Article

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

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Wildfire 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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... However, localized siliceous permineralized peats associated with silica-rich ash deposits (e.g., in the MacMillan Formation, Burngrove Formation, Fort Cooper Coal Measures, and Rangal Coal Measures) contain relatively uncompressed three dimensionally preserved plant remains that are locally differentiated into discrete organic microfacies. Intra-peat microfacies are variably dominated by (1) glossopterid leaf mats, (2) glossopterid roots and stems, and (3) fine organic components, such as seeds, charcoal, and other detrital remains (Mays and McLoughlin, 2022). These indicate subtle variations in organic matter accumulation through the peat profiles and across the peat landscape based on the topography of the mire surface and the local representation of vegetation. ...
... Until the rapid ecological collapse of the EPE, this flora largely resisted the global or regional environmental changes of the Lopingian with only slight family-level diversification shortly before this event. Glossopterids appear to have thrived through the late Permian of eastern Australia by adopting a range of ecological strategies involving deciduousness, varied seed production, epicormic buds, thick insulating bark, lignotubers, and wound healing that buffered them from both strong seasonality at high palaeolatitudes and local episodic disturbances, such as fire, herbivory, and ash defoliation (Glasspool, 2000;McLoughlin, 2011b;McLoughlin and Prevec, 2021;McLoughlin et al., 2021b;Mays and McLoughlin, 2022). Their aerated root systems were especially well-adapted to growth in waterlogged settings (Decombeix et al., 2009) but they are also represented in a range of clastic sediments away from coal seams indicating the presence of extensively vegetated lowlandseven in well-drained sites. ...
... CIA values remain low in the lower part of the formation, then rise progressively (from ~253 Ma) towards the end-Permian floral extinction level at the top of the Bandanna Formation (Frank et al., 2021; Fig. 7), suggesting increasingly warmer and more humid surface conditions over time. This warming climate has been linked to an increase in wildfire prevalence in eastern Australia (Mays and McLoughlin, 2022). Despite these climate-related changes, the micro-and macrofloral records reveal a relatively stable continental biome through accumulation of the Bandanna Formation. ...
Article
Full-text available
The upper part of the upper Permian succession in the Bowen Basin of Queensland, NE Australia, was investigated to ascertain the timeline and character of environmental changes in this high southern palaeolatitudinal setting leading up to the End-Permian Extinction (EPE). The study focused on (in ascending order) the Peawaddy Formation, Black Alley Shale, and Bandanna Formation, and laterally correlative units. In the western Bowen Basin, the base of the Peawaddy Formation (257 Ma) records the onset of thrust loading and volcanic activity associated with the Hunter-Bowen contractional orogeny. The Peawaddy Formation comprises a series of coarsening-upward, terrigenous clastic intervals interpreted as the product of repeated progradation of deltas into shallow, open marine environments. The overlying Black Alley Shale also comprises multiple deltaic coarsening-upward cycles, which accumulated in stressed, restricted marine environments. The uppermost Bandanna Formation and equivalents formed in extensive coastal plain to estuarine environments. All three formations accumulated under the influence of explosive volcanic activity from the emerging continental volcanic arc to the east of the foreland basin. Volcanism peaked during deposition of the Black Alley Shale around the Wuchiapingian–Changhsingian transition. Abundant dispersed gravel and glendonites (calcite pseudomorphs after ikaite) indicate that the Peawaddy Formation formed under the influence of cold conditions and possible glacial ice (P4 Glaciation; Wuchiapingian Stage). Direct evidence of cold conditions ends at the top of the Peawaddy Formation (254.5 Ma); however, Chemical Index of Alteration (CIA) data suggest that surface conditions remained cold through the accumulation of the Black Alley Shale, and the lower Bandanna until c. 253 Ma, before gradually rising through the upper Bandanna Formation. The end of P4 glaciation is also characterized by a major spike in the abundance of marine acritarchs (Magasella evansii Acme Zone), reflecting the development of a regional restricted basin of elevated nutrient concentrations but reduced salinity. In contrast to this short interval of stressed marine conditions, the fossil floras indicate remarkably consistent terrestrial ecosystems throughout the late Lopingian until the EPE. The terrestrial EPE is recorded by a distinctive, laminated mudrock bed (‘Marker Mudstone’) that records a palynological ‘dead zone’ above the uppermost coal seam or equivalent root-penetrated horizon followed by spikes in non-marine algal abundance. Overall, the time interval 257–252 Ma represented by the studied succession does not record a simple monotonic change in palaeoenvironmental conditions, but rather a series of intermittent stepwise changes towards warmer, and more environmentally stressed conditions leading up to the EPE in eastern Australia.
... Refinement of paleoclimate interpretations for the Lopingian on Gondwana do not support a cryic-gelic temperature regime 4,18,19 , therefore fire is the most parsimonious interpretation of anomalous inertinite abundances in Gondwanan coals 43 . Inertinite abundances in a continuous succession of Lopingian-Induan strata in eastern Australia and the Lambert Graben, East Antarctica provide a higher-resolution record of potential fire activity during this time interval 45 . This record indicates a prevalence of burned plant tissues from above-ground biomass in well-drained paleoenvironments, in addition to minor amounts of burning of below-ground biomass in wetland paleoenvironments. ...
... If a similar record is anticipated for these Antarctic successions, then it is likely that the Shackleton Glacier Area (CTAM) would have had a similar ignition trigger for wildfires as eastern Australia, where both areas underwent a similar trajectory in climate change. However, fire, if interpreted as a single mechanism that contributed to the extinction of the glossopterids, is complicated by the relatively surficial burning of glossopterid biomass 45 , and by the trajectory of increasing humidity of these areas during the Lopingian and into the Induan (i.e., an increase in the annual balance of rainfall versus evapotranspiration). In addition, the early Middle Triassic of the SVL area preserves evidence for the persistent re-occurrence of wildfire affecting above-ground biomass in well-drained paleoenvironments 46 . ...
... Refinement of paleoclimate interpretations for the Lopingian on Gondwana do not support a cryic-gelic temperature regime 4,18,19 , therefore fire is the most parsimonious interpretation of anomalous inertinite abundances in Gondwanan coals 43 . Inertinite abundances in a continuous succession of Lopingian-Induan strata in eastern Australia and the Lambert Graben, East Antarctica provide a higher-resolution record of potential fire activity during this time interval 45 . This record indicates a prevalence of burned plant tissues from above-ground biomass in well-drained paleoenvironments, in addition to minor amounts of burning of below-ground biomass in wetland paleoenvironments. ...
... If a similar record is anticipated for these Antarctic successions, then it is likely that the Shackleton Glacier Area (CTAM) would have had a similar ignition trigger for wildfires as eastern Australia, where both areas underwent a similar trajectory in climate change. However, fire, if interpreted as a single mechanism that contributed to the extinction of the glossopterids, is complicated by the relatively surficial burning of glossopterid biomass 45 , and by the trajectory of increasing humidity of these areas during the Lopingian and into the Induan (i.e., an increase in the annual balance of rainfall versus evapotranspiration). In addition, the early Middle Triassic of the SVL area preserves evidence for the persistent re-occurrence of wildfire affecting above-ground biomass in well-drained paleoenvironments 46 . ...
Article
Full-text available
The end-Permian extinction (EPE) has been considered to be contemporaneous on land and in the oceans. However, re-examined floristic records and new radiometric ages from Gondwana indicate a nuanced terrestrial ecosystem response to EPE global change. Paleosol geochemistry and climate simulations indicate paleoclimate change likely caused the demise of the widespread glossopterid ecosystems in Gondwana. Here, we evaluate the climate response of plants to the EPE via dendrochronology snapshots to produce annual-resolution records of tree-ring growth for a succession of late Permian and early Middle Triassic fossil forests from Antarctica. Paleosol geochemistry indicates a shift in paleoclimate towards more humid conditions in the Early and early Middle Triassic relative to the late Permian. Paleosol morphology, however, supports inferences of a lack of forested ecosystems in the Early Triassic. The plant responses to this paleoclimate change were accompanied by enhanced stress during the latest Permian as determined by high-resolution paleoclimate analysis of wood growth intervals. These results suggest that paleoclimate change during the late Permian exerted significant stress on high-latitude forests, consistent with the hypothesis that climate change was likely the primary driver of the extinction of the glossopterid ecosystems.
Article
Full-text available
Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. We demonstrate that climate changes and deforestation can drive recurrent microbial blooms, inhibiting the recovery of freshwater ecosystems for hundreds of millennia. From the stratigraphic successions of the Sydney Basin, Australia, our fossil, sedimentary and geochemical data reveal bloom events following forest ecosystem collapse during the most severe mass extinction in Earth's history, the end-Permian event (EPE; c. 252.2 Ma). Microbial communities proliferated in lowland fresh and brackish waterbodies, with algal concentrations typical of modern blooms. These initiated before any trace of post-extinction recovery vegetation but recurred episodically for >100 kyrs. During the following 3 Myrs, algae and bacteria thrived within short-lived, poorly-oxygenated, and likely toxic lakes and rivers. Comparisons to global deep-time records indicate that microbial blooms are persistent freshwater ecological stressors during warming-driven extinction events.
Preprint
Full-text available
Anthropogenic factors have significantly influenced the frequency, duration, and intensity of meteorological drought in many regions of the globe, and the increased frequency of wildfires is among the most visible consequences of human-induced climate change. Despite its role in determining biodiversity outcomes in different ecosystems, wildfires can cause negative impacts on wildlife. We conducted ground surveys along line transects to estimate the first-order impact of the 2020 wildfires on vertebrates in the Pantanal wetland, Brazil. We adopted the distance sampling technique to estimate the densities and the number of dead vertebrates in the 39,030 square kilometers affected by fire. Our estimates indicate that at least 16.952 million vertebrates were killed immediately by the fires in the Pantanal, demonstrating the impact of such an event in wet savanna ecosystems. The Pantanal case also reminds us that the cumulative impact of widespread burning would be catastrophic, as fire recurrence may lead to the impoverishment of ecosystems and the disruption of their functioning. To overcome this unsustainable scenario, it is necessary to establish proper biomass fuel management to avoid cumulative impacts caused by fire over biodiversity and ecosystem services.
Article
Full-text available
Biodiversity contributes to the ecological and climatic stability of the Amazon Basin1,2, but is increasingly threatened by deforestation and fire3,4. Here we quantify these impacts over the past two decades using remote-sensing estimates of fire and deforestation and comprehensive range estimates of 11,514 plant species and 3,079 vertebrate species in the Amazon. Deforestation has led to large amounts of habitat loss, and fires further exacerbate this already substantial impact on Amazonian biodiversity. Since 2001, 103,079–189,755 km² of Amazon rainforest has been impacted by fires, potentially impacting the ranges of 77.3–85.2% of species that are listed as threatened in this region⁵. The impacts of fire on the ranges of species in Amazonia could be as high as 64%, and greater impacts are typically associated with species that have restricted ranges. We find close associations between forest policy, fire-impacted forest area and their potential impacts on biodiversity. In Brazil, forest policies that were initiated in the mid-2000s corresponded to reduced rates of burning. However, relaxed enforcement of these policies in 2019 has seemingly begun to reverse this trend: approximately 4,253–10,343 km² of forest has been impacted by fire, leading to some of the most severe potential impacts on biodiversity since 2009. These results highlight the critical role of policy enforcement in the preservation of biodiversity in the Amazon.
Article
Full-text available
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.
Article
Full-text available
Northern peatlands are experiencing more frequent and severe fire events as a result of changing climate conditions. Recent studies show that such a fire-regime change imposes a direct climate-warming impact by emitting large amounts of carbon into the atmosphere. However, the fires also convert parts of the burnt biomass into pyrogenic carbon. Here, we show a potential climate-cooling impact induced by fire-derived pyrogenic carbon in laboratory incubations. We found that the accumulation of pyrogenic carbon reduced post-fire methane production from warm (32 °C) incubated peatland soils by 13–24%. The redox-cycling, capacitive, and conductive electron transfer mechanisms in pyrogenic carbon functioned as an electron snorkel, which facilitated extracellular electron transfer and stimulated soil alternative microbial respiration to suppress methane production. Our results highlight an important, but overlooked, function of pyrogenic carbon in neutralizing forest fire emissions and call for its consideration in the global carbon budget estimation. Warmer and drier conditions are increasing the frequency of forest fires, which in turn produce pyrogenic carbon. Here the authors show that accumulation of pyrogenic carbon can suppress post-fire methane production in northern peatlands and can effectively buffer fire-derived greenhouse gas emissions.
Article
Full-text available
Rapid climate change was a major contributor to the end-Permian extinction (EPE). Although well constrained for the marine realm, relatively few records document the pace, nature, and magnitude of climate change across the EPE in terrestrial environments. We generated proxy records for chemical weathering and land surface temperature from continental margin deposits of the high-latitude southeastern margin of Gondwana. Regional climate simulations provide additional context. Results show that Glossopteris forest-mire ecosystems collapsed during a pulse of intense chemical weathering and peak warmth, which capped ~1 m.y. of gradual warming and intensification of seasonality. Erosion resulting from loss of vegetation was short lived in the low-relief landscape. Earliest Triassic climate was ~10–14 °C warmer than the late Lopingian and landscapes were no longer persistently wet. Aridification, commonly linked to the EPE, developed gradually, facilitating the persistence of refugia for moisture-loving terrestrial groups.
Article
Full-text available
Aim Megafires are increasing in intensity and frequency globally. The impacts of megafires on biodiversity can be severe, so conservation managers must be able to respond rapidly to quantify their impacts, initiate recovery efforts and consider conservation options within and beyond the burned extent. We outline a framework that can be used to guide conservation responses to megafires, using the 1.5 million hectare 2019/2020 megafires in Victoria, Australia, as a case study. Location Victoria, Australia. Methods Our framework uses a suite of decision support tools, including species attribute databases, ~4,200 species distribution models and a spatially explicit conservation action planning tool to quantify the potential effects of megafires on biodiversity, and identify species‐specific and landscape‐scale conservation actions that can assist recovery. Results Our approach identified 346 species in Victoria that had >40% of their modelled habitat affected by the megafire, including 45 threatened species, and 102 species with >40% of their modelled habitat affected by high severity fire. We then identified 21 candidate recovery actions that are expected to assist the recovery of biodiversity. For relevant landscape‐scale actions, we identified locations within and adjacent to the megafire extent that are expected to deliver cost‐effective conservation gains. Main conclusion The 2019/2020 megafires in south‐eastern Australia affected the habitat of many species and plant communities. Our framework identified a range of single‐species (e.g., supplementary feeding, translocation) and landscape‐scale actions (e.g., protection of refuges, invasive species management) that can help biodiversity recover from megafires. Conservation managers will be increasingly required to rapidly identify conservation actions that can help species recover from megafires, especially under a changing climate. Our approach brings together commonly used datasets (e.g., species distribution maps, trait databases, fire severity mapping) to help guide conservation responses and can be used to help biodiversity recover from future megafires across the world.
Article
Full-text available
Aim To quantify the impact of the 2019–2020 megafires on Australian plant diversity by assessing burnt area across 26,062 species ranges and the effects of fire history on recovery potential. Further, to exemplify a strategic approach to prioritizing plant species affected by fire for recovery actions and conservation planning at a national scale. Location Australia. Methods We combine data on geographic range, fire extent, response traits and fire history to assess the proportion of species ranges burnt in both the 2019–2020 fires and the past. Results Across Australia, suitable habitat for 69% of all plant species was burnt (17,197 species) by the 2019–2020 fires and herbarium specimens confirm the presence of 9,092 of these species across the fire extent since 1950. Burnt ranges include those of 587 plants listed as threatened under national legislation (44% of Australia's threatened plants). A total of 3,998 of the 17,197 fire‐affected species are known to resprout after fire, but at least 2,928 must complete their entire life cycle—from germinant to reproducing adult—prior to subsequent fires, as they are killed by fire. Data on previous fires show that, for 257 species, the historical intervals between fire events across their range are likely too short to allow regeneration. For a further 411 species, future fires during recovery will increase extinction risk as current populations are dominated by immature individuals. Main conclusion Many Australian plant species have strategies to persist under certain fire regimes, and will recover given time, suitable conditions and low exposure to threats. However, short fire intervals both before and after the 2019–2020 fire season pose a serious risk to the recovery of at least 595 species. Persistent knowledge gaps about species fire response and post‐fire population persistence threaten the effective long‐term management of Australian vegetation in an increasingly pyric world.
Article
Full-text available
The Triassic sandstones of the Panchet and Parsora formations are deposited in the Damodar and Son basins of the Peninsular India. Though both the formations have similarity in depositional and lithification processes, their diagenetic history and authigenic clay minerals formation have little differences. To improve understanding of diagenesis and associated clay minerals, the present study examined in Triassic sandstones. The Lower Triassic Panchet sandstones are poorly sorted arkose and originate from nearby granitoid terrain. The early diagenetic assemblages of the sandstones are kaolinite–iron oxide, montmorillonite, quartz and cement in the sandstones formed in oxy-acidic environment under shallow burial condition. Authigenic chlorite and recrystallised interstitial components such as orthomatrix are the main late diagenetic products formed, respectively, at oxy-acidic and reducing alkaline conditions where carbonate and allogenic iron cements were emplaced as the latest events. The Panchet and the Parsora formations are the riverine Triassic deposits and have almost identical early diagenetic assemblages. The kaolinisation in sandstone is loss of feldspar and is more pronounced in the Parsora Formation. The late diagenetic products in both the formations essentially similar and differ only in their relative chlorite content, which was formed under elevated temperature as an effect of tectonic activity. Allogenic iron and carbonate cements are post-tectonic.
Article
Full-text available
Palaeo-wildfire, which had an important impact on the end Permian terrestrial ecosystems, became more intense in the latest Permian globally, evidenced by extensive occurrence of fossil charcoals. In this study, we report abundant charcoals from the upper part of the Xuanwei Formation and the Permian–Triassic transitional Kayitou Formation in the Lengqinggou section, western Guizhou Province, Southwest China. These charcoals are well-preserved with anatomical structures and can be classified into seven distinctive types according to their characteristics. Organic carbon isotopic analyses of both bulk rocks and charcoals show that the δ13Corg values in the Kayitou Formation are notably more negative than those in the Xuanwei Formation, with a negative excursion of 4.08‰ immediately above the volcanic ash bed in the middle of the uppermost coal bed of the Xuanwei Formation. Charcoals with high reflectance values (Romean = 2.38%) are discovered below the ash bed. By contrast, the reflectance values (Romean = 1.51%) of the charcoals in the Kayitou Formation are much lower than those of the Xuanwei Formation, indicating the palaeo-wildfire types have changed from crown fires to surface fires, which was probably due to the retrogression of vegetation systems during the extinction. Based on the above evidence, we suppose that palaeo-wildfires became more frequent and more severe since the climate became drier during the latest Permian in Southwest China, and the eventual vegetation changeover of the terrestrial ecosystems in Southwest China could be caused by volcanism.
Article
Full-text available
It is important to understand how Earth's surface conditions have changed over geological timescales and what has driven these changes. Much of this understanding comes from combining geological and geochemical data with global biogeochemical models, but designing and running computer models over these vast timeframes poses a serious challenge. Traditionally one must choose between running a climate-enabled model for sets of shorter-term scenarios or running a dimensionless ‘box’ model for long periods, but with a poor representation of climate. In this paper we introduce a method to run a climate-enabled biogeochemical model over Phanerozoic timescales: which we term Spatial Continuous Integration (SCION). This approach combines two key methods in the literature, which form the basis of the ‘GEOCLIM’ and ‘COPSE’ models respectively, and the resulting model is able to compute whole-Phanerozoic linked climate and biogeochemistry, as well as outputting geochemical isotope tracers to aid in hypothesis testing. This new model differs from GEOCLIM because it is able to run continuously over the whole Phanerozoic, and it differs from COPSE by having a spatial representation of climate and continental processes. Spatial representation of climate allows for detailed approximations for surface weathering processes through changes in temperature, erosion and runoff, and the SCION predictions for atmospheric CO2 variations over Phanerozoic time show better agreement with data than predictions from nondimensional models. Despite this, several inconsistencies remain with the geological record, most notably the inability of the model to reproduce transient late Ordovician cooling, and general over-estimation of CO2 levels during the Paleozoic. These discrepancies may be addressed in future work by including a scheme for positioning of highly-weatherable volcanic terranes, and by better capturing the behaviour of the terrestrial biosphere. The model approach we outline here is ideally suited for expansion to include these aspects.
Article
Full-text available
Teratological spores and pollen are widespread in sediments that record the Permian- Triassic mass extinction. The malformations are thought to be the result of extreme environmental conditions at that time, but the mutagenic agents and the precise timing of the events remain unclear. We examined the abundance of teratological sporomorphs and metal concentrations in a Permian-Triassic tropical peatland succession of southwestern China. We find a significant peak of spore tetrads of lycopsid plants (as much as 19% of all sporomorphs) coeval with increases in Cu and Hg concentrations above the main terrestrial extinction interval, which marks the loss of Permian Gigantopteris forests, increased wildfire activity, and the disappearance of coal beds. Thus, in tropical peatlands, mutagenesis affected only surviving plants. Mutagenesis was likely caused by metal toxicity, linked to increased Hg and Cu loading, but was not itself a direct cause of the terrestrial crisis.
Article
Full-text available
The newly defined Frazer Beach Member of the Moon Island Beach Formation is identified widely across the Sydney Basin in both outcrop and exploration wells. This thin unit was deposited immediately after extinction of the Glossopteris flora (defining the terrestrial end-Permian extinction event). The unit rests conformably on the uppermost Permian coal seam in most places. A distinctive granule-microbreccia bed is locally represented at the base of the member. The unit otherwise consists of dark gray to black siltstone, shale, mudstone and, locally, thin lenses of fine-grained sandstone and tuff. The member represents the topmost unit of the Newcastle Coal Measures and is overlain gradationally by the Dooralong Shale or with a scoured (disconformable) contact by coarse-grained sandstones to conglomerates of the Coal Cliff Sandstone, Munmorah Conglomerate and laterally equivalent units. The member is characterized by a palynological “dead zone” represented by a high proportion of degraded wood fragments, charcoal, amorphous organic matter and fungal spores. Abundant freshwater algal remains and the initial stages of a terrestrial vascular plant recovery flora are represented by low-diversity spore-pollen suites in the upper part of the unit in some areas. These assemblages are referable to the Playfordiaspora crenulata Palynozone interpreted as latest Permian in age on the basis of high precision Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-IDTIMS) dating of thin volcanic ash beds within and stratigraphically bracketing the unit. Plant macrofossils recovered from the upper Frazer Beach Member and immediately succeeding strata are dominated by Lepidopteris (Peltaspermaceae) and Voltziopsis (Voltziales) with subsidiary pleuromeian lycopsids, sphenophytes, and ferns. Sparse vertebrate and invertebrate ichnofossils are also represented in the Frazer Beach Member or in beds immediately overlying this unit. The Frazer Beach Member is correlative, in part, with a thin interval of organic-rich mudrocks, commonly known as the “marker mudstone” capping the Permian succession further to the north in the Bowen, Galilee and Cooper basins. The broad geographic distribution of this generally <5-m-thick mudrock unit highlights the development in eastern Gondwana of extensive, short-lived, shallow lacustrine systems with impoverished biotas in alluvial plain settings in the immediate aftermath of the end-Permian biotic crisis.
Article
Full-text available
Eruption of the Siberian Traps large igneous province (LIP) is thought to have triggered the Permian-Triassic biological crisis, the largest of the Phanerozoic mass extinctions. Mercury concentration enrichments have been widely used as a proxy for volcanic inputs to sediments, especially for ancient LIP eruptions. However, detailed correlations of magmatic pulses with extinction events in the terrestrial and marine realms are not fully resolved. Here we use paired coronene (a six-ring polycyclic aromatic hydrocarbon, a high-temperature combustion proxy) and mercury spikes as a refined proxy for LIP emplacement. In records from stratigraphic sections in south China and Italy, we identify two sets of paired coronenemercury spikes accompanied by land plant biomarker spikes, followed by a rapid decrease coinciding with terrestrial ecological disturbance and extinction of marine metazoans. Each short-term episode is likely caused by high-temperature combustion of sedimentary hydrocarbons during initial sill emplacement of the Siberian Traps LIP. These data indicate that discrete volcanic eruptions could have caused the terrestrial ecosystem crisis followed by the marine ecosystem crisis in ∼60 k.y., and that the terrestrial ecosystem was disrupted by smaller global environmental changes than the marine ecosystem.
Article
Full-text available
A monospecific flora containing a peltasperm species, Germaropteris martinsii, is discovered from the uppermost Permian Kayitou Formation of Southwest China. The epidermal characteristics of G. martinsii from the South China Block are described for the first time on the basis of charcoalified specimens. The plant is characterized by small, leathery foliage with prominent papillate epidermal cells, and slightly sunken stomata. The stomatal apertures are covered by the long papillae of the surrounding subsidiary cells. The specific epidermal traits suggest that G. martinsii is a highly environmentally tolerant taxon that probably formed monospecific communities during the dramatic degradation of the peat-forming rainforest ecosystems. The frequent appearance of charcoalified leaves in the flora demonstrates that intense wildfires were prevalent at the time. The appearance and reflectance value (1.33%) of these charcoalified leaves reveal that they were formed at temperatures of 450-500°C during brief surface fires. Our study indicates that the terrestrial ecosystems may have been frequently subjected to desiccation and was vulnerable to the spread of fires as a result of the end-Permian biotic crisis in the tropics of the eastern Tethys region.
Article
Full-text available
A distinctive burrow form, Reniformichnus australis n. isp., is described from strata immediately overlying and transecting the end-Permian extinction (EPE) horizon in the Sydney Basin, eastern Australia. Although a unique excavator cannot be identified, these burrows were probably produced by small cynodonts based on comparisons with burrows elsewhere that contain body fossils of the tracemakers. The primary host strata are devoid of plant remains apart from wood and charcoal fragments, sparse fungal spores, and rare invertebrate traces indicative of a very simplified terrestrial ecosystem characterizing a 'dead zone' in the aftermath of the EPE. The high-paleolatitude (~65-758S) setting of the Sydney Basin, together with its higher paleoprecipitation levels and less favorable preservational potential, is reflected by a lower diversity of vertebrate fossil burrows and body fossils compared with coeval continental interior deposits of the mid-paleolatitude Karoo Basin, South Africa. Nevertheless, these burrows reveal the survivorship of small tetrapods in considerable numbers in the Sydney Basin immediately following the EPE. A fossorial lifestyle appears to have provided a selective advantage for tetrapods enduring the harsh environmental conditions that arose during the EPE. Moreover, high-paleolatitude and maritime settings may have provided important refugia for terrestrial vertebrates at a time of lethal temperatures at low-latitudes and aridification of continental interiors.
Article
Full-text available
Earth has a long geological history and palaeo-wildfire is one of the key factors which is responsible for the evolution and extinction of our earth systems. The most important extinction of our earth systems is the Permian-Triassic mass extinction. The objective of this paper is to evaluate the product of wildfire in terms of distribution and occurrences from the Late Permian North China basin. Fourteen rock samples were collected from a drill core of Hanxing Coalfield of North China basin. The samples were analyzed by macro and micro petrography, Scanning Electron Microscopy (SEM), Gas Chromatography (GC) and Gas Chromatography–Mass Spectrometry (GC-MS) in order to study the evidence of wildfire. Charcoal (inertinite) particles are observed in the samples, which established the occurrences of wildfire during the upper Middle and Late Permian time in North China. Additionally, high-molecular-weight Polycyclic Aromatic Hydrocarbons (PAHs) were detected in the studied samples which also reinforce the presence of palaeo–wildfire events in the North China basin in Late Permian due to the fact that these aromatic compounds were formed under high temperatures.
Article
Full-text available
In the semiarid Southwestern USA, wildfires are commonly followed by runoff-generated debris flows because wildfires remove vegetation and ground cover, which reduces soil infiltration capacity and increases soil erodibility. At a study site in Southern California, we initially observed runoff-generated debris flows in the first year following fire. However, at the same site three years after the fire, the mass-wasting response to a long-duration rainstorm with high rainfall intensity peaks was shallow landsliding rather than runoff-generated debris flows. Moreover, the same storm caused landslides on unburned hillslopes as well as on slopes burned 5 years prior to the storm and areas burned by successive wildfires, 10 years and 3 years before the rainstorm. The landslide density was the highest on the hillslopes that had burned 3 years beforehand, and the hillslopes burned 5 years prior to the storm had low landslide densities, similar to unburned areas. We also found that reburning (i.e., two wildfires within the past 10 years) had little influence on landslide density. Our results indicate that landscape susceptibility to shallow landslides might return to that of unburned conditions after as little as 5 years of vegetation recovery. Moreover, most of the landslide activity was on steep, equatorial-facing slopes that receive higher solar radiation and had slower rates of vegetation regrowth, which further implicates vegetation as a controlling factor on post-fire landslide susceptibility. Finally, the total volume of sediment mobilized by the year 3 landslides was much smaller than the year 1 runoff-generated debris flows, and the landslides were orders of magnitude less mobile than the runoff-generated debris flows.
Article
Full-text available
Land degradation and water resources pollution caused by catastrophic wildfires is of growing concern in prone‐fire regions. Studies on the effects of wildfire on hydrology and erosion have mostly been conducted at plot or hillslope scale, while relatively few studies investigated post‐wildfire hydrological responses and erosion at the meso‐catchment scale (~>10 km²) in the Mediterranean. This study used measured discharge and suspended sediment at the outlet of a burnt catchment in southern Portugal, before and after a wildfire, to investigate post‐wildfire changes in hydrological and erosion responses to rainfall. Hydrological and sediment connectivity patterns were derived to investigate changing dynamics induced by the fire within the catchment. The main findings were: 1) although a large part of the catchment experienced moderate to high severity burning, post‐wildfire hydro‐sedimentary response was considerably limited; 2) meteorological variability determined hydrological responses and erosion more strongly than wildfire effects; 3) during the post‐wildfire vegetation recovery period, only rainfall events with a high return period (~ 2 years) enhanced the hydrological and erosion responses. This can be explained by the spatial scale dependency of these processes and limited fine sediment supply, or relatively low connectivity in the study catchment. While connectivity is only an indicator, this implies that, at the meso‐catchment scale, pollution of downstream water bodies by contaminated soil and ash may not occur immediately. Rather, because sediments and associated ashes and contaminants are first being transported to the areas around the stream networks, they only reach the outlet during heavy events which do connect the entire catchment. Thus, dynamic indices of connectivity that take rainfall event characteristics into consideration need to be further tested to assess and manage post‐wildfire soil and water contamination risk. This article is protected by copyright. All rights reserved.
Article
Full-text available
The trajectory and recovery time of fire-disturbed forests depend on the capacity of seedlings and resprouts to get established over time. Here, we investigated the mechanisms associated with fire effects on post-fire regeneration in the context of a large-scale fire experiment located in southeastern Amazonia. Specifically, we tested the hypothesis that recurrent understory fires reduce forest regeneration capacity by reducing the recruitment of seedlings, the viability of the soil seed bank, the seed rain, and the resprouts. The experiment was comprised of three 50-ha plots: an unburned control, and two plots that were experimentally burned three (triennially) or six (annually) times between 2004 and 2010. Seedlings represented 2.4 and 0.6% of the seed rain and soil seed bank in the Control and burned treatment plots, respectively. Compared to the control, the triennial burns caused more reduction than the annual ones in seed rain (−42 vs. −10%) and seed bank (−78 vs. −50%). These fire-related reduction in seed rain in both treatments explain most of the low post-fire density of seedlings (0.4 and 0.8 ind/m2, respectively), compared with the Control (2.9 ind/m2). The 3-year interval between fires contributed to highest mortality of seeds stored in the soil than in the annual burn treatment, where fires were less severe. However, there were 5.5 times more resprouting in the plot burned triennially compared with the one burned annually. In both treatments, though, the number of resprouts declined over time. In conclusion, seeds from both seed rain and seed bank and resprouting were negatively affected by both fire frequencies, reducing the likelihood of native species recovery by altering the regeneration pathways. This situation is expected to be increasingly common in southeastern Amazon forests, particularly under warmer and dryer climate conditions.
Article
Full-text available
Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal and the Permo‐Triassic boundary, either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.
Article
Full-text available
Records suggest that the Permo–Triassic mass extinction (PTME) involved one of the most severe terrestrial ecosystem collapses of the Phanerozoic. However, it has proved difficult to constrain the extent of the primary productivity loss on land, hindering our understanding of the effects on global biogeochemistry. We build a new biogeochemical model that couples the global Hg and C cycles to evaluate the distinct terrestrial contribution to atmosphere–ocean biogeochemistry separated from coeval volcanic fluxes. We show that the large short-lived Hg spike, and nadirs in δ²⁰²Hg and δ¹³C values at the marine PTME are best explained by a sudden, massive pulse of terrestrial biomass oxidation, while volcanism remains an adequate explanation for the longer-term geochemical changes. Our modelling shows that a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant biogeochemical changes, and cascaded organic matter, nutrients, Hg and other organically-bound species into the marine system.
Article
Full-text available
Large spikes in mercury (Hg) concentration are observed globally at the latest Permian extinction (LPE) horizon that are thought to be related to enhanced volcanic emissions of the Siberian Traps large igneous province (LIP). While forming an effective chemostratigraphic marker, it remains unclear whether such enhanced volcanic Hg emissions could have generated toxic conditions that contributed to extinction processes. To address this, we examined the nature of enhanced Hg emissions from the Siberian Traps LIP and the potential impact it may have had on global ecosystems during the LPE. Model results for a LIP eruption predict that pulses of Hg emissions to the atmosphere would have been orders of magnitude greater than normal background conditions. When deposited into world environments, this would have generated a series of toxic shocks, each lasting >1000 yr. Such repeated Hg loading events would have had severe impact across marine trophic levels, as well as been toxic to terrestrial plant and animal life. Such high Hg loading rates may help explain the co-occurrence of marine and terrestrial extinctions.
Article
Full-text available
Wildfire disturbances effect changes in vegetation communities that in turn influence climate. Such changes in boreal forest ecosystems can persist over decadal time scales or longer. In the ecotone between boreal forest and steppe in the region southeast of Lake Baikal in southern Siberia, shifts between the two vegetation types may be precipitated by variations in site specific conditions, as well as disturbance characteristics such as fire frequency and severity. Warmer, drier conditions in the region have been associated with a decrease in fire return intervals and greater burn severity that may, in turn, drive conversion of forests to steppe vegetation at a greater rate than has occurred prior to the onset of warming and drying. Stand-replacing fires in Pinus sylvestris stands in southern Siberia may lead to recruitment failure postfire, particularly on southwest to west-facing slopes, which are more often dominated by grasses. This study uses a combination of field data and remotely sensed indices of vegetation and moisture to distinguish between recruitment pathways in southern Siberia, and to study the influence of factors related to soils, topography, fire severity and winter snow cover on these. We expected that recruitment success would be associated with lower burn severity (higher NBR), higher greenness (NDVI) and moisture (NDMI), and winter snow (NDSI) postfire. We also expected phenological characteristics to differ among recruitment paths. Prior to burning, our sites are broadly similar in terms of remotely sensed indices of moisture (NDMI), vegetation (NDVI), and winter fractional snow cover (NDSI), but recruitment failure sites are generally drier and less green postfire. Initial differences in greenness and moisture among sites characterized by abundant recruitment (AR), intermediate recruitment (IR) and recruitment failure (RF) become more pronounced over the initial decades postfire. The earliest separability of AR and RF sites using remotely sensed indices occurs in the winter months 3-4 years postfire, during which time NDSI is highest for AR sites and lowest for RF. Although seasonality was important with regard to distinguishing among AR, IR and RF index values, the timing of phenological events such as start and end of season did not differ significantly among the sites.
Article
Full-text available
The size and frequency of large wildfires in western North America have increased in recent years, a trend climate change is likely to exacerbate. Due to fuel limitations, recently burned forests resist burning for upwards of 30 years; however, extreme fire-conducive weather enables reburning at shorter fire-free intervals than expected. This research quantifies the outcomes of short-interval reburns in upland and wetland environments of northwestern Canadian boreal forests and identifies an interactive effect of post-fire drought. Despite adaptations to wildfire amongst boreal plants, post-fire forests at paired short- and long-interval sites were significantly different, with short-interval sites having lower stem densities of trees due to reduced conifer recruitment, a higher proportion of broadleaf trees, less residual organic material, and reduced herbaceous vegetation cover. Drought reinforced changes in proportions of tree species and decreases in tree recruitment, reinforcing non-resilient responses to short-interval reburning. Drier and warmer weather will increase the incidence of short-interval reburning and amplify the ecological changes such events cause, as wildfire activity and post-fire drought increase synergistically. These interacting disturbances will accelerate climate-driven changes in boreal forest structure and composition. Our findings identify processes of ongoing and future change in a climate-sensitive biome.
Article
Full-text available
The collapse of late Permian (Lopingian) Gondwanan floras, characterized by the extinction of glossopterid gymnosperms, heralded the end of one of the most enduring and extensive biomes in Earth’s history. The Sydney Basin, Australia, hosts a nearcontinuous, age-constrained succession of high southern paleolatitude (∼65–75°S) terrestrial strata spanning the end-Permian extinction (EPE) interval. Sedimentological, stable carbon isotopic, palynological, and macrofloral data were collected from two cored coal-exploration wells and correlated. Six palynostratigraphic zones, supported by ordination analyses, were identified within the uppermost Permian to Lower Triassic succession, corresponding to discrete vegetation stages before, during, and after the EPE interval. Collapse of the glossopterid biome marked the onset of the terrestrial EPE and may have significantly predated the marine mass extinctions and conodont-defined Permian–Triassic Boundary. Apart from extinction of the dominant Permian plant taxa, the EPE was characterized by a reduction in primary productivity, and the immediate aftermath was marked by high abundances of opportunistic fungi, algae, and ferns. This transition is coeval with the onset of a gradual global decrease in δ13Corg and the primary extrusive phase of Siberian Traps Large Igneous Province magmatism. The dominant gymnosperm groups of the Gondwanan Mesozoic (peltasperms, conifers, and corystosperms) all appeared soon after the collapse but remained rare throughout the immediate post-EPE succession. Faltering recovery was due to a succession of rapid and severe climatic stressors until at least the late Early Triassic. Immediately prior to the Smithian–Spathian boundary (ca. 249 Ma), indices of increased weathering, thick redbeds, and abundant pleuromeian lycophytes likely signify marked climate change and intensification of the Gondwanan monsoon climate system. This is the first record of the Smithian–Spathian floral overturn event in high southern latitudes.
Article
Full-text available
Current large-scale deforestation poses a threat to ecosystems globally, and imposes substantial and prolonged changes on the hydrological and carbon cycles. The tropical forests of the Amazon and Indonesia are currently undergoing deforestation with catastrophic ecological consequences but widespread deforestation events have occurred several times in Earth's history and these provide lessons for the future. The end-Permian mass-extinction event (EPE; ∼252 Ma) provides a global, deep-time analogue for modern deforestation and diversity loss. We undertook centimeter-resolution palynological, sedimentological, carbon stable-isotope and paleobotanical investigations of strata spanning the end-Permian event at the Frazer Beach and Snapper Point localities, in the Sydney Basin, Australia. We show that the typical Permian temperate, coal-forming, forest communities disappeared abruptly, followed by the accumulation of a 1-m-thick mudstone poor in organic matter that, in effect, represents a 'dead zone' hosting degraded wood fragments, charcoal and fungal spores. This signals a catastrophic scenario of vegetation die-off and extinction in southern high-latitude terrestrial settings. Lake systems, expressed by laterally extensive but generally less than a few-metres-thick laminated siltstones, generally lacking bioturbation, hosting assemblages of algal cysts and freshwater acritarchs, developed soon after the vegetation die-off. The first traces of vascular plant recovery occur ∼1.6 m above the extinction horizon. Based on analogies with modern deforestation, we propose that the global fungal and acritarch events of the Permo-Triassic transition resulted directly from inundation of basinal areas following water-table rise as a response to the abrupt disappearance of complex vegetation from the landscape. The δ 13 C org values reveal a significant excursion toward low isotopic values, down to −31h (a shift of ∼4h), across the end-Permian event. The magnitude of the shift at that time records a combination of changes in the global carbon cycle that were enhanced by the local increase in microbial activity, possibly also involving cyanobacterial proliferation. We envisage that elevated levels of organic and mineral nutrients delivered from inundated dead forests, enhanced weathering and erosion of extra-basinal areas, together with local contributions of volcanic ash, led to eutrophication and increased salinity of basinal lacustrine-lagoonal environments. We propose that the change in acritarch communities recorded globally in nearshore marine settings across the end-Permian event is to a great extent a consequence of the influx of freshwater algae and nutrients from the continents. Although this event coincides with the Siberian trap volcanic activity, we note that felsic-intermediate volcanism was extensively developed along the convergent Panthalassan margin of Pangea at that time and might also have contributed to environmental perturbations at the close of the Permian.
Article
Full-text available
The Siberian Traps large igneous province (STLIP) was the likely trigger for the ca. 252 Ma latest Permian mass extinction (LPME), but direct evidence for global volcanic effects on land remains rare. Here, we used mercury (Hg) enrichments, a proxy for ancient volcanic activity, to assess volcanic inputs to two terrestrial Permian-Triassic boundary (PTB) sections that were separated by thousands of kilometers and represent different latitudinal zones-the peri-equatorial Lubei section (South China craton) and the high-latitude (40-60°N) Dalongkou section (Junggar terrane). Both sections exhibit strong Hg enrichment within a discrete (≤40 m) stratigraphic window representing the LPME. At Lubei, this interval is also characterized by negative mass-independent fractionation (MIF) of odd Hg isotopes, consistent with massive volcanogenic and/or terrestrial Hg inputs. These findings are significant in documenting Hg spikes and negative MIF excursions near the PTB in terrestrial sections for the first time, providing evidence of the global influence of the STLIP, as well as in demonstrating at high stratigraphic resolution its synchronicity with the PTB negative carbon-isotope excursion (CIE), supporting a common global cause for these anomalies.
Article
Full-text available
Premise of research. Permineralized peats are prized for hosting three-dimensionally preserved plant remains that provide insights into fossil plant anatomy and the composition of coal-forming ecosystems. A new record of siliceous permineralized peat is documented from a Lopingian-aged (upper Permian) strata from the southern Sydney Basin. It represents the fifth Permian permineralized peat identified from eastern Australia. Methodology. The single permineralized peat block was cut into smaller blocks, and both cellulose acetate peels and standard thin sections were prepared for study using transmitted light microscopy. Quantitative analysis of the peat was carried out using point counts perpendicular to bedding. One block examined using synchrotron X-ray computed tomography (CT) revealed the three-dimensional anatomy of abundant fossil seeds. Pivotal results. The peat contains a plant assemblage dominated by glossopterid leaves, seeds, and axes; although degraded, probable pteridophyte remains represent a significant subsidiary component of the assemblage. A new leaf form (Glossopteris thirroulensis McLoughlin et Mays sp. nov.) and a new type of seed (Illawarraspermum ovatum McLoughlin et Mays gen. et sp. nov.) are described. Leaf-, wood/seed-, and fine detritus-rich organic microfacies with gradational boundaries are evident within the peat. Conclusions. Regular growth rings in the small permineralized axes, together with the occurrence of autumnal mats of glossopterid leaves, signify a strongly seasonal climate. The presence of abundant charcoal in the peat indicates that fire was a significant influence on the high-paleolatitude mire ecosystem. Differentiation of organic microfacies within the peat profile indicates subtle variation in the contribution of plant components to the peat through time. The absence of mineral grains in thin section and CT, together with the presence of authigenic sulfides, indicates accumulation of organic matter in a stagnant mire away from the influence of clastic input.
Article
Full-text available
Tropical woody plants store ∼230 petagrams of carbon (PgC) in their aboveground living biomass. This review suggests that these stocks are currently growing in primary forests at rates that have decreased in recent decades. Droughts are an important mechanism in reducing forest C uptake and stocks by decreasing photosynthesis, elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. Tropical forests were a C source to the atmosphere during the 2015–2016 El Niño–related drought, with some estimates suggesting that up to 2.3 PgC were released. With continued climate change, the intensity and frequency of droughts and fires will likely increase. It is unclear at what point the impacts of severe, repeated disturbances by drought and fires could exceed tropical forests’ capacity to recover. Although specific threshold conditions beyond which ecosystem properties could lead to alternative stable states are largely unknown, the growing body of scientific evidence points to such threshold conditions becoming more likely as climate and land use change across the tropics. ▪ Droughts have reduced forest carbon uptake and stocks by elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. ▪ Threshold conditions beyond which tropical forests are pushed into alternative stable states are becoming more likely as effects of droughts intensify.
Article
Full-text available
Application of biochar to soils changes soil physicochemical properties and stimulates the activities of soil microorganisms that influence soil quality and plant performance. Studying the response of soil microbial communities to biochar amendments is important for better understanding interactions of biochar with soil, as well as plants. However, the effect of biochar on soil microorganisms has received less attention than its influences on soil physicochemical properties. In this review, the following key questions are discussed: (i) how does biochar affect soil microbial activities, in particular soil carbon (C) mineralization, nutrient cycling, and enzyme activities? (ii) how do microorganisms respond to biochar amendment in contaminated soils? and (iii) what is the role of biochar as a growth promoter for soil microorganisms? Many studies have demonstrated that biochar-soil application enhances the soil microbial biomass with substantial changes in microbial community composition. Biochar amendment changes microbial habitats, directly or indirectly affects microbial metabolic activities, and modifies the soil microbial community in terms of their diversity and abundance. However, chemical properties of biochar, (especially pH and nutrient content), and physical properties such as pore size, pore volume, and specific surface area play significant roles in determining the efficacy of biochar on microbial performance as biochar provides suitable habitats for microorganisms. The mode of action of biochar leading to stimulation of microbial activities is complex and is influenced by the nature of biochar as well as soil conditions.
Article
Full-text available
During the End-Permian mass extinction event (EPME) there is extensive evidence for depletion of oxygen in the marine realm. Atmospheric models based upon biogeochemical cycling predict a comparable decline leading up to this event and have been postulated as a possible driver for marine depletion. However, these models contrast with broadly contemporaneous empirical evidence from charcoal in coals. New charcoal data from the temporally well-constrained late Permian Xuanwei Formation coals of eastern Yunnan Province, China, deposited just prior to the onset of the Permian-Triassic Transitional Beds, supports the coarser analysis and further challenges these biogeochemical models. Inertinite group macerals, comprising fusinite, semifusinite, macrinite, inertodetrinite, secretinite, all funginite with elevated reflectance, and some micrinite, are proxies for wildfire activity, and indicate abundant evidence for this phenomenon in the latest Permian and preclude low levels of atmospheric oxygen concentration coevally. Henceforward, we will employ the term ‘inertinite group macerals sensu amplo’ to refer to just these precise macerals, though these encompass what are the overwhelming preponderance of inertinites in most coals. Both inertinite abundance and reflectance indicate an increase in fire activity and intensity towards the End-Permian faunal crisis. Quantitatively, these inertinite data indicate atmospheric oxygen concentration was high and at the close of the Paleozoic was probably elevated to levels well above those of the present-day. The elevated fire activity at this time may have functioned as a causal link to explain some localized oxygen depletion in the marine realm as a result of post-fire increased run-off and erosion. However, globally depressed atmospheric oxygen concentration at the End-Permian was not a driver of extensive marine anoxia at that time.
Article
Full-text available
Distribution and abundance of charcoal in coal seams (in form of pyrogenic macerals of the inertinites group) have been considered as a reliable tool to interpret the local and regional palaeo-wildfire regimes in peat-forming depositional environments. Although the occurrence of inertinites is globally well documented for the Late Palaeozoic, the description of palaeo-botanical evidence concerning the source plants of such charcoal is so far largely missing. In the present study, we provide the first detailed analysis of macro-charcoal preserved in the Barro Branco coal seam, Rio Bonito Formation, Cisuralian of the Paraná Basin, Santa Catarina State, Brazil. Charcoal, in form of macro-charcoal and inertinites, was documented in all the six coal-bearing strata that compose the succession, confirming the occurrence of recurrent palaeo-wildfires during its deposition. Reflectance values indicated a mean charring temperature reaching ~515˚C (and up to 1,045˚C in excess) and the macro-charcoal exhibits anatomical features of secondary xylem of Agathoxylon. Combination of results derived from palaeobotanical and petrological data demonstrates that gymnosperm-dominated vegetation was repeatedly submitted to fire events and reinforced the hypothesis that Gondwanan mires were high-fire systems during the Cisuralian.
Article
Full-text available
The New England Orogen (NEO), the youngest of the orogens of the Tasmanides of eastern Australia, is defined by two main cycles of compression–extension. The compression component involves thrust tectonics and advance of the arc towards the continental plate, while extension is characterised by rifting, basin formation, thermal relaxation and retreat of the arc towards the oceanic plate. A compilation of 623 records of U–Pb zircon geochronology rock ages from Geoscience Australia, the geological surveys of Queensland and New South Wales and other published research throughout the orogen, has helped to clarify its complex tectonic history. This contribution focuses on the entire NEO and is aimed at those who are unfamiliar with the details of the orogen and who could benefit from a summary of current knowledge. It aims to fill a gap in recent literature between broad-scale overviews of the orogen incorporated as part of wider research on the Tasmanides and detailed studies usually specific to either the northern or southern parts of the orogen. Within the two main cycles of compression–extension, six accepted and distinct tectonic phases are defined and reviewed. Maps of geological processes active during each phase reveal the centres of activity during each tectonic phase, and the range in U–Pb zircon ages highlights the degree of diachronicity along the length of the NEO. In addition, remnants of the early Permian offshore arc formed during extensive slab rollback, are identified by the available geochronology. Estimates of the beginning of the Hunter-Bowen phase of compression, generally thought to commence around 265 Ma are complicated by the presence of extensional-type magmatism in eastern Queensland that occurred between 270 and 260 Ma.
Article
Full-text available
Past studies of the end-Permian extinction (EPE), the largest biotic crisis of the Phanerozoic, have not resolved the timing of events in southern high-latitudes. Here we use palynology coupled with high-precision CA-ID-TIMS dating of euhedral zircons from continental sequences of the Sydney Basin, Australia, to show that the collapse of the austral Permian Glossopteris flora occurred prior to 252.3 Ma (~370 kyrs before the main marine extinction). Weathering proxies indicate that floristic changes occurred during a brief climate perturbation in a regional alluvial landscape that otherwise experienced insubstantial change in fluvial style, insignificant reorganization of the depositional surface, and no abrupt aridification. Palaeoclimate modelling suggests a moderate shift to warmer summer temperatures and amplified seasonality in temperature across the EPE, and warmer and wetter conditions for all seasons into the Early Triassic. The terrestrial EPE and a succeeding peak in Ni concentration in the Sydney Basin correlate, respectively, to the onset of the primary extrusive and intrusive phases of the Siberian Traps Large Igneous Province.
Article
The link between the Permian–Triassic mass extinction (252 million years ago) and the emplacement of the Siberian Traps Large Igneous Province (STLIP) was first proposed in the 1990s. However, the complex cascade of volcanically driven environmental and biological events that led to the largest known extinction remains challenging to reconstruct. In this Review, we critically evaluate the geological evidence and discuss the current hypotheses surrounding the kill mechanisms of the Permian–Triassic mass extinction. The initial extrusive and pyroclastic phase of STLIP volcanism was coeval with a widespread crisis of terrestrial biota and increased stress on marine animal species at high northern latitudes. The terrestrial ecological disturbance probably started 60–370 thousand years before that in the ocean, indicating different response times of terrestrial and marine ecosystems to the Siberian Traps eruptions, and was related to increased seasonality, ozone depletion and acid rain, the effects of which could have lasted more than 1 million years. The mainly intrusive STLIP phase that followed is linked with the final collapse of terrestrial ecosystems and the rapid (around 60 thousand years) extinction of 81–94% of marine species, potentially related to a combination of global warming, anoxia and ocean acidification. Nevertheless, the ultimate reasons for the exceptional severity of the Permian–Triassic mass extinction remain debated. Improved geochronology (especially of terrestrial records and STLIP products), tighter ecological constraints and higher-resolution Earth system modelling are needed to resolve the causal relations between volcanism, environmental perturbations and the patterns of ecosystem collapse. At the Permian–Triassic boundary (252 million years ago), a series of environmental crises triggered by the Siberian Traps eruptions caused the extinction of 81–94% of marine species and 70% of terrestrial vertebrate families. This Review discusses the relationships between volcanism, environmental perturbations and ecosystem collapse at the Permian–Triassic boundary. The Permian–Triassic mass extinction (252 million years ago) substantially reduced global biodiversity, with the extinction of 81–94% of marine species and 70% of terrestrial vertebrate families.Sedimentary, palaeontological and geochemical records of the mass extinction indicate that a cascade of environmental changes caused the extinction.The environmental changes can be linked (and attributed to) the effects of volcanic emissions (for example, CO2, SO2, halogens and metals) during the eruption of the Siberian Traps Large Igneous Province.The inferred volcanically driven environmental perturbations include: global warming, oceanic anoxia, oceanic acidification, ozone reduction, acid rain and metal poisoning.The crisis on land probably started about 60–370 thousand years before that in the ocean, indicating the different response times of terrestrial and marine ecosystems to volcanism, but the reasons for the earlier terrestrial crisis remain poorly understood. The Permian–Triassic mass extinction (252 million years ago) substantially reduced global biodiversity, with the extinction of 81–94% of marine species and 70% of terrestrial vertebrate families. Sedimentary, palaeontological and geochemical records of the mass extinction indicate that a cascade of environmental changes caused the extinction. The environmental changes can be linked (and attributed to) the effects of volcanic emissions (for example, CO2, SO2, halogens and metals) during the eruption of the Siberian Traps Large Igneous Province. The inferred volcanically driven environmental perturbations include: global warming, oceanic anoxia, oceanic acidification, ozone reduction, acid rain and metal poisoning. The crisis on land probably started about 60–370 thousand years before that in the ocean, indicating the different response times of terrestrial and marine ecosystems to volcanism, but the reasons for the earlier terrestrial crisis remain poorly understood.
Article
We review recent advances on glossopterid reproductive biology and their implications for seed plant phylogeny and the ecology of this widespread Permian Gondwanan group. Microsporangiate organs are interpreted to have been arranged in loose compound cones—an organization that evokes comparisons with Ginkgoales, Cordaitales and early conifers. The pollen was typically taeniate, bisaccate, and primarily adapted to wind dispersal. The diverse ovuliferous organs generally incorporated some form of marginal flange or wing. In most cases, the wing was probably protective, wrapping around the ovules during early development. However, we postulate that some conspicuous flanges were potentially analogous to angiosperm petals, functioning as corolla-like guides to attract insect pollinators. The arrangement of seed-bearing polysperms adnate to the subtending leaf to form a fertiliger in glossopterids represented another means of protecting the ovules. In some cases, highlighting the polysperm against the attached leaf might have increased the showiness of the ovule-bearing part for pollinators. In other cases, detachment of the fertiliger may have aided anemochory by retarding seed fall through rotation analogous to dispersal in extant Tilia. The microgametophyte in glossopterids is characterized by a short, weakly branched, haustorial tube, and the release of motile sperm cells. At least some seeds of glossopterids express polyembryony. Mature seeds possessed various micropylar modifications for the entrapment of pollen, and winged or bulbous expansions of the outer integument to aid anemochory or possibly hydrochory. Vegetative regeneration as a response to damage occurred via epicormic buds and possibly by the development of lignotubers.
Article
Biochar has received extensive attention because of its multi-functionality for agricultural and environmental applications. Despite its many benefits, there are concerns related to the long-term safety and implications of its application, mainly because the mechanisms affecting soil and organism health are poorly quantified and understood. This work reviews 259 sources and summarises existing knowledge on biochar's adverse effects on soil from a multiangle perspective, including the physicochemical changes in soil, reduced efficiency of agrochemicals, potentially toxic substances in biochar, and effects on soil biota. Suggestions are made for mitigation measures. Mixed findings are often reported; however, the results suggest that high doses of biochar in clay soils are likely to decrease available water content, and surface application of biochar to sandy soils likely increases erosion and particulate matter emissions. Furthermore, biochar may increase the likelihood of excessive soil salinity and decreased soil fertility because of an increase in the pH of alkaline soils causing nutrient precipitation. Regarding the impact of biochar on (agro)chemicals and the role of biochar-borne toxic substances, these factors cannot be neglected because of their apparent undesirable effects on target and non-target organisms, respectively. Concerning non-target biota, adverse effects on reproduction, growth, and DNA integrity of earthworms have been reported along with effects on soil microbiome such as a shift in the fungi-to-bacteria ratio. Given the diversity of effects that biochar may induce in soil, guidelines for future biochar use should adopt a structured and holistic approach that considers all positive and negative effects of biochar.
Article
The upper Paleozoic–lower Mesozoic strata in the northeastern Galilee Basin are important for their hydrocarbon and groundwater potential; however, despite numerous previous investigations, the nature of this stratigraphic interval remains enigmatic. This study integrates lithostratigraphy, palynology and U–Pb zircon geochronology of well-exposed Permian and Triassic sedimentary rocks and nearby stratigraphic cores from the Hughenden district to determine their maximum depositional ages and then revises the stratigraphy where necessary. The newly defined Galah Tuff Bed was discovered at the top of the Betts Creek beds in Porcupine Gorge and was dated at 251.9 ± 3 Ma. This provides an important age constraint for the Betts Creek beds and is a tie-point for correlations with coeval units in the adjacent Bowen Basin and the Sydney and Gunnedah basins to the southeast. The Galah Tuff Bed is interpreted to correlate with the Yarrabee Tuff in the Bowen Basin. Unconformably overlying the Betts Creek beds is a newly recognised stratigraphic unit, defined herein as the Porcupine Gorge Formation. Detrital zircon maximum depositional ages and palynology indicate a significant depositional hiatus of up to 20 million years between the Betts Creek beds and Porcupine Gorge Formation. The hiatus indicates that the lower part of the Porcupine Gorge Formation is at least upper Middle Triassic, whereas the upper part of the unit extends into the Late Triassic. This age also constrains the overlying Warang Sandstone, which is considerably younger locally than previously reported and is likely diachronous across the northeastern Galilee Basin. • KEY POINTS • An integrated lithostratigraphy, palynology and U–Pb detrital zircon geochronology methodology is applied to the Permian–Triassic succession the northeastern Galilee Basin. • Two new stratigraphic units were recognised: the upper Permian Galah Tuff Bed (251.9 ± 3 Ma) and the late Middle–Late Triassic Porcupine Gorge Formation (238.7 ± 3 Ma). • The Galah Tuff Bed, correlative of the Yarrabee Tuff in the Bowen Basin, is evidence for widespread volcanism in the late Permian. • The age of the Porcupine Gorge Formation indicates diachroneity of the Triassic succession in the Galilee Basin, warranting further examination.
Article
Despite a continuous increase in fossil charcoal records from Late Palaeozoic deposits, which are used as direct evidence for palaeo-wildfires, detailed studies on the charcoal particles are still rare. To investigate the relationship between wildfire activities and the evolution of the terrestrial ecosystem at the end of the Permian, we report on the charcoal recovered from the classic non-marine Permian–Triassic Dalongkou section in Jimsar, Xinjiang Uygur Autonomous Region, Northwest China. Allochthonous and parautochthonous charcoals, identified by both macroscopic and microscopic morphological techniques, were collected from several stratigraphic horizons. These charcoals were classified into 11 categories (which do not represent the taxonomic group) according to their anatomical characteristics and gross morphology. The reflectance values of the charcoals indicate that surface fires were dominant throughout the sequence, with fire regime changing in a distinct interval. The distribution and abundance of all categories and the reflectance of the charcoals suggest that the intensity of wildfires increased in the upper part of the Guodikeng Formation. This trend coincides with the Hg/TOC peaks and a conspicuous excursion in the organic carbon isotope (δ¹³Corg) values, which may indicate volcanic activities and the disturbance of the carbon cycle that occurred during the Permian–Triassic transition. It is reasonable to infer that the end-Permian mass extinction (EPME) is located at the intensive wildfire interval. The reduction in spore pollen and the decrease in charcoal reflectance hint at a vegetational impoverishment that occurred after this interval. We proposed that increased wildfires, promoted by dry climate conditions and volcanism, aggravated the collapse of the forest ecosystem during the latest Permian.
Article
Combustion-derived polycyclic aromatic hydrocarbons (PAHs) are frequently used as molecular proxies for wildfire in recent and ancient sediments. Here, we document the abundances of four hydrocarbon compounds, i.e., phenanthrene (Phe), benzo[e]pyrene (BeP), benzo[ghi]perylene (Bpery), and coronene (Cor), across the Permian–Triassic boundary (PTB) in five marine sections of South China. High values of PAHs are present below the end-Permian mass extinction (EPME) horizon, from the Clarkina changxingensis Zone to the Clarkina yini Zone, suggesting strong perturbations to terrestrial ecosystems predating the marine crisis. PAHs peaked in the uppermost C. yini Zone, correlative with the EPME, reflecting simultaneity of the most severe phases of the terrestrial and marine crises. The proxy records document suitable climatic conditions for wildfires (high pO2) throughout the P-Tr transition. The results of the present study are also significant in validating the utility of BeP, Bpery, Cor, and BeP/Phe as proxies for terrestrial wildfires in deep-time marine successions.
Article
In the late 1980's the discovery of late Permian helical burrow casts containing articulated skeletons of the small herbivorous therapsid Diictodon feliceps led to conjecture that they may have been used for oviposition/parturition and shelter for infants. Here we present new fossil evidence in support of this interpretation and discuss the possibility that some of the burrows were specially excavated as brood chambers. A re-investigation of the original helical burrow site recovered several more burrow casts containing scattered yet still-associated skeletons of Diictodon. Mechanical preparation of a complete terminal chamber revealed a disarticulated but anatomically-associated adult Diictodon skeleton along with a single tiny (5 mm long) humerus of an infant dicynodont. Nearby outcrops yielded a second association of an adult Diictodon skull (skull length 93 mm) on top of a tiny semi-articulated Diictodon skull and skeleton (skull length 19 mm) with a second infant mandible and a skeleton of the gracile therocephalian Ictidosuchoides longiceps. Synchrotron imaging of this putative burrow-fill confirmed that the humeral morphology of the infant skeleton closely matches the tiny humerus in the unequivocal burrow cast. The common occurrence of Diictodon remains within the casts, combined with their specialized limbs for digging and histological data that indicates uninterrupted growth to ca. 70% of adult size, strongly suggests that they dug underground primarily for thermo-regulation. Moreover, our new fossil evidence of behaviourally-associated neonate and adult Diictodon within these structures indicates that the terminal portions of underground burrows were facultatively used as brood chambers.
Article
A terrestrial ecosystem collapse event accompanied by extensive soil erosion has been widely recorded in marine sedimentary rocks at the vicinity of the end-Permian mass extinction. However, the precise timing of this event and its impact on the marine extinction have not yet been ascertained. Here we present an organic geochemical study of non-marine and marine sections from the South China Craton, which shows that terrestrial ecosystem collapse was accompanied by a soil erosion event, and was followed by the end-Permian marine extinction. Two separate events devastated the terrestrial ecosystem prior to the marine extinction event, over a timespan of dozens of kyr. Bacteria flourished in the non-marine section coeval with a decline in terrestrial plants and in the marine section during the end-Permian marine extinction. A proto-recovery of herbaceous plants (not woody plants) occurred dozens of kyr after the end-Permian marine extinction and coincided with a global warming maximum and oceanic anoxia/euxinia.
Article
Climate warming, probably as a result of massive degassing of greenhouse gases from the Siberian Traps magmatism, has often been acclaimed as a major cause of the end-Permian mass extinction. Indeed, several studies have documented a sudden rise in seawater temperatures during the latest Permian-earliest Triassic, as evidenced by oxygen isotopic records measured on conodont apatite. However, whether such a rapid increase in seawater temperatures occurred before, during, or after the mass extinction remains controversial. Moreover, the pattern of this rise in seawater temperatures and its timing relative to the latest Permian-earliest Triassic carbon cycle disruption, mass extinction, as well as the Siberian Traps magmatism still need to be rigorously examined in various regions. In this study, we present high-resolution oxygen isotopic records of conodont apatite (δ¹⁸Oapatite) from the Upper Permian-lowermost Triassic interval at the Abadeh section, central Iran that are analyzed with in situ secondary ion mass spectrometry (SIMS) method. The δ¹⁸Oapatite results from Abadeh demonstrate a clear pattern consisting of three phases: (1) From the lower Wuchiapingian Clarkina dukouensis Zone to the end-Permian mass extinction horizon, δ¹⁸Oapatite values are relatively stable, fluctuating in the range of 18.28-20.15‰ with an average of 19.44‰. (2) δ¹⁸Oapatite value remains high as 19.26‰ at the mass extinction horizon. Above this horizon, a sudden decrease occurs in the Clarkina hauschkei Zone and reaches a low value of 17.05‰ close to the Permian-Triassic boundary. (3) In the lowermost Triassic, δ¹⁸Oapatite values maintain a low baseline in the range of 16.92-17.39‰ with an average of 17.11‰. Overall, the most dramatic change in δ¹⁸Oapatite values (i.e., a decrease of ~2‰), converting into an abrupt warming of ~10 °C, occurred above the mass extinction horizon and below the Permian-Triassic boundary at Abadeh. The Abadeh δ¹⁸Oapatite record is consistent with previous results documented in South China, Iran, and Armenia in terms of the timing and magnitude of a substantial warming, and therefore represents a global signature. If applying the high-precision temporal framework established in the well-dated Meishan GSSP section to Abadeh, the abrupt warming of ~10 °C took only a maximum duration of ~37 kyr (thousand years). By projecting the carbon cycle change, temperature rise, mass extinction at the Abadeh and Meishan sections, and the temporal evolution of the Siberian Traps magmatism onto a unified timescale, the temporal correlation strongly suggests that the switch from dominantly extrusive eruptions to widespread sill intrusions is probably the most annihilating phase of the Siberian Traps magmatism, and is temporally consistent with the end-Permian mass extinction.
Article
The fully continental succession of the Beaufort Group, Karoo Basin, South Africa, has been used in the development of environmental models proposed for the interval that spans the contact between the Daptocephalus to Lystrosaurus Assemblage Zones, associated by some workers with the end-Permian extinction event. An aridification trend is widely accepted, yet geochemical data indicate that the majority of in situ paleosols encountered in this interval developed in waterlogged environments. To date, the presence of calcic paleosols in the latest Permian can be inferred only from the presence of calcite-cemented pedogenic nodules concentrated in fluvial channel-lag deposits. Here, we report on the first empirical evidence of in situ calcic Vertisols found in the upper Daptocephalus Assemblage Zone near Old Wapadsberg Pass, one of eight classic localities in which the vertebrate turnover is reported in the Karoo Basin. Seven discrete intervals of calcic Vertisols, exposed over a very limited lateral extent, occur in an ∼ 25 m stratigraphic interval. Estimates of mean annual temperature and mean annual precipitation are calculated from geochemical measurements of one paleosol, and these estimates indicate that the prevailing climate at the time of pedogenesis was seasonally cold and humid. Correlation with adjacent stratigraphic sections indicates that the late Permian landscape experienced poorly drained and better-drained phases, interpreted to reflect a climate that varied between episodically dry and episodically wet. In contrast to a paleoenvironmental reconstruction of unidirectional aridification from strata in the Wapadsberg Pass region, this study provides new evidence for a wetting trend towards the Daptocephalus–Lystrosaurus Assemblage-Zone boundary.
Article
Out-of-control blazes have killed a billion wild animals. Those remaining will struggle to survive in a scorched landscape, Michael Clarke tells Nature. Out-of-control blazes have killed a billion wild animals. Those remaining will struggle to survive in a scorched landscape, Michael Clarke tells Nature.
Article
The end-Permian mass extinction (EPME) is widely recognised as the largest mass extinction in Phanerozoic history. In marine strata the main extinction event is well constrained, and has been radiometrically-dated to an interval of some 60 kyr, approximately 251.9 million years ago. However, the age and duration of the EPME in the terrestrial realm, as well as its possible synchronicity with that of the marine realm, is debated. Here, we shed light on issues pertaining to the identification and position of the terrestrial EPME in southern Africa. Using recently collected sedimentological (facies sequences), palaeontological (biostratigraphic ranges), geochemical (stable isotope analyses) and detrital zircon (ID-TIMS) data from a new site in the Xhariep District of the South African Karoo Basin, we demonstrate that the Permian-Triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction. We conclude that the terrestrial EPME recorded in the Karoo may be regarded as essentially synchronous with the EPME currently defined in the marine realm, and was likely the result of the same volcanically-induced atmospheric disturbances. This study describes the first single, vertical succession of vertebrate and plant fossils that span the terrestrial Permian-Triassic boundary that are also well-constrained both by relative (stable isotopes) and absolute (detrital zircon geochronology) dating methods.
Thesis
High-precision geochronology is a prerequisite for solving numerous geological problems, including deciphering the stratigraphic record to reconstruct climate and biosphere evolution. At present, Phanerozoic rocks can be dated with U-Pb geochronology with a precision of 0.05% or better on a weighted mean age using ID-TIMS. We established high-precision U-Pb geochronology at the Research School of Earth Sciences at The Australian National University, complementing existing high spatial resolution dating techniques. Our implementation of the method includes new developments aimed at improving precision and accuracy. The method was applied to two geological problems of the Permian Period. One essential requirement for U-Pb ID-TIMS is a mixed U-Pb spike. We prepared and calibrated a new 202Pb-205Pb-233U-236U spike, with a U/Pb ratio optimised for dating Phanerozoic samples. For a further increase in precision two possible approaches were tested aiming for improving counting statistics. A multi-ion counting array offers the possibility to substantially increase the total number of ion counts and therefore potentially increase the precision. This approach however was unsuccessful due to design limitations of the multiplier array of the Triton plus. The second approach was increasing the ionisation efficiency for Pb by preparing a more effective ion emitter. Several different commercially available silicagels were tested with differing particle sizes and concentrations. The highest ionisation efficiency of ~ 6%was found for a silicagel from Sigma-Aldrich in a concentration of 0.4%. Pb loss and inheritance are the major problem for accurate U-Pb geochronology of magmatic zircons. The problem of Pb loss was largely resolved with the chemical abrasion technique developed for multi-grain zircon geochronology. We determined optimal conditions for chemical abrasion of single zircon grains to ensure complete removal of zones that were affected by Pb loss. The testing was performed on three different zircon standards with various ages using a three step partial dissolution technique. It was found that annealing at a temperature of 900 degree C for 48 h followed by leaching at 190 degree C for 15 h is produces optimal results. We applied the newly established and improved U-Pb ID-TIMS technique to refine the chronology of two geological provinces, both of Permian age. First, we determined ages of zircons from volcanic ashes collected from the southern Sydney Basin sequences. These sequences were correlated with the type section of the Guadalupian-Lopingian-Boundary in South China through C-isotope stratigraphy. Using our U-Pb age data and the C-isotope correlation, we have determined a date of 257.9 +/- 0.5 Ma as the age of the Guadalupian-Lopingian-Boundary, and estimated that a major sea-level regression, which is possibly coinciding with the mid-Capitanian mass extinction, occurred after 258.9 Ma. In the second application we dated four sills of the Tarim large igneous province (LIP), which erupted in the early Permian, using the U-Pb systematics of baddeleyite. This LIP erupted in two major pulses, where the second pulse lasted at least 1.8 +/- 0.8 Myr from 283.1 +/- 0.2 to 281.3 +/- 0.6 Ma.
Article
There is an urgent need to develop agricultural methods that balance water supply and demand while at the same time improve resilience to climate variability. A promising instrument to address this need is biochar – a charcoal made from pyrolyzed organic material. However, it is often unclear how, if at all, biochar improves soil water availability, plant water consumption rates and crop yields. To address this question, we synthesized literature-derived observational data and evaluated the effects of biochar on evapotranspiration using a minimal soil water balance model. Results from the model were interpreted in the Budyko framework to assess how climatic conditions mediate the impacts of biochar on water fluxes. Our analysis of literature-derived observational data showed that while biochar addition generally increases the soil water holding capacity, it can have variable impacts on soilwater retention relative to control conditions. Our modelling demonstrated that biochar increases long-term evapotranspiration rates, and therefore plant water availability, by increasing soil water retention capacity – especially in water-limited regions. Biochar amendments generally increased crop yields (75% of the compiled studies) and, in several cases (35% of the compiled studies), biochar amendments simultaneously increased crop yield and water use efficiencies. Hence, while biochar amendments are promising, the potential for variable impact highlights the need for targeted research on how biochar affects the soil-plant-water cycle.
Article
Reconstructing the terrestrial palaeoenvironment during the end-Permian is made challenging by widespread erosion and ecosystem destruction. High-resolution sampling for palynofacies and palynology in sections that preserve the boundary interval allows for detailed examination of the drastic environmental changes that characterize the Permian–Triassic mass extinction. In the Bowen and Galilee basins in eastern Australia, this environmental perturbation is recorded within a Marker Mudstone that occurs above the uppermost Permian coal seams. The Marker Mudstone is used as a stratigraphic reference level at many localities, but has previously only been studied at a single locality in the Bowen Basin. In the present study, borehole Tambo 1-1A drilled in the Galilee Basin was selected to clarify whether this black, organic-rich mudstone marks a marine transgression, and to examine potential indicators of the end-Permian mass extinction. A total of 22 samples were taken from the mudstone unit, and from the over- and underlying strata and processed for palynology, palynofacies, and carbon isotope analysis. Biostratigraphic data indicate that the Marker Mudstone itself covers the uppermost part of unit APP5, with the first index taxa of unit APP6 floras occurring in samples less than 80 cm above this interval. This can be correlated with several other localities in the Bowen and Sydney basins where this shift occurs just above the uppermost Permian coal seam. Palynofacies data agree with previous interpretations of a southwards prograding delta that subsides as base level rises to form an extensive waterbody in which the Marker Mudstone was deposited. A change from translucent phytoclast-dominated to opaque phytoclast-dominated palynofacies within the Marker Mudstone suggests a shift to more oxic conditions in the water column, while base level begins to fluctuate, or increased terrestrial input from fluvial systems as the hinterland rises. Algal bodies resembling Botryococcus are found in the strata above the Marker Mudstone, but differ in morphology from the algal bodies found in the deltaic facies below. The presence of acanthomorph acritarchs in the Marker Mudstone and in the overlying Rewan Formation may indicate marine influence. Forms resembling fungal spores are present, but they do not show a “spike” as seen in other P–T boundary localities. The relative position of unit APP6 to the P–T boundary itself remains unclear. APP6 assemblages are dominated by simple acavate trilete and cavate trilete spores, which suggests stressed environment dominated by ferns and lycopods. The presence of degraded phytoclasts towards the top of the Marker Mudstone may also be used to suggest a mass-extinction interval. They may also be indicative of shifting local palaeoenvironmental changes, an interpretation that is supported by the low magnitude negative excursion of the δ¹³C isotope values within the Marker Mudstone. More datasets from the Bowen and Galilee basins will be essential to decoupling these signals.