Petrography, diagenesis and geotechnical properties of the El-Rufuf Formation (Thebes Group), El-Kharga Oasis, Egypt

• Published in: Journal of African earth sciences (1994) 1997-10, Vol.25 (3), p.407-423
• Main Authors: Bashed, M.A., Sediek, K.N.
• Format: Article
• Language: English
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/S0899-5362(97)00113-9

The El-Rufuf Formation (Thebes Group) outcrops widely in Egypt. It is quarried as an ornamental building stone and used as slabs in walls and floors. It is also important in foundation construction. The geotechnical behaviour of these rocks is commonly related to stratigraphical position, controlled by their petrography and textural and diagenetic features. The El-Rufuf Formation of Naqb Assiut, El-Kharga Oasis, consists of 63 m of micritic and neomorphosed limestones which are marly at the base. Microfacies analysis of these limestones indicates an inner to middle shelf open marine environment. The most common diagenetic features are neomorphism, silicification, dissolution and stylolites. There are clear relationships between the measured compressive strength of rocks and the facies and diagenetic features. Neomorphic sparry limestone has the lowest compressive strength, while cherty biomicritic limestone shows the highest values. Micritic and biomicritic limestones show intermediate values. Some anisotropism of compressive strength values is recorded in the stylolitic limestones and in the foliated marly part of the formation. The present study reveals that the El-Rufuf limestones, according to Deere's (1968) classification, are low to medium strength rocks with low modulus ratios (DL-CL), while the marly parts of the formation are low strength rocks with low modulus ratios (EL). The rocks of the marly part of the El-Rufuf Formation are unstable with regard to water and therefore have a zero softness coefficient. La Formation d'El-Rufuf (Groupe de Thèbes) affleure abondamment en Egypte. Elle est exploitée en carrìere comme pierre d'ornement en construction et en dalles pour murs et sots. Elle est également importante pour les fondations des constructions. Le comportement géotechnique de ces roches est habituellement corrélé à leur position stratigraphique, en le contrôlant au moyen de la pétrographie et de leurs caractères texturaux et diagénétiques. La Formation d'El-Rufuf de Naqb Assiut, Oasis d'El-Kharga, consiste en 63 mètres de calcaire micritique et néomorphique, marneux à la base. L'analyse des microfaciés de ces calcaires indique un environnement marin ouvert de plate forme interne à interrnédiaire. Les caractères diagénétiques les plus communs sont le néomorphisme, la silicification, la dissolution et les stylolites. Il existe une relation nette entre la force de compression mesurée dans ces roches et les faciès et caractères diagénétiques. Le