Paleoenvironment and paleoclimate of the Late Cretaceous Ise Formation, Eastern Dahomey Basin.

Résumé

Abstract The paleoenvironment and paleoclimate of the Ise Formation remain poorly understood, despite its importance for the Late Cretaceous paleoenvironment and geology of the Dahomey Basin and Africa in general. This is due to the paucity of outcrops and drilled samples of the formation. This study investigates the paleoenvironmental and paleoclimatic setting of the Ise Formation through sedimentological and palynological analyses of fifty sediment samples. The sediments were recovered from four exposed sections of the formation, three of which are recently exposed, in the Eastern Dahomey Basin, SW Nigeria. The examined sediments are largely coarse-grained, poorly sorted, gravelly-sand to sandy-gravels, and are dominated by spores and pollens. The Laevigatosporites sp. and the Sapotaceae sp. are the most abundant spores and pollens in the sediments while minor occurrences of Monocolpites sp., Cyathidites minor, Retitricolporites sp., and Spinizonocolpites sp. were recovered. Concentricytes sp. was the only algae recovered, while microforaminiferal wall lining was the only foraminifera recovered. Textural properties of the sediments indicate textural immaturity and proximity to the source area. The occurrence of Monocolite sp., Foveotriletes margaritae, Echitriporites trianguliforms, Cyathidites, and Longapertites sp. indicate a Maastrichtian to Early Paleocene age for the Ise Formation. The vegetation cover was mainly mangrove with palms, shrubs, and forests, while the environment of deposition was swamp to marginal nearshore. A dominant mild to warm tropical climate during the deposition of the formation was inferred based on the recovery of Retitricolporites sp., Monocolpites marginatus, Sapotaceae sp., and Spinozonocolpites sp. from the samples. These conclusions support the hypothesis of a regional shallow environment setting during the Maastrichtian and a warm regional climate in Africa during the Early Paleocene.

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