Biogeography of the Saharan Gretaceous and Paleocene epicontinental transgressions     

R. A. Reyment 《Cretaceous Research》1980,1(4):299-327

The first trans-Saharan epicontinental transgression began in the Late Cenomanian and peaked in the Early Turonian. The sea entered through rifts (Nigeria) and subsiding areas (north Africa) and, at maximum extent, spilled out onto stable craton. The central Sahara was land in late Early Turonian time; the sea seems to have remained in the central part of the Benue rift, to sally forth again during the minor Coniacian transgressive pulse. The Coniacian transgression went no further than eastern and central Niger Republic. For a short time during the Cenomanian-Turonian link-up between the Tethys and the South Atlantic, some organisms (mainly ammonites and pelecypods) passed across the Sahara. The Coniacian marine deposits of eastern Niger contain several elements typical of the Mungo River Formation of Cameroun, and coastal Nigeria. These faunistic indications imply that the topographical obstacle formed by the Zambuk ridge of northeastern Nigeria was swamped at maximum transgression. A third, very extensive epicontinental transgression began in latest Campanian time and reached its acme in the Early Maastrichtian. In the central Sahara, at least, there was a retreat of the sea in later Maastrichtian times. A final transgression peaked during the Paleocene, after which the sea withdrew permanently from the northwest African hinterland. The same marine ostracod associations occur in the Paleocene of coastal Nigeria, the Sokoto embayment, Mali and Libya, thus providing strong evidence of a marine connexion, albeit brief, between the South Atlantic and the Tethys, despite the lack of outcrop evidence in the crucial Niger valley region.  相似文献   

Ecological patterns and sustainability of freshwater swamp forest ecosystems: assessing climate and disturbance interactions     

《Singapore journal of tropical geography》2018,39(1):62-74

Species composition and factors that control the distribution of freshwater swamp forests in West Africa are largely unknown. To achieve this, 24, one‐hectare forest plots were established to assess the tree species (DBH ≥ 10 cm) distribution across the ecosystem. A total of 138 species within 100 genera and 41 families were distributed across the forest plots and 47 species were identified as indicator species. These indicator species were used to constrain the species‐environmental categories across three broad habitat types: the disturbed freshwater zone, the mangrove‐freshwater transition zone and the intact freshwater zone. While 40 species are associated with one of the three forest categories, seven of them coexisted in disturbed and mangrove‐freshwater zones. Disturbance (local factors) was identified as the most important determinant of the species distribution followed by the climatic factors. Future climate predictions for the locations are quite variable and suggest that some species may be non‐viable as the ecosystem's composition may alter. While the indicator species provides insights on the species‐environment relationships, and is useful for informing forest conservation and planning, their tendency to continually co‐exist with others and provide vital functions is dependent on how sustainably the people use them.  相似文献   

The influence of pre-existing structure on the growth of syn-sedimentary normal faults in a deltaic setting,Niger Delta     

《Journal of Structural Geology》2015

Three dimensional seismic-reflection data from the western Niger Delta were used to investigate the segmentation and linkage of a syn-sedimentary normal fault array and to estimate the influence of a pre-existing normal fault on the geometry and growth of younger faults. The nucleation, growth and linkage of a regional (seaward-dipping) deltaic fault system were analyzed on reflectivity time-/horizon slices and vertical seismic sections. In the deep subsurface, a master fault that consists of two segments (northwestern, NW, and southeastern, SE) grew through time into a single fault by lateral tip propagation reaching a final length of about 15 km. After attaining this length, displacement along the fault system developed non-uniformly through time. The analysis of the hanging-wall sediments of the deep-seated master fault shows two different processes of vertical linkage above the NW and SE segment. The SE segment links vertically to several younger faults contemporaneously with displacement accumulation on the master fault; in contrast, fault linkage above the NW segment occurred only after an interval of master-fault inactivity connecting the deep-seated structure upwards to a single syn-sedimentary normal fault. The observed differences in fault development suggest that although multi-segment deltaic faults form single fault systems after segment linkage, individual pre-linkage characteristics can be preserved, supporting a possibly diverse upward growth and connection to younger faults in the overburden. The geological interpretations presented highlight the influence of large deep-rooted structures on the development, location and geometry of shallow deltaic faults, documenting the influence of an older structural grain on delta tectonics.  相似文献   

尼日尔三角洲的沉积-构造特征     

苏玉山  王桐  李程  张光亚  赵岩  李曰俊  赵巍  赵甜玉 《岩石学报》2019,35(4):1238-1256

尼日尔三角洲位于非洲大陆西海岸的几内亚湾,由尼日尔河注入大西洋形成的,是世界上最大的三角洲之一。它发育于冈瓦纳大陆裂解形成的中、西非裂谷系和大西洋被动大陆边缘交汇部位,主体位于大西洋洋壳之上,部分位于非洲前寒武纪结晶基底之上。中、西非中生代裂谷系通过控制贝努埃-尼日尔河系的发育,间接控制三角洲的形成演化。尼日尔三角洲是一个进积型三角洲,具有典型的进积三角洲沉积序列,自下而上依次是海相页岩(Akata组)、近海三角洲相砂岩-页岩互层(Agbada组)和陆相冲积砂岩(Benin组)。三个岩石地层单位均规律性穿时,向洋方向变新。尼日尔三角洲层序中发育一大型重力滑动构造。该重力滑动构造的主滑脱面位于Akata海相页岩中,可以划分出前缘挤压构造变形区和后缘拉张伸展构造变形区。挤压构造变形区发育褶皱冲断带,伸展构造变形区发育堑垒构造,两者之间的过渡带发育滑脱褶皱。尼日尔三角洲的重力构造伴生有广泛发育的泥构造。重力动构造的形成可能与新生代喀麦隆火山带(Cameroon volcanic line)有一定的关系。  相似文献   

尼日尔阿加德兹大型富铀成矿区成矿大地构造背景及成矿模式     

姚振凯  刘翔  郑大瑜 《铀矿地质》2019,(3):145-150

用活化构造成矿理论和大地构造控矿观点,探讨尼日尔阿加德兹大型富铀成矿区的成矿大地构造背景,从多阶段构造演化、多成矿铀源、多成因复合成矿角度,提出大型富铀成矿区铀成矿的复成因模式。  相似文献   

Future river flows and flood extent in the Upper Niger and Inner Niger Delta: GCM-related uncertainty using the CMIP5 ensemble   总被引：1，自引：1，他引：0  

Julian R. Thompson  Andrew Crawley  Daniel G. Kingston 《水文科学杂志》2017,62(14):2239-2265

A semi-distributed hydrological model of the Upper Niger and the Inner Niger Delta is used to investigate the RCP 4.5 scenario for 41 CMIP5 GCMs in the 2050s and 2080s. In percentage terms, the range of change in precipitation is around four times as large as for potential evapotranspiration, which increases for most GCMs over most sub-catchments. Almost equal numbers of sub-catchment–GCM combinations experience positive and negative precipitation change. River discharge changes are equally uncertain. Inter-GCM range in mean discharge exceeds that of precipitation by three times in percentage terms. Declining seasonal flooding within the Inner Delta is dominant; 78 and 68% of GCMs project declines in October and November for the 2050s and 2080s, respectively. The 10- and 90-percentile changes in mean annual peak inundation range from ?6136 km² (?43%) to +987 km² (+7%) for the 2050s and ?6176 km² (?43%) to +1165 km² (+8.2%) for the 2080s.  相似文献   

利用三维地震资料评估深水井位工程地质灾害   总被引：2，自引：0，他引：2  

李斌  杨文达  李培廉 《海洋地质与第四纪地质》2009,(1)

随着深水油气勘探开发的快速发展,因地质灾害而发生的石油钻井事故也不断增加。据统计深水钻井大约30%的花费用于解决安全事故,其中大部分用于因地质灾害而引起的安全事故。在钻探之前通过对设计井位进行井场及钻井工程地质灾害评估,找出潜在的危害钻井安全的地质因素,可以在很大程度上避免这类事故的发生。采用以油气勘探为目的的三维地震数据,经二维高分辨率处理,对尼日尔三角洲井场区及钻井过程中可能引起的工程地质灾害因素进行评估,这些因素包括海底滑坡、浅部断层、浅层气、天然气水合物、浅层高压水流、古河谷、泥穿刺与泥火山、异常高压等。研究结果表明,采用三维地震数据经二维高分辨率处理,可得到较为丰富的地质信息,可以满足深水井位对工程地质灾害评估的要求。  相似文献   

尼日尔三角洲天然气水合物体系地震特征研究          下载免费PDF全文

杨金秀  王红亮  何巍巍  王民  卢双舫 《地球物理学报》2017,60(10):3889-3898

天然气水合物体系一般由地震上的似海底反射层BSR和下伏强振幅带(解释为游离气FGZs)所指示,但并非所有BSR及下伏强振幅带都与水合物和游离气有关.本文通过提取多种属性剖面,优选出视极性属性来辅助判断与水合物有关的BSR和下伏FGZs.—般来说,BSR和FGZs的顶部反射层表现为负视极性、高振幅的强反射特征.研究发现,尼日尔三角洲南部的水合物主要分布在与重力作用有关的生长断层及伴生的滚动背斜地区,广泛发育的断层、气烟囱、不整合面,以及砂岩层都可作为流体运移通道.除为水合物体系提供气源,这些流体运移通道还在水合物分解或FGZs超压时发挥作用,使游离气沿通道在FGZs和含水合物地层间循环,部分游离气可运移至海底进入海水甚至大气中·总之,视极性是判断水合物相关地震指示标志的有效属性,流体运移通道对尼日尔三角洲的水合物成藏具有重要作用.  相似文献   

Crustal structure of the deepwater west Niger Delta passive margin from the interpretation of seismic reflection data     

Sepribo Eugene Briggs  Joe Cartwright  Richard J. Davies 《Marine and Petroleum Geology》2009

The interpretation of 2D and 3D seismic reflection data complemented with gravity data allows the crustal architecture of the deepwater west Niger Delta passive margin to be defined. The data show that the area is underlain by oceanic crust that is characterised by a thickness of 5–7 km and by internal reflectivity consisting of both dipping and sub-horizontal reflectors. Some of the dipping reflections can be traced up to the top of the basement where they offset it across a series of minor to major thrust faults. Other internal reflections are attributed to extensional shear zones and possibly due to intrusions in the lower crust. The Moho can be correlated as a discrete reflection over >70% of the study area. It is generally smooth, but localised relief of up to 1 km is observed. The southeastern part of the study area is dominated by a zone of SW–NE striking basement thrusts.  相似文献   

Rethinking corporate‐community engagement in the petro‐economy of the Niger Delta          下载免费PDF全文

Thaddeus Chidi Nzeadibe  Chukwuedozie Kelechukwu Ajaero  Mary Basil Nwoke 《Singapore journal of tropical geography》2015,36(3):376-393

This study applies the political ecology perspective in reframing corporate‐community engagement and adapts the community‐directed intervention (CDI) strategy using Global Memorandum of Understanding (GMoU) framework in relation to 30 rural communities that are likely to be affected by gas exploration and production activities in the Niger Delta region. The study draws attention to the indigenous structures and capacities of communities to implement CDI initiatives for possible replication in areas facing similar development challenges. Adopting the CDI framework as represented by the GMoU model could reconfigure social relations of power between companies and communities and fast‐track development and prevent or, at least, reduce corporate‐community tensions and conflicts in the petro‐economy of the Niger Delta.  相似文献