Understanding cave genesis along favourable bedding planes. The role of the primary rock permeability
Filipponi, Marco; Jeannin, Pierre-Yves; Tacher, Laurent
published: May 1, 2010
ArtNo. ESP023105402005, Price: 29.00 €
Recent studies on the complex 3D geometry of large cave systems around the World allowed us to get statistical evidence of the inception horizon hypothesis. It clearly confirmed the idea 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 can favour the earliest cave forming processes (Lowe 1992). In order to understand the reason(s) why a specific stratigraphical horizon is used for cave development we sampled 18 inception horizons of six cave systems as well as the surrounding rock mass. More than 200 rock micro-cores have been drilled and analysed to determine parameters controlling the speleogenesis, and to provide a better prediction of dissolution voids within a karstic rock mass. The analysis of these cores gives a first idea of the different properties of inception horizons. This paper only presents and discusses the results of the measurements of the primary rock permeability. The results indicate that the initial permeability contrast is not sufficient to explain alone the concentration of karst development along inception horizons. However, it is noticed that three types of inception horizons can be distinguished: type 1, where cave inception took place within the inception horizon and where the permeability of the inception horizon was slightly higher than that of the surrounding rock mass; type 2, where inception took place at the interface between the inception horizon and the surrounding rock mass, and where the permeability of the inception horizon is slightly lower than the surrounding rock mass; type 3, where the cave development took place along bedding plane fractures.