LITHOSTRATIGRAPHY, PETROGRAPHY AND DIAGENESIS OF UM BOGMA FORMATION IN TALET SELEIM AREA, SOUTHWESTERN SINAI, EGYPT

A detailed geologic map of Talet Seleim area was prepared. Ten stratigraphic sections of the Lower Carboniferous Um Bogma Formation were studied and used to construct a composite section and panel diagram The Um Bogma Formation could be subdivided into a lower siltstone-dolostone member, a middle siltstone-mudstone-dolostone member and an upper dolostone member. These rock units have unconformable contacts and show marked lateral variations in thickness and minor changes in lithology. The argillaceous rocks are texturally classified as mudstone, sandy mudstone, siltstone and sandy siltstone (in decreasing order of abundance). The carbonates, on the other hand, are classified as dolosparite and dolomitized intra-biosparite. The rocks display several primary sedimentary structures; the most common of which are various types of bedding, lamination and biogenic features. Also, the succession is affected by joints, faults and small scale folds and contains gypsum veins and clastic dykes. Diagenesis played a major role in modifying the original textural and, especially, compositional characteristics of the rocks. It involved compaction, cementation, replacement, alteration and dissolution. The extent of each of these processes varied markedly among the different lithologic types and rock units as well as the locations in Talet Seleim area. Most of the post-depositional processes commenced during the mesogenetic phase of diagenesis and became more profound during epigenesis.