Geophysical Modelling of a SedimentaryPortion of the White Volta Basin (Ghana)

This research deals with the essential steps carried out during the processing and inversion of the airborne time-domain electromagnetic (TEM) data used within the framework of the GhanAqua project – aiming at the groundwater development for sustainable agriculture in the White Volta basin in Ghana. The processing of pre-existing airborne TEM data has been performed with the state-of-the-art methodologies. In this respect, (1) the minimum possible gate-dependent lateral stacking between adjacent soundings has been performed for the preparation of the data; (2) a 1D nonlinear forward modelling has been used for the inversion of the stacked data; (3) even if the forward modelling was 1D, the data have been inverted by spatially constraining the adjacent models (in a pseudo-2/3D fashion). We adopted an iterative approach in which the processing and inversion parameters, and the type of stabilizer utilized, have been decided after an a-posteriori analysis. Hence, after every inversion, the results have been discussed with the geologists (1) to assess, at least qualitatively, the uncertainty of the solution features and (2) to, as much as possible, include prior geological knowledge into the geophysical analysis. The new geophysical insights detected geological features that might be interpreted as glacial paleovalleys. If confirmed, those structures can have a significant impact in terms of their socio-economic relevance (i.e. as groundwater reservoirs); as well as from a scientific point of view (as they would require rethinking the stratigraphy of the area). In addition, this kind of Sturtian glacial evidences in West Africa could support the Snowball Earth hypothesis.