Wei Wang

Calibrating the End-Permian Mass Extinction

High-precision geochronologic dating constrains probable causes of Earths largest mass extinction. The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

A mechanical assessment of flexible optoelectronic devices

This work has demonstrated novel experimental methods and their relevant analysis to evaluate the fracture properties of thin brittle films on compliant substrates for flexible optoelectronic devices. Based on the understanding of the failure mechanisms, mechanical calculation has been provided to estimate the thin film fracture toughness and film delamination toughness. These values serve as design parameters on the device flexibility and reliability.

The boundary between the Indian and Asian tectonic plates below Tibet

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.

The fracture of brittle thin films on compliant substrates in flexible displays

One mechanical issue in flexible organic light emitting displays (OLED) is the fracture of extremely thin brittle conducting transparent oxide films deposited on thin flexible substrates. Understanding the behaviour of these films under flexed condition is essential for designer of flexible OLED. Controlled buckling experiments on the film and substrate have been designed to study the fracture of the films under both tension and compression. Fracture of the film is superficially similar in both tension and compression. However, under tension a channelling crack is formed, while under compression, the film delaminates, buckles and cracks in a tunnelling motion. The fracture toughness of the film and the delamination toughness have been estimated from these experiments. Design to maximise the flexibility of the device is discussed.

The carbon isotope excursion on GSSP candidate section of Lopingian-Guadalupian boundary

An isotopic stratigraphically well-documented outcrop in Penglaitan, Guangxi Province, South China, has been proposed as a candidate GSSP for the Lopingian–Guadalupian boundary. Correlatable outcrops from the west wing (Tieqiao section) and east wing (Penglaitan section) of the Laibin Syncline exhibit synchronous excursions in carbon isotopes. The isotopic excursions (δ13C) show the best placement of the boundary may lie at the base of Bed 6k which coincides with the Clarkina postbitteri conodont zone and with eustatic change. δ13C increases during the uppermost Guadalupian (Jinogondolella granti conodont zone from the top of 3c to the base of 6i). A δ13C peak value of 5‰ is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression. A gradual depletion of carbon isotopes occurs in the C. postbitteri zone from Bed 6e to 7b, and this gradual δ13C excursion also suggests the sequences around the Guadalupian–Lopingian boundary at the candidate section are conformable. During the middle-later C. postbitteri zone a 3.5‰ dramatic δ13C depletion is recorded at the Tieqiao section, but only a 2‰ depletion at the deeper facies Penglaitan section, synchronous with conodont zones that mark eustatic changes.

Juvenile magmatism and crustal recycling at the end of the Neoarchean in Western Shandong Province, North China Craton: Evidence from SHRIMP zircon dating

Western Shangdong Province experienced major crustal growth as a result of 2.75 to 2.50 Ga tectonothermal events, different from other Archean areas in the North China Craton. Besides early Neoarchean tonalite-trondhjemite-granodiorite (TTG) and supracrustal assemblages, there are large volumes of late Neoarchean gabbroic, dioritic and granitic rocks in western Shandong. SHRIMP zircon dating of thirty-one samples of different rock types from late Neoarchean rocks yielded a narrow age range from 2560 to 2490 Ma. Based on these data and previously published results, the following conclusions can be drawn: 1) the Archean basement can be divided into three belts: a Late Neoarchean (2525-2490 Ma) crustally-derived granite belt in the northeast, an Early Neoarchean (2.75-2.60 Ga) rock belt in the center, and a Late Neoarchean (2550-2500 Ma) belt of juvenile rocks in the southwest; 2) the tectonic regime in western Shandong Province probably changed from compressional to extensional at around 2525 Ma (between 2530 and 2520 Ma); 3) crustal recycling with addition from the mantle occurred at the end of the Neoarchean; 4) the late Archean magmatic rocks were probably formed in an arc environment.

New Ediacara fossils preserved in marine limestone and their ecological implications.

Ediacara fossils are central to our understanding of animal evolution on the eve of the Cambrian explosion, because some of them likely represent stem-group marine animals. However, some of the iconic Ediacara fossils have also been interpreted as terrestrial lichens or microbial colonies. Our ability to test these hypotheses is limited by a taphonomic bias that most Ediacara fossils are preserved in sandstones and siltstones. Here we report several iconic Ediacara fossils and an annulated tubular fossil (reconstructed as an erect epibenthic organism with uniserial arranged modular units), from marine limestone of the 551–541 Ma Dengying Formation in South China. These fossils significantly expand the ecological ranges of several key Ediacara taxa and support that they are marine organisms rather than terrestrial lichens or microbial colonies. Their close association with abundant bilaterian burrows also indicates that they could tolerate and may have survived moderate levels of bioturbation.

Facies analysis and sea-level change at the Guadalupian–Lopingian Global Stratotype (Laibin, South China), and its bearing on the end-Guadalupian mass extinction

Abstract: The Guadalupian–Lopingian boundary stratotype at Penglaitan, and the nearby Tieqiao section, near Laibin, South China, record a series of major environmental changes within the Jiangnan Basin during a Mid-Permian biotic crisis. The sequence-stratigraphic, petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed. Mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea-level fall that led to the establishment of mid-ramp conditions (Laibin Limestone) in settings that were previously dominated by radiolarian mudstones. The regression also coincides with a low point of 87Sr/86Sr ratios. The lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the Emeishan flood basalt province 800 km to the west of Laibin. Thus, unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event. Subsequent environmental changes included transgression, spread of dysoxic waters, indicated by populations of small pyrite framboids, and a major negative C-isotope excursion. All these phenomena have been previously related to the end-Guadalupian extinction but they in fact post-date the crisis because a post-extinction fauna of foraminifers is encountered at this time.

Correlation between dark spot growth and pinhole size in organic light-emitting diodes

Our in situ experimental observations of dark spot growth in organic light-emitting diodes using optical microscopy show a linear rate of growth for the area of all the dark spots. We used uniformly sized silica micro particles to intentionally create size-controllable pinholes on the cathode protective layer. Subsequently, we observed initial formation of dark spots as a result of these pinholes and then monitored their growth. Due to usage of particles of various diameters, we were able to linearly correlate the growth rate with pinhole size. This allows us to estimate the original pinhole sizes that gave rise to the dark spots, which we believe were initiated by “dust” particles. Our studies verify that dark spot formation is due to pinholes on the protective layer that creates pathways for water or oxygen permeation, and that dark spot growth is dependent on the pinhole sizes.

∼2.7-Ga Crustal Growth in the North China Craton: Evidence from Zircon U-Pb Ages and Hf Isotopes of the Sushui Complex in the Zhongtiao Terrane

The major Precambrian crustal growth in the North China Craton (NCC) has been thought to have occurred at ∼2.5 Ga. Here we present secondary ion mass spectroscopy (SIMS) and laser ablation–inductively coupled mass spectrometry (LA-ICP-MS) zircon U-Pb ages and Hf isotope compositions from dioritic and tonalite-trondhjemite-granodiorite (TTG) gneisses of the Neoarchean-Paleoproterozoic metamorphic terrane in the central NCC. Zircons from the trondhjemitic samples yield emplacement ages at and Ma. Those from the dioritic gneiss yield an age of Ma. The TTG gneisses are characterized by a Na-rich and K-poor () nature; strongly fractionated rare earth element patterns (); high Sr (418‰, 318‰) and Sr/Y (78, 49); low Y (5.4‰, 6.4‰) and YbN (3.0, 3.6); and low MgO (0.89%, 1.10%), Mg# (47, 42), Cr (39‰, 20‰), and Ni (11‰, 8‰), Nb/Ta (16, 12), which suggests that magmas were derived from the partial melting of a flatly subducted oceanic slab. The dioritic gneiss shows higher MgO (3.17%), Mg# (50), Cr (44‰), and Ni (40‰) and lower Sr/Y (22) and (La/Yb)N (8) ratios, which suggests contamination with mantle peridotite. All zircon grains from these Neoarchean gneisses yield high positive ϵHf (t) values that range from +3.5 to +7.7 and Hf model ages between 2.70 and 2.85 Ga. We propose that the widespread ∼2.5-Ga plutonic event found elsewhere in the NCC may represent a major reworking (melting) event, whereas the ∼2.7-Ga magmatism likely represents the main crustal growth of the NCC, comparable to those of other cratons worldwide.