Taphonomy and its significant role in palaeoenvironmental reconstruction of the upper Turonian actaeonellid gastropod concentrations of Abu Roash, Western Desert, Egypt

The palaeoenvironment of the upper Turonian Trochactaeon salamonis shell concentrations in the Abu Roash area, the northern Western Desert of Egypt, is interpreted based on detailed taphonomic studies. A paucispecific gastropod assemblage of the Actaeonella-bearing limestone-marl member of the Turonian–Coniacian Abu Roash Formation has been studied in two sections. Both actaeonellid gastropod concentrations recorded are characterized by well preserved, moderately to densely packed, poorly to moderately sorted and reoriented specimens. In addition, the gastropod specimens are exclusively recrystallized (neomorphosed calcite), moderately to highly bored, but rarely fragmented, encrusted and/or abraded. The study of bioerosional structures revealed five different ichnotaxa, belonging to three ichnogenera (Clionolithes, Entobia, and Rogerella). Noteworthy is the occurrence of the ichnogenus Clionolithes for the first time in the Cretaceous of North Africa (the southern margin of the Neotethys Ocean). In addition, the ichnospecies Clionolithes cf. radicans has unusual dimensions and morphological features that are definitively an unknown feature for any dendrinid boring, suggesting a probable record for a new Clionolithes ichnospecies. The Trochactaeon salamonis concentrations studied are interpreted to represent a resedimented (parautochthonous) assemblage, which may have been influenced by shallow nearshore warm-water conditions in response to storm activity. Environmental parameters controlling the formation of these gastropod shell concentrations include substrate consistency, water energy, salinity, oxygen availability, and rate of sedimentation, respectively.