|PHOTO TO BE ADDED|
| Small exposures of the Glencar Limestone Formation, of Lower Carboniferous age, have yielded an exceptionally rich silicified fauna dominated by bryozoa and brachiopods. This material has formed the basis of numerous descriptive publications covering more than 130 species, for 29 of which this is the type locality.|
| The interest of this locality lies in various exposures around Carrick Lough (23/0954) and Bunnahone Lough (23/1055), to south and north respectively of the Derrygonnelly-Garrison road, and associated stretches of the Sillees River between the two loughs and downstream (east) of Bunnahone Lough. The geology of the region is fairly complex, being considerably faulted, but is largely in Dinantian (Lower Carboniferous) rocks extending up into the lower part of the Silesian (Upper Carboniferous). The area also has been extensively glaciated during at least the last glacial maximum. The lake basins and many of the larger rock exposures are due to glacial erosion but there has also been significant deposition of glacial till masking large areas of the solid geology. The fossiliferous horizon(s) lie near the top of the Glencar Limestone Formation, part of the Tyrone Group, and is of early Asbian age. There has been a fairly extensive literature describing elements of the fauna from these sites, particularly bryozoa (Tavener-Smith 1965a, b, 1971, 1973; Bancroft and Wyse Jackson 1995; Wyse Jackson 1996; Wyse Jackson and Buttler 1994; Wyse Jackson and Bancroft 1995) and brachiopods (Brunton 1966a, b, 1968, 1976, 1984), with a single additional publication on the sponges (Reid 1970). The palaeoecology of the fauna has been discussed by Brunton (1987) and Wyse Jackson (1996).|
| Carrick Lough, Bunnahone Lough and the Sillees River represent parts of a single fluvial drainage system draining south-eastwards to join the Lough Erne system just to the south of Enniskillen. Although the loughs are, in part, bounded by alluvium and glacial till, the levels of both loughs are actually controlled by rock barriers near their outlets.|
| Carrick Lough covers an elongate area of less than 0.5 km2 to the south of the Derrygonnelly-Garrison road. Small bluffs on the northern shore are of limestone-rich till but limestone appears to lie in situ on the steep wooded slopes on the southern shore, a short distance to the west of a ruined church, and also on the adjacent shore. At this locality, described by Tavener-Smith (1973) and Wyse Jackson (1996), the succession comprises alternations of shale and argillaceous limestone dipping north west at between 25 and 35 degrees. The total thickness of strata observed by Tavener-Smith was about 240 feet (74 metres), with the proportions of the two lithologies changing upwards through the succession from grey shale with thin (5-15 cm), dark, pyritous limestones to more massive, paler grey limestones with only thin shale partings. The thin limestones frequently display a more siliceous upper and lower surface, weathering as prominent crusts, with fossils in the intervening limestone also being preferentially silicified. Fairly massive limestone is also exposed just downstream of the V-notch weir in the artificially widened and deepened outlet channel immediately to the south of the road.|
| Bunnahone Lough has a more compact outline covering about 0.3 km2 some 0.6 km to the north-north-east of Carrick Lough on the north side of the Derrygonnelly-Garrison road. In situ limestone is not exposed at any point around the shores of the lough itself. To the north and west it is bounded by low ground while along the south shore a prominent small hill would appear, from the absence of any evidence of in situ rock despite its steep northern slope, to be a drumlin. The fossil site actually lies some 250-300 metres downstream of the outlet of Bunnahone Lough and can still be seen, albeit poorly, adjacent to a concrete weir. The fossil horizon was described by Brunton (1966a) as a 210-230 mm thick limestone band lying towards the top of the Glencar Limestone Formation and exposed on the south side and across the bed of the Sillees River at this point. The lower 70-80 mm is clearly delimited from the upper part of this limestone bed and contains irregular clasts of carbonate mudstone, up to 20 mm across, in a coarser silt-grade matrix.|
| In the winter of 1962-63 artificial deepening of the Sillees River between Carrick Lough and Bunnahone Lough, and downstream of Bunnahone Lough, lowered the levels of both lakes by approximately a metre thereby exposing significant areas of rock outcrop on the former lake floor as well in the sides and bed of the deepened channel. In addition to the sites already mentioned, in situ limestone is exposed over a short stretch of the deepened Sillees River channel between the two loughs, which otherwise is excavated largely through glacial till. This exposure appears not to have been investigated in any of the published palaeontological investigations. Judging from the descriptions of Brunton (1966a) and Tavener-Smith (1973) the outcrops on these newly emergent areas of lake floor remained fairly clear for several years but more than 30 years of weathering and vegetation growth has obscured them to a large extent. The exposures on the south side of Carrick Lough also are very scrappy and heavily vegetated. However, Brunton, Tavener-Smith and others evidently collected very substantial bulk samples (some 0.75 ton in the case of Tavener-Smith!) which they dissolved in dilute hydrochloric acid to release the silicified fossil remains. The material so obtained has been worked on by a number of others subsequently. The brachiopods have been worked on only by Brunton but the bryozoa have attracted the interest of several specialists, notable among these being Tavener-Smith and, more recently, Patrick Wyse Jackson who has largely completed the description and interpretation of this fauna. Other elements of the fauna, except for sponges (Reid 1970), remain largely uninvestigated.|
| The fauna is dominated by brachiopods and bryozoa. Fifty-six species of brachiopod have been described so far, including rhynchonellids, spiriferids, terebratulids and productids. The bryozoan fauna encompasses 69 species, dominated by fenestrates but including cryptostomes, trepostomes and cystoporates. The remainder of the documented fauna, encompassing trilobites, ostracods, crinoids, blastoids, gastropods, bivalves, sponges, corals and annelids, comprises fewer than 35 species (Brunton 1987, Wyse Jackson 1996). The named elements of the fauna are listed below.|
| Hexites paradoxus Wyse-Jackson, Nematopora hibernica Wyse-Jackson, Pseudonematopora planatus Wyse-Jackson, Rhabdomeson progracile Wyse-Jackson & Bancroft, Rhabdomeson rhombiferum (Phillips), Rhombopora cylindrica Wyse-Jackson, Rhombopora hexagona Wyse-Jackson, Streblotrypa pectinata Owen, Clausotrypa ramosa (Owen), Baculopora megastoma (M'Coy), Diploporaria marginalis Young & Young, Diploporaria tenella Wyse Jackson, Ichthyorachis newenhami M'Coy, Penniretepora pluma (Phillips), Penniretepora gracilis (M'Coy), Penniretepora frondiformis Olaloye, Penniretepora normalis Olaloye, Penniretepora cucullea Olaloye, Penniretepora cf. flexicarinata Young & Young, Penniretepora sinuosa (Hall), Penniretepora elegantula (Etheridge jun.), Penniretepora rotunda Olaloye, Penniretepora tortuosa Olaloye, Hemitrypa hibernica M'Coy, Fenestella frutex M'Coy, Fenestella ivanovi Shulga-Nesterenko, Fenestella multispinosa Ulrich, Fenestella modesta Ulrich, Fenestella hemispherica M'Coy, Fenestella parallela Hall, Fenestella rudis var. multinodosa Tavener-Smith, Fenestella plebeia M'Coy, Fenestella aff. arthritica (Phillips), Fenestella praemagna Shulga-Nesterenko, Fenestella fanata var. carrickensis Tavener-Smith, Fenestella cf. filistriata Ulrich, Fenestella subspeciosa Shulga-Nesterenko, Fenestella pseudovirgosa Nikiforova, Fenestella cf. albida Hall, Fenestella oblongata Koenig, Fenestella cf. delicatula Ulrich, Fenestella polyporata (Phillips), Fenestella irregularis Nekhoroshev, Levifenestella undecimalis Shulga-Nesterenko, Minilya plummerae (Moore), Minilya binodata (Condra), Minilya oculata (M'Coy), Polypora dendroides M'Coy, Polypora verrucosa M'Coy, Polypora stenostoma Tavener-Smith, Ptilofenestella carrickensis Tavener-Smith, Ptiloporella varicosa (M'Coy), Ptylopora pluma var. parva Tavener-Smith, Septopora hibernica Tavener-Smith, Thamniscus colei Wyse-Jackson, Rhombocladia dichotoma (M'Coy), Leioclema indentata Wyse-Jackson, Dyscritella miliaria (Nicholson), Tabulipora urii (Fleming), Tabulipora howsii (Nicholson), Tabulipora minima Lee, Stenophragmidium sp., Fistulipora incrustans (Phillips), Sulcoretepora parallela (Phillips), Goniocladia cellulifera (Etheridge jun.), and Goniocladia sp.|
| 'Crania' quadrata (M'Coy), Acanthocrania cf. laevis (Keyes), Philhedra trigonalis (M'Coy), Schizophoria resupinata var. dorsosinuata Demanet, Rhipidomella michelini (Leveille), Leptagonia analoga (Phillips), Brochocarina wexfordensis (Smyth), Apsocalymma sp., Serratocrista fistulosa Brunton, Schellwienella radialis (Phillips), Globosochonetes parseptus Brunton, Rugosochonetes silleesi Brunton, Rugosochonetes delicatus Brunton, Rugosochonetes transversalis Brunton, Plicochonetes buchiana (de Koninck), Heteralosia cf. fortispinosa (Hinchey & Ray), Dasyalosia panicula Brunton, Dasyalosia lamnula Brunton, Acanthoplecta mesoloba (Phillips), Plicatifera plicatilis (J de C. Sowerby), Productina margaritacea (Phillips), Overtonia fimbriata (J de C.Sowerby), Avonia (Quasiavonia) aculeata (J de C.Sowerby), Krotovia spinulosa (J. Sowerby), Krotovia lamellosa Brunton, Eomarginifera cf. setosus (Phillips), Eomarginifera trispina Brunton, Eomarginifera derbiensis (Muir-Wood), Echinoconchus punctatus (J. Sowerby), Pustula cf. pyxidiformis (de Koninck), Antiquitonia sp., Ovatia sp., Palmerhytis sp., Propriopugnus pugnus (Martin), Pleuropugnoides pleurodon (Phillips), Tretorhynchia trilatera (de Koninck), Coledium seminulum (Phillips), Hustedia radialis (Phillips), Hustedia ulothrix (de Koninck), Actinoconchus lamellosus (Leveille), Cleiothyridina fimbriata (Phillips), Cleiothyridina deroissei (Leveille), Crurithyris urei (Fleming), Nucleospira carlukensis (Davidson), Cyrtina hibernica Brunton, Tylothyris laminosa (M'Coy), Fusella rhomboidea (Phillips), Skelidorygma integricosta (Phillips), Spiriferellina insculpta (Phillips), Merospirifer linguifera (Phillips), Phricodothyris verecunda George, Minithyra lopha Brunton, Minithyra ernea Brunton, Cryptonella minranensis Brunton, Girtyella carrickensis Brunton, Alwynia reidi Brunton, and Beecheria treakensis Brunton.|
| Eocyphinium aff. castletonensis Osmolska, Cummingella carringtonensis (Woodward), Cummingella cf. insulae Osmolska, Brachymetopus ouralicus (de Verneuil), Weania cf. anglica Osmolska, ? Griffithides sp., and Namuropyga acanthina (Coignou).
MOLLUSCA - GASTROPODA
Platyceras sp., Euomphalus cf. tabulatus Phillips, ?Stegocoelia sp., and ?Zygopleurid.
MOLLUSCA - BIVALVIA
'Cypricardinia' cingulatus (M'Coy) and Girtypecten tessellatus (Phillips).
ARTHROPODA - OSTRACODA
Amplexizaphrentis sp., Cyathaxonia sp., and Cladoconchus sp.|
| The silicified faunas obtained from these small exposures at Carrick Lough and the Sillees River are of major importance for their richness and diversity, particularly for brachiopods and bryozoa. More than 150 species have been described or cited from the two sites, with brachiopods and bryozoa accounting for more than 80% of total species diversity. 16 brachiopod species and 13 bryozoan species, almost 20% of the fauna, have been described as new on the basis of material from these two sites. The richness and diversity of the site, combined with the silicified preservation of the fauna which allows for relatively easy recovery of large numbers of specimens, are the main factors which have led to such considerable interest in this site and resulted in a high number of publications. These publications have, in turn, enhanced the importance of the site at both national and international level. In a country where the geology is dominated by extensive tracts of Carboniferous Limestone, any descriptions of its contained fauna are valuable sources of reference which can help in the interpretation of local or regional palaeoenvironments. On an international scale, such descriptions and analyses of these faunas also are fundamental to research on Upper Palaeozoic bryozoa and, in broader terms, to analyses of palaeobiodiversity through time.|
| In the course of describing the rich and diverse fauna from these sites, their palaeoecological setting has been discussed on a number of occasions, notably by Tavener-Smith (1973), Brunton (1987) and most recently by Wyse Jackson (1996). Tavener-Smith (1973) considered the lithology of the bryozoan-bearing strata to be that of a proximal reef or off-reef facies while Wyse Jackson (1996) interpreted it as distal reef or off-reef deeper water facies. None of the bryozoa are in life position and most are fragmentary, though not heavily abraded, and lie on bedding planes stacked one upon another. Holdfasts are rare, with most of those recovered belonging to cystoporates. The muddy depositional environment indicated by the lithology would not have favoured bryozoan colonisation on account of water turbidity and limited availability of solid attachment sites. These factors, together with the fragmentary nature of most of the material and the lack of holdfasts indicates that the bryozoan fauna is allochthonous and has been transported downslope off the reef into deeper water. The limited abrasion, with even quite fine surface detail preserved, indicates that this distance cannot have been great, however; Tavener-Smith (1973) indicated that a reef lay only a short distance to the south of the collecting localities. In contrast, Brunton (1987) maintained that the bryozoans and brachiopods represent an autochthonous fauna, based on the preservation of fine ornament on brachiopod shells and their relatively even distribution through the mudstones rather than concentrated on particular bedding planes. Wyse Jackson (1996) considered the sedimentological and bryozoan evidence to favour an allochthonous origin for the fauna, although he did not discount the possibility of a mixed origin, with an allochthonous bryozoan fauna associated with an in situ brachiopod fauna. Minor differences in the fauna between Carrick Lough and the Sillees River localities he ascribed to the greater distance of the latter site from the reef facies.|
| Although these localities are noted particularly for the occurrence of rich silicified faunas, calcified and decalcified material also occur. The prevalence of silicified forms in the described fauna can be attributed to the ease with which such material can be recovered in large quantities. Wyse Jackson (1996) noted differences in the pattern of silicification across the fauna and concluded that replacement of the calcareous bryozoan colonies by silica was delayed and, in many case, incomplete.|
|Two rather small exposures of the Glencar Limestone, of early Carboniferous age, have yielded rich and diverse marine faunas dominated by brachiopods and bryozoa. Their silicified preservation has allowed large numbers of well-preserved specimens to be recovered and described, including many previously undescribed taxa, rendering the site of international importance palaeontologically. Sedimentological and taphonomic evidence indicates an allochthonous origin for much of the material followed by delayed, and in many cases incomplete, silicification of calcareous material.|
For general information and references on the Palaeontology of Northern Ireland see Key Site 109 - Palaeontological sites of N. Ireland - Introduction
|For other site specific information and references on the Palaeontology of Northern Ireland see Key Site 110 - Ballycastle Pellet Chalk, Key Site 111 - Ballypalady Plant, Bed Key Site 113 - Faragandoo, Key Site 114 - Minnis North Mudflow, Key Site 115 - Moyola River, Key Site 116 - Mullynaskeagh Clay Pit, Key Site 117 - Murlough Bay, Key Site 118 - Portnaloub, Key Site 119 - Sillees River, Glenasheevar, Key Site 120 - Tircrevan Burn, and Key Site 121 - Tullyconnell.|