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Earth Science Conservation Review
| Pomeroy - site of local interest | Tyrone |
| Site number: | 747 | ||
| Locality Type: | Inland exposure | Status: | local interest |
| Grid Reference: | H613726,H682679,H723663 Corners of site | ||
| Google maps: | 54.59837,-7.05154 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Highlights: | |
The deposits of the Pomeroy deglacial complex are located at the southern margins of the Sperrin Mountains and record complex evolution during deglaciation. The complex contains a wide range of deglacial landforms including proglacial, paraglacial, subaqueous and subglacial deposits. The area is 118km2 in extent and stretches from Sixmilecross [H570 679] to Galbally [H722 659] and from the southern margin of the Cregganconroe / Evishanoran highlands [H657 751] to the Owenbrack river valley [H613 726]. | |
| Description: | |
The deposits of the Pomeroy deglacial complex are located at the southern margins of the Sperrin Mountains and record complex evolution during deglaciation. An ice sheet which covered this area and the highland areas further north split into two lobes during the final stages of deglaciation upon entering this area during backwastage into the source areas of the Lough Neagh lowlands and the Omagh basin. Ice marginal deposition combined with bedrock topography resulted in the formation of an extensive subaqueous fan, high level Gilbert-type deltas (at 245m O.D.), extensive outwash plains and terraced valley-fills. An example of classic hummocky and ridge topography is located near Pomeroy. Ice pressure from the southwest (Omagh basin around Clogher) is indicated by a distinctive sandstone conglomerate contained in the complex and a glacially moulded bedrock knoll to the northwest of Carrickmore which shows ice flow direction to 120°N. The complex contains a wide range of deglacial landforms including proglacial, paraglacial, subaqueous and subglacial deposits. The area is 118km2 in extent and stretches from Sixmilecross [H570 679] to Galbally [H722 659] and from the southern margin of the Cregganconroe / Evishanoran highlands [H657 751] to the Owenbrack river valley [H613 726]. The deglacial features include: the Ballynapoll fan between Aghnaheragh [H636 716] and Crockroar [H657 719], Tremoge moraine-ridges from Tremoge [H658 729] to Rockstown [H623 727], Altanagh moraine [H624 699], Sluggan outwash [H653 706], Edenfore delta and Owenbrack outwash between Cranlome Hill [H659 639] and Lurganmore [H635 630], Pomeroy moraine between Limehill and Pomeroy forest [H706 727], and flat-topped terraces and dissected deposits at Altmore [H682 679] and Galbally [H723 663]. | |
| Importance: | |
This site is of some scientific significance due to: 1. Its demonstration of late-glacial ice retreat directions and thus ice-pressure for ice at the southern margins of the Sperrin Mountains towards the Omagh basin and the Lough Neagh lowlands; 2. The evidence for a late-glacial proglacial waterbody at an elevation of 245m O.D. in the deglaciated areas of the Fintona hills; 3. The classic hummocky moraine topography displayed by the Pomeroy moraine; 4. The evidence of deglacial processes in the splitting of the ice mass; 5. The evidence that the final centres of ice dispersal were in lowland, not upland areas. | |
| Interpretation: | |
Deglaciation in the Pomeroy valley and Fintona Hills is proposed to have happened as follows: during the deglaciation of the Sperrin Mountains the presence of glaciofluvial and glaciolacustrine deposits in the Cregganconroe highlands immediately north of the Pomeroy valley indicates the location of a former ice-margin. Ice-marginal gravels deposited against the northern margins of the valley, form the moraines at Lime Hill and Creggandevesky and indicate a generally southerly retreat of the ice-margin in the Pomeroy valley from the highlands to the north. With ice-pressure from the west and east together with down- and back-wastage of the ice into the valley, the margin split into two lobes, which retreated to the east and the west along the valley. At this time, a localised interlobate waterbody may have formed between the ice-margins and the rising ground to the north, allowing the deposition of the bergstones observed at Tremoge. A waterbody was impounded against the ice-margins and bedrock in the Pomeroy valley between the Fintona Hills and Cregganconroe. Sediment supply from the west along subglacial and probably ice-marginal conduits (at Altinagh Bridge) resulted in the development of a subaqueous fan at Ballynapoll which prograded eastward. The sediment supply route is recorded by the esker ridges immediately west and southwest of the deposit. Later, drainage of the proglacial waterbody westward resulted in the dissection of the fan and the infilling of one channel by reworked sediment at [H646 714]. Reworking of the sediment in the eastern half of the Pomeroy valley resulted in outwash sediments at Crockbrack and glaciofluvial terraces at Pomeroy. After it deposited the proglacial moraines at Limehill and at Pomeroy forest, the eastward retreating ice lobe deposited the well-preserved lateral moraine along the axis of the valley at Pomeroy, from an ice-marginal tongue located in the valley bottom. Ice located in the Fintona hills backwasted up the valleys of these hills from the western margins of the valleys away from the Omagh basin. This is recorded by a cross-valley morainic complex at Altinagh Bridge. After further retreat, valley-fill outwash plains were deposited at Owenbrack and Sluggan. A proglacial waterbody accumulated to a height of 245m O.D. in the deglaciated valleys of the Fintona hills between ice-margins located at the eastern edge of the Fintona hills and in the Omagh basin. At this time the deltaic deposits at Edenfore [H648 630] aggraded to this elevation. Large subglacial sediment supplies are recorded by the esker ridges to the east. Following drainage of the proglacial lake and further retreat of the ice-margin towards Lough Neagh, the flat-topped deltas at Altmore and deposits at Galbally formed in localised waterbodies impounded against the eastern margins of the Fintona hills. | |
| Notes: | |
See also ESCR Key Site 482 - Pomeroy Complex [Sand and Gravel Landscapes Block]. | |
| Keywords | |
|---|---|
| Rocks: | Gravel, Sand |
| Relations: | Deglacial sediments, Deltaic sediments, Ice retreat |
| Geomorph: | delta, esker, Gilbert-type delta, hummocky moraine, ice-marginal lake, moraine ridge, proglacial lake, subaqueous fan, outwash terrace |
| Paleoenv: | deglacial |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | Width: | Height: | |||
| Depth: | Area: | 118km2 | |||
| Access | |
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| Approach: | This site is located southwest of Pomeroy and between Carrickmore and Cappagh. |
| Uses | |
| Educ. Level: | The complex is of educational value to students and researchers of glaciology. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Pomeroy - site of local interest, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=747. Accessed on 2026-11-08. |
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