Geological and Geomorphological study of the original hill at the base of Fourth Dynasty Egyptian monuments. Etude géologique et géomorphologique de la colline originelle à la base des monuments de la quatrième dynastie égyptienne

22 pages; 20 figuresRock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' mastaba and the Abu Rawash pyramid. This study is based on geological and geomorphological observations, visual observation, and photomontages. Results, correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a characteristic of the construction methods under the Fourth Dynasty.Le substratum rocheux des pyramides de Kheops et Khephren est étudié en comparaison avec celui d'autres monuments de la quatrième dynastie de l'ancienne Egypte : le Sphinx, le mastaba de la reine Kentkawes et la pyramide d'Abu Rawash. Cette étude est basée sur des observations géologiques et géomorphologiques, l'observation visuelle et des photomontages, ainsi que des mesures réalisées sur le terrain. Les résultats, corrélés avec ceux d'études antérieures, démontrent l'existence de collines naturelles utilisées comme assises pour la construction des deux grandes pyramides. Le volume minimum de ces collines peut être estimé par rapport au volume total à 12% pour Khephren et 23% pour Kheops. L'utilisation de collines rocheuses pour asseoir la construction d'un monument apparaît être caractéristique des méthodes de construction utilisées sous la quatrième dynastie

Geological and topographical study of the original hills at the base of Fourth Dynasty Egyptian monuments of the Memphite plateau

Rock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' monument and the Abu Rawash monument. This study is based on geological and topographical observations, photomontages and field measurements. The results, which are correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a construction method under the Fourth Dynasty

Age and hafnium isotope evolution of Sudanese Butana and Chad illuminates the Stenian to Ediacaran evolution of the south and east Sahara

The Saharan Metacraton is a poorly known tract of pre-Neoproterozoic continental crust that occupies the area between the juvenile Arabian Nubian Shield, in the east, and the Tuareg Shield to the west. Neoproterozoic orogenesis (i.e. Oubanguides and East African orogenies) affect the west, the south and the east of the metacraton, respectively, which led to deformation, emplacement of igneous bodies, and localised episodes of rift-related magamatism. Details about interior regions of the Saharan Metacraton are poorly known, with much of it covered by Phanerozoic rocks. The basement outcrops in Sudan, Chad, Algeria and Libya have been the subject of few modern geochronological studies. Here we present results from the first zircon geochronology and in-situ zircon hafnium isotope investigations from both the Sudanese Butana and central Chad. The terranes in Butana, formed to the east of pre-Neoproterozoic continental crust of the Saharan Metacraton, with the oldest juvenile magmatism (ƐHf(t) of +4.89 to +7.89) at ca. 839 Ma, followed by subsequent magmatism at ca. 787 Ma. The ca. 787 Ma event (seen elsewhere in the East African Orogen) is interpreted to represent volcanic-arc collision and accretion with the kernel of the Saharan Metacraton. The ca. 839 Ma magmatism is contemporaneous with the accretion of the Tonian (ca. 850 Ma) arc terranes of the Arabian Nubian Shield and marks subduction to the east of the Saharan Metacraton. The magmatic history of the Ouaddaï region in Chad begins in the late Mesoproterozoic, with localised rifting, resulting in the emplacement of juvenile granites (ca. 1030 Ma). The Cryogenian and Ediacaran in the Saharan Metacraton reveal a complicated history of magmatism and deformation. Age data from Chad show the emplacement of granites (from melting of Mesoproterozoic crust: ƐHf(t) = +2.04 and −4.07) at ca. 665–654 Ma, coeval with the main East African Orogeny and accretion of the other ANS terranes to the Saharan Metacraton at ca. 650–580 Ma. The youngest tectonothermal event within the Saharan Metacraton is recorded by emplacement of granites between 580 and 550 Ma (ƐHf(t) values of −17 to −31) in southern Chad