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The Sichuan Basin was a part of the Yangtze Carbonate Platform (YCP) during the Cambrian–Ordovician, and marine carbonates were deposited in the basin during this interval. Although previous studies have evaluated the paleogeography, paleoclimate and paleoecology of this basin, they have primarily focused on the paleoecology and biological evolution in the basin; however, analysis of paleogeography and paleoclimate is lacking. This study integrated outcrop sedimentological and magnetic fabric data to document sedimentary differentiation and anisotropy of magnetic susceptibility (AMS) within the YCP. The aims of this study were to infer paleowind directions during each epoch of the Cambrian–Ordovician and to constrain the paleogeographic location of the YCP. The northwestern, central and southeastern sides of the YCP were characterized by high-energy deposition (e.g. sub-angular to rounded intraclasts), medium-energy deposition (e.g. sub-angular to sub-rounded intraclasts) and low-energy deposition (e.g. angular to sub-angular intraclasts), respectively. The centroid D-Kmax values for the Early, Middle and Late Cambrian were 116° ± 52°, 145° ± 57° and 159° ± 62° from the present north, respectively; corresponding values for the Early, Middle and Late Ordovician were 169° ± 70°, 139° ± 73° and 91° ± 68° from the present north, respectively. Sedimentary differentiation and AMS results indicated that the prevailing wind directions during the Early Cambrian, Middle Cambrian, Late Cambrian, Early Ordovician, Middle Ordovician and Late Ordovician were 296° ± 52°, 325° ± 57°, 339° ± 62°, 349° ± 70°, 319° ± 73° and 271° ± 68° from the present north, respectively. The present study provides evidence for the location of the YCP during the Cambrian–Ordovician via the correspondence between the paleowind directions over the YCP and the trade winds in the Northern and Southern hemispheres. The novelty of this study lies in the following aspects: (1) it integrates microfacies and AMS analyses to establish paleowind patterns; (2) it constrains the paleo-hemispheric location of the YCP during the Cambrian–Ordovician; and (3) it provides a reference for further studies of the paleoclimate and paleogeography of the YCP during the Cambrian–Ordovician. [ABSTRACT FROM AUTHOR]

T he long-term global record of surface PM 2.5 mass concentration is one of the important products from the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2). This long-time record began in the 1980s, whereby MERRA-2 has facilitated the study of the interactions between air pollution and climate change in China. In this study, the principal component analysis (PCA) method was applied to classify the PM 2.5 concentration distribution representing the primary states. It was also used to investigate relationships between PM 2.5 pollution distribution types and atmospheric circulation based on NASA MERRA-2 surface PM 2.5 mass concentration and ERA-5 reanalysis data. The distribution of the PM 2.5 concentrations in the central and eastern China over the winter was classified into five types. A typical pollution model (Type 2) was linked to the decrease in sea-land temperature differences as a result of increasing in land temperature, weakened air flow, reduced precipitation, stable vertical temperature, and relative humidity formation. For the typical clean models (Types 3 and 4), the meteorological conditions differed greatly from those of Type 2. Type 3 was related to the thermal effects of the Qinghai-Tibet Plateau, causing the diffusion conditions in the bottom layer in eastern China and being detrimental to pollution accumulation. Type 4 was related to good pollution diffusion conditions, caused by cold air and high pressure. Types 1 and 5 represent marginal pollution that are closely related to precipitation, pollution transport, temperature, and the vertical structure of relative humidity. A Gaussian log-likelihood mutation test of PM 2.5 concentration time series data in the central and eastern China showed that the mutation point appeared around the year 2000. This is related to the increasing impacts of climate change, such as rising land temperature and falling sea level pressure. This study provides new insights into the relationship between the distribution types of PM 2.5 pollution and atmospheric circulation; it elucidates the potential dynamic mechanisms controlling the severity and distribution of heavy air pollution. [Display omitted] [ABSTRACT FROM AUTHOR]

One of the important products of MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications) developed by NASA (National Aeronautics and Space Administration) is the long-term global records of surface PM 2.5 mass concentration since 1980s, providing the ability of studying the interactions between air pollution, weather and climate changes. In this study, the PM 2.5 mass concentrations of MERRA-2 are firstly validated across China mainland by independent surface measurements collected by Ministry of Ecology and Environment of People's Republic of China from 2014 to 2018. The results show that MERRA-2 well captures the spatial distribution and seasonal variation of PM 2.5 mass concentration in China mainland. The spatial and temporal evolution of large scale persistent PM 2.5 pollution event is also generally reflected by MERRA-2 by case study based on the target object match method. However significant underestimation of the PM 2.5 mass concentration in MEERA-2 is revealed across China mainland, especially in BTH region by 34.6 μg m−3, followed by 19.8 μg m−3 in YRD and 9.1 μg m−3 in PRD region. Such underestimation is most substantial in winter and autumn seasons. In addition, the discrepancy between MERRA-2 and observations increases significantly with the enhanced PM 2.5 level, for example, ranging from 29.9 μg m−3 in clean days, while 66.1 μg m−3 in polluted days in BTH region. We highlight the downward trends of PM 2.5 from 2014 to 2018 in China mainland estimated by MERRA-2 which is basically consistent in the observations, but with ~50% underestimation, indicating the potential applications of MERRA-2 for the future aerosol climatological studies. We suggest that the underestimations of both magnitude and variability of PM 2.5 in MERRA-2 probably result from the uncertainty of the magnitude of emission inventory used in GOES model (lower intensity and weaker variations), and the absence of nitrate in PM 2.5 constitution. A parameterized method for nitrate is proposed and evaluated by the sensitive study to improve MERRA-2 PM 2.5 underestimation by 19.2–23.6% in BTH region. However, the more comprehensive validations are still required in future studies, especially by the aerosol composition measurements. • The PM 2.5 mass concentrations of MERRA-2 are firstly validated across China mainland from 2014 to 2018. • Significant underestimation of the PM 2.5 concentration in MEERA-2 is revealed across China mainland. • A parameterized method for nitrate is proposed to improve MERRA-2 PM 2.5 underestimation. [ABSTRACT FROM AUTHOR]

In this study the interdecadal variations of haze pollution during recent 34 years from 1980 to 2013 over eastern China are investigated. It is found that opposite interdecadal variations of wintertime haze days (WHDs) between the North China Plain region (NCP) and the Yangtze River Delta region (YRD) occurred in this period, i.e., a decreased interdecadal trend of anomalous WHDs appeared in NCP and an increased trend in YRD. Meteorological factors driven the opposite interdecadal variations of anomalous WHDs are revealed. In the phase of interdecadal variations with more WHDs in NCP and less in YRD before 1996, there were weaker northerly winds in the lower troposphere over eastern China accompanied with a weakened Siberia High and mid-latitude westerly jet. The decreased northerly winds are conductive to the local accumulation of air pollutants in NCP and inhibition of air pollutants to be transported from North China to YRD. Consequently, more WHDs appeared in YRD and less in NCP. On the contrary, in the phase of interdecadal variations with less WHDs in NCP and more in YRD after 1996, stronger northerly winds associated with strengthened Siberia High and westerly jet, appeared over eastern China. The increased northerly winds are favorable for the dispersion of air pollutants in NCP and transport more pollutants from North China to the downstream area in YRD, resulting in less WHDs in NCP and more in YRD. Annual variations of the anomalous WHDs in the regions of NCP (34°–42°N,114°–120°E) (orange bars) and YRD (27°–34°N,114°–122°E) (green bars) from 1980 to 2013. The red and blue lines denote the linear trends of the anomalous WHDs in NCP and YRD, respectively. Unlabelled Image • Opposite variations of wintertime haze occurrence over North China Plain and Yangtze River Delta regions in 1980–2013. • Siberian High and mid-latitude westerly jet are key systems dominating the decadal various of WHDs in NCP and YRD. • The increased northerly winds are favorable for less WHDs in NCP and more in YRD. [ABSTRACT FROM AUTHOR]

The Tarim Basin was in the lower latitudes during the Cambrian-Ordovician, during which it experienced marine carbonate platform deposition. Although the platform is in the Trade Winds belt, the specific prevailing quantitative paleowind direction remains uncertain. This study integrated drill core and outcrop sedimentological data with outcrop magnetic fabric data to document sedimentary differentiation and anisotropy of magnetic susceptibility (AMS) within the Tarim Carbonate Platform (TCP). The aims of this study were to infer paleowind directions during each epoch of the Cambrian-Ordovician and to constrain the paleogeographic location of the TCP. The characteristics of the south, central, and northern sides of the platform were indicative of high-energy deposition (e.g., sub-angular to sub-rounded intraclasts with sparite cements), medium-energy deposition (e.g., angular to sub-rounded intraclasts with microspar and sparite cements), and low-energy deposition (e.g., angular to sub-angular intraclasts with microspar cements), respectively. AMS measurements yielded mean paleocurrent directions for the Early, Middle, and Late Cambrian of 226° ± 42°, 207° ± 43°, and 193° ± 36° from present north, respectively, whereas those for the Early, Middle, and Late Ordovician were 178° ± 39°, 165° ± 43°, and 155° ± 52° from present north, respectively. The results of sedimentary differentiation and AMS indicated that the prevailing wind directions of the Early Cambrian, Middle Cambrian, Late Cambrian, Early Ordovician, Middle Ordovician, and Late Ordovician were 226° ± 42°, 207° ± 43°, 193° ± 36°, 178° ± 39°, 165° ± 43°, and 155° ± 52° from present north, respectively. Since the TCP has rotated clockwise by ∼90° since the Ordovician, the paleowind directions of the Early, Middle, and Late Cambrian were 146° ± 42°, 117° ± 43°, and 103° ± 36° from paleo-north, respectively. The paleowind directions of the Early, Middle, and Late Ordovician were 88° ± 39°, 75° ± 43°, and 65° ± 52° from paleo-north, respectively. The TCP shifted from Southern Hemisphere to the Northern Hemisphere from the Early Cambrian to the Late Ordovician. The TCP was close to the Equator during the Early Ordovician. The novelty of this study related to: (1) integrating microfacies and AMS analyses to establish paleowind patterns; (2) constraining the paleo-hemispheric location of the TCP during the Cambrian-Ordovician; (3) providing references for the further study of paleoclimate and paleogeography of the TCP during the Cambrian-Ordovician. • Quantitative measurements of sediment properties across the platform were documented. • Quantitative measurements of anisotropy of magnetic susceptibility across the platform were documented. • Quantitative paleowind directions of the platform were reconstructed during the Cambrian-Ordovician. • Paleo-hemispheric location of Tarim Block was constrained during Cambrian-Ordovician. • An integrated methodology of standard petrographic and magnetic anisotropy data. [ABSTRACT FROM AUTHOR]

The Shijiutuo Uplift within the Bohai Bay Basin(BBB)has experienced a complex evolutionary history since the Cenozoic. Studies of the Cenozoic evolution of the Shijiutuo Uplift are important for basin tectonics and petroleum geology. The formation of uplifts in rift basins is generally controlled by regional tectonic event and fault-block tilting. In this study, apatite fission track (AFT) data from fourteen samples and seismic data analysis were used to study the processes of regional uplift and fault-block tilting. We further investigated the Cenozoic evolution and formation mechanism of the Shijiutuo Uplift. The results indicated that the Shijiutuo Uplift experienced a two-phase differential tectonic uplift and erosion history (1) Widespread rapid uplift and erosion during the early Cenozoic (65–55 Ma) (2) Widespread uplift and erosion from 40 Ma to 16 Ma. The uplift and erosion substages of 40–38 Ma and 26–16 Ma were mainly caused by regional uplift, whereas those of 38–26 Ma resulted from fault-block tilting. Since the end of the third member from the Eocene Shahejie Formation, the Shijiutuo Uplift began to rise, causing the greater Bozhong Depression to be separated into the independent Qinnan and Bozhong Sags. These tectonic uplift and erosion events have a wide range of responses and regional dynamics in eastern China. The findings of this study will lead to a better understanding of the evolution and formation of uplifts within the BBB. [Display omitted] • The Shijiutuo Uplift underwent two stages of tectonic uplift and erosion events in the Cenozoic. • Formation of the Shijiutuo Uplift was associated with regional uplift and fault-block tilting. • The Shijiutuo Uplift did not exist before the end of the third member from the Eocene Shahejie Formation. • The tectonic uplift and erosion events had a wide response in eastern China. [ABSTRACT FROM AUTHOR]

China hosts rich shale gas resources. The Longmaxi Formation (LF) in the Sichuan Basin is one of the important regions for shale gas exploration and extraction. Here, we investigate the pore structure and factors influencing the gas-bearing characteristics of the pores in the shale reservoirs in the LF. We employed scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), gas content testing, gas saturation testing based on nuclear magnetic resonance (NMR), overburden porosity and permeability analysis, distribution of pore size, specific surface area (SSA) analysis, and geochemical analysis. Our results show that the organic matter of the shale in the LF in the study area is highly favorable to shale gas conditions; the brittleness of the regional shale generally increases with an increase in depth. The pores in the LF mainly include organic matter-hosted pores, intergranular pores, intragranular pores, and microfissures, with mesopores dominating. Meanwhile, the gas content also increases with an increase in depth. The pore structure in the study area is affected by organic matter content and mineral components, with the development of organic matter-hosted pores. The porosity and the SSA are positively correlated with the total organic carbon (TOC), whereas clay minerals have an adverse effect on the SSA of pores in the study area. Higher TOC and vitrinite reflectance (Ro) indicate higher gas content. It can be inferred that as the content of brittle minerals increases, particles break to form storage spaces as the depth increases, causing the gas content to increase. Higher SSA and total pore volume indicate higher volume of adsorbed gas. The bound water in rocks tends to reduce the content of desorbed gas. Our results suggest high potential for shale gas extraction in this region. [ABSTRACT FROM AUTHOR]

Whether the Tibetan Plateau is a significant dust source area is of great importance, because this is related to the understanding of sources, accumulation and environmental effects of dusts on the Tibetan Plateau and in the Far East-Pacific Ocean regions as well as to the evolution of coupling of the Tibetan Plateau and atmosphere-ocean-continent exchange. Synoptic dynamics and remote sensing tracing of a dust storm on 3 to 5 March, 2003 in Lhasa on South Tibet demonstrate that the Tibetan Plateau possesses all factors and conditions of generating dust storms. Accompanied with this dust storm is a strong ascending stream on the Plateau which has raised various sizes of dust particles into different levels. The lifted coarse particles were largely fallen down and accumulated as loess on the eastern Tibetan Plateau, and the fine particles were translated by the westerly jet and subsided in the northern Pacific Ocean. The spatial-temporal distribution of dust-storms between years 1961 and 2000 on the Plateau shows that dust-storms mainly occur in winter and early spring with high frequency, and the path of dust storm moves gradually from south to north, which is closely coupled with the northward moving of the westerly jet from winter to spring over the Tibetan Plateau. Compared with other twelve dust source areas in China, the Tibetan Plateau is one of the key dust source areas for the long-distance transport because its high occurring frequency and elevation cause fine particles easily to be lifted into the zone of the westerly jet. [ABSTRACT FROM AUTHOR]

A visibility forecast model called a boosting-based fusion model (BFM) was established in this study. The model uses a fusion machine learning model based on multisource data, including air pollutants, meteorological observations, moderate resolution imaging spectroradiometer (MODIS) aerosol optical depth (AOD) data, and an operational regional atmospheric environmental modeling System for eastern China (RAEMS) outputs. Extreme gradient boosting (XGBoost), a light gradient boosting machine (LightGBM), and a numerical prediction method, i.e., RAEMS were fused to establish this prediction model. Three sets of prediction models, that is, BFM, LightGBM based on multisource data (LGBM), and RAEMS, were used to conduct visibility prediction tasks. The training set was from 1 January 2015 to 31 December 2018 and used several data pre-processing methods, including a synthetic minority over-sampling technique (SMOTE) data resampling, a loss function adjustment, and a 10-fold cross verification. Moreover, apart from the basic features (variables), more spatial and temporal gradient features were considered. The testing set was from 1 January to 31 December 2019 and was adopted to validate the feasibility of the BFM, LGBM, and RAEMS. Statistical indicators confirmed that the machine learning methods improved the RAEMS forecast significantly and consistently. The root mean square error and correlation coefficient of BFM for the next 24/48 h were 5.01/5.47 km and 0.80/0.77, respectively, which were much higher than those of RAEMS. The statistics and binary score analysis for different areas in Shanghai also proved the reliability and accuracy of using BFM, particularly in low-visibility forecasting. Overall, BFM is a suitable tool for predicting the visibility. It provides a more accurate visibility forecast for the next 24 and 48 h in Shanghai than LGBM and RAEMS. The results of this study provide support for real-time operational visibility forecasts. [ABSTRACT FROM AUTHOR]