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Earth Science Conservation Review
| Tempo Valley Delta Complex - Tempo and Pubble | Tyrone |
| Site number: | 514 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure, Pit | Status: | TBC |
| Grid Reference: | H340450,H322472,H366494 Corners of site, Not Entered | ||
| Google maps: | 54.35302,-7.47707 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Description: | |
This area extends from the end of the sand and gravel system at Tattinweer (see Key Site 513), to the head of the Lough Eyes moraine system in the south at Drumderg (H340450), and extends west as far as Ratoran (H322472). The area is 5km long and 4km wide. It is characterised by dissected sand and gravel hills up to 200m long and 15m high, separated by deeply incised meltwater channels, occasional kettleholes and flat alluvial spreads such as at Pubble. Sand and gravel sediments are superimposed upon ice scoured bedrock and isolated diamict hummocks and ridges. Sand and gravel dominates particularly in the area around Pubble between the higher ground to the northeast and southwest. There is one exposure, at Pubble. PUBBLE PIT The Pubble pit is a mainly disused sand pit covering an area of c. 1ha. Two faces are exposed. These faces are described separately below but interpreted together. Exposure A Facies description This exposure, 50m long and up to 5m high, is characterised by well-sorted cross-bedded, rippled, channelized and stratified beds of fine to coarse sand with discontinuous interbeds of well-sorted granules and pebbles (<4cm diameter). Beds are separated by sharp conformable or erosional contacts. The exposure can be split into three main units (lower, middle and upper) separated by erosional contacts. The lower unit up to 2m thick is composed of channelized and cross-bedded sands and granules. Planar crossbeds (0.5-1cm thick) of medium- and fine-grained sand are laterally continuous, interbedded with coarse sand crossbeds, and form laminated sand sheets that dip 020§ to 330§. Upsequence this crossbedded facies grades conformably into well-sorted climbing ripple sequences that occur within shallow (2-3m wide) channels infilled by well-sorted and bedded (cm scale) medium-grained sand. Ripples are developed in well-sorted medium-grained sand. The angle of ripple climb increases upwards within each rippled unit. The middle unit is composed of planar and cross-bedded massive and well-sorted granules and pebbles (<5cm diameter) in beds 0.2-0.5m thick supported in a unimodal fine sand matrix. The middle unit forms a broad wedge in the central part of the exposure, and is 30m long and up to 2.5m high. It generally wedges out downflow (towards the N/NNW), and becomes sand-dominated with isolated gravel pockets. The upper unit (<3m thick) is characterised by cross-bedded, stratified and rippled well-sorted medium- and fine-grained sand. The unit is also associated with shallow channels (2-3m wide, 0.3m deep) conformably infilled with planar bedded (cm scale) sands. Individual beds are laterally discontinuous with erosional lag-free contacts. The upper unit, texturally similar to the lower unit, is much more variable in bed morphology, continuity and thickness. Concretions occur within an undifferentiated medium-grained massive sand bed on the far right hand side of the exposure. These concretions are up to 10 x 6 x 0.5cm in dimensions. They are nodular, lie bed-parallel and are composed of cemented silt-sized particles. They are morphologically similar to those of Dooneen exposure A, but are finer grained and much better cemented. Exposure B Facies description This exposure, up to 60m long and 6m high, is characterised by interbedded facies of massive clast-supported gravel and massive, stratified, rippled and planar bedded well-sorted medium- and fine-grained sand. These facies are generally laterally continuous across the exposure and form rhythmic and conformable depositional sequences that are separated from adjacent sequences by laterally continuous undulatory erosional contacts. Infills therefore form a pinch-and-swell morphology. Sediments generally fine along the exposure from left to right, i.e. towards the north. This is in general agreement with Exposure A. The lowest facies (<1.5m thick) is composed of clast-supported granules and subrounded pebbles (<20cm diameter). The larger clasts generally show an a axis dip towards 330§. The facies also shows crude planar bedding conformable to the overlying well-sorted sand facies. These sand facies (10-20cm thick) are broadly channelized and infilled by massive and sorted granules with a minor matrix component of medium-grained sand. This is conformably succeeded by rhythmically bedded planar and stratified well-sorted interbedded sand units (10-20cm thick) which develop laterally (over 2m) into thicker (40cm) climbing ripple beds. Ripples dip 020§ to 225§, i.e. palaeoflow direction to the northeast. This is in contrast to the sedimentary beds which dip 010§ to 000§. Interbedded units are separated by undulatory erosional contacts. This contact is laterally continuous and arranged into broad hummocks (<1m high) spaced about 10m apart. The overlying rhythmically bedded sequence (4m thick) is characterised by interbedded planar units of massive and stratified medium-grained sand, and rippled cross-beds (individually 8-10cm thick). Rippled beds are composed of fine-grained sand. These facies are conformable to the basal undulatory contact, are well-sorted and arranged in laterally-continuous beds 30-40cm thick that extend to the top of the exposure. Towards the north (right side of the exposure) sediments are fine-grained with some discontinuous silty interbeds. Rhythmically bedded units are thinner (cm scale), dominate the top half of the exposure and are associated with conformable shallow channel infills. The lower part of the exposure is characterised by thickly bedded (<1m), laterally continuous and well-sorted fine-grained massive and rippled sand beds. These are interbedded with discontinuous wedges (1m deep by 3m wide) of well-sorted cross-bedded granules. Exposures A and B Facies interpretation These exposures record waterlain sediment deposition in a shallow proglacial environment with a water source from the south. Notable characteristics of these exposures include sediment rhythmicity and continuity, and the lack of evidence for contemporaneous or post-depositional deformation. Both of these elements are consistent with ice-distal sedimentation in an environment unaffected by ice marginal location. Further, the continuous record of sedimentation, and general lack of coarser sediments, indicates that ice retreat and/or decay was not characterised by a high level of activity and variations in meltwater expulsion. This may indicates that ice was stagnant and unaffected by seasonal climate cycles. No faulting due to ice meltout is observed in these exposures, which may be due to the distance of these sediments from the (inferred) ice margin. Unlike the exposures of Dooneen and Tonyglaskan (see Key Site 513), there are no directional indicators corresponding to water flow from the higher ground surrounding the depocentre. Fintona Hills ice may have retreated further from the lowlands, and did not contribute to this ponded system. This is consistent with a later deposition of sediments in the Pubble area than those of Dooneen or Tonyglaskan, thus that ice retreat was more advanced and the respective sediment systems more distinct. Diverging ice masses, and no ponded water deposition, also agrees with the development of cold climate subaerial sand wedges in the Pubble area (McCabe, 1969). | |
| Notes: | |
For site specific information on other sites within the Tempo Valley Delta Complex see the following sites: Key Site 513 - Tempo Valley Delta Complex - Glengesh and Tattinweer Key Site 515 - Tempo Valley Delta Complex - Lough Eyes Key Site 516 - Tempo Valley Delta Complex - Upland areas of the Fintona Hills For overview information and references on the Tempo Valley Delta Complex see the following site: Key Site 485 - Tempo Valley 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 | |
| Keywords | |
|---|---|
| Rocks: | Gravel, Sand |
| Relations: | Glacial deposit, Shallow water sediments |
| Geomorph: | outwash, proglacial |
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Tempo Valley Delta Complex - Tempo and Pubble, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=514. Accessed on 2026-11-07. |
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