  Reprocessing of regional-scale airborne electromagnetic data (AEM) is used to
build a 3D geomodel of the Nasia sub-basin. The resulting 3D geomodel
integrates all the prior pieces of information brought by electromagnetic data,
lithologic logs, and prior geological knowledge. The AEM data, consisting of
GEOTEM B-field data, were originally collected for mineral exploration. 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 inversions
provided a 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. The evidence of a system of
paleovalleys could be inferred from the AEM data. The stratigraphy of these
paleovalleys suggests a different glaciation history from the known Marinoan
events, commonly associated with the Kodjari formation of the Voltaian
sedimentary basin. The presence of the paleovalleys within the Panabako may be
correlated with mountain glaciation within the Sturtian age, though no
unequivocal glaciogenic strata have yet been identified. 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. The occurrence of those features not only has important
socioeconomic consequences - as the paleovalleys can act as reservoirs for
groundwater - but also from a scientific point of view, they could require a
revision of the present stratigraphy of the area.
