Fossil Charcoal Research Articles

A novel proxy for energy flux in multi-era wildfire reconstruction

Escalations in wildfire activity are of significant global concern, particularly within vulnerable wetland ecosystems integral to natural carbon sequestration and climate change mitigation. Our understanding and management of future wildfire activity may be better contextualised through the study of historic and ancient fire records, independent of human influence. Methods of study include ‘geothermometry’ - approximating ancient fire intensity from temperature-dependent changes in the chemistry of fossil charcoal. Though well established in their relation to experimental charcoalification, these methods still fail to quantify the true intensity of ancient fires, as a measure of energy release. As a result, their applicability, and contributions to the characterisation of modern fire activity, remain uncertain. Here, we present a novel measure of wildfire energy release, as a proxy for true intensity, through the co-application of cone calorimetry and Raman spectroscopy of charcoal. By applying a range of wildfire heat fluxes to variable peatland fuel mixes, this research demonstrates the complexity in correlating fire behaviour and charcoal microstructure. Further statistical analyses suggest a correlation between spectroscopic results, measures of CO and CO2 release, and fire severity. This offers a principal measure of ancient wildfire intensity, consistent with modern practices in wildfire modelling, monitoring, and management.

Thirty Years of Progress in Our Understanding of the Nature and Influence of Fire in Carboniferous Ecosystems

Until the late 20th century, the idea of identifying wildfires in deep time was not generally accepted. One of the basic problems was the fact that charcoal-like wood fragments, so often found in sedimentary rocks and in coals, were termed fusain and, in addition, many researchers could not envision wildfires in peat-forming systems. The advent of Scanning Electron Microscopy and studies on modern charcoals and fossil fusains demonstrated beyond doubt that wildfire residues may be recognized in rocks dating back to at least 350 million years. Increasing numbers of studies on modern and fossil charcoal assemblages from the 1970s through the 1990s established the potential importance of wildfires in the fossil record, using Carboniferous examples in particular. Since the 1990s, extensive progress has been made in understanding modern wildfires and their byproducts. New techniques to study ancient charcoals have allowed considerable progress to be made to integrate modern and ancient fire studies, both before and after the evolution of mankind. Four important developments have made a reassessment of Carboniferous wildfires necessary: the recognition of the role of atmospheric oxygen in controlling the occurrence of wildfire; the development of new microscopical techniques allowing more detailed anatomical data to be obtained from charcoal; the integration of molecular studies with the evolution of fire traits; and new developments in or understanding of post-fire erosion/deposition systems.

Temporal and spatial evolution of wildfires during the Jurassic: From regional to global scale

With ongoing global warming, the frequency of wildfires has increased in many regions worldwide. To fully understand the manifold interactions between warming climates and wildfires it is necessary to study wildfires during Earth's history, preferably during periods characterized by warm climates. The Jurassic was a significant greenhouse period in Earth's history, and although evidence of combustion has been widely reported from deposits of Jurassic age, the spatio-temporal patterns and processes of Jurassic wildfires have not been studied on a global scale. In this study, evidence for wildfires occurring in deposits of the Early Jurassic Sangonghe Formation within the Junggar Basin is reported for the first time. It was found that the range of burning temperatures of these wildfires decreased from the late Early Jurassic to the early Middle Jurassic. Additionally, a comprehensive database, consisting of 196 published records, of Jurassic combustion products, including fossil charcoal, pyrogenic inertinite (fossil charcoal in coal deposits), and pyrogenic polycyclic aromatic hydrocarbons (PAHs), was compiled from the literature and analyzed for this study. Spatially, the database shows a high concentration of published evidence for Jurassic wildfire records in warm temperate climate zones in the mid-latitudes of the Northern Hemisphere. Temporally, trends in the Jurassic wildfires may be related to changes in atmospheric oxygen levels, climate change and fuels. However, like other global compilations on this topic for different periods of Earth's history, these results have to be seen with some care, as various taphonomic biases, including researcher bias and preservation issues, cannot be ruled as complicating factors.

The optimum fire window: applying the fire–productivity hypothesis to Jurassic climate states

Abstract. Present-day fire frequency is related to a productivity–aridity gradient on regional and global scales. Optimum fire conditions occur at times of intermediate productivity and aridity, whereas fire is limited at the high productivity (moisture) and aridity (no fuel) endmembers. However, the current global fire activity pattern is reinforced by the predominant burning of grasslands. Here we test the intermediate fire–productivity hypothesis for a period on Earth before the evolution of grasses, the Early Jurassic, and explore the fire regime of two contrasting climatic states: the cooling of the Late Pliensbachian Event (LPE) and the warming of the Sinemurian–Pliensbachian Boundary (SPB). Palaeo-fire records are reconstructed from fossil charcoal abundance, and changes in the hydrological cycle are tracked via clay mineralogy, which allows inference of changes in fuel moisture status. Large fluctuations in the fossil charcoal on an eccentricity timescale indicate two modes of fire regime at the time. Wildfires were moisture-limited in a high-productivity ecosystem during eccentricity minima for both the SPB and the LPE. During eccentricity maxima fires increased, and an optimum fire window was reached, in which periodically greater seasonality in rainfall and temperatures led to intermediate states of productivity and aridity. The LPE experienced more extreme climatic endmembers compared to the SPB, with the fire regime edging closer to “moisture limitation” during eccentricity minima, and experienced more pronounced seasonality during eccentricity maxima, explained by the overall cooler climate at the time. This study illustrates that the intermediate-productivity gradient holds up during two contrasting climatic states in the Jurassic.

Depositional history of Devonian to lower Carboniferous (Tournaisian) strata, northern Wyoming and southern Montana, USA

The lower Frasnian (Upper Devonian) Maywood Formation records incision of valleys into lower Paleozoic bedrock in fluvial to estuarine settings in northern Wyoming and deposition in estuarine to marine environments in southern Montana (USA). A distinctive fossil assemblage of microconchids, plant compression fossils, fish fossils, and microspores represent fauna and flora that lived in, and adjacent to, salinity-stressed ecological niches in the upper reaches of the Maywood valleys. A similar fossil assemblage is recorded in older Devonian valley-fill deposits of the Lower Devonian Beartooth Butte Formation, indicating that valley incision and subsequent transgression, occurred repeatedly over a span of nearly 30 million years with organisms tracking the marine incursions into the valleys. The fossil charcoal in the Maywood Formation captures a record of fire in adjacent terrestrial ecosystems. The amount of dioxygen (O2) was thus above the fire window level (16% by volume) and might have been near modern levels in the earliest Late Devonian atmosphere. The nearshore deposits of the Maywood Formation are overlain by extensive shallow carbonate shelf strata of the Jefferson Formation, likely resulting from a global transgression in the earliest Frasnian. A paired positive and negative δ13Ccarbonate [carb] isotopic excursion in the Jefferson with a range of >6‰ is a signal of the globally recognized “punctata” Event. The unconformably overlying Madison Limestone is lower Carboniferous, except for a thin basal Upper Devonian unit with marine palynomorphs. The Madison regionally records eastward transgression and establishment of widespread marine deposition. It also contains two positive δ13Ccarb excursions (up to ∼7.5‰) that make up the mid-Tournaisian (= Kinderhookian−Osagean boundary) carbon isotope excursion (TICE/KOBE). These isotope data provide a framework for regional and global correlation of northern Rocky Mountain strata and an archive of environmental and evolutionary change during the middle−late Paleozoic transition.

Fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China, and its geological implications

Fossil charcoal can provide important evidence for understanding the ancient forest fires and predicting changes in vegetation, paleoclimate and paleoenvironment throughout geological history. In this research, a systematic study was conducted on fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China. The charred wood is secondary xylem, pycnoxylic and homoxyleous, composed of tracheids and parenchymatous rays. Based on their anatomical features, the charcoal fossils are identified as Protophyllocladoxylon sp. The presence of well-preserved macroscopic charcoal fossils, along with carbonized leaves, suggests that these fossils were formed as a result of local surface fires. Based on the analysis of the mean random reflectance (Romean) values of charcoal from the Karamay Formation, the estimated temperature range for the production of the charcoal is between 407.49 °C and 369.17 °C. This temperature range aligns with the typical temperatures associated with surface fires, indicating that the fires in this region during the Late Triassic were of low intensity and occurred under relatively low temperatures. The presence of fossil charcoal in Junggar Basin suggests that the paleoatmospheric oxygen level in northwest China during Late Triassic was above 13% or 15%, which is the minimum required for sustained burning of natural wildfires. This finding is in accordance with the paleoatmospheric oxygen concentration models on the basis of variations in inertinite content and Phanerozoic wildfire history combined with the phosphorus cycle. The abundant presence of fossil charcoal herein suggests a humid and warm climate with intermittent droughts in the Late Triassic Junggar Basin.

Winter determines the annual:seasonal temperature change of Asia temperate monsoon region since mid-Holocene

The evolution of global temperature during Holocene is crucial for understanding the mechanisms of climate change and future climate trends. However, there is a discrepancy between the temperature trends reconstructed from proxy and model, which is attributed to the seasonal biases and the appearance of the Holocene thermal maximum was dominated by the temperature of the warm season. In this paper, fossil charcoal assemblages from the southern Chinese Loess Plateau were analysed to provide quantitative mean annual temperatures (MAT) and four-season temperature records during 6.55–3.45 cal ka BP. The results indicate that both the seasonal temperatures and MAT during the middle Holocene reached warm peaks between 5.55 and 5.35 cal ka BP. The similar trend between the winter temperature (WIT) and MAT denotes the highest contribution of WIT changes to the MAT in the study area since the mid-Holocene.

A synthesis of the Cretaceous wildfire record related to atmospheric oxygen levels?

The Cretaceous was a significant greenhouse period in Earth's history with higher atmospheric CO2 levels and temperatures than today. Although evidence of combustion has been widely described from the Cretaceous deposits, our understanding of the spatiotemporal diversification pattern and process of the Cretaceous wildfires is still limited. In this study, we comprehensively synthesize a total of 271 published Cretaceous wildfire occurrences based on the by-products of burning, including fossil charcoal, pyrogenic inertinite (fossil charcoal in coal), and pyrogenic polycyclic aromatic hydrocarbons (PAHs). Spatially, the dataset shows a distinctive distribution of reported wildfire evidence characterized by high concentration in the middle latitudinal areas of the Northern Hemisphere (30°N–60°N) over the Cretaceous. Temporally, an overall increasing trend of the reported wildfire data from the Early Cretaceous to the Late Cretaceous is coincident with higher atmospheric O2 levels. However, the spatial and temporal patterns may result from many types of factors, such as taphonomy, preservation, and researcher biases, instead of a real picture of the Cretaceous wildfire evolution. To better understand the spatiotemporal diversification of the Cretaceous wildfire, more investigations on the record of wildfire occurrences during this period would be necessary in the future.

Wildfire activity and impacts on palaeoenvironments during the late Paleozoic Ice Age - New data from the North China Basin

The Late Paleozoic is widely recognized as a ‘high-fire’ world. However, the impact of wildfires on the vegetational change as well as the relationship between fire and low atmospheric pCO2 and high pO2 in the Late Paleozoic remains a matter of debate. New data on fossil charcoal and pyrogenic PAHs in coal deposits from the Yuzhou Coalfield, the southern part of the North China Basin, are integrated into previous studies to increase our current understanding of the role of wildfires on land and in marine environments during the late Carboniferous and early Permian. Analyses of bulk petrographic and organic geochemical data indicate that during deposition of the Taiyuan Formation (late Gzhelian and early Asselian Stage) wildfires were more prevalent and were characterized by a large proportion of crown fire. A previous plant macrofossil assemblage study of the Taiyuan and Shanxi formations, together with fire traits of ancient plant lineages, indicates that wildfire may likely be one of the major drivers of the thriving of the Cathaysian Flora during this period. Wildfire and post-wildfire processes might have acted as important controlling factors for organic carbon burial. Persistent organic carbon sequestration (as coals or charcoal) on land and increasing organic carbon burial in the ocean are coincident with the peak in pO2 during the apex of the Late Paleozoic Ice Age.

Paleo-wildfire signatures revealing co-occurrence of angiosperm-gymnosperm in the early Paleogene: Evidences from woody charcoal and biomarker analysis from the Gurha lignite mine, Rajasthan, India

Charcoal, a common product of wildfire, is abundant in many sedimentary rocks deposited in a wide range of environments, from terrestrial to marine. The analysis of paleofloras and the related paleoecological conditions is of great importance for the understanding of past environmental and paleoclimatic events. Woody charcoal is identified from the early Paleogene sediments of the Gurha lignite mine (Palana Formation), Bikaner, Rajasthan. This evidence is in the form of fragments of tracheids and vessels that show homogenized cell walls and well-preserved anatomical details, like pitting on cell walls, characteristic features of charcoal. These charcoal remains, most of which belong to angiosperms, represent the first verified occurrence of paleo-wildfires in this region during the early Paleogene. Moreover, a gymnospermous taxonomic affinity can be established for some of the charred woods and a relationship with conifers is likely, thus providing additional evidence for the taxonomic composition of early Paleogene floras in this region. Consecutively, the presence of diterpenoid compounds together with the occurrence of (mega-)sporinite in the lignite samples also shows the presence of gymnosperm vegetation (conifers).Furthermore, the petrographic composition reveals that the lignite samples are dominated and sub-dominated by the huminite (av. 43.2 vol%) and inertinite (av. 39 vol%) groups, respectively, followed by liptinite (av. 13.9 vol%) group of macerals. Fusinite, semifusinite (and inertodetrinite) macerals are commonly considered as fossil charcoal. The relatively higher content of these macerals in the studied lignite indicates the regular events of palaeofire during the deposition. Subsequently, the presence of unsubstituted polycyclic aromatic hydrocarbon (PAH) compounds identified in samples further suggests the occurrence of fire. Additionally, the inertinite (fusinite) reflectance indicates that the charcoal/inertinite was formed at a temperature above 300 °C, while the highest reflectance value suggests a burning temperature of ∼800 °C.

A baptism by fire: fossil charcoal from eastern Euramerica reveals the earliest (Homerian) terrestrial biota evolved in a flammable world

Charred fossils from the Wenlock (Wales) and Ludlow (Poland) are evidence of the earliest wildfires to date, showing that this phenomenon was contemporaneous with the earliest records of land plant macrofossils. These data indicate that fires began to influence Earth system processes alongside those wrought by the advent of an embryophytic terrestrial flora. By the mid-Silurian, fires affected atmospheric composition, sedimentary systems, carbon and nutrient cycling, landscape diversity, community composition and species interactions. As global heating alters wildfire regimes, greater recognition is being given to fires and their ecosystem impacts, a relationship we now know extends back >430 myr. Here we document the taxonomic composition of charred phytoclasts, evidence of wildfire activity, from two discrete Silurian localities: the Pen-y-lan Mudstone, Rumney, Wales, and the Winnica Formation, Holy Cross Mountains, Poland. Nematophytes dominate each mesofossil assemblage and quantitative reflectance data indicate generally low-temperature fires at both sites, but with locally intense conditions. These and other Silurian assemblages, herein documented as bearing charcoal, are used to evaluate the systematics, fuel load and burn temperatures of these earliest wildfires. We propose a diagrammatic reconstruction to explain the seeming disparity between the diminutive size of the embryophytic biota and the highest temperatures (>700°C) recorded in these charcoals. Supplementary material : Raw mean random reflectance ( R o %) data from Rumney Borehole, Winnica, Ludford Lane and North Brown Clee Hill, sorted by both locality and morphotype, are available at https://doi.org/10.6084/m9.figshare.c.6179309

Stable carbon isotopes of woods during carbonization and their correlation with climatic factors.

To explore the applicability of the carbon isotope composition (δ13C) of fossil charcoal for the quantitative reconstruction of paleoclimates, we selected five points in Shaanxi province, from north to south, to collect modern Pinus species and Quercus species to sample covering areas with obvious climatic differences. In order to reveal the relationships between δ13C of charcoal and climate variables on the basis of carbonization experiments, we evaluated the fractionation mechanism of δ13C of charcoal, and compared the differences between δ13C of charcoal in wildfire experiments and indoor experiments regarding genera and species. The results showed significant differences in δ13C between genera but no significant differences among species. Additionally, the δ13C of charcoal was significantly negatively correlated with precipitation and positively correlated with evaporation, which could be determined from δ13C values in the study area to reconstruct ancient precipitation and evaporation in the future.

END-PERMIAN BURNOUT: THE ROLE OF PERMIAN–TRIASSIC WILDFIRES IN EXTINCTION, CARBON CYCLING, AND ENVIRONMENTAL CHANGE IN EASTERN GONDWANA

ABSTRACTWildfire has been implicated as a potential driver of deforestation and continental biodiversity loss during the end-Permian extinction event (EPE; ∼ 252 Ma). However, it cannot be established whether wildfire activity was anomalous during the EPE without valid pre- and post-EPE baselines. Here, we assess the changes in wildfire activity in the high-latitude lowlands of eastern Gondwana by presenting new long-term, quantitative late Permian (Lopingian) to Early Triassic records of dispersed fossil charcoal and inertinite from sediments of the Sydney Basin, eastern Australia. We also document little-transported fossil charcoal occurrences in middle to late Permian (Guadalupian to Lopingian) permineralized peats of the Lambert Graben, East Antarctica, and Sydney and Bowen basins, eastern Australia, indicating that even vegetation of consistently moist high-latitude settings was prone to regular fire events. Our records show that wildfires were consistently prevalent through the Lopingian, but the EPE demonstrates a clear spike in activity. The relatively low charcoal and inertinite baseline for the Early Triassic is likely due in part to the lower vegetation density, which would have limited fire spread. We review the evidence for middle Permian to Lower Triassic charcoal in the geosphere, and the impacts of wildfires on sedimentation processes and the evolution of landscapes. Moreover, we assess the evidence of continental extinction drivers during the EPE within eastern Australia, and critically evaluate the role of wildfires as a cause and consequence of ecosystem collapse. The initial intensification of the fire regime during the EPE likely played a role in the initial loss of wetland carbon sinks, and contributed to increased greenhouse gas emissions and land and freshwater ecosystem changes. However, we conclude that elevated wildfire frequency was a short-lived phenomenon; recurrent wildfire events were unlikely to be the direct cause of the subsequent long-term absence of peat-forming wetland vegetation, and the associated ‘coal gap' of the Early Triassic.

Chemical evaluation of carbonized logs from Araucariaceae species: characterization of materials associated to multivariate analysis for environmental inferences

The main objective of this study was to develop a methodology to evaluate, by physical and chemical methods, artificially charred logs from three species of Araucariaceae, and compare them fossil charcoal collected in the Faxinal and Belvedere outcrops for possible paleoenvironmental inferences. The species studied were Araucaria angustifolia, Araucaria bidwillii and Araucaria columnaris. For fossil charcoal analyses we used samples from the Mina do Faxinal and samples from the Curva do Belvedere Outcrop. The carbonization process from species of Araucariaceae were Thermogravimetric Analysis (TGA) associated to the techniques of Fourier Transform Infrared Spectroscopy (FTIR) and multivariate analysis. The Principal Component Analysis (PCA) showed that it is possible to describe 90,9% of the data, grouping the samples into two main clusters. Both samples of fossil charcoal from Belvedere and Faxinal showed charring characteristics above 400ºC. Results showed that technical associations, such as TGA, FTIR and multivariate analysis may help to characterize the natural carbonization process and contribute to important paleoenvironmental and archaeological information and inferences.

Further evidence for Cretaceous wildfires: macro-charcoal from the Malha Formation at Wadi Budra, west-central Sinai, Egypt

Abstract Fossil evidence for wildfires, in form of fossil charcoal, is known from a large number of Cretaceous localities worldwide and it has repeatedly been argued that wildfires were connected to the evolution and radiation of angiosperms during this period. The present study provides new evidence (in form of macro-charcoal) for the occurrence of wildfires during deposition of the Lower Cretaceous (pre-Aptian) Malha Formation at Wadi Budra of the Sinai Peninsula, Egypt. Despite growing evidence for the worldwide occurrence of wildfires during the Cretaceous, the available database for pre-Aptian wildfires is still rather scarce for large regions when seen on a global scale, hampering causal interpretations concerning the interactions between fire ecology and the evolution of ecosystems during these stages.

New Evidence for Palaeo-wildfire in the Early Permian (Artinskian) of Gondwana from Wardha Valley Coalfield, India

Abstract 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.

Wildfire activity enhanced during phases of maximum orbital eccentricity and precessional forcing in the Early Jurassic

Fire regimes are changing due to both anthropogenic climatic drivers and vegetation management challenges, making it difficult to determine how climate alone might influence wildfire activity. Earth has been subject to natural-background climate variability throughout its past due to variations in Earth’s orbital parameters (Milkankovitch cycles), which provides an opportunity to assess climate-only driven variations in wildfire. Here we present a 350,000 yr long record of fossil charcoal from mid-latitude (~35°N) Jurassic sedimentary rocks. These results are coupled to estimates of variations in the hydrological cycle using clay mineral, palynofacies and elemental analyses, and lithological and biogeochemical signatures. We show that fire activity strongly increased during extreme seasonal contrast (monsoonal climate), which has been linked to maximal precessional forcing (boreal summer in perihelion) (21,000 yr cycles), and we hypothesize that long eccentricity modulation further enhances precession-forced fire activity.

Charcoalified vegetation from the Pennsylvanian of Yorkshire, England: Implications for the interpretation of Carboniferous wildfires

New data on some fossil charcoal deposits from the British Isles is integrated into previous studies to provide an indication of our current understanding of the role of fire on land in the Pennsylvanian and also provide strategies for obtaining new information in the future.The nature and occurrence of fossil charcoal (often called fusain) in sediments and coals (often described as inertinite/fusinite/semi-fusinite) is the main way that the history of Carboniferous fire has been studied. Fires have been shown to have been common in many Carboniferous ecosystems around the world, yet we still have little understanding of the details of what these fires were, where and how they occurred, or their effects upon both on the local ecosystem and the Earth System as a whole. Research has demonstrated that detailed scanning electron microscope studies of charcoal residues can provide data on the plants that have been charred by wildfires.Information on the amount of charcoal in coal globally appears to relate to atmospheric oxygen composition and this shows that throughout the Carboniferous oxygen levels were as high or higher than those of the present day, suggesting that wildfires were more frequent. Interpreting the frequency of fires in different ecosystems remains fraught with difficulty and calculations within peat (coal) systems are at an early stage. The impact of fire on vegetational change as well as the relationship between fire and climate in the Carboniferous remains little studied.A study of the inertinite (charcoal) distribution within the Low Barnsley Seam in Yorkshire, England indicates that levels remained high throughout much of the 1.8m thick coal seam. A previous palynological study of the seam has demonstrated three repeated successions of vegetational development interpreted as repeated phases of wet to dry mire development (rheotrophic swamp to ombrotrophic bog). Inertinite peaks above 20% background have indicated a minimum of 18 significant large fire events and an analysis of depositional rates suggests a fire return interval of these large fires to be 500 years or less.A study of charcoalified vegetation from fine-grained clastic sediments from Swillington Brickworks, Yorkshire recovered from bulk maceration of the sediment, that was not evident from bedding surface examination, has demonstrated that some levels contain abundant leaf charcoal, mainly from pteridosperms, in addition to wood charcoal derived from a range of gymnosperms. The charcoalified plants are interpreted as wildfire residues mainly from surface fires that have been transported and deposited on low-lying floodplains.

Wildfires in the Early Triassic of northeastern Pangaea: Evidence from fossil charcoal in the Bogda Mountains, northwestern China

Fires are an integral part of modern and ancient ecosystems, serving as friends for renewal or foes for complete destruction and extinction. Indicators of palaeowildfire were so far absent from the Lower Triassic. Lack of plants in the Early Triassic due to the end-Permian mass extinction event and low atmospheric oxygen levels were proposed as the major reasons for the scarcity of wildfires. We present macroscopic charcoals from the Olenekian (Lower Triassic) in northwestern China, indicating probable ground/smoldering fires occurred on landscapes in mid-latitudes of northeastern Pangaea. Atmospheric oxygen concentration during the Olenekian would have been above 18.5%. These findings demonstrate that wildfires continued to be a source of disturbance of terrestrial ecosystems in Bogda Mountains after the end-Permian marine biotic crisis. There were adequate supplies of fuels and oxygen during this critical time period in the Earth history.

Experimental production of charcoal morphologies to discriminate fuel source and fire type: an example from Siberian taiga

Abstract. The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes and make the method more relevant to studies of both plant evolution and fire management, the extraction of more information from charcoal particles is critical. Here, I used a muffle oven to burn seven fuel types comprising 17 species from boreal Siberia (near Teguldet village), which are also commonly found in the Northern Hemisphere, and built on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. I then combined these results with those from fossil charcoal from a peat core taken from the same location (Ulukh-Chayakh mire) in order to demonstrate the relevance of these experiments to the fossil charcoal records. Results show that graminoids, Sphagnum, and wood (trunk) lose the most mass at low burn temperatures (<300 ∘C), whereas heathland shrub leaves, brown moss, and ferns lose the most mass at high burn temperatures. This suggests that species with low mass retention in high-temperature fires are likely to be under-represented in the fossil charcoal record. The charcoal particle aspect ratio appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoal particles are the most elongate (6.7–11.5), with a threshold above 6 that may be indicative of wetland graminoids; leaves are the shortest and bulkiest (2.1–3.5); and twigs and wood are intermediate (2.0–5.2). Further, the use of fine diagnostic features was more successful in separating wood, graminoids, and leaves, but it was difficult to further differentiate these fuel types due to overlapping features. High-aspect-ratio particles, dominated by graminoid and Sphagnum morphologies, may be robust indicators of low-temperature surface fires, whereas abundant wood and leaf morphologies as well as low-aspect-ratio particles are indicative of higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires, combusting living shrubs and dead wood and leaves, and high-intensity crown fires that have burnt living trees. Distinct particle shape may also influence charcoal transportation, with elongated particles (graminoids) potentially having a more heterogeneous distribution and being deposited farther away from the origin of fire than the rounder, polygonal leaf particles. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in the more robust interpretation of fuel source and fire-type changes. Lastly, I highlight the further investigations needed to refine the histories of past wildfires.