European Frameworks for the Selection of Palaeozoic Palaeobotany Geosites

GEOLOGICA BALCANICA, 28, 3-4, Decemb., 1998, p. 59-66

European frameworks for the selection of Palaeozoic palaeobotany Geosites

1 2 C. J. Cleal , B. A. Thomas

1 Department of Biodiversity and Systematic Biology, National Museums and Galleries of Wales, CAthays Park. Cardi.ffCFJ 3NP. UK. ~Department of Geography, University of Wales Lampeter. Lampeter. Ceredigion SA48 7ED, UK

Abstract. Frameworks for the selection of palaeobotanical Geosites should be developed around four criteria: palaeofloristics, palae oecology, fossil preservation and biostratigraphy. For the Silurian and Devonian, there is a relatively low degree of provincialism, so comparisons have to be made on a global basis. As there is a more marked provincialism in the Carboniferous and Permian floras, European palaeobotanical sites must be compared mainly with others in the same low palaeolatitudes. Especially in the European Lower Devonian and Lower Carboniferous, there are two main habitats reflected in the plant fossil record: fluvio-deltaic and volca nic terrains. This palaeoecological distinction is also partly reflected through differences in preservation, with the floras in fluviodel llric deposits being mainly ad press ions, and those in volcanogenic deposits mainly petrifactions. The plant macrofossil biostratigra phy is well developed in the European Palaeozoic and so provides a useful temporal background to the fossil record. By integrating dlese four sources of data, it is possible to develop the frameworks for a reliable assessment of the European palaeobotanical sites.

Cleat, C. 1., Thomas, B. A. 1998. European frameworks for the selection of Palaeozoic palaeobotany Ge osites. - Geologica Bale., 28, 3-4; 59-66 Key words: palaeobotanical geosites, criteria for palaeobotanical geosites, Paleozoic fossil plant

Introduction both selection framework criteria and specific site proposals among the palaeobotanical community. The underlying philosophy behind the Geosites pro The canvassing has so far been mainly through the gramme (Wimbledon, 1996; Wimbledon et al., in International Organisation for Palaeobotany and the press) was intended to ensure that the voices of indi lUGS Subcommission on Carboniferous Stratigra vidual geologists would be heard in the site-selection phy, including the web pages of the former (Cleal & process. National working groups are being asked to Thomas, 1996 b, 1997). In this paper, we will sum collate the views of geologists within their country marise the results of the work by the palaeobotany and submit the resulting list to regional or continen specialist group, especially as it relates to the Palae tal working groups, who in tum will submit their col ozoic of Europe. bled lists to a global Geosites working group. How ever, against this background, there are specialist groups that can help to provide a global perspective Selection frameworks · certain fields. The role of such specialist groups will vary, but will be of most significance in fields As with all of the Geosites selection programmes, it ibich are not totally familiar to most geologists. has been essential to establish the frameworks with One such group has been organised for palaeobotany, in which the comparative analyses can be made. that for historical reasons has tended to be regarded There is no point in comparing, for instance, a Low more the remit of botanists and the life-sciences, er Permian boreal flora with a Middle Devonian rather than of geologists and the earth sciences. tropical flora (we should perhaps point out that we The two authors of this paper have been asked to are using the term flora here to refer to an assem cxrordinate the palaeobotany Geosites specialist blage of plant fossils, rather than an assemblage of group and we have been canvassing for opinions on plants; the significance of this difference will be-

59 come evident later). We must be comparing ' like proposed, but that most widely adopted in Europe with like' if the comparative analysis is to have any today is summarized in Cleal ( 1991 ). significance. Plant fossils can provide four main types of infor Silurian mation to the palaeobotanists and these control the frameworks within which sites can be meaningfully Other than the Baragwanathia found in Australia compared. (Lang & Cookson 1935; Tims & Chambers 1984), 1. Palaeofloristics. The broad pattern of geograph about whose age there are still some doubts, Silurian ical distribution of plant fossils is probably the single floras are mainly dominated by simple rhyniophy most important factor in delineating the Geosites se toids such as Cooksonia. The best known examples lection frameworks for palaeobotany. The best anal are found in the British Isles (reviewed by Cleal & ysis of palaeofloristics remains that of Meyen (in Thomas, 1995), but on the whole their preservation Vakhrameev et al., 1978), with shorter reviews pro is not as good as the slightly younger floras from the vided by Meyen ( 1987) and Cleal ( 1991 ). In such basal Devonian. The only Silurian site that has analyses, a nested hierarchy of palaeofloristic therefore been regarded as being sufficiently impor 'zones' or phytochoria are recognized, in descending tant as a palaeobotany Geosite is in Tipperary, Ire rank palaeokingdoms, palaeoarea and palaeoprov land, which has yielded the oldest known (Wenlock) ince. For the present analysis, the palaeoarea was examples of Cooksonia and represent the earliest found to be the lowest rank of phytochorion to cir known macrofossil evidence of land vegetation (Ed cumscribe a framework, since this reflects clear dif wards et al., 1983). ferences in the composition of the floras. Lower ranked phytochoria tend to be differentiated on the Devonian compositional balance of the floras, rather than the presence/absence of taxa. The Devonian palaeobotanical record reflects the 2. Palaeoecology. Environmental conditions and progressive early development of land plants, from intraspecific interactions are obviously major factors their early rhyniophytoid beginnings to the early in determining the distribution of plants. However, seed plants. Most of the well documented floras are as only a relatively narrow band of mainly lowland from Europe and North America. There is possible habitats is usually sampled in the fossil record, palae evidence of global provincialism in Devonian floras, oecology tends to be of less important for selecting but this is based on assemblages from places such as frameworks. This is not to say that palaeoecolgical Kazakhstan and China which have not been as exten studies should be ignored because, for instance, in sively studied as the European and North American the case of the fossil record of the Late Carbonifer assemblages. Until these other floras have been ous tropical swamp forests there are two quite differ more extensively studied, the comparative analysis ent and mutually exclusive vegetational habitats: the of Devonian palaeobotanical sites has to be in global lycopsid dominated back-swamp communities and frameworks, divided primarily on preservation. the more diverse, fern/pteridosperm levee communi Europe has proved especially important in the ties (Cleat & Thomas, 1994). In such examples as study of Early Devonian palaeobotany. The United this, the case for treating the two, or more, communi Kingdom and Belgium have the best available sites ties separately is compelling. for the study of the two Lower Devonian plant bio 3. Preservation. This controls the type of informa zones: sites in the Clee Hills for the Zosterophyllum tion that a fossil reveals: adpressions sensu Shute & Zone, Craig-y-Fro and Llanover quarries for the low Cleal ( 1986) normally provide the best morphologi er Psilophyton Zone, and sites on the northern mar cal data, whilst petrifactions sensu Bateman (in gins of the Dinant Basin for the upper Psilophyton Cleal, 1991) are best for anatomical studies. Hence Zone. The only Lower Devonian site outside of Eu the same original vegetation could be represented by rope which is of equivalent significance is Gasp, in sites in two quite different frameworks: one for ad Canada, which has yielded a classic flora of the up pression floras and one for petrifaction floras. The per Psilophyton Zone (Gensel & Andrews, 1984). preservational divide may also partly mirror differ For the lower Middle Devonian Hyenia Zone, the ences in habitat. In the above quoted Late Carbonif diverse floras of Elberfeld in Germany and Vesdre in erous example, the backswamp vegetation is mainly Belgium clearly stands out as the best in the world. represented by the coal-ball petrifactions, whereas The European record for the overlying Svalbardia the levee vegetation is mainly reflected in the ad pres and Archaeopteris Biozones in the upper Middle and sion record in the clastic deposits. lower Upper Devonian is much poorer and no sites 4. Biostratigraphy. This reflects the progressive can match those in North America, notably in the development of vegetation with time. For conve Catskill Mountains (Banks et al., 1985). However, nience, the stratigraphical column is divided into a for the topmost Devonian biozone, the Rhacophyton sequence of biozones based on this changing pattern Biozone, Belgium again includes some of the best of fossil occurrence. Various schemes have been sites near the northern margins of the Dinant Basin,

60 Table I Proposed Palaeozoic palaeobotany Geosites in Europe. Site Country Interest References Tipperary Ireland Oldest known example of Cook sonia Edwards et al. (1983) Clee Hills UK Best examples of Zosterophyllum Zone floras including anatomically preserved Cooksonia Edwards et al. ( 1992), Fanning et al. (1992) Craig-y-Fro and Llanover UK Best examples of lower Psilophyton Zone floras Oeal & Thomas ( 1995) Northern margins of Dinant basin Belgium Best examples of upper Psilophyton Zone floras Stock mans ( 1940), Gerrienne ( 1983) Bberfeld, Lindlar and Go, Germany and Belgium Best examples of Hyenia Zone floras Leclercq (1940), Schweitzer (1966, 1972, 1973) Ourthe, Hoyoux and Bocq Vallies Belgium Best examples of Rhacophyton Zone floras Fairon-Demaret (1996) Rhynie Chert UK Oassic Lower Devonian petrifactions Oeal & Thomas ( 1995) Berwickshire and E. Lothian UK Best examples of Tournai sian petrifactions, and especially important for early seeds Scott et al. (1984), Cleal & Thomas (1995) Montagne Noire France Cassie Tournaisian petrifactions, especially important for lycophytes and early ferns Gallier (1970), Scott et al. (1984) Pt:uycur UK Oassic Visean petrifactions of plants from a distrubed volcanic habitat Scott et al. (1984), Cleal & Thomas (1995) Kilpatrick Hills UK Oassic Visean petrifactions and adpressions Scott et al. (1984), Cleat & Thomas (1995) Meeuse Valley Belgium Best examples of Arnsbergian to Yeadonian adpressions Slockmans & WilliSre (1953) Gynneath- Ammanford UK Best examples of Langsettian to Bolsovian adpressions Cleal & Thomas (1995, 1996a). Guardo Coalfield Spain Best examples of Westphalian D and Cantabrian adpressions ~r (1966), Wagner et al. (1983) Sabero Coalfield Spain Best examples of Barruelian to Stephanian B adpressions bight (1983) Grand'Croix Frmce Cassie middle Stephanian petrified peat, especially important for ferns and sphenophytes Gallier & Scott (1981) and Gal tier & Phillips (1985)

61 Saar-Nahe Gennany Best Lower Permian flora Kerp & Fichter (I 985) Kupferschiefer Gennany Best Upper Permian flora Schweitzer (1986)

which complement the Bear Island flora in the Arc There are several good Lower Carboniferous ad tic (Schweitzer, 1967, 1969). pression sites in Europe, especially in the UK and Standing quite separate from this main global Germany (see Cleat & Thomas, 1995, for a review of framework is the classic Rhynie Chert flora. The as the former). However, none match the North Ameri semblage is totally different from any other known can sites for diversity and fine preservation: the Price assemblage, being chert petrifactions representing and Pocono Formations exposed in north-western the vegetation in a volcanic terrain. It should not Virginia (Read, 1955), and Horton Bluffs in northern therefore be interpreted within the same frameworks Nova Scotia (Bell, 1960). as the other Devonian sites, which preserve fluvio In contrast, Europe has by far the best petrifaction deltaic vegetation as adpressions or other, less per sites. For the Toumaisian, the Scottish sites in Ber fect types of petrifaction. wickshire and East Lothian have yielded the most diverse and well preserved petrifactions, and are es Lower Carboniferous pecially important for early gymnosperms; nowhere else has been found such a diverse range of structur The Lower Carboniferous reveals the first well-docu ally-preserved early seeds. Within this area, both mented evidence of floristic provincialism, most nota fluvio-deltaic and volcanic-terrain vegetation is pre bly in the distinctive Angaran floras from Siberia served, providing two contrasting views of the Tour (Meyen, 1982). Elsewhere, there is a less marked pro naisian tropical vegetation of this time. In addition, vincialism, which was recognized by Cleat & Thomas there is the classic floras from the phosphatic nod (in Cleal, 1991) as four palaeoareas: Gondwana, Ca ules within the Lydienne Formation, Montagne thaysia, Kazakhstania and Europe (which also includes Noire. These petrifactions reveal yet another type of North America and parts of north Africa) (Fig. 1). Toumaisian vegetation, with a much higher propor Within this Europe Palaeoarea, at least three quite tion of ferns and lycophytes. separate sets of palaeobotanical sites occur, which In the Visean, the classic Pettycur site stands out have to be assessed within their own frameworks: as the most important for petrifactions. Prior to the sites yielding adpressions from fluviodeltaic vegeta discovery of the Rhynie Chert, Pettycur had yielded tion, sites yielding petrifactions from fluviodeltaic the oldest known structurally-preserved plant fossils vegetation, and sites yielding petrifactions from vol and was pivotal for developing our understanding of canic terrains. early plant evolution. The Pettycur fossils are pre-

Fig. I. Phytogeographical map for the Lower Carboniferous. Thick solid line separates the named palaeokingdoms. Thick dashed line separates the unnamed palaeoareas in the Eurameria Palaeoldngdom (Europe, Gondwana, Kazakhstania, Cathaysia). Adapted from Cleat (199 I. fig. 4.2)

62 served in limestones caught-up in a volcanic deposit Upper Carboniferous sites can be more or less as and seems to represent the vegetation growing in a sessed within two frameworks: petrifaction sites, volcanically disturbed habitat. In contrast, the Visean mainly representing backswamp vegetation, and ad deposits of the Kilpatrick Hills, near Glasgow, repre pression sites mainly representing vegetation grow sents vegetation that grew in more tranquil condi ing on clastic substrates (e.g. levee banks). tions and is more typical for floras of this age, includ There has been much work on Upper Carbonifer ing abundant gymnosperms and progymnosperms. ous petrifactions, we have encountered problems in The Kilpatrick Hills sites (especially Loch Humphrey developing a comprehensive network of suitable Burn) is of particular interest as it has yielded some ad sites. The only European sites that could merit selec pressions together with the petrifactions, and thus has tion as a Geosite is the middle Stephanian Grand' gone some way to helping correlate the plant remains Croix. In North America, there is also the Washing preserved in these two modes of preservation. ton County site for the lower Namurian (Taylor & Eggert, 1967), and the Stuebenville and Hamilton Upper Carboniferous Quarries and for the middle-upper Stephanian (Roth well, 1988; Mapes & Mapes, 1988). However, for The floristic provincialism recognised in the Lower the bulk of the Upper Carboniferous, including the Carboniferous becomes even more marked in the classic lycophyte-dominated coal ball floras, it is vir Upper Carboniferous (Fig. 2), mainly through global tually impossible to identify suitable candidates to climatic cooling and high-latitude glaciation. The act as Geosites. high-latitude Angaran and Gondwanan floras are Despite the extensive research that there has been quite distinct and belong to their own palaeoking on the Upper Carboniferous adpression floras, find doms (Meyen, 1982; Rocha Campos & Archangel ing suitable surface exposures to represent them was sky, 1985). The plant fossils found in Europe belong far from easy; much of the work has been done on to the Euramerica Palaeokingdom, which represents material from temporary exposures or underground the tropical vegetation of the time, exemplified dur workings. However, we have eventually been able to ing the Westphalian Epoch by what has been referred develop a network of sites which cover the adpres to as. the Coal Forests. sions of this age, many of which are in Europe: the Within the Euramerica Palaeokingdom, four Meeuse Valley (Amsbergian to Yeadonian), Glyn palaeoareas have been recognized (Thomas & Cleal neath-Ammanford (Langsettian to Bolsovian), the in Cleat, 1991 ): Oregon and Cordillera Palaeoareas · Guardo Coalfield (uppermost Westphalian D and in western North America, Cathaysia Pa1aeoarea in Cantabrian) and the Sabero Coalfield (upper Barrue- tbe Far East, and the rest (mainly Europe and eastern 1ian to Stephanian B). North America) referred to as the Europe Palaeoarea. These are complemented by a number of North The European sites must therefore be assessed with American sites showing features not represented in in the context of this Europe Pa1aeoarea. Unlike the the European sites, including Joggins Cliffs for the Lower Carboniferous, there is not the range of volca unrivalled that they give of stumps of the lycophyte nogenic deposits containing plant fossils, and so the forests (Ferguson, 1988), the beautifully preserved

F;g. 2. Phytogeographical map for the Upper Carboniferous. Thick solid line separates the named palaeokingdoms. Thick dashed separates the unnamed palaeoareas (for Eurameria, Oregon, Cordillera, Europe. Cathaysia; for Angara, Kazakhstania, Kuznetsk). Adapted from Cleal (1991, fig. 4.4)

63 cuticles from the lower Cantabrian of Point Aconi Carboniferous of the Euramerican Palaeokingdom, (Cleat & Zodrow, 1989), the lower Cantabrian nod but with the addition of conifers and peltasperms. ule flora of Mazon Creek (Darrah, 1969), and the For the Upper Permian, the Kupferschiefer deposits 'upland' vegetation represented at Rock Island of central Germany (e.g. Mansfeld site, Ilmenau, (Leary, 1981 ). There is also the remarkable se Gera, Richelsdorf) provide the best palaeobotanical quence of floras represented within the New River evidence, representing the conifer-dominated vege Gorge Section of West Virginia, which demonstrates tation surrounding the Zechstein Sea. the changes that were taking place in the tropical flo ras through the entire Late Carboniferous (Englund et al., 1979). Discussion

Permian The proposed candidate Geosites are not intended to be anything more than suggestions, that may be mod Although the polar glaciation disappeared towards ified by the appropriate national working groups, as the end of the Carboniferous or in the early Permian, they see fit. As palaeobotany is an aspect of the earth floristic provincialism became even more marked sciences with which many geologists are Jess famil (Fig. 3). This can be seen by the segmentation of iar, the suggestions should prove a useful basis on both the Gondwana and Angara Palaeokingdoms which to start their discussions. However, we would into a series of palaeoareas, as the vegetation of the urge the adoption of our suggested selection frame higher palaeolatitudes became more diverse. The works, as they reflect the current thinking among the tropical zone was also segmented into three quite palaeobotanical community on palaefloristics, palae distinct palaeokingdoms: the Cathaysia Palaeoking oecology, taphonomy and biostratigraphy. For the dom, which continued to support a flourishing a di European Palaeozoic palaeobotanical sites they may verse tropical vegetation (Shen, 1995); the North be summarised as follows. America Palaeokingdom with its distinctive suite of 1. Silurian adpressions world-wide mainly gymnosperms representing drier habitat veg 2. Devonian adpressions world-wide etation (Read & Mamay, 1964; Mamay, 1976; 3. Devonian petrifactions world-wide Mamay & Watt, 1971 ); and the rump of the Euramer 4. Lower Carboniferous adpressions of the Europe ica Palaeokingdom, supporting a restricted, mainly Palaeoarea conifer dominated vegetation that survived the ef 5. Lower Carboniferous fluvio-deltaic petrifac fects of the Variscan tectonic uplift. tions of the Europe Palaeoarea Only two European sites have yielded sufficiently 6. Lower Carboniferous volcanic-terrain petrifac diverse floras to justify designation as Geosites. The tions of the Europe Palaeoarea best Lower Permian site is the Saar-Nahe Rotlieg 7. Upper Carboniferous ad press ions of the Europe end, which has yielded ferns, peltasperms, trigono Palaeoarea carpaleans, conifers and a possible early cycad. The 8. Upper Carboniferous petrifactions of the Eu assemblages clearly reflect their origin in the Late rope Palaeoarea

Fig. 3. Phytogeographical map for the Permian. Thick solid line separates the named palaeokingdoms. Thick dashed line separates the unnamed palaeoareas (for Gondwana, Nothoafroamerica, Ausrraloindia, PaJaeoanrarctica: for Chathaysia, North and South Chi na; for Angara, Kazakhstania, Pechora, Kuznetsk, Far East). Adapted from Cleat ( 1991 , fig. 4.6)

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