On the role of clay-carbonate reactions in speleo-inception, A contribution to the understanding of the earliest stage of karst channel formation
Jože Pezdič, France Šušteršič , Miha Mišič - (27/1,1998)
This report presents a previously undescribed potential mechanism for speleo-inception at contacts between limestone and dolomite. Experimental sites are provided by denuded caves in Laški Ravnik, about 3km northeast of the Planinsko polje, Slovenia. In this area many channels originated along the actual contact between the limestone and dolomite layers, or very close to it. The solubilities of calcite and dolomite within the temperature range 2oC to 16oC, and at CO2 partial pressures ranging from 0.1 to 10%, are described first. Different combinations of natural conditions and possible interactions are re-calculated using the PHREEQM computer program. Possible influences of residual marine formational water within carbonate sediment with a porosity of up to 20% are overviewed. The results suggest that speleo-inception can be best explained by the theory of de-dolomitization in the presence of clay minerals and dissolved silica species at relatively low temperatures, as the contact zone between dolomite and calcite is rich in clay and organic matter. The presence of CO2, clay minerals and dissolved sulphate species derived from pyrite oxidation can boost the proposed processes, while marine "formational" water can enhance the solubility of calcite and accelerate the precipitation of dolomite.