FACIES ARCHITECTURE AND SEQUENCE STRATIGRAPHY OF THE CONIACIAN-SANTONIAN MIXED SILICICLASTIC-CARBONATE MATULLA FORMATION, WEST CENTRAL SINAI, EGYPT

In the Gulf of Suez region, the most prolific oil fields in Egypt, the sediments of the Coniacian-Santonian Matulla Formation contain both reservoir and source rocks. Outcrops of the Matulla Formation at west central Sinai (eastern side of the Gulf of Suez) provide a useful analog to these subsurface reservoirs by providing insight into the facies heterogeneity resulted from the interbedding of siliciclastic and carbonate rocks. The Matulla Formation was studied in four outcrops in west central Sinai (Wadi Matulla, Wadi Budra, Gebel Ekma, and Gebel Qabaliat), to determine facies associations, depositional environments, facies stacking patterns and constrain a high resolution sequence stratigraphic framework.

The study revealed that the Matulla Formation is composed of wave and tide influenced mixed siliciclastic-carbonate rocks interbedded with some oolitic ironstone beds. Detailed facies analysis suggests deposition in coastal and shallow marine environments. The clastic facies are represented by conglomerate and planar laminated, cross bedded, bidirectional cross bedded, ripple cross laminated, flaser bedded, and massive sandstones, in addition to green sand, siltstone and shale. The carbonate facies are composed of lime-mudstone, skeletal and non-skeletal wackestone, packstone, and grainstone, as well as floatstone, rudstone and dolostone. Vertical and lateral facies successions revealed that the Matulla Formation is composed of three 3^rd order depositional sequences made of up higher frequency 4^th and 5^th order sequences and cycles. The diagenetic alterations present, exerted a strong effect in the reservoir quality and heterogeneity of the sandstones and carbonates of the Matulla Formation, and are affected by relative sea level change.