Inception and subsequent development of conduits in the Cuilcagh karst, Ireland
This thesis explores speleogenesis within the Dartry Limestone Formation of Cuilcagh Mountain by considering the hydrogeology of the aquifer in the modern setting but also by considering its evolution since it was deposited during Asbian (Dinantian) times. Due to the synclinal structure of the region, which gently plunges northwestwards, the aquifer remains buried beneath the upland and is not exposed to the south. However, the formation outcrops along its northern and eastern upland margins where resurgences drain the aquifer via an extensive network of cave systems, which include Marble Arch Cave. In the west, the aquifer lies near surface but a significant artesian resurgence, Shannon Pot Rising, emerges from the aquifer via c. 20m of overlying sandstones and shales. Water tracing experiments undertaken during this research project have added significant clarity to the hydrological regime that operates within this karst aquifer. These tests have shown that whilst extensive conduit systems are present at the eastern and northern margins of the uplands, Shannon Pot Rising in the west is the outlet for a regional conduit system that operates beneath Cuilcagh Mountain where the aquifer remains buried and in places confined. Water tracing has also identified that the boundary between the regional and marginal systems correlates to an igneous intrusion, the Cuilcagh Dyke. Hydrochemical data from Shannon Pot Rising indicates that the regional system has both shallow and deep flow components. This and hydrogeological evidence indicates that Shannon Pot developed as an overflow and that it's conduits formed at depth and unrelated to surface processes. Study of the cave systems at the eastern and northern margins have identified a number of lithological discontinuities within the sequence that have guided conduit inception within the aquifer. These early systems were later modified when the aquifer became unconfined and surface karst landforms developed.