Original paper

Sequence stratigraphy of the lower Upper Cretaceous (Upper Cenomanian - Turonian) of the Eastern Desert, Egypt

Wilmsen, Markus; Nagm, Emad

Abstract

Four Upper Cenomanian - Turonian sections of the Eastern Desert (Egypt) forming a 130-km distal-proximal transect at the southern margin of the Neotethys from Wadi Araba in the north to Wadi Qena in the south have been studied in great detail applying an integrated stratigraphic approach. The predominantly shallow-marine successions comprise the Galala, Maghra El Hadida and Umm Omeiyid formations which represent a mixed carbonate - siliciclastic ramp setting developing in response to the great early Late Cretaceous transgression. Sequence stratigraphic key surfaces and systems tracts have been identified and tracked across the transect, resulting in a detailed sequence stratigraphic subdivision. Six sedimentary unconformities (Cenomanian sequence boundaries SB Ce 4 and 5, and Turonian sequence boundaries SB Tu 1-4) have been recognized and tracked laterally, defining five 3rd-order depositional sequences (DS ED 1-5). DS ED 1 is of latest Middle to mid-Late Cenomanian age and characterized by the deposition of the lagoonal Galala Formation on top of continental deposits (Malha and Naqus formations). The basal sequence boundary of sequence DS ED 2 is represented by the Galala - Maghra El Hadida formational contact in the north (Wadi Araba) and a stratigraphic gap within the Galala Formation in Wadi Qena (Metoicoceras geslinianum Zone missing). This major unconformity (SB Ce 5) can be precisely dated as mid-Late Cenomanian (Neolobites vibrayeanus to Metoicoceras geslinianum zonal boundary). DS ED 2 comprises the mid-Upper Cenomanian to Lower Turonian and includes a major maximum flooding surface within the lower Lower Turonian. It is capped by a conspicuous unconformity in the Lower - Middle Turonian boundary interval (SB Tu 1), forming the base of DS ED 3. This lower Middle Turonian sequence comprises a part of the middle portion of the Maghra El Hadida Formation in Wadi Araba and the lower part of the Umm Omeiyid Formation in Wadi Qena. DS ED 4, delineated at the base by the mid-Middle Turonian SB Tu 2, is represented by a portion of the upper part of the Maghra El Hadida Formation in the north and the middle part of the Umm Omeiyid Formation in the southern part of study area. Its terminal unconformity, lower Upper Turonian unconformity SB Tu 3, and the Upper Turonian unconformity SB Tu 4 at the base of the overlying Matulla and Taref formations (uppermost Turonian?, Coniacian - Santonian) define the last Turonian sequence, DS ED 5. A sequential calibration of the sequence boundaries identified in the Eastern Desert shows a contemporaneity to equivalent surfaces in Sinai, Jordan, Tunisia, Europe, and the Arabian Plate, thus strongly supporting an isochronous formation of Cenomanian - Turonian unconformities and intercalated depositional sequences by eustatic sea-level changes.

Keywords

cretaceoussea-level changesunconformitiesdepositional sequencesinter-plate correlation