No abstract

No abstract

No abstract

HE Late Cretaceous-Early Eocene carbonate sequences of the White Desert of Egypt exhibit amazing complex paleo-humid karst landforms, so it was declared as a nature-protected area since 2002. Two karst depressions of El Sheikh Abdallah and the Crystal Mountain (Qaret El Sheikh Abdallah) are identified by detailed fieldwork and GIS morphometric analysis of the digital elevation model of the northern part of the White Desert. These depressions are verified as two separate karst uvalas between the major karst poljes of El Bahariya and Farafra karst territory with northeast alignment. The sea-level drops and uplifting phases of the carbonate sequences of the uvalas, associated with the major compressional events of the Syrian arc (Cretaceous-Paleogene) and Oligo-Miocene extensional tectonics in north Egypt caused the development of three major stratigraphic breaks (fossilized paleo-karst surfaces) of Late Cretaceous-Palaeocene, Palaeocene-Early Eocene, and post-Early Eocene (Oligocene-Miocene). Along these fossilized surfaces, paleokarst features and sediments are detected and described. El Sheikh Abdallah and the Crystal Mountain depressions (uvalas) are also dominated by exposed (surface) complex karst features such as unroofed caves, widened joints, sinkholes, collapse breccia's, and solution channels, together with sporadic remains of uncovered autochthonous and allochthones paleo-cave sediments. The recognized stratigraphic breaks and their paleokarst features and the subsequent surface denudation helped to propose a morphotectonic evolutionary model for the exposed karst landscape and the denuded karst features of El Sheikh Abdallah-Crystal Mountain uvalas.

Mazzini et al.Hydrothermal Venting in the Western Desert and the deformed structures located within the strike-slip zone suggest that faulting controlled the emplacement and the final shape of some of the hydrothermal vents. We speculate that this system may represent a palaeo sediment-hosted hydrothermal system and could be related to the opening of the Red Sea.

Aptian to early Albian times are marked by various geodynamic and paleoenvironmental events such as large igneous province volcanism , perturbations of climate and the carbon cycle, and sea-level changes. The Essaouira-Agadir basin (EAB), located on the Atlantic passive margin of Morocco, offers good and fossiliferous exposures of the Aptian-Albian sedimentary series. A detailed analysis of this succession made it possible to establish a biostratigraphic framework. The identification of discontinuities allowed to define eight depositional sequences. As most of them are correlatable with depositional sequences of other Tethyan areas, they suggest that eustacy was the main parameter controlling sedimentation. The analysis of sedimentary facies and nannofossil assemblages provides information on paleoenvironmental changes. Sedimentation in the EAB evolved from a very low energy, carbonate ramp in the early Aptian to a low energy, slightly deeper, mixed carbonate-clastic ramp in the early Albian. This change occurred along with an increase of clastic input, a change from oligotrophic to mesotrophic faunal assemblages, and a decrease of sea-surface temperatures. The occurrence of current sedimentary features, sporadic dysaerobic deposits and local phosphatic and glauconitic crusts suggests that upwelling currents were significant during this period. Paleogeographic and isopach maps support a transgressive trend in the late Aptian and early Albian, and unravel subsidence anomalies suggesting mild halokinetic movements during Aptian-early Albian times.

No abstract

The present study aims to integrate spectral analysis results of multispectral Landsat-8 and ASTER data besides airborne gamma-ray spectrometric data in geologic and radiometric mapping as well as alteration types of Wadi Fatirah area, North Eastern Desert, Egypt. The applied image processing techniques comprising Color Band Composites, Principal Component Analysis, Crosta technique and Band Ratio were efficient in lithological units discrimination and alteration types identification. The airborne gamma-ray spectrometric maps discriminate the younger granites in the study area but it could not differentiate between their phases. The remote sensing products are verified by detailed field, petrographic and radiometric analysis. The results are elaborated as a precise geological map of 1:50,000 scale with metavolcanics (oldest), older granitoids, Dokhan volcanics, younger gabbros, younger granites and post granitic dikes and pegmatites (youngest) rock units, and tracing the hydrothermal alterations in form of propylitic, phyllic and gossan as well as illite, kaolinite, limonite, hematite, ferromagnesian and hydroxyl distribution maps. Additionally, the radioactive anomalies are mainly related to the younger granites and pegmatite bodies that mainly associated with ferrugination (iron oxides and hydroxides alteration). The most promising radioactivity are delineated as pegmatite bodies at Wadi Abu Zawal and Wadi Abu Shihat.