Assessment of chemical and mineralogical composition of tertiary shales from the Nigerian sector of Iullemmeden basin: Implication for paleoclimate and provenance

The Sokoto basin of Nigeria is the southeastern sector of the larger Iullemmeden basin. Shales dated Maastrichtian to Late Paleocene were collected from Illela borehole and Tunga village, part of Sokoto basin and were assessed using chemical (xrf) and mineralogical (xrd) analyses. This was aimed at obtaining detailed information on provenance, paleoclimate and degree of weathering. Chemical composition as obtained from Al2O3/TiO2 ratios indicate mafic -intermediate source, the plot of log (K2O/Na2O) against SiO2 also indicates island arc active continental margin province. Paleoredox parameters such as Cu/Zn, Ni/Co and V/Cr suggest a well oxidizing condition of deposition. In addition, assemblage of clay minerals (high kaolinite with minor concentrations of Illite and chlorite) is an indicative of a warm and humid (seasonal) sub-tropical climate. Moreover, plotting Al2O3 against Na2O, most of the samples plot in the field of Amazon mud, while a few plots close to the post-Archean shale and this suggests that the sediments were exposed to increasing effects of weathering or they were derived from moderate to highly weathered terrain.