Dating the onset and nature of the Middle Permian Emeishan large igneous province eruptions in SW China using conodont biostratigraphy and its bearing on mantle plume uplift models

The Middle Permian Emeishan large igneous province of SW China has provided the quintessential example of the phenomenon of kilometre-scale pre-eruption domal uplift associated with mantle plume impingement on the base of the lithosphere. One key line of evidence is an interpreted zone of truncation of the platform carbonates belonging to the Maokou Formation that underlies the volcanic pile. Here we test this interpretation by conodont age dating the uppermost beds of the Maokou Formation in sections from Yunnan, Sichuan, Guizhou and Guangxi provinces, which span locations from the inner part of the igneous province to several hundred kilometres beyond its margins. The results show that eruptions began in the Jinogondolella altudaensis Zone ( 263 Ma) of the Middle Capitanian Stage and greatly increased in extent and volume in the J. xuanhanensis Zone ( 262 Ma). Pre-eruption uplift was muted, and most locations within the terrain and at many locations beyond its margins witnessed platform collapse (not uplift) with deep-water facies (radiolarian cherts, submarine fans) developing in the J. altudaensis Zone. The clearest evidence for an emergence surface occurs around the margins of the province in the J. xuanhanensis Zone. This is after the initial onset of eruptions and marks either a eustatic sequence boundary or a brief pulse of tectonic uplift contemporaneous with volcanism. As with recent studies on the basal volcanic successions of the Emeishan LIP, kilometre-scale plume-related domal uplift prior to Emeishan eruptions is not supported by these data; rather a more complex interaction between plume and lithosphere with minor localized uplift and subsidence is inferred

Comment on “Quantitative biochronology of the Permian–Triassic boundary in South China based on conodont unitary associations” by Brosse et al. (2016)

Recently, Brosse et al. (2016) have proposed the use of conodont Unitary Associations Zones (UAZs) to substantially modify the biostratigraphy of the Permian–Triassic transition and to redefine the Permian–Triassic boundary (PTB). However, in our opinion, the UAZ analysis presented by Brosse et al. (2016) is based on unreliable taxonomic data sets with unjustified taxonomic re-assessments. No evidence shows that the UAZ approach improves the biozone biostratigraphy currently used to date the PTB

Smithian platform-bearing gondolellid conodonts from Yiwagou Section, northwestern China and implications for their geographic distribution in the Early Triassic

Abundant platform-bearing gondolellid conodonts, including Scythogondolella mosheri (Kozur and Mostler), Sc. phryna Orchard and Zonneveld, and Sc. cf. milleri (Müller), have been discovered from the Yiwagou Section of Tewo, together with Novispathodus waageni waageni (Sweet) and Nv. w. eowaageni Zhao and Orchard. This is the first report of Smithian platform-bearing gondolellids from the Paleo-Tethys region. In addition, Eurygnathodus costatus Staesche, E. hamadai(Koike), Parafurnishius xuanhanensis Yang et al., and the genera Pachycladina Staesche, Parachirognathus Clark, and Hadrodontina Staesche have also been recovered from Dienerian to Smithian strata at Yiwagou Section. Three conodont zones are established, in ascending order: Eurygnathodus costatus-E. hamadai Assemblage Zone, Novispathodus waageni-Scythogondolella mosheri Assemblage Zone, and the Pachycladina-Parachirognathus Assemblage Zone. The platform-bearing gondolellids were globally distributed just after the end-Permian mass extinction, but the formerly abundant Clarkina Kozur disappeared in the late Griesbachian. Platform-bearing gondolellids dramatically decreased to a minimum of diversity and extent in the Dienerian before recovering in the Smithian. Scythogondolella Kozur, probably a thermophilic and eurythermic genus, lived in all latitudes at this time whereas other genera did not cope with Smithian high temperatures and so became restricted to the high-latitude regions. However, the maximum temperature in the late Smithian likely caused the extinction of almost all platform-bearing gondolellids. Finally, the group returned to equatorial regions and achieved global distribution again in the cooler conditions of the late Spathian. We conclude that temperature (and to a lesser extent oxygen levels) exerted a strong control on the geographical distribution and evolution of platform-bearing gondolellids in the Early Triassic

Evolution, systematics, and phylogeography of Pleistocene horses in the new world: A molecular perspective

The rich fossil record of horses has made them a classic example of evolutionary processes. However, while the overall picture of equid evolution is well known, the details are surprisingly poorly understood, especially for the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma) ago, and nowhere more so than in the Americas. There is no consensus on the number of equid species or even the number of lineages that existed in these continents. Likewise, the origin of the endemic South American genus Hippidion is unresolved, as is the phylogenetic position of the "stilt-legged" horses of North America. Using ancient DNA sequences, we show that, in contrast to current models based on morphology and a recent genetic study, Hippidion was phylogenetically close to the caballine (true) horses, with origins considerably more recent than the currently accepted date of c. 10 Ma. Furthermore, we show that stilt-legged horses, commonly regarded as Old World migrants related to the hemionid asses of Asia, were in fact an endemic North American lineage. Finally, our data suggest that there were fewer horse species in late Pleistocene North America than have been named on morphological grounds. Both caballine and stilt-legged lineages may each have comprised a single, wide-ranging species.Instituto Multidisciplinario de Biología CelularFacultad de Ciencias Naturales y Muse

Integrated Sr isotope variations and global environmental changes through the Late Permian to early Late Triassic

New 87Sr/86Sr data based on 127 well-preserved and well-dated conodont samples from South China were measured using a new technique (LA-MC-ICPMS) based on single conodont albid crown analysis. These reveal a spectacular climb in seawater 87Sr/86Sr ratios during the Early Triassic that was the most rapid of the Phanerozoic. The rapid increase began in Bed 25 of the Meishan section (GSSP of the Permian–Triassic boundary, PTB), and coincided closely with the latest Permian extinction. Modeling results indicate that the accelerated rise of 87Sr/86Sr ratios can be ascribed to a rapid increase (>2.8×) of riverine flux of Sr caused by intensified weathering. This phenomenon could in turn be related to an intensification of warming-driven runoff and vegetation die-off. Continued rise of 87Sr/86Sr ratios in the Early Triassic indicates that continental weathering rates were enhanced >1.9 times compared to those of the Late Permian. Continental weathering rates began to decline in the middle–late Spathian, which may have played a role in the decrease of oceanic anoxia and recovery of marine benthos. The 87Sr/86Sr values decline gradually into the Middle Triassic to an equilibrium values around 1.2 times those of the Late Permian level, suggesting that vegetation coverage did not attain pre-extinction levels thereby allowing higher runoff

Species-specific responses of Late Quaternary megafauna to climate and humans

Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary remain contentious. We use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, underscoring the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change.This paper is in the memory of our friend and colleague Dr. Andrei Sher, who was a major contributor of this study. Dr Sher died unexpectedly, but his major contributions to the field of Quaternary science will be remembered and appreciated for many years to come. We are grateful to Dr. Adrian Lister and Dr. Tony Stuart for guides and discussions. Thanks to Tina B. Brandt, Dr. Bryan Hockett and Alice Telka for laboratory help and samples and to L. Malik R. Thrane for his work on the megafauna locality database. Data taken from the Stage 3 project was partly funded by Grant #F/757/A from the Leverhulme Trust, together with a grant from the McDonald Grants and Awards Fund. We acknowledge the Danish National Research Foundation, the Lundbeck Foundation, the Danish Council for Independent Research and the US National Science Foundation for financial suppor

A review of the Late Permian – Early Triassic conodont record and its significance for the end-Permian mass extinction

As a marine microfossil with a long-lasting fossil record stretching from the Cambrian to the Triassic, the tiny conodont plays an important role for the study of the end-Permian mass extinction. In the past few decades, numerous studies on Permian-Triassic conodonts have been published. This paper summarizes the progress made on high-resolution conodont biostratigraphy, timing of the mass extinction across the Permian-Triassic Boundary, conodont apparatus and phylogeny, conodont size variation, conodont oxygen isotope as well as other isotopes and chemical elements. Finally, future perspectives are also discussed

Volcanism in association with the prelude to mass extinction and environment change across the permian-triassic boundary (PTB), Southern China

In order to better understand the provenance of the sediments and environmental change associated with the Permian-Triassic (P/T) biotic crisis, a comparative clay mineralogical study of the Permian-Triassic boundary (PTB) sediments between the Meishan section (the Global Stratotype Section and Point of the PTB) and the Xiakou section, southern China, was undertaken using X-ray diffraction and differential scanning calorimetry (DSC). The results showed that clay minerals of the packstone bed 24e, in which the preludial mass extinction occurred at Meishan, consist of 56% mixed-layer illite-smectite (I-S), 39% illite, and 5% kaolinite. A dehydroxylation effect was measured at 652°C, indicating that I-S and illite of this bed contain mainly cis-vacant (cv) layers related to volcanic origin. The dehydroxylation event correlates with bed P257 at Xiakou. The white clay bed 25 also corresponding to the main extinction event at Meishan contains 95% I-S and 5% kaolinite, with a strong endothermic effect at 676°C and a weaker one at 514°C in the DSC curve. These results are attributed to dehydroxylation of cv layers in I-S clays, suggesting that I-S in the white clay bed was derived from marine alteration of volcanic ash, in agreement with the conodont-correlated clay (P258) at Xiakou. (Conodonts are tooth-like microfossils and are usually used as an indicator of age in PTB stratigraphy.) Increases in chlorite and illite contents in the black clays (bed 26) at Meishan and the conodont-correlated black clay layer (P259b) at Xiakou probably indicate stronger erosional processes under cooler and more arid conditions. Volcanic materials found in a bed which marked the prelude to the main episode of mass extinction reinforce the temporal link between volcanism and the mass extinction