Oral presentations, abstracts

FERGUSON, D.: Catastrophic events as a taphonomic window on plant communities

KUNZMANN, L. et al.: The Miocene leaf flora of Wiesa near Kamenz (Saxony, Germany) - a taphonomic puzzle?

OPLUSTIL, S. et al.: Whetstone Horizon - the westphalian fossiliferous tuff layer from the continental basins of central and western Bohemia, Czech Republic

PSENICKA, J. et al.: In situ peat-forming forest from the tuff bed of the Whetstone Horizon from Czech Republic (Bolsovian, Upper Carboniferous)

RÖßLER: R. Explosive volcanism - catastrophe or chance?

SAKALA, J.: Plant taphonomy in the Tertiary of Europe: two case studies from the Early Miocene of Bilina (Czech Republic) and one case study from the Early Eocene of Dangu (France)

WALTHER, H. & KUNZMANN, L.: Taphonomy of three leaf fragments of Ilex hibschii in a lower Oligocene "interrupted" Maar structure in the "Richter"-Phonolith Quarry of Hammerunterwiesenthal (Erzgebirge Mts., Saxony, Germany)

Poster presentations, abstracts

DIETRICH, D., et al.: Thermogravimetric and Ramanspectroscopic investigations on different coals in comparison to dispersed anthracite found in Chemnitz permineralisations

LIBERTIN, M: & DASKOVA, J.: The floristic assemblage from the pyroclastics rocks of the Tlustice Relict, Bolsovian, Czech Republic

MELLER, B. & HOFMANN, C.-C.: Taphonomic biasses of co-occurring diaspores and palynomorphs - an example from a Late Miocene deposit in Austria

Thermogravimetric and Ramanspectroscopic investigations on different coals in comparison to dispersed anthracite found in Chemnitz permineralisations

Dagmar Dietrich¹, Klaus Nestler², Günter Marx³, Klaus Witke⁴ & Ronny Rößler⁵

1 Reichenhainer Str. 198, 09125 Chemnitz
2 Technische Universität Chemnitz, Institut für Physikalische Chemie, 09107 Chemnitz
3 Technische Universität Chemnitz, Institut für Physikalische Chemie, 09107 Chemnitz
4 Bundesanstalt für Materialforschung und -prüfung/BAM, Richard Willstätter-Straße 1, 12489 Berlin
5 Museum für Naturkunde, Theaterplatz 1, 09111 Chemnitz

Permineralized samples of Medullosa, Psaronius und Dadoxylon from the Lower Permian Rotliegend "Petrified forest of Chemnitz" show delicate three-dimensional preservation of cellular tissues. Sometimes anatomical detail can be distinguished very well, when former cell walls are preserved as black coloured organic matter. Raman spectroscopic investigations evidenced that these fossilized tissues turned to disperse carbon, which structure seems to correspond to anthracite. The aim of this work is the experimental confirmation of the carbon structure by means of thermogravimetry and Raman spectroscopy by comparison of coal samples of different rank, especially anthracite samples from different stratigraphic positions and localities.

Coal maturation involves the sequence peat-lignite-anthracite-microcrystalline graphite by increasing carbon content and specific energy. The loss of in situ moisture (typically up to 200°C) and volatiles (up to 600°C) has been acquired by thermogravimetry. The increasing density causes changes in structure, which result in Raman spectra with typical band shape of the D- and G-peaks. We used these methods to characterize and compare different coal samples to the dispersed carbon inclusions in permineralized plants.

Catastrophic events as a taphonomic window on plant communities

David K. Ferguson
Department of Palaeontology, Geocentre, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
E-mail: david.kay.ferguson@univie.ac.at

Introduction
In general taphonomic processes have the effect of reducing the amount of information about past vegetation, which the palaeobotanist can expect to extract from plant assemblages. By concentrating on catastrophic events, it is possible to keep these losses to a minimum. The following examples should clarify this point.

Floods
Flooding can be caused by melting snow or continuous rainfall. This causes surface run-off, which washes seeds and sporomorphs into rivers. Due to the sheer force of water, organic debris dams are washed away, allowing transport of all sorts of plant parts to take place unimpeded. During spate erosion becomes a significant factor. River banks with a variety of plants which would otherwise remain invisible ("silent taxa") are undercut, releasing mosses, ferns and other herbs into the sediment-laden waters. Increasing water pressure from rapidly rising rivers will cause the levees to collapse (Aalto et al., 2003: 496). At these locations crevasse splays are created. Because of a reduction in the kinetic energy, the river drops most of its bed load and some of the plant detritus. The high rate of deposition means that the sediments at the bottom of the crevasse splay soon become anoxic, thereby preserving the plant material. When flood waters fill the flood-plain, litter from the overbank vegetation will be added to the rest of the thanatocoenosis (Spicer, 1980: 178). Seeds in particular are liable to be mobilized at this stage (Burgh, 1995). Flooding has the effect of overcoming tidal influences, which results in terrestrial plant megafossils being found in marine sediments.

Storms
With wind speeds in excess of 120 km/hour, hurricanes are responsible for stripping plants of their branches and leaves and transporting them over greater distances than is the norm. As the winds pass over a lake, the water is whipped up and the shallow-water sediments remobilized. Some of the detritus is captured by the wind-waves and settles to the lake bottom along with plant parts derived from local sources. Thus hurricanes increase our knowledge of the regional vegetation. As the process of redeposition of the remobilized sediments can lead to them being focused in deeper water, such storm assemblages should be looked for above intercalations of coarser sediments (Watts & Hansen, 1994: 165).

Fire
Depending on the nature of the fire, the vegetation may be completely destroyed or only singed. Since combustion is rarely complete, a certain amount of charcoal is invariably produced as a by-product of wildfire (Scott, 1989; Jones, 1993, 1996). Charcoal being very light can be carried aloft by the parcels of hot air (thermals). In this way it can be spread over an area of tens of kilometres. By removing the intervening vegetation, wildfires facilitate the unimpeded downhill transport of disseminules from the hinterland into the valley bottoms where they can become fossilized (Baker et al., 1996: 228). In this fashion a broader picture of the vegetation emerges.

Volcanism
A volcanic eruption can be likened to a gigantic fire which draws charcoal high up into the atmosphere and distributes it along with the air-fall tephra over a wide area. This tephra buries the herbaceous vegetation and preserves it in situ. The coating of ash on trees and shrubs reduces the amount of light the leaves receive and thereby triggers the processes leading to abscission. Under the weight of a new fall of ash the leaves are shed and embedded in the tuff (Spicer, 1989: 168). Paradoxically the most destructive form of volcanism, the explosive type, is the most effective at preserving plant material. The blast blows down trees and covers them in ignimbrite immediately. Leaching of these tuffs can result in silicification. Since volcanism is independent of drainage basins, it contributes information on plant communities which normally remain invisible in the fossil record. Once the volcano has become quiescent, the crater can fill with water. The great depth of the water column means that the bottom sediments are anoxic. Such crater lakes have yielded some of our best Lagerstätten and without them the fossil record would be considerably poorer.

Conclusion
While we have to accept the fact that we can only ever know a fraction of the plants that once lived on Earth, it is possible to expand our knowledge by concentrating our efforts on particular catastrophic events (Event taphonomy).

References
Aalto, R.; Maurice-Bourgoin, L.; Dunne, T.; Montgomery, D.R.; Nittrouer, C.A. & Guyot, J.-L. 2003. Episodic sediment accumulation on Amazonian flood plains influenced by El Nino/Southern Oscillation. - Nature, 425: 493-497.
Baker, R.G.; Bettis, E.A.; Schwert, D.P.; Horton, D.G.; Chumbley, C.A.; Gonzalez, L.A. & Reagan, M.K. 1996. Holocene paleoenvironments of northeast Iowa. - Ecological Monographs, 66: 203-234.
Burgh, J. van der 1995. Upper Miocene flora and vegetation in the Lower Rhine Embayment. Poster 7th Plant Taphonomy Meeting, Texel.
Jones, T.P. 1993. New morphological and chemical evidence for a wildfire origin for fusain from comparisons with modern charcoal. - Special Papers in Palaeontology, 49: 113-123.
Jones, T.P. 1996. A fire-related origin for fusain: comparisons with selected physicochemical characteristics of laboratory produced carbon. - Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 202: 159-168.
Scott, A.C. 1989. Observations on the nature and origin of fusain. - International Journal of Coal Geology, 12: 443-475.
Spicer, R.A. 1980. The importance of depositional sorting to the biostratigraphy of plant megafossils. In: Dilcher, D.L. & Taylor, T.N. (Editors), Biostratigraphy of fossil plants: successional and paleoecological analysis. Dowden, Hutchinson and Ross, Stroudsburg, pp. 171-183.
Spicer, R.A. 1989. The formation and interpretation of plant fossil assemblages. - Advances in Botanical Research, 95-191.
Watts, W.A. & Hansen, B.C.S. 1994. Pre-Holocene and Holocene pollen records of vegetation history from the Florida peninsula and their climatic implications. - Palaeogeography, Palaeoclimatology, Palaeoecology, 109: 163-176.

The Miocene leaf flora of Wiesa near Kamenz (Saxony, Germany) - a taphonomic puzzle?

L. Kunzmann¹, D.H. Mai², & H. Walther³

1 Staatliche Naturhistorische Sammlungen Dresden, Germany. E-Mail: kunzmann@snsd.de
2 Museum für Naturkunde der Humboldt-Universität, Invalidenstraße 43, 10115 Berlin, Germany
3 Staatliche Naturhistorische Sammlungen Dresden, Germany. E-Mail: walther@snsd.de

Wiesa is one of the classical localities for the palaeobotanical research in the Tertiary, and it is a well-known site of a "Mastixioideae Flora". The outcrop yielded during the 20th century thousands of fruits, seeds, cones, leaves and wood. The flora of Wiesa is also the type flora of the floral complex "Wiesa-Eichelskopf" in the Central European Tertiary. It’s probably uppermost Lower Miocene in age. Actually it consists of 132 taxa of fossil plants. The carpoflora has been reinvestigated and revised by Mai (2000), while the leaf flora is just under investigation (Kunzmann & Mai in prep.). Most of the plant remains were collected from fine grained sediments of a channel-like/lense-like fluvial structure. Only a few taxa were recognized from a small coal seam, which overlies the fluvial sediments. Unfortunately, nobody was studying the sediments in detail during the period of exploitation to reconstruct the sedimentary facies types. And also nobody recorded exactly, how the fossil remains were distributed within the profile. Because most of the leaves were washed out of the sediments, typical taphonomic data of leaf floras (planar orientation, adaxial:abaxial ratio orientation, clustering of distinct taxa, palaeocurrent pattern) can’t be observed. So, there are problems to explain the specific features of the composition of the taphocoenoses of this important flora.

The discrepancy between the number of identified carpological and leaf taxa is conspicuous. Up to now only 18 of all known taxa are leaf morphospecies, 12 of them are conifers. This result is based on the determination of hundreds of leaf remains by their cuticles. The preservation of the fossil leaf remains is excellent (mummified leaves). An enormous amount of conifer and angiosperm leaves are preserved with their complete laminae. Cross sections of leaves are showing cells of the different tissues of the leaf laminae. Except for Ginkgo adiantoides these taxa are characterized by large, entire-margined, lauraceous leaf laminae mainly with drip tips. Although the contribution of sedimentological data to the interpretation of the taphocoenoses is limited, one could give two hypotheses about the origin or development of the fossil assemblage. The first interpretation is, that the angiosperm leaf taxa (excluding Ginkgo) could be interpreted as a more or less complete fossil leaf assemblage of a distinct vegetation type, a Trigonobalanopsis-Lauraceae community, which grew nearby the river. Then, the taphocoenoses of the carpoflora could be understood as a mixture of remnants of different vegetation types of the surrounding area, originated by different transportation processes. In contrast with this interpretation one could conclude, that this is a typical taphocoenoses in a fluvial environment under warm-temperate to subtropical und humid climatic conditions. The leaves of angiosperms are the remnants of a diverse Mixed Mesophytic Forest with an extreme high percentage of evergreen elements (Mai, 2000). Seen from this point of view, it has to be explained, why we can’t find other lauraceous leaves like Gordonia, Illicium, Quercus, Symplocos, Toddalia and Mastixiaceae within the assemblage.

Selected references
Mai, D.H. 2000. Die untermiozänen Floren aus der Spremberger Folge und dem 2. Flözhorizont in der Lausitz, Teil IV: Fundstellen und Paläobiologie. - Palaeontographica B 254 (4-6): 65 - 176.
Kunzmann, L. & Mai, D.H. (in prep.). Die Koniferen der klassischen Mastixoideen-Flora von Wiesa bei Kamenz (Sachsen, Miozän) unter besonderer Berücksichtigung der Nadelblätter. - Palaeontographica B.

The floristic assemblage from the pyroclastics rocks of the Tlustice Relict, Bolsovian, Czech Republic

Milan Libertin¹ & Jirina Daskova²
1 Vaclavske namesti 68, 115 79 Prague 1, Czech Republic
2 Academy of Sciences of the Czech Republic, Laboratory of Palaeobiology and Palaeoecology, Rozvojova 135, 165 00 Prague 6, Czech Republic

Characteristic
Stilec (Tlustice) locality (inactive opencast mine) is situated on the tectonically delimited Carboniferous area near the southern part of the central and Western Bohemian Carboniferous Basins of the Bohemian Massif. Plants are preserved in the 30-40 mm thick layer of the clayey silty tuff close to the overlying Lower Radnice Bed. Tuff very rapidly changes to the sandy porphyric tuff ("belka") 0,4-0,9 m thick. Clayey tuffit - whetstone ("brousek") 7-8 m thick overlying "belka". "Belka" and clayey siltstone yielded strange plant assemblage consisting of 6 taxa (Spencerites sp., Stylocalamites sp., Desmopteris alethopteroides, Kidstonia heracleensis, Sphenopteris flexuosisima, Corynepteris angustissima). Whetstone rocks possesses only redeposited crushed plant remains.

Methods
Each fossiliferous layer had been took away and all fossil remains were noted down on a scale 1 : 10. The area of about 20 square meters was studied up to now.

Preservation of the plants
Plant assemblage was relatively rapidly covered by volcanic ash two during volcanic eruptions. It is documented by impressions of the raindrops 150 mm over the base. Clayey siltstone representing the finest part of the pyroclastic fall yielded the richest findings of plants. Plant remains are the most abundant near the base and only standing stems of Stylocalamites shoot the upper parts. Plants are often preserved-fossilised in their original position, including fronds of ferns. The whole plants including their fertile parts are often preserved in volcanic rocks. The plant assemblage is characterised by the occurrence of autochtonous herbaceous and pseudo-herbaceous taxa. The direction of the deposition is observed only at the highest (1-1,5 m) genus Stylocalamites and can be influenced by the "domino-effect". Stems were broken in their basal parts (the first third) or close to the connection with strobili (Palaeostachya feistmantelii). Foliated sterile zones of pseudo-herbaceous lycopod Spencerites were broken near the point of the branching 100 - 150 mm above the base). Other plant remains belong to the coenopterid ferns with creeping phylophors. Some orientation is seen only on phylophors climbing on the Stylocalamites plants. Large megaphyllous leaves are distorted by the compression pressure from top-down.

Financial support: GACR - GA205/02/1121, MSM 113100006

Taphonomic biasses of co-occurring diaspores and palynomorphs - an example from a Late Miocene deposit in Austria

Barbara Meller & Christa-Charlotte Hofmann

Institute of Palaeontology, University of Vienna, Geocenter, Althanstraße 14, A - 1090 Vienna, Austria.
e-mail: barbara.meller@univie.ac.at, christa.hofmann@univie.ac.at

A clay pit near Fehring, at the SE margin of the Eastern Styrian Basin in Austria offers an excellent outcrop of Late Miocene sediments of the Pannonian Basin system to investigate the fauna and flora and facies development. A combined methodology comprising palynology and carpology, as well as sedimentary and organic facies analysis was used at an about 30m long profile for the reconstruction of the depositional environments and vegetation types.

All assemblages occur in different litho- and organic facies throughout the lacustrine to lacustrine-deltaic succession. The results contribute greatly to the floristic content and vegetation ecology, but also discuss the different taphonomic biases (pollination and diaspore dispersal mechanisms, hydrodynamic behaviour, preservation potential) of the diaspore and palynomorph assemblages. Together with this taphonomic background, the limits of a single palaeobotanical discipline (e.g. only palynology or only carpology) for a subsequent reconstruction of habitats and vegetation types are demonstrated.

The comparison of the general floristic compositions of diaspore and palynomorph assemblages reveals differences (e.g.):

- The aquatic- und lakeshore vegetation and freshwater marshes are altogether represented by 20 diaspore and only 6 pollen and spore taxa and shows clearly, that pure palynology gives a very incomplete picture of such vegetation types.

- No Pinaceae and fern megaspores are documented in the diaspore record, but occur frequently and abundantly in the palynomorph record.

- Numerous taxa originating from mesophytic and wetland forests (Carya, Castanea/ Lithocarpus, Trigonobalanopsis, Engelhardia, Pterocarya, Quercus, and Styracaceae) are preserved in the pollen record and are lacking in the diaspore record, despite their general good preservation potential (mostly woody).

The investigations are supported by P13742 and P13739

Perispore: an overlooked feature in pteridophyte reproductive biology

Susannah Moore

School of Earth, Ocean and Planetary Sciences, Cardiff University, PO Box 914, Park Place, Cardiff CF10 3YE, Wales UK, e-mail: MooreS@cf.ac.uk

Most spores of the pteridophyta are surrounded by an outer layer, called the perispore, whose chemistry, development function and evolution is largely unknown. Whereas spores of genera such as Equisetum, Azolla, Salvinia, Pilularia, Marsilea and Regnellidium are characterized by an epispore, the megaspores of the heterosporous genera Selaginella and Isoetes form a unique siliceous outer exospore. One of the first questions to be addressed is if perispore, epispore and outer exospore are homologous features.

The overall aim of the project is to gather more information on the chemistry of perispore by different analytical methods, the evolutionary origin of this layer, its probable functions and the way it develops.

Whetstone Horizon - the westphalian fossiliferous tuff layer from the continental basins of central and western Bohemia, Czech Republic

Opluštil¹, S., Pšenicka², J., Bek³, J., Libertín⁴, M., Dašková⁵ J., Drábková⁶, J., & Šimunek⁷, Z.

1 Department of Geology and Palaeontology, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic, e-mail: oplustil@mail.natur.cuni.cz
2 Department of Palaeontology, West Bohemian Museum in Pilsen, Kopeckého sady 2, 301 36 Pilsen, Czech Republic, e-mail: Jpsenicka@zcm.cz
3 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 00 Prague 6, Czech Republic, e-mail: mrbean@gli.cas.cz
4 National Museum, Prague, Václavské Námestí 1, 110 00 Prague 1, Czech Republic, e-mail: milan.libertin@nm.cz
5 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 00 Prague 6, Czech Republic, e-mail: daskova@gli.cas.cz
6 Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech Republic, e-mail: drabkova@cgu.cz
7 Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech Republic, e-mail: simunek@cgu.cz

The Late Carboniferous fossiliferous tuff layers are known only from several, mostly continental coal basins of Europe. Those which preserve in situ buried plants provide direct insight into the structure of original phytocoenosis and its species composition. In the Czech Republic, the fossiliferous tuffs are quite common in the Late Palaeozoic continental basins of central and western Bohemia. Most of them are related to coal seams thus providing information of wetland plant assemblages of mixed to peat substrates. Among them, the well known and most important is the Whetstone Horizon (lower Bolsovian) in the roof of the Lower Radnice Seam, Radnice Member. This horizon is irregularly distributed following the former depocentre of the Radnice Member, which consists of dendritic system of narrow river valleys incised into the pre-Carboniferous basement.

In its typical development, the Whetstone Horizon consists of about 50 cm thick layer of pale yellow, massive vitrocrystallic fine sand-grained tuff (called „belka“ by miners) followed by several metres thick layer of grey bedded and locally laminated tuffitic mudstone (called „brousek“ or „whetstone“) in which the content of pyroclastic material decreases upward. Belka contains in situ buried coal-forming assemblage preserved often as large fragments or nearly complete aerial parts of plants either in upright or sub-horizontal to horizontal positions. In the upper part of the tuff, there are two horizons with raindrop imprints. Whetstone contains either standing trunks continuing from the underlying tuff into various levels of the horizon, maximally to the height of 6 m. Plant compressions are quite rare, being either scattered or concentrated into particular bedding planes. Most of these remains are only small fragments and taphonomical studies indicate their allochtonous origin. Upper part of whetstone contains frequent insect, fish and amphibian trace fossils. The Upper Radnice Seam overlies the Whetstone Horizon.

Detailed study of the Whetstone Horizon revealed that belka is a rhyolitic tuff generated by volcanic ash fall of at least three phases of volcanic eruptions. Compaction of peat changed the former mire into a shallow lake gradually filled by redeposited volcanic ash washed from adjacent slopes of basement topography. As the compaction potential of peat layer diminished, lake gradually shallowed and changed into the mire of the Upper Radnice Seam.

Increasing thickness of the basal tuff layer to the north indicates the hypothetical location of volcanic centre to the area between Eger River and central part of the Erzgebirge Mountains. Since the distance of volcanic centre from the central and western Bohemia varies between 50 and 80 km, the "pressure effect" related to volcanic eruption was probably very low if any. It is indicated also by the results of several excavations at two localities at which small plants often occur in upright position. Preferential orientation at these localities is probably a product of domino-like effect of falling trees since it differs between localities. New method for palaeoecological research of fossiliferous tuffs was developed.

This research is a part of the grant project 205/02/1121 supported by the Grant Agency of the Czech Republic.

In situ peat-forming forest from the tuff bed of the Whetstone Horizon from Czech Republic (Bolsovian, Upper Carboniferous)

Pšenicka¹, J., Opluštil², S., Bek³, J., Libertín⁴, M., Dašková⁵ J., Drábková⁶, J., & Šimunek⁷, Z.

1 Department of Palaeontology, West Bohemian Museum, Kopeckého sady 2, 301 36 Pilsen, Czech Republic, e-mail: psenda.paleobot@iol.cz
2 Department of Geology and Palaeontology, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic
3 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 00 Prague 6, Czech Republic
4 National Museum, Prague, Václavské Námestí 1, 110 00 Prague 1, Czech Republic
5 Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 00 Prague 6, Czech Republic
6 Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech Republic
7 Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech Republic

Taphonomy plays an important role in the determination of original biocoenosis. Many previous works have mentioned the importance of tuffs where an association of fossil plants is preserved in situ and thus corresponds with original phytocoenosis. Based on this fact, the Charles University in Prague, the West Bohemian Museum in Pilsen, the National Museum in Prague and the Czech Geological Survey have started research on the fossiliferous tuff beds in the Czech Republic. We would like to present preliminary results of the study of a fossil plant assemblage buried in the volcanic ash bed of the Whetstone Horizon, at the abandoned opencast mine Ovcin in the Radnice Basin. This horizon overlies the roof of the Lower Radnice Coal that belongs to the Radnice Member, Kladno Formation (Bolsovian). Consequently, the flora preserved in this tuff represents a peat-forming assemblage. In several excavations of total area c. 100 m² we recognised about 25 biological species belonging to lycopsids, sphenopsids, ferns, pteridosperms and cordaites. Lycopsids, sphenopsids and ferns show approximately 80 per cent of all fossil plants, pteridosperms and cordaites comprise the remaining 20 per cent. The assemblage at this locality can be characterised as a well-diversified lycophyte-tree dominated forest, which is structured into the following storeys: arborescent storey, l ow-tree storey, shrubby storey and understorey.

The arborescent storey is composed of Lepidodendron simile Kidston, L. selaginoides Sternberg and Lepidofloyos acerosus Sternberg the height of which varied between 10 and 20 m. Nevertheless, it is impossible to define exactly the height of these species since only lower parts of trunks in upright position or fallen trunks of several metres length were found. The spatial distribution of trees varies usually between 2 and 5 m and the diameter of the tree casts is 5 to 25 cm. Cordaites borassifolius (Sternberg) Unger probably belongs to the arborescent storey, too. This species is represented by branches with leaflets, trunks and reproductive organs (Cordaianthus). The low-tree storey comprises arborescent plants, the height of which reached around 5 m. The dominant elements of this storey are Psaronius and Calamites sp. A. The Psaronius sp. trunks were associated with fern fronds of the Pecopteris aspidioides-type.

The shrubby storey is represented by plants ranging from 1 to 3 m in height. This horizon consists of Spencerites havlenae n. sp. (lycophyta), Sphenopteris mixta, Sphenopteris sp., (both pteridosperms) and Calamites sp. B (Sphenophyta). Regarding its height we found almost complete plants. The most species-diversified part of the phytocoenoses was the understorey, the density of which varied from place to place. The plants of this storey are preserved in the basal 50 mm of the tuff bed just above the roof of the Lower Radnice Coal. Dominant elements of this storey are Corynepteris angustissima (Sternberg) Nemejc (pteridophyta) and Sphenophyllum majus Bronn (sphenophyta) with co-dominant species Selaginella sp., Sphenophyllum brasense n. sp., Sphenophyllum n. sp., Sphenopteris cf. schatzlarensis, Sphenopteris sp., Hymenotheca sp., Desmopteris longifolia and Palmatopteris furcata. Lianas are represented by Selaginella sp. (lycophyta), Eusphenopteris nummularia (Gutbier) van Amerom, E. obtusiloba (Brongniart) van Amerom, Laveinopteris loshii (Brongniart) (all pteridosperms), Desmopteris longifolia (Sternberg in Göppert) Stur, Senftenbergia plumosa (Artis) Bek & Pšenicka, Oligocarpia lindsaeoides (Ettingshausen) Stur (all pteridophyta).

Based on the composition of plants, this phytocoenosis probably belongs to a climax or pre-climax succession stage of forest development. Arborescent plants formed a relatively dense forest with a rich canopy.

This project is supported by GACR (205/02/1121), Research program of (RK01P03OMG023) of the Ministry of Culture of the Czech Republic and IGSP 469.

Explosive volcanism - catastrophe or chance?

Ronny Rößler
Museum für Naturkunde Chemnitz, Theaterplatz 1, 09111 Chemnitz, Germany
E-mail: naturkundemuseum@stadt-chemnitz.de

Nothing better and more dramatically illustrates the dynamic nature of the Earth than volcanic eruptions. During the geological history they have provided special habitats but their activity also caused fatal destruction. This study aims to show some cases of volcanic influence on the preservation of plants.

The process of fossilisation depends on a whole suite of favourable conditions; only very few organisms become fossilised. Preservation caused by volcanic processes has clear advantages: plants were quickly embedded, in or very near their original habitat. Moreover, mineral solutions often resulted in excellent three-dimensional preservation showing cellular details. Because of the rapidity and intensity of the processes related to volcanigenic fossilisation I would like to claim that some of the most complete and perfectly preserved fossil assemblages are formed.

Which features characterise exceptionally preserved fossil plant assemblages?
Firstly, this might be true for fossil plant assemblages showing organ connections up to almost complete plants. Secondly, we think highly of fossil asemblages that improve our knowledge about ontogenetic stages of former plants. Third, we owe specimens that enable the recognition of the growth form of extinct plants.

Moreover, fossil remains that originated during volcanic processes show a variety of preservation types - one of them is fusain, the fossil charcoal. One the other hand there are more than 50 minerals that cause permineralisations. The colour of petrified wood is mainly determined by small amounts of iron or cobalt compounds in the silica matrix. Silicification is one of the most common and most important preservation types of fossil plants. Silicified plants are known from different geological periods, from the Devonian onwards. Since the early days of palaebotany numerous specialists have investigated the problem of the origin of permineralisations. However, there are still many unresolved questions especially with regard to the causes and processes. Only very recently we got the first evidence that the permineralisation of the Permian woods from Chemnitz was a polyphase process (Götze & Rößler, 2000). First pore filling took place, and afterwards cell walls were mineralised. Organic remains are transformed into highly carbonised carbon that was proofed to be of anthracite structure (Dietrich et al., 2000). In the permineralised trunks from Chemnitz not only silicification, but also preservation by fluorite played a noteworthy role. Beside silicified trunks there is a variety of fossiliferous cherts. We know famous chert localities around Chemnitz that have been investigated since the 18. century (Barthel et al., 2001).

Further there are combined preservation types, which arise, when plant organs were incorporated in volcanic ash (Rößler & Barthel, 1998). Surficially they look like compressions but in many cases they show three-dimensional preservation of anatomical features, like cuticles, sporangia or conducting tissue.

Another point offered by volcanic influence is the preservation possibility of extrabasinal elements or samples of habitats that are poorly represented or otherwise absent in the sedimentary record. In some cases we get nearly the first appearance of new or modern forms, as for instance conifers or cycads from the middle Carboniferous onward.

The majority of the Permian rocks in the Chemnitz area are of volcanic nature. Beside fallout deposits a noteworthy part of the erupted material was transported as pyroclastic flows, hot dense and unsorted particle systems that incorporated different plant organs and caused impressions, casts, molds and mainly permineralisations. Pyroclastic flows are often connected with so called surges, tremendous lateral blasts, those force and direction are strikingly demonstrated by the parallel alignment of toppled large trees broken off at their base. This pattern dominates among all petrified trees lying at the base of the Zeisigwald tuff horizon in Chemnitz, only in few cases trunks remained standing.

References
Barthel, M.; Rößler, R. & Weiss, H.-J. (2001). Sächsische Madensteine - Irrtümer und Fortschritte. - Geologica Saxonica, 46/47: 197-202; Dresden.
Dietrich, D.; Witke, K.; Rößler, R. & Marx, G. (2001): Raman spectroscopy on Psaronius sp.: a contribution to the understanding of the permineralization process. - Applied Surface Science, 179: 230-233; Amsterdam.
Götze, J. & Rößler, R. (2000). Kathodolumineszenz-Untersuchungen an Kieselhölzern aus dem Perm von Chemnitz. - Veröffentlichungen Museum f. Naturkunde Chemnitz, 23: 35-50; Chemnitz.
Rößler, R. & Barthel, M. (1998). Rotliegend taphocoenoses preservation favoured by rhyolitic explosive volcanism. - Freiberger Forschungsheft, C 474: 59-101; Freiberg.

Taphonomy of three leaf fragments of Ilex hibschii in a lower Oligocene "interrupted" Maar structure in the "Richter"-Phonolith Quarry of Hammerunterwiesenthal (Erzgebirge Mts., Saxony, Germany)

Harald Walther and Lutz Kunzmann
Staatliche Naturhistorische Sammlungen Dresden, Germany

In the northern environs of the Ohre Rift near the state border Germany/Czech Republic a lower Oligocene Maar structure is located in a quarry of phonolithe in the village of Hammerunterwiesenthal. Since 1982 plant remains (fossil leaves, fruits, seeds and fragments of wood) have been found from a small seam of intercalated pyroclastic rocks (coarse debris flows and turbidites). Later on the Museum of Mineralogy and Geology Dresden started a special extrication in the laminated clastics. The turbidites contain rarely leaf fragments. More than 800 samples of plant megafossils have been collected. Besides poorly preserved gastropods, insects and two skeletons of salamander Archeotriton basalticus are also present. The status of preservation of the leaf remains is impression and very rarely also compression. The determination is only possible by the morphology. The flora is dominated by species of angiosperm genera, which are well known from the Palaeogene "volcanic" floras in Central Europe. The flora belongs to the Lower Oligocene Floral Assemblage "Seifhennersdorf-Kundratice" (Kvacek & Walther, 2001), which is characterized by elements of a Mixed Mesophytic Forest e.g. Tetraclinis (1), Pinus sp., Liriodendron (1), Magnolia sp., Laurophyllum (3), Daphnogene (2), Cercidiphyllum (1), Ulmus (1), Trigonobalanopsis (1), Alnus (1), Engelhardtia (1), Craigia (1), Hydrangea (1), Acer (4), Vitis sp., Sabal sp. and div. Monocots.

Three leave remains of Ilex hibschii were found in September 2003 in the turbidites. The excellent preservation demonstrates detailed information about the leaf architecture. Never before one had an idea, what type of leaf structure characterizes the important Lower Oligocene species Ilex hibschii. The detailed characteristics of the leaf venation and the structure of the lamina demonstrate typical sclerophyllous leaves. These results are very important for palaeoclimatic and palaeoecologic research studies.

Selected references:
Kvacek, Z. et Walther, H. 2001. The Oligocene of Central Europe and the development of forest vegetation in space and time based on megafossils. - Palaeontographica, B 259: 125-148; Stuttgart.
Walther, H. 1998. Die Tertiärflora von Hammerunterwiesenthal (Freistaat Sachsen). - Abhandlungen des Staatlichen Museums für Mineralogie und Geologie Dresden, 43/44: 239-264.

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