Bollettino della Società Paleontologica Italiana Modena, Novembre 1999
Late Viséan conodont biostratigraphy and biofacies in the Kingscourt area, Ireland
H.E. Anne SOMERVILLE Ian D. SOMERVILLE Department of Geology University College Duolin
KEYWORDS- Conodonts Biostratigraphy, Biofacies, Carboniferous, Late Viséan, Kingscourt, Ireland.
ABSTRACT - The Gnathodus bilineatus and Lochriea nodosa zones are recognised in the Kingscourt area, Ireland in both platform and basinal facies. The base ofthe nodosa Zone ù defined by the synchronous first occurrence ofL. nodosa and L. mononodosa in the same bed. Severa! conodont species (e.g. Mestognathus bipluti, Idioprioniodus healdi and Kladognathus macrodentata) are mostly restricted to the Brigantian (upper part ofthe bilineatus and nodosa zones). The richest and most diverse conodont faunas dominated by species ofGnathodus and Lochriea are Jrom late platform and basinallimestones within the L. nodosa Zone (Gnathodus-Lochriea Biofacies) . Lower yields and diversity are recorded Jrom early Brigantian platform limestones (upper p art ofthe G. bilineatus Zone); with the poorest conodont yields in late Asbian platform limestones and mudmounds ofthe lower G. bilineatus Zone. T here is a significant rise in the abundance and diversity of conodonts above the Asbian/Brigantian bounda'} a change which coincides with changes in foraminiferal assemblages and lithofacies; this indicates probable transgressive environmental injluences. A second major increase in conodont abundance and diversity is recognised at the base ofthe nodosa Zone, in platform and basinal {acies. Shallow-water, coarse-grainedAsbian platform limestones are dominated by Synclydognathus geminus and Kladognathus tenuis compfectens (Synclydognathus-Kladognathus Biofacies), the elements of which are ojten abraded and fragmented. The best preserved faunas are mostly from the wackestones in the nodosa Zone at Poulmore, which have the best representation ofall apparatus components. The late Viséan conodont faunas from Kingscourt are comparable in diversity, abundance and taxa present to those in northern England, North Wales and Poland where cyclothemic sequence limestones occur. The upper beds ofPoulmore probably correlate with uppermost Viséan limestones in northern England and Lublin Basin, SE Poland.
RIASSUNTO- [Biostratigrafia a conodonti e biofacies del Viseano superiore nell'area di Kingscourt, Irlanda]- Le biozone a Gnathodus bilineatus e Lochriea nodosa sono state riconosciute nell'area di Kingscourt, Irlanda, sia in facies di piattaforma, che di bacino. La base della nodosa Zone è definita dalla prima comparsa, sincrona, di L. nodosa andL. mononodosa. Numerose specie di conodonti (es.: Mestognathus bipluti, Idioprioniodus healdi andK!adognathus macrodentata) sono per lo più limitate al Brigantiano (parte alta delle biozone a bilineatus e a nodosa). Le faune a conodonti più abbondanti epiù differenziate sono dominate da specie di Gnathodus e Lochriea eprovengono da calcari di piattaforma e di bacino del Brigantiano superiore, corrispondenti alla bio zona a nodosa (bioJacies a Gnathodus e Lochriea). Ritrovamenti inferiori sia per a6bondanza che per diversità avvengono nei calcari ai piattaforma del Brigantiano inf (parte alta della bio zona a G. bilineatus), mentre faune ancora più scarse sono rinvenute nei calcari di piattaforma e nei mud-mound della parte inferiore della biozona a G. bilineatus (Asbiano sup.). Sopra a/limite Asbianol Brigantiano si verifica un aumento significativo nell'abbondanza e nella diversità dei conodonti; tale variazione coincide con quelle delle associazioni a foraminiferi e defle litofacies e indica probabili variazioni ambientali dovute a una trasgessione marina. Un secondo significativo aumento della abbondanza e della diversità dei conodonti si è verificato alla base della biozona a nodosa, sia in facies di piattaforma, sia bacinale. I calcari grossolani e di acqua bassa delle piattaforme Asbiane sono dominati da Synclydognathus geminus e Kladognathus tenuis (biofacies a Synclydognathus- Kladognathus), i cui elementi sono però spesso danneggiati eframmentati . Le faune meglio conservate provengono soprattutto dai wackestones dell'area di Poulmore (biozona a nodosa, dove tutti i componenti degli apparati sono ben documentati. Le faune a conodonti del Viseano sup. dell'area di Kingscourt sono confrontabili per diversità, abbondanza e composizione con quelle di Inghilterra settentrionale, Nord Galles e Polonia, tiove affiorano sequenze cicliche di calcari. Gli strati più giovani di Poulmore, probabilmente, sono equivalenti ai calcari del Viseano terminale del nord dell1nghilterra e del Bacino di Lublino (SE Polonia).
INTRODUCTION Processing produced over 40,000 specimens referred to l O genera an d 17 multielement species. The results This paper presents data on conodonts from late of the conodont biostratigraphy and biofacies are Viséan (Asbian and Brigantian stages) rocks around summarised here with reference to four main Kingscourt in eastern Ireland (Text-fig. 1), an area from stratigraphic sections which yielded nearly 36,000 which very little conodont data has previously been specimens or 90% of the total number of conodont published. The area has a great variery of depositional elements. environments including shallow-water carbonate platforms, mudmounds and basinal sequences (Strogen et al., 1996; Text-fig. 2). Detailed investigation into GEOLOGICAL SETTING the conodont biostratigraphy and biofacies of these rocks involved the collection of over 240 samples of The Lower Carboniferous (Dinantian) rocks of the approximately 2 kg weight each at approximately 2 m Kingscourt area in eastern Ireland form an outlier intervals from 17 measured quarry and river sections. within the Ordovician and Silurian Lower Palaeozoic 444 H.E.A. SOMERVILLE, ID. SOMERVILLE
rocks of the Longford-Down Massif. The Dinantian rocks occur mosdy within counties Meath and Monaghano The Kingscourt Oudier, extends 30 km N-S and 25 km E-W and is largely bounded to the ./ west by the major N-S trending Kingscourt Fault (Text- / figo l) oElsewhere Dinantian strata li e unconformably / Fautt / o n Lower Palaeozoic rockso The Kingscourt Fault forms • a hinge fault to a half-graben, preserving younger Upper Towns Carboniferous and Permo-Triassic age rocks (Strogen • etalo, 1995)0
LATE VISÉAN STRATIGRAPHY
The late Viséan succession in the Kingscourt area consists of the Milverton Group, deposited on the Ardagh Platform in the nonh, and the contempo- raneous Finga! Group which accumulateci in the Dublin Basin to the south (Text-figo 2; Strogen et al., 1995)0 The platform facies of the upper two formations of the Milverton Group which were sampled include the Mullaghfin Formation (Asbian) and Deer Park E:;] Permian and Triassic Formation (Brigantian)o The Loughshinny Formation Westphalian (Brigantian), representing the basinal facies of the Namurian 80 Fingal Group was also sampledo Fingal Group ; Mitverton Group Cruicetown Group 5 Navan Group MmLAGHFIN FoRMATION DUBLIN BASIN D Lower Palaeozoic IJ Rocks 75 80 85 90 95 The Mullaghfin Formation forms most of the outcrop of pale, massive and well-bedded platform limestones betweenArdagh and Carrickmacross (Text- Texr-fìg. l - Geologica! maf of rhe Kingscourt Oudier showing rhe lirhologica groups of rhe Dinantian and rhe figo l) and is approximately 500 m thick (Strogen et location of sections sampled for conodonts (adapred al., 1995) olt consists mainly of coarse-grained crinoidal from Srrogen et al., 1995). packstones and grainstones, with rare micritic lime-
N s MOKEER AN QY. DEER PARK SOUTH ALTMUSH ARDAGH QY. BALLINAVORAN CREGG NOBBER STREAM
<( z
ARDAGH PLATFORM N. DUBLIN BASIN
Texr-fìg. 2 - Schemaric N-S section from rhe Ardagh Plarform ro rhe Dublin Basin showing rhe approximate srrarigraphic inrervals of Sections 1-4 (indicared by rhick verticallines) and orher secrions referred to in rhe rext (see Texr-fìg. l for geographic locarion of secrions)o LATE VISÉAN CONODONTS FROM IRELAND 445 stones which form pseudobreccias. The formation is CONODONT BIOFACIES AND also characterised by the development of palaeokarst BIOSTRATIGRAPHY and palaeosol horizons, as weli as smali rugose coral colonies. Over 120m are exposed in Mokeeran Quarry S ECTION l : BARLEY HILL Q UARRY (ASBIAN PLATFORM (N 839 994) in the north (Text-fig. l) and FAC lES) approximately 25 m of the upper part the Muliaghfin Formation is exposed in Barley Hili Quarry (N 827 Conodont abundance and diversity 965) (Section l; Text-fig. 2). Also near the top of the formation, are massive, pale grey, micritic mudbank Fifteen samples were coliected from Asbian platform limestones which form conspicuous knolis more than limestones of the Muliaghfin Fm. in the 25 m thick 90 m high, as at Ardagh Quarry and Cregg (Text-fig. Barley Hill Quarry section, which includes the 2; Strogen eta!., 1995; Somervilie eta!., 1996, 1997). underlying beds below the quarry. The samples yielded 329 conodont elements (Tab. 1), an average of 12.1 DEER PARK FoRMATION elements/kg. The range in the total number of conodont elements is relatively smali compared with The Deer Park Formation is a poorly-exposed Sections 2-4, from very low values of 1.3/kg to Brigantian platform sequence, which directly succeeds moderatevalues of39/kg (sample lOOG). Throughout the Asbian Muliaghfin Formation and crops out NW most of Section l the samples yielded <20 elements/ of Ardagh Quarry (Text-fig. 2) . Although the top is kg, but sample l OOG forms a conspicuous peak (Text- erosional (Strogen eta!. , 1995), it is up to 100m thick. fig. 3) . There is a large variation in the number of This formation is composed of a variety of lithofacies species present in the samples, ranging from l species including (i) medium grey, thickly-bedded, crinoidal in sample l 000 to 7 species in samples l OOE an d l OOF packstones (ii) dark grey to black, cherty, thinly-bedded (Tab. 1). The average is 4.2 species/sample for the entire argiliaceous brachiopod wackestones and packstones section. and (iii) massive, pale grey, crinoidal grainstones and rudstones. The main section sampled for conodonts Conodont species present in the Deer Park Formation is in smali scarps south of Deer Park House (Text-fìg. 2, Section 2) and at In total, eleven conodont species are present in the Poulmore Scarp (N 823 959) at the top of the Barley Hili Quarry section (Text-fig. 4). These are listed formation (Text-fig. 2; Section 3). The limestones at in the order of their abundance ofPa (platform) (or P) Poulmore are unconformably overlain by Namurian elements, Pb, M and S elements contained in a single sandstones of Arnsbergian (E2) age Qackson, 1955, sample (Tab. l), but this listing is problematical. Two 1965). of the species Synclydognathus geminus and Kladognathus tenuislcomplectens have a good representation of ali the LOUG HSHINNY fORMATION components of their multielement apparatus, and to a lesser extent Lochriea commutata, while the gnathodids Basinal facies of the Brigantian Loughshinny are represented mainly by their Pa elements only. K Formation are known from outcrops to the south of tenuislcomplectens is represented by at least 8 discrete Ardagh, mainly in river sections. The base of the elements, comprising 2 Pa-Pb, 2M, l Sa, 2 Sb-Sc and formation is seen only in the River Dee section NW possibly l Sd element types. In recent reconstructions ofNobber (Text-figs. l, 2). The thickest section in the of the Kladognathus apparatus the two species erected Loughshinny Formation (> 60 m thick) is the Altmush have vicariously shared M and S elements and are Stream section (N 788 87 1) (Text-fig. 2; Section 4) distinguished only by the Magnilaterella (Pa-Pb) which consists of weli-bedded, fine-grained an d coarse- elements present. (See Mapes & Rexroad, 1986; grained limestones, interbedded with shales and rhin Rexroad & Horowitz, 1990; Purneli, 1993; Skompski, laminated calcisiltites. The weli-bedded limestones are 1996), (P l. l). However, in this study no evidence frequently graded, laminated and typically have erosive emerged (either biostratigraphicaliy or by association) bases. They contain shale rip-ups, a shallow-water fauna to determine which Magnilaterella elements were and flora, intraclasts, micritised grains and ooids. These associateci biologicaliy; they are here ali considered K beds have been interpreted as calciturbidites containing tenuislcomplectens. Synclydognathus geminus is repre- much shallow-water, platform-derived materia! sented by 8 discrete elements, comprising l Pa, l Pb, (Strogen et al. , 1995). Very coarse-grained crinoidal and 6 S element types, including a symmetrical Sa calcirudites also occur in this formation. The upper element, as in recent reconstructions of S. geminus contact of the formation is conformable with the (Rexroad & Varker, 1992; Skompski, 1996), (P late l). succeedingArdagh Shale Formation ofPendleian (basai When ali elements are counted, Synclydognathus Namurian, Ela) age, based on the presence of the geminus and Kladognathus tenuis are dominant. zonally diagnosti c goniatite Cravenoceras leion Qackson, However, when considering Pa elements only (or Pa 1955, 1965). equivalent elements in the case of Kladognathus), 446 H.E.A. SOMERVILLE, I.D. SOMERVILLE
No. mult ielement conodont species/ sample
10m
5
o -E LL .r:; :l .::t:...... -o a.. Cf) ...... ::t:...... Q) Q) a.. o ..... Q) - oQ) c: ca ·-...c: Conodont species ca C) a.. ·-m 150/1
c: ca ·-.c 0 <( No. of conodont elements Wt. dlssolved/kg
FfH Coarse grained crinoidal packst./grainst. * Conodont sample =a Fine grained cherty 1.·.·} Brachiopod-rich 11111 wackest./packstones
Text-fìg. 3 - Composite lithostratigraphical section of Barley Hill Quarry (Mullaghfìn Formation) and Deer Park South (Deer Park Formation) showing variation in conodont abundance (total number of conodont elements/wt. dissolved kg) and diversiry (number of species/sample). ibÌ ><
q'<
0(') (l) o 3 .,';j'"O o Late Asbian o 01 o 3 gr.(/)(l)
"'(l) ....., ()M ()Q- · o-·..., ., ::l '"O ,_2": o o o o o o o o o cm m o 01 01 01 w w w w w w o o o o w o o o o o o o o o o o 1\) 1\) ...... (l) (l) --.. --.. o ;?g_ m ..... N )> CD O O m "Tl G)IC:...... :::.: to O )> O O CD )> CD CD l l ..... '"0::> Ol(JQ Lochriea commutata ..., (l) :>;""() • • • • • • • • .. •1• • • •SynclydQgnathus geminus • T • • • • • o'Tl:;- ., § ;::: ;::; o> O' : : • : : : • : : : :• , : : • : : • : • : c. '""t o () Gnathodus girtyi ::l o • • • • • • •• l • • • • • • è 9 9 • • • .:...._ o Cì zg.- Gnathodus bilineatus t • ::l l • l. • • • • : •• o:!..., Hindeodus cristula g • • !f· sp.• s_e . sr.juv. Mestognathus• beckmann• i sp. • 'f· sp. • • • • Gnathodus homopunctatus• • • ;;j ::n...,s· .... l...... •(f) 9 (!). • q'<:;- sp. sp. Vogelgnathus campbelli sp. (l) t..;> o; • • • • • • ® Ere! naviculus? • • • • • • ' • 9-::r:: Mestognathus bipluti • 1 o-· J - o-= ldiopri niodus healdi l • r • • • • 5 Hindeodontoides spiculus Multielement species present 1 (l) "' ::l Kladognathus macrodentata ...._. c.. ::r . l; Multielement species abundant o Lochriea mononodosa • • • • ::l First appearance of biostratigraphically Il significant species Lochriea nodosa E... • • • • High diversity peaks ::n Gnathodus Lochriea nodosa ..,::l o § c; · 2-.., ::l 0... -....] 448 H.E.A. SOMERVILLE, ID. SOMERVILLE
Formation Base MULLAGHFIN FORMATION Too Sample No. (and lithotype) 112/ 112/ 100 100 100 100 100 100 100 100 100 100 163 162 100 Tot. 6 1 z A B c D E F G H J 1 1 K Els Multielement species (W) (W) (G) (W) (W\ I IW/P) IG\ (W\ (W\ (P/G) (G\ IW\ l IW/P\ IW\ lP\ Cavusgnathus naviculus? P a 1 1? 1 3 Pb 1? 1 Gnathodus spp. P a 1 1 G. bilineatus P a 2 1 3 G. girtyi P a 4 1 2 4 2 3 3 19 G. homopurctatus P a 1 9 16 3? 29 Hindeodus cristula P a 1 1 1 3 Kladogn. tenuis/complectens (DE Magnilat. clarkei) Pa-Pb 1 1 (DE Magnilat. contraria) Pa-Pb 1? 1 (DE Magnilat. complectens) Pa-Pb 1? 1 (DE Magnilat. robusta) Pa-Pb 1 1 (DE Mag. sp.) Pa-Pb 2 2 (DE Neo. peracutus) M 1? 2 3 (DE Neo. scitulus) M 2 1 1 4 (DE Neo. sp.) M 2 1 3 6 (DE Hib. miliari) Sa 1 1 1? 3 (DE Lig. tenuis) Sb-Sc 1 1 1 1 4 (DE Lig. lavis) Sb-Sc 1 1 1 1 4 Kladognathid fragments 3 1 2 4 6 2 1 1 20 Lochreia commutata P a 2 2 1 4 1 1 1 12 Pb 1 1 2 M 2 2 1 1 1 1 1 1 10 s 1 1 1 3 Mestognathus spp. P a 1 1 1? 4 7 M. beckmanni P a 1 1 M. bipluti P a 1 1 Syrclydognathus gemi nus P a 2 2 1 1 1 1 8 Pb 1 1 2 s 5 1 2 2? 4 1? 4 2 4 3 1 1 30 Vogelgnathus sco. P a 1 1 Platlorm (Pa) fragments 2 3 4 1 10 M fragments 1 1 1 3 Hindeodellan fragments 4 3 1 2 3 5 12 14 1 8 10 63 lndet. ramiforms 7 10 2 2 1 5 12 20 4 2 2 67 To tal 32 26 2 5 13 16 2 28 53 78 13 21 31 5 4 329 Wt. diss. Kg 1,6 2,0 1,4 1,6 1,0 2,0 1,6 1,9 2,0 2,0 2,0 2,0 2,0 2,0 2,0 27,1 Abundarce/Kg 19,4 13 1,4 3,1 6,8 8 1,3 14,7 26,5 39 6,5 10,9 16,5 2,5 2 12,1a No. multiel. specJsample 5 5 2 3 4 5 1 7 7 6 2 5 6 3 2 4,2a
T ab. l - Numbers of elements of conodont species from samples in the Barley Hill Quarry section (Mullaghfin Formation). The following abbreviations for lithorypes are used here and in Tables 2-4. W=Wackesrone, P=Packsrone, G=Grainsrone, R=Rudsrone, D=Dolomite, CS=Calcisiltite, LB=Limesrone breccia. Wr. diss. kg = weight dissolved/kilogram.
Gnathodus homopunctatus dominates, followed by Gnathodus bilineatus (=G. bilineatus bilineatus of other Lochriea commutata and G. girtyi. I t is also noteworthy authors), G. girtyi (=G. girtyi girtyi of other authors) that Synclydognathus geminus and Kladognathus tenuis and G. homopunctatus, which together with Mesto- complectens are very consistent in their occurrence gnathus bipluti, indicate an horizon within the lower throughout Section l, whereas Gnathodus homopun- part of the Gnathodus bilineatus Zone, oflatest Asbian- ctatus occurs in only 4 of the 15 samples with more early Brigantian age (Metcalfe, 1981; Varker & than 50% of the total number of specimens present in Sevastopulo, 1985; Armstrong & Purnell, 1987; Riley, one sample (in lOOG). Gnathodus girtyi occurs in 7 1993; Perret & Weyant, 1994; Jones & Somerville, samples again represented by Pa elements only and G. 1996; Skompski, 1996). bilineatus is recorded in only 2 samples. Lochriea commutata while it is common in its occurrence is Conodont biofocies sparse in numbers, often recorded by the presence of its M or Pb elements only. Synclydognathus gemi nus occurs as S elements in ali Other species present include: Cavusgnathus sp., lower samples, from samples 112/6 to lOOE, but the Hindeodus cristula, Mestognathus sp., M. bipluti (only first Pa element appears only in sample l OOE. The in sample 163/1) and Vogelgnathus sp. Ali are sparsely dominance of S over Pa elements in samples has been represented by Pa elements only. noted from elsewhere (Davies, 1980). According to Austin (1976), Austin & Davies (1984) and Davies et Biostratigraphically important conodont species al. ( 1994) this species is indicative of near-shore, high- energy facies in possibly stressful euryhaline Biostratigraphically important conodont taxa in the environments. However, other possible near-shore Barley Hill Quarry section (Text-fìg. 4) include species indicators, such as Cavusgnathus sp. and LATE VISÉAN CONODONTS FROM IRELAND 449
Mestognathus sp., highlighted by the same workers, are Conodont species present sparse at Barley Hill. The common association of Synclydognathus geminus and Kladognathus tenuisl Sevenreen conodont species were recovered from complectens has permitted the recognition of the Deer Park Sourh (Text-fìg. 4); the section is dominated Synclydognathus-Kladognathus Biofacies, for shallow- by species of Gnathodus and Lochriea, together with water, high-energy, open-marine platform environ- Synclydognathus geminus and Kladognathus tenuisl ments. complectens. Gnathodus girtyi is the most abundant Gnathodids are present mainly as Pa elements with species (Tab. 2) and is present in 12 of the 19 samples, a notable paucity of associated ramiform elements, with the greatest number ofPa specimens being present particularly in grainstones (Tab. 1). These conodont in sample l 07A/l . Gnathodus homopunctatus is present elements are much abraded throughout the Barley Hill in 12 samples, mostly in small numbers, with the section, suggesting a turbulent depositional environ- highest yields in samples l 07A-1 07B. Kladognathus ment and much reworking. Perhaps the gnathodid tenuislcomplectens is present in 11 of the 19 samples, ramiform elements were winnowed out and selectively with the greatest yields in samples 152/1 and l 07A. sorred, leaving only Pa elements? Such low-diversity, Synclydognathus geminus is present in 13 samples and low-abundance conodont faunas suggests facies is most abundant in samples 152/1 and 130. Lochriea contro!. Many of the limestone samples are also rich commutata occurs in 12 samples, mainly in small in red an d green algae an d foraminifers, implying very numbers, except in samples 130 an d l 07A. Gnathodus shallow-water platform sedimentation during the late bilineatus is present in 9 samples, but is generally Asbian (Strogen et al. 1995; Adams et al. , 1992; present in small numbers in all samples. Lochriea Horbury & Adams, 1996). The unusual abundance mononodosa and L. nodosa occur together in severa! of conodont elements, particularly Gnathodus homo- samples from the top of the section, all with very low punctatus, in the packstones and grainstones of sample numbers. l OOG, can no t be explained readily by a different Other species present in small numbers include: microfacies, as most grainstones in the section have a Hindeodus cristula, Hindeodontoides spiculus, Mesto- poor yield (Tab. 1). Moreover, sample lOOG has gnathus sp., M. bipluti (sample 131D), M. beckmanni abundant indeterminate ramiform elements, more (sample 107B), and Cavusgnathus naviculus? (samples characteristic of wackestones in the section. 131B and 130). Vogelgnathus campbelli is present asPa elements in 3 samples, mostly in small numbers, except for an unusually high number in sample 130, the S ECTION 2: DEER p ARK SOUTH (BRIGANTIAN PLATFORM highest recorded for any sample from the Kingscourt FACIES) area. Kladognathus macrodentata was recovered in this section from samples l OSA an d l 08B and is regarded Conodont abundance and diversity as an element of a separate species of Kladognathus (see Rexroad & Merrill, 1996 for further discussion). The Nineteen samples were collected from the only other species present is Idioprioniodus healdi which discontinuous outcrop in the >90 m thick Deer Park was recovered from 7 samples, mostly from the upper Sourh section (Section 2) . The samples yielded 1644 part of the section.l healdi is represented by 7 elements elements (Tab. 2) with samples averaging 44.7 including, l Pa, l Pb, l M, l Sa, and 3 Sb-Sc elements elements/kg. There is a wide range in the total number (see Stone & Geraghry, 1994; Purnell & von Bitter, of specimens recovered from 2/kg to high values of 1996) (Pl. 1). 181.5/kg. Throughout much of the section samples have low to moderate yields, but at the base of the Biostratigraphically important conodont species Deer Park Formation (sample 152/ l) an d near the top of the section (samples l 07A and 130), they have over Biostratigraphically important conodont taxa in the l 00 elements/kg and form conspicuous peaks (Text- Deer Park South section include Mestognathus bipluti, fìg. 4). Kladognathus macrodentata, Gnathodus bilineatus, and There is great variation in the number of species G. homopunctatus (in the lower part), and Lochriea present in the samples, from l species at the base nodosa and L. mononodosa (both fìrst appearing (sample 154/1) to 12speciesnearthetop (sample 130) together in sample l 07A). Thus the section extends (Text-fìg. 4; tab. 2). The average is 6.4 species/sample from the lower part of the Gnathodus bilineatus Zone, for the entire section (excluding samples 154/ l an d of latest Asbian-early Brigantian age to the L. nodosa 153/ l, which belong t o the top of the Mullaghfìn Zone, of middle to late Brigantian age (Text-fìg. 4) , Formation). Samples which contain the high est (Metcalfe, 1981; Varker & Sevastopulo, 1985; number of specimens, also have the greatest diversity; Armstrong & Purnell, 1987; Riley, 1993; Perret, 1993; however, in sample 131D a prominent peak occurs Perret & Weyanr, 1994; Alekseev et al., 1996; with a low yield. Skompski, 1996). The youngest Brigantian conodont 450 H.E.A. SOMERVILLE, !.D. SOMERVILLE
Formation Base DEER PARK FORMATION Top Sample No. (and lithotype) 154/ 153/ 152/ 151 / 150/ 132 132 131 131 131 131 108 108 107 107 107 130 107 107 Tot. 1 1 1 1 1 B c A c D B A B A A1 B c D Els MuHielement specles (G) l (W/P) (W) (P) (G) ry.I/Pl [P) _{P/G) LrNIPJ (W) (G) 0Nl fY'/) (P) (P) (P) (P) (P) (P) Cavusgnathus naviculus? P a 1 3 4 3 3 14 Pb 1 1 M 1 1 Gnathodus spp. P a 2 2 2 1 2 5 14 Pb 4? 1 1 1 7 M 1 1 2 Sa 1 2 3 Sb 1 1 2 Se 1 2 3 Sd 1 1 G. bilineatus P a 8 1 3 1 4 5 12 7 2 43 G. girtyi P a 13 4 10 2 1 4 41 57 32 16 5 10 195 G. homopunctatus P a 4 3 1 3 1 1 2 50 42 28 9 7 151 Pb 6 1 7 Hindeodontoides spiculus P a 1 1 2 Hindeodus cristula P a 1 1? 1 8 11 ldioprioniodus healdi (DE Lonch. ponderosa) ? 1? 1 (DE Prion. clar1 Tab. 2- Numbers of elements of conodont species from samples in the Deer Park South section [Mullaghfìn Formation (samples 154/1 and 153/1) and Deer Park Formation]. zone in Britain, the G. girtyi collinsoni Zone ofRhodes The L. nodosa Zone (as used in Austin et al., 1970; et al., (1969) and Varker & Sevastopulo, (1985), is Metcalfe, 1981; Austin & Davies, 1984; Perret & no t distinguished in Kingscourt, although occasionally, Weyant, 1994; Alekseev et al., 1996; Skompski, 1996) some specimens of G. girtyi recovered in the late is recognised in preference to the L. mononodosa Zone Brigantian closely resemble the subspecies collinsoni. (as used in Varker & Sevastopulo, 1985). Kladognathus LATE VISÉAN CONODONTS FROM IRELAND 451 macrodentata occurs at the top of the bilineatus Zone; and grain size, as well as changes in the other however, in Poulmore Scarp and Altmush Stream i t is microfossil groups such as foraminifers and calcareous found only in the succeeding nodosa Zone (see below). algae, notably Koninckopora. The formation boundary also coincides with the Asbian/Brigantian stage Conodont biofocies boundary in the Kingscourt area (Strogen et al., 1995). Similar lithofacies and microfossil changes at Samples 154/1 and 153/1 from the base ofthe Deer the Asbian/Brigantian stage boundary were noted by Park South section have low conodont diversity and Somerville & Strank, (19S4) in North Wales and low abundance. These samples are from massive, fine- northern England. grained grainstones (sample 154/ l) or intraclastic The second major peak in conodont diversity and wackestone/packstone beds (sample 153/1) which can abundance near the top of the section coincides with be correlateci with the same beds at the top of Barley another abrupt change in lithofacies, from dark grey, Hill Quarry (Text-fig. 3). Both sections expose the fine-grained, thinly-bedded cherty limestones, to pale uppermost Mullaghfin Formation which has a paucity grey, coarse-grained, thickly-bedded crinoidal-rich of conodonts in the Kingscourt area. These beds are limestones (sample l 07A). This boundary coincides locally rich in calcareous algae such as Koninckopora as with the base of the L. nodosa Zone. These rapid well as foraminifers (Strogen et al., 1995), and represent changes in facies may be related to relative sea-level very shallow-water, offshore shelf environments. The changes (shallowing or deepening events), and/or basal beds of the succeeding Deer Park Formation changes in the rate of sedimentation. (sample 152/1) mark an abrupt change in facies to The cherty wackestone/packstone interval in the wackestones and coarser grained crinoidal grainstones middle of the Deer Park Formation (samples 131A- with abundant and diverse conodont faunas, and an 1OSA) containing local concentrations ofbrachiopods, absence of Koninckopora. an impoverished conodont fauna and an almost The overlying strata (samples 132B-C) are mosdy complete absence of species of Gnathodus, Lochriea and peloidal intraclastic packstones with low numbers of Idioprioniodus, suggests stressful, low-energy, near-shore conodont elements and average diversity. These beds environments (Davies et al., 1994). Similar gigan- are locally rich in the green alga Nanopora anglica. In toproductid-rich limestones with low conodont yields the middle of the section (samples 131A-B) the are recorded from the late Viséan Yoredale Group limestones are mainly dark grey, fine-grained cherty cyclothems in the north of England (Davies, 19SO; wackestones and packstones with very low conodont Armstrong & Purnell, 19S7; Davies et al., 1994). yields and below average diversity (except for sample 131 D). These samples have very sparse gnathodids an d lochreiids. The brachiopod-rich wackestone bed SECTION 3: PouLMORE ScARP (BRIGANTIAN PLATFORM (sample l OSA) similarly has a very low yield and FACIES) diversity, with complete absence of Gnathodus girtyi and Lochriea commutata, but with rare Kladognathus Conodont abundance and diversity macrodentata. The incoming of thickly-bedded, well-sorted, Twenty samples were collected from Poulmore coarse-grained crinoidal packstones and grainstones Scarp, a 11 m thick section a t the top of the Deer Park near the top of the Deer Park South section (samples Formation (Text-fig. 5). Every bed was sampled and l 07A-D) coincides with a dramatic rise in the in some cases severa! samples were taken from the same abundance an d diversity of conodonts, reaching a peak bed, in order to detect any variation in the number of in samples l 07A and 130 (see also the succeeding conodont specimens from bottom to top within Poulmore Scarp section described below). These individuai beds, and between successive beds. Poulmore samples include platform and ramiform elements of Scarp is by far the most productive section sampled Gnathodus and Lochriea, together with ramiform anywhere in lreland, with 2S,52S elements recovered elements of Kladognathus tenuis/complectens and from the 20 samples (averaging 726 elements/kg). Idioprioniodus healdi. There is a great range in the total number of conodont elements recovered per sample from relatively low values Summary of 42/kg in sample PH6 to exceptionally high abundance of3174/kg in sample PH15 (Tab. 3; text- There are 2 prominant diversity and abundance fìg. 5). In the middle of the section many samples have peaks in the Deer Park South section, peaks that yielded over l 000 elements/kg. coincide with major facies changes. The fìrst peak near Upward in the Poulmore section there is an increase the base of the section (sample 152/ l) marks the in species diversity, from a low value of 6 species near boundary between the Mullaghfin and Deer Park the base, to the high est value of 11-13 species (samples formations, a boundary which is clearly recognisable PH9, 16 and 17) ali from Bed 7 (Text-fig. 5); the by a colour change in the limestones, bed thickness average is 9 species per sample (Tab. 3). lnterestingly, 452 H.E.A. SOMERVILLE, !.D. SOMERVILLE Formation Base DEER PARK F ORMA T IO N Top Sample No. (and lilhot}?e) PH PH PH PH PH PH PH PH PH PH PH PH PH PH PH PH PH PH (height above the base) (m) t 12 6 7 2 13 8 14 20 15 3 9 16 17 10 PH4 .l PH18 11 5 19 To t. 0,25m 0,75 1,25 2,0 3,0 3,1 3,8 4,3 4,8 5,05 5,6 6,8 7,4 7,8 8,0 8,6 8,9 9,1 9,9 10,8 Els MutUelement species (G) (G) I !W/P (P) (P/G) (P) (W/P (P/G) (P/G) (P) (G) (G) (G) (G) (P) l (W/P) . (G) (P/R) (P/G) (W/P) Cavusgnathus naviculus? P a 3 6 1 11 1 1 23 Pb t 2 2 2 1 8 M t 1 2 4 s 4 6 4 3 17 Cavusgnathus naviculus P a 2 2 Cavusqnathus unicomis P a t 1 1? 7 10 Gnathodus spp. P a 2 11 2 62 13 3 1 30 6 130 Pb 3 2 98 12 84 31 38 10 2 3 11 3 9 49 22 377 M 2 3 34 25 6 16 2 28 5 3 2 4 2 17 7 156 Sa 12 4 1 6 1 2 1 2 2 2 33 Sb 2 1 2 25 3 5 10 13 1 2 2 5 1 22 10 104 Se 1 2 4 29 24 5 20 1 14 3 3 4 3 2 2 22 6 145 Sd 4 1 30 4 11 4 5 2 1 2 4 2 12 3 85 G. bilineatus P a 9 8 552 209 405 34 1725 462 33 17 19 6 153 324 60 61 126 4203 G. girtyi P a 77 70 1 12 17 268 192 1335 148 1311 598 1367 283 226 1 10 90 23 325 193 6547 Hindeodus cristula P a 7 13 9 2 1 32 Pb 1 1 2 M 2 4 1 1 8 s 10 3 13 ldioprioniodus healdi (DE Lonch. ponderosa) ? 1 15 2 12 2 23 5 8 3 3 2 3 3 1 10 4 97 (DE Pnon. elarki) ? 1 1 9 11 8 2 18 6 10 2 2 3 6 3 82 (DE Neo. eonjunctus) M 5 4 7 2 12 9 7 2 1 1 2 7 2 61 (DE Hib. subaeodus) Sa 7 3 16 2 22 10 4 1 1 1 4 2 2 1 4 80 (DE Meta. bidentata) ? 9 3 9 1 21 8 15 1 1 1 3 72 (DE Lon. lexingtonensis) ? 1 1 13 7 21 25 19 20 8 1 2 1 6 7 7 139 (DE Lig. !}?a) Se 1 25 15 44 7 69 33 14 2 6 5 12 11 244 fraqs 2 2 3 26 3 41 3 51 89 40 7 8 3 6 7 7 298 Kladogn. tenuis/complectens (DE Magnilat. elarkei) Pa-Pb 1 1 1 3 1 1 1 9 (DE Magnilat. eompleetens) Pa-Pb 2 7 2 1 1 4 2 1 1 2 23 (DE Magnilat. eontrana) Pa-Pb 4 2 17 23 (DE Magnilat. robusta) Pa-Pb 6 1 1 1 2 11 (DE Magnilat. sp.) Pa-Pb 1 1 1 2 5 (DE Neo. peraeutus) M 5 1 5 30 21 7 36 27 12 1 5 8 9 2 3 10 16 198 (DE Neo. seitulus) M 1 1 1 3 7 2 2 2 1 6 26 (DE Neo. sp.) M 4 1 1 5 11 (DE Hib. millen) Sa 1 1 2 1 2 1 1 2? 1 3 1 1 6 23 (DE Lig. tenuis) Sb-Se 3 6 1 1 1 2 4 2 2 2 2 26 (D E Lig. tevis) Sb-Se 1 2 3 4 4 5 2 3 24 (DE Klad. maerodentata) ? 2 18 2? 3 8 1 2 9 7 1? 4 6 13 76 (DE Lig. sp.) ? 12 1 2 8 11 10 6 7 57 Kladognathid fragments 34 34 2 8 11 3 226 24 11 82 6 33 34 6 61 28 7 19 97 102 828 Loehnea spp. P a 2 5 58 2 59 5 3 3 7 5 5 3 157 L. commutata P a 29 6 3 19 19 214 154 581 58 316 133 23 22 10 5 15 30 6 71 43 1757 Pb 5 10 7 11 75 187 8 77 9 3 21 4 1 7 5 2 24 19 475 M 7 1 9 22 17 56 97 489 28 177 35 16 16 13 6 31 16 4 71 38 1149 Sa 1 12 2 9 1 4 3 5 37 s 2 2 5 14 57 122 12 55 1 4 17 3 3 8 1 1 27 10 344 Lochriea mononodosa P a 1 9 10 33 12 165 26 156 227 11 8 4 2 5 38 14 19 22 762 Lochreia nodosa P a 1 3 3 22 29 6 78 62 5 4 4 4 45 12 8 9 12 307 L. mononodosa/nodosa P a 2 15 5 22 Mestognathus spp. P a 11 4 15 Pb 10 10 M 3 3 s 14 14 M. bipluti P a 2 2 Syrclydognathus geminus P a 16 3 1 1 1 2 3 7 6 7 2 1 1 51 Pb 1 1 1 2 2 1 2 10 s 14 12 1 1 3 7 13 11 29 12 12 19 3 7 144 Vogelgnathus spp. P a 5? 3? 7 1 1 17 s 3? 9? 1 13 Vogelgnathus eampbelli P a 2 2 1 22 5 1? 3 36 Platform Pa fragments 14 4 1 5 124 68 283 29 438 232 128 72 33 14 41 15 39 35 1575 Pb fragments 1 2 1 136 11 152 100 7 30 10 12 2 6 8 4 7 31 520 M fraoments 6 4 15 1 6 2 37 8 13 5 2 5 3 107 Alate (Sa) fragmerrts 3 2 8 12 25 37 1 4 1 1 12 6 112 Hindeodellan fraoments 25 4 11 63 57 270 518 1209 139 696 87 585 141 112 40 71 50 35 245 166 4524 lndet. ramiforms 31 22 7 5 15 130 118 380 41 442 53 280 137 67 26 63 39 6 87 94 2053 To tal 305 212 55 177 186 2000 2110 5710 622 6368 2189 2861 939 625 215 588 767 234 1298 1068 28528 Wl. diss. Kg 2,0 2,0 1,3 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2,0 39,3 Abundance/Kg 152 106 42,3 89 93 1000 1055 2855 311 3189 1099 1431 469 312 108 294 384 117 649 534 726a No. speeJsample 9 6 6 8 8 8 9 10 8 11 8 13 11 12 8 11 11 9 9 10 9,2(a) Bed number 1 2 3 4 5 6 7 8 9 1 o T ab. 3 - Numbers of elements of conodonr species from samples from the top of rh e Deer Park Formarion in rhe Poulmore Scarp secrion. LATE VISÉAN CONODONTS FROM IRELAND 453 the samples from Bed 7 have not yielded the highest yields in samples PH14 and PH15. L. mononodosa number of specimens. Also, several beds record higher and L. nodosa occur together in most samples (except species diversity at the base, compared to the middle in samples PH1 and PH12). Large numbers of or top of the same bed. specimens of both species are recorded in samples PH14, PH15 and PH3, but in almost every sample, Conodont species present L. nodosa is subordinate in number to L. mononodosa, except in sample PH4. The most abundant conodont in the Poulmore Other species in the Poulmore section occur usually section is Gnathodus girtyi which is present in every in smaller numbers. They include: Synclydognathus sample and is particularly abundant in samples PH3, gemi nus in 16 of the 20 samples, Cavusgnathus sp. in 6 9, 14 an d 15 (Tab. 3). Gnathodus bilineatus is also very samples, Hindeodus cristula only in 5 samples, Mesto- abundant and is present in every sample, except the gnathus bipluti from only sample PH15. Vogelgnathus lowest three samples. lt is most abundant in sample sp., is recorded in 10 samples (as V. campbelli in 7 PH 15. This species shows notable variations within samples), mainly in small numbers, but locally rich as individua! beds, e. g. in Bed 4, where there is a marked in sample PH16. Idioprioniodus healdi present in all decrease (>60%), from the base to the top of the same 20 samples, is variable in number, with high values in bed, in the number ofPa elements. Similarly in Bed 5, several samples (samples PH3, 13, 14 and 15; Table a >80% decrease (from the middle to the top of the 3) . The genus Kladognathus is represented by two bed). Lochriea commutata is present in all samples. lt species K tenuislcomplectens and K macrodentata. K has a great variati o n in abundance, but has the high est tenuislcomplectens occurs in moderate to large numbers No. multielement conodont species 5 11 18 4 10 17 16 9 3 15 20 14 8 3000 No. Conodont elements Wt. dissolved (kg) Text-fìg. 5- Lithosrratigraphical section ofPoulmore Scarp (top of the Deer Park Formation) showing variation in conodom abundance (tora! number of conodom elemems/wt. dissolved kg), tora! number ofPa elemems/wt. dissolved kg), and diversity (number of species/sample). 454 HE.A. SOMERVILLE, !.D. SOMERVILLE in all samples. K macrodentata is present in 13 shallow water, in probably less than l O m deep samples and is most abundant in sample PH8. turbulent conditions. Austin (1976), von Bitter (1976), von Bitter et al. (1986), Davi es et al. (1994) an d Pectiniformlramiform element ratios and species Krumhardt et al. ( 1996) suggested that Cavusgnathus composition and Mestognathus probably inhabited near-shore restricted environments. lnterestingly, 5 of the 7 The range in the number of pectiniform (Pa samples containing Vogelgnathus campbelli are from platform) elements (both assigned species and the base of beds. This species shows similar fragments of Pa blades and platforms combined) in characteristics in late Viséan rocks in northern Spain the samples is very large, from a very low value of7 /kg (van den Boogaard, 1992). (sample PH6) to a very high value of2130/kg (sample Severa! samples (PH 5, 7, 8, and 19) are from fìne- PH15) (Text-fìg. 5). Most samples with high values grained wackestones and packstones at the top of in the total number ofPa elements have large numbers individuai beds; they were probably sedimented un der of ramiform elements/kg, especially those in the middle quiet-water lagoonal conditions, in the lee of shoals, of the section (samples PH13, 14, 15-9) (Tab. 3). In with little turbulence and sorting. These samples have the majority of samples the Pa elements represent high proportions of ramiform elements and excellent between 40-65% of the total. However, in two samples preservation, especially in samples PH5 and PH8. (PH18 and PH3) theyexceed 75%, with a consequent A distinctive facies present near the top of the under-representation of ramiform elements. Poulmore section in samples PH4, 10 and 11 (Text- Conversely, in samples PH7, 8, 10 and 5-19, ramiform fìg. 5) has some of the lowest conodont yields, but elements form 60-75% of the total. with an average number of species. These limestones Analysis of the conodont species composition from are mainly poorly-sorted, intraclastic, crinoidal the Poulmore section (Tab. 3) shows that in 15 of20 packstones, with a diverse fauna and flora; the latter samples the fìve most abundant species containing Pa include the codiacean green alga Calci{olium okense, elements are Gnathodus girtyi, G. bilineatus, Lochriea and foraminifers, but are characterised by fragmented commutata, L. mononodosa and L. nodosa. They bioclasts. represent over 90% of ali conodont species containing Pa elements. The other species, belonging to the genera Summary ofBrigantian platjòrm focies Mestognathus, Cavusgnathus, Hindeodus, Synclydo- gnathus and Vogelgnathus, generally account for less than Brigantian platform rocks of the lower part of the 10% (of the conodont species containing Pa elements), Deer Park Fm., have higher conodont yields (averaging except in sample PHl, where they exceed 35%. 44 elements/kg) and diversity (averaging 6 species/ sample) than those from the underlying Asbian Conodont biofocies platform limestones of the Mullaghfìn Formation (averaging 12 elements/kg and 4 species/sample, The samples with the highest yields (samples PH 14, respectively). The yields are highest in thin-bedded, 15, 3 and 9) are in thickly-bedded, well-washed, fìne-grained limestones in which Gnathodus girtyi is medium to coarse-grained, crinoidal packstones and dominant, followed by approximately equa! numbers grainstones. These samples, with an exceptionally high of G. homopunctatus, G. bilineatus and Lochriea average of 1-3000 elements/kg, also have high diversity commutata. The faunas are similar to those of the ranging from 8-12 species. Most of these samples, Mullaghfìn Fm, but additionally, Mestognathus bipluti, particularly those which show cross-stratifìcation such Vogelgnathus campbelli, Idioprioniodus healdi and as samples PH15, PH9 and PH3, or from the base of Kladognathus macrodentata are present. The upper beds beds, have the poorest preserved conodont elements, of the Deer Park Fm. yielded Lochriea mononodosa, (especially the ramiform elements, which are frequendy and L. nodosa from the nodosa Zone (Text-fìg. 4), but broken, and perhaps over-represented). Moreover, in G. homopunctatus is not recorded from the youngest some samples (e.g. PH9) a single species such as beds of the nodosa Zone in the Poulmore section. Gnathodus girtyi may dominate the population. These Samples from the upper Deer Park Formation at features suggest turbulent sedimentation and hydraulic Poulmore (ali within the nodosa Zone) have excep- action in shoals was responsible for selective removal tionally high yields (averaging 726 elements/kg) and of the lighter, less robust ramiform elements, concen- high diversity (averaging 9 species/sample) but were trating the pectiniform elements. not expected to yield many conodonts, especially Ali of the large, robust Cavusgnathus and gnathodids, because of the predominant coarse- Mestognathus Pa elements were recorded only from grained, crinoidal-rich limestone shoal facies. However, coarse-grained limestones in beds l , and 6-8, often similar extraordinarily high yields (>2000 elements/ from the base of beds, where the samples have the kg) and very high diversity (6-8 genera) were recorded largest grain size (e.g. samples PH15 and 9). These from high-energy packstones in Upper Carboniferous beds were deposited above fair-weather wave-base in (Pennsylvanian) rocks from Utah an d Colorado (D riese LATE VISÉAN CONODONTS FROM IRELAND 455 et al., 1984) and interpreted as shallow-water conodont elements, particularly the more robust nearshore conodont biofacies. These high-energy pectiniform elements; their abundance is only shoal deposits in near-shore settings usually have a comparable in rocks belonging to the basinal facies, paucity of conodont elements (although sample 152/ within the nodosa Zone (see below). Some wackestones l from near the base of the Deer Park Formation had from Poulmore also have high yields with similar high yields from this lithofacies) and are commonly diversity to the grainstones; their faunas are much fragmented (Davies, 1980; Austin, 1987). Local better preserved and more likely to be representative sedimentological factors apparently transported and of the population before transport and mixing. concentrateci exceptionally large numbers of No. multielement conodont specles/sample AL TMUSH STREAM 2 4 6 8 10 12 14 56 96K 53 ...... ,...Qap 3m,- ....50 ALT9 ...... gap 3m_: 47 ' ' 96H - ""'"'"'' ' ' ' ' ' ' ' ' ' - of conodont elements "'""'"',/' ' ' ' , ' , ' , ' ' ' ' ' ' ' ' - , , , , .. ,',','"';':':' ..... 96G 40 Conodont species ALT7 30 l-l" \ ALT6 ALTS ALT3 ALT2 20 ALT1 gap 2m 96F .... 96E o 960 .. 96C 966 Om ?-r. 7 96A 200 800 1 000 1200 1400 Thickly-bedded No. conodont elements * Conodont sample coarse-gr. skel. Dolomite intracl. grsts. Wt. dlssolvecl (kg) .1. Gradedbed Massive crinoidai L11:.1011 • . -- Chert m sp1cullt1c grainstone/rudstone III:ICII L1mestone breccia calcisilts & thin shales A A Shaie clasts Text-fìg. 6 - Lithostratigraphical section of Altmush Stream (Loughshinny Formation) showing variation in conodont abundance (rotai number of conodont elemenrs/wr. dissolved kg), and diversity (number of species/sample). 456 H.E.A. SOMERVILLE, ID. SOMERVILLE SECTION 4: ALTMUSH STREAM (BRIGANTIAN BASINAL ALT 1-9) were collected from the discontinuous FACIES outcrop of the 56 m thick Altmush Stream section (Text-fìgs. l, 2, 6). The Altmush Stream is the second Co nodo n t abundance and diversity most productive section in Kingscourt, after Poulmore, with 5,431 specimens or an average of 170.3 elements/ Basinal Brigantian limestones of the Loughshinny kg. Formation from Altmush Stream yielded similar The range in the total number of conodont conodont assemblages to those of the Deer Park Fm, elements is very high, from relatively low values of particularly the upper part. Eighteen samples (96A-K; between 6. 7-46.3 elements/kg, to very high values of AL TMUSH STREAM l l l l o .. I 4 0 - ..... - ,.-V\""/ ALT6 ALT5 ")'")' ALT3 ALT2 20 ..;.;. ALT1 - ::;, ·::::::- E Q) E .Q o Cll "t -s ,SI c:Cll g ...... l '-1 96B l Om 7 .,_, ?' _... 96A l C'· Text-fig. 7 - Biostratigraphical range chart for conodont species in the Altmush Stream section (Brigantian Loughshinny Formation) (N.B. see Text-fig. 6 for lirholog ornament). LATE VISÉAN CONODONTS FROM IRELAND 457 1113/kg (sample ALT9). The stratigraphically lower in the section (samples 96C and ALT7) have highest four samples (ALT9 to 96K) have an average high diversity peaks, but have much lower total of over 650 elements/kg and forma conspicuous;eak number of specimens (Text-fig. 6). (Text-fig. 6). The species diversity in most o the section is variable (3-8 species) (Text-fig. 7; tab. 4), Conodont species present but from sample ALT9 to the top of the section four samples have values ranging from 8-13 species Fifteen species, dominated by species of Gnathodus (highest in sample ALT9). The average for the entire and Lochriea (Text-fig. 7), are present in the Altmush section is 6 species per sample. Two samples from Stream section. The most abundant species is Formati o n Base LOUGHSHINNY FORMATION T Gnathodus girtyi present in 16 of 18 samples, with the as the Gnathodus-Lochriea Biofacies. However, similar greatest number of specimens in samples 961, 96] and limestones in the lower section (samples 96A-F) have ALT9 (Tab. 4). Gnathodus bilineatus is also abundant, generally low yields (Tab. 4). Some of these samples, but is present in only 7 samples, all from the upper from the base ofgraded limestones (samples 96D, 96E), part of the section (ALT7-96K), with the highest yields may have suffered loss from the redistribution of in samples 96] and ALT9. Lochriea commutata occurs elements during accumulation of the beds. Samples in 14 samples, with the largest number of Pa elements with very low yields, are in calcisiltites (e.g. sample in samples ALT9 and 961. Gnathodus homopunctatus ALTI) or cherty/dolomitic limestones (e.g. samples was only recovered in small numbers from sample 96A, 96D). ALT9. Other species of Lochriea represented include The unusually high conodont abundance and L. mononodosa and L. nodosa, both of which are present diversity in sample ALT9 may be partially explained in the upper four samples (ALT9 to 96K) and ALT?. by the facies, a polymict limestone breccia, this litho- Large numbers of specimens of both species are logy suggests reworking of older rocks and probable recorded in samples ALT9, 961 and 96]. concentration of conodont elements from the adjacent Other species present in Altmush Stream section contemporaneous platforms. However, the sample not include Kladognathus tenuislcomplectens and Idioprio- only has large numbers of Pa elements, but also has niodus healdi. K tenuislcomplectens is present in 15 abundant Pb, M and S elements of Gnathodus and samples, usually in small numbers, except in sample Lochriea, as well as of Kladognathus and Idioprioniodus. ALT9, which has >50% of the total number of These might not be expected to survive transport and specimens. Idioprioniodus healdi is present in 12 abrasion together with the more robust platform samples, most of which have low yields, except for elements which would be preferentially concentrated. samples ALT9, 961-96] (Tab. 4). The other 8 species The massive, coarse-grained and graded crinoidal occur in small numbers and include Cavusgnathus uni t near the top of the section (samples 96G and 96H) naviculus (in 4 samples) and C unicornis? (sample shows a distinct uniformity of microfacies and fauna. ALT2) . (All cavusgnathids were recovered from the The conodont yield is poor an d diversity is low in both lower part of the section). In contrast, Mestognathus as samples, although Gnathodus girtyi Pa elements are M. bipluti is present only in the upper part of the present in similar numbers, as in stratigraphically o l der section (sample 96]). Synclydognathus geminus is present samples. This facies, occuring in the L. nodosa Zone, is in 8 samples, Hindeodus cristula occurs only in fìve, comparable with the coarse crinoidal grainstones at and Vogelgnathus campbelli only in 4 samples. the top of the Deer Park South an d in Poulmore Scarp sections within the same zone, and probably represents Biostratigraphically important conodont species a transported platform fauna. Biostratigraphically important conodont taxa at Summary Altmush Stream (Text-fìg. 7) include in the upper section the lowest co-occurrence of Lochriea nodosa an d The samples from Altmush Stream were expected L. mononodosa in sample ALT? which defìne the base to have high conodont yields because of the of the L. nodosa Zone. A rich fauna in sample ALT9 predominandy deeper-water basinal facies and the within the nodosa Zone includes Mestognathus bipluti, known associati o n of species of Gnathodus and Lochriea Gnathodus bilineatus, and the only records of Gnathodus in deeper-water, open-marine facies (Austin, 1976; homopunctatus and Kladognathus macrodentata. lnter- Davies, 1980; Austin, 1987). However, conodonts are estingly, Gnathodus bilineatus is no t recorded from the only abundant in the upper section, within the L. bilineatus Zone in this section. nodosa Zone. Not only is there great abundance, but The unusually rich conodont concentration in the also large diversity of conodonts with up to 13 species youngest samples occurs dose to the Brigantian/ present in samples. Namurian boundary in Altmush Stream, as the basai Namurian zonal goniatite Cravenoceras leion is present near the base of the succeeding Altmush Shale COMPARlSON W1TH OTHER LATE VISÉAN Formation Qackson, 1965). SECTIONS IN EUROPE Conodont biofocies CONODONT BIOSTRATIGRAPHY The samples with the highest yields (samples 961- Higgins (1975, 1981) regarded late Viséan and early K) near the top of the section are in mainly thickly- Namurian conodont faunas of Europe to be a bedded, medium to coarse-grained, intraclastic-skeletal continuation of faunas characterised by the genera packstones and grainstones, or limestone breccia Gnathodus and Lochriea established in basinal (sample ALT9). The conodont faunas are dominated environments in mi d-Viséan time. This evolutionary by species of Gnathodus and Lochriea, referred to here sequence is recognised from lreland to the Donets Basin LATE VISEAN CONODONTS FROM IRELAND 459 and in the Pyrenean region ofFrance (Perret & Weyant, Brigantian boundary; i t is therefore of local biostra- 1994) and the Cantabrian Mountains of Spain tigraphical significance 0 o n es & Somerville, 1996). (Boogaard, 1992; Belka & Lehmann, 1998). The faunas However, M bipluti has also been reported from the are mostly from deeper-water basinal and pelagic bilineatus Zone in the Cantabrian Mountains (Park, platform facies, but comparable shallow-water faunas 1983). are known from Ireland, England (Yorkshire), Scocland, and Poland from the late Viséan and early Namurian (Pendleian-Arnsbergian, El and E2) (Higgins, 1981, CoNODONT BIOFACIES Skompski, 1996; Skompski et al, 1995). Three species of Lochriea occur in late Viséan rocks Shallow-water platjòrm faunas of northern Europe; Lochriea commutata, the unornamented, long-ranging species, and the Limestones of the Asbian Mullaghfin Formation ornamented species L. nodosa an d L. mononodosa which from Barley Hill Quarry and from a thicker sequence originate in the Brigantian (Pl) and all extend up to in Mokeeran Quarry to the north (Text-figs. l, 2), E2b (Arnsbergian) or Serpukhovian (Higgins, 1981; contain a mainly sparse conodont fauna dominated Skompski et al. , 1995). In addition two new species of by Synclydognathus geminus, Kladognathus tenuis/ Lochriea (L. senckenbergica, L. ziegleri) first appear at complectens (Synclydognathus -Kladognathus Biofacies) the Viséan/Namurian boundary or early Namurian widi cavusgnathids, rare Gnathodus girtyi and Lochriea (Nemirovskaya et al. , 1994, Skompski et al., 1995, commutata, but with local concentrations of Gnathodus Skompski, 1996). Lochriea nodosa is the eponymous homopunctatus. Moreover, severa! samples from rocks taxon defining the L. nodosa Zone which succeeds the of this age from the Kingscourt area were barren. Gnathodus bilineatus Zone; both zones are recognised Similar low-diversity faunas occur in the Yoredale all over the world (Perret & Weyant, 1994). Lochriea Group of northern England (Varker, 1968; Higgins & nodosa, in particular, is recognised worldwide in both Varker, 1982; Rexroad & Varker, 1992) and South shallow- (Rexroad & Horowitz, 1990; Armstrong & Wales (Rhodes et al., 1969; Austin & Davies, 1984), Purnell, 1987) and deep-water biofacies (Higgins & and are typical of Asbian shallow-water, partially- Wagner-Gentis, 1982). Furthermore, in many sections restricted platform environments. in Britain and Poland, as well as in Ireland Lochriea Many of the thickly-bedded, pale limestones of the mononodosa and L. nodosa appear simultaneously Mullaghfin Formation contain abundant foraminifers, (Davies, 1980; Metcalfe, 1981; Armstrong & Purnell, red and green algae (including Koninckopora), and 1987; Skompksi eta!., 1995). lt is significant that at display palaeokarsts and palaeosols. This is a very Kingscourt both L. mononodosa and L. nodosa appear shallow-water facies which was occasionally exposed together for the first time in the platform facies ofDeer subaerially. Such environments were presumably Park South section (sample l 07A) and in the basinal unfavourable for the conodont animai. This late Asbian facies in Altmush Stream (sample ALT?). In both interval showing a paucity or absence of conodonts is sections this co-occurrence coincides with a major recognised in bedded platform limestones and increase in conodont diversity and abundance. mudmounds in Ardagh Quarry (N 835 955) In lreland as in Poland (Skompksi et al. , 1995; (Somerville et al., 1996, 1997). Indeed, these massive Skompski, 1996) the L. nodosa Zone is characterised mudmounds at Ardagh Quarry have the poorest by an abundance of Gnathodus bilineatus, G. girtyi, conodont yields of any known depositional Lochriea mononodosa, L. nodosa, associated with environment in the Kingscourt area. Kladognathus tenuislcomplectens, K macrodentata, The conodont fauna from the platform limestones Synclydognathus geminus, Mestognathus bipluti, of the Brigantian Deer Park Formation is abundant Cavusgnathus unicornis, C. naviculus and rare Gnathodus and diverse and has more in common with the deeper homopunctatus. A similar diverse assemblage was water Gnathodus-Lochriea Biofacies of basinal recorded from Brigantian rocks of the north crop, environments. Gnathodids are the dominant and most South Wales (Rhodes et al. , 1969; Austin & Davies, abundant forms, particularly G. girtyi and G. bilineatus, 1984), North W ales (Aldridge et al., 1968; Reynolds, together with Lochriea commutata and locally abundant 1970), the Yoredale Group of northern England, L. mononodosa and L. nodosa. In addition Kladognathus especially from the Gayle Limestone (Davies, 1980; tenuislcomplectens and Idioprioniodus healdi form a Davi es et al., 1994), an d in the NW an d W of Ireland significant part of the fauna, as in the Yoredale (Austin, 1974; Austin & Husri, 1974; Austin et al. , limestones, with less common Syncf]dognathus geminus, 1970). M. bipluti is first reported from the nodosa cavusgnathids and mestognathids (Varker 1967, 1968, Zone in Britain, Belgium, Poland and the Pyrenees 1993). These platform limestones with a rich benthic (Varker & Sevastopulo, 1985; Groessens, 1974; Belka, fauna of crinoids, brachiopods, and calcareous algae 1983; Skompski eta!., 1989; Marks &Wensink, 1970; (including Nanopora) are characteristic of shallow- Perret & Weyant, 1994), but a t Kingscourt i t occurs water, high-energy platform environments similar to earlier, in the bilineatus Zone, near the Asbian/ those in the Yoredale Group of northern England and 460 H.E.A. SOMERVILLE, ID. SOMERVILLE SE Poland (Varker, 1968; Davies, 1980; Davies et al., (diagenetic?) contro l (see Davi es et al. (1994). Similar 1994; Varker in Skompski et al., 1995; Skompksi, shallow-water facies with comparable ecologica! 1986, 1996). constraints occur in limestone beds within uppermost The nodosa Zone of the upper Deer Park Formation Viséan cyclothemic sequences in northern England at Poulmore Scarp has exceptionally rich and diverse (Three Yard limestone to the Great = Main limestone) faunas; however, many samples are ramiform element (Johnson & Nudds, 1996; Skompski, 1996) and in deficient; and pectiniform elements may constitute boreholes from the Lublin Basin of SE Poland over 80% of the total number ofelements. This suggests (Skompski, 1996). In ali three areas the late Brigantian some form of winnowing during sediment transport, limestones are rich in foraminifers and calcareous activity of predators or selective preservation algae, including species of Calcifolium. EXPLANATION OF PLATE l Ali specimens illustrateci (SEM photographs) referto National Museum ofireland, Dublin collections (NMI). Specimens in figs. l, 3, 9-1 O, 19-22, 26 were collected from Alrmush Stream section (Loughshinny Fm.); specimens in figs. 2, 4-6, 7-8, 12-18, 23-25, 27-31 were obtained from Poulmore Scarp (Deer Park Fm.), Specimens in figs. 11, 32 carne from the Deer Park South section (Deer Park Fm.). Fig. l - Cavusgnathus naviculus (Hinde). a) inner latera! view, Pa element (x 40), specimen number F23001/l, Sample ALT6.; l b) upper view, Pa element (x 40) Fig. 2 - Cavusgnathus unicornis (Youngquist & Miller). Inner latera! view, Pa element (x 40), specimen number F23001111, Sample PHl Fig. 3 - Mestognathus bipluti Higgins. Inner latera! view, Pa element (x 40), specimen number F23002/l, Sample 96]. Figs. 4-6 - Hindeodus cristula (Youngquist & Miller). 4) latera! view, Pa element (x 65), specimen number F23003/l, Sample PH16; 5) latera! view, Pb element (x 65), specimen number F23003/2, Sample PH16; 6) latera! view, S element (x 65), specimen number F23003/3. Sample PH16. Figs. 7-8 - Synclydognathus geminus (Rexroad & Varker). 7) latera! view, Pa element (x 65), specimen number F23004/l, Sample PH9; 8) latera! view, S element (x 80), specimen number F23004/2, Sample PH9. Fig. 9 - Gnathodus bilineatus (Roundy). Upper view, Pa element (x 40), specimen number F23006/l, Sample ALT9. Fig. 10 - Gnathodus girtyi (Hass). Upper view, Pa element (x 40), specimen number F23006/2, Sample ALT9. Fig. 11 - Gnathodus homopunctatus Ziegler. Upper view, Pa element (x 65), specimen number F23007/l, Sample 107C. Fig. 12 - Vogelgnathus campbelli (Rexroad). Latera! view, Pa element (x 65), specimen number F23003/4, Sample PH 16 Figs. 13-18 - Idioprioniodus healdi (Roundy). 13) latera! view, (x 35), specimen number F23008/l, Sample PH3.; 14) latera! view, M element (x 35), specimen number F23008/2, Sample PH3; 15) latera! view, (x 40), specimen number F23008/3, Sample PH3; 16) posrerior view, Sa element (x 40), specimen number F23009/l, Sample PH19; 17) latera! view, (x 30), specimen number F23008/5, Sample PH3; 18) latera! view, Se element (x 30), specimen number F23008/6, Sample PH3. Fig. 19 - Lochriea commutata (Branson & Mehl). Upper view, Pa element (x 65), specimen number F23006/3, Sample ALT9. Fig. 20 - Lochriea mononodosa (Rhodes, Ausrin & Druce). Upper view, Pa element (x 65), specimen number F23006/4, Sample ALT9. Fig. 21 - Lochriea nodosa (Bischoff). Upper view, Pa element (x 65), specimen number F23006/5, Sample ALT9. Figs. 22-24 - Lochriea sp. 22) latera! view, M element (x 40), specimen number F23006/6, Sample ALT9; 23) latera! view, Pb element (x 40), specimen number F23009/2, Sample PH19; 24) latera! view, S element (x 40), specimen number F23009/3, Sample PH19. Fig. 25 - Kladognathus macrodentata? (Higgins). Latera! view, Pa/Pb? element (x 80), specimen number F23010/l, Sample PH8. Fig. 26 - Kladognathus macrodentata (Higgins). Latera! view, Pa/Pb? element (x 80), specimen number F23006/7, Sample ALT9. Figs. 27-31 - Kladognathus tenuis/complectens (Branson & Mehl), emend. Rexroad 27) latera! view, Se element (x 30), specimen number F23009/4, Sample PH19; 28) latera! view, M element (x 35), specimen number F23009/5, Sample PH19; 29) latera! view, M element (x40), specimen number F23010/2, Sample PH8; 30) latera! view, Pa/Pb element (x 65), specimen number F23009/6, Sample PH19; 31) posrerior view, Sa element (x 110), specimen number F23010/3, Sample PH8. Fig. 32 - Hindeodontoides spiculus (Youngquist & Miller). Latera! view, Pa e1ement (x 110), specimen number F23005/l, Sample 131D. HE.A. SOMERVILLE, !.D. SOMERVILLE, LATE VISÉAN CONODONTS FROM IRELAND Pl. l 462 H.E.A. SOMERVILLE, l.D. SOMERVILLE Deeper-water, basinal founas dominated by the Synclydognathus-Kladognathus Biofacies, the elements of which are often abraded The conodont faunas of the Altmush Stream section and fragmented. The best preserved faunas are are dominated by abundant Gnathodus bilineatus, G, mostly from wackestones in the Gnathodus-Lochriea girtyi, Lochriea commutata, L. nodosa, L. mononodosa Biofacies within the nodosa Zone at Poulmore. These and rare specimens of Cavusgnathus an d Mestognathus faunas also have the best representation of ali ( Gnathodus-Lochriea Biofacies). Faunal diversity is as apparatus components. high as that of the coeval shelf faunas and the faunas 5. Exceptionally rich and diverse conodont faunas have much in common. Notably, Synclydognathus is from the top of the Deer Park Formation may be rare in the basin facies as in the platform facies of the explained in part by local sedimentological factors, Deer Park F m. G. homopunctatus is extremely rare in resulting in the concentration of elements, particu- the upper part of the nodosa Zone in Altmush Stream, larly Pa elements, in high-energy shallow-water but is absent in Poulmore. Factors controlling the shoal deposits. Similar deposits are known from the distribution of conodonts in both basin and platform Pennsylvanian in the USA. depositional settings were probably numerous and 6. The late Viséan conodont faunas from Kingscourt interrelated. However, the most important were likely are comparable in diversity, abundance and by the water depth, food availability, and the energy of the presence of biostratigraphically important taxa, to environment. Similar conclusions were reached by those in northern England, North Wales and Poland Davies (1980), Austin & Davies (1984) and Davies where limestones occur in cyclothemic sequences. et al. (1994). The upper beds at Poulmore, in particular, may be correlated with uppermost Viséan limestones in northern England (Three Yard Limestone to Main CONCLUSIONS Limestone) and Lublin Basin, Poland (Unit A3, Huczwa Fm.). l. The Gnathodus bilineatus and Lochriea nodosa zones are recognised in the Kingscourt area in platform and basinal facies. The base of the nodosa Zone is defìned by the synchronous fìrst occurrence of L. ACKNOWLEDGEMENTS nodosa and L. mononodosa in the same bed, in both We would like to thank the two anonymous referees who the Deer Park and Loughshinny formations Severa! offered many useful suggestions and helped us to make substantial species (e.g. Mestognathus bipluti, Idioprioniodus improvements to the manuscript. healdi an d Kladognathus macrodentata) are virtually restricted to the upper part of the bilineatus and the nodosa zones of the Brigantian and may be of REFERENCES local biostratigraphical use. 2. The richest conodont faunas were obtained within ADAMs, A. E., HORBURY, A.D. & RAMsAY, A.T.S., 1992, Signifìcance the L. nodosa Zone from late Brigantian platform of palaeoberesellids (Chlorophyta) in Dinantian sedimen- and basinallimestones. Moderately rich an d diverse tation, U.K.: Lethaia, 25: 375-382. 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MEISCHNER, D., NEMIROVSKAYA, T., proposed Mid-Carboniferous boundary stratotype localiry at PERRET, M-F. & VARKER, W.J., 1995, Conodont distriburion Stonehead Beck, Cowling, No nh Yorkshire, England: Annales across rhe Viséan/Namurian boundary: Courier Forschungs- de la Société Géologique de Belgique, 116 (2) (1993): 301- institur Senckenberg, 188: 177-209, 4 pls. 321. SOMERVILLE, I.D., & STRANK, A.R.E., 1984, The recognition of VARKER, W.J. & SEVASTOPULO, G. D., 1985, The Carboniferous rhe Asbian/Brigantian boundary fauna and marker horizons System: Pare l - Conodonts of rhe Dinantian Subsysrem from in rhe Dinanrian ofNorth Wales: Geologica! Journal, 19: 227- Great Brirain and Ireland. In Higgins, A.C. & Ausrin, R.L. 237. (eds), A Srrarigraphical index of conodonts: 167-209. 6 pls.; SOMERVILLE, I. D., STROGEN, P., }ONES, G.LJ. & SOMERVILLE, H.EA., Ellis Horwood, Chichesrer 1996, Late Viséan buildups at Kingscourt, Ireland. In Srrogen, VON BITTER, P. H., 1976, Paleoecology and distriburion ofWindsor P., Somerville, I. D. & Jones, G.Ll. (eds.), Recent advances in Group (Visean-?Early Namurian) conodonts, Porr Hood Lower Carboniferous Geology: Geologica! Sociery ofLondon, Island, Nova Scoria, Canada: Geologica! Association of Special Publication, 107: 127-144. Canada, Special Paper 15: 225-241. SoMERVILLE, I.D., STROGEN, P., & SoMERVILLE, H.EA., 1997, VON BITTER, P. H., SANDBERG, C.A & ORCHARD, M.J., 1986, Upper Viséan plarform carbonares and buildups in rhe Phylogeny, speciarion and palaeoecology of rhe Early Kingscourr Ourlier, Ireland: Proceedings of rhe XIII Carboniferous (Mississippian) conodonr genus Mestognathus: Inrernational Congress on rhe Carboniferous and Permian, Royal Onrario Museum, Life Sciences Conrriburions, 143: 28th August-2nd September 1995 Krakow, Poland. Pare 2: 1-115, 29 pls. 143-152. STONE, J.J. & GERAGHTY, DA., 1994, A predicrive template for rhe appararus archirecrure of rhe Carboniferous conodont Idioprioniodus: Lerhaia, 27: 139-142. (manuscript received December 9, 1998 STROGEN, P., SoMERVJLLE, I.D., PrcKARD, N. &JoNES, G.Ll., 1995, acceptedjune 11, 1999) Lower Carboniferous (Dinantian) stratigraphy and strucrure in rhe Kingscourt Outlier, Ireland: Geologica! Journal, 30: 1- 23. STROGEN, P., SOMERVILLE, I.D., PICKARD, N. & ]ONES, G.Ll. & H.E. Anne SOMERVILLE FLEMING, M., 1996, Controls on ramp, plarform and basinal sedimentarion in rhe Dinantian of rhe Dublin Basin and Ian D. SoMERVILLE Shannon Trough, Ireland. In Strogen, P., Somerville, I.D. & Jones, G. LI. (eds.), Recent advances in Lower Carboniferous Deparrmenr of Geology, Universiry College Dublin Geology: Geologica! Sociery ofLondon, Special Publication, Belfìeld, Dublin 4, Ireland 107: 263-279. e-mail address: [email protected]