Depositional environment and organic matter accumulation of Upper Ordovician–Lower Silurian marine shale in the Upper Yangtze Platform, South China

Li, Yangfang; Zhang, Tongwei; Ellis, Geoffrey S.; Shao, Deyong

doi:10.1016/j.palaeo.2016.11.037

Cited by 184 publications

(105 citation statements)

References 89 publications

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“…Volcanic activity is another reason for the difference in redox environment and biological productivity between the Wufeng Formation-the lower section of the Longmaxi Formation 1st member and the upper section of the Longmaxi Formation 1st member. Influenced by the collision between the Yangtze Plate and the Cathaysian Plate, during the deposition of the Wufeng Formation-the lower section of the Longmaxi Formation 1st member, volcanic activity was frequent and intense, leading to dramatic climate changes, improving the reducibility of the lower water [37,38,[76][77][78][79][80]. After the ash materials formed by volcanic eruption subsiding into surface water, minerals [68] and Zhang et al [30].…”

Section: Volcanic Activity Analysis and Its Effect On The Enrichment mentioning

confidence: 99%

Mechanism Analysis of Organic Matter Enrichment of Upper Ordovician-Lower Silurian Shale in Upper Yangtze Area-Taking Jiaoye-1 Well in Jiaoshiba Block as an Example

Liu¹,

Jiang²,

Zhang³

et al. 2019

Geological Society of America Abstracts With Programs

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Organic matter is the material basis of shale hydrocarbon generation. The current organic matter content in shale is controlled by the original sedimentary organic matter abundance. Therefore, the study of the enrichment mechanism of sedimentary organic matter in shale has become an important issue to be solved. The Upper Yangtze area is the important exploration and exploitation area of marine shale gas in China. The shale of the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in the Yangtze area is the research object. Choosing redox indicator and biological productivity indicator, the study explores the enrichment mechanism of sedimentary organic matter from two aspects, sealing of water and volcanic activity. The results show that excess siliceous mineral in the shale of the Wufeng Formation-Longmaxi Formation in the Upper Yangtze area is bioorigin. Excess siliceous mineral can be used as one of the indicators of biological productivity. On the one hand, layer phenomenon occurred since the strong water sealing during the sedimentary period of Wufeng and the lower section of the Longmaxi Formation, which results in the high content of oxygen in surface water. On the other hand, the active volcanic activity brought volcanic ash which was beneficial to biological reproduction. Both of these factors led to higher biological productivity during this period. At the same time, the strong sealing of water made the lower layer of the water more reductive, and the active volcanic activity caused climate change, enhancing the reduction of the lower layer of the water, which made the rich organic matter deposited from the surface water well preserved. In the sedimentary period of the upper section of the Longmaxi Formation 1st member in the Upper Yangtze area, on the one hand, due to the weakened sealing of water, the oxygen content of the upper water decreased. On the other hand, the volcanic activity weakened until it stopped, and the source of volcanic ash rich in nutrient elements decreased. These two aspects led to lower biological productivity during this period. At the same time, the weaker water sealing could lead to a decrease in the reduction of the lower layer of the water, and the gradual cessation of volcanic activity no longer affected the climate, causing the destruction of sedimentary organic matter by oxidation.

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Section: Volcanic Activity Analysis and Its Effect On The Enrichment mentioning

confidence: 99%

Mechanism Analysis of Organic Matter Enrichment of Upper Ordovician-Lower Silurian Shale in Upper Yangtze Area-Taking Jiaoye-1 Well in Jiaoshiba Block as an Example

Liu¹,

Jiang²,

Zhang³

et al. 2019

Geological Society of America Abstracts With Programs

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“…Organic-rich shale is a result of the synergistic effect of paleoclimatology, paleoceanology, and paleontology caused by geological events [2,3]. Previous studies have shown that factors affecting organic matter accumulation may include sea level rising, anoxic events, plankton proliferation, and seawater stratification [4][5][6]. However, there is no widely accepted accumulation mechanism of organic matter.…”

Section: Introductionmentioning

confidence: 99%

Paleoenvironment and Organic Matter Accumulation of the Upper Ordovician-Lower Silurian, in Upper Yangtze Region, South China: Constraints from Multiple Geochemical Proxies

et al. 2020

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The origin of the organic-rich shale in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation is complex and controversial. This paper reports the geochemical data of Wufeng-Longmaxi Formations in the Upper Yangtze region to restore the paleoenvironment and explore the accumulation mechanism of organic matter. The total organic carbon (TOC) content of the Wufeng Formation was relatively high, with an average of 2.86%. The Lower Longmaxi Formation showed the highest TOC content, with an average of 3.99%, and the upper part was a continuously low value with an average of 1.22%. The paleoproductivity proxies (Babio, Cu/Al, Ni/Al, Siexcess) showed that in the Katian and Rhuddanian-Aeronian Stages, the Upper Yangtze Sea had high primary productivity, indicating that organic matter accumulation was more affected by terrigenous influx and redox conditions. Al, Zr, and Zr/Al indicated that terrigenous influx was relatively high in the Kaitian-Hirnantian Stages, it was at a constant low in the Rhuddanian Stage, and increased again in the Aeronian Stage. The correlations between redox-sensitive trace elements (Mo, U, V) and TOC indicate that the organic-rich shale of the Wufeng Formation was deposited in the anoxic–euxinic environment. In the Longmaxi Formation, organic-rich shales formed in a more hypoxic environment, and overlying organic-lean shales formed in a suboxic environment. Therefore, the anoxic–euxinic conditions of the Late Ordovician Yangtze Sea were the main reason for the organic matter accumulation, but the high terrigenous influx caused by regression and/or structural controls diluted the organic matter to some extent. For the Early Silurian, a complete transgression–regression cycle changed terrigenous influx and redox conditions, resulting in significant differences in organic matter accumulation.

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“…The Late Ordovician to Early Silurian interval contained a critical part of Earth's history marked by large‐scale glaciation, mass extinction, major plate tectonic reconfigurations, extensive volcanism, and sea level and global environmental change (Algeo, Marenco, & Saltzman, ; Brenchley, ; Brenchley et al, ; Chen, Melchin, Sheets, Mitchell, & Fan, ; Chen, Rong, Li, & Boucot, ; Delabroye & Vecoli, ; Fan, Peng, & Melchin, ; Li, Zhang, Ellis, & Shao, ; Melchin, Mitchell, Holmden, & Štorch, ; Munnecke, Calner, Harper, & Servais, ; Sheehan, ; Yan, Chen, Wang, & Wang, ; Yan, Chen, Wang, & Wang, ; Yan, Chen, Wang, & Wang, ; Zhou et al, ). The strata of the Late Katian to Hirnantian interval in South China, named as the Wufeng Formation, consists mainly of black carbonaceous shale, siliceous rocks, and mudstone.…”

Section: Introductionmentioning

confidence: 99%

“…The Wufeng Formation contains abundant organic matter and experienced high levels of thermal stress and associated natural gas generation. Thus, this unit is considered as an excellent target for the exploration and development of shale gas in China (Dai et al, ; Li et al, ; Liang, Jiang, Yang, & Wei, ; Zou et al, ).…”

Section: Introductionmentioning

confidence: 99%

Geochemical characteristics of siliceous rocks of Wufeng Formation in the Late Ordovician, South China: Assessing provenance, depositional environment, and formation model

Men

Mou

et al. 2019

Geological Journal

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During the Late Ordovician, abundant siliceous rocks interlayered with K‐bentonites were widely distributed in the Wufeng Formation in the north‐western part of the Sichuan Basin, South China. In order to analyse the material provenance, redox condition, sedimentary environment, and their formation, here we present mineralogical and geochemical investigations on siliceous rocks samples collected from three sections. The presence of massive radiolarian tests, high Si/Si + Al + Fe + Ca ratios (0.87–0.99) and Al–Fe–Mn diagram plotting at nonhydrothermal area, reflects that the deposition of the siliceous rocks was simultaneous, effected by biogenic and terrigenous origin. The TiO2–Zr, La/Th–Hf, and La/Yb‐∑REE bivariate diagrams indicate that the provenance of Late Ordovician siliceous rocks was primarily from felsic igneous rocks. According to the palaeoredox indicators (V/(V + Ni), V/Cr, V/Sc, U/Th, and Ni/Co) and the size of framboidal pyrite, it is considered that the water column conditions of the Late Ordovician siliceous rocks were likely to be anoxic in all three sections. The application of parameters for relatively immobile elements allowed us to establish a continental margin for most samples from the three sections. Finally, we propose that the deposition of siliceous rocks was related to the accretion of the Cathaysia Block to the Yangtze Block. During the Late Ordovician, huge amounts of volcanic ash were released by intensified volcanic eruptions and fell into the ocean, triggering the proliferation of radiolarians. The abundant radiolarians and the persistent continental detritus constituted the major components of siliceous rocks in the Upper Yangtze Block.

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Depositional environment and organic matter accumulation of Upper Ordovician–Lower Silurian marine shale in the Upper Yangtze Platform, South China

Cited by 184 publications

References 89 publications

Mechanism Analysis of Organic Matter Enrichment of Upper Ordovician-Lower Silurian Shale in Upper Yangtze Area-Taking Jiaoye-1 Well in Jiaoshiba Block as an Example

Mechanism Analysis of Organic Matter Enrichment of Upper Ordovician-Lower Silurian Shale in Upper Yangtze Area-Taking Jiaoye-1 Well in Jiaoshiba Block as an Example

Paleoenvironment and Organic Matter Accumulation of the Upper Ordovician-Lower Silurian, in Upper Yangtze Region, South China: Constraints from Multiple Geochemical Proxies

Geochemical characteristics of siliceous rocks of Wufeng Formation in the Late Ordovician, South China: Assessing provenance, depositional environment, and formation model

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