Contamination status and source identification of heavy metals in the riverbank soils and sediments of Ona River, Ibadan, southwest Nigeria

The present study investigated the pollution levels, sources, and contamination status of trace metals (Pb, Cd, Fe, Zn, Cu and Mn) in riverbank soils and sediments at three different sections of Ona River bordering residential area. The relationship of studied metals with selected soil chemical properties was also examined. The average concentration of each of the studied metals in soils and sediments at each sampling site was less than 1 mg/kg having a decreasing trend of Zn > Cu > Fe > Cd > Pb > Mn and Zn > Cd > Fe > Cu > Pb > Mn, respectively in soils and sediments. Results of enrichment factors (EF) were generally less than 1.5 for all assessed metals; index of geoaccumulation (Igeo) in soils and sediments of the investigated sites were less than 1 while contamination factor (CF) of assessed metals were in the range: 1< CF < 3. The results of integrated pollution indicators support lithogenic sources and a low-to-restrained pollution of the considered soils/sediments by metals. The environmental risks indices of sampling sites that could be ascribed to the metals revealed low mean ecological risks potential in soils and sediments. The values of co-efficient of variation (CV) of analyzed metals were less than 50%, indicating absence of strong anthropogenic inputs, while Fe-Zn, Fe-Pb, and Pb-Zn pairs in soils and sediments exhibited strong positive correlations, an indication of common sources due to lithogenic processes. Inverse relation between analyzed metals and organic matter further confirmed little impact of anthropogenic inputs as sources of metals in soil/sediment. This study elucidated that the area was not heavily polluted by metals and revealed that the investigated riverbank areas were mildly contaminated by assessed metals, thus posing a low ecological risk

INVESTIGATION OF b-VALUE VARIATIONS IN THE AFRICAN AND PARTS OF EURASIAN PLATES

Numerous earthquakes have occurred along the collision zones of the African and parts of Eurasian plates. Some of these earthquakes along these zones have generated tsunamis. To mitigate this hazard, knowledge of b-values of the Gutenberg – Richter relation for tectonic earthquakes in the African and parts of Eurasian plates is essential. The temporal variations of b-values were evaluated using sliding time windows with each window containing a total of 100 events with a view to utilizing the results as a precursor for the earthquake occurrence. The spatial variation of b-values of the study area was also delineated by dividing it into grids and calculating the b-values for each grid using constant radius and constant number of events. Results obtained from the temporal variation of b-values showed that earthquakes of large magnitudes occurred when the b-values were low while earthquakes of small magnitudes occurred when the b-values were high throughout the study period. The results of the spatial distribution of b-values also showed that earthquakes of large magnitudes occurred in areas of low b-values while earthquakes of small magnitudes occurred in areas of high b-values. The study therefore concluded that the temporal and spatial variations of b-values might be considered as a precursor for earthquake prediction

Evidence of basement controlled faulting of cretaceous strata in the Middle Benue Trough, Nigeria from lineament analysis of gravity data

The Bouguer anomaly map of part of the Middle Benue Trough, Nigeria, was used to investigate the genetic relationship between the basement and intra-sedimentary structures in the study area. This was with a view to establishing the evidence of possible basement controlled faulting of the Cretaceous strata. Regional-residual separation of the anomalies was carried out to produce the gravity maps associated with crustal masses at deep and intermediate depth layers. The derived maps were further processed to produce Horizontal Gradient Magnitude (HGM) maps that were used to infer deep seated structures and structures existing at intermediate depth layer of the study area. HGM maxima of the anomaly at various altitudes of upward continuation were used to highlight the locations and dip directions of subsurface structures as controlled from deep to shallow zones. The results of this study showed that the structures at different depth layers dominantly trend in the same direction (N-S, NNE-SSW and NE-SW) and that the deep seated faults reflect structurally in the overlying sedimentary column. It was therefore concluded that basement faulting might have influenced the structures in the overlying sedimentary rocks.Keywords: Cretaceous Sediments, Lineaments, Azimuth-frequency, Fault Propagatio

Evidence of basement controlled faulting of cretaceous strata in the Middle Benue Trough, Nigeria from lineament analysis of gravity data

The Bouguer anomaly map of part of the Middle Benue Trough, Nigeria, was used to investigate the genetic relationship between the basement and intra-sedimentary structures in the study area. This was with a view to establishing the evidence of possible basement controlled faulting of the Cretaceous strata. Regional-residual separation of the anomalies was carried out to produce the gravity maps associated with crustal masses at deep and intermediate depth layers. The derived maps were further processed to produce Horizontal Gradient Magnitude (HGM) maps that were used to infer deep seated structures and structures existing at intermediate depth layer of the study area. HGM maxima of the anomaly at various altitudes of upward continuation were used to highlight the locations and dip directions of subsurface structures as controlled from deep to shallow zones. The results of this study showed that the structures at different depth layers dominantly trend in the same direction (N-S, NNE-SSW and NE-SW) and that the deep seated faults reflect structurally in the overlying sedimentary column. It was therefore concluded that basement faulting might have influenced the structures in the overlying sedimentary rocks.Keywords: Cretaceous Sediments, Lineaments, Azimuth-frequency, Fault Propagatio