THE APPLICATION OF GEOCHEMICAL AND MINERALOGICAL STUDIES OF CRETACEOUS SHALES IN WEST SIBAIYA AREA, EGYPT TO INVESTIGATE THEIR TECTONIC AND SEDIMENTOLOGICAL ORIGIN WITH ENVIRONMENTAL IMPACTS | ||||
| Nuclear Sciences Scientific Journal | ||||
| Article 7, Volume 6, Issue 1, 2017, Page 111-122 PDF (760.2 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/nssj.2017.30776 | ||||
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| Authors | ||||
| IBRAHIM H. ZIDAN; RAMAG A. OSMAN | ||||
| Nuclear Materials Authority,Cairo, Egypt | ||||
| Abstract | ||||
| Sibaiya area is located at the southwestern corner of the Qena bend, Nile Valley, Egypt. The area is covered by Campanian to Maastrichtian rocks composing a number of shale layers in three formations. The present investigation comprises insights in the geochemical composition and clay minerals included in the Cretaceous shale–bearing sediments in Sibaiya west. Fifteen representative trench samples were collected from a vertical lithostratigraphic section including all the geological formations (Qusir Shale Member of Nubia Formation, Duwi Formaton and Dakhla Formation) in present area. They were subjected to mineralogical and chemical analyses using modern methods and application of the proper techniques of data processing and analyses. The data were utilized to investigate the tectonic province of the source rock of Sibaiya shales by displaying the analyzed SiO2% against log (K2O/Na2O) on the tectonic discrimination diagram. This application obviously indicated that the source rock is of the arc tectonic province. In order to confirm this origin, trials were also made to construct an upper crust normalization pattern of Sibaiya shale–bearing sediments using the chemical analyses of major and trace elements. The diagram obviously indicates that the tectonic province of the source rock cannot belong to the upper continental crust (UCC). In addition, the display of the TiO2% against the Al2O3% diagram and correlation with the UCC, basalt and other global shales, of known tectonic origin, has also indicated that the origin of Sibaiya shales is comparable with basalt. This also supports a more basic source and infers an arc province origin. The immobile element values, specially the relatively higher values of trace elements (Cr, V, Ni and Ti) provide a strong evidence that supports a basic origin of Sibaiya shales and also suggests a dominance of mafic volcanic source in general, whilst, the high V/Cr and Ni/Cr ratios, in particular, may indicate that the investigated sediments were deposited under oxidizing environment. Both the geochemical indices and the geochemical ratios reveal that there are no obvious differences between the distribution of major and trace elements in most Campanian to Maestrichtian shales in Sibaiya. This pattern of distribution suggests a single chemical clan and most of the investigated sediments are related mainly to the same rock source which is dominated by mafic volcanic rocks. Therefore ,the tectonic setting studies indicated that the investigated Sibaiya shales were derived mainly from mafic volcanic source rocks, most probably the Eastern Desert of basaltic and andesitic rocks. The study of the weathering trends and chemical mobility was also undertaken using the chemical and mineralogical analyses. In this respect, the chemical Index of alteration (CIA) was calculated for all the samples and revealed that Sibaiya shales describe low to moderate chemically weathered terrain. Beside, the fluviatile of post deposition contributions from local sources, such as the basement rocks in the Egyptian Eastern and Western deserts, can be considered as subordinate sources. This is represented by the relative abundance of kaolinite in the clay minerals. Additional environmental investigations were also undertaken in order to explore any environmental radiation impact that may arise from the utility of these shales in any domestic purposes by the locals and/ industry. The calculation of geo-accumulation index in Sibaiya shales was used to study the pollution pattern and revealed that these shales describe a low to moderate polluted terrain. However the dilution factor when mixed with other material during domestic utility may make it an environmentally safe product. | ||||
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