Palaeoecological and palaeoenvironmental analyses of Cenomanian–early Turonian macrobenthic faunas from the northern Eastern Desert of Egypt

Abstract

The palaeoecology and palaeoenvironments of the Cenomanian–lower Turonian succession in the northern Eastern Desert of Egypt are interpreted, based on a detailed study of macrofaunal assemblages and sedimentary facies. The abundant molluscs and echinoids of the mixed carbonate-siliciclastic Galala and Abu Qada formations have been studied in three sections with ammonites that provide a well-correlated stratigraphical framework. Three unconformities (two Cenomanian sequence boundaries and a first Turonian one) bound two third-order depositional sequences. Facies development shows a strong relationship to the sequence architecture recognised. In addition, the facies characteristics indicate depositional palaeoenvironments ranging from lagoonal to deep subtidal settings on a homoclinal carbonate ramp that was proximally influenced by clastic input. The macrobenthic taxa identified in 51 samples, collected from the sections studied, are grouped into seven assemblages (A–G) that are described and interpreted as remnants of communities. The faunal distribution and trophic structure of most of the assemblages recorded confirm fully oxygenated and euhaline shallow-marine environments with mesotrophic productivity level, i.e., relatively stable and low-stress conditions. The trophic structure of some other assemblages, in contrast, reflects the influence of particular environmental parameters, dissolution of aragonitic shells and/or sample size effects. Environmental parameters controlling the faunal distribution include substrate consistency, bathymetry, water energy, surface-water productivity, rate of sedimentation and oxygen availability. The integrated litho- and biofacies results certify that the sequences were deposited during an interval dominated by different perturbations that resulted in a wide spectrum of depositional features and significant palaeoecological variations.