Redox conditions across the G–L boundary in South China: Evidence from pyrite morphology and sulfur isotopic compositions

Wei, Hengye; Wei, Xuemei; Qiu, Zhen; Song, Huyue; Shi, Guo

doi:10.1016/j.chemgeo.2016.07.009

Cited by 79 publications

(61 citation statements)

References 83 publications

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“…Based on the formation mechanism of pyrite framboids, the pyrite framboids can be used as an indicator of paleoredox conditions [13][14][15][16][17]38,60]. Syngenetic framboids will not grow after pyrites are precipitated from the water and deposited in the sediments [13,66].…”

Section: Pyrite Morphology As An Indicator Of Paleoredox Conditionsmentioning

confidence: 99%

“…This process results in the size of the early diagenetic framboids being large and variable. Hence, the framboids' mean size and standard deviation/skewness values of the populations can be used to estimate the paleoredox conditions in the water body [13][14][15]37,38].…”

Section: Pyrite Morphology As An Indicator Of Paleoredox Conditionsmentioning

confidence: 99%

“…However, the δ 34 S in pyrites of bulk rock is often measured through a mass spectrometer coupled to an elemental analyzer, and the measured sulfur isotope is derived from the mixed values of sulfur isotopes from sedimentary pyrite and diagenetic pyrite. In addition to the above experimental method, the diagenetic and syngenetic pyrite populations are usually distinguished by the smaller mean size of the framboids and standard deviation/skewness values of the populations [14,15,37,38]. Because the diagenetic framboids vary in size, the standard deviation/skewness values of diagenetic framboids are larger than those of syngenetic framboids.…”

Section: Introductionmentioning

confidence: 99%

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Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China

et al. 2019

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Pyrite is the most common authigenic mineral preserved in many ancient sedimentary rocks. Pyrite also widely exists in the Longmaxi and Wufeng marine shales in the middle Yangtze area in South China. The Longmaxi and Wufeng shales were mainly discovered with 3 types of pyrites: pyrite framboids, euhedral pyrites and infilled framboids. Euhedral pyrites (Py4) and infilled framboids (Py5) belong to the diagenetic pyrites. Based on the formation mechanism of pyrites, the pyrites could be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. Under a scanning electron microscope (SEM), the syngenetic pyrites are mostly small framboids composed of small microcrystals, but the diagenetic pyrites are variable in shapes and the diagenetic framboids are variable in sizes with large microcrystals. Due to the deep burial stage, the pore space in the sediment was sharply reduced and the diameter of the late diagenetic framboids that formed in the pore space is similar to the diameter of the syngenetic framboids. However, the diameter of the syngenetic framboid microcrystals is suggested to range mainly from 0.3 µm to 0.4 µm, and that of the diagenetic framboid microcrystals is larger than 0.4 µm in the study area. According to the diameter of the pyrite framboids (D) and the diameter of the framboid microcrystals (d), the pyrite framboids could be divided into 3 sizes: syngenetic framboids (Py1, D < 5 µm, d ≤ 0.4 µm), early diagenetic framboids (Py2, D > 5 µm, d > 0.4 µm) and late diagenetic framboids (Py3, D < 5 µm, d > 0.4 µm). Additionally, the mean size and standard deviation/skewness values of the populations of pyrite framboids were used to distinguish the paleoredox conditions during the sedimentary stage. In the study area, most of the pyrite framboids are smaller than 5 µm, indicating the sedimentary water body was a euxinic environment. However, pyrite framboids larger than 5 µm in the shales indicated that the sedimentary water body transformed to an oxic-dysoxic environment with relatively low total organic carbon (TOC: 0.4–0.99%). Furthermore, the size of the framboid microcrystals could be used to estimate the gas content due to thermochemical sulfate reduction (TSR). The process of TSR occurs with oxidation of organic matter (OM) and depletes the H bond of the OM, which will influence the amount of alkane gas produced from the organic matter during the thermal evolution. Thus, syngenetic pyrites (d ranges from 0.35 µm to 0.37 µm) occupy the main proportion of pyrites in the Wufeng shales with high gas content (1.30–2.30 m3/t), but the Longmaxi shales (d ranges from 0.35 µm to 0.72 µm) with a relatively low gas content (0.07–0.93 m3/t) contain diagenetic pyrites. Because of TSR, the increasing size of the microcrystals may result in an increase in the value of δ13C1 and a decrease in the value of δ13C1-δ13C2. Consequently, the size of pyrite framboids and microcrystals could be widely used for rapid evaluation of the paleoredox conditions and the gas content in shales.

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Section: Pyrite Morphology As An Indicator Of Paleoredox Conditionsmentioning

confidence: 99%

Section: Pyrite Morphology As An Indicator Of Paleoredox Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China

et al. 2019

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“…Framboids developed under euxinic conditions are generally small, with a narrow size range (4.3 -6.1 µm), while diagenetic framboids developed in sediments underlying oxic-dysoxic water column are larger (5.7 -11.9 µm) with a wider size range (Wilkin et al, 1996). Therefore, framboids in the studied sediments, with diameters ranging between 4 and 30 m and a mean value of 12 m, could have been formed in sediments underlying oxic-dysoxic water column (Wilkin et al, 1996, Wei et al, 2016. Pyrite framboids formation would require the presence of reactive Fe 2+ and H 2 S, both likely provided by the activity of Fe reducing bacteria and SRB in anoxic conditions (Canfield 1989, Wilkin andBarnes, 1997), being SO 4 = availability a limiting factor in fresh water environments (Davidson et al, 1985;Marnette et al, 1993).…”

Section: Type I and Ii Aggregatesmentioning

confidence: 88%

“…Taking into account the largest and the smallest measured diameter in the studied case, Type I and II framboids would be constituted by approximately 10 3 to 30 x 10 3 crystals, which is the range of NM showed by framboids in modern sediments (Wilkin et al, 1996). Size distribution of pyrite framboids is considered to be an indicator of the environmental conditions under which they were formed (Wilkin et al, 1996;Wignall and Newton, 1998;Wei et al, 2016). Framboids developed under euxinic conditions are generally small, with a narrow size range (4.3 -6.1 µm), while diagenetic framboids developed in sediments underlying oxic-dysoxic water column are larger (5.7 -11.9 µm) with a wider size range (Wilkin et al, 1996).…”

Section: Type I and Ii Aggregatesmentioning

confidence: 97%

Fe-rich microspheres pseudomorphs after pyrite framboids in Holocene fluvial deposits from NE Spain: Relationship with environmental conditions and bacterial activity

Mayayo

Yuste

Luzón

et al. 2019

Sedimentary Geology

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Three iron oxides-rich microsphere types (Type I to III) were detected in an Holocene 17 mthick stratigraphic succession located in the Iberian Range (NE Spain). Lithofacies features indicate that the studied materials were generated in an alluvial-dominated setting, with a channeled area fringed by floodplain zones. During high water levels and high-energy floods, gravels and sands deposited in the active area and in lateral overbank areas. In these lateral areas, mud settling took place when flood decreased and then anoxic conditions could be reached due to microbial oxidation of organic matter and the low permeability of the marly sediment. X-ray diffraction (XRD) analysis of 32 samples and microtextural observation of 10 samples by Field Emission Scanning Electron Microscopy (FESEM) revealed the occurrence of Fe oxi-hydroxides microspheres showing different surficial structure. These microspheres are pseudomorphs after pyrite framboids although the formation of some primary Fe oxyhydroxides aggregates cannot be rejected. Pyrite framboids genesis in sediments underlying oxic-dysoxic water column would have been favored by anoxic conditions reached in lateral overbank areas after main flooding, involving the activity of Fe reducing bacteria and sulfatereducing bacteria (SRB), given the high SO 4 = availability provided by the highly mineralized groundwater from the upstream Baños de Ariño spring. Subsequent change to oxic conditions

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Chemostratigraphy and pyrite morphology across the Wuchiapingian‐Changhsingian boundary in the Middle Yangtze Platform, South China

Wei

Tang

et al. 2021

Geological Journal

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Handling Editor: C. Cao Separated mass extinction occurred at the beginning and the ending of the Late Permian, called end-Guadalupian and end-Permian mass extinctions, respectively. Palaeoenvironmental changes in the middle of the Late Permian could give more insights into the environmental causes for the Permian extinctions. In this contribution, we analysed carbonate carbon isotope and carbonate-associated-sulphate sulphur isotope compositions to constrain the carbon and sulphur cycles across the Wuchiapingian-Changhsingian boundary (WCB) at Yanglinqiao in Zigui in the Middle Yangtze Platform.Pyrite morphology and pyrite framboids size distribution were used to analyse redox conditions variations across the WCB. Our results show that an episodic euxinia event occurred across the WCB. This anoxic/euxinic event across the WCB was a global event, and was mainly caused by the upwelling during the cooling event. Both inorganic-and organic-carbon isotopic compositions show covariance of a negative shift across the WCB at Yanglinqiao and other places in South China. This carbon-isotopic negative excursion across the WCB was a regional carbon cycle perturbation and may be linked to the light-carbon input from the upwelling water mass. Although the seawater δ 34 S across the WCB recorded a negative excursion in two locations in South China, it reflects the riverine input of 32 S-enriched sulphate and represent a regional signal.These environmental anomalies such as oceanic anoxia/euxinia, global carbon cycle perturbation, cooling, end of the Emeishan large igneous province movement across the WCB may have delayed the recovery from the end-Guadalupian mass extinction.

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Redox conditions across the G–L boundary in South China: Evidence from pyrite morphology and sulfur isotopic compositions

Cited by 79 publications

References 83 publications

Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China

Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China

Fe-rich microspheres pseudomorphs after pyrite framboids in Holocene fluvial deposits from NE Spain: Relationship with environmental conditions and bacterial activity

Chemostratigraphy and pyrite morphology across the Wuchiapingian‐Changhsingian boundary in the Middle Yangtze Platform, South China

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