Integrated Biostratigraphy and Sequence Stratigraphy of the Cenomanian-Turonian Successions at West Gabal Thelmet Area, North Eastern Desert, Egypt

Document Type : Original Article


Geology Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, B.O. BOX: 11884, Egypt.


The exposed Cenomanian-Turonian succession at West Gabal Thelmet area has been measured and detailed examined for its foraminiferal and macrofaunal contents. Lithostratigraphically, this succession is classified into Galala, Abu Qada and Wata formations, from base to top, and it is underlain by Malha and overlain by Matulla formations with unconformity surfaces. Twenty - two foraminiferal species have been identified, of them seventeen species are planktonics and five are benthonics. On other hand, sixty-four macro-fossil species were identified; of them, twenty-three belong to the Cephalopoda, eleven to the Gastropoda, Twenty-two to the Bivalvia and eight to the Echinoidea. The identified fauna is used, to establish two biostratigraphic schemes, one based on the foraminiferal assemblages, and the other on the macrofossils. The Integration between these two schemes is attempted, to reach a high-resolution stratigraphic scheme during the studied time interval. The foraminiferal assemblages are used, to classify the studied interval into one benthonic biozone of the Middle Cenomanian and three planktonic foraminiferal biozones: (one of the Latest Cenomanian, one of the Early Turonian; and one of the Early to Late Turonian), in addition to two barren intervals. Also, this interval is classified into seven macrofaunal biozones: one of the Middle Cenomanian; three of the Late Cenomanian; two of the Early Turonian; and one of the Late Turonian; in addition to two barren intervals intervene these established biozones. The integration between the lithologic characters, detailed field examination for the stratigraphic surfaces and the faunal biostratigraphic studies led to classify this interval into four 3rd depositional sequences bounded by five type-one sequence boundaries represented by unconformity surfaces. These four depositional sequences are two in the Cenomanian Galala Formation; one in the Lower Turonian Abu Qada Formation; and one in the Upper Turonian Wata Formation. The first and fourth depositional sequences are subdivided into transgressive and highstand systems tracts; while the second and third are represented by transgressive systems tracts only. The lowest and system tracts are missed in all the distinguished depositional sequences, due to the fast change in the relative sea level over the study area. The correlations of the recorded sequence boundaries in the studied section with those of the previous studies inside /outside Egypt were done.