Der Einfluss regionaler Grundwasserfließsysteme auf die Initialphase der Speläogenese tiefer Karstsysteme

摘要

This paper gives an overview of the key principles necessary for an understanding of Speleogenesis, including selected speleogenetic models. The most popular of these models at the moment is the four-state model, which attributes the depth of a karst system principally to the depth and spatial distribution of the geological-tectonic bedding planes. According to this model, thick or steeply inclining planes lead to deep phreatic loops, while shallower and more interconnected planes lead to horizontal karst systems more heavily influenced by the water table. The key to understanding the initial karstification is the particular dissolution kinetics of limestone dissolution. While the dissolution of limestone by limestone-aggressive water leads to a first order dissolution kinetic, this changes to a higher order dissolution kinetic as full saturation is approached. Because of this phenomenon, full saturation and loss of aggressiveness do not occur, and the widening of initial fissures is possible even without the constant addition of fresh carbon dioxide to the system. In numerical models these processes can be simulated with significant simplifications and using various key parameters. The paper summarizes the current development status of these models. The main part of the paper presents the synthesis of the results of numerical modeling and the author's own hydro-geological/speleological research. The author has developed speleogenetic models for complex karst systems in the Steinernes Meer (Austria), the Sierra el Abra and Sierra Juarez (both in Mexico) and the Rheinische Schiefergebirge (Germany). The paper discusses the key hydro-speleological parameters and the influence of regional groundwater flow-systems during the initial karstification and the resulting template for the future development of the karst system. Guidelines for the duration of the initial karstification can be derived from the numerical models. These correspond with the geological/speleological findings. Especially in a very early phase of the initial karstification lasting over a million years, the almost saturated water leads to an ongoing widening of the initial fissures. The groundwater flow obeys the laws of groundwater flow in a porous and homogeneous medium (Hubbert 1940). As a result, deep phreatic flow paths form even at a very early stage of speleogenesis. These then have a developmental headstart during the breakthrough phase so that karst systems develop with deep phreatic tubes. The actual distribution of the bedding planes, which the four-state model considers decisive, plays only a minor role.