This area, 4km long by up to 3.5km wide, extends from the northeastern-most frontal moraine system at Murrinmaguiggan [H562 788] to the major point of dissection near Cashel Bridge [H581 821]. It is constrained laterally by the uplands of Mulderg and Loughmacrory Hill [H590 773] to the west and east respectively, and Binnafreaghan and Cashel Rock [H600 809] to the north. These bedrock areas acted as points against which sand and gravel surfaces could accumulate. The outwash surface is at 216-220m O.D. There are several exposures at different ends of the outwash system: two mainly disused sand and gravel pits near Cashel Bridge and one large pit at Murrinmaguiggan.
The Cashel Bridge pit records the deposition of distal sediments in a subaquatic environment subject to little variability in energy and sediment input. Inferred processes of deposition include mass and debris flows and suspension settling through the water column. Local shallow scour and fill promote facies interbedding. Scours may have formed by high-density turbid mass and debris flows across the subaqueous sediment apron. These flows may also have prompted sediment size-sorting, inverse grading and outsized clasts. Variations in cross-bed height in these exposures record changes in water depth related to the position of the southward ice margin. The Murrinmaguiggan pit is a large, partly worked sand and gravel pit. Exposures here demonstrate the range of differential depositional processes associated with a changing ice-marginal glaciolacustrine environment. In this pit the type of depositional environment is strongly controlled by the relationship of sediments and sediment geometry and structures to the inferred location of the ice margin, and in particular to changing energy and water levels. Exposures are characterised by interbedded, discontinuous and eroded gravel, sand and silt units. In addition, individual facies are well-sorted, clasts are subrounded and facies do not display significant lateral variability in sorting or texture. These characteristics indicate that sedimentation was episodic and was punctuated by short-lived erosional events in which the proglacial or ice-marginal zone changed morphology in response to changes in the energy and sediment input system. Changes in these characteristics may be related to ice-marginal oscillations. This site does not show any evidence of extensive braided outwash environments instead favouring deposition into an impounded water body.
