LAUSR

Abstract This contribution presents a comprehensive review of the Upper Cretaceous geological evolution of Nigeria focusing on the Benue Trough and adjacent basins. It addresses the controversies regarding potential pathways of ingression during transgressive episodes that led to the establishment of the Trans-Saharan seaway. An improved understanding of the paleogeographic evolution is essential for assessing the economic potential of the region, including the Upper Cretaceous petroleum system and coal deposits, as well as groundwater and mineral resources. Two transgressive episodes connected much of Nigeria's sedimentary terrain in the Upper Cretaceous. The first transgression, which followed the opening of the Equatorial Atlantic Ocean in mid-Albian times, established the Trans-Saharan seaway that connected the Tethys and the South Atlantic oceans through an eastward route via the Benue Trough in the Turonian. This resulted in widespread deposition of commercially exploited marine limestone and clay deposits, and subordinate coal, with sediments possessing very limited groundwater resource potential. This marine connection ceased with the continent-wide Santonian inversion tectonics that led to folding, faulting, uplift, and intrusion of older strata. A second transgression, commencing in the Campanian, reestablished the Trans-Saharan seaway through a westward Bida Basin route in the Maastrichtian, culminating in widespread, mostly marginally marine conditions in the Sokoto, Bida, Anambra, and Benin basins as confirmed in this review. The influx of marine waters from the Tethys Ocean, limited in extent by the uplifted region of the southern Benue Trough brought about marginally marine conditions in the Chad Basin and the northern and central Benue Trough. Widespread deposition of coal, clay, ironstone, and good to prolific aquiferous units occurred during this time.