Hydrologic Evolution of a Carbonate Aquifer (Dinaric Karst, Croatia)

Abstract

Dinaric Karst terrains contain specific, lam inatedspeleothems, which line all surfaces of subterraneanvoids including Cretaceous bedrock limestone, and oldervadose speleothems and clastic sediments. The speleotherms may attain a thickness of one metre. Deposition of these speleothems took place during a longterm phreatic period in the Late Quaternary. This is incont rast to well-known, widespread speleothems, whichwere, and are deposited in vadose and uppermost phreaticsettings. Furthermore, the origin of these phreaticspeleothems departs from common experience by the dominant dissolutional widening of underground conduits when saturated. Phreatic speleothems can be importantstrat igraphic marker for the stratigraphy of cavesediments. This approach revealed a sequence of threehydrologic stages: (1) prephreatic stage with dominantvadose conditions and dissolution processes, (2) phreaticstage when the ground-water level was very high inthe large karst area, and when the volume of the voidsdecreased, and (3) the last, dominantly vadose stageduring which voids were enlarged for the second time,and phreatic speleothems may be covered by youngerclastics and vadose speleothems.