New regional stratigraphic insights from a 3D geological model of the Nasia Sub-basin, Ghana, developed for hydrogeological purposes and based on reprocessed B-field data, originally collected for mineral exploration

Abstract

Abstract. Re-processing of regional-scale airborne electromagnetic data is used in building a 3D geological model of the Nasia Sub-Basin, Northern Ghana. The resulting 3D geological model consistently integrates all the pieces of information brought by the electromagnetic data, lithologic logs, ground-based geophysical surveys and the prior geological knowledge of the terrain based on previous research. The geo-modelling process is aimed at defining the lithostratigraphy of the area, chiefly to improve the stratigraphic definition of the area as well as for hydrogeological purposes. The airborne electromagnetic measurements, consisting of GEOTEM B-field data, were originally collected for mineral exploration purposes. Thus, those B-field data had to be (re)processed and properly inverted as the original survey and data handling were designed for the detection of potential mineral targets and not for detailed geological mapping. These new geophysical inversion results, compared with the original Conductivity Depth Images, provided a significantly different picture of the subsurface. The new geophysical model led to new interpretations of the geological settings and to the construction of a comprehensive 3D geomodel of the basin. In this respect, the evidences of a hitherto unexposed paleovalley could be inferred from the airborne data. The stratigraphic position of these paleovalleys suggests a distinctly different glaciation history from the Marinoan events, commonly associated with the Kodjari formation of the Voltaian sedimentary basin. Indeed, their presence may be correlated to mountain glaciation within the Sturtian period though no unequivocal glaciogenic strata have yet been identified. This pre-Marinoan glaciation is recorded in rocks of the Wassangara group of the Taoudeni basin. The combination of the Marinoan and, possibly, Sturtian glaciation episodes, both of the Cryogenian period, can be an indication of a Neoproterozoic Snowball Earth. Hence, the occurrence of those geological features, do not only have an important socio-economic consequences – as the paleovalleys can act as reservoirs for groundwater – but, also from a scientific point of view, could be extremely relevant – as their presence would require a revision of the present stratigraphy of the area.

Geophysical Modelling of a Sedimentary Portion of the White Volta Basin (Ghana)

“…Considering, for example, Fig. 5 a, as discussed in detail in the recent [ 20 ], CDI’s lateral heterogeneity is evident not only in the shallow, right, portion of the section, where resistive inclusions are evident, but, also, at depth, along the flight line, where spurious lateral oscillations of the electrical properties are visible. On the other hand, the MGN result in the same figure (Fig.…”

“…This research is intended to further elaborate on the recent results discussed in [ 20 ]. In [ 20 ], Dzikunoo et al discuss the stratigraphic interpretation of reprocessed airborne electromagnetic data in the Nasia basin in Northern Ghana; here, we show some of the geophysical inversions performed in the sedimentary portion of the White Volta basin that were partially used for the construction of the geomodel of the Nasia basin.…”

Instantaneous Inversion of Airborne Electromagnetic Data Based on Deep Learning

“…The recorded time series in turn decays exponentially over time due to ohmic loss and downward propagation and shows great sensitivity to conductivity anomalies. As the technology develops, AEM survey has been applied extensively in groundwater detection (Ball et al., 2020; Klee, 2013; Mikucki et al., 2015; Minsley et al., 2021; Thomsen et al., 2004; Viezzoli et al., 2010), mineral exploration (Koné et al., 2021; Okada, 2020; Roach et al., 2014), urban investigation (Steuer et al., 2020) and geological mapping (Dzikunoo et al., 2020; Jordan et al., 2009; Ley‐Cooper & Brodie, 2020; Rey et al., 2019; Silvestri et al., 2019; Wong et al., 2020). Recently, it has been exploited specifically in confined aquifer detection (Dugan et al., 2015), subglacial hydrology (Blatter et al., 2018), and volcano hazards (Dumont et al., 2019; Peterson et al., 2021).…”