Sandstone composition expressed as a function of SiO2
percentage against total percent of Al2O3, K2O and Na2O
(Fig. 11) is used to discriminate the paleoclimatic signature
and to give an idea about the chemical maturity of the studied
sandstones. The majority of the studied sandstones plot in arid
field with low maturity. Immaturity of the studied sandstones
is also inferred from thin sections with prevailing angular to
subangular grains and common lithic components mainly of
carbonates and chert. Garver et al. (1996) suggested that
elevated Cr and Ni (Cr > 150 ppm and Ni > 100 ppm) and
low Cr/Ni ratios (between 1.3 and 1.5) are indicative of
ultramafic rocks in the source area of shales, although Cr/Ni
ratios were much higher (>3.0) for sandstones from the same
area.