东尼日尔盆地海侵的微体古生物和地球化学证据  

Marine Transgression of the Eastern Niger Basin in the Late Cretaceous: Paleontological and Geochemical Evidences

作　　者：刘邦[1] 潘校华[1] 万仑坤[1] 毛凤军[1] 刘计国[1] 吕明胜[1] 王玉华[1] 

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《现代地质》2011年第5期995-1006,共12页Geoscience

基　　金：国家科技重大专项(2008ZX05029)

摘　　要：东尼日尔盆地是中西非裂谷系中典型的中—新生代裂谷盆地,位于尼日尔东部,包括Termit、Tefidet、Tenere、Grein、Bilma等5个坳陷。在对位于Tenere坳陷的Saha-1井和位于Termit坳陷的Helit-1井的上白垩统泥岩岩屑样品的微体古生物分布和地球化学特征分析的基础上,论证了东尼日尔盆地晚白垩世发生海侵。Saha-1井上白垩统泥岩岩屑样品微体古生物鉴定结果显示,样品中含有海相沟鞭藻、介形类、钙质超微、有孔虫等化石;地球化学特征表现为具有高丰度的伽马蜡烷、β-胡萝卜烷,且指示海相沉积环境的标志物甲藻甾烷丰富。微体古生物分布和地球化学特征均表明,晚白垩世地层沉积于海相环境。晚白垩世为全球海平面高位期,东尼日尔盆地发生大规模海侵。在早白垩世,东尼日尔盆地以陆相沉积为主;在晚白垩世热沉降和海侵的背景下,东尼日尔各坳陷成为一个统一的海相盆地,沉积了巨厚的海相地层。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.

关 键 词：海侵 微古生物 β-胡萝卜烷 甲藻甾烷 晚白垩世 东尼日尔盆地 

分 类 号：TE121.3[石油与天然气工程—油气勘探]