Cenomanian–Turonian facies, sequence stratigraphy and sea–level changes from east–central Sinai (Egypt)

Abstract

The widely exposed Cenomanian–Turonian successions in east–central Sinai display well–marked vertical and lateral changes in lithology, biofacies and depositional sequences. Three sections were studied (from northeast to southwest: Gebel Themed, Sheikh Attiya and Gebel Shiti, respectively) to document sequence stratigraphy. Twenty–four microfacies types grouped into nine lithofacies associations ranging from peritidal to mid– to outer ramp settings were identified. These microfacies reveal a general shallowing trend towards the southwest (Gebel Shiti section) in a mixed siliciclastic/carbonate ramp, whereas the northwest (Gebel Themed section) is marked by a deeper carbonate–dominated regime. The Cenomanian–Turonian succession is divided into six third–order depositional sequences (SD1 to SD6) that are bracketed by basin–wide sequence boundaries (SB AIB to SB Tu3) of varied time span and marked by vertical changes in lithofacies, microfacies and faunal content. Within these depositional sequences, six maximum flooding surfaces are also recorded. In most depositional sequences, the absence of lowstand and falling systems tract are marked, possibly as a result of the lack of accommodation space due to the proximal position of the studied sections. The identified sequence boundaries are also compared with those identified in Egypt, Jordan, Tunisia and the Arabian Plate. The present sequence boundaries match with those documented from the Arabian and African plates as also with the eustatic sea–level falls. However, for those noted across the Cenomanian/Turonian boundary and during the early–middle Turonian transition, there is discordance, possibly due to the influence of regional tectonics, that caused major hiatuses and amalgamated several of them. The chronostratigraphic assignment followed in the present study is based on ammonites, enabling the recognition of five zones, upper Cenomanian Neolobites vibrayeanus and Vascoceras cauvini, lower Turonian Choffaticeras (Choffaticeras) segne and Wrightoceras munier and the middle–upper Turonian Coilopoceras requienianum Zone.