Application of Remote Sensing for the Mapping of Geological Structures in Rainforest Area: A Case Study at the Matomb-Makak Area, Center-South Cameroon

Abstract

In the areas with rainforest vegetation, the use of SRTM (Shuttle Radar topography Mission) data because of their penetrative characters, high quality and availability, offers a new approach for the detection and interpretation of the geological structures. This paper presents the new structural mapping results of the Matomb-Makak area (western part of the Pan-African Yaounde series), based on the combined field survey and satellite image processing methods. The study area is characterized by dense forest vegetation with difficult access, scarcity and discontinuity of the available outcrops. As a consequence, geological mapping in this type of environment is difficult, time-consuming, expensive, and even dangerous and not accurate. During the field work, 280 outcrops have been investigated in which five main lithological units have been distinguished. In order to identify the foliation trajectories and the fractures network of kilometric scale, the techniques of remote sensing were used. The processing of SRTM data led to the detection of linear anomalies. These anomalies have been verified and validated to structural map on the basis of field data. The analysis of the structural map indicates: (1) two directions of S2 foliation (NE-SW major direction, locally folded and NW-SE secondary direction), (2) one family of faults trending NW-SE which locally displace the foliation, (3) a ductile shear zone with NNE-SSW trends which deflects the S2 foliation. The two directions of foliation observed in the Matomb-Makak area as well as the NW-SE direction of fault are similar to those observed in the Yaounde series by other authors. However, the structural map obtained from the interpretation of field data is quite different to that obtained from remote sensing. We have noticed that the folding structures resulting from the interpretation of the field data are not observed on the structural map obtained from the interpretation of satellite image processing. Thus, the mapping of foliation trajectories in the rainforest area on the solely basis of the field measurements, is most of the time, an extrapolation which does not represent the structural architecture at regional scale. It is concluded that the combination of field-based mapping and remote sensing methods are useful tool for the mapping of geological structures within the densely vegetated regions of southern Cameroun.