Ahmed M. El-Sabbagh

Biostratigraphy, taphonomy and palaeoecology of two tropical Coniacian-Santonian oyster species from Wadi Sudr, western Sinai, Egypt

The Upper Cretaceous carbonates of Egypt provide numerous opportunities to fill in palaeobiogeographical and palaeoecological gaps in tropical hard substrate communities. One such unit is the Coniacian-Santonian Matulla Formation exposed at Wadi Sudr, western Sinai. It is a fossiliferous and argillaceous limestone, marl, shale and sandstone about 110 m thick. The oysters Pycnodonte (Costeina) costei (COQUAND, 1869) and Oscillopha dichotoma (BAYLE, 1849) are abundant in the middle (Coniacian) and upper (Santonian) members of this formation, respectively. Biostratigraphically, they represent the most characteristic index oyster species for the ConiacianSantonian formations of Egypt. Their palaeobiogeographic distribution confirms the strong affinity to the Mediterranean Province of the Tethyan Realm. Taphonomic observations indicate that abrasion and highly fragmented shells are generally lacking. However, the thick shells of P. (C.) costei and O. dichotoma at Wadi Sudr are highly altered by disarticulation, encrustation and bioerosion. The common encrusters include ostreids, cheilostome bryozoans, serpulid worms, foraminifera and plicatulid bivalves. Bioerosion structures include Tiers D, E, F, G and H. They are represented by traces of acrothoracican cirripeds (Rogerella), clionaid sponge (Entobia), bivalves (Gastrochaenolites) and polychaetes and/or sipunculans (Maeandropolydora, Trypanites and Caulostrepsis). The distribution and frequency of the observed taphonomic features are varied greatly between the studied shells of both species, as well as within the shells of the same species. The oysters and their skeletozoans, the associated faunal content and sedimentological framework show a high-energy, intertidal to shallow subtidal marine environment with normal salinity, low rate of sedimentation and high productivity level.

Macro-borings on Late Cretaceous oysters of Egypt

The present study investigated traces of bioerosion in parautochthonous associations of oysters from the Upper Cretaceous of Egypt. These traces occurred in great quantity in the exterior surfaces of left valves and more abundantly than occurred in the interior surfaces, as well as in the surfaces of right valves. The most common bioerosion traces were formed pre- and/or post-mortem. The recognised borings appeared as systems of chambers and tunnels that were attributed to the ichnogenera Entobia (traces of clionaid sponges), Maeandropolydora (traces of polychaetes) and Gastrochaenolites (mostly traces of bivalves). Of these, the ichnogenus Entobia represents the most destructive component. The distribution and frequency of the observed borings varied greatly in the shells from one species to another, and sometimes within the same species. Patterns of borings (i. e., size, shape, distribution and frequency) indicated that the studied oyster species were lived in nearshore, shallow, relatively low-energy marine environments with low sedimentation rate and high level of productivity, i.e., optimal conditions for several bioeroders and, hence, pronounced bioerosion. These environmental aspects prevailed during and after the life of these oyster assem- blages before final burial in the Late Cretaceous.

Taphonomy and paleoecology of Cenomanian oysters from the Musabaa Salama area, southwestern Sinai, Egypt

This work is a taphonomic and paleoecologic study of Cenomanian oysters from the Musabaa Salama area, southwestern Sinai, Egypt. Disarticulation, fragmentation, encrustation and bioerosion are considered as the most predominant taphonomic features recorded in the studied oyster assemblages. Their distribution and frequency are greatly varied within the shells of the same species, as well as between shells of different species through the recorded oyster zones. Bioerosion structures include Tiers D, E, F, G and H. The multivariate statistical analyses document some characteristic ichnocoenoses. They include a sponge-dominated community (Entobia ichnocoenosis), a bivalve-dominated community (Gastrochaenolites ichnocoenosis), a serpulid-polychaete-dominated community (Maeandropolydora, Trypanites and/or Caulostrepsis ichnocoenosis), and an acrothoracican cirriped-dominated community (Rogerella ichnocoenosis). With rare exceptions, E. cretacea, G. torpedo and M. decipiens are common to abundant ichnospecies (>43%). E. ovula, E. retiformis and R. pattei are frequent to common ichnospecies (>5%). Other ichnospecies, including C. cretacea, G. orbicularis, T. solitarius, E. geometrica and C. taeniola are rare to frequent (<3%). Careful investigation of the host shells and the preserved encrusters and/or bioerosion sculptures provided data concerning the substrate characteristics, time of encrustation and bioerosion, rate of sedimentation, nutrients availability, and the general bathymetry and the rate of transgression.

Middle–Upper Jurassic marine gastropods from central Saudi Arabia

Ferrari, M., El-Hedeny, M., Zakhera, M., El-Sabbagh, A. & Al Farraj, S., May 2018. Middle‒Upper Jurassic marine gastropods from central Saudi Arabia. Alcheringa. A total of 68 gastropod specimens are reported from the Middle‒Upper Jurassic sedimentary successions exposed at central Saudi Arabia. The studied material comes from the Tuwaiq Mountain and Hanifa formations at the Khashm al Qaddiyah, Dirab, Jabal al Abakkayn and Maáshabah sections. Thirteen species are identified, described and illustrated. Among them, a new Aporrhais species (A. sauditica sp. nov.) is introduced. In addition, two further possible new Pseudomelania species from the same strata are mentioned. Other members of the assemblage include Kosmomphalus? sp. aff. K. reticulatus Fischer, Bourguetia? sp. aff. B. saemanni (Oppel), Bourguetia? sp., Ampullospira sp., Globularia? sp. cf. G. bajociana Fischer, Purpuroidea sp. aff. P. glabra Morris and Lycett, Purpuroidea sp., Cossmannea sp. aff. C. desvoidyi (d’Orbigny), Cryptoplocus sp. aff. C. depressus (Voltz) and Actaeonina? sp. Stratigraphically, seven species of this gastropod assemblage were only reported from the Middle Jurassic, whereas the other six ones are extending from the Middle to the Upper Jurassic of the studied succession. As compared with their gastropod content, the Khashm al Qaddiyah represents the richest section (33 out of 68 specimens, 48.5%), whereas the Maáshabah section showed an impoverished gastropod assemblage (only three specimens, 4.4%). The species reported here show paleobiogeographical affinities with coeval gastropod assemblages from India, east Africa, Middle East (Israel, the Sinai of Egypt) and western Tethys. The identified species confirm three depositional settings: open shelf lagoon, shoal/fore-shoal and open marine environments. The lower degree of fragmentation, poor sorting and scarcity of abrasion indicate a parautochthonous faunal assemblage. Mariel Ferrari [mferrari@cenpat-conicet.gob.ar] Instituto Patagónico de Geología y Paleontología (IPGP-CCT CONICET-CENPAT), Bvd. Brown 2915, U9120CD, Puerto Madryn‒Chubut, Argentina; Magdy El-Hedeny* [mmelhedeny@gmail.com] Department of Geology, Faculty of Science, Alexandria University, Alexandria 21568, Egypt; Mohamed Zakhera† [zakhera40@yahoo.com] Department of Geology, Faculty of Science, Aswan University, Aswan 81528, Egypt; Ahmed El-Sabbagh [ah.elsabbagh@gmail.com] Department of Geology, Faculty of Science, Alexandria University, Alexandria 21568, Egypt; Saleh Al Farraj [salfarraj@hotmail.com] College of Science, King Saud University, Riyadh 12371, Saudi Arabia. *Also affiliated with Deanship of Scientific Research, King Saud University, Riyadh 11451, Saudi Arabia. †Also affiliated with Vice Rectorate for Development and Quality, Najran University, Najran 11001, Saudi Arabia.