Abstract
In the Tempo Valley, north‐central Ireland, flat‐lying calcareous concretions are found within massive sand beds of glaciofluvial outwash which were deposited during the late Weichselian deglacial cycle. (c. 17 000 14 000 BP). Morphologically, concretions (< 20 cm long. I I cm wide, 3 cm thick) arc bladcd to disc‐shaped, lie parallel to sediment bedding planes, and have long axes aligned perpendicular to ice retreat direction. Internally, concretions are massive to framework‐supported and were formed as calcareous cements precipitated from solute‐rich groundwatcrs. Concretions, related to steep groundwater gradients and vigorous groundwater circulation cells, were formed proglacially at the base of a thin (1.5‐2.0 m deep) layer of discontinuous permafrost as meltwater was actively expelled from the retreating ice margin. The presence of a discontinuous permafrost substrate can also help explain regional‐scale geomorphic patterns indicating stagnation zone retreat of the Tempo Valley ice mass.
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