Provenance history, depositional conditions andtectonic settings during late Cenomanian – early Turonian time in the Gongola Sub-Basin of the Upper Benue Trough Nigeria: Evidence from major and trace elements geochemistry of the Kanawa shales from the Pindiga Formation

Abstract

Newly analysed major and trace element compositions of the Kanawa shales deposited in the Pindiga Formation reveal the provenance history and depositional conditions during the late Cenomanian - early Turonian time in the Gongola Sub-Basin of the Upper Benue Trough. We conclude that the source of the siliciclastic detritus in the Kanawa shales of the Pindiga Formation are igneous rocks of predominantly intermediate chemistry with a temporal trend towards more felsic compositions. The source rocks presumably underwent intense chemical weathering with CIA, PIA and CIW values up to 89.51, 97.30, and 97.56, respectively, which led to enhanced shale deposition in the Gongola Sub-basin. Obtained relatively high Fe/Mn and Zr/Rb ratios in the Kanawa shales suggest deposition under relatively strong hydrodynamic conditions in presumably shallow water. Additionally, integrated bivariate plots of Ga/Rb vs. K2O/Al2O3, SiO2 vs. Al2O3+K2O + Na2O with the ratios of Sr/Ba, Rb/K, MgO/Al2O3x100, V/Cr, V/(V + Ni) V/(V + Cr), P/Ti and Ba/Ti indicate deposition under a warm, humid climate in dominantly anoxic and brackish water conditions under relatively low primary productivity conditions. This interpretation aligns with the global climate and redox conditions during the late Cenomanian – early Turonian times. The tectonic setting bivariate diagrams of K2O/Na2O vs. SiO2 and SiO2/Al2O3 vs. K2O/Na2O, as well as the high and low quartz multidimensional diagrams, reveal a rift basin in a passive margin depositional environment, confirming earlier works on the evolution of the Benue Trough.