Lineament studies of rocks in Omifunfun area, southwestern Nigeria: Remote sensing and petrologic observations

Omifunfun area is situated in the southern part of Ife-Ilesa Schist Belt of the basement complex of southwestern Nigeria. The study area is  traversed by the Ifewara Fault Zone which divides the area into east-west with contrasting lithologies that have been variously mylonitized. To the east, is quartzite and to the west migmatite gneiss which are intruded by prophyritic granites. The objective of this study is to delineate deformation linear structures from Landsat imageries over the study area, and attempt to correlate the information with microtectonic structures and field observations with the aim of better understanding the geologic terrain. Lineaments were extracted from Landsat images covering Omifunfun area. The analysis of these lineaments indicates low density in three prominentorientations corresponding to 0000–0350 and 0600–0900 with minor northwest-southeast structures. The most prominent of these directions is the 0000–0350 which incidentally include mylonite and mineral lineations within the Ifewara Fault system. Microtectonic observations reveal  analogous results with three prominent foliation directions. The dominant one strikes in the same direction with the same Ifewara mylonitic foliation. These directions correspond to two major planar surfaces S1 and S2 and were respectively produced during two episodes of deformation (D1 andD2).KEYWORDS: Ifewara Fault Zone, Lineament, Microtectonic Structures, Mylonitization, Remote Sensin

A preliminary assessment for groundwater in a part of North Central Nigeria using Landsat ETM

In a basement environment where groundwater is restricted to secondary permeability, structural analysis using remote sensing is a reliable and cheap method for the start-up process for groundwater exploration. In this study, remote sensing and GIS technology were employed as a major tool for groundwater prospecting in a part of North Central Nigeria; an area prone to water scarcity for more than half of every year.The geological map of the study area, Landsat7 ETM+, and Shuttle Radar Topographic Mission (SRTM) imageries covering the area were employed in this study. Edge enhancements and directional filtering were carried out to enhance the visibility of lineaments on the Landsat imagery. To eliminate bias and subjectivity, Normalized Difference Vegetation Index (NDVI) and Digital Elevation Model (DEM) of the study area were processed for further lineament detection.Results indicate that lineaments extracted from the Landsat imagery were in agreement with those obtained from the DEM. Those obtained from the NDVI analysis were also in agreement, except for a number of entirely new lineaments detected. This showed the importance of healthy vegetation aligned in a linear or curvilinear way as a major guide to detecting subsurface water-bearing zones that are not visible on the surface. Results also show that the dominant lineaments trend along the NE-SW direction. The northwest and central parts of the study area have relatively high lineament density, while the southern part has very low lineament density. These areas with high lineament density values are more feasible zones for groundwater prospecting.Keywords: Basement complex, Edge enhancement, Groundwater exploration, Landsat ETM+, NDV

Talus Caves: Geotourist Attractions Formed by Spheroidal and Exfoliation Weathering on Akure-Ado Inselbergs, Southwestern Nigeria.

Spheroidal weathering of granites in Akure-Ado axis have resulted in the formation of talus caves as well as smooth rock boulders which are dramatically arranged, thereby giving the formation an overall aesthetic value to the observer. Unique talus boulders exist in Akure inselbergs, southern margin of the Ikere-Ado batholith. This paper looks at the uniqueness of these formations as well as their economic potentials for leisure and recreation purposes. Much attention has been given to Olumo Rock in Abeokuta, Riyom Rock and the Shere Hills both in Jos Plateau. With the clamour for developing other sources of revenue beside oil, the Akure-Ado inselbergs require attention toward proper development and packaging as potential tourist sites with the aim of enlarging the nation’s reserve of tourism products as they will draw local as well as international tourist traffic.Keywords: Sustainable tourism, Talus Cave, Spheroidal weathering, Exfoliation, Granite pluton, Basement complex, Akure area, Ikere Batholith

A study of basement fracture pattern around Akoko area of southwestern Nigeria for groundwater potential using high-resolution satellite imagery and electrical resistivity

The basement complex of southwestern Nigeria has undergone severe tectonic deformation over the geologic past, resulting in various degrees of fracturing and folding, even to the extent of complete obliteration of primary structures except for some places. This study focuses on Akoko area which is dominated by hills of crystalline rocks that have made groundwater resource exploration difficult, thereby affecting the socio-economic activities of the inhabitants. High-resolution multispectral ASTER imagery acquired at the peak of the dry season was used to delineate fractures. Additional characterization employed electrical resistivity soundings. Results indicate the existence of four sets of fractures mostly occurring within the central and north-eastern parts. More fracture intersections occupy the central part. Ground truthing shows that the fractures mostly occur in gneisses, granites and quartzites, while geophysical data interpretation revealed fracture depths typically ranging between 32 and 65 metres. In this hard rock terrain with only a veneer of weathered materials, these fractures are the targets of most groundwater exploration activities. This study further asserts the effectiveness of integrated approach to fracture characterization and its usefulness in groundwater exploration especially in a terrain that had hitherto beenhydrogeologically classified as difficult