关键词: 海侵, 微古生物, &beta, -胡萝卜烷, 甲藻甾烷, 晚白垩世, 东尼日尔盆地

Abstract:

The Eastern Niger Basin is a typical MesozoicCenozoic intracontinental rift basin of the central and western African rift system. Located in the Eastern Niger, the basin includes five depressions, namely Termit, Tefidet, Tenere, Grein and Bilma depressions. Based on paleontological and geochemical characteristics of the Upper Cretaceous mudstone cuttings in wells of Saha-1 and Helit-1, located in the Tenere and Termit depressions, respectively, this study provides evidences for marine transgression happened in the Eastern Niger Basin in the Late Cretaceous. Paleontological results of cutting samples in well Saha-1 show that they contain marine microfossils including calcareous microalgae, ostracod fauna, dinoflagellate, foraminifera, etc. The main geochemical characteristics of these samples are high abundance of gammacerane, β-carotane and dinosteranes which are marine biomarkers. Both microfossil distribution and geochemical characteristics suggest that the Upper Cretaceous strata were deposited in a marine environment. Marine transgression happened in the Eastern Niger Basin in the Late Cretaceous, coinciding with the worldwide eustatic sea level highstand. In the Early Cretaceous, the basin was dominated by continental deposits, whereas under the background of thermal subsidence and marine transgression, the Eastern Niger Basin became a unified basin in the Late Cretaceous, depositing massive marine strata.

Key words: marine transgression；microfossil；&beta, -carotane；dinosterane；Late Cretaceous；Eastern Niger