Abstract James Robert Temple Hazell, known to many as Robin Hazell, passed away in March 2017, in Bodmin, Cornwall, aged 89, after a professional life spanning close to 70 years. Robin’s main contributions addressed the exploration for and development of groundwater especially in hard rock areas. Much of this work was undertaken in the country of his first overseas posting, Nigeria, and was primarily spent in the field. He started his career in south and east Nigeria mapping groundwater resources and uncovering links between geology, baseflow and the likelihood of surface water being contaminated. In northern Nigeria he developed conceptual models for how groundwater existed in fractured rocks, and the importance of mineralogy and fractures, and used this knowledge to help site many thousands of successful boreholes. Perhaps Robin’s greatest legacy, however, was his generosity in teaching and mentoring other hydrogeologists. Robin’s last public contribution was his paper at the conference on Groundwater in Fractured Rocks, the subject of this Special Publication.

Abstract: Rollover is the folding of the hanging-wall sedimentary record in response to slip on listric normal faults, and is a common feature of sediment-rich, gravity-driven tectonic provinces. Rollovers have been extensively studied by means of geometrical reconstruction, and numerical and analogue modelling. However, the detailed interaction between the kinematics of bounding listric normal faults and their hanging-wall deformation is not yet fully understood. In this study, we use 3D seismic-reflection data from the Forcados-Yokri area, western Niger Delta, Nigeria, to study the lateral linkage and landwards backstepping history of an array of listric normal faults, particularly focusing on their influence on the development and evolution of hanging-wall rollovers. Five individual, partly overlapping rollover structures have been studied with respect to their relative initiation and decay time, their spatial distribution, and their relationship to the tectonic history of their respective bounding faults. We demonstrate that the studied rollovers are highly dependent on the development of their bounding faults in terms of initiation time, lateral linkage, internal structural development and decay. Fault–rollover interaction is dynamic and changes through time depending on the temporal evolution of listric faults. Four genetic types of fault–rollover interaction were identified in this study: (1) the rotation of a rollover–crestal-collapse system, controlled by a changing lateral bounding-fault orientation during fault growth; (2) a stepwise shift of rollover–crestal-collapse systems associated with rollover abandonment, controlled by the initiation of a new fault in the footwall of an older structure; (3) a gradual shift of successive rollovers controlled by branching main faults; and (4) a general landwards and upwards migration of crestal-collapse faults within a rollover above stationary listric main faults.

We reviewed the current state of waste management practices in Nigeria using examples from different parts of the country. Commonly practiced waste disposal methods in Nigeria, such as burial, open-air burning, and open dumping, were found to be ineffective and detrimental to public health and the environment. It was also shown that waste management cannot be successfully operated as a social service. Rather, the generator of waste must be held responsible. Problems confronting efficient waste management in Nigeria include the proliferation of unplanned settlements, traffic congestion, insecurity, and ignorance. An experimental model being used in Lagos State for the management of wastes may be the solution. Given the rate of population growth, industrialization, and urbanization, forward-looking and effective waste management plans need to be set in motion for the protection of public health. Such plans must involve all stakeholders, including the waste generators, the private sector, the informal sector, and regulatory agencies.

Abstract Nigeria’s under explored and poorly understood frontier basins include the Nigeria, Chad, Bida, Dahomey, Sokoto, and Benue basins. They have their origins in the multi-phased rift systems that were formed during the breakup of Gondwanaland in Early Cretaceous time. The rifting is widely attributed to the stretching and subsidence of the African crustal blocks accompanied by reactivated plate movements in the early Tertiary. These basins are part of the West African Rift Subsystem (WARS) of the West and Central African Rift Systems (CARS). The Chad basin, the largest, is an intracratonic rift basin having an area of 2,335,000 km 2 that covers Chad, Niger, Cameroun Republics, and the northeastern part of Nigeria. Only about 10% of the Chad basin lies within Nigeria. It is a two-stage rift basin comparable with the petroliferous south Chad basins (Doba, Doseo) by having (A) a Lower Bima early rift stage generated by east–west gravity faults of Albo-Aptian age, followed by an Upper Bima Sag phase (Albian); and (b) an Upper Cretaceous rift phase with deposition of lower Fika source rocks followed by a mild Tertiary sag phase corresponding to the sedimentation of Lower Kerri Kerri and Chad formations. Of the 23 dry wells drilled in the Chad basin, only the Wadi-1 and Kinasar-1 wells recorded non-commercial gas accumulations. Three possible petroleum systems have been mooted. The petroleum systems of this and other Nigeria frontier basins are discussed. Suggestions are made for the successful search for hydrocarbons in these basins.

Alkaline magmatism along the Cameroon Line has been active for at least 67 m.y. and is currently defined by an almost SW-NE geological lineament (mean value: N30°E). Available petrological, geochemical, and structural data obtained over the last 20 yr lead us to reappraise its mechanism of emplacement. Known as the second most important geological curiosity in Africa, after the East African Rift system, it displays a continental part and an oceanic part, a unique feature in Africa and even in the world. The continental part contains both plutonic and volcanic massifs, and the oceanic part consists only of volcanic massifs. Plutonic rocks as a whole define a complete series of gabbro-diorite-monzonite-syenite-granite type, whereas volcanic rocks display abundant basic (basalt-hawaiite) and felsic (trachyte-phonolite-rhyolite) lavas with very few intermediate ones (mugearite-benmoreite). The formerly entire alkaline nature of these rocks is here ruled out by the discovery of volcanoes with geochemically transitional affinities in some areas of the continental sector. On the other hand, new K-Ar and 40 Ar/ 39 Ar dates confirm the absence of any age migration associated with the SW-NE linear trend. This lack of steady time-space migration and the SW-NE trend have also been observed in the magmatic provinces of Nigeria and Benue Trough, which share similar geochemical features with the Cameroon Line, and along the NE-SW major igneous lineaments in South Africa. The mechanism of such episodic emplacement of alkaline magmatism can be better explained in terms of complex interactions between hotspots and lithospheric fractures during African plate motion.