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Authigenic pyrite aggregates and authigenic gypsum of core EC2005（modified after references［5， 20， 21］ ） （a） 充填在有孔虫中的生物状自生黄铁矿； （b） 管状和他形聚集体； （c~e） 莓状黄铁矿及表面有溶解坑的八面体微晶； （f） 硫化物氧化形成的自生石膏 （a）Authigenic pyrite growing in foraminifera； （b）Tubular and irregular authigenic pyrite aggregates； （c~e）Pyrite framboid and octahedral microcrystals with dissolution pits on the surface； （f）Authigenic gypsum caused by sulfide oxidation
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The formation process of marine authigenic pyrite (FeS2) is closely related to the organic mineralization process, representing an important part of the global C-S-Fe biogeochemical cycle. Since the Holocene highstand of sea level, the shelf of the Yellow Sea and the East China Sea have developed mud deposits extensively, in which a large number of...
Citations
... Based on the findings of this research, the predominant types of pyrite found within the shale reservoirs of the Wufeng-Longmaxi Formation located in the Sichuan Basin were FPy and its aggregates, which are linked to OM. Wufeng-Longmaxi shale is a marine shale abundant in OM, and it is formed under a favorable reducing environment with Fe and S elements, low temperature, and organic richness, resulting in significant FPy formation [53][54][55][56][57][58][59][60]. The finding is consistent with a sulfur-rich sedimentary environment, as indicated by the S/Fe atomic number ratio ranging from 1.8 to 2.1 in pyrite samples [61]. ...
Uncertain provenance and tectonic setting of shale has constrained the exploration and exploitation of natural gas in the Wufeng–Longmaxi Formation in the southern Sichuan Basin, China. Therefore, this study analyzed the mineral petrology and geochemistry to assess the effects of sorting, recycling, weathering, and paleoclimate on the deeply buried shale. The findings revealed that the mineral composition is dominated by biogenic quartz, terrigenous clay minerals, and carbonate minerals. Combinations of clay lamina and silty lamina occur in black shale. The geochemical characteristics of these sedimentary rocks remain unaffected by sedimentary sorting and recycling processes. The clastic sediments primarily originate from the felsic igneous rock source that underwent moderate weathering during its initial deposition in the collision environment. Based on the comprehensive analysis of the paleoclimate and paleoprovenance characteristics, Wufeng–Longmaxi Formation characteristics are considered to have undergone six stages, among which the stage of relative enrichment of organic matter corresponds to LM1, LM2–3, and LM4. Following the Hirnantian glacial period, the era has witnessed global warming, marked by glacier melting, a rise in global sea level, and a decrease in terrestrial debris supply, collectively facilitating organic matter enrichment. During the LM5 and LM6–8 periods, the increase in source supply caused by the Leshan–Longnvsi and Qianzhong–Xuefeng uplift inhibited organic matter enrichment.
... Authigenic pyrite is widely developed on the inner shelves of the Yellow Sea and the East China Sea. Early pioneering research on the distribution, morphological type, formation, and control factors of authigenic pyrite developing in the sea area indicated that its formation process and characteristics are closely related to the sedimentation process and are controlled by different factors, including organic matter content, system openness, anaerobic oxidation of methane (AOM), and sedimentation rate (Kang et al., 2014;Chang et al., 2020;Liu et al., 2022). In addition, pyrite abundance and morphological characteristics may be influenced by local depositional environments, particularly during physical reworking and bioturbation (Richardson et al., 2019;Liu et al., 2022). ...
... The offshore core JC-1 in Zhoushan contained a considerable amount of framboidal pyrite, which occurred as spheroidal, cubic, irregular particles, and tubular or rod-shaped monomers. These pyrite characteristics resemble those of authigenic pyrite reported in the sediments of the East and Yellow seas (Chen, 1981;Chang et al., 2020). Nevertheless, the pyrite morphology and size varied significantly at different depths. ...
Offshore Zhoushan sediments are a potential area for shallow gas resources in China, where authigenic pyrite is widely distributed. Pyrite content, size distribution, and morphology are influenced by depositional conditions and are sensitive to environmental changes. This study investigated the authigenic pyrites or gypsums of core JC-1 offshore of Zhoushan. Scanning electron microscopy was used to observe the pyrites and identify various aggregations. Changes in lithology, chlorine content, and stable isotope values of organic matter were analyzed to indicate the evolution of ancient marine, floodplain estuary, tidal flat environments, and shallow marine sedimentary facies. The morphology and microcrystalline structure of these types of pyrites can be divided into spherical framboid aggregates, sub-euhedral aggregates, and microcrystalline euhedral pyrites with different sedimentary facies. Gypsum minerals and the coexistence of pyrite and gypsum were found in the enriched authigenic pyrites at the SMTZs. The sources of sulfate formed by authigenic gypsums may originate from overlying seawater and pyrite oxidation, whereas calcium ions may come from the dissolution of carbonate or calcareous shells caused by local environmental acidification. The various aggregations of pyrites observed may be related to SO4-AOM in different environments. The findings suggest that authigenic gypsums form due to local environmental acidification and that the sources of the formed sulfate may be from overlying seawater and pyrite oxidation. This study provides a new perspective for understanding the responses of different sedimentary environments to sea level rise and climate change.
Pyrite is a mineral that is commonly found in shale gas reservoirs. Its genetic mechanism and impact on pore and organic matter in shale gas reservoirs are critical for shale gas exploration. This study selects the Longmaxi shale (Lower Silurian) in the Changning area of the southern Sichuan Basin by comprehensively using a scanning electron microscope (SEM), X-ray diffraction (XRD), total organic carbon (TOC), and image processing technology. The type and characteristics of pyrite in shale reservoirs are studied, the sedimentary environment and genetic mechanism of pyrite are analyzed, and the influence of pyrite formation on organic matter enrichment and reservoir formation is evaluated. The results showed that pyrite in shale primarily forms framboidal pyrite, euhedral pyrite, and subhedral pyrite, with particle sizes ranging from 1 to 15 μm. The maximum framboid diameter (MFD) is less than 20 μm, with the average particle size distribution of 3–5 μm. These parameters indicate the vulcanization and blocking environment. The reducing environment promotes organic matter enrichment and preservation. Framboidal pyrite has two genetic sequences: rich organic matter and poor organic matter. The development of organic matter will limit the continuous radial growth of pyrite and is conducive to the protection of pores, and the formation of pyrite can reduce the activation energy of kerogen reaction and catalyze the hydrocarbon generation of organic matter, resulting in higher gas content. The framboidal pyrite content can be used to predict high-quality shale gas reservoirs.
