الفهرس 
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Abstract
The present thesis aims to study the lithostratigraphy and sequence stratigraphy of the Middle Miocene Marmarica Formation in the Siwa Oasis. The alveolinid Borelis melo melo is considered as the index fossil of the Middle Miocene. One hundred and twenty-nine samples were collected. The amounts of Ca and Mg in carbonate samples were determined by the titration method using EDTA. Four rock samples from the three members of Naqb El-Migahhiz section were mineralogically analyzed by XRD method. The petrographic analysis was performed on 62 thin-sections. Three representative rock samples from the Marmarica Formation at the Naqb El-Migahhiz section were selected for investigation under scanning electron microscope. The lithology of the Marmarica Formation in the Siwa Oasis is dominated by dolostone, limestone and shale. The Oasis Member consists of carbonate rocks intercalating with shale. There is a high diversity in megafossils of the Oasis Member. The Siwa Escarpment Member and El Diffa Plateau Member consist only of carbonates. The main lithology of the Siwa Escarpment Member is dolostone, argillaceous dolostone, limestone, calcitic dolostone and dolomitic limestone. The boundary between the Oasis Member and the Siwa Escarpment Member is demarcated by the presence of Thalassinoides cylindrical burrows and this is observed in all the studied sections. The beds of the Siwa Escarpment Member are fossiliferous with bryozoans, echinoderms, bivalves (e.g., oysters and pectinids), and gastropods.The El Diffa Plateau Member is characterized by chalky looking. Petrographic analysis shows that the Marmarica Formation contains mud-supported microfacies and grain-supported microfacies. The dominant facies is mud-supported and most of them are highly affected by dolomitization. from microscopic analysis, there are eight microfacies representing the carbonate rocks of the Marmarica Formation in Siwa Oasis. The described diagenetic alterations of the studied carbonates include borings, burrowing, marine cementation, dolomitization, aggrading neomorphism and dissolution-precipitation in addition to late diagenetic processes which include deposition of halite and gypsum within vugs and fractures. from the contents of Ca and Mg of the studied carbonate rocks, dolomitization is considered as a major diagenetic process that affected the carbonate sediments of the Marmarica Formation at Siwa Oasis. The mineralogical analysis performed by XRD on four rock samples revealed the presence of dominant dolomite in addition to some calcite and other non-carbonate minerals such as quartz, anhydrite and halite. The studied rocks were deposited on ramp and this is inferred by the absence of genuine reefs either along the southern outcrop in Siwa Oasis or the coastal exposures at Salum. The studied microfacies includes inner ramp and mid ramp facies. The studied Marmarica Formation in Siwa Oasis comprises three third-order depositional sequences and two sequence boundaries of type 1 and type2, respectively.