Petrology and geochemistry of sandstones in the southern Benue Trough of Nigeria:Implications for provenance and tectonic setting

Petrographic and geochemical analyses of three Cretaceous lithostratigraphic sandstone units were un-dertaken to constrain their provenance and tectonic setting. Petrographic analysis showed that there are differences in composition between the three sandstone bodies,which can be attributed to differences in provenance relief,trans-port distance and geology of the terrain. Composition of the three lithostratigraphic sandstone bodies fall within the craton interior field. Framework mode and chemical features indicated their derivation from basaltic volcanics,source rocks during the early rifting stage,and felsic,intermediate and mafic igneous source rocks located at the southeast basement complex terrain,with minor sedimentary components from the uplifted and folded older Cretaceous strata. The chemical composition of the sandstones is mainly related to source rocks,chemical weathering conditions and transport agents. The source rocks were derived mainly from the southeastern Precambrian basement of Nigeria. Through examination of the sandstones,the tectonic setting was modeled. The Benue Trough belongs to a continen-tal sedimentary basin of the passive margin type. The tectonic evolution from Albian to Maastrichtain of the trough is contributed to the difference in framework mode and chemical composition of the sandstones. The evolution of the basin was reconstructed in terms of sand-stone petrology and geochemistry. The tectonic evolution can be subdivided into three stages from the petrology and geochemistry data. The first stage covers Albian; the second stage the Turonian-Coniacian,and the third stage the Campanian-Maastrichtain. These are the three mega discontinuities in the sandstone composition among these three stages. These three discontinuities signify the influence of tectonism.