ESCR - Ballygawley Delta Complex - Lurganboy Delta and Outwash

Earth Science Conservation Review

Summary Full report
Ballygawley Delta Complex - Lurganboy Delta and Outwash	Tyrone

Site number:	492
ESCC:	IS
Locality Type:	Inland exposure	Status:	TBC
Grid Reference:	H590644,H586660,H605675 Corners of site, Not Entered
Google maps:	54.52499,-7.08877
County:	Tyrone	Council area:	Fermanagh & Omagh District Council
Period:	Quaternary

Site Description
Description:
The area around Lurganboy, characterised by largely undissected flat surfaces of deltaic and associated outwash sediments, extends from the northern limit of the dissected deposits near Altamooskan (H590644) and Fallaghearn, to the area around Foremass (H586660) and Bernisk Glen (H605675) where ridge morphologies dominate. This area of outwash is about 2.5km by 4km in extent. Meltwater channels are fewer in number than in the area around Fallaghearn, are often wider and with postglacial alluvial infills. Continuous flat surfaces are therefore preserved. There are generally few exposures, but one large pit at Lurganboy. The Lurganboy pit, 7km southeast of Sixmilecross, is a new sand and gravel pit about 150m long and 30m wide. It is characterised by generally poorly-sorted stacked facies of clast and matrix-supported gravel interbedded with massive and stratified well-sorted medium and coarse-grained sand. Sand beds are generally laterally discontinuous with graded contacts. There are two main exposures. These are described separately but interpreted together. Exposure A - Facies description This exposure, 4m high and 12m long, is characterised by a generally fining-up sequence of stacked beds of massive unstratified gravel and well-sorted beds of massive, planar and rippled medium and fine-grained sand. Towards the top of the sequence, sand facies dominate and are often interbedded with discontinuous lenses or stringers (1m across and 0.2m deep) of well-sorted granules. The nature of bed contacts changes upsequence from graded to sharp, occasionally erosional, with scour and fill structures. Major facies are laterally continuous across the exposure. Minor facies are often erosionally wedged out, such as rippled sand units. A drape of silt and fine sand occurs above a massive, normally graded medium to fine sand bed in the middle of the sequence. This facies association is continuous across the exposure. Exposure B - Facies description This exposure, approximately perpendicular to that of Exposure A, is up to 4m high and 20m long. It is characterised by stacked beds (0.4-1.0m thick) of well-sorted granule to pebble-sized clasts (<8cm diameter) interbedded with laterally continuous interbeds (5-10cm thick) of well-sorted medium to coarse sand. In more detail, this section shows a fining-up sequence. Pebble gravel beds at the base of the section are matrix-supported by coarse sand and granule. Beds are vaguely stratified (dm scale) and may be both normally and inversely graded. Upsequence, gravels become granule-dominated and better stratified (cm scale). Upsequence, sand facies become less continuous and channelised. Sand bed dip direction changes from 270° at the base of the exposure to 300° at the top. Facies interpretation The sediment sequence in exposures A and B records the deposition of material provided and regulated by the input of sediment pulses into a subaqueous environment. An upsequence change in depositional direction and increase in interbedding and channelisation records water shallowing and local flow events emanating from adjacent high ground. This may be associated with a change from a deltaic to an outwash depositional setting at 195-200m a.s.l. (Dardis, 1982). Directional indicators show sediment input was from the southeast from an ice source in the upper Owenbrack valley (H630650), and was not derived from the Todd's Leap ice that formed the deltas of the area around Fallaghearn. Charlesworth (1924, pp.274-5) relates the deposition of the Lurganboy sediments to the northward retreat of an Omagh Basin ice margin which then linked separate lakes existing in the Fallaghearn and Owenbrack valleys. The Lurganboy deposits were derived from the retreating ice margin. Dardis (1982) interpreted this area as recording ice retreat to the southwest, with outwash sediments extending along the Owenbrack valley. He records glaciotectonic deformation, faulting and intraformational diamicts at Lurganmore (H643640), a site inferred to be more ice-proximal than the Lurganboy site.
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 493 - Ballygawley Delta Complex - Tiroony Ridges 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 738 - Lurganboy.

Keywords
Relations:	Deltaic sediments, Glacial deposit
Geomorph:	deltas, outwash
Paleoenv:	delta


Record type:	ESCR report
Entered by:	E M Porter
Last updated:	23 Dec 2003

Enlander, I., Dempster, M. & Doughty, P., 2026. Ballygawley Delta Complex - Lurganboy Delta and Outwash, County Tyrone, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=492. Accessed on 2026-11-05.