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

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.