BROCK, F.: Plant pyritization: Microbial model experiments
CHANNING, A.: Development of silica fabrics during hot spring permineralisation
COLLINSON, M.E.: Leaf cuticles, colour, chloroplasts and DNA: Planned
investigations of preservation in leaves from the Miocene of Clarkia, Idaho, USA
CRIPPS, J.A. et al.: An assessment of the environmental impact of Deccan volcanism, using palynology
(Are flood basalts damaging to your health?)
DIÉGUEZ, C. & LOPEZ-GOMEZ, J.: Fungus-plant interaction in a Thuringian
(Upper Permian) Dadoxylon sp. in the SE Iberian Ranges, Eastern Spain: Anatomical and taphonomical characteristics and
FALCON-LANG, H.: Ecology of some mid-Cretaceous polar forests, Alexander Island,
FIGUEIRAL, I. et al.: Fossil wood and charcoal in the Lower Rhine Embayment (Germany):
a progress update
FRANCIS, J.: Frozen or fried? Middle Jurassic plants from Allan Hills, Antarctica
GASTALDO, R.A.: Taphonomic implications of pollen records in transitional
HEMSLEY, A.: Rotting bryophytes, one year on!
HOFMANN, C.-C. & ZETTER, R.: Tertiary terrestrial ecosystems of Austria - reconstructed with palynomorphs and
organic facies data
JOLLEY, D.: Plant fossils and palaeocommunities in the North Atlantic Igneous
MARTÍN-CLOSAS, C.: Plant taphonomy in a Stephanian intramontane basin
MCCOBB, L.: Dishing the dirt on our ancestors: Fossilisation in archaeological
MELLER, B. & DENK, T.: Beech cupules from beach deposits and the problem of
fossil Fagus species
PHOENIX, V.: Well'ard bugs: how they survive mineralisation and how they use it
to their advantage
SIMPSON, N.: Carbon isotopic fractionation during burning: Modelling fire
dynamics experimentally in C3 and
TITCHENER, F.: Leaf feeding traces: Indicators of taphonomic threshold
(Abstracts adapted from
F. Brock, D.E.G. Briggs & R.J. Parkes
Biogeochemistry Research Centre, Dept. of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ
Plant material may be preserved as fossil charcoal, macromolecular organic remains, or as a result of the formation of authigenic minerals. Pyrite is the most frequently involved of these minerals, but the mechanics of its formation, and the timescales involved in the preservation processes, are still poorly understood. Laboratory microbial model experiments are used to decay a variety of plant material, in particular twigs, under a range of conditions such as freshwater/marine, and oxic (open)/anoxic (closed). These experiments are inoculated with sulphate-reducing bacteria which play a vital role in iron sulphide formation. Results demonstrate that iron sulphide precursors to pyrite can form rapidly within plant material (less than 12 weeks). The mineral forms on cut surfaces of plant material, usually precipitating between cell walls and at cell wall junctions, but can also coat and even partially infill cells. Such mineral formation is associated with cytoplasmic degeneration, deterioration of pit closing membranes and enlargement of pits, and flaking and pulling apart of cell walls. Observations on the experiments also show clear evidence of bacteria and bacterial activity such as films and glycocalyx. These experiments allow geochemical and morphological comparisons with pyritized plant material (in particular the Eocene London Clay) to help achieve greater understanding of the conditions under which the material was preserved, and of the taphonomic biases involved.
Margaret E Collinson1, Bill Rember3, Paul Finch2, Pim F. van Bergen4 &
Jan de Leeuw5
1. Department of Geology and 2 Centre
for Chemical Science, Royal Holloway, University of London, Egham, Surrey, TW20 0EX. 3. Department of Geology, University of Idaho, Moscow,
ID 83844-3022, USA. 4. Organic Geochemistry Group, Faculty of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht,
The Netherlands. 5. Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands
Leaves from the Miocene of Clarkia, Idaho, USA have been the subject of several studies which have suggested that they represent
a rather special case of preservation. Firstly the leaves are said to exhibit 'autumnal colours of red, brown and blackish green'
on initial splitting of the rock (Giannasi & Niklas in Smiley 1985). Secondly, extraction of
these leaves has yielded coloured solutions reported to contain a variety of relatively labile biochemical
markers (Giannasi & Niklas; Niklas & Giannasi in Smiley 1985). Thirdly, ultrastructure of organelles
(chloroplasts, mitochondria and nuclei) has been reported in TEM preparations of some leaves (Niklas et al in Smiley 1985).
Fourthly, leaves can be removed from the rock intact by short HF treatment (Rember this work). Fifthly, in 1990 the journal
Nature carried a report of ancient DNA in a Magnolia leaf from Clarkia and subsequent work reported DNA fragments from Clarkia
material of Taxodium, Metasequoia, Quercus and Cocculus (Golenberg 1991). In spite of these claims for exceptional preservation,
the state of preservation of the least labile chemical entity in the leaves, the leaf cuticle, has not been studied. Furthermore,
there has been no detailed study looking at a range of taxa from any one group of plants. Using the framework and methods established by
our earlier work (Collinson et al 1998; van Bergen et al. in press) we will study the chemistry and ultrastructure of the fossil leaf
cuticles (selected angiosperms and conifers) and compare this with that of their nearest living relatives. TEM studies of the leaves
will also enable us to ascertain the presence or absence of cellular structure or organelle ultrastructure in samples from the same
leaf specimens. Fieldwork at Clarkia in Summer 1999 has shown that leaves are represented by a variety of preservation states for which
the chemistry and ultrastructure can be compared and the fate of 'lost' components considered. Our ultimate aims are to understand
the mechanism of fossil cuticle, and hence fossil leaf, preservation and the impact of this on preservation of other leaf
components as well as on the fossil record of plants in general. References Collinson, M.E., Mšsle, B., Finch, P., Scott, A.C. &
Wilson, R. 1998. The preservation of plant cuticle in the fossil record : A chemical and microscopical investigation.
Ancient Biomolecules, 2, 251-265. Golenberg, E.M. 1991. Amplification and analysis of Miocene plant fossil DNA. Phil.
Trans. Roy. Soc. Lond., B, 333, 419-427. Smiley, C.J. (Editor) 1985. Late Cenozoic history of the Pacific Northwest.
American Association for the Advancement of Science, California Academy of Science, San Francisco, California. 417pp.
Van Bergen, P.F., Collinson, M.E. & Stankiewicz, B.A. in press. The importance of molecular palaeobotany. Acta Palaeobotanica.
Diéguez, C.1 and Lopez-Gomez, J.2
1: Museo Nacional de Ciencias Naturales, CSIC, José Gutierrez Abascal, 2. 28006 Madrid,
Spain. 2: Instituto de Geologia Economica-Depto. Estratigraf’a, CSIC-UCM, Facultad de Geologia, Universidad Complutense, 28040
The Permian sediments of the SE Iberian Ranges are well known since the last century. However, scarce well-preserved flora have been described from these sediments. This work is based on a detailed study of a singular specimen, a well-preserved trunk of 6.2 m long and 1.1 m wide, located in a siltstone bed close to the top of a fine- medium grain subarkosic sandstones in the proximity of Landete, Cuenca province. The trunk shows clear permineralization processes of silica. The anatomy of the specimen was observed after studying different transversal, radial and tangential thin sections of the secondary xylem. The traqueids of the secondary xylem show isodiametric, oval or polygonal forms. The lamellae are not well perceptible between the thick and well lignified walls. Lengthed and dark cells separated with 2 to 7 rows of traqueids are constituting the rays of the xylem. In a radial section, the terminal walls of the traqueids show bordered pits (up to 39), mono and/or biseriate in their radial, with a general big and circular lumem. The general anatomical characteristics allow us to classify the specimen as Dadoxylon sp., in the Coniferophyta Division with a single and homogeneous secondary xylem. The Araucaria brasiliana Rich (Araucariacea) could be a similar specie in the present days. From the taphonomical point of view the trunk shows that part of the intracellular content is absent and the xilema is fractioned, what could indicate a death of the trunk before falling down. The described anathomy characteristics could indicate that the action of saprofitic fungus , in the way described by Taylor and Osborn (1992), could be, among others, the cause of the above mentioned death of the trunk. The presence of the fungus could be the answer to the areas of the trunk with total absence of traqueids or areas almost empty of traqueids surrounded by cells with a clear distorted secondary walls. The burial of the trunk should be rapid if considering the good quality of preservation. Probably silicification and carbonization processes occured at the same time and later, different Alpine tectonic phases allowed the appearance of microfolds and microfractures that favoured the fluid circulation in different later phases. From the paleogeographical point of view, the sediments indicate that the trunk grew and was deposited in a floodplain crossed by braided and sporadic fluvial systems of less than 300 m wide. The important subsidence of this distensive basin at the end of the Permian allow the frequent avulsion of the systems, probably also favoured by the humid climate that corresponded to this area very close to the Ecuator at that time, and the rapid burial of the sediments, included the trunk.
Figueiral, I., Mosbrugger, V., Rowe, N. P., & Jones, T. P.
Fossil wood and charcoal preserved in the Miocene lignites of the Lower Rhine Embayment have been collected from Hambach opencast browncoal mine. The taxonomic assemblages identified can be directly correlated with the palynological and the 13C data from the surrounding matrix with implications for taphonomy, transportation and preferential preservation. Results so far include material from Garzweiler Seam (subdivided in 3 units) and Frimmersdorf Seam (subdivided in 2 units). The majority of woody remains from the Garzweiler Seam consists of gymnosperms (70%), mostly Taxodiaceae and Cupressaceae. Only 19.5% of the fragments identified belong to angiosperms. These results are not consistent with the palynological and 13C data. The results from pollen analysis show a dominance of angiosperm taxa with 31 angiosperm families identified. The carbon isotope results from macrofossils reveal a clear isotopic difference between angiosperm and gymnosperm wood. According to the mean carbon isotope values found for gymnosperms, angiosperms and the brown coal matrix the peat-forming vegetation of the Garzweiler Seam was dominated by angiosperms. Our study clearly supports the idea that, on average, angiosperm wood decays more rapidly than gymnosperm wood. This possibility is further supported by latest results for Garzweiler and Frimmersdorf Seams, where angiosperms have been well-preserved in charcoal horizons.
Alan R. Hemsley
Last year I reported on the early stages of bryophyte degredation in a year-long experiment to assess "rotability" of some bryophytes (Marchantia, Polytrichum and Bryum) and a vascular plant leaf (Osmunda regalis) under controlled conditions. This experiment has ended with some comforting, and some disturbing results. It would seem that bryophytes do have a good preservational potential and, as we might expect, long term preservation is most likely in an organic-rich substrate. However, these results make the paucity of Carboniferous bryophytes all the more perplexing!
Dept. Earth Sciences, Cardiff University, Wales. E-mail: CHANNING@CARDIFF.AC.UK
Recent field work and observation suggests that in hot spring environments the dominant process of plant silicification is void filling, on many scales, by amorphous silica particles. This process occurs rapidly, often prior to cellular decomposition and degradation, as demonstrated by both in vitro silicification and by in vivo experiments undertaken in Medusa Hot spring, Yellowstone N.P. Particle growth, sedimentation, coalescence and cementation increase the structural rigidity of inter and intra-cellular silica deposits. This faithfully replicates and fills void space within a plants organic frame and promotes three dimensional preservation. The dominance of particle supported fabrics in the earliest phases of the silicification process allows the continued circulation of hot spring fluids. Extended periods of immersion in this hot often highly alkaline environment may result in the complete removal of the organic structure of a plant. Subsequent silica influxesmay fill remaining void space producing plant pseudomorphs of apparently homogeneous silica.
Howard J. Falcon-Lang1, David J. Cantrill1 & Gary J. Nichols
1 British Antarctic Survey, High Cross, Madingley Rd,
Cambridge CB3 0ET, UK. 2 Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX
Fossil conifers are abundant in the mid-Cretaceous (Late Albian) Triton Point Member of the Pluto Glacier Formation, Fossil Bluff Group. They represent the remains of forest vegetation which grew at a palaeolatitude of 75*S; a polar environment characterised by about 10 weeks of unbroken darkness each winter. The Triton Point Member is a non-marine sedimentary wedge which comprises of braided alluvial plain and meandering coastal plain facies associations. Standing silicified trees (up to 7.5 m high and 50 cm diameter) occur at more than 17 stratigraphic intervals, where they are found rooted in thin carbonaceous mudstones interpreted as immature podzolic soils and emtombed by coarse-grained sandstone units interpreted as flood-deposits. Drifted silicified logs and foliage are found in coarse-grained channelised sandstone units interpreted as major river channel deposits and in laminated siltstone units interpreted as floodplain lake deposits. Analysis of wood taxonomy in the braided alluvial plain association shows that this environment was colonised podocarpaceous (97% Podocarpoxylon) and taxodiaceous (3% Taxodioxylon) conifers (N=42). In contrast, the coastal plain association characterised by meandering channel geometries supported forests comprising of araucariaceous (4% Araucarioxylon and 31% Araucariopitys) and podocarpaceous (65% Podocarpoxylon) conifers (N=26). This conifer diversity and environmental distribution is also reflected in the foliage fossil record which includes Araucaria, Araucarites, Podocarpites, Arthrotaxites, Podozamites, Elatocladus, Pagiophyllum and Brachyphyllum. Stump diameter and distribution measurements on several exposed bedding surfaces show that trees were up to 29 m high, of low spatial density and irregularly scattered; reminiscent of broken woodlands with large canopy gaps rather than thick forests (420 trees.h-1). Analysis of growth rings in the silicified woods show that trees on the braidplain were ecological stressed and subject to frequent flood events which perturbed growth; growth rings in these trees have a mean sensitivity of 0.404 (N=1330). Trees growing in the coastal plain environment exhibit much more uniform growth patterns however; growth ring sequences have a mean sensitivity of 0.276 (N=318). Analysis of growth rings, leaf traces and leaves demonstrate that the podocarpaceous and araucariaceous conifers were evergreen with long leaf rentention times (>4 years) whilst taxodiaceous conifers were deciduous. Traumatic parenchyma, fraas-filled chambers and fungal patch rots in the latewood of many wood specimens show that trees were particularly suspectible to arthropod and fungal attack during the long dark winter months. In this presentation, these geologic data are synthesised with the results of climatic and ecological models to provide an overview of southern polar vegetation in mid-Cretaceous times.
David W. Jolley
Centre for Palynology University of Sheffield Dainton Building Brook Hill Sheffield S3 7HF
Within the lava fields of the North Atlantic Igneous Province (NAIP), both plant macrofossils and palynomorphs occur commonly. Some examples are well known, e.g. Ardtun leaf bed of Mull, but recent fieldwork and examination of hydrocarbon exploration boreholes has yielded a far more extensive data set that provides an insight into the modes of preservation of the plant material and the environments plants colonised. Leaf macrofossils are recorded from east Greenland, the Faeroe Islands, Mull, Skye, Rum and Antrim providing a rich dataset over the late Palaeocene to early Eocene. Woody macrofossils are less well known and often undescribed, but they form the greatest fraction of the plant macrofossil material preserved within the NAIP. While petrifaction fossils occur, lava moulds and casts of woody material are common, as are rootlet structures in palaeosols. Together with the palynomorphs preserved in the boles beneath flows, these help to give a picture of the forest vegetation of the NAIP during erruption. A series of palynological and macrofossil assemblages from Skye and Mull are used as examples of the variation in taphonomic processes present. In particular, the variation in sedimentary facies and composition of the associated floras help us to understand the structure of the vegetation and the mode of emplacement of the enveloping lavas.
Martín-Closas Carles* and Galtier Jean**
* Departament d´Estratigrafia i Paleontologia, Facultat de Geologia, 08071 Barcelona, Catalonia,
Spain. ** Laboratoire de Paléobotanique. Institut des Sciences de l´Evolution. UMR 5554 CNRS, Université de Montpellier II,
Place E. Bataillon, 34095 Montpellier Cedex, France
Graissessac Basin is a small intramontane basin located in the southern margin of the Montagne Noire Massif (Languedoc, France). The basin is oriented East to West, bordered to the South by a major late Hercinian listric fault. During Stephanian a fluvio-palustrine sedimentation occurred within the basin following a main drainage axis oriented West to East. Fluvial sedimentation dominated in the western part of the basin whereas a significant development of palustrine coal seams occurred in the eastern part, close to the northern margin. A preliminary taphonomical study of this area allowed us to recognise five main plant taphofacies, which developed linked to particular depositional environments: (1) Large allochthonous trunks and eroded woody plant remains occur as lag deposits in the base of large tabular hectometric sandy to gravelly bodies attributed to first order braided channels. (2) Autochthonous lycophyte remains in coal seams. Coal seams are 2-4 m thick and usually develop on first order abandoned channels. They are attributed to permanent wooded marshes. When identifiable macroscopically, plant remains forming coal seams belong to compressed Sigillaria logs which are several metres long. Underground Stigmaria systems habe been found immediately beneath the coal and tridimensionally preserved erect stumps of Sigillaria (Syringodendron state) occur in roof-shales. Rarely, these remains are associated to rootlets and logs of Psaronius. In contrast to North American Stephanian swamps, South European swamps appear to be dominated by sigillarian lycopsids whereas ferns and pteridosperms are subsidiary constituents. (3) Parautochthonous fronds of ferns (Pecopteris, Sphenopteris) and pteridosperms (Odontopteris, Dicksonites, Callipteridium) are found in even laminated black silts, or silts with ripple marks, intercalated with shales. This facies is attributed to a permanently inundated flood plain. Flood-plain facies present a diverse assemblage of fronds, which may be large and well preserved but are not associated to large stems or rootlets. This is thought to indicate parautochthony. A proximal flood plain is distinguished from a distal flood plain by the higher content of the latter in shales and its higher abundance in plant remains. This appears to indicate that the source area of fronds is located outside the flood plain. (4) Autochthonous and parautochthonous remains of sphenophytes including Calamites, Calamostachys, Annularia, Asterophyllites and Sphenophyllum occur in proximal flood plain facies, separately from the more frequent taphofacies of parautochthonous fronds. Erect, autochthonous stems of Calamites are preserved in sand dunes isolated within flood plain silts and shales indicating autochthony and preference of these sphenophytes for sandy well-drained substrates. (5) Allochthonous monotypic assemblage of Cordaites leaves. Cross-bedded, fine sands forming up to 100 m laterally continuous bodies are found interbedded in flood plain silts and shales. They are attributed to second order channels connecting the plain with first order channels. The monotypic nature of plant remains may indicate selection by floating.
Lucy M. E. McCobb
Department of Earth Sciences, University of Bristol, Queen's Road, Bristol BS8 1RJ
Archaeological fossils are a valuable source of information about fossilisation processes in terrestrial environments, revealing the early effects of the diagenetic processes which ultimately shape the ancient fossil record. Biological remains and sediments from ancient cess pits in York have been investigated. The fossils recovered include bones, and mineralised and organic arthropod remains and seeds. Mineralised fossils are replaced by calcium phosphate and are often preserved within faecal concretions. Generally only soft tissues, such as fly pupae and seed embryos, are preserved in this way. The fossil seeds show a high level of structural preservation under SEM, retaining cell walls in the endosperm and cotyledon tissues, and possibly nutrient bodies within the cotyledons. The closed conditions required for phosphatisation may have developed through daily addition of organic matter to the pits or, on a localised scale, within seed coats. Ion concentrations in the phosphatised fossils suggest that iron-reduction and manganese-reduction were important microbial metabolic pathways involved in their decay. Non-mineralised organic remains are represented principally by seed coats and arthropod cuticles, which show a high level of morphological preservation under SEM. Py-GC/MS (flash pyrolysis-gas chromatography/mass spectrometry) reveals that the bulk of the plant remains comprise well-preserved organic material, exemplified by blackberry (Rubus fruticosus) seed coats which retain a near-pristine ligno-cellulose composition. Pyrolysis of crab apple (Malus sylvestris) and corncockle (Agrostemma githago) seed coats reveals a similarly high level of preservation, although these seed coats do not have a typical dicotyledon lignin/cellulose composition. The crab apple seed coat pyrolysate is dominated by phenol, 4-ethylphenol and 1, 2-benzenediol (catechol), which are typically rare in angiosperm lignin, and which are attributed to non-hydrolysable tannins. Corncockle seed coats also yielded an unusual pyrolysate, in which typical lignin products are not very abundant. Instead, the pyrolysate is dominated by polysaccharide products and by phenol, 4-methylphenol, catechol and 2-methylphenol, compounds which may be derived from tannins and/or from amino acids. Further research in this area will investigate the taphonomic biases associated with the preservation of seeds in cess pits and other archaeological deposits. In addition, it will highlight the range of variation of seed coats from a typical lignin-cellulose composition and the impact this has on preservation potential.
Barbara Meller, Vienna and Thomas Denk, Stockholm
Most of the Fagus cupules from Oligocene to Pliocene localities in Europe
have been assigned to Fagus deucalionis Unger 1847 and Fagus decurrens Reid & Reid 1915. Both fossil
species are assumed to be related to the extant European Fagus sylvatica L., the
North American/Mexican Fagus grandifolia Ehrl., and to the Japanese Fagus crenata Blume.
Unambiguous identification of fossil Fagus cupules at the specific level, however, is often hampered by a)
the lack of clearly defined diagnostic features (Reid & Reid did not even mention Fagus deucalionis in their
original paper on Fagus decurrens), b) different states of preservation, such as impressions, casts, or coalified
material (coalified material extracted by washing and sieving might be more likely to exhibit shorter (ie broken?)
peduncles than material obtained by splitting the sediment, as is the case, for example, for the type material of
Fagus deucalionis Unger from Pocerny), c) the change and/or loss of specific features during taphonomic processes.
In addition, based on the high intra-specific variability and the considerable evidence of morphological paralellism
found in extant species of Fagus, high variability might be expected also for fossil beech species. Taphonomic field
observations of Fagus sylvatica bring to light some interesting facts: - Dimensions of cupules found in modern beach
deposits near Poti, on the Black Sea, are extremely variable. This could be due either to a lack of selection for particular
cupule sizes during transportation and thus the cupules could have originated from one stand yielding both small and large cupules,
or to the fact that they come from several stands, each characterized by a different cupule size (e.g., lowland versus mountainous stands). As dry cupules can float for a long time, long-distance transport has to be considered. - Transported cupules display different stages of degradation expressed by different cupule ornamentations. This might be due to different durations of transport and supports the assumption of more than one Ňsource-areasÓ. Interestingly, these different stages of degradation result in some of the diagnostic features of fossil Fagus ÓspeciesÓ. - Larger cupules tend to exhibit longer peduncles and thicker valves than smaller cupules. Therefore, we assume the chance of loosing the peduncle to increase with the duration of the transport. Based on these observations, the reliability of Fagus deucalionis, Fagus decurrens and a third cupule type, Fagus microcarpa Miki emend. Uemurae, described from the Neogene of Europe, are all open for discussion.
School of Earth Sciences, University of Leeds, Leeds, LS2 9JT
The biomineralisation of microorganisms is commonplace in many hot spring environments, and is also believed to have occurred on bacteria inhabiting the Precambrian oceans. A key question is whether bacteria can survive this mineralisation process, and how they may then interact with their mineral coating. By analysing rates of photosynthesis of laboratory silicified cyanobacteria we show that the microorganism may still function with a mineral coating. This is confirmed by TEM and autofluorescence analysis. The key to surviving mineralisation appears to ally with the production of an extracellular polysaccharide coating, known as the sheath (oo-err missus). It is evident that this sheath may act as an alternative mineral nucleation site preventing mineralisation of 'metabolically sensitive' components of the microbe such as the cell wall and cytoplasm. Analysis of the sheaths electrostatic characteristic and permeability using an Fe-cored protein (PCF), clearly demonstrates that the sheath may provide an alternative nucleation site. Furthermore the sheath may behave as a filter, preventing colloidal silica (a key component of silica biomineralisation) from reaching the cell wall and cytoplasm. Once mineralised the mineral coating may act as a shield against UV radiation and high intensity sunlight, a characteristic beneficial to both modern and ancient microbes. Detailed examination of silica stromatolites from the Krisuvik hot spring in Iceland reveals biomineralisation also plays a key role in the binding and integral strength of a stromatolitic community.
Dept of Earth Sciences, Open University
The physical and chemical behaviour of burning biomass during a fire is dependent on factors such as fire temperature, fire duration, surface area to volume ratio of the plant material, vegetation density and oxygen availability. Savanna fires act on relatively sparse vegetation with comparatively large surface area to volume ratio and are among the hottest conflagrations known (some reaching > 800űC). High-temperature burning with few restrictions on oxygen availability leads to rapid ash formation. Savannas can be dominated by C4 grasses, and studies of processes occurring on savannas environment could indicate processes likely to preserve C4 plants. The organs of maize and wheat were charred under laboratory conditions under conditions open to oxygen and restricted conditions. The d13C of mildly charred material (brown in colour) and blackened material remained similar to the original carbon isotopic composition of the plant organs. Hence, singed and blackened semi-fusainised grass fossils should retain a C4 isotopic signature. SEM observations of brown and black charred maize organs showed that detailed cellular anatomy was retained, thus it should be possible to detect Kranz anatomy in fossil grass charcoal. However, isotopic fractionation became noticeable after the transition between black charcoal and ash. Ash with < 5% carbon could be enriched in 13C by up to 4ä following a Rayleigh pattern. Rayleigh fractionation occurred more rapidly at ashing temperatures (550-650űC over one hour of charring, and > 280űC if charring duration was not limited), in organs with large surface to volume ratios, such as leaves, and when plant organs were open to oxygen. Fractionation in maize cobs heated at 350űC for 72 hours showed a different type of fractionation during ashing, following a linear pattern. This is probably an effect of fire chemistry. SEM studies and laboratory observations showed that fractionated, ashed material was friable and failed to retain the original structure of the plant organs. Thus, fractionated, ashed plant organs would neither retain Kranz anatomy, nor be preserved in the plant fossil record.
(Abstracts adapted from
J.A. Cripps, M. Widdowson, R.A. Spicer
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
Abstract The environmental impact of CFB volcanism across K-T boundary in India is being assessed. If Deccan volcanism played a role in the global demise of a range of organisms then evidence should be present from fossils within contemporary regional sediments. A study of Indian floral recolonisation, during periods of volcanic quiescence, is in progress.
Environmental disturbance, induced by eruptions, should be reflected in a succession of plant communities. Resulting community compositions and dynamics can be appraised through studies of pollen and spore (palynomorph) assemblages. Palynomorphs are being found in sediments between successive lava flows, known as “intertrappeans”. So far, palynological samples have been extracted from sediments bounded by basalts representing early, middle and late phases of volcanism. Preliminary findings indicate that angiosperms, pteridophytes and fungi occupied regions in the Deccan throughout the volcanic period. Palaeontological studies point to similar groups inhabiting large areas, preferring river floodplain or lakeside habitats. From palynological, palaeontological and sedimentary evidence, it is concluded a number of water bodies formed in depressions, particularly around the edges of the Deccan, away from the region of principal uplift and volcanism in the West. Such palustrine ecosystems may have been buffered from negative environmental effects resulting from ongoing volcanism.
Christa-Charlotte Hofmann & Reinhard Zetter
During the Tertiary, Alpine geodynamic processes constantly created new spaces for the development of terrestrial ecosystems.
These are now preserved in clastic sediments cropping out in relatively small-scale intra-montane and molasse basins. These sediments are typically associated with either coal-bearing strata or, to a lesser extent, oil shale-bearing lacustrine series. Organic facies, palynological and sedimentological data obtained from different basins fills of the Eastern Alps have been used to reconstruct the palaeo-habitats. In combination, this information gives an insight into how terrestrial ecosystems worked and how both plant diversity/productivity and the preservation potential of plant derived organic carbon in coal-bearing/oil shale strata was controlled. Case studies from different time slices (Upper Palaeocene to Upper Miocene) were chosen from which a few simple relationships emerged. Although the biohabitats reconstructed mostly have a lowland wetland character, the palynofloras represent both azonal and zonal habitats. Plant diversity in wetlands was controlled by edaphics and hydrology with long hydroperiods and poor soil conditions leading to a decrease in diversity and vice versa. High bio-diversity was characteristic of transitional and zonal vegetations (better drained and more nutritous soils) and may have led to a high net primary production of biomass, but this does not necessarily mean that lots of plant derived organic matter has been preserved in the sediments (except soil humus). In wetlands, vegetation was less diverse and primary production was probably not as high, but carbon storage within the sediments was enhanced by prolonged hydroperiods and consequent oxygen depletion. Thus in these environments, there appears to be an inverse relationship between biomass production and preservation.