Influence of geology, glacial processes and land use on soil composition and Quaternary landscape evolution in The Burren National Park, Ireland

Abstract

The Burren in County Clare, western Ireland is a glaciated karstic landscape with a fragmented soil and vegetation cover on a predominantly limestone substrate. A representative area approximately 4 km 2 in extent located within The Burren National Park was studied in order to determine the distributions of soil types and relate these to geology, glacial erosion and deposition, post-glacial mass movements and land use. Mineralogical and particle size analyses indicate the presence of two distinct soil types, one shale-bearing, the other granite-bearing. Geochemical analyses confirm this division and also reveal soils of mixed composition and a distinctive subtype of granite-bearing soil that occurs exclusively on drumlin-like landforms. The soils on the drumlins formed by the decalcification of limestone-rich glacial diamicton (till) containing granite and metamorphic rocks derived from County Galway to the north. The occurrence of mineralogically similar though geochemically heterogeneous soils throughout the area suggests that there was once an extensive thin cover of diamicton, which has almost entirely vanished because of pedogenesis and erosion. Soils containing shale fragments occur in a glacial dispersion train extending south from outcrops of a small body of shale-rich limestone breccia. Isolated patches of shale-bearing soil occurring up to 1.2 km from these outcrops may have formed by the weathering of ice-transported boulders. The presence of relatively deep soil cover on outcrops of the shale/limestone unit is attributed to Holocene weathering to form an erosion-resistant clay-rich soil. Tree charcoal, 14C-dated to 3300 BP and buried to a depth of 2 m by mixed granite- and shale-bearing soil, indicates that Bronze Age deforestation triggered mass movement and soil erosion. Denudation processes are still active in the Burren landscape.