Electrical conductivity and Paleo-Proterozoic foredeeps

Sedimentary facies associated with Paleo-Proterozoic foredeeps are apparently highly conductive. The conductive lithology appears to be a euxinic carbonaceous shale deposited on preforedeep continental margin facies. The shale is overlaid by axial turbidites and often incorporated into the succeeding fold and thrust belt. Carbonaceous shales can be made highly conducting if graphitized by exposure to temperatures exceeding 400 degrees C. Although foredeep facies develop diachronously, the most conductive unit is usually found in the core of the fold and thrust belt, suggesting that deformation may be essential for the complete graphitization of the carbon. The foredeep hypothesis offers an attractive explanation for several highly conductive features detected in the upper and middle crust in Laurentia, and possibly throughout the world. The euxinic facies represent highly specific, tectonic marker horizons that are readily delineated by using electromagnetic methods.