Master Thesis Petrography and Geochemistry of Gargaresh Formation from Tajoura to Ras Jdeir, Jifarah plain, NW Libya

Abstract

III ABSTRACT The present work attempts to characterize the petrography and geochemistry of the Quaternary calcarenite (Gargaresh Formation) along the Mediterranean Coast from Tajoura to Ras Jdeir, Jifarah plain, NW Libya. The Gargaresh Formation can be subdivided into two members: Kaam Member (upper member) and Karrot Member (lower member). Both of these members are detected in the studied coast. The Karrot Member on its cliffs on the shoreline of the study area reaches its maximum thickness in the area between Tripoli and Sabratah. It diminishes towards the west of Sabratah. According to texture, morphology, sedimentary structure and fossil content, the Karrot Member could be divided into four units. Except unit 1, all other units are only detected from station no. 2 (Tripoli) to station no. 7 (Sabratah). The Kaam Member is only detected in the area between Tripoli and Sabratah. It is represented by one unit. Geochemically, the major oxides CaO and MgO are the main constituents of the calcite. SiO2 is mainly in the form of quartz. Sometimes a high quotient of SiO2 together with the oxides; Al2O3, K2O and partly of Na2O, TiO2 and Fe2O3 are essentially allocated within the structure of the feldspars and clay minerals. Part of Na2O and the content of Cl belong mainly to halite. Sr, Pb and REE are basically controlled by the carbonate fraction, while Ni, Co, Cu and Zn are strongly correlated with Al2O3. Th and U are positively correlated with Zr suggesting that they are contained in zircon. The prevailing well oxidizing coastal environments are well expresses by the low authigenic uranium and low Cu/Zn, Ni/Co and U/Th ratios. Karrot Member shows more or less flat REE pattern with positive and negative Ce anomalies (ΔCe: 0.68 to 1.45), while Kaam Member shows convex REE pattern with negative Ce anomalies ((ΔCe: 0.86), indicating Kaam Member (upper member) of aeolian origin and Karrot Member (lower member) of marine origin. In Karrot Member, ΔCe values are negatively correlated with Pb in agreement with shallow marine depositional environments of Karrot Member.