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Mourne Plain Complex - Cranfield MoraineDown
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Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: J32633168
Rocks
Rock Age: Quaternary (Late Midlandian)
Interest
Other interest: No data, Glacial deposit, Glaciomarine deposit, Glaciotectonic, ice lobe, moraine ridge, outwash

Summary of site:

A striking feature of the lowland Mourne Plain west of Kilkeel is a prominent ridge of almost circular plan coming ashore at Cranfield Point, arcing east and then north through Dunraval and Ballyardel then swinging north west along the southern slopes of Knockchree, across the White Water valley about 1 km south of Tullyframe, then sweeping across the southern skirts of Rocky Mountain and Formal. The crest stands at 20 m above sea level at Cranfield and reaches its maximum height of 100 m at Tullyframe. It is up to 300 m wide in the plain but along the mountain slopes it is no more than 100 m.

At Glenloughan, south west of Knockchree, sand quarrying has exposed three well-defined units of sediment. The first is a diamict, a mixture of rock particles from clay to cobbles in size showing the effects of water winnowing and underwater flow down steep slopes. Above it are alternating beds of sand and silt reflecting settling from different rates of flow in a subglacial environment, a less energetic environment than that of the diamict. The third unit consists of beds some of which show a progressive reduction of grainsize towards their tops while others show exactly the reverse. These reflect rapid changes in flow characteristics and particle supply during deposition, again in an underwater environment. There are small faults and some associated slumping that has generated small folds. The form of the ridge and the nature of the deposits observed near Glenloughan make clear the origin of the feature. It was formed as a terminal moraine fronting glacial ice flowing unconfined into the sea at Carlingford Lough. As it spread into open water it formed a broad lobe which for a time was melting at the same rate that it was flowing so that as ice melted and calved into ice floes, the released sediment was driven by meltwater into the form we see now. Sites providing evidence for this interpretation are described separately.


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