SEQUENCE STRATIGRAPHIC ANALYSIS OF THE
CONIACIAN-SANTONIAN SEDIMENTS (MATULLA AND
THEMED FORMATIONS), SINAI, EGYPT.
FAROUK M. EL-FAWAL
Geology Department , Faculty of Sciences,Suez Canal University, Ismailia-41522,Ismailia, Egypt |
Field and microlithofacies sedimentological studies carried out on the Coniacian-Santonian sediments of Sinai including Matulla Formation of Ghorah (1961) and Themed Formation of Zico a.o. (1993) have indicated that they were deposited as a mixed siliciclastic-calcareous succession on a ramp which was dipping very gently toward the north. The regional and stratigraphical distribution of the examined sediments have revealed a cyclic sedimentary history that included depositional phases commonly succeeded major tectonic events that affected the ramp during the development of the Syrian Arc folded belt in north Sinai.
The examined succession was found to include three third-order depositional sequences (SQ-I, SQ-II and SQ-III). The lowest SQ-I unconformably overlies the Turonian Wata Formation (Type-I sequence boundary) due to the late Turonian-early Coniacian tectonic event. It displays considerable thickness in the south while it is absent in the north. It is represented by siliciclastic facies with some calcareous units. At the closing times of SQ-I, several folded uplifts and SW-ward basin tilt took place at the end of the middle Coniacian in the northern parts of the SQ-I ramp. At this stage, a phase of a marked sea level drop prevailed associated with subaerial erosion (Type- I sequence boundary). The eroded detritals were redeposited as shoal facies(LST-2 of SQ-Il) above the submerged northern domes whereas the lowlands in between were flooded by deep water. During the transgressivc phase of SQ-II (TST-2), the rates of both basin subsidence and the basin filling were in a status so that the accommodation did not extend beyond the latitude.; 29º N, submerging this area by relatively deep water and producing facies of significant bathyrnetry. At the end of SQ-II, the early Santonian uplift resulted in a northward sea retreat where frequent criteria of land emergence were recorded all over Sinai (Type-I sequence boundary). SQ-III started by an extensive marine transgression that drowned all parts of Sinai. The early facies (LST-3) display regular siliciclastic-calcareous composition in most parts of Sinai. The transgressive phase ([SI -3) is represented by outer shelf facies in the north whereas deep subtidal and shelf lagoons dominated the south. The dolostones and sandstone with phosphatic remains are common in the HST-3. A major late Santonian tectonic event took place at the end of SQ-III which led to a northward withdrawal of the Santonian sea closing the history of the examined succession in Sinai. The tectonic event resulted in a SW-ward tilt reflected in the angular unconformable relation t (Type- I sequence boundary) with the overlying Campanian-Maastrichtian Sudr Chalk reported all over northern Sinai.
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