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<p>The Permian–Triassic boundary section of Guryul Ravine, Kashmir Himalaya is one of the best preserved section of its time. It is one of its kind in the world to understand the Permian–Triassic changes that led to the great mass extinction of life on Earth. It displays a continuous, well-exposed section containing rocks from Upper Permian to Lower Triassic Periods. The petro-mineralogical study of&#xa0;Guryul Ravine&#xa0;indicates that the section experienced periodic influences from oxic-dysoxic to anoxic conditions during their deposition, as shown by the presence of magnetite and various forms of pyrite in Zewan Formation as well as in the Khunamuh Formation. Serpentine has been observed in some of the calcareous sandstone, limestone, and shale beds of the Zewan Formation as well as in the Khunamuh Formation, indicating that the rocks at the Permian–Triassic section have undergone weak metamorphism, however, the original mineralogy and texture of the rock units have not been completely altered. The end of shallow water taxa as sea levels rose suggests a gradual rather than abrupt shift at the Permian–Triassic boundary (PTB). In Zewan Formation, the section contains well-preserved fossil imprints of brachiopods, crinoids, and bryozoans; in Khunamuh Formation, ammonites predominate, which is unique to that time period. The present study utilizes the size of the pyrite framboids to differentiate between syngenetic and diagenetic pyrite, which has ultimately led to the determination of paleoredox conditions of the section under study. Pyrites could be classified as syngenetic, early diagenetic, or late diagenetic based on their formation mechanism. Syngenetic pyrites are primarily small framboids made up of small microcrystals with a diameter (D) less than 6 ± 4&#xa0;μm, but the diagenetic pyrites exhibit a range of shapes and sizes containing massive microcrystals with a diameter (D) greater than 7.7 ± 4.1&#xa0;μm. In the present paper, pyrites were classified as both syngenetic and diagenetic. Syngenetic framboids typically have a diameter (D) less than 10&#xa0;μm, while diagenetic framboids have a diameter (D) greater than 10&#xa0;μm. The presence of Syngenetic pyrite framboids and framboid microcrystals at the PTB indicates that there was widespread anoxia at the boundary, which could be one of the main causes of mass extinction.</p>

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Mineralogical and petrological characteristics of the Permian–Triassic boundary (PTB) section, Guryul Ravine, Kashmir Himalaya, India: emphasizing on paleoenvironmental conditions at PTB

  • 期刊论文

  • 发表日期：

    2025年7月12日

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  • Nozmul Karim,
  • Shamim A. Dar,
  • H. Wani

摘要

The Permian–Triassic boundary section of Guryul Ravine, Kashmir Himalaya is one of the best preserved section of its time. It is one of its kind in the world to understand the Permian–Triassic changes that led to the great mass extinction of life on Earth. It displays a continuous, well-exposed section containing rocks from Upper Permian to Lower Triassic Periods. The petro-mineralogical study of Guryul Ravine indicates that the section experienced periodic influences from oxic-dysoxic to anoxic conditions during their deposition, as shown by the presence of magnetite and various forms of pyrite in Zewan Formation as well as in the Khunamuh Formation. Serpentine has been observed in some of the calcareous sandstone, limestone, and shale beds of the Zewan Formation as well as in the Khunamuh Formation, indicating that the rocks at the Permian–Triassic section have undergone weak metamorphism, however, the original mineralogy and texture of the rock units have not been completely altered. The end of shallow water taxa as sea levels rose suggests a gradual rather than abrupt shift at the Permian–Triassic boundary (PTB). In Zewan Formation, the section contains well-preserved fossil imprints of brachiopods, crinoids, and bryozoans; in Khunamuh Formation, ammonites predominate, which is unique to that time period. The present study utilizes the size of the pyrite framboids to differentiate between syngenetic and diagenetic pyrite, which has ultimately led to the determination of paleoredox conditions of the section under study. Pyrites could be classified as syngenetic, early diagenetic, or late diagenetic based on their formation mechanism. Syngenetic pyrites are primarily small framboids made up of small microcrystals with a diameter (D) less than 6 ± 4 μm, but the diagenetic pyrites exhibit a range of shapes and sizes containing massive microcrystals with a diameter (D) greater than 7.7 ± 4.1 μm. In the present paper, pyrites were classified as both syngenetic and diagenetic. Syngenetic framboids typically have a diameter (D) less than 10 μm, while diagenetic framboids have a diameter (D) greater than 10 μm. The presence of Syngenetic pyrite framboids and framboid microcrystals at the PTB indicates that there was widespread anoxia at the boundary, which could be one of the main causes of mass extinction.