In this work we have applied the Kiraly structural-geological methodology to determine the hydraulic conductivity of the hydrogeological complexes outcropping in the M. Catria-M. Nerone, Cingoli and M.gna dei Fiori carbonate ridges (central Apennines, fig. 1). The objective was to verify whether the results would confirm the groundwater circulation pattern for the above mentioned hydro-structures, whose general features have already been described in previous studies. The outcropping Umbrian-Marchean sequence is composed of an 800 m thick carbonate neritic unit (Calcare massiccio: Upper Triassic-Lower Lias), overlain by bedded calcareous, marly and cherty pelagic sequences with thickness ranging from 900 m to 1400 m. The hydrostructures considered in this paper are represented by the Massiccio, Maiolica and Scaglia complexes. They have similar features to those of other (Umbrian-Marchean) Apenninic carbonate ridges. Mean effective infiltration for the Massiccio complex ranges from 860 mm/y to 1160 mm/y, whereas lower values (with maximum of 600 mm/y) are typical of the Maiolica and Scaglia complexes. The results of Kiraly's methodology have confirmed the ground water circulation pattern obtained from standard hydrogeological studies. The main hydraulic conductivity direction is in fact strongly controlled by tectonic lines trending parallel to the ridge axis (NNW-SSE). The highest values in hydraulic conductivity (k <sub>e</sub> congruent to 10 (super -4) m/s) for the Massiccio complex have been found in Jurassic structural highs, where the complex is composed by the Calcare massiccio del M. Nerone and the Maiolica Formations. The Maiolica complex in basinal areas and the Scaglia complex show lower values (k <sub>e</sub> congruent to 10 (super -6) /10 (super -6) m/s), in good agreement with a relative permeability scale based on lithology. Nonetheless these values are not high enough to explain some characteristics of the groundwater circulation obtained from measurements of springs and rivers, such as the extreme variability in discharge and chemistry connected to rainfall: actual hydraulic conductivity values must be greater than those obtained with structural-geological analyses as they are greatly influenced by karst phenomena. Downflow velocity is thus controlled by karst phenomena, which allows a fairly rapid hydraulic circulation at depth. The role of the eastern thrust front as a low permeability boundary for groundwater circulation is confirmed in the M. Catria-M. Nerone ridge; such tectonic lines normally represent the eastern border of the Apenninic ridges. The main flow direction is apenninic; other directions (opposite or radial to the flanks of antiforms) can be superimposed on the main one in areas of great tectonic complexity such as the Jurassic structural highs. Extensional Jurassic faults striking N-S, interpreted as transfer faults for NNW-SSE thrust sheets, can create hydraulic continuity among different carbonate ridges along an Apenninic direction.

You do not currently have access to this article.