Geochemical Changes in the Late Ordovician to Early Silurian Interval in the Northern Margin of the Upper Yangtze Platform, Southern China: Implications for Hydrothermal Influences and Paleocean Redox Circumstances

Abstract

A comprehensive chemostratigraphic study, including evaluation of rare earth elements and trace elements, was conducted to explain the paleoenvironments of the northern margin of the Upper Yangtze Platform. Trace elements, like Ba, U, V, Cu, and Zn, tended to be more abundant in these formations than in the upper continental crust. The authigenic abundances of Al-normalized U and V, as well as the Th/U and V/Sc ratios, were used as indicators of the redox circumstances. In the Nanjiang area, the redox circumstances of the bottom water during the Ordovician–Silurian transition changed from oxic in the Late Katian to slightly anoxic in the Hirnantian and then gradually became anoxic in the Early Rhuddanian. In the Chengkou area, the redox circumstances of the bottom water during the Ordovician–Silurian transition abruptly changed from oxic in the Late Katian to strongly anoxic in the Hirnantian and continued to become more anoxic until the Rhuddanian. The total organic carbon concentrations were well correlated with the redox circumstances of the bottom water. We conclude that the transient hydrothermal activity was not widely distributed during the Late Ordovician–Early Silurian transition, and it might also have been only a local event in the Upper Yangtze Platform. The enrichment in organic matter was mostly sourced from the photic zone and was governed by the redox circumstances of the bottom water.

Rare Earth Element Characteristics of Shales from Wufeng–Longmaxi Formations in Deep-Buried Areas of the Northern Sichuan Basin, Southern China: Implications for Provenance, Depositional Conditions, and Paleoclimate

“…Some scholars also believe that the deposition of this set of shales is the result of the synergistic effect of paleoclimate and paleoceanic factors caused by geological time such as volcanic eruption, undercurrent intrusion, and terrigenous detrital input. ,, In summary, there is still a great deal of controversy regarding the formation environment of the Wufeng–Longmaxi Formation shale, and there is also less research on the source background. Currently, previous studies on the geochemical characteristics of the Wufeng–Longmaxi Formation black shales buried less than 3500 m have been conducted in depth. − However, due to the lack of deep drilling in the deep-buried areas of the Wufeng–Longmaxi Formations in the Sichuan Basin, representative samples cannot be collected systematically, which leads to the relatively slow evaluation of deep shale gas resources in deep-buried areas.…”

Characterization of Coal Particle Methane Desorption and Optimization of Desorption Model Based on Desorption Damage

“…A significant outburst of coal and gas accidents will be accompanied by energy release, which produces strong power in the period of underground mining. − Gas outburst produces a large amount of pulverized coal, and the desorption gas of pulverized coal will further facilitate the outburst. − Therefore, gas significantly influences the gestation and occurrence of gas outbursts. − As coal mining depths increase, the amount and intensity of gas emissions also increase, which will induce more gas calamities. − In addition to the high-intensity mining stage of deep coal seams, the coal has been strongly damaged many times during the coal-forming process, leading to the gas migration in the coal body and the circumstance of gas desorption–pulverization–desorption. , Consequently, studying the law of gas desorption in coal under damage conditions is crucial for understanding gas emission laws and gas flow mechanisms and predicting coal and gas outbursts. − …”

Analysis and Prevention of Rock Burst Risk of Working Face under the Influence of Continuous Irregular Triangular Coal Pillar Stress Concentration Area

“…More than 95% of the raw coal is mined via underground mining methods. , The production mode of underground operations is very different from that of surface mining. There are many technical problems in underground mining, and many coal mine production accidents will be faced at the same time. − Rock burst is a dynamic phenomenon in which the elastic potential energy of the surrounding coal and rock mass is suddenly and violently released under certain conditions during coal mining production, resulting in severe vibration and severe damage to the coal and rock mass, making this phenomenon very destructive. − …”