DEPOSITIONAL MODEL AND SEQUENCE STRATIGRAPHY OF THE MIDDLE - UPPER EOCENE SUCCESSION, NORTHERN PLATEAU OF THE BAHARIYA DEPRESSION, WESTERN DESERT, EGYPT

This study aims to reconstruct a depositional model and establish a sequence stratigraphic framework of the exposed Middle-Upper Eocene succession along the northern escarpment of the Bahariya Depression, Western Desert, Egypt. This has been done via field observation and microscopic investigation of the representative rocks. Eighteen sedimentary facies are identified and grouped into five facies associations that are attributed to middle ramp, ramp crest, shoreface/foreshore, lagoon and tidal flat depositional environments. The stacking pattern of the recognized sedimentary facies enables us to subdivide the studied stratigraphic succession into three 3^rd order depositional sequences (S1, S2 and S3) bounded regionally by subaerial unconformities corresponding to sea-level falls. These depositional sequences have a long-term transgressive-regressive evolution, which was mainly controlled by eustatic sea-level changes, tectonics and sediment supply. Sequence S1 includes the carbonate-dominated middle to inner ramp of the Qazzun Formation. Sequence S2 comprises the mixed siliciclastic-carbonate middle to inner ramp of the lower part of Hamra Formation. It is made up of two medium-scale sequences separated by a transgressive surface. Sequence S3 represents the mixed siliciclastic-carbonate inner ramp of the upper part of Hamra Formation. It consists of a number of shallowing-upward small-scale cycles that stacked to form four medium-scale sequences bounded by wave ravinement surfaces. The recorded small-scale depositional cycles were a result of an interaction of short-term climatic and sea-level variations and changes in sediment supply.