REMOTE SENSING ANALYSES OF LINEAMENTS AND SPRINGS OF PART OF OKEMESI FOLD BELT, SOUTHWESTERN NIGERIA.

Abstract

The project entails the study of lineament, springs and the geology of part of Okemesi Fold Belt, Southwestern Nigeria. The study area is a typical Precambrian tract in Southwestern Nigeria. Rock types in the study area include: Banded-gneiss, Quartzite, Quartz-schist, Mica-schist, Amphibolite-schist, with various structures found on the outcrops such as joints, fractures, solution holes, micro folds, and above all, the presence of an asymmetric and overturned fold detected from the cross-section of the geologic map produced. This study was carried out to illustrate the application and emphasize the importance of remote sensing and Geographic Information System (GIS) techniques for efficient lineament and spring resources exploration. These demonstrate the use and extraction of LANDSAT-8 OLI imagery and Radar Imagery; Digital Terrain Model (DTM) from Shuttle Radar Topographic Mission (SRTM) and also, geological map for mapping and analyses of lineaments. Digital image processing techniques involving linear/edge enhancement and directional filtering were applied on the image to enhance the edge of the linear features using ENVI 4.7 software. ERDAS 10.3 Imagine® 2015 was the preferred software for this study for conducting image analysis because of its robust filtering algorithms suitable for lineament mapping. The filters applied to the several bands therefore, helped in extracting structures and identifying their trends using several image enhancement techniques. The enhanced image, the normalized differences vegetation index (NDVI), image and hill shaded relief image (Processed SRTM-DEM) were visually interpreted through GIS overlay operation for lineaments extraction through on-screen digitizing using ArcGIS 10.2 software. The extracted lineaments and spring were statistically analyzed to determine lengths, densities, flow direction and intersections of the lineaments to generate rose diagram, lineament density, lineament intersection and spring distribution map. The DEM was processed for topography and establishing the intersection between tilted plates which helped in recognizing different structures were used.The interpretation process involved correlating drainage, vegetation patterns and topography of the area with structures using visual interpretation elements of texture, color, tonal differences and orientation. The color and pattern of the geology and geomorphology of the area were also used to infer the different types of lineaments. Throughout this study, panchromatic only Landsat band-2-7 was used for auto extraction under suggested parameters values within PCI Geomatica software. Three geospatial analyses were applied in order to evaluate the lineaments, these are: length, density and orientation analyses. The interpreted lineaments have been classified into three major groups on the basis of their geometry and orientation, it is inferred that the NNE-SSW, NNW-SSE and ENE-WSW trending lineaments falls in major frequency domain. The satellite data has shown significant morphological expression of folds, faults and lineaments. A total of ten (10) spring water samples were collected from the study area. The analyses revealed the samples have concentrations of anions and cations in the spring (water) samples are; Cl⁻(1.77 – 8.86mg/l), NO₃⁻ (0.68 – 5.09mg/l), HCO₃⁻ (2.50 – 32.0mg/l), SO₄²⁻ (0.01 – 0.04mg/l), Ca²⁺ (1.60 – 24.05mg/l), K⁺ (0.40 – 1.30mg/l), Mg²⁺ (1.37 – 15.60mg/l) and Na⁺ (1.20 – 1.70mg/l). Comparison of the results by plots of concentration of elements against anions and cations showed that most of the elements have high concentration around Olutokin spring, which lie in the western part of the study area. The underlying lithology (quartzite) probably played a major role in the distribution of these elements. Which aren’t to World Health Organization (WHO) standards and may have harmful effect on inhabitant leaving around Okemesi area, unless adequate treatment is provided for domestic consumption, but can be used for agricultural purposes without subjecting it to any further chemical treatment.