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Ballygawley Delta Complex - Tiroony RidgesTyrone
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Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: H571679
Rocks
Rock Age: Quaternary
Interest
Other interest: No data, Glacial deposit, moraine ridge

Summary of site:

A series of north-east / south-west oriented linear ridges and aligned mounds characterise the area around Tiroony, extending to Gortfin and thence to Sixemilecross, 6km to the south west. They were deeply dissected by meltwater channels as the final ice field of the last glaciation surrendered to the warming climate around 10,000 years ago.

Two limited exposures, one 2.5m high and 24m long, the second 10m high and 35m long, show that the ridges are composed of stacked pebble and grit beds with particles in firm contact, separated by thin sandy lenses up to 30cm thick. A channel filled with silt can be seen in the first, with pods of winnowed sand where the finer sediment has been swept off. Pebbles and cobbles up to 20cm in diameter occur throughout. The second exposure, through a ridge, is composed of mixed particle sizes from sand to pebbles and occasionally aligned cobbles up to 35cm across. Generally the ridge core tends to be of grit to pebble sized material, with the flanks a more chaotic mix of particle sizes. Although there is no direct evidence of ice effects, the ridges and mounds are interpreted as moraines (glacial accumulations built by the release of rock particles of all sizes at the edge of an ice sheet where the rate of flow and rate of melting roughly balanced out). The ice around Tiroony was retreating to the south east but there is clear evidence around Sixmilecross of moraine ridges banked against an ice sheet that eventually retreated northwards. It is possible that the moraine complex is composite and the ridge line marks the separation of the ice sheet before its final retreat from the lowlands on to adjacent high ground to the south east and north.


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