Effects of volcanic activities in Ordovician Wufeng–Silurian Longmaxi period on organic-rich shale in the Upper Yangtze area, South China

Wu, Lanyu; Lu, Yongchao; Jiang, Shu; Liu, Xiaofeng; He, Guisong

doi:10.1016/s1876-3804(18)30089-2

“…The shales between the upper Ordovician Wufeng Formation and lower Silurian Longmaxi Formation are as thick as 500-600 m, whereas the organic-rich shales reside mainly in the Wufeng Formation and the lower Longmaxi Formation, which is siliceous shale or silica-bearing shale [1,6,10]. This study mainly investigated logging data from Upper Yangtze Well N211, as an example to demonstrate the vertical changes of the organic-rich shales in the Wufeng and Longmaxi Formations.…”

Section: Vertical Change Characteristics Of the Organic-rich Shales Imentioning

confidence: 99%

“…In addition, high sea surface productivity can also lead to organic enrichment in sediment [11] and thus can lead to a series of changes in GR value and U content. Lu et al [9] and Wu et al [10] noted that volcanic ash played an important role in increasing the sea surface productivity during the deposition of the organic-rich shales in the Wufeng and Longmaxi Formations. Biogenic barium (Ba bio ) is an important proxy of productivity.…”

Section: The Effects Of Sea Level Change and Volcanic Ash On Organic mentioning

confidence: 99%

“…Studies on the cause of high paleo-productivity are scarce in the current literature. Lu et al [9] and Wu et al [10] suggested that volcanic ash provided abundant nutrients for marine organisms and played a positive role in the enhancement of marine surface primary productivity, providing a material basis for the organic-rich shales in the Wufeng and Longmaxi Formations. Modern marine research shows that upwelling plays an important role in enhancing marine surface primary productivity.…”

Section: Introductionmentioning

confidence: 99%

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Development of Upwelling during the Sedimentary Period of the Organic-Rich Shales in the Wufeng and Longmaxi Formations of the Upper Yangtze Region and Its Impact on Organic Matter Enrichment

Zhao

¹

,

Li

²

,

Min

³

et al. 2019

JMSE

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This study uses logging data, mineral component content, total organic carbon (TOC) content, and microscopic characteristics of the organic-rich shales in the Wufeng and Longmaxi Formations, as well as data reported by other researchers, to demonstrate that upwelling has played an important role in the organic matter enrichment. The results show that (1) the organic-rich shales of Well N211 in the Upper Yangtze region are located in the Wufeng Formation and the lower Longmaxi Formation, with a burial depth between 2308–2357 m. (2) The organic-rich shales are enriched in biogenic silica. (3) Based on paleogeographic location and characteristics of organisms, this study determines that upwelling occurred during the deposition of the organic-rich shales in the Wufeng and Longmaxi Formations, promoting the enrichment of organic matter in the shales. (4) The upwelling intensity gradually increased from the sedimentary period of the organic-rich shales in the mid-lower Wufeng Formation to the sedimentary period of the Guanyinqiao Member, and then decreased gradually from the sedimentary period of the Guanyinqiao Member to the sedimentary period of the organic-rich shales in the Longmaxi Formation, and leads to the different enrichment of organic matter in the vertical direction. The different developments of upwelling led to the coexistence of both high and low TOC contents in the Guanyinqiao Member along the vertical direction.

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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

0

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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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“…Wedepohl [33], Adachi et al [34], and Yamamoto [35] proposed a method for determining whether siliceous mineral is of hydrothermal origin or bioorigin by using the Al-Fe-Mn ternary diagram. Li et al [36], Shu et al [37], and Wu et al [38], after giving detailed description of the shale core of the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation, found bentonite in some layers, which was derived from volcanic activity. This paper firstly determines the redox indicator and biological productivity indicator, and then discusses the degree of water sealing and the influence of volcanic activity on sedimentary organic matter enrichment, and establishes the Late Ordovician-Early Silurian sedimentary organic matter enrichment model in the Upper Yangtze area.…”

Section: Introductionmentioning

confidence: 99%

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

Liu

¹

,

Jiang

²

,

Zhang

³

et al. 2019

Self Cite

View full text Add to dashboard Cite

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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Effects of volcanic activities in Ordovician Wufeng–Silurian Longmaxi period on organic-rich shale in the Upper Yangtze area, South China

Cited by 51 publications

References 23 publications

Development of Upwelling during the Sedimentary Period of the Organic-Rich Shales in the Wufeng and Longmaxi Formations of the Upper Yangtze Region and Its Impact on Organic Matter Enrichment

Development of Upwelling during the Sedimentary Period of the Organic-Rich Shales in the Wufeng and Longmaxi Formations of the Upper Yangtze Region and Its Impact on Organic Matter Enrichment

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 the Upper Yangtze Area: Taking Jiaoye-1 Well in the Jiaoshiba Block as an Example

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