-1 alkali basalts from Z-3 picrite parental magma. V Simple mass-balance calculations suggest that the melting assemblages of picrites and basanites consisted of forsteritic olivine, diopsidic clinopyroxene, Ti-magnetite. While the alkali basalts and more differentiated magmatic rocks, mass-balance calculations suggest that the melting assemblages consisted of sodic plagioclase, magnesiotaramitic amphibole, diopsidic pyroxene, Ti-magnetite, K-feldspar with sub amounts of apatite and sphene.
سمية عون (2015)