Evidence of inception horizons in karst conduit networks

This paper outlines the conclusion from an analysis of 18 large cave systems around the world, comprising more than 1500 km of conduits. The 3D geometry of complex cave systems have been analysed in relation to their geological context as well as their hydrogeological boundary conditions. The methodology allowed for the first time statistical evidence of the inception horizon concept. Thereby it confirms that the development of karst conduits under phreatic conditions is strongly related to a restricted number of so called inception horizons. An inception horizon is a part of a rock succession that is particularly susceptible to the development of karst conduits because of physical, lithological or chemical deviation from the predominant carbonate facies within the limestone sequence. It passively or actively favours the localisation of dissolutional voids. The methodology based on detailed geological 3D models and cave survey allowed us to demonstrate the existence of inception horizons in karst conduit genesis. This fact improves significantly the prediction of karst conduits, knowledge that is of relevance for geological engineering problems (e.g. tunnelling, oil industry. hydrogeology) as well as for the scientific understanding of the evolution of karst systems. (C) 2008 Elsevier B.V. All rights reserved.