Geochemical characteristics in the Longmaxi Formation (Early Silurian) of South China: Implications for organic matter accumulation

Yan, Detain; Wang, Hua; Fu, Qilong; Chen, Zhonghong; He, Jin; Gao, Zhan

doi:10.1016/j.marpetgeo.2015.04.016

Cited by 130 publications

(35 citation statements)

References 64 publications

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“…Additionally, the Ba bio content of LLA in both the Jiaoshiba and Zhaotong areas was significantly smaller than that of LLB (Table 1). This result is consistent with recent studies on the Longmaxi Formation in the Sichuan Basin (Yan et al, 2015;Li et al, 2015;Zhao et al, 2016). Since it is possible for barite to dissolve in sulfatereducing conditions, leading to Ba loss (van Os et al, 1991;Torres et al, 1996;van Santvoort et al, 1996), the Ba bio content might not completely reflect the paleoproductivity of the Longmaxi Formation shale.…”

Section: Implications For the Paleoenvironment 511 Primary Productisupporting

confidence: 87%

“…Although the Longmaxi Formation shale is generally considered to have been deposited in an oxygendeprived deep-sea environment, the abundance of organic matter in the Longmaxi Formation shale shows strong vertical and lateral heterogeneity (Zhang et al, 2012;Guo, 2013;Guo and Zhang, 2014;Li et al, 2016). Therefore, numerous studies have been conducted on the mechanism of the organic-matter enrichment in the Longmaxi Formation shale in the Sichuan Basin and its peripheral areas Wang et al, 2015;Yan et al, 2015;Zhao et al, 2016;Wu et al, 2017;Zhang et al, 2018). These studies have generally suggested that the lower part of the shale, characterized by high organic-matter abundance, was deposited in an anoxic or dysoxic environment, while the upper shale, characterized by low organic-matter content, was deposited in an oxic environment.…”

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confidence: 99%

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Geochemistry, Paleoenvironment and Mechanism of Organic‐Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

Chen

Cui

Ren

et al. 2019

Acta Geologica Sinica (Eng)

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To investigate the mechanism of the organic‐matter enrichment in the Lower Longmaxi Formation shale, the geochemistry and total organic carbon (TOC) of the Longmaxi Formation black shales in the Jiaoshiba, Zhaotong, and Weiyuan areas of the Sichuan Basin were analyzed. Paleoproductivity proxy parameters (Babio, Siex, and Ni/Al), clastic influx proxies (TiO2 and Ti/Al), redox indices (V/Cr, Ni/Co, V/(V+Ni), and U/Th), and hydrothermal indicators (Fe, Mn, and Y concentrations; Fe/Ti ratio and a Ni‐Zn‐Co diagram) were employed to decipher the paleoenvironment of the Lower Longmaxi Formation shales. TiO2 and Ti/Al indicated low terrigenous detrital influx in all three areas. However, Babio, Siex, and Ni/Al indicated high productivity in the Jiaoshiba area. V/Cr, Ni/Co, and U/Th indicated higher oxygen content with larger fluctuations in the Zhaotong and Weiyuan areas. Fe, Mn, and Y concentrations and the Fe/Ti ratio implied greater active hydrothermal activity in the Weiyuan area. These heterogeneities were considered to be closely related to the paleoenvironment and paleogeography, and the large basement faults that developed during the Chuanzhong paleo‐uplift could have provided vents for deep‐hydrothermal‐fluid upwelling. The redox indices (V/Cr, Ni/Co, and U/Th) and a paleoproductivity proxy (Ni/Al) displayed a significant correlation with the TOC, suggesting that both excellent preservation conditions and high paleoproductivity were the controlling factors for the enrichment of organic matter in the Longmaxi Formation shale. There was no obvious correlation between the clastic influx proxy (Ti/Al) and the TOC due to the extremely low supply of terrigenous debris. The hydrothermal indicator (Fe/Ti) was negatively correlated with the TOC in the Weiyuan area, indicating that hydrothermal activity may have played a negative role in the accumulation of organic matter. This study suggests that the enrichment of organic matter in the Longmaxi Formation marine shale varied according to the paleogeography and sedimentary environment.

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Section: Implications For the Paleoenvironment 511 Primary Productisupporting

confidence: 87%

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confidence: 99%

Geochemistry, Paleoenvironment and Mechanism of Organic‐Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

Chen

Cui

Ren

et al. 2019

Acta Geologica Sinica (Eng)

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“…The late Ordovician-early Silurian Longmaxi Formation in the Middle-Upper Yangtze is a laterally continuous stratum seen as a hydrocarbon source, and now proven to be productive in Fuling of Upper Yangtze, which is now under commercial exploration with a gas flow of (15.3-155.8) × 10 4 m 3 /day [1]. The lower member of Longmaxi Formation formed under deep shelf environment, along with euxinic and reductive water background, appropriate sedimentary rateis of high hydrocarbon generation potential [2][3][4]. The hydrocarbon source rock quality of the upper member is generally deteriorating as tectonic transformations leading to a shallower basin [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

The Early Silurian Sedimentary Environment of Middle-Upper Yangtze: Lithological and Palaeontological Evidence and Impact on Shale Gas Reservoir

Zhu

Wang

et al. 2019

Minerals

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The organic-enriched thick shale at the bottom of Longmaxi Formation is laterally continuous distributed and has been proven to be of good production capability in Fuling of Upper Yangtze. Uplifts that developed during the sedimentation influenced the reservoir characteristics by taking control of the sedimentary environment and provenance. The sedimentary environments are mainly deep-water shelf, shallow-water shelf, and tidal flat. By analyzing reservoir characteristic of these three environments, the deep-water shelf, which dominated the early stage of sedimentation, formed a high-quality reservoir with high TOC (Total Organic Carbon) content, porosity, and brittleness, while the environment was maintained around the basin centre until the Early Silurian. The shales deposited under the shallow-water environment were of low porosity because of the increasing calcareous and argillaceous contents. Sediments which formed on the tidal flat were arenaceous and of the lowest TOC content as the organic preservation conditions deteriorated. The good correlation of graptolite abundance and TOC content, and high porosity within graptolite fossils emphasize the importance of palaeontological development. The argillaceous cap over the Longmaxi shale is of good sealing capability, and the continuous sedimentation zone along southern Sichuan–eastern Chongqing is the best optimized hydrocarbon-bearing system. However, a weak interface on the discontinuity is the potential lateral pathway for gas diffusion at Northern Guizhou and Western Hunan, but on the southeast margin where the dark shale and the tidal sandstone contact, it promises to form a tight gas reservoir.

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“…A recent study of the Longmaxi Formation in the southeastern Sichuan Basin has documented sequence stratigraphic control on mudstone heterogeneity (Chen et al, 2015). However, as one of the most important source rocks and unconventional reservoirs in China and a prime example for a Lower Paleozoic deep shelf succession deposited during a worldwide marine transgression after the Early Silurian melting of Gondwana glaciation (Mu et al, 1981;Wang and Mo, 1995;Chen et al, 2004;Guo, 2013;Guo and Zhang, 2014;Yan et al, 2015;Yang et al, 2016), a detailed depositional model that explains the influences of depositional processes and water column conditions on organic matter accumulation in the prolific lower Longmaxi Formation is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Geochemistry and sedimentology of the Lower Silurian Longmaxi mudstone in southwestern China: Implications for depositional controls on organic matter accumulation

Fan

et al. 2016

Marine and Petroleum Geology

106

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similar to the ratios of modern sediments deposited in anoxic-euxinic environments, suggesting moderate basin restriction during deposition. The mudstone in the lower Longmaxi Formation may be part of the globally abundant organic-rich mudstones of Early Silurian age, whose depositional mechanism have yet to be fully explored. The distribution of lithofacies in the studied interval shows an overall trend from deep water to shallow water depositional environments. We developed a detailed depositional model to interpret the evolution of depositional environments of the lower Longmaxi Formation. This study provides an example to how better characterize unconventional hydrocarbon systems through coupling of rigorous geochemical and sedimentological analysis.

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Geochemical characteristics in the Longmaxi Formation (Early Silurian) of South China: Implications for organic matter accumulation

Cited by 130 publications

References 64 publications

Geochemistry, Paleoenvironment and Mechanism of Organic‐Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

Geochemistry, Paleoenvironment and Mechanism of Organic‐Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

The Early Silurian Sedimentary Environment of Middle-Upper Yangtze: Lithological and Palaeontological Evidence and Impact on Shale Gas Reservoir

Geochemistry and sedimentology of the Lower Silurian Longmaxi mudstone in southwestern China: Implications for depositional controls on organic matter accumulation

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