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Abstract:
A natural conduit that had formed along a fault was exposed in Upper Cretaceous limestones during construction of a tunnel near Postojna,. Slovenia. The conduit is filled with poorly indurated clastic sediments. Slickensides found on the margin of the sediment deposit show sinistral fault motion that is consistent with regional tectonism. Analysis of the sediments revealed reversed magnetic polarity. The minimum age for latest movement on the fault, origin of the cave, and deposition of these sediments is 780 ka. Present-day tectonic stresses are concordant with the fault movement, and it is likely that the fault has been continuously active throughout growth, infilling, and hydrologic abandonment of the conduit. Based upon known and modeled growth rates for conduits, this system is recording a period of growth and abandonment that exceeds 100,000 years. The role that rock discontinuities play in groundwater flow may vary over these timescales, and it may be important to account for tectonism when evaluating the long-term evolution of aquifers