Brittle deformation in the Afikpo Basin (Southeast Nigeria): Evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough, Nigeria

作     者：Odigi M.I. Levi C. Amajor 

作者机构：Department of Geology University of Port HarcourtPort Harcourt Nigeria 

出 版 物：《Chinese Journal Of Geochemistry》 (中国地球化学学报)

年 卷 期：2009年第28卷第4期

页      面：369-376页

核心收录：

学科分类：070904[理学-构造地质学] 0709[理学-地质学] 07[理学] 

主　　题：白垩纪末期 伸展变形 尼日利亚 盆地 海槽 脆性变形 菲 证据 

摘      要：This paper deals with the regional and structural framework of the Cretaceous rocks in the Afikpo Basin located in the southeastern part of the Lower Benue Trough. Results from regional tectonics are presented together with those of the microtectonic analysis of microfaults in the Owutu-Afikpo-Adadama area in the basin. The Owutu-Afikpo-Adadama ridge at the north-central part of the basin marks the boundary between the Late Cenomanian-Turonian-Conianian sediments and the Campanian-Maastrichtian sandstones. This ridge trends N45oE on average and is faulted in three main directions, namely: (1) N-S normal faults; (2) NE-SW strike-slip faults; and (3) NW-SE strike-slip faults. The faulted rocks along these brittle discontinuities are mainly cataclastics with internal fracture cleavage and sigmoidal quartz mosaics that are reminiscent of extensional deformation. The cataclasites often bear slickenside striations. The NE-SW and NW-SE strike-slip faults are the results of the youngest brittle events on the Owutu-Afikpo-Adadama ridge. These faults were reactivated after deposition of the Campanian-Maastrichtain sediments (post-depositional faults) and, therefore, are post-Maastrichtain. Microfault analysis of these fault trends suggests an extensional regime that prevailed in the Lower Benue Trough. These results are of significance because this event is least poorly understood and less documented in contrast to the Cenomanian and Santonian events that affected the older Cretaceous strata in this region.