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Earth Science Conservation Review
| Devonian - Shanmullagh Formation; Miospore localities | Tyrone |
| Site number: | 1151 | ||
| Locality Type: | Pit, Quarry (disused) | ||
| Grid Reference: | H2860,H3464 Approximate, Not Entered | ||
| Google maps: | 54.48813,-7.56793 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Devonian | ||
| Stages: | Famennian, Frasnian | ||
| Lithostrat: | Fintona Group, Shanmullagh Formation (Form Blm) | ||
| Site Description | |
|---|---|
| Highlights: | |
Fossiliferous green mudstones containing miospores occur at many localities in the Shanmullagh Formation of the Irvinestown Segment and are the first undisputed Devonian fossils to be collected from the Fintona Block and in Northern Ireland. | |
| Introduction: | |
In 1990 (p.412) Mitchell and Owens demonstrated a late Vis‚an- early Namurian age for the sandstones at the locality near Lisbellaw, Co. Fermanagh from where Harper and Hartley (1938) recovered fossil fish fragments which are now thought to be reworked from older Devonian rocks (Blieck, 1991). Richardson (in Mitchell and Owens, 1990, p.412) tentatively assigned a Lower Devonian (Siegenian) age to the Shanmullagh Formation on the basis of miospore assemblages consisting of abundant, but poorly preserved, specimens. Since then green mudstones, which contain the miospores, have been found at 47 localities in the Irvinestown Segment of which 22 have yielded identifiable specimens. The preservation and content of the assemblages is variable and none of them contain any significant Devonian index taxa. Nevertheless there are other factors which suggest that the miospores are of Upper Devonian age, in particular the Frasnian and Lower Famennian Stages. Location: The 2 sites selected as III and IV are located near the northern margin of the Irvinestown Segment between Irvinestown and Dromore. III is a shallow pit that is still accessible but the rock is usually covered, at the north side, by a veneer of soil. IV is a quarry working a small knoll from which rock, for farm fill, may still be drawn. Bibliograph Review: In addition to the paper by Mitchell and Owens (1990) and the contribution by Richardson therein (op. cit.) the only other recent work of significance dealing with the Fintona Block is that of Simon (1984). However, because he was unable to recover any miospores from the Fintona Group he had no biostratigraphical control over correlations between superficially similar lithological units from various parts of the outcrop and his proposals are now known to be incorrect. General Geology: Although there are subtle differences in the generic composition of some of the miospore assemblages recovered from the 22 separate localities in the Shanmullagh Formation, their significance is not yet fully understood and cannot be used to assign them to different miospore zones or stages beyond the Upper Devonian (Frasnian - Lower Famennian). Despite the considerable areal extent of outcrops of the Shanmullagh Formation, no internal lithostratigraphy can be defined with confidence in this uniform sequence of red-beds. It is therefore not possible to place the fossiliferous green mudstones within the sequence nor is the total thickness of the formation known. | |
| Description: | |
For sites III and IV specific information see; Key Site 318 - Lisdoo Townland pit Key Site 319 - Knockaraven Townland quarry. | |
| Interpretation: | |
The green mudstones were deposited in a shallow lake which periodically received small amounts of sand either blown in by wind action from the surrounding desert or, in the case of thicker beds, due to transport by temporary rivers. There is no evidence of rhizoliths (plant roots) in the mudstones which were periodically (subaerially)? exposed and subjected to desiccation resulting in disruption of the laminated mudstones. The miospore assemblages listed for III and IV are indicative of a Middle-Upper Devonian age and are unlikely to be Lower-Middle Devonian in age. It is considered most likely that the assemblages are not older than Eifelian, not younger than Lower Famennian and are most probably Frasnian - Lower Famennian in age. The main indicators of this age range are as follows: 1:- Although the assemblages lack the presence of any significant Devonian index taxa they include, as relatively common components, camerate miospores including camerate miospore tetrads. This morphological character evolved first in miospores in Givetian times and only became relatively abundant in the Upper Devonian. 2:- The most distinctive taxa present in the assemblages are species of Emphanisporites, a genus which first appears in the Silurian and occurs throughout the Devonian and, rarely, into the Lower Carboniferous. The species of Emphanisporites recorded in the assemblages from III and IV are plainly ornamented and do not include the variously sculptured forms commonly seen in Lower Devonian miospore assemblages. Clayton et al. (1974) and Higgs et al. (1988) noted the occurrence of E. rotatus, E. annulatus and E. hibernicus (possibly Emphanisporites sp.A from III, in this report) in strata of Upper Devonian - Lower Carboniferous age (Famennian-Tournaisian Stages) in southern Ireland. The species of Emphanisporites most commonly recorded in the Shanmullagh Formation are E. rotatus and E. sp.A. | |
| Conclusions: | |
CONCLUSION It is unfortunate but palynologically some doubt must remain as to the age, within the Devonian, of the miospore assemblages recovered from the Shanmullagh Formation including those from III and IV, until such time as some definitive taxa are recovered. For the moment it is suggested that the assemblages indicate an Upper Devonian (Frasnian - Lower Famennian) age for this formation. These miospore assemblages are however the first undoubted Devonian fossils found in the Fintona Block and in Northern Ireland. | |
| Notes: | |
For general information and reference list on the Shanmullagh Formation with respect to stratotype see; Key Site 1150 - Shanmullagh Formation; Stratotype localities. For general information and reference list on the Devonian System in N. Ireland see; Key Site 1147 - The Devonian System in N. Ireland - Introduction. | |
| Keywords | |
|---|---|
| Rocks: | Mudstone, Sand, Sandstone, Siltstone |
| Fossil Groups: | Miospore, Miospores |
| Paleoenv: | lacustrine |
| References (6) | |||
|---|---|---|---|
| Blieck, A., 1991. Reappraisal of the heterostracans (agnathan vertebrates ) of Northern Ireland. Irish Journal of Earth Sciences, vol. 11 pt. 1, pp.65-69. | |||
| Clayton, G., Higgs, K. & Keegan, J.B., 1974. Late Devonian and Early Carboniferous occurrences of the spore genus Emphanisporites McGregor in Southern Ireland. Pollen et Spores, vol. 19 pt. 3, pp.415-425. | |||
| Harper, J.C. & Hartley, J.J., 1938. The Silurian inlier of Lisbellaw, Co Fermanagh, with a note on the age of the Fintona Beds. Proceedings of the Royal Irish Academy, vol. B45, pp.73-87. | |||
| Higgs, K., Clayton, G. & Keegan, J.B., 1988. Stratigraphic and systematic palynology of the Tournaisian rocks of Ireland. Special Papers of the Geological Survey of Ireland, numb. 7, pp.1-93. | |||
| Mitchell, W.I. & Owens, B., 1990. The geology of the western part of the Fintona Block: evolution of Carboniferous basins. Geological Magazine, vol. 127 pt. 5, pp.407-426. | |||
| Simon, J.B., 1984. Sedimentation and tectonic setting of the lower Old Red Sandstone of the Fintona and Curlew Mountain districts. Irish Journal of Earth Sciences, vol. 6, pp.213-228. | |||
| Map(s): | GSNI 1:50,000 Sheet 45 (Enniskillen); GSNI 1:50,000 Sheet 46 (Clogher); O.S. 1:50,000 Sheet 18 (Enniskillen). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 8 Jan 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Devonian - Shanmullagh Formation; Miospore localities, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1151. Accessed on 2026-11-07. |
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