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Pyrite micromorphology in the Longmaxi and Wufeng Formations. (a) Syngenetic framboids (SF), early diagenetic framboids (EDF), late diagenetic framboids (LDF) and infilled pyrite framboids (IPF) in the Longmaxi silty shale, 2330.46 m, well JY1; (b) infilled pyrites framboids (IPF) and euhedral pyrites (EP) in the Longmaxi black silty shale, 17.43 m, well X; (c) euhedral pyrites (EP) and clustered pyrite framboids (CPF) in the Longmaxi black silty shale, 45.91 m, well X; (d) syngenetic framboids (SF), early diagenetic framboids (EDF) and euhedral pyrites (EP) in Longmaxi black-gray silty shale, 2346.5 m, well JY1; (e) early diagenetic framboid (EDF) and irregular aggregation of pyrite microcrystals (IAPM) in the Longmaxi shale, 2397.13 m, well JY1; (f) aggregation of pyrite microcrystals (APM) in the Wufeng black shale, 72.78 m, well X.
Source publication
Pyrite, as a characteristic mineral in organic-rich marine shale, is a significant index for the interpretation of paleoredox conditions. In this study, based on drilling cores and focused ion beam-scanning electron microscopy (FIB-SEM), the occurrence, diameter and particle size distribution of pyrites from 32 samples obtained from the Wufeng–Long...
Contexts in source publication
Context 1
... pyrite framboids are mainly composed of euhedral pyrite microcrystals with a uniform size (0.1 µm to 1 µm). Abundant intercrystal nanopores can be found in normal spherical pyrite framboids (Figure 3a). The pyrite framboids can be divided into four types: syngenetic framboids (SF, D < 4.8 µm, d ≤ 0.4 µm) developed in the organic matter enrichment area (Figure 3a tion of pyrite microcrystals (IAPM) (Figure 3e). ...
Context 2
... intercrystal nanopores can be found in normal spherical pyrite framboids (Figure 3a). The pyrite framboids can be divided into four types: syngenetic framboids (SF, D < 4.8 µm, d ≤ 0.4 µm) developed in the organic matter enrichment area (Figure 3a tion of pyrite microcrystals (IAPM) (Figure 3e). (5) Aggregation of pyrite microcrystals (APM). ...
Context 3
... intercrystal nanopores can be found in normal spherical pyrite framboids (Figure 3a). The pyrite framboids can be divided into four types: syngenetic framboids (SF, D < 4.8 µm, d ≤ 0.4 µm) developed in the organic matter enrichment area (Figure 3a tion of pyrite microcrystals (IAPM) (Figure 3e). (5) Aggregation of pyrite microcrystals (APM). ...
Citations
... This indicates that some parts of the deep groundwater system are more acidic than the shallow groundwater system. This can be attributed to areas of organically rich marine shale as they contain pyrite (Exhibit 3) (Chen et al., 2022). If the pH exceeds its highest desirable limit (6.5-8.5) in drinking water, it harms the mucous membrane in the eyes, nose, mouth, abdomen, anus, etc. (Ibrahim et al., 2015;Subba Rao, 2020). ...
This study aimed to investigate the hydrochemical and hydrogeochemical facies and
mechanisms controlling groundwater quality from the northern and eastern parts of
Kilwa district and Songosongo Island in Tanzania. Multifaceted methods were used to analyze the hydrochemical properties of water in relation to local geology and proximity to the Indian Ocean. The pH of the groundwater ranged from 5.18 to 7.56 with an average value of 6.64 which is slightly acidic. Electrical Conductivity (EC) ranged from 354 to 1429.50 µS/cm with an average value of 1652.6 µS/cm while Total Dissolved Solids (TDS) values varied from 170 to 1825 mg/L with an average value of 918.8 mg/L. The average values for Ca2+, Mg2+, Na+, and K+ were 36.9, 21.4, 152.5, and 13.31 mg/L, while for NO3−, Cl−, HCO3−, and SO42- were 2.1, 256.3, 156.6, and 45.8, respectively. The study found that groundwater closest to the ocean had elevated values of TDS, Na+, and Cl− and were more affected by seawater intrusion compared to those further inland. The dominant groundwater type was established to be Na-Cl mostly nearest to the ocean while Ca-Mg-Cl was more encountered towards the inland. The groundwater in the northern and eastern parts of Kilwa is mainly controlled by seawater intrusion and recharge water. The Neogene formations consisting of clay, silts, coastal sands, and alluvium had lower Na+, Cl−, EC, and TDS values than the Paleogene which is more influenced by marine sediments. Thus, these findings call for improved groundwater monitoring to track changes in water quality since several parameters including sodium, magnesium, chlorides, TDS, EC, and pH were higher than recommended values for drinking purposes. However, the majority of the water samples were suitable for human consumption.
... Redox-sensitive elements (e.g., V, Cr, Co, Ni, and U) and their ratios are widely used widely to distinguish marine redox conditions (Tribovillard et al. 2007;Algeo and Tribovillard 2009;Algeo and Rowe 2012). Using a single index to reflect paleoredox information is unreliable because each geochemical index has its application limitations (Chen et al. 2022;Fan et al. 2022). Therefore, the Ni/Co, V/Cr, and U/Th ratios were used to comprehensively judge the depositional environment in this study. ...
Based on total organic content (TOC) tests and major-trace element test data, this study examined organic matter accumulation and controlling factors of the Longmaxi Formation shale in the Changning area, southern Sichuan Basin. The results showed that (1) TOC content of the Long11 submember (S1l1¹) shale was between 0.46% and 8.35%. Vertically, TOC revealed a ‘sandwich cake’ pattern with a high TOC content concentrated in the 1st layers of Long11 submember (S1l11–1) and 3rd layers of Long11 submember (S1l11–3) and a lower TOC content in the 2nd layers of Long11 submember (S1l11–2) and 4th layers of Long11 submember (S1l11–4). Spatial distribution of TOC showed variations and migration in S1l1¹. (2) S1l1¹ shale TOC showed a logarithmic correlation with sedimentary environment index, negative correlation with terrigenous influx, and complex correlation with paleoproductivity. (3) Factors controlling organic matter accumulation were mainly redox conditions, followed by paleoproductivity and terrigenous input in Changning area. When the paleoproductivity index (Babio) was less than 2200 μg/g, the redox conditions was the controlling factor of organic matter accumulation. On the contrary, it is ultrahigh paleoproductivity. Vertically, organic matter accumulation mode evolved from “preservation conditions” to “productivity–preservation conditions synergy mode” to “productivity mode”. (4) An anoxic condition was the basis of organic matter accumulation. Medium–high paleoproductivity was the key to organic matter accumulation. These study results are expected to contribute to shale gas exploration and development.
... P, Mo, Cu, Zn, and other trace elements are the main nutrients that living organisms depend on to survive. The content of these elements controls the aerobic plankton in the ocean, which in turn controls the primary productivity of the ocean [58,59]. P and other elements are easily affected by sedimentary organic matter or authigenic minerals. ...
... In an anoxic environment, Mo is also one of the main indicators of water body productivity [56]. Cu and Zn are easily absorbed by microorganisms under photosynthesis, and their concentrations in water bodies decrease accordingly [58,61]. The organic particles transported by weathering undergo partial decomposition during their sedimentation in the water, and some of these nutrients are released back into the water and re-enter the cycle, while the remainder settles to the seafloor with the organic matter particles and is further decomposed by bacteria before being released back into the overlying water, with the residual fraction being buried and preserved [62]. ...
The relationship between the Late Ordovician–Early Silurian sedimentary system, weathering, paleoclimate, and primary productivity in the Yangzi region is not well understood. In this study, by analyzing the sedimentation cycle and major trace elements of the Youc well 2 in the southeast Sichuan Basin, the coupling relationships of weathering indicators, terrigenous debris input indicators, paleoclimate, redox condition indicators, U-Mo covariance model, Mo/TOC relationship, and paleoproductivity indicators are investigated. The results show that single-well logs delineate four third-order sedimentary sequences (SS1, SS2, SS3, and SS4), two sedimentary subfacies, and four sedimentary microfacies in the Wufeng Formation–Longmaxi Formation. The weathering degree is stronger at the bottom where the climate shifts from warm–wet to cold–dry, and the seawater is in an oxidic–anoxic–oxidic–anoxic environment. While the primary productivity and material source input decreases gradually in the middle and upper part, the climate becomes dry and cold, and the seawater is in an anoxic–oxidic environment. Thus, a rock enrichment model for the organic matter shale of the Wufeng Formation–Longmaxi Formation in southeast Sichuan has been established. This provides more information on the control factors concerning organic matter enrichment and their interactions.
