Re–Os and Sr Isotopic Study of Permian–Triassic Sedimentary Rocks from the Himalaya: Shale Chronology and Carbonate Diagenesis

Sedimentary rocks from the Himalayas are well-preserved archives of the Neo-Tethys oceanic conditions. In this contribution, Re–Os isotopic systematics of black shales from the Gungri Formation, Spiti valley and siltstones from the Khunamuh Formation, Guryul Ravine have been investigated to constrai...

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Bibliographic Details
Published in:Minerals (Basel) 2021-04, Vol.11 (4), p.417
Main Authors: Mandal, Anirban, Tripathy, Gyana Ranjan, Goswami, Vineet, Ackerman, Lukáš, Parcha, Suraj K., Chandra, Rakesh
Format: Article
Language:English
Subjects:
Age
Algae
Archives
Carbon
Carbonates
Diagenesis
Extinction
Isotopes
Manganese
Osmium isotopes
Oxidoreductions
Paleoceanography
Permian
Ratios
Redox properties
Regional studies
Rhenium isotopes
Sedimentary rocks
Shale
Shales
Stratigraphy
Strontium 87
Strontium isotopes
Systematics
Triassic
Uptake
Vertical distribution
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Summary:Sedimentary rocks from the Himalayas are well-preserved archives of the Neo-Tethys oceanic conditions. In this contribution, Re–Os isotopic systematics of black shales from the Gungri Formation, Spiti valley and siltstones from the Khunamuh Formation, Guryul Ravine have been investigated to constrain their depositional ages. The Re–Os isochron for the Gungri shales yields a depositional age of 255 ± 22 Ma (2σ; n = 8; MSWD (Mean Square Weighted Deviation) = 5.7), consistent with available biostratigraphic information. The initial 187Os/188Os ratio (0.60 ± 0.13) is similar to that reported for the Late Permian shales, indicating the connection of the Neo-Tethys with the global ocean. In contrast, the Re–Os systematic is found to be non-isochronous for the Guryul Ravine section, a proximal site with a strong influence of seismic/Tsunami events. Global compilation of 187Re/188Os ratios in Late Permian shales and bathymetric distribution of the Re/Os ratios point to strong role of Re/Os uptake by macroalgae, in addition to oceanic pH and redox state, in regulating the Re–Os systematic in shales. The 87Sr/86Sr ratios for the Induan carbonates from the Spiti (0.71551–0.71837) are higher than to that expected for the Lower Triassic ocean (~0.707). Co-variations of Sr and 87Sr/86Sr with Mn concentrations establish the diagenetic alteration of these carbonates.
ISSN:2075-163X
2075-163X
DOI:10.3390/min11040417