Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling ...enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic
Claraia
Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.
During the earliest Triassic microbial mats flourished in the photic zones of marginal seas, generating widespread microbialites. It has been suggested that anoxic conditions in shallow marine ...environments, linked to the end‐Permian mass extinction, limited mat‐inhibiting metazoans allowing for this microbialite expansion. The presence of a diverse suite of proxies indicating oxygenated shallow sea‐water conditions (metazoan fossils, biomarkers and redox proxies) from microbialite successions have, however, challenged the inference of anoxic conditions. Here, the distribution and faunal composition of Griesbachian microbialites from China, Iran, Turkey, Armenia, Slovenia and Hungary are investigated to determine the factors that allowed microbialite‐forming microbial mats to flourish following the end‐Permian crisis. The results presented here show that Neotethyan microbial buildups record a unique faunal association due to the presence of keratose sponges, while the Palaeotethyan buildups have a higher proportion of molluscs and the foraminifera Earlandia. The distribution of the faunal components within the microbial fabrics suggests that, except for the keratose sponges and some microconchids, most of the metazoans were transported into the microbial framework via wave currents. The presence of both microbialites and metazoan associations were limited to oxygenated settings, suggesting that a factor other than anoxia resulted in a relaxation of ecological constraints following the mass extinction event. It is inferred that the end‐Permian mass extinction event decreased the diversity and abundance of metazoans to the point of significantly reducing competition, allowing photosynthesis‐based microbial mats to flourish in shallow water settings and resulting in the formation of widespread microbialites.
After the end‐Permian mass extinction, microbialites filled the ecological niche previously occupied by metazoan reefs. The factors that allowed microbialite‐forming microbial mats to flourish are, however, hotly debated. By investigating the faunal composition and depositional setting of Permian/Triassic boundary microbialites, we propose that the impact of the extinction event on the abundance of metazoans suppressed the biological controls that were previously excluding microbialite development from subtidal environments.
With the increase in global wildfire activity in response to global climate warming, the reconstruction of long-term fire histories and their links to environmental and anthropogenic factors has ...recently become an important focus of palaeoenvironmental research. Here we compare the precisely radiocarbon (14C) dated long-term histories of vegetation change and fire activity from lakes Ochaul (Cis-Baikal) and Kotokel (Trans-Baikal) in the Lake Baikal Region (LBR) of Siberia, a known source region of wildfires whose past and future relationships with climate, vegetation structure and human economy are still poorly understood. Our results show that under cold and dry glacial climate conditions (32–18.2 ka BP) fire frequencies in both study regions were low. Deglaciation, which was characterised by the spread of woody plants, began around 18.2 ka BP, accompanied by a slight increase in fire activity. Differences in the fire records from both subregions are observed from the end of the Lateglacial (LG), with peak fire activity in Cis-Baikal during the Early Holocene (EH) and in Trans-Baikal during the Middle Holocene (MH). During the Late Holocene (LH) both regions are marked by generally low fire activity. We propose that the long-term spatiotemporal differences in fire activity during the EH–MH interval are primarily driven by vegetation composition and landscape openness and the resulting changes in fire regime. Interestingly, both peaks are also observed in a global-scale fire record, which suggests spatiotemporal complexity of the Holocene fire history. Low charcoal accumulation rates in both records during the Middle Neolithic (ca. 6660–6050 a BP) “cultural hiatus” archaeologically documented for Cis-Baikal suggest an LBR-wide population decline. On the other hand, the spread of Late Bronze and Iron Age cultures into the LBR from 3.5 ka BP may have at least partly driven the increase in fire frequency around Lake Kotokel.
•Spatiotemporal complexity in the AMS-dated vegetation and fire records from Siberia.•Increase in fire activity coincides with the onset of deglaciation ca. 18.2 ka BP.•Peak fire activities occur in the Early (Cis-Baikal) and Middle Holocene (Trans-Baikal).•Climate change and vegetation composition controlled glacial-interglacial fire activity.•Holocene fire trends partially correlate with human activities in the Lake Baikal Region.
The body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end‐Permian mass extinction (c. 252 Ma). ...However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end‐Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post‐extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end‐Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperature–size rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress.
Mass extinction events are characterized by major losses in faunal diversity and are associated with several other ecological effects, e.g., reductions in tiering, selective losses of ecological ...lifestyles, and body size reductions. The latter has received considerable attention and debate, as to whether the reduced size of post-extinction organisms is due to the selective extinction of large species, absence of large species as a stochastic effect of low-diversity faunas (the Gulliver absence effect), a size decrease within surviving genera and species (the Lilliput effect), or a combination of these factors. Here, we investigated both evolutionary and ecophenotypic controls on body size distributions following the end-Permian mass extinction event by investigating size changes in bivalves (Claraia, “Unionites”, and Neoschizodus) from the Werfen Formation (Dolomites, Italy) and the Bódvaszilas Sandstone Formation (Aggtelek Karst, Hungary). Our results show that the Early Triassic shell size increase of bivalve genera was driven by both evolutionary and ecophenotypic responses. First, genera Claraia and “Unionites” show significant increases in body size with the appearance of the new species C. clarai and “U”. canalensis, respectively, suggesting that evolution played a role on Early Triassic bivalve body size dynamics. Further, the same genera record significant within-species increases in average and maximum body size into the late Griesbachian and Dienerian stages (the Brobdingnag effect), indicating that within-species ecophenotypic changes were also involved on observed long-term body size trends. These increases are associated with invigorated ocean circulation, improved oxygenation of the seafloor, and probably increased food supply. We, therefore, hypothesize that both growth-limiting environmental conditions (deoxygenation and reduced primary productivity) and the extinction-induced absence of large species led to small-sized species dominating early Griesbachian benthic invertebrate communities.
•Recovery of bivalve body size driven by evolutionary and ecophenotypic responses.•Early Griesbachian faunas lack large species (i.e., Gulliver absence effect).•Bivalves show within-species body size increases (i.e., Brobdingnag effect).•Body size increase associated with increased seafloor oxygenation and food supply.
ABSTRACT
A new accerator mass spectrometry (AMS)‐dated sedimentary record from Lake Ochaul (54°14′N, 106°28′E; 641 m a.s.l.) in Eastern Siberia covers the interval from ca. 27 850 to 20 400 cal a bp ...at ca. 180‐year resolution and contributes to a better understanding of the complex spatial vegetation pattern during the Last Glacial Maximum (LGM). Non‐arboreal pollen taxa are abundant in the pollen assemblages (mean value ca. 92.6%), but boreal trees are represented by all major taxa that grow in the lake catchment today, including Betula sect. Albae (0.6–4.8%), Picea (0.6–2.8%), Pinus sibirica (Haploxylon type) (up to 1.5%), Pinus sylvestris (Diploxylon type) (up to 2%), Larix (up to 0.6%) and Abies (up to 0.6%). Betula sect. Nanae/Fruticosae (2–5.2%) and Salix (up to 3.2%) are the most representative boreal shrub taxa. Together with existing modern and fossil pollen data from the wider study region, the current record provides further evidence for the long‐debated presence of boreal trees and shrubs in Eastern Siberia throughout the LGM. Our results show that the Upper Lena was a region in which refugia for arboreal taxa existed and that far‐distant pollen transport can be ruled out as the source of the detected arboreal pollen.
The biggest known mass extinction in the history of animal life occurred at the Permian–Triassic boundary and has often been linked to global warming. Previous studies have suggested that a ...geologically rapid (<40 kyr) temperature increase of more than 10°C occurred simultaneously with the main extinction pulse. This hypothesis is challenged by geochemical and palaeontological data indicating profound environmental perturbations and a temperature rise prior to the main extinction. Using secondary ion mass spectrometry (SIMS), we measured oxygen isotope ratios from Changhsingian (late Permian) ostracods of north‐western Iran. Our data show that ambient seawater temperature began to rise at least 300 kyr prior to the main extinction event. Gradual warming by approximately 12°C was probably responsible for initial environmental degradation that eventually culminated in the global end‐Permian mass extinction.
In the current study, different geochemical and biological proxies, including pollen, non-pollen palynomorphs, ostracods and molluscs, from an AMS radiocarbon-dated sediment core from Lake Ochaul ...(54°14′N, 106°28′E; 641 m a.s.l.) are presented and discussed. Ochaul is a fresh-water lake and an archaeological site situated ca. 100 km northwest of Lake Baikal in the upper reaches of the Lena River. The 260-cm-long sedimentary record presented here spans the Lateglacial–Holocene interval, between ca. 13,500 cal yr BP and the present. The reconstructions of the postglacial vegetation and lake system development are discussed along with the regional climate dynamics and the hemispheric-scale environmental changes. During the Allerød interstadial the region around Lake Ochaul was dominated by sparse taiga forests. Cooling during the Younger Dryas led to a more open tundra landscape where trees formed patchy forest stands in climatically favourable environments. This facilitated a rapid spread of forests at the onset of the Early Holocene during which the study region was probably characterized by seasonally dry climate controlled by the interplay of higher insolation, lower global sea levels and remaining ice sheets in the North Atlantic region. After thermal and moisture optimum conditions and a maximum spread of forests during the Middle Holocene, continuous cooling and a trend to more open forests landscapes marked the Late Holocene. These long-term trends were interrupted by several relatively short episodes of change in the vegetation and algal records, which coincide with short-term (centennial-scale) Northern Hemisphere cooling/drying phases. This shows that the regional vegetation reacted sensitively to these climate oscillations. Six AMS radiocarbon dates of bone material of large herbivorous animals from the Ochaul archaeological site located at the northern shore of the lake provide important information about prehistoric hunter-gatherers and indicate that activities at the site took place at ca. 27,780–27,160 cal yr BP (95% probability range) as well as during the Mesolithic (ca. 8850–8450 cal yr BP), Early, Middle and Late Neolithic (between ca. 6840 and 5490 cal yr BP) and the Iron Age (ca. 2120–1930 cal yr BP). Our results demonstrate that despite major environmental transformations following the Last Glacial Maximum, Lake Ochaul and the Malaya Anga River valley remained attractive for large herbivores and for prehistoric hunter-gatherers, even during the Middle Neolithic cultural “hiatus” (ca. 6660–6060 cal yr BP) in Cis-Baikal, as documented by the published archaeological records.
The Aras Valley section (north‐west Iran) exposes a sedimentary succession that allows the study of ostracod diversity patterns during/across the end‐Permian mass extinction. For the present study, ...59 samples were investigated for their ostracod abundances, which ranged from 4 to 31 500 specimens per 500 g. In 45 sample horizons, the ostracods were identified to the species level. In total, 3 425 specimens were determined and 62 species were identified, of which one genus and ten species are described for the first time: Fabalicypris veronicae Gliwa, sp. nov., Orthobairdia capuliformis Gliwa, sp. nov., Araxobairdia formosa Gliwa, gen. et sp. nov., Bairdiacypris kathleenae Gliwa, sp. nov., Eumiraculum mettei Gliwa, sp. nov., Liuzhinia julfensis Gliwa, sp. nov., Carinaknightina hofmanni Gliwa, sp. nov., Cavellina fosteri Gliwa, sp. nov., Cavellina hairapetiani Gliwa, sp. nov. and Hungaroleberis striatus Forel, sp. nov. The assemblages show, at the end‐Permian mass extinction event, a complete turnover from a low‐diversity Fabalicypris‐dominated pre‐extinction community to a more diverse Bairdiacypris‐dominated post‐extinction community. The turnover coincides with the significant temperature increase that was previously recorded from north‐west Iranian sections. The low diversity in the horizon immediately below the extinction horizon indicates that environmental changes, such as thermal stress, may have had an impact on the ostracod assemblages prior to the extinction event. In comparison with other diverse ostracod assemblages from the Palaeotethyan realm, the ostracods of the Aras Valley section are not associated with microbialites.
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