typologie des eaux souterraines de la molasse entre chambéry et linz

Abstract
Considerably high silicon contents are linked to the quartzitic and fine grained aquifers of the brackish marine
molasse in Bavaria. Both, petrographical composition and slow flow rate are favouring the water-rock interaction.
Caracteristic lithium footprints are found in several waters, as in the aquifers composed of the "Glimmersande",
the gypse-bearing molasse, the Rigi-conglomerates, the brackish and the estuarine marine molasse.
Chromium strongly marks the waters originating from the Swiss marine Molasse aquifers. It is probably
related to ophiolithic detritus derived frome the flysch of the Prealpes.
A couple of waters show weak anomalies of cobalt, which are nevertheless intimately linked to the presence of
ophiolithic components in the sediments. Cobalt might be used as a hydrostratigraphical tool to identify
greenstone inputs.
Analysed colloidal aluminum may serve as a hydrodynamical parameter, indicating microturbidity within the
aquifer. High amounts of aluminum varying in time, have been found in estuarin deposits of the OMM.
Generally speaking, we propose three main origins of trace elements in the spring water of the Molasse basin:
• presence of certain petrographical components within the sediments such as basic and ultrabasic rocks, heavy
minerals and evaporites.
• a small flow rate through interstitial porosity of fine grained sediments, favouring water-rock interaction.
• the abundance of colloidal material in the waters which depends on the petrographical composition of the
aquifer and on sample treatment, e.g. filtration techniques.
Deep groundwater network
A second observation network composed of 21 borehole waters has been added for comparison. Compared to the
subsurface waters, deep water chemistry might differ. The following reasons seem to be responsable:
• Long residence times of water in the underground favours slow reaction kinetics.
• Chemistry of very deep water can be influenced by mixing with older formation waters.
• Most of the deep boreholes in the Swiss Molasse basin are situated in the OMM and therefore represent a
likely homogenous lithology.
Borehole waters, because of different aquifer rock types and unknown surface and borehole influences, are least
likely to represent typical Molasse water composition.