Subglacial hydrology and drumlin sediments in connemara, western ireland

Abstract

Sediment‐cored drumlins are uncommon across the glacially eroded granite bedrock of Connemara (west County alway, western reland). This paper describes the internal sediments from two significant drumlin exposures at rdmore and allyconneely. Both drumlins show a lowermost lithofacies association comprising overconsolidated subglacial diamicton with clast lithology, strong fabrics and overfolds indicative of regional east/southeast to west/northwest late eichselian ice flow. This lithofacies association is overlain at both sites by west‐dipping, stratified, graded gravel and diamicton beds that downlap onto laminated silts. These beds reflect episodic debris flows into a leeside cavity developed following creation of relief by deposition and deformation of a subglacial diamicton nucleus located up‐ice. Variations in substrate hydrological processes are identified in both drumlins based on the presence of clastic dikes, flame structures and debris flow‐deposited gravels which are present at different locations spatially within the drumlin and at different stratigraphic levels. These features reflect the close connection between subglacial hydrological and sedimentary processes and their changes over time as the drumlin form develops.