Untersuchungen zur Verkarstungsfähigkeit von Molassekonglomeraten des Hochgrat-Adelegg-Fächers im Südwesten Bayerns (Allgäu) | Investigations on the karstifiability of Molasse conglomerates of the Hochgrat-Adelegg Fan in southwestern Bavaria (Allgäu)
2012
Flechtner, Ferdinand | Scholz, Herbert
During the course of geological mapping in southwestern Bavaria (Oberallgäu), several phenomena within the upper Oligocene and lower Miocene carbonate-rich conglomerates of the Lower Freshwater Molasse (LoFM) were observed which would be expected only in karst areas, e.g. sinkholes, ponors, gully klints, karren and caves. However, there is no evidence for karstification of adjacent and very similar conglomeratic successions belonging to the Upper Marine Molasse (UpMM) or the Upper Freshwater Molasse (UpFM). An explanation was sought for the obviously different karstifiability of the Molasse successions. A total of eight coarse-grained conglomerate samples were collected (LoFM, UpMM, UpFM), which were comparatively analyzed to identify significant differences. The karstifiability is dependent on significant differences in the total carbonate content, the fraction of calcite and dolomite grains and the proportion of insoluble components. The karstifiability of Molasse conglomerates starts at a fraction of about 70 to 80 weight-% carbonate. The content of insoluble material exceeding 25 to 30 % leads to a clogging of pores (colmatation), reducing water conductivity and results in an obstruction of karstification. These values coincide very well with threshold values indicated for the karstifiability of massive carbonate rocks in the relevant literature.
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