TOWARDS PREDICTIVE MODELS OF LANDSCAPE GEOCHEMISTRY IN DEEPLY WEATHERED TERRAINS USING ELECTROMAGNETICS

Nearly 25% of the Earth's continental surface area is affected by tropical climatic conditions that result in intense chemical weathering. These areas often display lateritic profiles that may reach depths of up to 100m. Understanding the geology of these regions is problematic due to the lack of fresh bedrock outcrop and their complex weathering histories, as many of these areas display weathered profiles, which have been developing for millions of years. Thus, many of these regions correspond to ancient, stable and weathered landscapes, as is the case for several regions in Australia.

The development of links between landscape geochemistry in deeply weathered terrains and geophysical datasets is a key element to understand better the extent and evolution of weathering. Intensely weathered landscapes can be characterized by delineating their stratigraphy, relative age and depth. This allows the generation of 3D models of the cover architecture and, therefore, the delineation of weathering fronts. This combined approach contributes to the generation and evolution of predictive and detective models of the geochemical evolution of a landscape since it has the potential to provide lateral and vertical trace element dispersion.

The data density and the depth of ground penetration (>400 m) of airborne electromagnetics (AEM) is ideally suited for inferring the buried geology between known stratigraphic cover profiles. AEM has the potential to significantly improve weathered cover architecture reconstruction and, therefore, the interpretation of the landscape geochemistry, erosion and deposition.

In this study we present specific models on the interpretation of AEM for deeply weathered terrains, to understand better the complex weathering processes and their implications for geochemical dispersion in areas of overprinting weathering.