DETERMINATION OF ORIGIN OF GROUNDWATER FROM ONSHORE MUD VOLCANOES WITHIN THE UPPER BENUE TROUGH, NIGERIA, USING ISOTOPIC ANALYSES

Abstract

 Onshore mud volcanoes found in parts of the Upper Benue Trough extrude either slurry of mud and water or fresh water, sometimes intermittently, or periodically but from different craters. While the source of the clays is attributed to the Yolde Formation, The source of the water seeping out of the craters is yet to be determined. This study is aimed at using the application of isotopes to determine the source or origin of the groundwater seeping out through the craters of these onshore mud volcanoes. Isotopic composition of groundwater usually reveals the origin, movement and distribution processes of groundwater. Onshore mud volcanoes found in parts of the Upper Benue Trough are characterized with typical craters through which groundwater seeps out to the surface. Five (5) water samples were collected from the craters of five selected fields of mud volcanoes at Todi (K4), Lallapido (01), Laturu (09), Gujuba (O6) and Pamadu (K5). Results from the isotopic analysis show that the groundwater which seeped out from the mud volcano craters at Gujuba and Pamadu, fell close to the Global Meteoric Line (GMWL) with low values of Hydrogen (δ2 H) ranging from -5.21 to -6.77 and oxygen (δ18 O) ranging from -32.6 to -40.5, and, reveals their origin from meteoric water source, while analyzed samples from Todi, Lallapido and Laturu has high value of Hydrogen (δ2 H) ranging from -2.07 to -3.43 and high value of Oxygen (δ18 O) ranging from -16.7 to -23.9,which reveals slight evidence of evaporation, but their slight closeness to the GMWL also indicate a mixed source of connate and meteoric groundwater. Therefore, this study has confirmed that this groundwater seeping through the craters to the surface are of mixed origin of connate and meteoric, mineralized and may be considered for therapeutic purposes.