الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 201 |  |  |
| | | from | 201 | | |
Abstract
The thesis deals with a study of the Middle–Upper Eocene rocks of the northern plateau in the Bahariya Oasis. The studied sections representing this area consist of mixed carbonate-siliciclastic sediments. This study is based on field work and study of the sedimentological and stratigraphic characteristics of the Middle–Upper Eocene sediments in order to build a depositional model for the ramp that forms the northern plateau of the Bahariya Oasis.
In order to reach our objectives of this study, four representative sections were measured, and all field data were collected from rock units, different geological and sedimentary structures, and a detailed stratigraphic description of the sections. This is in addition to collecting rock samples and making and analysing thin sections using a polarizing microscope in order to identify the different facies, as well as the determine different diagenetic process.
Through field work and the study of thin sections, 21 different facies were identified in the northern plateau of the Bahariya Oasis. They were grouped into five facies associations, and they were described as follows: (1) mid ramp facies association dominated by Assilina and Operculina, (2) ramp crest facies association distinguished by Nummulites banks and Ostrea banks, (3) shoreface–foreshore facies association, (4) lagoon facies association and (5) tidal flat facies association.
The studied area was affected by several diagenetic processes: marine digenesis including micritization and marine cementation, meteoric diagenesis including dissolution, cementation and syntaxial overgrowth finally burial diagenesis including compaction, fractures, and dissolution seams, silicifications and dolomitization. The primary porosity recorded of the Middle–Upper Eocene succession enhanced by dissolution processes. The main pore types observed in the studied successions are intergranular, intragranular, biomoldic, solution seams and fracture porosity. The porosity ratio decreases in the deeper facies. Compaction and cementation are the main reasons for porosity reduction.
The Middle–Upper Eocene successions is subdivided into four third-order transgressive–regressive sequences. Sequence S1 is assigned to the Qazzun Formation. It is a carbonate dominant mid to inner ramp prograditional regressive sequence (HST). Sequence S2 is mixed silisiclastic carbonate sequence of the Lower Member of the Hamra Formation. It is based by sequence boundary SB1 and capped by SB2. Sequence S2 is marks facies dislocation from mid ramp and ramp crest in the TST to lagoon facies in the HST. Sequence S3 is a mixed siliciclastic- carbonate sequence located at the lower part of the Upper Hamra Member. It is formed of four fourth-order cycles separated by flooding surfaces demarcated by Glossifungites Ichnofacies firmground (S3-FSs/GS). Sequence S4 is a mixed siliciclastic-carbonate package marks the upper part of the Upper Hamra Member at El-Behour and El-Qara El-Hamra sections. It consists of three fourth-order (transgressive–regressive) parasequences bounded by flooding surfaces demarcated by firmground suites of the Glossifungites Ichnofacies (S4-FSs/GS).
The accumulation of the studied carbonate ramp sediments was controlled by a set of interrelated variables. In the studied Middle–Upper Eocene successions Nummulites flourish in oligotrophic conditions with nutrients deficient. Nummulites may represent a good substrate for encrusting organisms but it rarely to moderate to be encrusted by bryozoans, oysters, serpulids and benthic burrowing organisms like echinoderms, bivalve and gastropods are spread in mid ramp/ ramp crest (bank) setting. Nummulites tests shape and size play important role in the environmental interpretation. The large and flat Nummulites tests in association of Assilina and Operculina deposited in deeper environment mid ramp (mesophotic–oligophotic zone). Small and lenticular Nummulites tests are located in shallower setting back bank/ inner ramp/ Lagoonal setting (mesophotic–euphotic zone). Nummulites accumulate due to wave and current actions with para-autochtonous to allochtonous origin.