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Relatively high-resolution clay mineralogical and chemical index of alteration (CIA) analyses were conducted on the terrestrial Lubei section in southwestern China, to gain a better understanding of the paleoclimatic/paleoenvironmental evolution on land during the Permian-Triassic transition (P-Tr transition). Clay-mineral species include illite-smectite mixed layers (I/S), illite, irregular chlorite-expandable mixed layers (C/E), chlorite, kaolinite, vermiculite, hydroxyl-interlayered mineral (HIM), and corrensite. CIA values are as high as approaching 100 in the Permian and show a gradual and subtle decrease towards the lowermost Triassic, where a sudden decrease to persistently < 60 occurs with only periodic positive excursions. Diagenetic alteration is important at the study section and include chloritization, illitization of smectite in the Permian-lowest Triassic, transformation of smectite to corrensite in the upper sampled Triassic and potassium-addition induced decrease of CIA values throughout the section. However, with the integration of climate-sensitive sedimentary features, paleoclimatic/paleoenvironmental information was extracted from both clay-mineral composition and CIA. The dominance of precursor smectite together with the occurrence of kaolinite, Gigantopteris -type flora and coal seams, indicates an overall warm and semi-humid to semi-arid climate for the Permian part, and a general drying-out trend is suggested by the gradual decrease and final disappearance upsection of kaolinite, Gigantopteris -type flora and coal seams, as well as decreasing CIA values. Chemical weathering decrease is minor up to the lowest Triassic, which is mainly manifested by the subtle decrease of CIA values and which is probably partly due to the augmentation by acidification as indicated by the presence of vermiculite and HIM clay minerals. The short-term lingering (preliminarily estimated as < 0.08 Myr) of relatively intense chemical weathering after the extinction event was followed by an abrupt drop of CIA values to < 60, which indicates the onset of a rapid and enhanced dry-out condition unfavorable for chemical weathering. In association with the general drying-out trend is an increase in climate periodicity and/or seasonality, which is manifested by increasingly prominent laminations, lithological alternation and intermittent large excursions of CIA values, suggesting a more complicated climate condition during the Early Triassic than previously recognized. While drying-out rather than acidification is suggested in this study to have been a killer agent to land plant at the Lubei section, the real relationship between environmental deterioration and the end-Permian mass extinction is still enigmatic and needs further investigation. This is the first relative high-resolution clay mineralogical and CIA investigation on a well-preserved and continuous terrestrial Permian-Triassic section. [ABSTRACT FROM AUTHOR]

Pyrite morphology, iron speciation, and pyrite sulfur isotope data from the Xiakou section (Hubei Province, South China) were integrated to explore oceanic environmental variations through the Permian–Triassic transition and their possible relations to the largest mass extinction in Earth history. High ratios of highly-reactive iron to total iron (Fe HR /Fe T > 0.6) and pyrite iron to highly-reactive iron (Fe Py /Fe HR > 0.7) together with a high abundance of small (mean diameter <5 μm) framboidal pyrite show that euxinic conditions existed in the late Permian (pre-extinction interval). High ratios of Fe HR /Fe T (mostly >0.6) along with lower values of Fe Py /Fe HR (<0.7) and more variable framboid content among samples indicate anoxic but dominantly ferruginous conditions punctuated by episodic euxinic events in the latest Permian to earliest Triassic (post-extinction interval). The largest fluctuations of these redox proxies are observed in the ∼1.0 m of strata directly overlying the first (latest Permian) extinction horizon, indicating unsettled marine environmental conditions marked by frequent perturbations during the ∼60-kyr interval immediately following the mass extinction. The two largest redox events at Xiakou coincided with deposition of volcanic ash layers that have been correlated with Beds 25 and 28 of the Meishan D section, each of which was associated with an extinction pulse (the first and second extinction horizons of latest Permian and earliest Triassic age, respectively). Thus, our observations document two pulses of oceanic environmental change during the Permian–Triassic transition, each associated with a faunal crisis and possibly triggered by contemporaneous volcanic activity. [ABSTRACT FROM AUTHOR]

High–resolution clay mineralogical investigations were conducted on the Permian–Triassic (P–Tr) carbonate– and siliceous rocks from the Shangsi section, South China. The clay mineralogy is dominated by illite and illite/smectite mixed–layers (I/S) throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 (approaching the End–Permian mass extinction horizon–EPME) onwards. Positive correlations of clay fraction with mainly land–derived TiO 2 and magnetic susceptibility (MS) indicate a primary continental origin of the clay minerals. Rock–Eval pyrolysis analysis, palynomorph coloration, scanning electron microscope (SEM) and Transmission Electron Microscope (TEM) observations, all suggest that the rocks experienced thermal diagenesis which mainly promotes illitization processes of smectite clay minerals while discrete clay minerals are merely affected. Despite this diagenetic effect, clay minerals still carry valuable paleoenvironmental and paleoclimatic information in the Shangsi section. The overall illitic composition of the clay minerals and nearly absence of kaolinite suggest a general semi–arid condition during the P–Tr interval. Appearance of chlorite from bed 24 onwards suggests further aridification compared to the Late Permian. Occurrence of vermiculite from beds 24–28 in association with abundant volcanogenic materials, most negative δ 13 C carb values as well as enhanced soil–derived moretane abundance, suggests catastrophic soil erosion and likely soil acidification during the P–Tr transition in the source area(s) in relation with the active volcanism in that time. Further, decrease of chemical weathering and increase of physical weathering are indicated by increased input of primary clay minerals such as chlorite, a better illite crystallinity and increase of Al 2 O 3 /TiO 2 ratios. A climate cooling period corresponding to the Clarkina changxingensis – Clarkina deflecta conodont zone to the lower Clarkina zhangi conodont zone is indicated by higher abundance of illite, lower terrigenous TiO 2 , MS and Al 2 O 3 /TiO 2 in comparison with the overlying uppermost Permian strata. [ABSTRACT FROM AUTHOR]

The change of the primary productivity across the Permian-Triassic boundary (PTB) remains controversial. In this study, records from two deep-water sections in South China (Xiakou and Xinmin sections) show the primary productivity decreased gradually from the latest Permian to the earliest Triassic, and five evolutionary stages Increase-Decrease-Recovery-Recession-Stagnation) can be observed from Clarkina changxingensis-C. deflecta to Hindeodus parvus-Isarcicella isarcica zones. Primary productivity decreased abruptly from the base of C. meishanensis zone. Besides, for adjusting to the deterioration of the oceanic environment, the primary producers in the oceanic surface had changed to acritarch and cyanobacteria, which were more tolerant of stressful environment. Then the producers were under huge stagnation in the H. parvus-I. isarcica zone. The values of quantitative calculation of the primary productivity from the black rock series in the Dalong Formation were very high, corresponding to that of an upwelling area in modern ocean, which shows that the strata of the Dalong Formation in the study region are potential hydrocarbon source-rocks. This result may come from the fact that South China craton was located at the equatorial upwelling area during the Permian-Triassic transitions. But organic matter contents were different in various sections because they could be affected by redox conditions and diagenesis process after burial. [ABSTRACT FROM AUTHOR]

Abstract: Brachiopod miniaturization is both the reduction in size of individuals of a species over time, and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time. This paper investigates this phenomenon prior to and during the end-Permian crisis in a deep water setting in South China, based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species. The process of miniaturization near the Permian–Triassic boundary in deep water environments is characterized by: (1) Larger species, including Martinia sp., Costatumulus dongpanensis, and Anidanthus mucronata, reduced in average body size and abundance over time towards the end-Permian brachiopod extinction event. (2) Small species, including Attenuatella mengi and Spinomarginifera semicircridge, showed a mixed response with either no size change, or a reduction in average body size, while these species increased in abundance over time, indicating they were less sensitive to the stressed environmental setting. (3) Both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end-Permian crisis. Regression, an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization, based on the biotic replacement and changes in sea-water chemistry. Among these factors, the fall in sea level is perhaps the primary factor, and led to a decline in productivity and an increased input of terrestrial material into the marine setting. [Copyright &y& Elsevier]

Oceanic environments and biotas were in a state of near-continuous perturbation during the Early Triassic, the ~5-million-year interval following the latest Permian mass extinction (LPME), but the underlying cause(s) remain uncertain. The role of episodic volcanic or intrusive magmatic activity in triggering global-scale perturbations during this interval is suspected but has not been strongly evidenced to date. Here, we investigate the record of volcanism through the Early Triassic (with a focus on the Smithian-Spathian Boundary, or SSB) using mercury (Hg) concentrations in marine sediments as a proxy. This study examines five marine sections from three paleo-oceans (Paleo-Tethys, Neo-Tethys, and Panthalassa) representing a range of depositional settings from shallow platform to deep slope. Our results suggest that volcanic and magmatic activity of the Siberian Traps Large Igneous Province (STLIP) was most intense during the first ~1.3 million years following the LPME, and that termination of its most active stage was responsible for a sharp cooling event at the SSB. Variations in the intensity of STLIP activity are thus likely to account for the large (>8‰) fluctuations of δ13C carb and related changes in oceanic redox and environmental conditions that characterized the Griesbachian to Smithian substages of the Early Triassic in marine sections globally. We hypothesize that a strong reduction or cessation of STLIP activity at the SSB set the stage for the recovery of marine biodiversity and ecosystems in the Spathian and later. • First Hg concentration records spanning the full Early Triassic from five sections with a global distribution (581 analyses). • Hg data provide a proxy record of the timing and intensity of Siberian Traps volcanic activity during the Early Triassic. • Peak Hg inputs occurred around the Permian-Triassic boundary, when Hg/TOC rose to ~3–8× Late Permian background values. • High Hg inputs during the Griesbachian-Smithian, with a secondary peak coinciding with the Late Smithian Thermal Maximum. • Hg inputs were modest during the Spathian and returned to background levels at the Early/Middle Triassic boundary. [ABSTRACT FROM AUTHOR]

Vast emissions of volcanogenic greenhouse gases resulted in rapid global warming during the latest Permian mass extinction (LPME, ∼252 Ma), the impact of which on continental chemical weathering conditions was complex. Here, we compile Chemical Index of Alteration (CIA) records from 25 terrestrial and 12 marine sections with a near-global paleogeographic distribution to reconstruct the evolution of chemical weathering intensity of silicates during the LPME. This compilation shows that the CIA profiles, except those from the Australian Sydney and Bowen basins of the high-latitude Southern Hemisphere, exhibit either indiscernible changes or decreases through the LPME interval, contrary to previous inferences of increased silicate chemical weathering intensity. The lack of major changes in silicate chemical weathering intensity is further supported by the near uniformity of clay mineral assemblages through the LPME interval, with only minor increases of illite and chlorite and, if present, decreases in kaolinite content in some terrestrial sections. We infer a shift from dominantly transport-limited to kinetic-limited weathering regimes, likely caused by environmental climate factors such as widespread devegetation, river-flow changes (i.e., toward flashier and more intense discharge), and aridification during the earliest Triassic that effectively reduced water availability on land for water/rock reactions. Combined with limited changes in chemical weathering fluxes from previous estimates, our data imply possibly ineffective climate regulation by silicate chemical weathering at a (near-)global scale, despite high erosion rates, amid the intense global warming that followed the LPME. • Global CIA records from terrestrial and marine Permian-Triassic transition sections. • CIA records document decreased chemical weathering intensity in earliest Triassic. • Weathering changes due to shift from transport-limited to kinetically limited regime. • Linked to widespread soil erosion, devegetation, aridification, and fluvial changes. • Resulting in inefficient operation of climate-stabilizing weathering-CO 2 feedback. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations. Highlights • Eight genera and twenty-five species (belong to four forms) of acritarchs were record from eight sections in South China. • Two extinction events for the acritarchs across the Permian-Triassic transition. • The second event were more severe than the first one. This may result from the different causes for the two events. [ABSTRACT FROM AUTHOR]

Abstract: Abundant volcanic ash layers, largely altered to clay, characterize the Permian–Triassic boundary beds of the Daxiakou section, South China. Volcanism may have had an important role in the Permian–Triassic mass extinction, so it is important to understand the origin of these ash beds. The lithology of ash bed 260, as constrained by modes of crystal fragments (66.7% plagioclase, 7.2% alkali feldspar, and 26.1% quartz), suggests that the ash represents dacitic volcanism. The U–Pb ages, trace elements and Hf-isotope compositions of zircons from ten ash beds have been analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons can be divided into two groups: magmatic zircons (~97%, 227–279Ma) and inherited zircons (~3%, 678–2424Ma). Magmatic zircons have Y, Hf, Th and U contents and Nb/Ta ratios typical of zircons from silicic calc-alkaline volcanism. εHf(t) values of magmatic zircons vary from −10.9 to +5.3, implying magmatic mixing between juvenile crustal material (probably Neoproterozoic in age) and ancient crustal material (probably Archean). Beds 252–259-b have relatively depleted Hf-isotope compositions with εHf(t) values of −10.9–+5.3 and averages of −5.0–−2.5, while other beds have εHf(t) values of −10.8–+4.4 (mostly −10.8–−3.5) and averages of −8.9–−6.8, implying more input of juvenile crustal material in the volcanism of Beds 252–259-b. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggests that the volcanism producing the ashes took place along the convergent continent margins during the formation of the Pangea supercontinent. This intense silicic volcanism may have played an important role in causing the Permian–Triassic mass extinction in South China. [Copyright &y& Elsevier]

Abstract: Changes in marine primary productivity following the latest Permian mass extinction (LPME) have been debated at length, with little resolution to date owing to a paucity of quantitative data. Herein, we report total organic carbon (TOC) concentrations and organic carbon accumulation rates (OCAR) for 40 Permian–Triassic boundary (PTB) sections with a near-global distribution and consider their implications for changes in marine productivity during the boundary crisis. Many sections in South China exhibit abrupt declines in TOC and OCAR from the Changhsingian (latest Permian) to the Griesbachian (earliest Triassic), a pattern not observed for sections in other regions. This pattern cannot be explained through secular changes in sedimentation rates, sedimentary facies, or redox conditions, all of which would have favored higher (rather than lower) TOCs and OCARs during the Griesbachian. Further, back-calculation of OC fluxes demonstrate that this pattern cannot be attributed to diagenetic loss of OC in the sediment or, possibly, to OC remineralization in the water column. The most likely explanation is a collapse of marine primary productivity across the South China region concurrently with the LPME and continuing for an extended interval into the Early Triassic. The productivity crash as well as the coeval decimation of benthic marine fauna coincided with deposition of the “boundary clay” at Meishan D, suggesting that both events were related to a large explosive volcanic eruption of uncertain provenance. In other PTB sections having a wide geographic distribution, OCARs increased on average by a factor of ~4× across the LPME, largely owing to a concurrent increase in bulk accumulation rates (BARs). Radiometric dating uncertainties can account at most for only a fraction of the secular change in BARs, which are likely to reflect an increase in subaerial weathering rates and elevated fluxes of detrital material to Early Triassic marine systems. Intensification of chemical weathering relative to physical weathering may have increased the flux of nutrients to the Early Triassic ocean, enhancing marine productivity and contributing to the widespread development of marine dysoxia–anoxia. [Copyright &y& Elsevier]

The Permian–Triassic boundary interval in shallow shelf seas of South China shows Upper Permian limestones overlain by lowermost Triassic microbialites. Global sea-level rose across the Permian–Triassic boundary, but an irregular top-Permian erosion surface across a 10 km north–south transect of the Great Bank of Guizhou contains evidence of sea-level fluctuation. The surface represents the ‘event horizon’ of mass extinction, below the biostratigraphic Permian–Triassic boundary defined by first appearance datum of conodont Hindeodus parvus. An Upper Permian foraminiferal grainstone beneath this surface contains geopetal sediments, etched grains, and pendent and meniscus cements interpreted here as vadose. However, these latter diagenetic processes occurred before the event horizon and were followed by erosion of the final Permian surface. This erosion cuts previous fabrics but lacks evidence of weathering or bioerosion. A few centimetres below is an earlier grainstone that was also eroded but lacks proof of sub-aerial processes. Samples therefore reveal one, or possibly two, small-scale relative sea-level changes before the Triassic transgression in this area, and these may relate to local tectonics. The final Permian surface is subject to at least four interpretations: (i) sub-aerial physical erosion and dissolution by carbon dioxide-enriched fresh water or carbon dioxide-enriched mixed water, prior to Triassic transgression; (ii) sub-aerial physical erosion overprinted by dissolution related to carbon dioxide-enriched sea water in the Early Triassic transgression; (iii) submarine dissolution affected by acidified sea water due to rapid increase in volcanically-derived carbon dioxide and oxidized methane released from marine clathrates; (iv) submarine dissolution due to acid anoxic waters rising across the continental shelf, unrelated to atmospheric carbon dioxide or oxidized methane. Field and petrographic evidence suggests that (i) is the simplest option; and it is possible that (ii) and (iii) occurred, but none are proved. Option (iv) is unlikely given the evidence and modelling of supersaturation of upwelled waters with respect to bicarbonate. [ABSTRACT FROM AUTHOR]