The uppermost deposits of the stratigraphic succession of the Farafra Depression (Western Desert,Egypt): Evolution to a Post-Eocene continental event |
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| Institution: | 1. Dpto. Petrología y Geoquímica, Facultad Ciencias Geológicas, Universidad Complutense de Madrid (UCM), C/José Antonio Novais 12, 28040 Madrid, Spain;2. Geology Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt;3. Dpto. Estratigrafía, Facultad Ciencias Geológicas, Universidad Complutense de Madrid (UCM), C/José Antonio Novais 12, 28040 Madrid, Spain;4. Instituto de Geociencias (CSIC, UCM), C/José Antonio Novais 12, 28040 Madrid, Spain;1. Istituto Nazionale di Geofisica e Vulcanologia, sez. CNT, Roma, Italy;2. National Research Institute of Astronomy and Geophysics, Cairo, Egypt;1. Departamento de Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Rua Sílvio Lima, Pólo II, 3030-790 Coimbra, Portugal;2. Centro de Investigação da Terra e do Espaço, Universidade de Coimbra, Observatório Astronómico, Almas de Freire, Santa Clara, 3040-004 Coimbra, Portugal;3. Grupo de Investigación IberCreta, Departamento de Geología y Geografía, Facultad de Ciencias, Universidad de Alcalá, 28871 Alcalá de Henares, Spain;4. Grupo de Investigación Procesos Bióticos Mesozoicos, Departamento de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040 Madrid, Spain;5. Museu Nacional de História Natural e da Ciência, Universidade de Lisboa, 1250-102 Lisboa, Portugal;1. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences (CAS), Nanjing 210008, China;2. Department of Earth Sciences, Natural History Museum, London, SW7 5BD, UK;3. Department of Natural Sciences, Amgueddfa Cymru-National Museum Wales, Cardiff, CF10 3NP, UK;1. Department of Geoinformation Photogrammetry and Remote Sensing of Environment, Faculty of Mining Surveying and Environmental Engineering, AGH University of Science and Technology, Poland;2. Department of Hydraulic and Sanitary Engineering, The Section of Hydraulic Engineering, Faculty of Environmental Engineering and Spatial Management, Poznan University of Life Sciences, Poland;3. Department of Ecology and Environmental Protection, Faculty of Environmental Engineering and Spatial Management, Poznan University of Life Sciences, Poland;4. Institute of Civil Engineering and Geoengineering, Faculty of Environmental Engineering and Spatial Management, Poznan University of Life Sciences, Poland;5. Department of Forest Management, Faculty of Forestry, Poznan University of Life Sciences, Poland |
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| Abstract: | This paper gives insight into continental sedimentary deposits that occur at the uppermost part of the stratigraphic succession present in the north-eastern sector of the Farafra Depression (Western Desert, Egypt). Using space imagery to complete the field work, the geology of the area has been mapped and the presence of a N–S oriented fault system is documented. The analysis of the morphotectonic features related to this fault system allows reconstructing the structural and sedimentological evolution of the area. The study indicates that the continental deposits were accumulated in alluvial systems that unconformably overlie shale and evaporitic rocks attributable to the Paleocene–Eocene Esna Formation. The deposits of the Esna Formation show soft-sediment deformation features, which include slump associated to dish and pillar sedimentary structures and provide evidence of syndepositional tectonic activity during the sedimentation of this unit. The outcrops are preserved in two areas on separated fault-bounded blocks. Proximal alluvial fan facies crop out in a dowthrown block close to the depression boundary. The proximal facies are made up mostly by polymictic conglomerates which occasionally contain boulders. The conglomerate clasts are mainly quartz, carbonate, anhydrite satin spar vein, mudrock, ironstone and nummulite fossils. The mid-fan facies consist of trough cross-bedded, rippled and cross-laminated quartzarenites with reworked glauconite grains and carbonate rock fragments, interpreted as deposited by distributary streams. The distal alluvial fan deposits consist of sandy marls that evolve toward the top of the sections into root-bioturbated lacustrine limestone beds that are locally silicified. The limestones are biomicrites containing characea, ostracods and gastropods with fenestral porosity.A number of features, including clast provenance (mainly from marine Paleocene and Eocene rocks), the observed fractural pattern (N–S direction related to the opening of the Red Sea), and the sedimentary relationships, suggests that the continental deposits were accumulated during the Oligocene–Miocene interval. |
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| Keywords: | Farafra Depression Alluvial fans Lacustrine deposits Esna Formation Seismites Sabkha |
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