Altered fluvial patterns in North China indicate rapid climate change linked to the Permian-Triassic mass extinction

The causes of the severest crisis in the history of life around the Permian-Triassic boundary (PTB) remain controversial. Here we report that the latest Permian alluvial plains in Shanxi, North China, went through a rapid transition from meandering rivers to braided rivers and aeolian systems. Soil carbonate carbon isotope (δ13C), oxygen isotope (δ18O), and geochemical signatures of weathering intensity reveal a consistent pattern of deteriorating environments (cool, arid, and anoxic conditions) and climate fluctuations across the PTB. The synchronous ecological collapse is confirmed by a dramatic reduction or disappearance of dominant plants, tetrapods and invertebrates and a bloom of microbially-induced sedimentary structures. A similar rapid switch in fluvial style is seen worldwide (e.g. Karoo Basin, Russia, Australia) in terrestrial boundary sequences, all of which may be considered against a background of global marine regression. The synchronous global expansion of alluvial fans and high-energy braided streams is a response to abrupt climate change associated with aridity, hypoxia, acid rain, and mass wasting. Where neighbouring uplands were not uplifting or basins subsiding, alluvial fans are absent, but in these areas the climate change is evidenced by the disruption of pedogenesis

Improving paleoenvironment in North China aided Triassic biotic recovery on land following the end-Permian mass extinction

The driver of the Early–Middle Triassic biotic recovery on land following the end-Permian crisis is puzzling. Here, we show the biotic recovery was gradual and spanned up to 8 Myr after the end-Permian mass extinction, based on continuous, well-dated sections over large areas in the northeastern Ordos Basin, North China. Initial recovery began in the Olenekian, marked by the disappearance of microbially induced sedimentary structures and reappearance of bioturbation, and continued in the Anisian, with a bloom of plants and tetrapods and intense bioturbation. Sedimentary environments changed from Induan braided-eolian conditions to Olenekian–Anisian shallow lacustrine and meandering river systems, marking an overall deepening lacustrine system. Carbonate δ13C and geochemical proxies of weathering intensity, salinity and clayiness reveal an overall warm and semi-humid paleoclimate in the Olenekian–Anisian. This improved stable paleoenvironment of warm and semi-humid conditions likely contributed to the biotic recovery following the Permian-Triassic hyperthermal-related crisis

On the Paleo-Mesoproterozoic boundary from the breakup event of the Columbia supercontinent

In the International Precambrian Stratigraphic Chart, the Paleo-/Mesoproterozoic boundary is always set at 1.6Ga while in Chinese literatures, this boundary is always placed at 1.8Ga. The fundamental reason for this difference is the understanding of the nature of the geological events in this period. This paper focuses on discussing the boundary between Paleoproterozoic and Mesoproterozoic from the nature of the geological events during 1.8 similar to 1.6Ga. A large amount of geological data shows that the Columbia/Nuna supercontinent began to stretch and breakup from 1.8Ga to 1.75Ga and formed a series of intracontinental rifting-sag basins, such as Thelon basin in North America (Laurentia), Leichhardt superbasin in northern Australia, Sao Francisco basin in South America, Xiong'er rifting basin in the southern margin of the North China Craton, Dongchuan basin in the southwestern margin of the Yangtze Block, and others. During the early stage of basin formation, the clastic rocks of alluvial fan facies and fluvial facies were deposited, followed by extensive volcanic eruptions. During the middle and late stage, the ealier fluvial facies and lacustrine facies rocks were overlied by carbonate platform sediments deposited in shallow sea, which reflects a process of stretching and breakup. Anorogenic magmatic rocks of 1.78 similar to 1.72Ga distributed widely in continents/blocks that formed the Columbia supercontinent, including bimodal igneous rocks, AMCG assemblages (anorthosite, mangerite, charnockite and granite), rapakivi granite, A-type granite, etc., as well as widely distributed mafic dyke swarms. All these igneous rocks reflect the stretching and breaking process. During 1.8 similar to 1.6Ga, both sedimentary events and magmatic events were related to the stretching and breaking of the supercontinent, but did not show the characteristics of orogeny, continental solidation and cratonization. Therefore, it is not appropriate to use the Statherian to summarize the nature of the geological events in this stage. In Columbia supercongtinent, many intracontinental basins experienced a wide uplift at around 1.6Ga, resulting in a short interval of sedimentation. After that, the original basins continued to develop and accepted a wider range of sedimentation, which sustained until about 1.4 similar to 1.3Ga. Magmatic events related to supercontinental stretching and breaking can also be intermittent from 1.78Ga to 1.4 similar to 1.32Ga. From 1.8Ga (or 1.78Ga) to 1.4 similar to 1.3Ga, both sedimentary events in the basins and magmatic events related to stretching and breaking are basically continuous. Therefore, the set of Paleo-Mesoproterozoic boundary at 1.6Ga artificially destroys the continuity of global sedimentary events and magmatic events, which were obviously contrary to the principle that the major sequences of sedimentation, igneous emplacement, or orogeny should be cut off as little as possible in the Precambrian stratigraphic division. Since the time of the successive depositional events in rifting-basins and of the anorogenic magmatic events in continents can be traced back to 1.8Ga (or 1.78Ga), we propose to place the Paleo-Mesoproterozoic boundary at 1.8Ga or 1.78Ga, rather then 1.6Ga. Considering that the rifting process leads to the development of the overlying strata on the preexisting supercontinent or craton, we suggest classifying the sediments of ca. 1.8 similar to 1.4Ga into the Calymmian

Electric field analysis and structure design of the box of bird guard used in 220 kV transmission line

Bird activities including the defecation, nesting, and flight are easy to cause electrical faults of overhead transmission lines, study on the prevention measures of bird damage to transmission lines is of great significance to ensure the stable and reliable operation of the power system. With the establishment of finite element simulation model, the effects of box of bird guard with different material on the electric field and potential distribution on transmission line insulators are studied. Besides, combined with the theory of air discharge and the results of simulation, the influence of rainwater on the air gap around the insulator breakdown characteristics is studied when the water is drained from a scupper at the bottom of the box of bird guard, and a reasonable design scheme for the box of bird guard scupper is proposed. The research results here can provide a guidance for the selection and key parameters’ design of the box of bird guard

Sedimentary response to the intracontinental orogenic process: insight from the anatomy of a small Mesozoic basin in western Yanshan, northern North China

<p>The intra-continental orogeny and tectonic evolution of the Mesozoic Yanshan fold-thrust belt (YFTB) in the northern North China Craton (NCC) have been strongly debated. Here, we focus on the Shangyi basin, located in the centre of the YFTB. An integrated analysis of sedimentary facies, palaeocurrents, clast compositions, and detrital zircon dating of sediments was adopted to determine the palaeogeography, provenance, basin evolution, and intra-continental orogenic process. The Shangyi basin comprises the well-exposed Early–early Middle Jurassic Xiahuayuan Formation and the Longmen Formation, and the Late Jurassic–Early Cretaceous Tuchengzi Formation. Based on the 18 measured sections, five facies associations – including alluvial fan, fluvial, delta, lacustrine, and eolian facies – have been identified and described in detail. The onset of the Shangyi basin was filled with fluvial, deltaic, and lacustrine deposits controlled by the normal fault bounding the northern basin, corresponding to the pre-orogeny. In the Middle Jurassic, the cobble–boulder conglomerates of alluvial fan, as molasse deposits, were compatible with the syn-orogeny of the Yanshan movement, which played a critical role in northern North China and even East Asia. After the depositional break in the Middle–Late Jurassic, the Shangyi basin, controlled by the normal fault present in the north of the basin, re-subsided and quickly expanded southward with thick sedimentation, which is correlative with the post-orogeny. Combined with A-type granites, metamorphic core complexes, mafic dikes, and rift basins of the Late Jurassic–early Early Cretaceous present in the northern NCC and Mongolia, significant extension was widespread in the northern NCC and even in northeast Asia. Moreover, vertical changes of provenance indicate that the Taihang Mountain and the Inner Mongolia palaeo-uplift (IMPU) present at the west and north of the basin, respectively, experienced uplift twice in the Middle–Late Jurassic and Early Cretaceous, resulting in a regional depositional break.</p

Table 2: Isotopic and elemental compositions of Mesoproterozoic carbonates from Yanshan, North China

In Yanshan, located in the northern part of North China, Mesoproterozoic carbonate sequences (1.6-1.4 Ga) form a 10, 000m thick succession in an aulacogen basin. Carbon and oxygen isotope (d13O and d18O, resp.) data were obtained from 110 carbonate samples across three sections of these Mesoproterozoic deposits. From the early to late Mesoproterozoic, low negative values of d13O appear, followed by low positive variation and then a stable increase. An abrupt decrease in d13O values, with subsequent rapid increase, is found at the end of the Mesoproterozoic. During the whole Mesoproterozoic, d18O shows a mainly negative trend and occasional highly negative isotopic shifts (from lower to upper deposits). Whole-rock carbon and oxygen isotopic compositions and profilesmust be studied to provide a paleogeochemical record that can be associated with paleocean sedimentary environments, temperature, biological productivity, and sea-level fluctuations. Results of the present study correlate well with other international carbon and oxygen isotope profiles, suggesting that a global marine geochemical system existed during the interval of 1.6-1.4 Ga under a globally united tectonic, sedimentary, and geochemical background

Modeling and Optimal Design for a High Stability 2D Optoelectronic Angle Sensor

The structural deformations caused by environmental changes in temperature, vibration, and other factors are harmful to the stability of high precision measurement equipment. The stability and optimal design method of a 2D optoelectronic angle sensor have been investigated in this study. The drift caused by structural deformations of the angle sensor has been studied and a drift error model has been achieved. Key components sensitive to thermal and vibrational effects were identified by error sensitivity analysis and simulation. The mounts of key components were analyzed using finite element analysis software and optimized based on the concept of symmetric structures. Stability experiments for the original and optimized angle sensors have been carried out for contrast. As a result, the stability of the optimized angle sensor has been improved by more than 63%. It is verified that the modeling and optimal design method is effective and low-cost, which can also be applied to improve the stability of other sensors with much more complex principles and structures