Geophysical Assessment of the Upper Dja Series Using Electrical Resistivity Data

Abstract

The upper Dja series consists of carbonates and shales deposits that date 580 ± 150 Ma. Petrography and mineral chemistry studies helped to differentiate this series into many sequences including massive limestone layers with calcite (CaO3) contents of about 30 to 42%. In order to determine the subsurface distribution of these sequences, a geophysical prospection campaign was carried out in which a total of 24 vertical resistivity soundings were recorded over a surface area of 9 km2. The processing and interpretation of data using the IX1D and OpendTect modeling tools permitted the distinction of two massive limestone layers in the upper Dja series. The first layer of about 10 to 35 m thick and outcrop in few places is characterized by resistivity ranging between 1110 and 2377 Ωm, while the second layer located beyond 50 m deep is separated by a very conductive clay stone layer with a capped thickness of 15 to 35 m. 3D modeling of the top and base of these formations indicates that, the whole Upper Dja series of about 190 m thick presents folded structure. These results can constitute a useful base of information in regards to a large scale economic study of the Upper Dja limestone series.