EARLY DEVONIAN MICROVERTEBRATES FROM PWLL-Y-WRACH,

TALGARTH, SOUTH WALES

SUSAN TURNER, J o M.J. VERGOOSSEN & RODERICK B. WILLIAMS

TURNER S., VERGOOSSEN J.M.J. & WILLIAMS R.B. 1995. Early Devonian microvertebrates from Pwll-Y- Wrach, Talgarth, South Wales. [Microvert6br6s du D6vonien inf6rieur de Pwll-y-Wrach, Talgarth, Pays-de-Galles du sud]. GEOBIOS, M.S. n ° 19 : 377-382.

ABSTRACT

Agnathan and gnathostome fish microfossils from an Early Devonian site in the St Maughan's Group of South Wales include heterostracans, cephalaspids, dominant thelodont scales including Turinia pagei, nostolepid and gomphonchid acanthodian remains, Nostolepis arctica for example, at least one chondrichthyan with scales called "Nostolepis" robusta, and placoderm plates.

KEY-WORDS : DEVONIAN, UNITED KINGDOM, HETEROSTRACI, CEPHALASPIDAE, THELODONTI, ACANTHODII, CHONDRICHTHYES.

RESUMI~

Des microrestes, Agnathes et Gnathostomes, du Groupe de St Maughan's, D6vonien inf6rieur du Pays-de-Galles du sud, comprennent des H6t6rostrac6s, des C6phalaspides, des 6cailles de Th61odontes, qui est le groupe domi- nant (dont Turinia pagei), des 6cailles d'Acanthodiens nostol6pides et gomphonchides, au moins un Chondrich- thyen dont les 6cailles 6voque "Nostolepis" robusta, et des plaques de Placodermes.

MOTS-CLI~S : DI~VONIEN, ROYAUME-UNI, HETEROSTRACI, THELODONTI, ACANTHODII, CHONDRICHTHYES.

INTRODUCTION Macrovertebrates are recorded from the St Mau- ghan's Group (equivalent Psamrnosteus Lime- stone Group -PL) of South Wales (e.g., Squirrel & Downing 1969) but scales and other microfos- sils receive only passing mention. New co-opera- tive work is underway on a measured section yielding Late Silurian to Early Devonian fish from near Talgarth, Breconshire (Figs 1, 2). Here we present a preliminary report on the early Lochkovian microvertebrate remains. Specimens are from the R.B. Williams collection ; figured specimens to reside at the National Museum of Wales (NMW), Cardiff.

GEOLOGY The new fossil section is located within and ad- jacent to the Pwll-Y-Wrach Nature Reserve ow- ned by Brecknock Wildlife Trust. Permission to visit should be obtained from the t rust office at

Brecon. The name Pwll-Y-Wrach means "The Pool of the Witch". This area is designated a Na- ture Conservancy Council Site of Special Scienti- fic Interest and this work adds to its geological significance (Hawley 1991). The River Enig tra- verses the deeply-incised valley of Pwll-Y-Wrach cutting through typical Upper Silurian to Lower Devonian Old Red Sandstone facies. Red beds do- minate the sequence, harder bands forming wa- terfalls (Anonymous 1992). The new fish remains are derived from several horizons, one of which (designated Site 4 by RBW) is reported here ; this site is not in the Reserve itself but on adja- cent privately-owned land. Two other fish-bea- ring beds comprise : Site 5, geographically higher but may be older, containing ,a traquairaspid and KaUostrakon cf. K. podura ; and a bed bearing pteraspids and cephalaspids about 130m above Site 4. These will be dealt with elsewhere.

One waterfall to the west of the Reserve is for- med where the Enig flows over a band locally

378

W A L E S v

T o T h e e o c k

. . . . . . / ' '~ t(/]/±Talg arth

~-~'~j//]? ~/~I MidwaIes Hospita,

i~Trefecca ~----~"er~ig~ ~'~ /a: II _~o~ ))\\\

I~rTO Uangorge ~1~/// ~ To Abergavenny

Figure 1 - Location of Site 4 adjacent to the Pwll-Wrach Nature Reserve near Talgarth, Breconshire, South Wales. Lo- calisation du site 4 contigu ~t la r6serve naturelle de Pwll- Wrach pros de Talgarth, Bre- conshire, Pays-de Galles du sud.

e l

~ ' . ~ . . . ~ ~ Footpat 4 • ~g 1 #'~e~ ~n ~'-- " "

,] e

equivalent to the Main Psammosteus Limestone of the Brown Clee Hill (Fig. 1). About 1-1.5 me- tres ups t ream is a cornstone pavement on the north bank sandwiched between two mudstones which consti tutes Talgarth Site 4 (Fig. 2). The lo- wer band contains reworked calcrete nodules. The bed is a muddy-red conglomeration of gravel and calcrete about 0.3 metres in thickness. The extent of the cornstone sheet or lens is not known; it disappears into the north bank of the s t ream and there is no apparent sign of it in the opposite bank. Current bedding is not seen in the bed but microfossils do appear to be concentrated in linear bands of short extent. Macrovertebrate material is f ragmentary and waterworn and all but the thelodont scales fragile. Probably the bed was deposited vir tually in one sheet at the time of flash-flood and chemical transformation perhaps linked to pedogenic processes might have affected the material producing a mottled muds- tone. Generally speaking, the rock sequence abo-

ve the Psammosteus Limestone is more indicative of a fluviatile origin ; below the red mudstone, or marl, shows signs of the upward-burrowing trace fossils known as Skolithos, which would indicate marginal marine conditions. Some burrows can be traced for a metre or more, showing rapid re- deposition of mud and silt possibly on a flat coas- tal plain.

MATERIAL

Site 4 rock samples were broken down by one of us (RBW) with 20% acetic acid and small plates and spines extracted. Thelodont scales were sent to ST and unprepared rock samples for the s tudy of acanthodian scales were sent to JMJV. Some specimens need fine cleaning of adhering red hae- matitic quartz grains with brush and needle.

The microvertebrate fauna comprises an indeter- minate cephalaspid ; heterostracans include frag-

1.0

SITE 4

1.5

2.0

2.5

3.0

3.5 y nodules

4.0

4.5'

5 .0

5.5

of Waterfall

act l imestone

scing nodules

nodules

KEY

0.5

Limestone

t - O CO ¢D E

o ~

¢n

tD

O E E ¢/1

e" | m

O o

~ . .

I I : .

• . .

,,~ Mar l

, ~ C r o s s l a m i n a t i o n

~ - ~ Flaggy lamination

Calcareous nodules

Shales

Sandstones

Figure 2 - Sketch log of upper Pridoli-lower Lochkovian sec- tion a t Pwll-Y-Wrach near Talgarth, Breconshire, South Wa- les. Vertical section above and below Pwll-Y-Wrach Waterfall to show rela t ionship of site 4. Notes from the base upwards : BED A, marl-calcareous mudstone in terpreted as flat coastal plain under t idal influence ; BE D B, sandstone with mica fla- kes ; BED D, finely laminated black sandstone with signs of cros s laminat ions ; BED E, green fine-grainded flaggy sands- tone the top of which is invaded by rubbly nodules becoming progressively larger and finally coalescing into the massive l imestone which forms the waterfall. The beds above this l imestone (some of which is obscured by modern day sedi- ments) appears to be mud/si l ts tone mar l wi th calcareous no- dules ripped up from the l imestone beneath. Above this is the Site 4 (fish Band) cornstone covered by a fur ther muds- toneJsiltstone horizon which does not contain nodules. Meas- urements in metres. Colonne stratigraphique schgmatique de la coupe d'etge Pridoli supdrieur - Lochkovien infdrieur & Pwll- Y-Wrach, pros de Talgarth, Breconshire, Pays de Galles du sud. La coupe au-dessus et en-desous de la chute d'eau montre les relations avec le site 4.

379

ments of pteraspid plates, Lepidaspis sp. tesserae (Fig. 3.1), fragments of Tesseraspis tessellata, Corvaspis cf. C. kingi, a t raquairaspid and/or ?Weigeltaspis. There are numerous scales of Turi- nia pagei (Figs 3.2-8, 9), and possible Turinia po- lira. Acanthodians include fragments of climatiid and other spines, scales, tesserae and one umbel- late scales : Nostolepis arctica VIETH, 1980 ; "Nostolepis" robusta (BROTZEN, 1934), considered to be a chondrichthyan (Vergoossen in press) ; Nostolepis striata ; forma N. gracilis ; Gomphon- chus sandelensis ; Poracanthodes sp. cf. puncta- tus; undetermined teeth, and unidentified scales (Fig. 3.10). Other remains include chondrich- thyan scales and placoderm scales.

S I G N I F I C A N C E

Very little microvertebrate work has been carried out in the classic Old Red Sandstone outcrops of South Wales. Welch & Trotter (1961) and Squir- rel & Downing (1969) did mention microremains such as thelodont and acanthodian scales but do not elaborate. Turner (1973) recorded material from only one spot sample from the Lower Devo- nian. This material from above the Psammosteus Limestone Formation at Cwm Mill, Abergavenny, which contained a mixed fauna with elements of the late Pridoli thelodont fauna associated with the Turinia pagei assemblage and Nostolepis arc- tica. New work from measured sections is needed and the assemblages at Talgarth are providing a more detailed assessment of the microfauna across the S/D boundary.

Lepidaspis has not been recorded previously from Britain. Lepidaspis serrata DINELEY 8~ LOEFFLER, 1976 was first described from transitional facies presumed Lower Devonian between the Delorme and Road River formations of Arctic Canada. Blieck (1982, pl. 11 ; Blieck et al. 1987, fig. 4.3) recorded Lepidaspis sp. indet, in Ben Nevis For- mation vogti horizon of Spitsbergen, about mid Ditton (Lochkovian) and uncertainly in the Fraenkelryggen Formation, primaeva, polaris and

Description des bancs : BED .4, marnes /argile calcaire, inter- prdtde comme un ddp6t de plaine c6ti~re d'gpandage sous in- fluence tidale ; B E D B, gr~s & paillettes de mica ; BED D, gr~s noir f inement litg avec des indications de stratification entrecroisge ; BED E, gr~s f in vert dont le sommet est envahi de nodules "rubbly" devenant de p lus en plus gros puis coales- cents dans le calcaire mass i f qui forme la chute d'eau. Les bancs au-dessus de ce calcaire, dont une partie est cachge par des sgdiments modernes, appairaissent comme dtant des mar- nes argileuses /silteuses & nodules calcaires, issues du calcaire sous-jacent. Au-dessus de ces bancs, le site 4 (niveau & pois- sons) est un "cornstone" recouvert par un autre horizon argi- leux/ silteux sans nodules. Echelle en m~tres.

380

Anglasp i s hor izons ( lower Dit ton) of the Red Bay Group (Blieck 1983, pl. III.7). This and such o ther h e t e r o s t r a c a n t axa as, e.g., Tesseraspis tes- sellata, Kal los trakon, Corvaspis, are all common in the basal Devon ian Old Red Sands tone facies in the Welsh Border land , and its equiva lents in n o r t h e r n France-Be lg ium, Spi tsbergen, Podolia and the eas t Baltic. The type Lepidaspis occurs in mar ine l imes tones (Dineley & Loeffler 1976 ; El l iot t & Loeff ier 1989). The acan thod ian an d chon d r i c h thya n scales, especial ly N. arctica and "hr'. robusta, are typical of the basal Devonian in the Welsh B orde r l and and e l sewhere in the n o r t h e r n h e m i s p h e r e (Vergoossen in press). Pora- canthodes porosus s.1. and Gomphonchus cf. hop- pei, which so fa r are only known f rom the ear l ies t Lochkovian ( lower P L Group) or older sed iments in the Welsh Border land , have not been seen in Si te 4. However , t h e y are wel l - represen ted f rom the n e a r b y T a l g a r t h Si te 5, s i tua ted about 2 me- t res above P L (Vergoossen in press). One scale can be r e f e r r ed wi th c e r t a i n t y to N. striata typi- cal of la te Pr idol i and t he ent i re Lochkovian in the Welsh B or de r l and (Vergoossen in press). G. sandelensis ha s the same d is t r ibu t ion bu t doubt ar ises about the i den t i t y of the scales re fe r red to th is t axon because of the large size of most speci- mens ; such scales a re u n k n o w n in the type spe- cies and h a v e not been observed (by JMJV) among t housa nds of scales ex t rac ted f rom La te S i lu r ian e r ra t ics in the n o r t h e r n Ne the r l ands .

The f i sh-bear ing hor izon a t Si te 4 falls wi th in the Phialaspis symonds i zone and contains e lements of the c o m m u n i t y def ined by Dineley & Loeffier (in press). The occurrence of Tur in ia pagei, Lepi- daspis, ce r t a in a can thod i an taxa , and a possible p teraspid , places t hese beds wi th in the lowest Lochkovian.

Acknowledgemen t s - We are indebted to Mr Duncan Hawley for geological discussions and to Dr Alain Blieck for his help with identification of heterostracan remains. Many thanks to Mrs Dora Aitken for SEM work under the auspices of ARC grant n ° A39132723.

This is a contribution to IGCP 328. Palaeozoic Micro- vertebrates.

R E F E R E N C E S

ANONYMOUS 1992 - Geology trail highly recommended. Geology Today, May-June 1992 : 79.

BLIECK A. 1982 - Les H~t~rostrac~s (Vertebras Agna- thes) de l'horizon Vogti (Groupe de Red Bay, D~vo- nien inf~rieur du Spitsberg). Cahiers de Paldontolo- gie, CNRS, Paris : 51 p.

BLIECK A. 1983 - Biostratigraphie du D~vonien inf~- rieur du Spitsberg : donn~es compl~mentaires sur les H~t~rostrac~s (Vertebras, Agnathes) du Groupe de Red Bay. Bulletin du Musdum national d'His- toire naturelle, Paris, 4, 5, C (1) : 75-111.

BLIECK A., GOUJET D. • JANVmR P. 1987 - The verte- brate stratigraphy of the Lower Devonian (Red Bay Group and Wood Bay Formation) of Spitsbergen. Modern Geology, 11 : 197-217.

DINELEY D.L. & LOEFFLER E.J. 1976 - Ostracoderm faunas of the Delorme and associated Siluro-Devo- nian Formations, North West Territories, Canada. Special Papers Palaeontology, 18 : 214 p.

DINELEY D.L. & LOEFFLER E.J. in press - Upper Silu- rian and Lower Devonian vertebrate communities from the Welsh Borderland. In BOUCOT A.J. & LAW- SON J. (eds) : International Geological Correlation Programme, Project Ecostratigraphy, Final Report. Cambridge University Press, Cambridge.

ELLIOTT D.I~ & LOEFFLER E.J. 1989 - A new agnathan from the Lower Devonian of Arctic Canada, and a review of the tessellated heterostracans. Palaeonto- logy, 32 : 883-891.

HAWLEY D. 1991 - Pwll-Y-Wrach - Geology Trail (pam- phlet) : Brecknock Wildlife Trust.

P L A T E 1

Lower Lochkovian microvertebrates from site 4, Pwll-Y-Wrach near Talgarth, Breconshire, South Wales (National Museum of Wales, Cardiff, numbers for specimens) : 1, NMW 95.17G. 1, Tessera of Lep idasp i s sp., antero-dorsal view ; 2-8, 9? T u r in ia page i - 2, NMW 95.17G.2, cephalo-pectoral scale in dorsal view ; 3, NMW 95.17G.3, post-pectoral scale with a deep base in antero-lateral view ; 4, NMW 95.17G.4, cephalo-pectoral scale in lateral view ; 5, NMW 95.17G.5, oral scale in lateral view ; 6, NMW 95.17G.6 post-pectoral scale in dorsal view ; 7, NMW 95.17G.7, post-pectoral scale in basal view ; 8, NMW 95.17G.8, post-pectoral scale in dorso-lateral view ; 9?, NMW 95.17G.9, pinnal scale in lateral view ; 10, NMW 95.17G.10, acanthodian scale cf. of northern Netherlands, crown view. All R.B. Williams coll. ST SEM Negatives File 1993/26 at Queensland Museum. Microvertdbrds du Lochkovien infdrieur du site 4, Pwll-yoWrach pros de Talgarth, Breconshire, Pays de Galles du sud (spdcimens du Musde National du Pays-de-Galles, Cardiff) : 1, tessere de Lepidasp is sp. N M W 95.17G.1, vue antdro-dorsale ; 2-8, 9? T u r in ia page i - 2, dcaille cdphalo-pectorale N M W 95.17G.2 ; 3, gcaille post-pectorale NMW 95.17G.3, vue dorsale ; 4, dcaille cdphalo-pectoraIe N M W 95.17G.4, vue latdrale ; 5, gcaille orale N M W 95.17G.5, vue latgrale ; 6, dcaiUe post-pectorale N M W 95.17G.6, vue dorsale ; 7, dcaille post-pectorale N M W 95.17G.7, vue basale ; 8, gcaille post-pectorale N M W 95.17G.8, vue dorso-latdrale ; 9? dcaille pinnale N M W 95.17G.9, vue latdrale ; 10, dcaille d'Acanthodien cf. N. s t r ia ta des Pays-Bas du nord NMW 95.17G.10, rue dorsale. Collection R.B. Williams. Ndgatifs MEB de ST, fichier 1993/26, Queensland Museum. Spdcimens devant ~tre ddposds au National Museum of Wales, Cardiff.

G e o b i o s P1. 1 M.S. n ° 19 S. T u r n e r , J .M. J . V e r g o o s s e n & R.B. W i l l i a m s

i88u 5

~ e 0 u

382

SQUIRREL H.C. & DOWNING R.A. 1969 - Geology of the South Wales Coalfield Pt 1. The Country around Newport (Mon.) (Explanation of One-inch Geologi- cal Sheet 249, New Series). HMSO, I~ndon : 333 p.

TURNER S. 1973 - Siluro-Devonian thelodonts from the Welsh Borderland. Journal of the geological Society, 1 2 9 : 557-584.

VERGOOSSEN J.M.J. lin press}- On Siluro-Devonian mi- crofossils of Acanthodii and Chondrichthyes (Pisces) from the Welsh Borderland. Modern Geology.

VIETH J. 1980 - Thelodontier-, Acanthodier- und Elas- mobranchier-Schuppen aus ~' dem Unter-Devon der kanadischen Arktis (Agnatha, Pisces). G6ttinger Ar- beiten in Geologie und Pal~iontologie, 2 3 : 1-69.

WELCH F.B.A. & TROTTER F.M. 1961 - Geology of the Country around Monmouth and Chepstow. (Expla- nation of One-inch Geological Sheets 233 and 250, New Series). H.M.S.O., London : 164 p.

S. TURNER Queensland Museum

P.O. Box 3300 S. Brisbane, Qd 4101, Australia

J.M.J. VERGOOSSEN Paleontologische Werkkamer

Biologisch Centrum Rijks Universiteit Groningen

P.O. Box 14 9750 AA Haren, The Netherlands

R.B. WILLIAMS 54 Woodlands Avenue

Talgarth, Brecon Powys LD3 OAT, U.K.