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Earth Science Conservation Review
| Ballygawley Delta Complex - Tiroony Ridges | Tyrone |
| Site number: | 493 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure | Status: | TBC |
| Grid Reference: | H571679 Approximate | ||
| Google maps: | 54.55665,-7.11743 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Description: | |
The area around Tiroony is characterised by hummocky mounds and aligned ridges of sand and gravel. Amplitude of relief is generally 5-10m. Ridges are often oriented northeast-southwest. Both ridges and mounds occur as high level undulatory surfaces dissected by infrequent but large meltwater channels over 20m deep. Two main exposures near Tiroony show interbedded sand and gravel facies. Exposures are described separately but interpreted together. Exposure A - Facies description This exposure, up to 2.5m high and 24m long, is characterised by stacked clast-supported and openwork granule and pebble gravel (<6cm diameter) beds (30-40cm thick) interbedded with discontinuous massive fine sand and silt stringers (c. 1m long). The exposure is capped by a continuous silt layer (30cm thick) which overlies silt and sand facies which compose a channel infill. Facies are laterally continuous (to 4m). Gravel facies are composed of local lenses 1.0-1.5m wide and 40-60cm deep. Pods are often normally or inversely graded, sometimes with basal lags. Constituent clasts show an a(t) fabric dipping 040° to 330°. Pods often show graded lower contacts, especially with sand interbeds, and sharp erosional upper contacts. Larger pebble and cobble clasts (<20cm diameter) are dispersed throughout. Silt facies in the upper part of the exposure are massive and unstructured. Dispersed pebbles are also found in this upper facies which has a graded basal contact. Exposure B - Facies description This exposure, up to 10m high and 35m long, 100m south of exposure A, dissects a sand and gravel ridge. The exposure is characterised by poorly-sorted heterogeneous granule to pebble-sized clasts (<8cm diameter), with dispersed and occasionally aligned cobble clasts (35cm diameter). These facies are generally matrix-supported by silt to coarse sand. In detail, the core of the ridge is composed of sorted granule to pebble clasts. The flanks of the ridge are composed of more heterogeneous and chaotic sediments with some discontinuous (to 50cm) coarse sand stringers. The flanks also contain thin (<20cm) silty facies with included pebbles and are topped by a matrix-supported (85%) diamict with dispersed pebbles (<6cm diameter). No distinctive glaciotectonic structures are identified, though this may be due to the poor condition of the exposure. Facies interpretation Exposures A and B record sequences of change in the ice marginal environment. Sediment sequences have been strongly affected by their morphological position and relationship to other elements of the landscape. Both exposures are dominated by interbedded sand and gravel facies. General lack of stratification is attributed to continuous sediment deposition and the reworking of material by unconfined slope processes such as gravity flows. Diamict facies on the ridge flanks of Exposure B can be interpreted as later resedimentation on palaeo-high ground. Infilled channels of silt and fine sand in Exposure A can be interpreted as resulting from its palaeo-low ground position. Vague cross-beds occur in the ridge section (Exposure B). Cross-bed dip is approximately perpendicular to ridge long axis, which leads to the interpretation that ridges in the Tiroony area are of ice-marginal morainic origin with ice retreating to the southeast. Ridges extend from Tiroony in the northeast to Sixmilecross in the southwest (6km). Northeast to southwest ridge morphology changes from well-defined ridges in a generally flat landscape to a more chaotic series of aligned rounded hills. Width of the ridge zone also widens from about 0.2 to 1.5km. Charlesworth (1924, pp.265, 274) believed that a northward-retreating ice margin gave rise to the moraine system around Sixmilecross. This interpretation is advocated here, i.e. that the moraine is of composite form and is related, at its northeastern extent, to two ice margins. No sections are recorded in the moraine further towards Sixmilecross. | |
| Notes: | |
For site specific information on other sites within the Ballygawley Delta Complex see the following sites: Key Site 491 - Ballygawley Delta Complex - Fallaghearn Deltas Key Site 492 - Ballygawley Delta Complex - Lurganboy Delta and Outwash For overview information and references on the Ballygawley Delta Complex see the following site: Key Site 483 - Ballygawley Delta Complex - Overview For general information and references on the sand and gravel landscapes of N. Ireland, and for directions to other regional sand and gravel sites, see the following site: Key Site 439 - Introduction to the Sand and Gravel Landscapes of N. Ireland This site is also a Site of Local Nature Conservation Importance. See Key Site 756 - Tiroony. | |
| Keywords | |
|---|---|
| Relations: | Glacial deposit |
| Geomorph: | moraine ridge |
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 23 Dec 2003 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Ballygawley Delta Complex - Tiroony Ridges, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=493. Accessed on 2026-11-05. |
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