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Charcoal in the Early Devonian: A wildfire-derived Konservat–Lagerstätte
Abstract
Anatomically preserved Earliest Devonian plant mesofossils from a stream section in the Welsh Borderland are quantitatively demonstrated to be charcoal, and are the pyrolysis products of ancient wildfires. These wildfire events preserved a diversity of plants and a level of anatomical detail that is unrivalled by other Lochkovian localities, and as a result have provided important insights into the early evolution of land plants. This diverse assemblage, which displays exceptional preservation of volatile non-mineralised tissues, is an example of instantaneous fossilization and the locality is proposed as a Konservat–Lagerstätte. It is the first record of a wildfire-derived Lagerstätte and as such, expands the diversity of recognized conservation traps.
... WORLDWIDE, charcoal accumulations are recorded in the sediments from the late Silurian and early Devonian sediments [1][2][3] to recent lake sediments [4][5][6][7] . In India, the fossil charcoal is reported from the subsurface sediments of middle to late Permian Raniganj Formation in the south Karanpura coal fields 8 . ...
... GLOBALLY, the oldest wood-boring trace fossils were reported from the Carboniferous and Early Permian sediments [1][2][3][4][5][6][7] . Later, the diverse insect records matching the number of modern insect families were reported from Cretaceous and Neogene deposits of Germany 8,9 . ...
Presence of charcoal in intertrappean lake sediments associated with the Malwa Group of the Deccan trap, India is recorded. The finding provides the first evidence of palaeofire in the Indian late Cretaceous. Though previous studies have shown the presence of carbonaceous clays and coal bands in the Deccan vol- canic associated sediments, the presence of fossil char- coal in the sediments is rarely reported. The fossil charcoal was identified based on optical microscope, Scanning Electron Microscope and Pyrolysis-Gas Chromatography Mass Spectrometer (Py-GC-MS). This study indicates that charcoal is derived from burning of plants caused by forest fire during the Maastrichtian (Chron 30N).
... Yangın, çoğu kez insan kaynaklı olarak düşünülmesine rağmen aslında vejetasyon yangınının tarihi insandan çok eskiye uzanmaktadır. İlk yangın izleri Silüriyen dönemine (yaklaşık 440 milyon yıl önce) kadar gitmektedir (Glasspool et al., 2006). İlk yangın izlerine yangının ortaya çıkması için gerekli olan, yanıcı madde görevi görecek karasal bitkilerin atalarının ilk ortaya çıkışıyla rastlanmaktadır. ...
... Yangının insanlık tarihinden çok öncelerine uzanan varlığı üzerine elde edilen bulgular, onun ekosistemlerin doğal bir bileşeni olduğu konusundaki görüşü perçinlemiştir (Scott and Glasspool, 2006;Bond and Keeley, 2005;Glasspool et al., 2006;Pausas and Keeley, 2009). Geçmişte orman yangınlarının yalnızca insan ile ilişkili olduğu hâkim bir görüş iken, günümüzde yangın rejimlerini çoğu ekosistemde doğal ve antropojen faktörlerin birlikte şekillendirdiği bilinmektedir (Syphard et al., 2007;2009). ...
The aim of this project is to investigate the relative role of anthropogenic and natural drivers shaping fire regimes in Mediterranean type ecosystems of Turkey. In the study, three groups of data including climatic, topographic and anthropogenic factors were evaluated in addition to the fire data. Fire data were included satellite fire records of NASA. BIOCLIM variables were used to investigate the effect of climatic factors on fire regimes. Road net, population and demographic data, agriculture and livestock activities data were used to investigate the effect of anthropogenic factors on fire regimes. Other natural variables that were accounted on in the study based on geographic and topographic data, PET and forest structure. The data was statistically analyzed by generalized linear models analysis, and regression techniques. Our results showed that despite the intense effects of humans, natural factors are still the main drivers of fire regime in the study area Moreover, study showed that elevation from sea level also had a significant effects on fire regimes. Lastly, results also showed agricultural lands have serious potential to distort results while investigating natural fire regimes. This study is the most comprehensive study on pyrogeography in Turkey. Moreover, this thesis is also contributing to close the lack of data and information on fire regimes in the eastern Mediterranean Basin.
... Studies into the understanding of palaeowildfires-those occurring over decadal, centennial, millennial, and deep time scales-have often focused on the assessment of the driving forces behind changes in wildfire intensity, for example, climatic, atmospheric oxygen, and ecosystem fluctuations (Scott, 1989). Considerable insight has been drawn into the interactions between fire, palaeobotany and palaeoclimate throughout the early Palaeozoic (e.g., Edwards and Axe, 2004;Glasspool et al., 2004;Glasspool et al., 2006;Rimmer et al., 2015), late Palaeozoic (e.g., Nichols and Jones, 1992;Scott and Jones, 1994;Jasper et al., 2013;Benicio et al., 2019), Mesozoic (e.g., Harris, 1958;Belcher et al., 2010;Belcher and Hudspith, 2016a;Zhang et al., 2020) and into the Cenozoic (e.g., Keeley and Rundel, 2005;Zhou et al., 2014;Korasidis et al., 2016). Studies into recent sediment records have focused significantly upon the role of humans in utilising fire and modifying environments, often with insights into anthropogenic climate change and its effects (Marlon et al., 2013). ...
Charcoal geothermometry continues to offer considerable potential in the study of palaeowildfires over decadal, centennial, millennial, and deep time scales—with substantial implications for the understanding of modern wildfire intensification. Recent developments in the application of Raman spectroscopy to carbonaceous organic material have indicated its capability to potentially reconstruct the palaeocharcoal formation temperature, and equivalent palaeowildfire pyrolysis intensity. Charcoal reflectance geothermometry (which also relies upon microstructural change with thermal maturation) has also been the subject of extensive modern evaluation, with multiple studies highlighting the key influence of energy flux on the resultant charcoal microstructure. The ability to accurately quantify modern wildfire temperatures based upon novel Raman-charcoal analyses has not yet been attempted. Using Raman band width-ratios (i.e., FWHMRa) and accompanying geothermometric trends to natural wildfire charcoals, our results identify differences between microstructurally-derived fire temperatures compared to those recorded during the fire event itself. Subsequent assessments of wildfire energy flux over time indicate no dominant influence for the observed differences, due to the inherent complexity of natural fire systems. Further analysis within this study, regarding the influence of reference pyrolysis methodology on microstructural change, also highlights the difficulty of creating accurate post-fire temperature reconstructions. The application of Raman spectroscopy, however, to the quantification of relative changes in fire temperature continues to prove effective and insightful.
... Latest Silurian fire was documented first from Ludford Lane, Welsh Borders (Glasspool et al., 2004;Fig. 3 Glasspool et al., 2006) charcoal exists in the Welsh Borders, and these and more regional data are herein confirmed ( Fig. 3; see the Supplemental Material discussion). Our Rumney and Winnica data add to this record, pushing the fire threshold back to at least the early Wenlock (ca. ...
The earliest evidence of wildfire is documented from two localities: the early mid-Silurian Pen-y-lan Mudstone, Rumney, Wales (UK), and the late Silurian Winnica Formation, Winnica, Poland. Nematophytes dominate both charcoal assemblages. Reflectance data indicate low-temperature fires with localized intense conditions. Fire temperatures are greater in the older and less evolved assemblage. These charcoal assemblages and others, new and previously documented, from the Silurian and earliest Devonian are compared to box models of atmospheric oxygen concentration (pO2). Based on modern charring experiments, these data indicate pO2 is divergent from the broad trends predicted by the COPSE-revisited and GEOCARBSULFOR models. Sustained burns require a minimum pO2 threshold of 16%, or ~0.75 present atmospheric level. This threshold was first met and, our charcoal data indicate, was exceeded in the mid-Silurian and then, later in the Silurian, attained again repeatedly.
... Naturally ignited wildfires are a major driver of forest ecosystem disturbance that are reported in the paleoecological record as fossilized charcoal and pollen since the Devonian era (Glasspool et al., 2006;Scott, 2000). Forest fires are responsible for tree mortality, combustion of organic matter horizon (OM) on the forest floor, loss of mineral soil where high intensity convection and erosion transport particles, and stimulation of nutrient transformations (Agee, 1993;Bormann et al., 2008;DeLuca and Sala, 2006). ...
... The Podolian material is perfectly three dimensionally preserved. Glasspool et al. (2006) emphasised the important role of wildfires in exceptional preservations of delicate plant tissue. However there are two possibilities for the formation of fossil charcoal: plants could have been either burned before fossilization or heated during metamorphism. ...
Among the diverse and numerous organic macerals collected from the Lower Devonian of Podolia are several specimens classified as fragmentary nematophytalean remains belonging to Nematasketum spp. One homogenised specimen with distinctive, possibly parasitic, borings and well preserved fragments of associated tubes remain undetermined. All the remaining specimens are represented by more or less curved tubes with different external and internal ornamentation (Laevitubulus or Porcatitubulus). The analysed material is preserved as three-dimensional charcoal (pyrofusinite) with remarkable cellular preservation. The internal construction of the individual tubes is not visible in all specimens. The coexistence of Nematasketum spp., with the dispersed phytodebris (resembling banded tubes), and similarity of their skeletal elements suggests possible relationship between those two groups. The presence of unrelated organic remains within the Nematasketum sp. tissues suggests a parasitic or saprotrophic nature of some nematophytes, as is the case in some terrestrial fungi. Natural combustion before sedimentation is confirmed by vitrinite reflectance, the frequent presence of the framboid pyrite crystals, as well as other characteristic features, such as homogenization of cell walls and the presence of small, crater-shaped, structures.
... In the Early Devonian early land plants were small and herbaceous, lacking both secondary tissues and macrophyllous leaves (Edwards, 1996). The reproductive strategies of these plants dictated their growth near to water courses and so their patchiness across the landscape (Algeo and Scheckler, 1998) would have meant they could not have supported extensive fires, although scattered records of charcoal do exist (e.g., Glasspool et al., 2006). The lack of any significant charcoal records in the Middle Devonian , despite the growth of the first forests at this time (Stein et al., 2007), has led to this interval being termed a "charcoal gap", the existence of which has been correlated with low levels of p(O 2 ) rather than an absence of fuel . ...
Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world.
... Lagerstätte (exceptionally preserved) grade anatomical data preserved in many charred fossil assemblages (e.g. Glasspool et al., 2006) have the potential to elucidate the nature of the vegetation burned, and particularly where reproductive structures have been charred (e.g. Axe, 2004, Friis et al., 2006) to yield important taxonomic insights not obtainable from compression fossils, especially when techniques such as X-ray micro-tomography can be applied (Friis et al., 2007). ...
Fire has been an important element of the Earth system since the Silurian Period, when vascular plants first evolved and spread on land. Our understanding of the fossil record of fire comes from a diversity of fire residues and fire signals including charcoal (both macroscopic and microscopic), soot and black carbon, polyaromatic hydrocarbons (PAHs) and evidence of fire scars in tree rings. However, it is the use of macroscopic charcoal that has proved most useful in the recognition of deep time fire activity and forms the major focus of this chapter. In identifying past fire events more detailed study of charcoal can yield a wide range of data. Other topics covered are charcoal sedimentation, the impacts of fire on run-off and erosion, and stand replacement events.
... The oldest evidence of wildfire is known from the Silurian (410 Ma) in the form of charred remains of a rhyniophytoid plant (a small leafless plant) (Glasspool et al., 2004 ). This indicates that the first land plants were capable of being ignited and providing a small amount of fuel to carry a fire (Glasspool et al., 2006). Between 395 and 360 Ma Earth's terrestrial flora evolved from small primitive plants to vegetation that included trees (Edwards, 1996; Meyer-Berthaud et al., 1999; Edwards and Richardson, 2004; Meyer-Berthaud and Decombeix, 2009). ...
This chapter reviews the 450-mllion-year history of fire, and shows how it links to the environmental and evolutionary innovations that have led to the diversity of life on our modern planet. In order for a fire to exist it requires three key elements, illustrated by the fire triangle. The fire triangle shows that fire requires an ignition source, a supply of oxygen and fuel in order that it can burn. The chapter shows how interplay between fuel and past atmospheric composition has potentially influenced broad trends in fire activity. It also shows the significance of changes in atmospheric oxygen concentrations to altering fire activity.
... Through the Early Devonian, plants became diverse and widespread in coastal and alluvial environments, building up coal-like accumulations in places (Wehrmann et al., 2005;Kennedy et al., 2012aKennedy et al., , 2013Morris et al., 2012). Charcoal is known from latest Silurian and Lower Devonian tidal and alluvial deposits (Glasspool et al., 2004(Glasspool et al., , 2006Davies and Gibling, 2010a;Glasspool and Scott, 2010), showing that sufficient biomass covered the land surface, at least locally, for wildfires to join the spectrum of terrestrial processes. ...
As vegetation evolved during the Palaeozoic Era, terrestrial landscapes were substantially transformed, especially during the ~120 million year interval from the Devonian through the Carboniferous. Early Palaeozoic river systems were of sheet-braided style – broad, shallow, sandbed rivers with non-cohesive and readily eroded banks. Under the influence of evolving roots and trees that stabilised banks and added large woody debris to channels, a range of new fluvial planform and architectural styles came to prominence, including channelled- and island-braided systems, meandering and anabranching systems, and stable muddy floodplains. River systems co-evolved with plants and animals, generating new ecospace that we infer would have promoted biological evolution. By the end of the Carboniferous, most landforms characteristic of modern fluvial systems were in existence.
... Although crevasse splays on floodplains can contain fragments transported for some distance, wetland deposits usually show autoch- thonous or parautochthonous assemblages ( Gastaldo et al., 1987;DiMichele and Gastaldo, 2008), and this probably applies to most plant assemblages in the Campbellton Formation. Charcoalified plant fossils that preserve fine detail have been observed in earlier or coeval for- mations ( Glasspool et al., 2006;Davies and Gibling, 2010), but none were observed in the Campbellton Formation, suggesting that wildfire was still a relatively rare event. ...
The Paleozoic spread of plants, beginning in the Ordovician and reaching a phase of accelerated diversity and dispersal hi the Early Devonian, was a critical episode hi Earth history. The Lower Devonian (Emsian) Campbellton Formation represents a subtropical basin comprising coastal and fluvial-lacustrine intermontane environments. Although the formation has been recognized for a rich fossil assemblage since the mid-19th century, this is the first attempt to correlate the tracheophyte fossil record with physical attributes of the environment as inferred from the sedimentology. Marginal lacustrine beds contain a parautochthonous collection of plants interpreted as dislodged from lakeside plant stands and buried by density flows. Shallow, oxygen-depleted lakes or ponds subjected to fluctuations in water level collected a more diverse assemblage from the surrounding flooded marsh. Plants within fluvial sandstones were transported by ephemeral flows, and typically display poorer preservation. Although some plants showed adaptations to drier environments, there is little evidence of the environmental partitioning identified at contemporaneous localities between rhyniaceans, basal euphyllophytes (trimerophytes), zosterophylls, and lycopsids, all of which are here found hi nearly every identified setting. Plant occupation of basin margins or upland areas is suggested by the occurrence of plant-bearing strata within blocks transported cohesively by hyperconcentrated flows.
... Strother and Traverse, 1979;Richardson, 1985Richardson, , 1988Richardson, , 1992Strother et al., 1996;Wellman, 1996;Steemans and Wellman, 2004;Steemans et al., 2009;Rubinstein et al., 2010). Recent studies on mesofossils produced on charring of some Upper Silurian and Lower Devonian plants in the Welsh Borderland, which show excellent cellular preservation in terminal sporangia and spores (Edwards, 1996;Glasspool et al., 2004Glasspool et al., , 2006, have substantially advanced our knowledge of dyads and their producers (Morris et al., 2011a, in press;Edwards et al., 2012). These have demonstrated that, using sporangium architecture together with variation in dyad ultrastructure and their permanence, a number of clades/lineages of dyad producing plants that are separate from the trilete-bearing early tracheophytes had evolved in the Lower Devonian. ...
A small number of very fragmentary sporangia containing tetrads are described using light, scanning and transmission electron microscopy as part of a study on diversity and disparity in Lower Devonian (Lochkovian) vegetation in the Welsh Borderland. The dispersed genus for permanent sculptured tetrads, Acontotetras, is recorded in two isolated discoidal sporangia, one of which has a similar sporangial wall construction to that in Cooksonia, the other with a non-cellular covering reminiscent of the recently described Lenticula theca and Paracooksonia. Conversely, the dispersed spore genus for permanent, enveloped laevigate tetrads, Cheilotetras, is found within two sporangia with valvate construction. Another example of the latter contains unique sculptured monads. Further diversity is exemplified by spore masses containing tetrads belonging to Velatitetras and Cheilotetras, but some evidence of splitting in specimens of the latter genus led to discussion on the state of maturity of the in situ spores, and as to whether or not the dispersed palynomorphs would have been so as permanent tetrads or trilete monads. Such studies add to diversity, although a dearth of well-preserved specimens preclude erection of new taxa, and to disparity in local Early Devonian vegetation that was dominated by plants of very low stature. (C) 2012 Elsevier B.V. All rights reserved.
... Spores have been extracted from coalified compressions (e.g. Edwards and Richardson, 1974;Gensel, 1976;Fanning et al., 1988;Fanning et al., 1992), but more successfully from two assemblages of minute plants, preserved as mesofossils following charring via smouldering wildfires (Edwards and Axe, 2004;Glasspool et al., 2006), in Upper Silurian and Lower Devonian rocks of the Welsh Borderland. These have yielded terminal sporangia with exceptional cellular preservation and in situ spores (Edwards, 1996(Edwards, , 2000. ...
New data on trilete spore producers are presented from a Lower Lochkovian locality in the Welsh Borderland. U. K. Discoidal sporangia assigned to Cooksonia pertoni subsp. apiculispora illustrate further variation within the Streelispora-Aneurospora morphon. Laevigate crassitate spores belonging to Ambitisporites warringtonii were found in sporangia assigned to C. pertoni subsp. pertoni which possesses notably different sporangial wall anatomy from C. pertoni subsp. apiculispora. A separate group of discoidal sporangia is similar to C. pertoni subsp. reticulispora based on gross morphology and reticulate in situ spores, but the presence of a thick cuticular covering sets these specimens apart. After close inspection of their ultrastructure, the spores were assigned to Synorisporites, despite their resemblance to Chelinospora. New data on Cooksonia banksii include the recognition of an additional layer encasing the spore mass, which is associated with globules interpreted as Ubisch bodies. Their in situ spores are unusual, possessing distal polar thickenings, features that are rarely seen in the coeval dispersed spore record. Sections reveal that the spores possess spongy areas that coincide with these thickenings. Therefore, it is considered that C. banksii does not belong to Cooksonia and is assigned to a new genus, Concavatheca. Two spheroidal specimens contain spores with proximal 'emphanoid' muri and apiculate distal surfaces and are assigned to Iberoespora, based on their additional thickenings on the proximal surfaces. Spores similar to Emphanisporites sp. A were found within a discoidal spore mass, which is contradictory to previous studies where Emphanisporites is found within elongate sporangia. It is suggested that 'emphanoid' muri represent a convergent character. The in situ spores in Tortilicaulis are assigned to Apiculiretusispora, although they are unusual because they possess minute sculpture on both the distal and proximal surfaces, and sectioning reveals a tri-layered ultrastructure. (C) 2012 Elsevier B.V. All rights reserved.
... was established for an isotomously branched axis with a fusiform sporangium at the tip of one branch from the Lower Devonian Ditton Group (Lochkovian) near Monkhopton, Shropshire, England (Wellman et al., 1998, p. 123) and subsequently used by some authors (Edwards, 2000;Edwards and Wellman, 2001;Carrión and Cabezudo, 2003;Glasspool et al., 2006;Raymond et al., 2006;Gensel, 2008). The genus only contains one species Fusitheca fanningiae Wellman, Edwards et Axe. ...
... High atmospheric oxygen levels and high concentrations of fossil charcoal are positively correlated (Wildman et al., 2004). Charcoal has been identified from a variety of stratigraphical intervals, the oldest known being of Late Silurian (Glasspool et al., 2004) and Early Devonian age (Glasspool et al., 2006). Charcoal is common in Early Cretaceous sediments (Collinson et al., 2000;Scott, 2000;Scott and Stea, 2002), indicating a high wildfire prevalence. ...
Pedogenic nodules, calcitic shells, dispersed organic carbon and bulk rocks affected by low diagenesis are judged to be reliable tools for carbon-isotope chemostratigraphy. Up to now no systematic study has been carried out to check the reliability of fossil wood material for carbon-isotope chemostratigraphy in terrestrial settings. The 235-m thick Wealden facies sediments of the Danube-Bouchon quarry at Hautrage (Hautrage Clays Formation, Mons Basin, Belgium) encompass dark to grey clays and sands, rich in organic matter and coalified–charcoalified fragments of fossil wood, deposited in an alluvial plain during middle Barremian to earliest Aptian. We measured and compared the carbon-isotope ratios of 110 levels of the stratigraphic succession for dispersed organic carbon (δ13CDOC), and fossil wood (δ13CWOOD) collected in the same geological level. In the whole succession, the averages of δ13CDOC and δ13CWOOD have a significant difference of about 0.9‰. The δ13CWOOD is usually heavier than the δ13CDOC, which is consistent with measurements on different constituents of modern trees (branches versus leaves and tissues). In one single stratigraphic level, the variability of δ13CWOOD is much higher (up to 7.3‰) than that of δ13CDOC (0.4‰). Four main causes may explain these results. Firstly, the δ13CDOC averages the isotopic signal of different compounds and tissues (such as leaves, seeds, cuticles) as they become mixed and dispersed. The δ13CWOOD reflects the carbon-isotope ratio of a small part only of one single tree, which is a complex system with δ13C variations over a range of 4‰. Secondly, there is strong δ13C variability between different species of plants. In Hautrage, several gymnosperm genera were collected (including Podocarpoxylon, Taxodioxylon, Brachyoxylon, and Thujoxylon) and numerous fern taxa. Thirdly, coalification and charcoalification can affect the δ13C of the DOC and the various kinds of woods in a different way. Fourthly, the wood fragments may be reworked several times from more ancient geological levels, especially in the alluvial plain environment of Hautrage where thick levels of fluviatile coarse sand deposits are observed. However, in the whole succession, both δ13CWOOD and δ13CDOC curves show similar trends. This suggests that carbon-isotope curves on fossil wood can be matched to carbon-isotope curves on DOC. For the whole trend fossil wood is a relatively good chemostratigraphic tool when sufficient samples are measured in the succession. Whenever possible both control of the wood taxa, and estimation of degree of (char)coalification are however recommended. In one single level, charcoal has more stable δ13CWOOD values than δ13CWOOD of coalified fragments. The δ13C positive trend can be due to several causes, including global pCO2 variations and/or regional changes and/or local environmental conditions in the alluvial plain. If global, the dating of the Hautrage succession may be refined to the late Early Barremian–early Late Barremian by matching palynological and carbon-isotope chemostratigraphical data.
... Isotopic excursions documented in marine carbonates ( Fig. 1) are consistent with greatly increased vegetation cover at the Siluro-Devonian boundary 34 . By the Early Devonian, the presence of charcoal testifies to the earliest forest fires 35 , the first wood appeared 36 , and vegetation was sufficiently abundant to accumulate locally as peat 14 . ...
Fluvial landscapes diversified markedly over the 250 million years between the Cambrian and Pennsylvanian periods. The diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover. In the absence of widespread vegetation, landscapes during the Cambrian and Ordovican periods were dominated by rivers with wide sand-beds and aeolian tracts. During the late Silurian and Devonian periods, the appearance of vascular plants with root systems was associated with the development of channelled sand-bed rivers, meandering rivers and muddy floodplains. The widespread expansion of trees by the Early Pennsylvanian marks the appearance of narrow fixed channels, some representing anabranching systems, and braided rivers with vegetated islands. We conclude that the development of roots stabilized the banks of rivers and streams. The subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels. Our contention is supported by studies of modern fluvial systems and laboratory experiments. In turn, fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems. We suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms.
... In order to be able to compare the anatomy of extant lichens with that of the fossils, which are presumed to be charcoalified (Edwards & Axe, 2004;Glasspool et al., 2006), extant cyanobacterial lichens with Nostoc photobiont (Leptogium lichenoides (L.) Zahlbr. and Peltigera canina (L.) Willd.) and free-living colonies of Nostoc commune Vaucher ex Bornet & Flahault were freshly collected in the Botanical Garden of the University of Zurich, transported to Cardiff in the desiccated state and made into charcoal within 3 d of collection. ...
Lichenization is assumed to be a very ancient mode of fungal nutrition, but fossil records are rare. Here we describe two fragments of exceptionally preserved, probably charred, lichen thalli with internal stratification. Cyanolichenomycites devonicus has a cyanobacterial and Chlorolichenomycites salopensis a unicellular, presumably green algal photobiont. Fruiting bodies are missing. Cyanolichenomycites devonicus forms asexual spores in a pycnidium. All specimens were examined with scanning electron microscopy techniques. The fossils were extracted by maceration. Extant lichens and free-living cyanobacteria were either experimentally charcoalified for comparison or conventionally prepared. Based on their septate hyphal structure, both specimens are tentatively interpreted as representatives of the Pezizomycotina (Ascomycota). Their presence in 415 million yr (Myr) old rocks from the Welsh Borderland predates existing Late Cretaceous records of pycnidial conidiomata by some 325 Myr and Triassic records of lichens with broadly similar organization by some 195 Myr. These fossils represent the oldest known record of lichens with symbionts and anatomy as typically found in morphologically advanced taxa today. The latter does not apply to Winfrenatia reticulata, the enigmatic crustose lichen fossil from the Lower Devonian, nor to presumed lichen-like organisms such as the Cambrian Farghera robusta or to the Lower Devonian Spongiophyton minutissimum.
... Fire is an important element today in a range of terrestrial ecosystems (Bowman et al., 2009) and has been since soon after the appearance of plant life on land (Glasspool et al., 2004Glasspool et al., , 2006 Scott, 2000 Scott, , 2009 Scott, , 2010 Scott and Glasspool, 2006). By the Late Devonian wildfires are increasing in frequency and distribution as oxygen levels rose (Cressler, 2001; Fairon-Demaret and Hartkopf-Fröder, 2004; Marynowski and Filipiak, 2007; Prestianni et al., 2010; Rimmer and Scott, 2006; Rowe and Jones, 2000; Scott and Glasspool, 2006). ...
Wildfires play a crucial role in recent and ancient ecosystem modeling but their detailed history on the Earth is still not well recorded or understood. The co-occurrence of charcoal and pyrolytic polycyclic aromatic hydrocarbons (PAHs) is used for the recognition of wildfires in geological record that may have implications for the analysis of the terrestrial environment, ecosystems, climate and the level of atmospheric oxygen. Here we present the first multi-proxy evidence of wildfires on the Gondwana continent during the Jurassic, based on the occurrence of charcoal and pyrolytic PAHs in the Middle Jurassic of the Neuquén Basin, Argentina. This is the first evidence of wildfire in the Aalenian, the lowest stage of the Middle Jurassic, and one of the few records of wildfires in the Bathonian. Temperature interpretations, derived from charcoal reflectance data, show that charcoals formed in low temperature surface fires that only sporadically reached the higher temperatures, possibly related to crown fires. The occurrence of charcoals in the Middle Jurassic deposits confirms recent results that the atmospheric oxygen level reached at least 15% during the Middle Jurassic times.
... Approximately 14 species have so far been described. These have been collected in North America [1,[7][8][9][10], northern Europe (UK [3,11,12], Germany [1,[13][14][15][16][17]), North Africa (Libya [18,19]), western Asia (Saudi Arabia [20,21]) and Australia [1]. Prototaxites spp. ...

The affinities of Prototaxites have been debated ever since its fossils, some attaining tree-trunk proportions, were discovered in Canadian Lower Devonian rocks in 1859. Putative assignations include conifers, red and brown algae, liver- worts and fungi (some lichenised). Detailed anatomical investigation led to the reconstruction of the type species, P. logani, as a giant sporophore (basidioma) of an agaricomycete (1⁄4 holobasidiomycete), but evidence for its reproduction remained elusive. Tissues associated with P. taiti in the Rhynie chert plus charcoalified fragments from southern Britain are investigated here to describe the reproductive characters and hence affinities of Prototaxites. Thin sections and peels (Pragian Rhynie chert, Aberdeenshire) were examined using light and confocal microscopy; Pridoli and Lochkovian charcoalified samples (Welsh Borderland) were liberated from the rock and examined with scanning electron microscopy. Prototaxites taiti possessed a superficial hymenium comprising an epihymenial layer, delicate septate paraphyses, inoperculate polysporic asci lacking croziers and a subhymenial layer composed predomi- nantly of thin-walled hyphae and occasional larger hyphae. Prototaxites taiti combines features of extant Taphrinomycotina (Neolectomycetes lacking cro- ziers) and Pezizomycotina (epihymenial layer secreted by paraphyses) but is not an ancestor of the latter. Brief consideration is given to its nutrition and potential position in the phylogeny of the Ascomycota.

... Isotopic excursions documented in marine carbonates ( Fig. 1) are consistent with greatly increased vegetation cover at the Siluro-Devonian boundary 34 . By the Early Devonian, the presence of charcoal testifies to the earliest forest fires 35 , the first wood appeared 36 , and vegetation was sufficiently abundant to accumulate locally as peat 14 . ...
... The oldest known charcoal comes from the Silurian [110]. However, wildfires did not become prominent until the appearance of forests in the Middle Devonian [111,112]. By the Carboniferous, high-biomass forests were episodically swept by fires, ultimately producing coal that contains as much as 20% charcoal by volume [99]. ...
Under conditions where buried wood is protected from microbial degradation and exposure to oxygen or harsh chemical environments, the tissues may remain unmineralized. If the original organic matter is present in relatively unaltered form, wood is considered to be mummified. Exposure to high temperatures, whether from wild fires or pyroclastic flows, may cause wood to be converted to charcoal. Coalification occurs when plant matter undergoes gradual metamorphosis, producing bituminous alteration products. Examples of all three types of non-mineralized wood are common in the geologic record. This report describes some of the most notable occurrences, reviews past research and introduces data from several localities in North America.
... In the literature fossil charcoal is also known as fusain, or as coal macerals of the inertinite group, i.e., fusinite, semifusinite and inertodetrinite (e.g., Scott, 2000;Scott and Glasspool, 2007). Due to its chemical inertness it can easily be preserved in the fossil record as it is largely resistant against chemical and biological decay (Scott 2000(Scott , 2009(Scott , 2010Friis et al., 2006;Glasspool et al., 2006). The occurrence of charcoal in sediments indicates the occurrence of past wildfires and, as fire regimes are coupled to certain climatic parameters, it is also useful in understanding some of the effects of climate change on past ecosystems (Power et al., 2008). ...
Macroscopic fossil charcoal fragments have been recovered from the borehole AK-19 (at a depth of 120.00 m) drilled at the Astona-Kothurna coal block, Wardha valley coalfield. In general, the occurrence of charcoal in sediments is accepted as a direct indicator for palaeo-wildfires. The charcoal fragments exhibits well preserved homogenized cell walls as well as anatomical details such as uniseriate and biseriate pitting patterns on tracheid walls under Field Emission Scanning Electronic Microscope (FESEM), suggesting a gymnospermous wood affinity of the studied material. The excellent preservation, their large size and almost unabraded edges of charcoal fragments suggest a par-autochthonous origin. These findings add further evidence for the widespread occurrence of such wildfires during the Early Permian not only in India, but on the entire Gondwana continent.
... The oldest known charcoal comes from the Silurian [110]. However, wildfires did not become prominent until the appearance of forests in the Middle Devonian [111,112]. By the Carboniferous, high-biomass forests were episodically swept by fires, ultimately producing coal that contains as much as 20% charcoal by volume [99]. ...
Under conditions where buried wood is protected from microbial degradation and exposure to oxygen or harsh chemical environments, the tissues may remain unmineralized. If the original organic matter is present in relatively unaltered form, wood is considered to be mummified. Exposure to high temperatures, whether from wild fires or pyroclastic flows, may cause wood to be converted to charcoal. Coalification occurs when plant matter undergoes gradual metamorphosis, producing bituminous alteration products. Examples of all three types of non-mineralized wood are common in the geologic record. This report describes some of the most notable occurrences, reviews past research and introduces data from several localities in North America.
... Ruptures may be present or absent regardless of ray width and have already been mentioned for various species in different climatic conditions and carbonization systems (McGinnes et al. 1971 The fibre walls acquired a homogeneous and amorphous appearance (vitrification) in the charcoals (e.g., Apuleia leiocarpa, Dinizia excelsa and Laetia procera), with no sign of the middle lamella, as already evidenced by previous studies (MCginnes et al. 1971;Prior & Alvin 1983;Prior & Gasson 1993;Kim & Hanna 2006;Marguerie & Hunot 2007;Kwon et al. 2009;McParland et al. 2010;Gasson et al. 2017). After carbonization, in addition to woody tissues, other tissue such as fungal hyphae can be preserved (Glasspool et al. 2006;Marguerie & Hunot 2007). The recognition of fungal hyphae in charcoal is important because the charcoal ultrastructure can become degraded (Moskal-del Hoyo et al. 2010), and thus become difficult to analyse, leading to charcoal misidentification. ...
The production of illegal charcoal, associated with other local human practices, is responsible for the degradation of native forests, especially in the Brazilian Amazon. The need for market control and charcoal production is accompanied by the lack of comparative charcoal materials from the Amazon. Here, we describe charcoal samples of 21 Brazilian species and provide SEM images that can facilitate the charcoal identification. It is possible to distinguish the species on the basis of anatomy. Features such as vessel groupings, vessel–ray pitting, perforation plates, axial parenchyma, ray cellular composition, storied structure and secretory elements were chosen as primary diagnostic features for the identification of species. We highlight vessel groupings, axial parenchyma type and in some cases even perforation plates, which were easily observed in low magnification SEM images and can assist in the supervision by government agents. From our descriptions, evaluations and photomicrographs, it will be possible to compare charcoal from commercial species from the Amazon.
... Much of this new evidence is not derived from the adpression fossils of Cooksonia that are so familiar in classic textbooks. Rather, our insights come from exquisite three-dimensional and anatomically preserved charred fossils that represent some of the earliest evidence of wildfire known on the planet (Fig. 15.14; Glasspool et al. 2006). Studied by SEM, these fossils exhibit incredible, even subcellular, anatomic details. ...
Massive changes in terrestrial paleoecology occurred during the Devonian. This period saw the evolution of both seed plants (e.g., Elkinsia and Moresnetia), fully laminate∗ leaves and wood. Wood evolved independently in different plant groups during the Middle Devonian (arborescent lycopsids, cladoxylopsids, and progymnosperms) resulting in the evolution of the tree habit at this time (Givetian, Gilboa forest, USA) and of various growth and architectural configurations. By the end of the Devonian, 30-m-tall trees were distributed worldwide. Prior to the appearance of a tree canopy habit, other early plant groups (trimerophytes) that colonized the planet’s landscapes were of smaller stature attaining heights of a few meters with a dense, three-dimensional array of thin lateral branches functioning as “leaves”. Laminate leaves, as we know them today, appeared, independently, at different times in the Devonian. In the Lower Devonian, trees were not present and plants were shrubby (e.g., Aglaophyton major), preserved in a fossilized community at the Rhynie chert locality in Scotland and other places. Many of these stem-group plants (i.e., preceding the differentiation of most modern lineages) were leafless and rootless, anchored to the substrate by rhizoids. The earliest land plant macrofossil remains date back to the Silurian, with the early Silurian Cooksonia barrandei from central Europe representing the earliest vascular plant known, to date. This plant had minute bifurcating aerial axes terminating in expanded sporangia. Dispersed microfossils (spores and phytodebris) in continental and coastal marine sediments provide the earliest evidence for land plants (= Embryophytes), which are first reported from the Early Ordovician.
... Their discovery and characterization are based on one exceptional geological site in the Welsh Borderland that dates to the early part of the Devonian Period (Lochkovian Stage, c. 410-419 Myr ago). Here, fossils are formed of charcoal, which was a product of one of the earliest incidences of wildfire in the geological record (Edwards & Axe, 2004;Glasspool et al., 2006). Although quite fragmentary, the charcoal preserves details of cellular structure with exceptionally high fidelity. ...
Key sources of information on the nature of early terrestrial ecosystems are the fossilized remains of plants and associated organic encrustations, which are interpreted as either biofilms, biological soil crusts or lichens. The hypothesis that some of these encrustations might be the remains of the thalloid gametophytes of embryophytes provided the stimulus for this investigation. Fossils preserved in charcoal were extracted from Devonian Period (Lochkovian Stage, c. 410–419 Myr old) sediments at a geological site in Shropshire (UK). Scanning electron micrographs (SEMs) of the fossils were compared with new and published SEMs of extant bryophytes and tracheophytes, respectively. One specimen was further prepared and imaged by transmission electron microscopy. Fossils of thalloid morphology were composed almost entirely of cells with labyrinthine ingrowths; these also were present in fossils of axial morphology where they were associated with putative food‐conducting cells. Comparison with modern embryophytes demonstrates that these distinctive cells are transfer cells (TCs). Our fossils provide by far the earliest geological evidence of TCs. They also show that some organic encrustations are the remains of thalloid land plants and that these are possibly part of the life cycle of a newly recognized group of plants called the eophytes.
... A transition from hair-like, millimetre-scale rhizoids to centimetre-scale roots reaching deeper into the soil took place over this time, followed by the evolution of deep-rooting trees over the Middle to Late Devonian, with each innovation occurring in parallel in multiple distinct lineages. Vascular plants thrived in coastal and riverine riparian niches and were dense enough to establish peatlands 86 and promote a primitive fire ecology 67 . Nonetheless, much of the landscape through the Devonian might have remained dominated by low-bryophyte-grade plants hugging the substrate and microbial soil crusts 87 (although there was also a substantial outlier with Prototaxites, several metres tall and most likely a fungus) 88 . ...
The Palaeozoic evolution of land plants revolutionized river geomorphology. However, the relationships between biotic forcing and channel dynamics are still debated and, as such, the impacts of anthropogenic stressors such as climate change, reduced biodiversity and aridification on modern meandering rivers and their biogeochemical fluxes remain poorly understood. In this Review, we propose a unifying framework based on field and modelling data that describes the stability and dynamics of meandering rivers in both the presence and the absence of land plants. Based on evidence from the pre-vegetation rock record and from modern systems, we emphasize that meandering streams can indeed arise in the absence of land plants. However, plant evolution provided widespread settings suitable for stable meandering systems through retention of floodplain mud, sediment baffling and mechanical strengthening of channel banks. Altogether, these processes slowed the characteristic rates of meander growth and floodplain-soil reworking by up to an order of magnitude. Continued anthropogenic removal of riparian and watershed vegetation due to increased urbanization, deforestation, aridification and pollution could revert streams to pre-vegetation functioning, thereby increasing their channel and sediment mobility. Future research can use this framework to constrain the pace of ancient landscape processes on Earth and Mars, in addition to modern terrestrial rivers impacted by humans.
... Evidence for wildfires is recorded from the Late Silurian (~420 Ma) to the present (Scott and Glasspool, 2006), and is related to the appearance of vascular plant life on land and atmospheric oxygen levels (Scott, 2000;Glasspool et al., 2004;Berner, 2006;Glasspool et al., 2006;Scott, 2009;Scott, 2010;Shao et al., 2012;Glasspool et al., 2015;Yan et al., 2019). Records of wildfire during Jurassic have been relatively scarce (Cope et al., 1993;Morgans et al., 1999;Nielsen et al., 2010;Scott, 2010;Marynowski et al., 2011;Tanner et al., 2012). ...
As an important terrestrial carbon reservoir, peatland has the potential to influence the global carbon cycle and global climate. In recent decades, the frequency and extent of peatland wildfires in boreal and tropical regions are increasing owing to climate change and human activity. However, the processes that govern changes in peatland wildfire are poorly understood over long timescales, particularly on the orbital scales. We analyzed coal petrology and geochemistry in coal seams of the Aalenian Yan'an Formation in Ordos Basin to identify peatland wildfire records based on the co-occurrence of charcoal and pyrolytic polycyclic aromatic hydrocarbons (PAHs).
In addition, the presence of widespread peatland wildfires has suggested that atmospheric oxygen concentration at the time should be substantially higher than the minimum needed for sustained combustion. Spectral analysis of vitrinite/inertinite (V/I) and inertinite reflectance data demonstrate that peatland wildfires were controlled
by precession cycles owing to a shift in the seasonal contrast and amount of rainfall. Our results provide essential context for understanding the importance of peatland wildfires carbon emissions in a coupling of orbital forcing, climate, and the carbon cycle.
... Wildfires are episodic ecological disturbances the origins of which can be traced back to the late Silurian/early Devonian period (Gibling and Davies, 2012;Glasspool et al., 2004Glasspool et al., , 2006. They are caused by either natural events (e.g., lightning) (Price and Rind, 1994;Stocks et al., 2003;Veraverbeke et al., 2017) or anthropogenic activities (e.g. ...
Wildfires are episodic disturbances that exert a significant influence on the Earth system. They emit substantial amounts of atmospheric pollutants, which can impact atmospheric chemistry/composition and the Earth’s climate at the global and regional scales. This work presents a collection of studies aimed at better estimating wildfire emissions of atmospheric pollutants, quantifying their impacts on remote ecosystems and determining the implications of 2000s-2050s global environmental change (land use/land cover, climate) for wildfire emissions following the Intergovernmental Panel on Climate Change (IPCC) A1B socioeconomic scenario.
A global fire emissions model is developed to compile global wildfire emission inventories for major atmospheric pollutants [greenhouse gases (CO2, CH4, N2O), air pollutants and tropospheric O3 precursors (nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOCs) (alkanes, alkenes)), aerosols and their precursors (particulate matter (PM2.5), black carbon (BC), organic carbon (OC), sulfur dioxide (SO2)) and mercury (Hg)] and quantify the impacts of 2000s-2050s global change. The estimated Hg wildfire emissions (2000s) are used in a global chemical transport model (GEOS-Chem) to determine the contribution of wildfire emissions to Hg pollution in the Arctic.
Significant perturbations to wildfire emissions of atmospheric pollutants in the context of global change are estimated, mainly driven by the projected changes in climate, land use/land cover and in the case of Hg, anthropogenic emissions as well. A continuing increase in anthropogenic influence on wildfires in the coming decades is predicted. Greater human occupation of the African continent and increase in cropland coverage cause significant declines in wildfire emissions of atmospheric pollutants from the continent. Anthropogenic factors play an important role in the changes in emissions from other continents as well. Future changes in climate and land cover contribute to significant increases in global emissions for all the species.
Wildfires are estimated to contribute 10% of global annual deposition to the Arctic with boreal fires in Asia contributing the most. Wildfires in Eurasia contribute 5.3% of annual Hg deposition followed by Africa (2.5%) and North America (1%). Wildfires contribute to Arctic Hg deposition throughout the year with the highest deposition occurring during the boreal fire season.
... Wildfires are episodic ecological disturbances the origins of which can be traced back to the late Silurian/early Devonian period (Gibling and Davies, 2012;Glasspool et al., 2004Glasspool et al., , 2006. They are caused by either natural events (e.g., lightning) (Price and Rind, 1994;Stocks et al., 2003;Veraverbeke et al., 2017) or anthropogenic activities (e.g. ...
Wildfires are episodic disturbances that exert a significant influence on the Earth system. They emit substantial amounts of atmospheric pollutants, which can impact atmospheric chemistry/composition and the Earth’s climate at the global and regional scales. This work presents a collection of studies aimed at better estimating wildfire emissions of atmospheric pollutants, quantifying their impacts on remote ecosystems and determining the implications of 2000s-2050s global environmental change (land use/land cover, climate) for wildfire emissions following the Intergovernmental Panel on Climate Change (IPCC) A1B socioeconomic scenario. A global fire emissions model is developed to compile global wildfire emission inventories for major atmospheric pollutants [greenhouse gases (CO2, CH4, N2O), air pollutants and tropospheric O3 precursors (nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOCs) (alkanes, alkenes)), aerosols and their precursors (particulate matter (PM2.5), black carbon (BC), organic carbon (OC), sulfur dioxide (SO2)) and mercury (Hg)] and quantify the impacts of 2000s-2050s global change. The estimated Hg wildfire emissions (2000s) are used in a global chemical transport model (GEOS-Chem) to determine the contribution of wildfire emissions to Hg pollution in the Arctic. Significant perturbations to wildfire emissions of atmospheric pollutants in the context of global change are estimated, mainly driven by the projected changes in climate, land use/land cover and in the case of Hg, anthropogenic emissions as well. A continuing increase in anthropogenic influence on wildfires in the coming decades is predicted. Greater human occupation of the African continent and increase in cropland coverage cause significant declines in wildfire emissions of atmospheric pollutants from the continent. Anthropogenic factors play an important role in the changes in emissions from other continents as well. Future changes in climate and land cover contribute to significant increases in global emissions for all the species. Wildfires are estimated to contribute 10% of global annual deposition to the Arctic with boreal fires in Asia contributing the most. Wildfires in Eurasia contribute 5.3% of annual Hg deposition followed by Africa (2.5%) and North America (1%). Wildfires contribute to Arctic Hg deposition throughout the year with the highest deposition occurring during the boreal fire season.
... We focus on a Lower Devonian charcoal Lagerstätte, which has provided remarkable insights into herbaceous groundcovering vegetation some 415 million years ago (Edwards and Axe, 2004). Reflectance values indicate that the majority of the plant remains were partially charred by lowtemperature smoldering wildfires (Glasspool et al., 2006), possibly initiated by lightning and facilitated by oxygen levels approximating those of the present day (Lenton et al., 2016). The plant fossils are found within siltstones of fluvial origin, often accumulated within ripple troughs and foreset laminations, and thus were transported away from their growth position and deposited elsewhere. ...
... The paleobotanic record shows a geologically (Hueber 2001;Boyce et al. 2007). By the end of the Silurian, enough biomass was present to promote wildfires caused by lightning and to generate charcoal (Glasspool et al. , 2006. This further increased into the Lower Devonian, recorded by the first coals and coaly shales in wetland settings by the Emsian (Kennedy et al. 2013 (Meyen 1982;Gastaldo et al. 2009), and the origination and diversification of the earliest cordaitaleans and conifers (DiMichele et al. 2010). ...
Synopsis
The invasion of the land was a complex, protracted process, punctuated by mass extinctions, that involved multiple routes from marine environments. We integrate paleobiology, ichnology, sedimentology, and geomorphology to reconstruct Paleozoic terrestrialization. Cambrian landscapes were dominated by laterally mobile rivers with unstable banks in the absence of significant vegetation. Temporary incursions by arthropods and worm-like organisms into coastal environments apparently did not result in establishment of continental communities. Contemporaneous lacustrine faunas may have been inhibited by limited nutrient delivery and high sediment loads. The Ordovician appearance of early land plants triggered a shift in the primary locus of the global clay mineral factory, increasing the amount of mudrock on the continents. The Silurian-Devonian rise of vascular land plants, including the first forests and extensive root systems, was instrumental in further retaining fine sediment on alluvial plains. These innovations led to increased architectural complexity of braided and meandering rivers. Landscape changes were synchronous with establishment of freshwater and terrestrial arthropod faunas in overbank areas, abandoned fluvial channels, lake margins, ephemeral lakes, and inland deserts. Silurian-Devonian lakes experienced improved nutrient availability, due to increased phosphate weathering and terrestrial humic matter. All these changes favoured frequent invasions to permament establishment of jawless and jawed fishes in freshwater habitats and the subsequent tetrapod colonization of the land. The Carboniferous saw rapid diversification of tetrapods, mostly linked to aquatic reproduction, and land plants, including gymnosperms. Deeper root systems promoted further riverbank stabilization, contributing to the rise of anabranching rivers and braided systems with vegetated islands. New lineages of aquatic insects developed and expanded novel feeding modes, including herbivory. Late Paleozoic soils commonly contain pervasive root and millipede traces. Lacustrine animal communities diversified, accompanied by increased food-web complexity and improved food delivery which may have favored permanent colonization of offshore and deep-water lake environments. These trends continued in the Permian, but progressive aridification favored formation of hypersaline lakes, which were stressful for colonization. The Capitanian and end-Permian extinctions affected lacustrine and fluvial biotas, particularly the invertebrate infauna, although burrowing may have allowed some tetrapods to survive associated global warming and increased aridification.
... The fossils were recovered from the macerates by sieving and sorted under a stereo light microscope, followed by screening by scanning electron microscopy (SEM). Reflectance values measured from the plant remains indicate that they were partially charred by low-temperature wildfire (Glasspool et al., 2006). Charcoalification has allowed for some three-dimensional preservation, but they have also been subjected to varying degrees of shrinkage, compression and homogenization (Edwards & Axe, 2004), which tends to be greatest in the narrower and perhaps younger axes. ...
The earliest evidence for land plants comes from dispersed cryptospores from the Ordovician, which dominated assemblages for 60 million years. Direct evidence of their parent plants comes from minute fossils in Welsh Borderland Upper Silurian to Lower Devonian rocks. We recognize a group that had forking, striated axes with rare stomata terminating in valvate sporangia containing permanent cryptospores, but their anatomy was unknown especially regarding conducting tissues. Charcoalified fossils extracted from the rock using HF were selected from macerates and observed using scanning electron microscopy. Promising examples were split for further examination and compared with electron micrographs of the anatomy of extant bryophytes. Fertile fossil axes possess central elongate cells with thick walls bearing globules, occasional strands and plasmodesmata‐sized pores. The anatomy of these cells best matches desiccation‐tolerant food‐conducting cells (leptoids) of bryophytes. Together with thick‐walled epidermal cells and extremely small size, these features suggest that these plants were poikilohydric. Our new data on conducting cells confirms a combination of characters that distinguish the permanent cryptospore‐producers from bryophytes and tracheophytes. We therefore propose the erection of a new group, here named the Eophytidae (eophytes).
Structures, termed microbioids, comforming to bacteria in size and shape (e.g. rods, spheres, chains and clusters of spheres) have been observed by field emission scanning electron microscopy (FE-SEM) on coalified Silurian and Lower Devonian spores, sporangia, cuticles and coprolites. Some were sectioned for transmission electron microscopy. The elemental composition of both microbioids and ‘substrates’ was investigated using a X-ray microanalysis system. These analyses combined with comparative studies on recent bacteria and cyanobacteria were undertaken to evaluate the biogenicity, nature and age of the microbioids. Spheres with a Si signature (0.03–0.5 μm diameter) and assumed composed of silica are interpreted as artefacts produced abiotically during the extraction procedures. A similar origin is proposed for hollow spheres that are composed of CaF2. These occur singly, in short chains simulating filaments, and in clusters. Considerable differences in size (0.2–2.0 μm diameter) and appearance relate to local variation in the chemical environment during extraction. Spheres (0.2–1.5 μm diameter), that lack a mineral signature, with a framboidal surface ornament and occur within sporangia are identified as by-products of spore development. A biotic origin is also postulated for C-containing rod-shaped structures (>3.1 μm long, <1.4 μm wide), some with collapsed surfaces, although comparisons with living bacteria indicate recent contamination. More elongate rod-shaped microbioids (<8.6 μm long, 1.2 μm wide) have been identified as detrital rutile crystals (TiO2). Minute naviculate structures (<2.2 μm long) resembling diatoms are of unknown origin but are probably composed of thorium hydroxide. Unmineralized filaments of cyanobacterial morphology are recent contaminants. Some of the sporangia and spore masses are partially covered by associations of fragmented sheets, interconnecting strands, rods and spheres that are interpreted as dehydrated biofilms. Being unmineralized they are probably also of recent origin, although they might have survived wild-fire along with the charcoalified mesofossils. Many of the structures illustrated here were initially identified casually as bacteria on the small fossils extracted for biodiversity studies using well-tried, conventional, palaeobotanical techniques. Our subsequent more detailed analyses have shown how such processes can produce artefacts that are morphological analogues of mineralized bacteria, leave residues that mimic bacterial shapes and, despite some efforts such as storage in dilute HCl to eliminate living bacteria, introduce contamination. They reinforce previous concerns that verification of the biogenicity and syngenicity of bacterial-like objects in ancient Earth and extra-terrestrial rocks should not only rely on size and morphological look-alikes, but must encompass a thorough understanding of fossilization processes and extraction techniques plus, ideally, other measures of biogenicity (e.g. biomarkers) and syngenicity.
Eukaryotic microbes participate in many biogeochemical cycles, although quantifying their role is not easy, and the discussion below comes generally to only qualitative conclusions. Eukaryotes lack a number of the biogeochemically important functions that are carried out only by archaea (e.g., methanogenesis), bacteria (the anammox chemolithotrophic denitrification reaction), or archaea and bacteria (e.g., chemolithotrophy, diazotrophy, and dissimilatory reduction of sulfate). Microbial eukaryotes have one ancestral attribute, phagotrophy, which adds a novel link to food webs and thus modifies biogeochemical cycles, and have endosymbioses as well as ectosymbioses which can recruit metabolism from archaeans (methanogenesis) and bacteria (chemolithotrophic sulfide oxidation, diazotrophy). The ability of eukaryotes to carry out oxidative phosphorylation and the related respiratory carbon metabolism, and photosynthesis, as genetically integrated processes is an outcome of bacterial symbioses. The biogeochemical importance of fungi is significant in several key areas. These include organic and inorganic transformations, nutrient and element cycling, rock and mineral transformations, bioweathering, mycogenic mineral formation, fungal-clay interactions, and metal-fungal interactions. Although such transformations can occur in both aquatic and terrestrial habitats, it is in the terrestrial environment where fungi probably have the greatest influence especially when considering soil, rock and mineral surfaces, and the plant root-soil interface. Of special significance are the mutualistic symbioses, lichens and mycorrhizas. Geochemical transformations that take place can influence plant productivity and the mobility and speciation of toxic elements, and are therefore of considerable socioeconomic relevance. Some fungal transformations have beneficial applications in environmental biotechnology, e.g., in metal and radionuclide leaching, recovery and detoxification, and xenobiotic and organic pollutant degradation. They may also result in adverse effects when these processes are associated with the degradation of foodstuffs, natural products and building materials, including wood, stone and concrete.
Recently, major advances have been made in understanding terrestrialization processes and the development of early vegetation. This chapter reviews the major steps in the evolution of early land plants, with focii on cryptospores, trilete spores and on the meso- and megafossil remains of Silurian and Devonian plants. The major morphological innovations of plants and their spores are described. Cryptospores are the earliest fossil record of a terrestrial vegetation cover; the oldest indisputable specimens are observed from Darriwilian (mid-Ordovician) strata in Saudi Arabia and the Czech Republic. The biological affinities of cryptospores are discussed. It is generally agreed that cryptospores were derived mainly from ‘bryophytes’, but some cryptospores may have arisen from early tracheophytes or their immediate ancestors. The earliest trilete spores are Ordovician in age. Most trilete spores are considered to have tracheophyte affinities; we discuss possible relationships between trilete spores and several cryptospores in dyads or monads. The earliest record of plant mesofossils comes from Middle Silurian strata. The evolution and affinities of the major groups of Late Silurian and Devonian land plants are presented within a phylogenetic and a stratigraphic framework.
Ecologists, biogeographers, and paleobotanists have long thought that climate and soils controlled the distribution of ecosystems, with the role of fire getting only limited appreciation. Here we review evidence from different disciplines demonstrating that wildfire appeared concomitant with the origin of terrestrial plants and played an important role throughout the history of life. The importance of fire has waxed and waned in association with changes in climate and paleoatmospheric conditions. Well before the emergence of humans on Earth, fire played a key role in the origins of plant adaptations as well as in the distribution of ecosystems. Humans initiated a new stage in ecosystem fire, using it to make the Earth more suited to their lifestyle. However, as human populations have expanded their use of fire, their actions have come to dominate some ecosystems and change natural processes in ways that threaten the sustainability of some landscapes.
The discovery of land plant spores with permanent tetrad and dyad configurations in Middle Ordovician rocks indicated a pioneering phase of phytoterrestrialisation that predated trilete spore-bearing tracheophytes. Limited studies on Upper Silurian and Lower Devonian examples suggest that the producers possessed characters of both tracheophytes and bryophytes, leading to the erection of a new clade of eophytes. Here we present an unprecedented comprehensive survey of hundreds of charcoalified eophytic mesofossils from a Lower Devonian (Lochkovian) Lagerstätte in the Welsh Borderland, UK, which reveals a wide range of branching in smooth axes with occasional stomata and conducting cells interpreted as predominantly involved in nutrient transport. Similar anatomy was discovered in fossils with usually fragmentary terminal sporangia containing evidence for permanent cryptospores. This raises the possibility that these small sporophytes of narrow axial diameter exhibited matrotrophy although the nature of the autotrophic gametophytes remains elusive. The sheer numbers of these tiny mesofossils in the fine-grained rocks at the locality indicate that these small plants were an important part of vegetation in Early Devonian times – a component that disappeared as vascular plants diversified and increased in size. Whether or not the pioneering Ordovician vegetation had exactly similar characteristics requires more information of gross morphology and anatomy of fossils in the intervening years.
Microfossil tubes with internal thickenings, so-called banded tubes, are a conspicuous but enigmatic element of terrestrial palynomorph assemblages of Silurian to Early Devonian age. Their biological affinities and functions are controversial. Most researchers favor derivation from nematophytes, themselves an enigmatic group of organisms that are often considered to represent early terrestrial fungi-like organisms. Here we present the first transmission electron microscope (TEM) ultrastructural analysis of these banded tubes and show that their walls are homogeneous and lack preserved ultrastructure. Gross wall structure is extremely variable with respect to the nature of the thickenings, suggesting that the tubes were derived from a variety of sources or were highly variable within the source organism. Ultrastructurally, the tubes differ markedly from contemporaneous vascular plant tracheids. We discuss the affinities of the tubes based on the new ultrastructural and structural information, and we conclude that they most likely derive from nematophytes, heterotrophic organisms with fungal-like ecology, where they served as hyphal-like structures, anchoring the organism and transporting nutrients.
Coal, especially the inertinite in it, is highly sensitive to climate changes, showing an obvious response to paleoclimate conditions, in particular, to paleo-oxygen concentration ( p O 2 ). In this study, the inertinite abundance data of typical coal-forming periods in China were systematically collected and analyzed. Its characteristics and control factors were studied, and its evolution was established. Based on inertinite abundance data, p O 2 evolution curves of various coal-forming periods in China were established, which fluctuated between 15% and 30% during the entire Phanerozoic. The inertinite abundance in coal deposits during Paleozoic in China was basically consistent with that of other areas of the world, while it was quite different globally from the Mesozoic to the Cenozoic. The results show that the inertinite abundance in coal deposits is controlled by p O 2 and other factors including climatic zones, plant differentiation, sedimentary environments, and tectonic activities. The inertinite abundance in coal deposits in China during the Jurassic was high, suggesting dry paleoclimate of inland China.
The Late Devonian witnessed landscape evolution, increased atmospheric O2 level, intense organic and volcanic activities and initial expansion of earliest wildfires. This paper is focused on petrographic and geochemical studies of Famennian inertinite-bearing marine shale facies in northern Kerman (central Iran), a Late Devonian key area in north of Gondwana. Our studies point to a wildfire activity. During the Famennian, the wildfire activity occurred in lowland vegetation (covered by lycopods) under warm and humid conditions. The moderately hot burning temperature (446.7 °C to 487.9 °C) of the fire and the type of the land vegetation suggest prevalence of a surface wildfire. Following the burning of the land plants, the ground became exposed to weathering that could result in erosion of the soil. Inputs of terrestrial organic matter, nutrients (particularly phosphate) and detrital materials into a nearshore marine environment were mainly controlled by proximity of the depositional environment to the terrestrial source, intense continental weathering of rocks and the soil in the land, wildfire and continental runoff during rainfall. Generally, preservation and enrichment of organic matter and formation of macerals were controlled by wildfire activity, transportation, oxidation, bacterial/fungal degradation and detrital input.
Short chains of discoidal, rarely spheroidal, structures, recovered by acid maceration of Lower Devonian (Lochkovian) siltstones from the Welsh Borderland are interpreted as coprolites because they comprise comminuted or homogenized tissues. They are placed in a new species of the ichnogenus Lancifaex. Tissues include the smooth and banded tubes of Nematasketum, a close ally of Prototaxites, and rarer cuticles of Nematothallus and Cosmochlaina. All these taxa have been assigned to an extinct class, Nematophytales Lang 1937, which Lang thought was intermediate between higher plants and algae. More recently, there is more compelling evidence, particularly from Prototaxites, that the class had fungal affinities. We thus conclude that the producers of the coprolites were selective feeders on nematophytes, and hence on fungi. Prior evidence for the reconstruction of terrestrial ecosystems in the mid-Paleozoic has been dominated by mega-and mesofossils of primary producers because body fossil records of consumers, whether carnivores, herbivores, or detritivores, are rare. Coprolites previously described from the locality that contain spores and residues of higher plants provide indirect evidence, based on consideration of comparative body size of coeval animals recorded elsewhere, for detritivory, probably in millipedes. In a similar approach involving mites, collembolans and millipedes— animals known to be mycophagous today—it is concluded that millipedes were the most likely producers of the coprolites described here.
Evidence of wildfires in deep time is preserved as fossilised charcoal fragments in the rock record and inertinite macerals in coal. Historically, charcoal reflectance has been utilised to assess the formation temperature of these charcoals, and thus burning intensities of prehistoric fires. This is achieved by quantifying reflectance variability as a function of changes in charcoal microstructure with temperature. Raman spectroscopy been shown to similarly assess microstructure in carbonaceous organic matter with thermal maturation. However, there have been few applications of Raman spectroscopy to wildfire-derived charcoals, modern or prehistoric. Little consideration has also been paid to the nature and applicability of derived parameters in assessing intensity. This study presents a novel assessment of Raman spectroscopy as a method for interpreting palaeowildfire burning intensity. Spectra were obtained from experimentally pyrolysed Calluna vulgaris material, generated across a range of natural wildfire temperatures, and subsequent derived parameters were compared with established principles. For assessing changes in palaeowildfire intensity, this study has found the best correlations between thermal maturity and; D-band full-width at half-maximum (D-FWHM) and the D−/G-band full-width at half-maximum ratio (D-FWHM/G-FWHM). Additional parameters, commonly applied to Raman studies of charcoal, are otherwise influenced by non-linearity. The influence of precursor material on charcoal microstructure has also been derived, indicating further complexity when assessing heterogenous samples. Our results indicate that, whilst Raman spectroscopy offers extraordinary potential for understanding prehistoric and modern wildfire intensity, parameters and further analyses used require measured consideration.
This chapter reviews the role of wildfires as an essential element of the Earth system. After a brief explanation of systems theory, we will discuss how fire regulates the oxygen cycle and climate. We will then travel across the Earth’s history to understand how wildfires have shaped the Earth as we know it today. We will cover how fire activity has varied across geological scales and how different processes, including mass extinctions, have been affected by wildfire activity. We will then review fire-human interactions. Wildfires have served as a powerful tool for human alteration of landscape structure. We will provide examples of how humans have modified African, Australian, American, and European landscapes through the use of fire. We will finally discuss the cost of fire to human lives, as the number of fire-induced fatalities from smoke is on the rise. Although wildfires are often perceived as a major environmental problem, their effect over the Earth system makes them an essential element for life.
Fossil charcoal provides direct evidence for fire events that, in turn, have implications for the evolution of both terrestrial ecosystems and the atmosphere. Most of the ancient charcoal record is known from terrestrial or nearshore environments and indicates the earliest occurrences of fire in the Late Silurian. However, despite the rise in available fuel through the Devonian as vascular land plants became larger and trees and forests evolved, charcoal occurrences are very sparse until the Early Mississippian where extensive charcoal suggests well-established fire systems. We present data from the latest Devonian and Early Mississippian of North America from terrestrial and marine rocks indicating that fire became more widespread and significant at this time. This increase may be a function of rising O2 levels and the occurrence of fire itself may have contributed to this rise through positive feedback. Recent atmospheric modeling suggests an O2 low during the Middle Devonian (around 17.5%), with O2 rising steadily through the Late Devonian and Early Mississippian (to 21-22%) that allowed for widespread burning for the first time. In Devonian-Mississippian marine black shales, fossil charcoal (inertinite) steadily increases upsection suggesting the rise of widespread fire systems. There is a concomitant increase in the amount of vitrinite (preserved woody and other plant tissues) that also suggests increased sources of terrestrial organic matter. Even as end Devonian glaciation was experienced, fossil charcoal continued to be a source of organic matter being introduced into the Devonian oceans. Scanning electron and reflectance microscopy of charcoal from Late Devonian terrestrial sites indicate that the fires were moderately hot (typically 500-600 °C) and burnt mainly surface vegetation dominated by herbaceous zygopterid ferns and lycopsids, rather than being produced by forest crown fires. The occurrence and relative abundance of fossil charcoal in marine black shales are significant in that these shales may provide a more continuous record of fire than is preserved in terrestrial environments. Our data support the idea that major fires are not seen in the fossil record until there is both sufficient and connected fuel and a high enough atmospheric O2 content for it to burn.
This chapter describes investigations into how in test fires the rate of spread and probability of ignition varied with the concentration of atmospheric oxygen. It discusses two sets of experiments in more detail to present the results and compare them briefly with subsequent investigations of similar intent, and to draw attention to the implications for the regulation of the oxygen content of the atmosphere over time. It describes the methods and results, first for the rate-of-spread of flames experiments, and then for the probability-of-ignition investigation, in each case as a function of the oxygen concentration of the atmosphere and the moisture content of the fuel. Comparison with other studies is then made, and finally the biogeochemical and Earth system implications are briefly discussed.
The progressive oxygenation of the Earth's atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (∼21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435-392 Ma, and the appearance of fossil charcoal indicates O2 >15-17% by 420-400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ∼470 Ma onward, were responsible for this mid-Paleozoic oxygenation event, through greatly increasing global organic carbon burial-the net long-term source of O2 We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today's global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ(13)C) record by ∼445 Ma, and predict a corresponding rise in O2 to present levels by 420-400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2 levels.
Presence of charcoal in intertrappean lake sediments
associated with the Malwa Group of the Deccan trap,
India is recorded. The finding provides the first
evidence of palaeofire in the Indian late Cretaceous.
Though previous studies have shown the presence of
carbonaceous clays and coal bands in the Deccan volcanic
associated sediments, the presence of fossil charcoal
in the sediments is rarely reported. The fossil
charcoal was identified based on optical microscope,
Scanning Electron Microscope and Pyrolysis-Gas
Chromatography Mass Spectrometer (Py-GC-MS).
This study indicates that charcoal is derived from
burning of plants caused by forest fire during the
Maastrichtian (Chron 30N).
Evidence for a wildfire origin of fusain is examined. Charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance. Artificially charred leaves and naturally burnt wood are illustrated using the SEM. Reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis. The ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the Late Devonian.
A FEW remarkable finds document the colonization of land by animals and
plants in the mid-Palaeozoic1-3, but much rarer is
unequivocal evidence for plant-animal interaction4,5. Here we
announce the discovery of coprolites (fossil faeces) in Upper Silurian
(412 Myr) and Lower Devonian (390 Myr) rocks from the Welsh Borderland
that pre-date examples of similar composition in the Carboniferous by
about 90 million years6,7. The majority consist predominantly
of undigested land-plant spores with varying proportions of cuticles,
tubes and less readily identifiable (presumably plant) material. Because
coeval animal fossils of suitable size are carnivores8,
direct evidence for the coprolite producers is lacking, but we speculate
that they could have been spore eaters (and hence the earliest example
of herbivory of higher plants) or detritivores similar to modern
millipedes. In either case, they demonstrate the cycling of primary
productivity in early terrestrial ecosystems.
By comparing Silurian through end Permian [≈250 million years (Myr)] charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long-term variations in fire occurrence and fire system diversification are related to fluctuations in Late Paleozoic atmospheric oxygen concentration. Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (≈420 Myr) to the present. Its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13% to 35% (the “fire window”). Herein, we observe that, as predicted, atmospheric oxygen levels rise from ≈13% in the Late Devonian to ≈30% in the Late Permian so, too, fires progressively occur in an increasing diversity of ecosystems. Sequentially, data of note include: the occurrence of charcoal in the Late Silurian/Early Devonian, indicating the burning of a diminutive, dominantly rhyniophytoid vegetation; an apparent paucity of charcoal in the Middle to Late Devonian that coincides with a predicted atmospheric oxygen low; and the subsequent diversification of fire systems throughout the remainder of the Late Paleozoic. First, fires become widespread during the Early Mississippian, they then become commonplace in mire systems in the Middle Mississippian; in the Pennsylvanian they are first recorded in upland settings and finally, based on coal petrology, become extremely important in many Permian mire settings. These trends conform well to changes in atmospheric oxygen concentration, as predicted by modeling, and indicate oxygen levels are a significant control on long-term fire occurrence.
• Earth system processes
• global change
• coal
• charcoal
• inertinite
Charcoal is produced by pyrolysis of plant material and its occurrence in the fossil record can be broadly equated with the incidence of palaeowildfire. The past record of such naturally occurring fire, and tha availability of the biomass which represents its fuel, put two constraints on oxygen levels. For combustion of plant material to occur at all requires that the atmospheric oxygen did not drop below a threshold of 13%. Increasing inflammability of plant material at higher oxygen levels suggests that 35% would be a ceiling above which plant biomass would ignite and burn so readily as to be incompatible with sustained forest growth. As we have more or less continuous fossil evidence of forest trees from the Late Devonian onwards, and a similarly sustained record of fossil charcoal from that time to the present (Cope, 1984), this constraints oxygen levels between 13% and 35% over that period (Rabash and Langford, 1968; Watson et al., 1978). However, further experimental work is required to establish the validity of these oxygen values under appropriate conditions and also to sharpen the certainty by which we can discriminate between fusain produced by pyrolysis, and inert wood degradation products produced by other (? biogenic) means. We discuss experiments directed at attempting to establish the validity of physical parameters by which pyrolytically produced fusain can be characterized. The most convincing evidence of pyrolysis hitherto recognised is the apparent homogenization of xylem cell walls, as seen under SEM. Work on charcoal from both wildfires and laboratory wood charring under controlled conditions confirms the homogenization as seen under both SEM and TEM. Controlled temperature experiments show that a further rise in temperature causes the cell walls, initially homogenized, to crack and separate along the site of the middle lamella, giving the charcoal a characteristic fibrous texture. Both of these distinctive phases of response to pyrolysis can be observed in fossil charcoals.
A standard terminology is proposed applicable to all disciplines that produce, use, or examine fire-altered plant matter. The different materials are defined by macroscopic, microscopic, or chemical characteristics that can be determined using generally available equipment. No new terms are introduced. It is recommended that certain terms that have precise meanings in other fields should be either used with caution or discarded. Several existing terms should be disregarded, because they pre-suppose a mode of formation or structure for which the evidence is poor or incorrect.
Coalified residues of the xylem and peripheral structure tissues (stereome) from permineralized (CaCO3) Lower DevonianPsilophyton dawsoniihave been analysed by flash pyrolysis-gas chromatography-mass spectrometry. Both yielded C0-C1alkylphenols, C1-C3alkylbenzenes, C0-C1alkylnaphthalenes, although with varying relative abundances. The stereome also generated a series ofn-alk-1-enes andn-alkanes (C8-C24, maximum at C10) which is believed to be derived from the cuticle. The sources of the aromatic compounds are discussed, and while it is concluded that those in the xylem are derived from lignin, the macromolecule having been degraded by diagenesis and thermal maturation, the molecular sources of those from the stereome may also include a wide range of substances including simple phenolic acids, flavonoids and non-lignin polyphenolics. Possible functions for the stereome are discussed.
The Devonian flora discovered and collected by W.E. Logan in 1843 remained unstudied until 1855 at which time the collections were offered to J.W. Dawson. His attention was immediately drawn to a single large specimen in the collections, which he identified and described as partially rotted wood of a conifer (Dawson, 1857). He proposed the name Prototaxites (Dawson, 1859) thereby expressing his concept of the genus. That concept remained unchallenged until Carruthers (1872) heatedly ridiculed both the name and the author and illegitimately substituted the name Nematophycus. His subjective opinion was that the fossil represented a fragment of a very large alga, like Lessonia. His classification, challenged only once (Church, 1919), persisted in all subsequent reports. Dawson remained adamant in his definition of Prototaxites until he illegitimately substituted the name Nematophyton for Prototaxites (Dawson, 1888) and denied (Dawson, in Penhallow, 1889) that he had ever classed the genus with the conifers. The names Nematophycus and Nematophyton are later synonyms of Prototaxites and, although inappropriate in connotation, Prototaxites is nomenclaturally valid. No undoubted original nor associated specimens are available for choice of a lectotype. This report has a triple purpose: (1) to name, as neotype, a recognizable specimen collected by Dawson for which the locality and stratigraphic data are known, (2) to redescribe the genus as structurally composed of three interactive forms of hyphae, i.e. large thin-walled, septate, branching, generative hyphae; large thick-walled, non-septate, skeletal hyphae; and small thin-walled, septate, branching, binding hyphae, which combine to form a gigantic, phototropic, amphigenous, perennial sporophore with saprobic nutrition, and (3) to classify it in the Kingdom Fungi. Generic synonymy with Prototaxites is proposed for Nematophycus (Carruthers, 1872).
Preservation of soft-bodied fossil biotas (Konservat-Lagerstäten) that preserve traces of volatile nonmineralized tissues (readily degraded by bacteria) are not evenly spaced through geologic time. When compared to outcrop area, exceptional faunas appear to be over-represented in the Cambrian and Jurassic. These concentrations in time correspond to particular environments, indicating that controls on the distribution of exceptional faunas may have operated on a global scale. The reduction in the number of exceptional faunas after the Cambrian may reflect the evolution and diversification of deep bio- turbators. Specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks.
The chemical and physical characteristics of laboratory produced charcoals, natural charcoals, fungal decayed woods and inertinite from a variety of Western Canadian coals have been investigated using FTIR and standard petrologic techniques. Our studies confirm and extend earlier work in showing that almost all inertinite macerals can be attributed to wildfire in peat swamps, and that variation in the petrological characteristics of inertinite are a product of temperature, duration of heating and the nature of the initial plant material. The relationships between reflectance and temperature, as well as heating duration of charcoal formation are established as a reference for the examination of inertinite and the probable temperature of inertinite precursor (fossil charcoal) formation in paleo-wildfire. Fungi do not directly contribute to the formation of charcoal and inertinite apart from the fungal bodies themselves (funginite: sclerotia and hyphae) and perhaps by increasing the extent of shrinkage and cracking (increasing surface area) of the plant materials and thus susceptibility to charring. Evidence of fungal activity progressively decreases with increasing degree of charing in response to duration of heating or increased charing temperature. The reflectance values and FTIR spectral characteristics of inertinites in Western Canadian coal suggest that most inertinite formed by wildfires at temperatures over 400°C. The great abundance of semifusinite in Western Canadian coal may reflect frequent but short duration wildfires in precursor peat swamps.
The coalified remains of three extinct nonvascular Lower Devonian plants (Prototaxites Dawson, Pachytheca Hooker, and Parka Fleming) have been analysed using flash pyrolysis-gas chromatography-mass spectrometry, FTIR, and 13C solid-state NMR. The affinities of these fossils are unknown and their habitats remain conjectural. Host rock lithology and grain size correlate with the state of morphological and chemical preservation of Prototaxites. The flash pyrolysates of well-preserved Prototaxites and Pachytheca were dominated by aromatic hydrocarbons and alkylphenols. Given their resistance to compression when compared with associated lignified vascular plant fossils, it is possible that Prototaxites and Pachytheca contained an extinct polyphenolic structural biomacromolecule that was a failed experiment during terrestrialization. Precise affinities for the enigmatic fossils Prototaxites, Pachytheca, and Parka are still to be confirmed, although Prototaxites and Pachytheca are chemically distinct from Parka.
Charcoal is produced by pyrolysis of plant material and its occurrence in the fossil record can be broadly equated with the incidence of palaeowildfire. The past record of such naturally occurring fire, and tha availability of the biomass which represents its fuel, put two constraints on oxygen levels. For combustion of plant material to occur at all requires that the atmospheric oxygen did not drop below a threshold of 13%. Increasing inflammability of plant material at higher oxygen levels suggests that 35% would be a ceiling above which plant biomass would ignite and burn so readily as to be incompatible with sustained forest growth. As we have more or less continuous fossil evidence of forest trees from the Late Devonian onwards, and a similarly sustained record of fossil charcoal from that time to the present (Cope, 1984), this constraints oxygen levels between 13% and 35% over that period (Rabash and Langford, 1968; Watson et al., 1978). However, further experimental work is required to establish the validity of these oxygen values under appropriate conditions and also to sharpen the certainty by which we can discriminate between fusain produced by pyrolysis, and inert wood degradation products produced by other (? biogenic) means. We discuss experiments directed at attempting to establish the validity of physical parameters by which pyrolytically produced fusain can be characterized. The most convincing evidence of pyrolysis hitherto recognised is the apparent homogenization of xylem cell walls, as seen under SEM. Work on charcoal from both wildfires and laboratory wood charring under controlled conditions confirms the homogenization as seen under both SEM and TEM. Controlled temperature experiments show that a further rise in temperature causes the cell walls, initially homogenized, to crack and separate along the site of the middle lamella, giving the charcoal a characteristic fibrous texture. Both of these distinctive phases of response to pyrolysis can be observed in fossil charcoals.
Preservation of non-mineralized structures (including plants) and of articulated skeletons results from extraordinary hydrographic, sedimentational and early diagenetic conditions. The corresponding chief causative effects (stagnation, obrution and bacterial sealing) define a conceptual continuum into which individual occurrences may bc mapped. A more pragmatic, typological classification of conservation deposits, using a standard questionnaire, reveals ecological replacements, as well as trends related to the evolution of the biosphere, through geological time.
The angiosperme, or flowering plants, are believed to have originated
and diversified during the Cretaceous. The earliest angiosperm fossils
are pollen and leaf impressions found in late early Cretaceous
strata1,2. We now describe the discovery of fossil flowers in
the Upper Cretaceous of Sweden which represent a significant addition to
our very limited knowledge of the floral structure of Cretaceous
angiosperms.
THE late Silurian–early Devonian genus Cooksonia, characterized by smooth isotomously branching axes and solitary, terminal sporangia1, has long been regarded as the archetypal vascular plant because of its age and simplicity of
organization. The discovery of stomata, sterome2 and thick-walled spores1,3 in Cooksonia pertoni and C. hemisphaericaconfirmed its land-plant status, but tracheids have never been demonstrated in attached axes4.
Here we report on tubes with differentially thickened walls typical of tracheary elements found in the central region of axes of Lower Devonian unequivocal C. pertoni, vindicating Lang's belief that Cooksonia was a vascular plant1.
EVIDENCE for terrestrial vegetation in Ordovician and Silurian
times, before the advent of vascular plants, comes from palyno-morphs
(cryptospores1), that is, non-dissociating tetrads and
dyads2,3 and cuticles4. The lack of a megafossil
record for the spore producers is usually attributed to low fossilization
potential of vegetative tissues, and this, plus spore type5,
contributes to the hypothesis that the plants were embryophytes/archegoniates
at a bryophyte level of organization3,5,6 and perhaps most
similar in organization to modern hepatics5. Here we describe a minute
coal-ified fossil from the Lower Devonian (Lochkovian:
micrornatus-newportensis Spore Biozone) of the Welsh
Borderland7, which contains obligate, smooth-walled tetrahedral
tetrads, similar (by scanning electron microscopy) to those first recorded in
the Ordovician. To our knowledge, these are the first data on the gross
morphology and tissues of the plants that comprised the earliest embryophyte
land flora (Gray's Eoembryophytic epoch3), albeit obtained from
a relict Devonian example fossilized at a time when the composition of
dispersed spore and megafossil assemblages suggests that tracheophytes and
tracheophyte-like plants (rhyniophytoids) had generally begun to dominate land
vegetation (Gray's Eotracheophyta3). Its anatomy in toto
finds no exact parallels in embryophytes, but many of the individual cellular
features match those in extant hepatics (liverworts).
A new taxon Sporathylacium salopense gen. et sp. nov. is based on small isolated coalified sporangia from the Lower Devonian (Lochkovian: micrornatus—newportensis spore zone) from the Welsh Borderland. The sporangia have two equal valves with multi-layered walls and thickened borders, and contain trilete crassitate, non-curvaturate isospores that are completely covered by a microgranular ornament with possible distal verrucate/murornate structures. They differ from zosterophyll sporangia in details of the presumed dehiscence zone extending around the entire free convex margin, particularly in the presence of a wedge of amorphous material between the valves, and in spore characters. Absence of any information relating to water-conducting cells prevents further assignment within the embryophytes. Spherical bodies associated with spores and a resilient sporangial lining are compared with similar structures in extant free-sporing plants and with Ubisch bodies. The mode of sporangial dehiscence involving anatomical modifications of the valve margins and the novel wedge of tissue which connects them remains speculative.
FANNING, U., EDWARDS, D. & RICHARDSON, J. B., 1992. A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland. Nine rhyniophytoid taxa are described from an early Gedinnian locality (middle micromatus-newportensis spore Biozone) near Ludlow, England. They include Cooksonia pertoni, C. hemisphaerica, C. cambrensis, Tortilicaulis transwalliensis and three new taxa, Salopella marcensis sp. nov., Uskiella reticulata sp. nov. and Tarrantia salopensis gen. et sp. nov. Isolated sporangia of reniform shape, and those subtended by short lengths of axis, contain spores of Apiculiretusispora type and may belong to C. caledonica or Renalia. Morphologically distinctive forking, terminal sporangia lacking identifiable spores are not placed in a new taxon, because evidence based on in situ spores from elsewhere suggests they may belong to Salopella. Structures previously interpreted as clusters of sporangia of Yarravia-type are shown to be ± globular sporangia longitudinally split into valves. Sterile axes are dominated by smooth forms; although rare examples possess small enations. Tracheids have not been seen in axes of fertile specimens nor in sterile coalified compressions. A single pyrite permineralization contains tracheids of zosterophyll type. The assemblage demonstrates diversity among rhyniophytoids in the early Devonian and the existence of low vegetation ‘alongside’ the much larger zosterophyll dominated type.
A diverse assemblage of coalified sporangia from Lochkovian/Gedinnian, fluvial rocks imicrornatus-newportensis Spore Biozone) contains fusiform forms assignable to Salopella Edwards & Richardson and Tortilicaulis Edwards. Both show bifurcation within some sporangia. In specimens assigned to Salopella cf. marcensis, longitudinal dehiscence produces two equal valves revealing spores resembling Aneurospora, although trilete marks may be difficult to distinguish. The spores are in two forms with distal ornament of either coarse or fine coni, each occurring in separate sporangia. A further sporangium of Salopella shape contains distally apiculate, hilate cryptospores. Elongate sporangia exhibiting spiralling of superficial cells and sometimes gross twisting, are placed in a new species of Tortilicaulii, T. offaeus. Anatomical data include details of irregularly thickened epidermal cells, sporangial wall and in situ spores. The latter are trilete, equatorially thickened and highly distinctive, because the entire exospore surface is covered with grana, a feature not common in dispersed spores of this age. The nomenclatural and curatorial problems associated with these small, coalified fossils, whose anatomical examination by scanning electron microscope necessitates elimination of gross morphology, are discussed.
New collections of coalified mesofossils of Cooksonia have been made from a Lochkovian (Lower Devonian) locality in Shropshire, England. They allow detailed description of sporangial anatomy in Cooksonia pertoni ssp. apiculispora with inferences for spore dispersal involving disintegration of the distal sporangial wall and maintenance of a rigid rim. Trilete spores, Aneurospora sp. and Streelispora newportensis have been recovered from the same sporangium. A new subspecies Cooksonia pertoni subsp reticulispora contains miospores with laevigate proximal surface bearing a simple triradiate apertural fold, equatorial crassitude and a coarse reticulum of muri on a slightly thickened distal wall. Spores are tentatively assigned to Synorisporites sp.. Cooksonia banksiisp. nov. is based on terminal sporangia in which the spore-containing area is enclosed within the expanded apex of the subtending axis. The cavity is lined by a smooth resilient acellular layer. Well-defined cells are apparent only in the pronounced sporangial rim. Spores are assigned to Ambitisporites avitus, a taxon of particular significance, because it is recorded in the Upper Ordovician and Lower Silurian assemblages which contain the earliest trilete monads. However, it is concluded that spores of such simple morphology may have been produced by a variety of taxa and that ultrastructural studies are necessary to confirm this possibility. These new specimens thus allow further insights into the disparity (via anatomy and in situ spores) of very simple plants and, in providing information on cell construction and arrangement, allow for functional interpretations, particularly relating to spore dispersal. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 139, 339–359.
Coalified residues of the xylem and peripheral structure tissues (stereomc) from perminei alized (CaCO3) Lower Devonian Psilophyton dawsomi have been analysed by Hash pyrolysis-gas chromatography-mass spectrometry. Both yielded C1-C3 alkylphenols, C1-C3 alkylbenzenes, C1-C3 alkylnaphthalenes, although with varying relative abundances. The stereomc also generated a scries of n-alk-1-cries and H-alkanes (C3C24, maximum at C10) which is believed to be derived from the cuticle. The sources of the aromatic compounds are discussed, and while it is concluded that those in the xylem are derived from lignin, the macromolecule having been degraded by diagencsis and thermal maturation, the molecular sources of those from the stereomc may also include a wide range of substances including simple phenolic acids, flavonoids and non-lignin polyphenolics. Possible functions for the stereome are discussed.
Xylem and peripheral support tissues are described in axes of Gosslingia breconensis preserved as iron sulphide permineralizations. The distribution of coalified (organic) material and the various textures of pyrite are explained in terms of the relative decay rates of cell contents, cellulose and lignin, and the microbial anaerobic production of iron sulphide. It is suggested that coalified layers mainly represent regions of lignification. The xylem, described using Bierhorst's terminology, comprises indirectly attached both spiral and annular elements and is considered similar to that in many other zosterophylls, in plants of more controversial affinity, e.g. Baragwanathia and Drepanophycus, and in some extant pteridophytes.
The inertinite group macerals include fusinite, semifusinite, inertodetrinite, macrinite, micrinite and, funginite and secretinite, which together replace sclerotinite. The macrolithotype fusain comprises fusinite and semifusinite, and is now widely accepted as charcoal formed by wildfire activity. However, alternative origins for fusinite and semifusinite are still claimed. This paper considers the use of the terms pyrofusinite, degradofusinite, rank fusinite and primary fusinite misleading, while the definitions of the terms funginite and secretinite are also considered problematic. Observations made on modern, wildfire derived and volcanogenic, charcoal assemblages using reflectance and scanning electron microscopy, together with experimental charcoalification studies, demonstrate that most, if not all, inertinite macerals have acquired their optical and physical characteristics through the action of elevated temperatures. The criteria for the identification of charcoals produced by wildfire and volcanic activity are outlined and the role of the petrographic nomenclature system is discussed.
Abrupt changes (jumps) in reflectance values and chemical compositions of charcoals during heating experiments in muffle and thermal gravimetric analyzer ovens occur at mean maximum reflectance values of about 0.50–0.60%, 1.10–1.20%, 1.40–1.50%, 2.20–2.30%, 2.80–2.90% and 3.70–3.90% (Rmax). These abrupt changes are similar to the so called `coalification jumps' in vitrinite or liptinite in coals. Jumps are much more notable in low temperature charcoals (formed at less than 400°C) than in high temperature charcoals (formed at greater than 400°C). Abrupt changes in chemical composition are coincident with jumps in reflectance as evident from sudden decreases or increases in functional groups as determined by FTIR-spectra. The jumps in composition of charcoals (intertinites) during charring experiments explains the multi-modal reflectance distributions commonly documented in coals. The distribution of reflectance values and FTIR spectral characteristics of inertinite in some Western Canadian coals is consistent with a model of charring that incorporates discrete compositional jumps. The `jumps' in reflectance values and chemical compositions probably reflect progressive breaking of chemical bonds in response to attainment of specific threshold activation energies.
Although evidence for land vegetation comes from the Silurian, and maybe even earlier, the first record of fossil charcoal (fusain) is from the late Devonian. For this period there are only one or two isolated records. Not until the Early Carboniferous is there a record of extensive charcoal deposits, mainly preserved in near-shore clastic sediments, which provide evidence of significant and widespread wildfires. By the late Carboniferous charcoal was common or abundant in a wide range of facies, including tropical wetland peats. Wildfire played an important role in shaping the environment at this time. The latest Palaeozoic and early Mesozoic records of charcoal are fewer, whereas important deposits of late Mesozoic age are found worldwide. The occurrence of charcoal at the Cretaceous–Tertiary Boundary has been highlighted as evidence for a global fire following a meteorite impact, but this interpretation is questionable. Charcoal has been widely reported from Tertiary sediments and its appearance in the Quaternary and Recent is not solely as a result of human impact. Through the past 400 million years there have been major changes in atmospheric oxygen levels that affected fire intensity and frequency. Fire systems thus have a long history and their impact on shaping the environment is assessed.
In May 1995, fire burnt an area of heathland with stands of pine and birch trees in the Frensham Common Country Park near Tilford in Surrey, southeast England. Extensive areas were burnt by a rapidly spreading surface fire, and charcoal was produced from both the living plants and plant litter. Flames reached a height of no more than 2 m so that whilst much of the low growing vegetation was destroyed, the trees generally survived the burn. Samples were taken of unburnt living plants and unburnt litter as well as charcoal from heathland and adjacent woodland and small channels running through the locality. Much of the heathland charcoal was produced from living vegetation and included wood, leafy shoots, flowers and fruits of Calluna vulgaris (common heather) and rachises and pinnae of the fern Pteridium aquilinum (bracken). The surface peaty layer here was only charred to a depth of 1 or 2 mm. In contrast, the bulk of the charcoal from the Pinus sylvestris (scots pine) and Betula pendula (silver birch) trees was from litter, none of the lower branches of the trees having caught alight. Only a few fallen logs produced much wood charcoal. Fallen P. sylvestris female cones were typically only charred upon their upward-facing surface. Strong winds across the heathland following the fire gathered the charred C. vulgaris small leafy shoots, flowers and fruits into ripple concentrates. Movement of the charcoal by water following rain storms was also tracked from the heathland onto bare crossing paths and into depressions and channels as well as into a small nearby lake. Water transport resulted in selective bias in favour of wood charcoal. None of the other charred organs reached the lake. Scanning electron microscopy shows that a wide range of plant taxa and organs may be anatomically preserved by charcoalification, and plants covered with fungal hyphae (possibly indicating decomposition) were also found charred. Studies of samples in polished blocks show that all plant organs have increased reflectance under oil. Mean random reflectance under oil of all samples was 1.53 (range 0.13–6.22), which indicates that if preserved in the fossil record, they would be classified as the coal maceral semifusinite. Comparisons with fossil deposits are made, and this study may contribute to our understanding of charcoalified flower concentrates (e.g the late Cretaceous of Sweden and the USA) and deposits rich in fern charcoal (e.g. of the early Cretaceous of southern England).
A model for the combined long-term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the GEOCARB III model [Berner R.A., Kothavala Z., 2001. GEOCARB III: a revised model of atmospheric CO2 over Phanerozoic time. Am. J. Sci. 301, 182–204] for CO2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for O2 [Berner R.A., 2001. Modeling atmospheric O2 over Phanerozoic time. Geochim. Cosmochim. Acta65, 685–694]. New isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models. Sensitivity analysis is done by determining (1) the effect on weathering rates of using rapid recycling (rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks); (2) the effect on O2 of using different initial starting conditions; (3) the effect on O2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic δ13C for the past 200 million years; (4) the effect on sulfur isotope fractionation and on O2 of varying the size of O2 feedback during sedimentary pyrite formation; (5) the effect on O2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion, and the degree of exposure of coastal lands by sea level change; (6) the effect on CO2 of adding the variability of volcanic rock weathering over time [Berner, R.A., 2006. Inclusion of the weathering of volcanic rocks in the GEOCARBSULF model. Am. J. Sci.306 (in press)]. Results show a similar trend of atmospheric CO2 over the Phanerozoic to the results of GEOCARB III, but with some differences during the early Paleozoic and, for variable volcanic rock weathering, lower CO2 values during the Mesozoic. Atmospheric oxygen shows a major broad late Paleozoic peak with a maximum value of about 30% O2 in the Permian, a secondary less-broad peak centered near the Silurian/Devonian boundary, variation between 15% and 20% O2 during the Cambrian and Ordovician, a very sharp drop from 30% to 15% O2 at the Permo-Triassic boundary, and a more-or less continuous rise in O2 from the late Triassic to the present.
Plant fossils showing vitrinite-semifusinite(-fusinite) transitions and permineralised-semifusinite transitions were collected from Lower Carboniferous locations within the British Isles. Several were obtained from East Kirkton Quarry, Bathgate, Scotland, and one fusinite-semifusinite-vitrinite-semifusinite-fusinite transition fossil was collected at Muckros Head, County Donegal, Ireland. The Muckros Head fossil was found in a limestone sea-cliff face, where it had been weathered proud of the rock matrix, thus enabling a detailed examination and interpretation of the macroscopic appearance of the specimen. The distinctive ‘sandwich-like’ cross-section of the fossil is interpreted as being caused by the burial and coalification of a partially charred plant stem, with recent exposure and weathering resulting in the loss of its ‘shattered’ edges. Under S.E.M. and reflected light microscopy, non-permineralised transition fossils are seen to grade from structureless vitrinite into compressed and “bogen-structured” semifusinite, and occasionally continue through to structured uncompressed fusinite; with corresponding increases in reflectance. These gradations parallel the reflectances seen in modern, partially charred stems. Stable carbon isotopic analysis of the transition fossils (δC13 = −17.19%0 to −19.26%0; −22.46%0; to 24.54%0; −24.47%0; −24.47%0 to −26.20%0), show a significant difference between the vitrinite and semifusinite(-fusinite), with the semifusinite(-fusinite) isotopically heavier. The various techniques employed to investigate these transition fossils all indicate that they represent coalified, partially charred stems. Correlation of the properties and characteristics of the semifusinite(-fusinite) in transition fossils, with the properties and characteristics of isolated semifusinite and fusinite fragments collected from rocks of the Lower Carboniferous through to the Tertiary, supports the view that most of these isolated fragments also represent fossil charred wood and charcoal.
The recognition of fossilized charcoal has revealed a long history of wildfire, although the earliest (pre-Late Devonian) records remain conjectural. A variety of approaches (experimental and natural charring, comparative anatomy of a range of plant tissues following combustion, and preliminary reflectance studies) demonstrates that smoldering surface fires already occurred ∼405 million years ago (Lochkovian; Early Devonian) in a vegetation of short stature composed mainly of small plants with smooth stems and terminal sporangia. In addition, the textures recorded in pyrite permineralizations are anomalous when compared with those of Lower Devonian and later examples, and indicative of the involvement of different taphonomic processes. From comparison with experimentally pyritized charcoal, they further suggest that the plants were burned before fossilization. The small millimeter-sized fossils (mesofossils) with remarkable, uncompressed cellular preservation indicate the importance of charcoalification in the determination of affinities and functioning of early land plants, and hence the reconstruction of ancient ecosystems.
A comprehensive survey of plant assemblages from Upper Silurian (Gorstian–Přídolí) and Lower Devonian (Lochkovian–Pragian) localities in South Wales and the Welsh Borderland is presented, together with some comments on recent improvements in dating and correlation. Spore assemblages provide a stratigraphic framework for plant evolutionary studies and, along with microvertebrates, enable correlation from continental to marine rocks, i.e. near-shore to shelf deposits. While it is recognized that the assemblages provide the most complete and extensive record of the history of vascular plants in a restricted geographical area during the time interval, it seems likely that major evolutionary innovation occurred elsewhere. The plants themselves display a number of types of fossilization. Particularly important are the pyrite permineralizations which have helped in the elucidation of the ultrastructure of tracheids in early vascular plants. Minute, coalified, relatively uncompressed fossils (mesofossils) from the Přídolí Lochkovian of the Welsh Borderland are hypothesized to be the products of wildfire, the earliest records to date. In addition to displaying often exquisite anatomical detail, the sporangia contain spores which have been linked to those in dispersed assemblages. Such relationships are helpful in the reconstruction of local and regional vegetation, even in the absence of meso- and megafossils. However, because these fossils are allochthonous and preserved in fluvial sediments, the habitats of the plants remain uncertain. A new hypothesis suggests that interfluvial areas, where calcretes are interpreted as relicts of vertisols and a seasonally dry climate, provided refugia in the Lower Devonian for the cryptospore-producing plants which dominated Ordovician and Lower Silurian land vegetation, while vascular plants colonized areas in the immediate vicinity of rivers. Variation in regional vegetation is explored via comparisons of composition of spore assemblages in southern Britain and Scotland and timing of appearances of derived taxa, integrated with limited information on the spore producers. Copyright © 2004 John Wiley & Sons, Ltd.
A fossil flora is described from clay-filled fissures in the Carboniferous Limestone near Bridgend, South Wales. Nearly all the specimens belong to the conifer Cheirolepis muensteri. Most of them are charred fragments of various organs in which internal tissues are preserved. Cheirolepis was previously known from compressed German specimens yielding cuticles but no other tissues. The leaf is found to have a single vascular bundle and the wood is of somewhat Taxodiaceous structure but without xylem parenchyma. The bark produces thin scales of secondary phloem and cork. The male cone bears microsporophylls spirally; they are essentially dorsiventral and probably bear two pollen sacs only. The pollen is of unusual structure. The seed is orthotropous and the testa appears to be double. Other species are rare fragments of cuticle representing several Mesozoic genera and isolated spores, three of which have been determined. The age of the flora is between Rhaetic and Lower Liassic; it most resembles a flora in south-west Germany which is regarded as Lias $\alpha $. Reasons are put forward for supposing that the forest or scrub was burnt, and then the charred fragments were washed into water-courses in limestone fissures which soon after were submerged by the rising Liassic sea.
RL. 10. Transverse section of sporangium, (arrow a) highly reflective fusinitic ( ⁎ C) wall, (arrow b) partially charred, less reflective semifusinitic area of spores, RL. 11 Molecular characterization of some enigmatic Lower Devonian fossils
- G D Abbott
- G Ewbank
Tangential section through Pachytheca with high reflectance ( ⁎ C) and excellent preservation ( ⁎ C), RL. 10. Transverse section of sporangium, (arrow a) highly reflective fusinitic ( ⁎ C) wall, (arrow b) partially charred, less reflective semifusinitic area of spores, RL. 11. Prototaxites, reflectance (Ro) 4.54% ( ⁎ C), RL. 12. Highly reflective ( ⁎ C) heterogeneous degraded tissues, possibly part of a litter layer, RL. References Abbott, G.D., Ewbank, G., Edwards, D., Wang, Guang-Xu, 1998. Molecular characterization of some enigmatic Lower Devonian fossils. Geochim. Cosmochim. Acta 62, 1407–1418.
Integrated approaches to the cycling of primary produce in early terrestrial ecosystems
- K S Habgood
Habgood, K.S., 2000. Integrated approaches to the cycling of primary
produce in early terrestrial ecosystems [Ph D. thesis].