The late Cenomanian maximum flooding Neolobites bioevent: A case study from the Cretaceous of northeast Egypt

Abstract

Late Cretaceous environmental changes are manifested in several bioevents, which have been used as important tools for basin analysis, sequence stratigraphic interpretation and global correlations. One of these events is the hitherto poorly known late Cenomanian Neolobites bioevent. The present study introduces the first detailed documentation for this bioevent from northeast Egypt. The Neolobites bioevent consists of three limestone–marly limestone couplets with autochthonous biogenic concentrations. Within the study area, the bioevent displays a wide geographic distribution in Sinai and the Eastern Desert with a thickness range from 8 to 4.5 m. The Neolobites bioevent is characterised by diagnostic faunal change, condensed deposits and rich molluscan content. In addition to abundant oysters, cephalopods are present and are very commonly represented by the ammonite Neolobites vibrayeanus (lower upper Cenomanian index of the bioevent) and the nautiloid Angulithes mermeti. Sequence stratigraphic analysis of the studied succession shows that the occurrence of the Neolobites bioevent formed within late the transgressive to early highstand interval of a third-order depositional sequence and not during a transgressive stage as previously described. Therefore, the bioevent is considered here as a maximum flooding bioevent, which commonly occurs in mixed siliciclastic–carbonate systems. Palaeoecology and sedimentary facies of the bioevent indicate shallow marine conditions (deep lagoon to shallow subtidal) during a maximum rise of sea-level interval, with euhaline, moderate water energy and well-oxygenated stable sea floor sediments. The marker ammonite Neolobites vibrayeanus shows a wide palaeogeographic distribution in western Tethys and North Atlantic oceans. The maximum flooding position of the Neolobites bioevent provides a high potential for an excellent interbasinal correlation.