Distinguishing rift-related from inversion-related anticlines: Observations from the Abu Gharadig and Gindi Basins, Western Desert, Egypt

Distinguishing the tectonic origin of anticlinal structures is problematic in regions with a complex history of rifting and inversion. We present the results of seismic mapping, in the form of time-depth (isochron) and time-thickness maps to characterize how sedimentary thickness differentials evolved in response to normal faulting and to inversion events on faults within the Abu Gharadig and Gindi Basins in the Western Desert of Egypt. Late Cretaceous rift-related faults in the Abu Gharadig Basin strike NW-SE, W-E and SW-NE. In the eastern part of the basin, a prominent SW-NE trending interbasinal saddle formed in response to preferential subsidence forming half-grabens to its north-west and southeast, during the Mid-Turonian to Santonian interval. Santonian to Palaeogene inversion in the Abu Gharadig Basin developed on its northern basin margin, the absence of SW-NE striking faults in the eastern central basin resulting in any inversion effects being minor. In the central Gindi Basin, Upper Cenomanian to Lower Turonian SW-NE striking rift faults underwent inversion as early as the Mid-Turonian. The orientation of existing rift faults and modification of the local stress fields control the extent to which inversion was taken up in each basin trough time. The Abu Gharadig and Gindi Basins are two of the rift basins developed in West and Central Africa that underwent rifting, inversion and dextral shearing during the Late Cretaceous. We emphasize the value of high-resolution stratigraphic mapping to characterize short-lived and subtle pop-up events that may have gone unnoticed

Planktonic Foraminifera of the Mokattam Formation (Eocene) of Gebel Mokattam, Cairo, Egypt

Abdel-Kireem M.R. Planktonic Foraminifera of the Mokattam Formation (Eocene) of Gebel Mokattam, Cairo, Egypt. In: Géologie Méditerranéenne. Tome 11, numéro 1-2, 1984. C.A.M. IXe colloque africain de micropaléontologie. Paris, Museum d'Histoire Naturelle, du 3 au 6 octobre 1983. p. 241

Neogene planktonic foraminiferal biostra-tigraphy of Nile Delta

This investigation deals with the litho-and biostratigraphy of the Middle Miocene and Pliocene subsurface successions of the Nile Delta region, Egypt. Fifty planktonic foraminiferal species have been recorded from the Abu Madi-1 well. The stratigraphical distribution of these planktonic Foraminifera in the studied well permits recognition of four zones. The Globorotalia mayeri Zone of Middle Miocene ; the Sphaeroidinellopsis seminulina -subdehiscens, the Globorotalia puncticulata Zones of Early Pliocene and the Globigeri-noides obliquus extremus Zone of Middle Pliocene. These zones are correlated with zones elsewhere in the world. The Miocene/Pliocene boundary is found to be marked by a distinct unconformity due to the missing of the Late Miocene «evapo-ritic phase». The paleoecology of the studied rock units and their planktonic foraminifera are interpreted.Ce travail étudie le Miocène moyen et le Pliocène reconnu en sondage dans le delta du Nil (Egypte). La distribution stratigraphique des Foraminifères planctoniques permet de reconnaître les quatre biozones suivantes : L. à Globorotalia mayeri (Miocène moyen) L. à Sphaeroidinellopsis seminulina-subdehiscens L. à Globorotalia puncticulata et L. à Globigerinoides obliquus extremus du Pliocène. La limite Mio-Pliocène est marquée par une discordance : absence de dépôt du Miocène supérieur (phase évaporitique). Une interprétation paléoécologique des formations étudiées est fournie à partir des Foraminifères planctoniques.Abdou H.F., Abdel-Kireem M.R., Samir A.M. Neogene planktonic foraminiferal biostra-tigraphy of Nile Delta. In: Géologie Méditerranéenne. Tome 11, numéro 1-2, 1984. C.A.M. IXe colloque africain de micropaléontologie. Paris, Museum d'Histoire Naturelle, du 3 au 6 octobre 1983. pp. 193-205