The Turonian Marine Incursion and the Trans-Saharan Seaway: A Critical Synthesis of the Nigerian Benue Trough Record

Abstract

The Benue Trough of Nigeria preserves one of the most extensively documented onshore records of the Cenomanian–Turonian marine transgression that is widely held to have linked the South Atlantic and the Tethys Sea across the West African craton, an episode commonly termed the Trans-Saharan Seaway. Because the trough exposes marine and paralic strata along an axis that crosses several structurally distinct sub-basins, it offers an opportunity to examine how a regional rift architecture governed the entry, timing and biotic character of a globally significant sea-level event. This review synthesises the tectonic, stratigraphic, biostratigraphic and geochemical literature on the Turonian incursion in the Benue Trough, with the aim of establishing which conclusions are well supported, which remain contested, and where the regional record does or does not align with the global expression of the Cenomanian–Turonian boundary event, including the associated Oceanic Anoxic Event 2. Evidence is drawn from studies of the trough's wrench-related and extensional tectonic framework, from formation-level stratigraphic and sedimentological descriptions across the Yola, Gongola, Middle and Southern sub-basins, from ammonite, echinoid, ostracod and palynological biostratigraphy used to date and correlate the transgressive interval, and from organic-geochemical studies of the associated black shales and their petroleum significance. The synthesis indicates strong convergence on a latest Cenomanian to early Turonian onset of marine flooding and on the broad lithostratigraphic expression of the event, but persistent disagreement over the precise pathway, duration and directionality of the connection, over the reliability of foraminiferal and lithological correlation across sub-basins, and over how closely the regional organic-carbon record tracks the global Oceanic Anoxic Event 2 signal. Methodological constraints, including uneven outcrop access, reliance on a small number of historically collected faunal sections, and limited high-resolution geochemical sampling, are identified as the principal sources of continuing uncertainty. The review closes by identifying research priorities capable of resolving these disagreements and by situating the Benue Trough within the broader family of Cretaceous trans-continental seaways.