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TitleIntegrated bio-chemostratigraphy of Lower and Middle Triassic marine successions at Spiti in the Indian Himalaya: implications for the Early Triassic nutrient crisis
AuthorSun, Y D; Richoz, S; Krystyn, L; Grasby, S EORCID logo; Chen, Y L; Banerjee, D; Joachimski, M M
SourceGlobal and Planetary Change vol. 196, 103363, 2020 p. 1-25,
Alt SeriesNatural Resources Canada, Contribution Series 20200602
PublisherElsevier B.V.
Mediapaper; on-line; digital
File formatpdf; html
AreaHimalayas; Spiti Valley; India
Lat/Long WENS 78.4500 78.5000 32.5000 32.2833
Subjectsstratigraphy; paleontology; geochemistry; sedimentology; Science and Technology; Nature and Environment; Middle Triassic; Lower Triassic; micropaleontology; microfossils; conodonts; carbon isotopes; sea level changes; extinctions, biotic; paleoenvironment; paleogeography; trace element geochemistry; metals; phosphorites; biostratigraphy; sedimentation rates; facies; phosphorus geochemistry; Permo-Triassic Mass Extinction; Lilang Super Group; Mikin Formation; Kaga Formation; Gondwana; Ammonoids; Neotethys Ocean; Phanerozoic; Mesozoic; Triassic; Paleozoic; Permian
Illustrationslocation maps; diagrams; tables; stratigraphic colums; cross-plots
ProgramGEM2: Geo-mapping for Energy and Minerals Western Arctic-Beaufort-Northern Yukon
Released2020 11 01
AbstractIn this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate - siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (delta-13Ccarb) show an increase from -2.6 to 0 per mille from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to -3 per mille in the Smithian substage and a large positive excursion from -3.0 to 3.5 per mille across the Smithian-Spathian boundary. A short negative shift to -1.0 per mille occurred in the early Spathian substage, and is followed by a positive trend from ~-1.0 to 1.0 per mille in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (delta-13Corg) co-vary with delta-13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian-Spathian boundary. Thus, in the Spiti area, the positive delta-13Ccarb excursion across the Smithian-Spathian boundary is recorded in generally well-oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian-Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.
Summary(Plain Language Summary, not published)
This paper examines why there was a signficant decline in marine productivity during the Early Triassic and how global warming created a nutrient stressed ocean at that time. This led to signficant changes in normal marine bioproductivity.

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