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Fintona Hills Complex - Crockfadda outwash-moraine systemFermanagh, Tyrone
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Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: H346544, H390565
Rocks
Rock Age: Quaternary
Rock Type: Gravel, Sand
Interest
Other interest: No data, Glacial deposit, moraine, outwash

Summary of site:

The main features of this area are substantial moraine ridges aligned east-north-east/west-south-west, roughly parallel with the adjacent fringe of the Fintona Hills and extensive areas of glacial outwash spread over the land exposed by the retreating ice margin. The moraine ridges are almost 1km long, 300m wide and up to 20m high. Some are separated by narrow, deeply-cut meltwater channels up to 50m wide. Eskers, kettle holes, and proximity to bedrock are associated features.

Meencrim Pit exposes typical outwash deposits that appear to have accumulated in a local depression defined by bedrock. Sediments filling it vary from sands to clays and are well bedded, in broad channels with marked rhythms of deposition (repeated cycles of sediments) and structures suggesting the periodic escape of enclosed water. There are stacked ripples (called climbing ripples) that form in areas of steady deposition and constant directional water flow. All these features suggest deposition from meltwater, with marked seasonal flow, into shallow, standing water. The source could well have been meltwater from ice tunnels. In two neighbouring localities near Crocknaconspody there are large limestone boulders alien to the area that could have been washed into place by sudden, powerful, torrential flooding as an adjacent glacial lake breached the watershed. At Crocknaboortan there is a section through a moraine ridge about 25m long and 5m high, showing sand and pebble gravel in beds 40-60cm thick, stacked one on top of another. They do not persist laterally and they contain normal and reverse faults aligned north/south. Such sediments are typical ice margin deposits and their position here, north of Brougher Mountain, suggests a lateral moraine banked against its northern slopes and held in place by ice. Collapse of the decaying ice at the flanks of the ice sheet (promoting the faulting in the unsupported moraine) and the consequent escape of ponded water are common features of moraines. Kettle holes provide evidence of large masses of static ice that became smothered in the moraine sediment.


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