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A new early Westphalian D flora from Aberdulais Falls, South Wales
A new early Westphalian D flora from Aberdulais Falls, South Wales Barry A. Thomas l & Christopher J. Cleaf THOMAS, B. A. & CLEAL, C. J. 2001. A new early Westphalian D flora from Aberdulais Falls, South Wales. Proceedings of the Geologists ' Association, 112, 373-3 77. A newly discovered fossil flora from the Brithdir Member in South Wales is shown to be Westph alian D in age, despite the absence of what is widely regarded the index species of that stage Neuropteris ovata. Th e flora is dominated by sphenophytes and ferns, and probably repr esents the vegetation growing around the margins of a floodplain lake. llnstitute of Rural S tudies. University of Wales Aberystwy th, Llanbadarn Campus, Aberyst wyth S Y23 2A L, UK. 2 Department of Biodiversity and Systematic Biology , Natio nal Museums and Galleries of Wales, Cathays Park, Cardiff CF/O 3NP, UK.
1. INTRODUCTION Aberdulais Falls is on the River Dulais near its junction with the River Neath, about 3 km NE of the town of Neath, Port Talbot in South Wales [OS SS 772995] (Fig. 1). Since 1981 it has been part of a Nat ional Trust site, where the landscape and industrial heritage of the area is conserved. The Falls is a Devensian feature resulting from erosion by glacial meltwater (Johns,
1987). The bedrock is part of the South Wales Pennant Form ation , belonging to the Brithdir Member (senslI Cleal & Thomas 1996) and is early Westphalian D in age (Cleal 1978). There is a thin coal at the base of the Falls, which John s (1987) describes as being the Brithdir Rider Seam, but which the 10 560 geological map (British Geological Survey) shows to be some 27 m above that level, but still well within the middle Brithdir Member (Fig. 1).
500111
Aberdulais Cool
Torma
( 'nnamcd Scam
~1. C \ d OfAbcn1UIJi~ Fells FI0f"3
Brithdir Rider Scam
(jraig . 'am
eath I
nrilhdir Scam
Fig. 1. Location map for Aberdul ais Falls, near Neath, South Wales (left). Also, a generalized litho stratigraphical section through the Brithdir Member in this part of South Wales, showing the level from which the macroflora was collected (right). Proceedings of the Geologists' Association, 112, 373- 377.
0016-7878/01 SI5.00
© 2001 Geologists' Association
374
B . A . THOMAS C . J . C LEAL
Fig. 2. Plant fossils from the Westphalian D of Aberdulais Falls, near Neath (all x 2): (a) shoot of Sphenophyllum emarginatum Brongniart ; (b) compressed stem of Calamites cf. suckowii Brongnia rt; (c) part of bipinnate segment of ?Ze illeria a voldensis (Stur) Kidston.
In 1991 , excavations were made to fit a hydroelectric turbine at the base of the Falls. The excavations were made by large boring machines, producing cores of 140 mm and 180 mm diameter. Immediatel y below the coal, the borings passed through argillaceous deposits, which yielded a diverse assemblage of well preserved plant macrofossils. The cores with the fossiliferous shales were acquired
by the Nat ional Museums & Galleries of Wales, Cardiff, and form the basis of the present short commun ication. 2. PALAEOBOTANY
The fossils are preserved as coalified compressions in the grey shales and siltstones. The site lies near the
A N EW E A RLY W ESTPHALIAN F L O R A , WALES
centre of the South Wales Coalfield, where the coals have a low volatiles content (Jones, 1951) so there is no possibility of the fossils yielding cuticles. The following species have been identified. Lycoph ytes: Lepidocarpon sp. S tigma ria fico ides Brongniart
Sphenophytes: An nularia stellata (Sternberg) Wood (Fig. 3b) A. sphenophylloides (Zenker) Gutbier (Fig. 3b) Calam ites cf. sucko wii Brongn iart (Fig. 2b) Sphenophyllum emarginatum Brongniart (Fig. 2a)
Ferns : Pecopt eris cf. dufa yi Dalinval (Fig. 3c-d) P. unita Brongniart Renaultia chaerophylloides (Brongniart) Zeiller
(Fig . 3f) R. cf. crepinii (Stur) Kidston (Fig. 3e) ?Zeilleria avoldensis (Stur) Kid ston (Fig. 2c)
Pteridospenns: Macroneuropteris scheuchz eri (Hoffmann) Cleal et al. Trig onocarpus sp. (Fig. 3a)
Corda ites: Cordaites sp.
The flora is dominated by Sph enophyllum emarginatum (Fig. 2a), although it also has a high proportion of Annularia (Fig. 3b), Calamites (Fig. 2b) and frond fragments of various ferns. Seed plants are rare; there are only a few isolated pinnules of Ma croneuropteris scheuchzeri and a single Trigonocarpus seed (Fig. 3a). Club-mosses are all but absent except for Stigmar ia rooting stru ctures and a single sporangium of Lepidocarpon. The fossils occur in an interval of mudstone in an otherwi se alluvial sandstone-dominated sequence typical of the South Wales Pennant Formation (e.g. Kelling, 1974). Elsewhere in Britain, such mudstones have been interpreted as overbank deposits or distal crevasse-delta deposits in floodpl ain lakes (Fielding, 1984). Although the alluvial setting of the Pennant Formation is rather different from that studied by Fielding, we suggest that the mudstone deposits were nevertheless formed in a similar lacustrine environment. Calamites were adapted to growth around the shores of such lakes, being capable of regenerative growth when subjected to periodic burial (Gastaldo, 1992). We therefore speculate that the bulk of the Aberdul ais flora (i.e. the sphenophyte and probably fern components) represents the vegetation growing around the margins of a floodplain lake. The fragments of seed plants were probably from the levee vegetatio n, having drifted along the rivers that fed the lake via the crevasse. The greatest diversity in the flora is in the ferns. The most abundant is an unusual pecopteroid with slender pinnules, having, in some cases, a decurrent base, but in others a slightly constricted base (Fig. 3c). There is a strong midvein but much thinner later al veins that fork , usuall y once, and meet the pinnule margin at
375
c.70·. One specimen also appea rs to be fertile with a row of Asterotheca-like synangia on either side of the midvein (Fig. 3d). There is some similarity to the elongate pinnules seen in Pecopt eris plumosa (Artis) Brongniart, but that species has a venation that is not as oblique to the pinnule margin and later al veins not so widely forked. P. plumosa also has S enft enbergia sporangia that are quite unlike the As terotheca-like reproductive structures in the Aberdulai s specimen. A closer comparison can be made with some specimens figured by Dalinval (1960, pI. 45, figs 1- 2) as Pecopteris (A sterotheca) dufayi Danze that have pinnules with a similar shape and venation. According to Danze , this species is very variable but, because it has pinnules that are far larger than anything seen at Aberdulais, we have only tentatively assigned our material to Danze's species. The numerous fragments of sphenopteroid fern are mostly sterile, but one shows a few sporangia similar to those of Renaultia. In most specimens, the pinnules are up to 5 mm long, with an approximately ovoid outline (Fig. 3f), and compare well with specimens illustrated by Brousmiche (1983) as Renaultia chaerophy lloides (Brongniart) Zeiller. A single specimen shows significant ly smaller pinnules (Fig . 3e), which we have tentatively compared with Renaultia crepinii (Stur) Kidston . There are a few fragments of pecopteroid frond , with obliquely attached pinnules having constricted aero scopic sides (Fig. 2c). Although most pinnules have a smooth margin , occasionally the distal margin shows small teeth and the lateral margins sometimes have a shallow sinus. There is some similarity to Z eilleria a voldensis as figured by Brousmiche & Laveine (1982), although the pinnules in that species are not normally so obliquely attached . Z. a voldensis was regarded by Kidston (1924) as uncommon in Britain, although Brousmiche & Laveine (1982) record it as abundant in the Bolsovian and lower Westphalian D of Saar-Lorraine, albeit often misidentified as other species. As none of our specimens are fertile and the pinnule form is not completely typical, we have only tentatively assigned it to that species. 3. COMPARISONS
There are no known floras from this part of the sequence in the western part of the South Wales Coalfield. On the east crop, there are some lowdiversity floras associated with the Brithdir Seam (sometimes known locally as the Tillery Seam - see Sullivan & Moore, 1956). Cleal (l97 8) reported some restricted assemblages from this level, based on specimens in the Kidston Collection. However, by far the most diverse assemblage was reported from a tip at the West Blaina Red Ash Colliery, in the Ebbw Fawr valley (Sullivan & Moore , 1956). Although the flora was not figured, the published species list clearly reflects a diverse flora dominated by pteridosperms and some lycophytes, with much rarer ferns (oth er than Lobat opt eris) and sphenophytes. The assemblage is
376
B. A. THOMAS C. J. CLEAL
Fig. 3. Plant fossils from the Westphalian D of Aberdulais Falls, near Neath ( x Za-f): (a) pteridosperm ovule Trigonocarpus sp.; (b) two species of sphenophyte foliage, the larger whorls Annularia stellata (Sternberg) Wood, the smaller whorls Annularia sphenophylloides (Zenker) Gutbier; (c) sterile portion of fern frond, Pecopteris cf. dufayi Dalinval; (d) fertile portion of P. cf. dufayi Dalinval frond showing what appear to be Asterotheca-like synangia; (e) pinnae of the small-pinnuled fern Renaultia cf. crepinii (Stur) Kidston; (f) pinna of Renaultia chaerophylloides (Brongniart) Zeiner, which has significantly larger pinnules than the previous species.
A NEW EARLY WESTPHALIAN FLORA, WALES
thus quite different in composition and diversity to that found at Aberdulais. 4. Discussion
For many years, there was a problem locating the base of the Westphalian D Stage in South Wales. This was because of the poor palaeobotanical record between the No. 1 Rhondda Seam and its rider (middle Rhondda Member - Westphalian C), and the Hughes Seam (base of Hughes Member - middle Westphalian D). The problem was not resolved until the rediscovery in the David Davies Collection (National Museums and Galleries of Wales, Cardiff) of small but unequivocal lower Westphalian D floras associated with the Captain and Cuckoo Seams (Cleal, 1978), allowing the base of the stage to be placed in the upper Rhondda Member. As the Aberdulais flora is from the Brithdir Member, which overlies the Rhondda Member (Cleal & Thomas, 1996), it must be stratigraphically higher than the Cuckoo Seam and thus early Westphalian D in age. Significantly, however, there is no evidence of the pteridosperm frond Neuropteris ovata Hoffmann, whose lowest occurrence is an important index to the base'of the Westphalian D (Cleal, 1984). The range of N. ovata has long been linked with the definition of the Westphalian D, and some authors have gone as far as to regard them as effectively synonymous (e.g. Bode, 1970). Notwithstanding that biostratigraphy and chronostratigraphy should be kept strictly separate, basing a stage boundary on the range of a single species is bound to cause difficulties. For this reason Laveine (1977) proposed a series of other biostratigraphical criteria for recognizing this stage boundary, and this was the model used by Cleal (1978) to locate the boundary in South Wales. A similar situation has been found in the Sydney Coalfield of Nova Scotia, where Zodrow & Cleal (1985) showed that N. ovata is absent from the lower Westphalian D, when the age is determined using the biostratigraphical criteria proposed by Laveine (1977). ACKNOWLEDGEMENTS Thanks go to Mr Russel Ellis, who in 1991 was Project Archaeologist with the National Trust, and who made these fossils available to us. Thanks also go to Dr Deborah Spillards, who helped collect the specimens and took the photographs illustrating this paper.
377
REFERENCES BODE, H. 1970. Der stratigraphische Wert der Neuropteris ovata und ihre Bedeutung fiir die Kennzeichnung der Westfal/Stefan-Grenze. Compte rendu 6e Congres International de Stratigraphie et de Geologie du Carbonifere, 2, 517-522. BROUSMICHE, C. 1983. Les fougeres sphenopteridiennes du bassin houiller Sarro-Lorrain. Publication Societe Geologique du Nord, 10, 1-480. BROUSMICHE, C. & LAVEINE, J.-P. 1982. Caracteres, repartition et synonymie du Pecopteris avoldensis (Stur) dans Ie bassin houiller sarro-lorraine. Annales de la Societe geologique du Nord, 101, 51-63. CLEAL, C. J. 1978. Floral biostratigraphy of the upper Silesian Pennant Measures of South Wales. Geological Journal, 13, 165-194. CLEAL, C. J. 1984. The recognition of the base of the Westphalian D Stage in Britain. Geological Magazine, 121, 125-129. CLEAL, C. J. & THOMAS, B. A. 1996. British Upper Carboniferous stratigraphy. Chapman and Hall, London. DALINVAL, A. 1960. Contribution a l'etude des Pecopteridees, Les Pecopteris du bassin houiller du Nord de la France. Etudes Geologiques pour l'Atlas Topographie Souterraine, 1(3), 1-222. FIELDING, C. R. 1984. Upper delta lain lacustrine and fluviolacustrine facies from the Westphalian of the Durham coalfield, NE England. Sedimentology, 31, 547-567. GASTALSO, R. A. 1992. Regenerative growth in fossil horsetails following burial by alluvium. Historical Biology, 6,203-219. JOHNS, R. 1987. Aberdulais Falls. A geological evolution. The Journal of the Gower Society, 38, 67-74. JONES, O. T. 1951. The distribution of coal volatiles in the South Wales Coalfield and its probable significance. Quarterly Journal of the Geological Society of London, 107, 51-83. KELLING, G. 1974. Upper Carboniferous sedimentation in south Wales. In (Owen, T. R.; ed.) The Upper Palaeozoic and post-Palaeozoic rocks of Wales. University of Wales Press, Cardiff, 185-244. KIDSTON, R. 1924. Fossil plants of the Carboniferous rocks of Great Britain. Part 5. Memoirs of the Geological Survey of Great Britain, Palaeontology, 2, 377-522. LAVEINE, J.-P. 1977. Report on the Westphalian D. In (Holub, V. M. & Wagner, R. H.; eds) Symposium on Carboniferous stratigraphy. Geological Survey, Prague, 7187. SULLIVAN, H. 1. & MOORE, L. R. 1956. The horizon of the Tillery Vein in Monmouthshire. Geological Magazine, 93,409-417. ZODROW, E. L. & CLEAL, C. J. 1985. Phyto- and chronostratigraphical correlations between the late Pennsylvanian Morien Group (Sydney Nova Scotia) and the Silesian Pennant Measures (south Wales). Canadian Journal of Earth Sciences, 22, 1465-1473.
Manuscript received 24 January 2001; revised typescript accepted 2 April 2001
1. INTRODUCTION Aberdulais Falls is on the River Dulais near its junction with the River Neath, about 3 km NE of the town of Neath, Port Talbot in South Wales [OS SS 772995] (Fig. 1). Since 1981 it has been part of a Nat ional Trust site, where the landscape and industrial heritage of the area is conserved. The Falls is a Devensian feature resulting from erosion by glacial meltwater (Johns,
1987). The bedrock is part of the South Wales Pennant Form ation , belonging to the Brithdir Member (senslI Cleal & Thomas 1996) and is early Westphalian D in age (Cleal 1978). There is a thin coal at the base of the Falls, which John s (1987) describes as being the Brithdir Rider Seam, but which the 10 560 geological map (British Geological Survey) shows to be some 27 m above that level, but still well within the middle Brithdir Member (Fig. 1).
500111
Aberdulais Cool
Torma
( 'nnamcd Scam
~1. C \ d OfAbcn1UIJi~ Fells FI0f"3
Brithdir Rider Scam
(jraig . 'am
eath I
nrilhdir Scam
Fig. 1. Location map for Aberdul ais Falls, near Neath, South Wales (left). Also, a generalized litho stratigraphical section through the Brithdir Member in this part of South Wales, showing the level from which the macroflora was collected (right). Proceedings of the Geologists' Association, 112, 373- 377.
0016-7878/01 SI5.00
© 2001 Geologists' Association
374
B . A . THOMAS C . J . C LEAL
Fig. 2. Plant fossils from the Westphalian D of Aberdulais Falls, near Neath (all x 2): (a) shoot of Sphenophyllum emarginatum Brongniart ; (b) compressed stem of Calamites cf. suckowii Brongnia rt; (c) part of bipinnate segment of ?Ze illeria a voldensis (Stur) Kidston.
In 1991 , excavations were made to fit a hydroelectric turbine at the base of the Falls. The excavations were made by large boring machines, producing cores of 140 mm and 180 mm diameter. Immediatel y below the coal, the borings passed through argillaceous deposits, which yielded a diverse assemblage of well preserved plant macrofossils. The cores with the fossiliferous shales were acquired
by the Nat ional Museums & Galleries of Wales, Cardiff, and form the basis of the present short commun ication. 2. PALAEOBOTANY
The fossils are preserved as coalified compressions in the grey shales and siltstones. The site lies near the
A N EW E A RLY W ESTPHALIAN F L O R A , WALES
centre of the South Wales Coalfield, where the coals have a low volatiles content (Jones, 1951) so there is no possibility of the fossils yielding cuticles. The following species have been identified. Lycoph ytes: Lepidocarpon sp. S tigma ria fico ides Brongniart
Sphenophytes: An nularia stellata (Sternberg) Wood (Fig. 3b) A. sphenophylloides (Zenker) Gutbier (Fig. 3b) Calam ites cf. sucko wii Brongn iart (Fig. 2b) Sphenophyllum emarginatum Brongniart (Fig. 2a)
Ferns : Pecopt eris cf. dufa yi Dalinval (Fig. 3c-d) P. unita Brongniart Renaultia chaerophylloides (Brongniart) Zeiller
(Fig . 3f) R. cf. crepinii (Stur) Kidston (Fig. 3e) ?Zeilleria avoldensis (Stur) Kid ston (Fig. 2c)
Pteridospenns: Macroneuropteris scheuchz eri (Hoffmann) Cleal et al. Trig onocarpus sp. (Fig. 3a)
Corda ites: Cordaites sp.
The flora is dominated by Sph enophyllum emarginatum (Fig. 2a), although it also has a high proportion of Annularia (Fig. 3b), Calamites (Fig. 2b) and frond fragments of various ferns. Seed plants are rare; there are only a few isolated pinnules of Ma croneuropteris scheuchzeri and a single Trigonocarpus seed (Fig. 3a). Club-mosses are all but absent except for Stigmar ia rooting stru ctures and a single sporangium of Lepidocarpon. The fossils occur in an interval of mudstone in an otherwi se alluvial sandstone-dominated sequence typical of the South Wales Pennant Formation (e.g. Kelling, 1974). Elsewhere in Britain, such mudstones have been interpreted as overbank deposits or distal crevasse-delta deposits in floodpl ain lakes (Fielding, 1984). Although the alluvial setting of the Pennant Formation is rather different from that studied by Fielding, we suggest that the mudstone deposits were nevertheless formed in a similar lacustrine environment. Calamites were adapted to growth around the shores of such lakes, being capable of regenerative growth when subjected to periodic burial (Gastaldo, 1992). We therefore speculate that the bulk of the Aberdul ais flora (i.e. the sphenophyte and probably fern components) represents the vegetation growing around the margins of a floodplain lake. The fragments of seed plants were probably from the levee vegetatio n, having drifted along the rivers that fed the lake via the crevasse. The greatest diversity in the flora is in the ferns. The most abundant is an unusual pecopteroid with slender pinnules, having, in some cases, a decurrent base, but in others a slightly constricted base (Fig. 3c). There is a strong midvein but much thinner later al veins that fork , usuall y once, and meet the pinnule margin at
375
c.70·. One specimen also appea rs to be fertile with a row of Asterotheca-like synangia on either side of the midvein (Fig. 3d). There is some similarity to the elongate pinnules seen in Pecopt eris plumosa (Artis) Brongniart, but that species has a venation that is not as oblique to the pinnule margin and later al veins not so widely forked. P. plumosa also has S enft enbergia sporangia that are quite unlike the As terotheca-like reproductive structures in the Aberdulai s specimen. A closer comparison can be made with some specimens figured by Dalinval (1960, pI. 45, figs 1- 2) as Pecopteris (A sterotheca) dufayi Danze that have pinnules with a similar shape and venation. According to Danze , this species is very variable but, because it has pinnules that are far larger than anything seen at Aberdulais, we have only tentatively assigned our material to Danze's species. The numerous fragments of sphenopteroid fern are mostly sterile, but one shows a few sporangia similar to those of Renaultia. In most specimens, the pinnules are up to 5 mm long, with an approximately ovoid outline (Fig. 3f), and compare well with specimens illustrated by Brousmiche (1983) as Renaultia chaerophy lloides (Brongniart) Zeiller. A single specimen shows significant ly smaller pinnules (Fig . 3e), which we have tentatively compared with Renaultia crepinii (Stur) Kidston . There are a few fragments of pecopteroid frond , with obliquely attached pinnules having constricted aero scopic sides (Fig. 2c). Although most pinnules have a smooth margin , occasionally the distal margin shows small teeth and the lateral margins sometimes have a shallow sinus. There is some similarity to Z eilleria a voldensis as figured by Brousmiche & Laveine (1982), although the pinnules in that species are not normally so obliquely attached . Z. a voldensis was regarded by Kidston (1924) as uncommon in Britain, although Brousmiche & Laveine (1982) record it as abundant in the Bolsovian and lower Westphalian D of Saar-Lorraine, albeit often misidentified as other species. As none of our specimens are fertile and the pinnule form is not completely typical, we have only tentatively assigned it to that species. 3. COMPARISONS
There are no known floras from this part of the sequence in the western part of the South Wales Coalfield. On the east crop, there are some lowdiversity floras associated with the Brithdir Seam (sometimes known locally as the Tillery Seam - see Sullivan & Moore, 1956). Cleal (l97 8) reported some restricted assemblages from this level, based on specimens in the Kidston Collection. However, by far the most diverse assemblage was reported from a tip at the West Blaina Red Ash Colliery, in the Ebbw Fawr valley (Sullivan & Moore , 1956). Although the flora was not figured, the published species list clearly reflects a diverse flora dominated by pteridosperms and some lycophytes, with much rarer ferns (oth er than Lobat opt eris) and sphenophytes. The assemblage is
376
B. A. THOMAS C. J. CLEAL
Fig. 3. Plant fossils from the Westphalian D of Aberdulais Falls, near Neath ( x Za-f): (a) pteridosperm ovule Trigonocarpus sp.; (b) two species of sphenophyte foliage, the larger whorls Annularia stellata (Sternberg) Wood, the smaller whorls Annularia sphenophylloides (Zenker) Gutbier; (c) sterile portion of fern frond, Pecopteris cf. dufayi Dalinval; (d) fertile portion of P. cf. dufayi Dalinval frond showing what appear to be Asterotheca-like synangia; (e) pinnae of the small-pinnuled fern Renaultia cf. crepinii (Stur) Kidston; (f) pinna of Renaultia chaerophylloides (Brongniart) Zeiner, which has significantly larger pinnules than the previous species.
A NEW EARLY WESTPHALIAN FLORA, WALES
thus quite different in composition and diversity to that found at Aberdulais. 4. Discussion
For many years, there was a problem locating the base of the Westphalian D Stage in South Wales. This was because of the poor palaeobotanical record between the No. 1 Rhondda Seam and its rider (middle Rhondda Member - Westphalian C), and the Hughes Seam (base of Hughes Member - middle Westphalian D). The problem was not resolved until the rediscovery in the David Davies Collection (National Museums and Galleries of Wales, Cardiff) of small but unequivocal lower Westphalian D floras associated with the Captain and Cuckoo Seams (Cleal, 1978), allowing the base of the stage to be placed in the upper Rhondda Member. As the Aberdulais flora is from the Brithdir Member, which overlies the Rhondda Member (Cleal & Thomas, 1996), it must be stratigraphically higher than the Cuckoo Seam and thus early Westphalian D in age. Significantly, however, there is no evidence of the pteridosperm frond Neuropteris ovata Hoffmann, whose lowest occurrence is an important index to the base'of the Westphalian D (Cleal, 1984). The range of N. ovata has long been linked with the definition of the Westphalian D, and some authors have gone as far as to regard them as effectively synonymous (e.g. Bode, 1970). Notwithstanding that biostratigraphy and chronostratigraphy should be kept strictly separate, basing a stage boundary on the range of a single species is bound to cause difficulties. For this reason Laveine (1977) proposed a series of other biostratigraphical criteria for recognizing this stage boundary, and this was the model used by Cleal (1978) to locate the boundary in South Wales. A similar situation has been found in the Sydney Coalfield of Nova Scotia, where Zodrow & Cleal (1985) showed that N. ovata is absent from the lower Westphalian D, when the age is determined using the biostratigraphical criteria proposed by Laveine (1977). ACKNOWLEDGEMENTS Thanks go to Mr Russel Ellis, who in 1991 was Project Archaeologist with the National Trust, and who made these fossils available to us. Thanks also go to Dr Deborah Spillards, who helped collect the specimens and took the photographs illustrating this paper.
377
REFERENCES BODE, H. 1970. Der stratigraphische Wert der Neuropteris ovata und ihre Bedeutung fiir die Kennzeichnung der Westfal/Stefan-Grenze. Compte rendu 6e Congres International de Stratigraphie et de Geologie du Carbonifere, 2, 517-522. BROUSMICHE, C. 1983. Les fougeres sphenopteridiennes du bassin houiller Sarro-Lorrain. Publication Societe Geologique du Nord, 10, 1-480. BROUSMICHE, C. & LAVEINE, J.-P. 1982. Caracteres, repartition et synonymie du Pecopteris avoldensis (Stur) dans Ie bassin houiller sarro-lorraine. Annales de la Societe geologique du Nord, 101, 51-63. CLEAL, C. J. 1978. Floral biostratigraphy of the upper Silesian Pennant Measures of South Wales. Geological Journal, 13, 165-194. CLEAL, C. J. 1984. The recognition of the base of the Westphalian D Stage in Britain. Geological Magazine, 121, 125-129. CLEAL, C. J. & THOMAS, B. A. 1996. British Upper Carboniferous stratigraphy. Chapman and Hall, London. DALINVAL, A. 1960. Contribution a l'etude des Pecopteridees, Les Pecopteris du bassin houiller du Nord de la France. Etudes Geologiques pour l'Atlas Topographie Souterraine, 1(3), 1-222. FIELDING, C. R. 1984. Upper delta lain lacustrine and fluviolacustrine facies from the Westphalian of the Durham coalfield, NE England. Sedimentology, 31, 547-567. GASTALSO, R. A. 1992. Regenerative growth in fossil horsetails following burial by alluvium. Historical Biology, 6,203-219. JOHNS, R. 1987. Aberdulais Falls. A geological evolution. The Journal of the Gower Society, 38, 67-74. JONES, O. T. 1951. The distribution of coal volatiles in the South Wales Coalfield and its probable significance. Quarterly Journal of the Geological Society of London, 107, 51-83. KELLING, G. 1974. Upper Carboniferous sedimentation in south Wales. In (Owen, T. R.; ed.) The Upper Palaeozoic and post-Palaeozoic rocks of Wales. University of Wales Press, Cardiff, 185-244. KIDSTON, R. 1924. Fossil plants of the Carboniferous rocks of Great Britain. Part 5. Memoirs of the Geological Survey of Great Britain, Palaeontology, 2, 377-522. LAVEINE, J.-P. 1977. Report on the Westphalian D. In (Holub, V. M. & Wagner, R. H.; eds) Symposium on Carboniferous stratigraphy. Geological Survey, Prague, 7187. SULLIVAN, H. 1. & MOORE, L. R. 1956. The horizon of the Tillery Vein in Monmouthshire. Geological Magazine, 93,409-417. ZODROW, E. L. & CLEAL, C. J. 1985. Phyto- and chronostratigraphical correlations between the late Pennsylvanian Morien Group (Sydney Nova Scotia) and the Silesian Pennant Measures (south Wales). Canadian Journal of Earth Sciences, 22, 1465-1473.
Manuscript received 24 January 2001; revised typescript accepted 2 April 2001