Ahmed S. Kassab

Upper cretaceous ammonites of Duwi Formation in Gabal Abu Had and Wadi Hamama, Eastern Desert, Egypt

Abstract This paper is an attempt to clarify the paleontologic, chronostratigraphic, paleoecologic and biogeographic relations of the heteromorph and sphenodiscid ammonites. The specimens were collected from sharply defined stratigraphic horizons of the Duwi Formation in two sections exposed at G. Abu Hab and Wadi Hamama to the northeast of Qena. Two ammonite zones are recorded in the Duwi Formation: Libycoceras ismaeli (Zittel) Zone and Bostrychoceras polyplocum Zone. The ammonites of the first zone are restricted to the first lower phosphate bed and are only represented by a frequent association of the species Libycoceras ismaeli . This zone defines the base of the Duwi Formation in the area of study. The second zone in the topmost part of the formation is rich in the index species and the other heteromorph ammonites. It is represented by a bed of very hard limestone of thickness about 20 cm at top of the Duwi Formation. The maximum bulk thickness of the formation is 105 m. The stratigraphic range of the fossils of both zones assigns a Campanian age for the sediments of the Duwi Formation in the area of study. Furthermore, the Campanian-Maastrichtian boundary is fixed above the bed with Bostrychoceras polyplocum . The Libycoceras ismaeli (Zittel) is found in a stratigraphic position lower than that published before. The paleontological study of the ammonites led to the recognition of 11 species belonging to 6 genera ( Libycoceras Hyatt, Nostoceras Hyatt Solenoceras Conrad, Bostrychoceras Hyatt, Baculites Lamarck, Exiteloceras Hyatt), and representing 3 families (Sphenodiscidae, Hyatt; Nostoceratidae, Hyatt and Baculitidae Meek). Two new subspecies are described Solenocera a humei aequicostata and Exiteloceras unciforme Lewy qenaense , besides many species which are recorded for the first time in the Egyptian ammonites, they include the followings: Solenoceras cf. reesidei, S. humei densicostata, Nostoceras (Planstoceras) rehavami, Nostoceras cf. dracone and Baculites scotti . Paleoecologically, the Libycoceratids from the base of Duwi Formation lived in Late Campanian partly isolated marine basin of abnormal bottom conditions. On the other hand, the mode of life of the heteromorph ammonites collected from the topmost part of the formation was diverse.