Abstract
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.
Highlights
The Late Permian mass extinction (LPME) event was the largest biotic crisis on Earth, wiping out around 90% of marine and 75% of terrestrial species [1,2,3]. This extinction event, which possibly occurred in two episodes during the Late Permian (~252.28 Ma) and the early Triassic (~252.10 Ma; [4,5]) periods, was triggered by Siberian trap eruption and subsequent global warming and ocean anoxia [6,7,8,9,10]
The Guryul Ravine samples were collected from the bed 52 where the index fossil for the P–T boundary (Hindeodus parvus) has been reported
Wt%, with relatively higher total organic carbon (TOC) content being observed for the Spiti samples (1.41 ± 0.08 wt%) than that for the Guryul Ravine samples (0.9 ± 0.2 wt%)
Summary
The Late Permian mass extinction (LPME) event was the largest biotic crisis on Earth, wiping out around 90% of marine and 75% of terrestrial species [1,2,3]. Bolide impact [11,12] and increased sediment fluxes [13,14] have been invoked as possible causative factors for the LPME Both extinction intensity and pattern show significant latitudinal variations, with higher impact in the high latitudinal zone than tropical ecotypes [15,16]. The global correlation of these regional studies requires the precise estimation of the depositional ages of sedimentary succession
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