The Late Permian Sunjiagou Formation and Early Triassic Liujiagou Formation were studied to understand the palaeoclimatic and palaeoenvironmental changes in the southwest margin of the North China Craton across the Permian-Triassic boundary, as well as the tectonic evolution of their provenance sediment. Major, trace, and rare earth elements in 20 clastic rock samples from the strata above and below the boundary were analysed. Overall, the Sunjiagou Formation samples showed an average index of compositional variability (ICV) and chemical index of alteration (CIA) of 1.53 and 73.59, respectively, indicating high-maturity sediments in a warm and humid environment with moderate chemical weathering, whereas Liujiagou Formation samples had an average ICV and CIA of 2.40 and 70.1, respectively, indicating lowmaturity sediments in a cold and dry environment with mild chemical weathering.These strata were composed of first-cycle sediments in a tectonically active area.The provenance of the Sunjiagou Formation was dominated by quartz-rich sedimentary rocks, whereas that of Liujiagou Formation had both quartz-rich sedimentary rocks and intermediate volcanic rocks. The provenance tectonic settings were mainly the continental island arc and active continental margin. Thus, the study area was in a terrestrial, freshwater sedimentary environment from the Late Permian to Early Triassic, and the climate gradually changed from warm and humid to dry and hot, with multiple small-scale periodic evolutions. Taken together, these findings further confirm that the entire study area was in an oxidizing environment and the oxidation degree in the Early Triassic was higher than that in the Late Permian.
Paleo-wildfires can help elucidate the transition trends of Earth from “icehouse” to “greenhouse,” thereby allowing us to forecast the current changes associated with wildfires of this era. In this study, the early Permian Shanxi Formation in the Pingdingshan coalfield, located south of the North China Basin, was selected as a study site. Based on data on inertinite content, inertinite reflectance, nine polycyclic aromatic hydrocarbons (PAHs), paleo-wildfires, and their paleoclimate effect during the early Permian coal formation were systematically analyzed. The inertinite content in coal in the study area ranged from 9.76 to 29.65%, with an average of 19.32%. Meanwhile, the average inertinite reflectance values ranged from 2.41–4.74%, with an average of 2.75%. PAHs in the study area were mainly tricyclic and tetracyclic; the contents of fluorene, phenanthrene, pyrene, bypyrene, benzo[b]fluoranthene, and benzo[e]pyrene were higher than those of other PAHs in the same stratum. The total concentration of PAHs varied widely between layers (3601–21,894 ng/g). The presence of paleo-wildfires was confirmed by the contents of inertinite and PAHs. It can be concluded that paleo-wildfires in the study area were dominated by surface fires at low and medium temperatures based on the combustion equation. The oxygen content in the paleo-atmosphere of the Early Permian Shanxi Formation in the study area was 24.29%, which provided the necessary conditions for the occurrence of wildfires.
Microbially enhanced coalbed methane (MECBM) has important theoretical and practical significance for reforming coal reservoir structure, alleviating greenhouse effects and energy crises and developing new sources of clean energy. In this study, No. 3 coal seams in Qinshui Basin were taken as research objects to analyze the pore structure characteristics after microbial treatment by means of low-temperature nitrogen adsorption (LTNA), mercury porosimetry (MP), and isothermal adsorption/desorption experiments. The results showed that after bioconversion, the specific surface area and pore volume increased from 1.79 m2/g and 0.0018 cm3/g to 4.01 m2/g and 0.0051 cm3/g respectively under liquid nitrogen testing; however, the specific surface area was reduced from 5.398 m2/g to 5.246 m2/g and the pore volume was increased from 0.053 cm3/g to 0.0626 cm3/g under MP. The fractal dimension based on the LTNA data indicated that the fractal dimension of micropores and minipores was increased from 2.73 to 2.60 to 2.89 and 2.81, however the fractal dimension of meso-macropores was decreased from 2.90 to 2.85. The volatile matter and fixed carbon were both reduced from 6.68% to 78.63%–5.09% to 75.63%, and the Langmuir volume and Langmuir pressure were increased from 34.84 cm3/g and 2.73 MPa to 36.34 cm3/g and 3.28 MPa, respectively. This result indicated that microorganism participated in the degradation of coal reservoir and promoted the production of methane gas, the meso-macropores were more obviously modified by microorganism, so that the pore diameter stabilized, the pores became smoother, the specific surface area decreased, and the pore volume increased. These are more beneficial to the adsorption and production of coalbed methane (CBM) after microbial treatment.
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