Response of a coastal aquifer system to holocene sea level change

摘要

The Ribe Formation in western Jylland constitutes the largest aquifer in Denmark. Hydrochemistry and isotopes show that the Ribe Formation generally contains high quality groundwater ranging in age from Holocene to Pleistocene. Seismic surveys show that the Ribe Formation is continuous offshore and is overlain by fine-grained sediments in some areas along the coast. During the Pleistocene, global sea level was lower than present and base level for the Ribe Formation was a river system off of the present west coast. During this period of low base level freshwater was emplaced offshore at depth within the Ribe Formation as regional flow paths extended 50 to 100 km off of the present coast. Holocene sea level rise inundated the offshore river system at which time the Ribe Formation became a coastal aquifer. Offshore hydraulic gradients decreased by orders of magnitude as coastal discharge zone advanced landward. This essentially 'trapped' freshwater offshore within the Ribe Formation.