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.