Abstract The Benue Trough is a contiguous intracontinental basin that formed part of the mega west and central African rift system (WCARS). The Cretaceous sedimentary succession preserved up to 6 km thick. The Aptian-Albian Bima Sandstone non-conformably overlies the Precambrian basement rock and the sandstone is the oldest Cretaceous succession in the Upper Benue Trough. This paper aimed at understanding its lithofacies and depositional environment in Girei and environs within Yola arm of the Upper Benue Trough. From the field studies, 13 lithofacies were identified; massive matrix supported and gravel dominated facies (Gmm), matrix supported gravel (Gmg), clast supported gravel (Gci), gravel stratified (Gh), and gravel stratified trough cross-bedded sandstone (Gt), sand, fine to very coarse grained trough crossbedded sandstone (St), sand, fine, medium, coarse to very coarse grained group planar cross-bedded sandstone (Sp), low angle planar crossbedded sandstone (Sl), sand, fine to coarse grained ripple cross laminated sandstone (Sr), sand, very fine, pebbly coarse grained horizontal bedded sandstone(Sh), Sand, fine to coarse grained massive sandstone (Sm), Convuluted sandstone (Sc), silt and mud (Fsm), and mudstone (Fm). The Bima Sandstone in the study area is sub-divided into proximal alluvial fan facies are composed of Gmm, Gmg, Gci, and Fsm, lithofacies, while the mid and distal fan facies are sequentially characterised by Gh, Gt, St, Sp, Sl, Sr, Sm, Sc, and Fm lithofacies. The alluvial fan facies are matrix supported and are restricted to the basin margin, and it may represent the basal part of the outcrop lithosections, the lack of internal organization of these lithofacies reflects high-strength viscous debris flow and it speaks volume of emergence of stream near the upland, however, the Gci facies probably indicate advancement of stream influence and reduction of gravity, the associated Fsm facies could be a backswamp and/or abandoned channel deposits. The mid fan facies have basal surface that is concave-upward in transverse crossection, well-developed thick amalgamated trough crossbedded sandstone (St) facies, theses attribute represent deep channel deposits, high flow regime, and continuous creation of accommodation space, it also points towards deep perennial sand braided river system. The distal fan facies is composed of amalgamated planar cross-bedded sandstone (Sp) associated with horizontal bedded sandstone (Sh), ripple cross lamination (Sr) and mudstone (Fm) facies with better developed floodplain deposit, pointing towards the influence of steady periodic high flow with topographic difference and it reflects shallow perennial sand-bed braided river. The lithofacies of the Bima Sandstone in Girei and environs, within the Yola arm generally show architectural stacking pattern that is generally thinning and fining upward indicating inactivity and/or fan retrogradation, the and the depositional paleoenvironment varies from alluvial to braided river setting. The mid to distal fan facies of the Bima Sandstone can serve as good reservoir for hydrocarbon mudstone in which floodplain can serve as the seals and/or traps for the accumulated hydrocarbon.

中文翻译：

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尼日利亚东北部上贝努埃海槽 Yola Arm Girei 及周边地区 Bima 砂岩的岩相和沉积古环境

摘要 贝努埃海槽是一个连续的陆内盆地，是西非和中非大裂谷系统（WCARS）的一部分。白垩纪沉积层序保存厚达 6 公里。Aptian-Albian Bima 砂岩不整合地覆盖在前寒武纪基底岩上，该砂岩是上贝努埃海槽中最古老的白垩纪层序。本文旨在了解其在吉雷及上贝努埃海槽约拉臂内的岩相和沉积环境。通过实地研究，确定了 13 个岩相；块状基质支撑和砾石主导相 (Gmm)、基质支撑砾石 (Gmg)、碎屑支撑砾石 (Gci)、砾石层状 (Gh) 和砾石层状槽交错砂岩 (Gt)、砂、细粒至极粗粒槽交错砂岩（St），砂，细，中、粗至极粗粒组平面交错层状砂岩 (Sp)、低角度平面交错砂岩 (Sl)、砂、细粒至粗粒波纹交错层状砂岩 (Sr)、砂、极细、含卵石粗粒水平层理砂岩（Sh）、砂、细粒至粗粒块状砂岩（Sm）、旋涡砂岩（Sc）、粉砂泥（Fsm）和泥岩（Fm）。研究区毕马砂岩细分为近端冲积扇相，由 Gmm、Gmg、Gci 和 Fsm 岩相组成，中、远端扇相依次为 Gh、Gt、St、Sp、Sl 、Sr、Sm、Sc 和 Fm 岩相。冲积扇相是基质支撑的，限于盆地边缘，它可能代表露头岩层的基底部分，这些岩相内部组织的缺乏反映了高强度粘性泥石流，它说明了高地附近河流的涌现量，然而，Gci 相可能表明河流影响的推进和重力的降低，相关的 Fsm 相可能是一个后退和/或废弃的渠道沉积物。中扇相为基底面在横断面上上凹，发育较厚的混合槽交错砂岩（St）相，这些特征代表深水道沉积，高流态，连续创造可容纳空间，也指出向深的多年生沙辫状河流系统。远端扇相由与水平层理砂岩（Sh）相关的混合平面交错层状砂岩（Sp）组成，波纹交叉层理（Sr）和泥岩（Fm）相，泛滥平原沉积物发育较好，表明受稳定的周期性高流量和地形差异的影响，反映了浅层多年生沙床辫状河。Girei 和周围地区的 Bima 砂岩岩相，在 Yola 臂内，通常显示出建筑堆叠模式，通常向上变薄和细化，表明不活动和/或扇形回生，沉积古环境从冲积河到辫状河环境不等。毕马砂岩中远段扇相可以作为油气泥岩的良好储集层，其中漫滩可以作为油气聚集的封闭和/或圈闭。指向稳定的周期性高流量与地形差异的影响，它反映了浅层多年生沙床辫状河。Girei 和周围地区的 Bima 砂岩岩相，在 Yola 臂内，通常显示出建筑堆叠模式，通常向上变薄和细化，表明不活动和/或扇形回生，沉积古环境从冲积河到辫状河环境不等。毕马砂岩中远段扇相可以作为油气泥岩的良好储集层，其中漫滩可以作为油气聚集的封闭和/或圈闭。指向稳定的周期性高流量与地形差异的影响，它反映了浅层多年生沙床辫状河。Girei 和周围地区的 Bima 砂岩岩相，在 Yola 臂内，通常显示建筑堆叠模式，通常向上变薄和细化，表明不活动和/或扇形回生，沉积古环境从冲积河到辫状河环境不等。毕马砂岩中远段扇相可以作为油气泥岩的良好储集层，其中漫滩可以作为油气聚集的封闭和/或圈闭。在 Yola 臂内通常显示建筑堆叠模式，通常向上变薄和细化，表明不活动和/或扇形退化，沉积古环境从冲积河到辫状河环境各不相同。毕马砂岩中远段扇相可以作为油气泥岩的良好储集层，其中漫滩可以作为油气聚集的封闭和/或圈闭。在 Yola 臂内通常显示建筑堆叠模式，通常向上变薄和细化，表明不活动和/或扇形退化，沉积古环境从冲积河到辫状河环境各不相同。毕马砂岩中远段扇相可以作为油气泥岩的良好储集层，其中漫滩可以作为油气聚集的封闭和/或圈闭。