CONTRIBUTION TO THE PETROLOGY OF LOWER EOCENE
ROCKS, ELQUSSAIMA AREA, NORTHEAST SINAI, EGYPT
BOTHAINA M. MOUSSA
Desert Research Center, Cairo, Egypt.
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Thirty-seven samples of the Early Eocene rocks (Thebes Fm) and Upper Esna Shale were collected and analyzed for major elements; 13 samples for some trace elements; 20 samples for petrographical study and 7 water samples for hydrochemical analysis.
The petrography reveals 9 rock types affected by cementation, recrystallization, dolomitization, silicification and ferrugination. Cementation and recrystallization are more abundant in Thebes Fm. Moreover, mixed phreatic? marine water caused calcitization and recrystallization of both matrix and skeletal particles. These rock types were deposited in sublittoral environment with marine-phreatic effect. The Thebes can be subdivided into three zones; 1) Dominated by packed biomicrite; 2) sparse foraminiferal biomicrite, and 3) mixed combination of the two.
From the geochemical studies, [he 2nd zone has low Sr and Ba contents than the other two zones. The presence of Fe-oxide and MgO in the 3rd zone in higher amounts indicates the shallowness of the environment and nature of dolomitization. Also, the high Ba content in the 3rd zone is associated with the presence of gypsum. The Upper Esna Shale Fm is differentiated from the shale in the Thebes Fm by the high
TiO2, Na2O and P2O5 contents.
The hydrochemical characteristics of the fractured limestone of the Thebes Fm indicate fresh water for springs and brackish for hand dug wells; arid one water type (chloride-Na).
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