Biomarker and isotopic trends in a Permian-Triassic sedimentary section at Kap Stosch, Greenland
We report a geochemical study of a composite sedimentary section that captures the Permian-Triassic (PT) transition at Kap Stosch, East Greenland. The samples were from the original paleontological collection of early PT researchers. The rocks, which include samples from four proximal outcrop locali...
| Published in: | Organic Geochemistry |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2012
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| Subjects: | |
| Online Access: | https://researchers.mq.edu.au/en/publications/30bfd91f-fe11-4c57-83d4-c112dd834cf1 https://doi.org/10.1016/j.orggeochem.2011.10.010 http://www.scopus.com/inward/record.url?scp=84455202311&partnerID=8YFLogxK |
| Summary: | We report a geochemical study of a composite sedimentary section that captures the Permian-Triassic (PT) transition at Kap Stosch, East Greenland. The samples were from the original paleontological collection of early PT researchers. The rocks, which include samples from four proximal outcrop localities, were deposited during the Late Permian and Early Triassic at the margin of the Boreal Sea with a depositional hiatus and erosional event of unknown duration. Bulk geochemical measurements for most of the samples show good correlation between S2 and TOC% which, combined with low T max values, indicate that the organic matter (OM) that formed contemporaneously with sediment deposition is of relatively low maturity. Significant changes through the PT transition include a pronounced switch in the δ 13 C of TOC from high values near -24‰ to lower values averaging -32‰, that is matched by a significant increase in the hydrogen index (HI) of the kerogen. The Permian samples containing 13 C enriched OM also have low Rock-Eval HI values and anomalous pyrograms, indicating that the kerogen is heterogeneous in terms of source and maturity, as confirmed by microscopic analysis of the kerogen concentrates. Samples from the Permian section contain an abundance of black angular fragments of woody tissue in addition to gymnosperm pollen and spinose acritarchs of the Vittatina-Association (Balme, B., 1979. Palynology of Permian-Triassic boundary beds at Kap Stosch. Meddeleleser om Gronland 200, 1-36). In contrast, black woody tissue is rare in samples from the Early Triassic section with well preserved gymnosperm and lycopod pollen and spores of the Protohaploxypinus and Taeniaesporites associations. Biomarkers indicate moderate maturity for Permian samples, with the C 27 sterane 20S/(20S+20R), C 31 homohopane 22S/(22S+22R) ratio and Ts/(Ts+Tm) values all being higher than those for Triassic sediments. The marked switch in maturity indicators across the PT transition suggests an unconformity consistent with palynological ... |
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