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Sedimentary organic matter from a cored Early Triassic succession, Georgetown (Idaho, USA)


Schneebeli-Hermann, Elke; Bagherpour, Borhan; Vennemann, Torsten; Leu, Marc; Bucher, Hugo (2020). Sedimentary organic matter from a cored Early Triassic succession, Georgetown (Idaho, USA). Swiss Journal of Palaeontology, 139:5.

Abstract

The plant fossil record from Lower Triassic sedimentary successions of the Western USA is extremely meager. In this study, samples from a drill core taken near Georgetown, Idaho, were analyzed for their palynological content as well as their stable carbon isotope composition. The concentration of palynomorphs is generally low. The lowermost part of the drilled succession represents Dinwoody/Woodside Formation and contains spore and pollen assemblages with Permian and Early Triassic affinity. Representatives of lycophytes (Densoisporites spp., Lundbladisporites spp.) were found in the overlying Meekoceras Limestone, in agreement with middle Smithian assemblages elsewhere. Ammonoids and conodonts are extremely rare, but confirm a middle Smithian age. Bulk organic and carbonate carbon isotope composition provide a stratigraphic framework. Carbonate carbon isotope compositions are compatible with the Smithian–Spathian global trend, with a middle Smithian shift towards lower δ13C values followed by a late Smithian shift towards higher values. Bulk organic carbon isotope compositions have been influenced by changes in the constitution of organic matter. A comparison with other paired carbon isotope datasets from the same basin is difficult due to lithostratigraphic inconsistencies (Hot Springs, ID) or biochemical mediated disturbance of isotope signals (Mineral Mountains, UT).

Abstract

The plant fossil record from Lower Triassic sedimentary successions of the Western USA is extremely meager. In this study, samples from a drill core taken near Georgetown, Idaho, were analyzed for their palynological content as well as their stable carbon isotope composition. The concentration of palynomorphs is generally low. The lowermost part of the drilled succession represents Dinwoody/Woodside Formation and contains spore and pollen assemblages with Permian and Early Triassic affinity. Representatives of lycophytes (Densoisporites spp., Lundbladisporites spp.) were found in the overlying Meekoceras Limestone, in agreement with middle Smithian assemblages elsewhere. Ammonoids and conodonts are extremely rare, but confirm a middle Smithian age. Bulk organic and carbonate carbon isotope composition provide a stratigraphic framework. Carbonate carbon isotope compositions are compatible with the Smithian–Spathian global trend, with a middle Smithian shift towards lower δ13C values followed by a late Smithian shift towards higher values. Bulk organic carbon isotope compositions have been influenced by changes in the constitution of organic matter. A comparison with other paired carbon isotope datasets from the same basin is difficult due to lithostratigraphic inconsistencies (Hot Springs, ID) or biochemical mediated disturbance of isotope signals (Mineral Mountains, UT).

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Scopus Subject Areas:Physical Sciences > Paleontology
Uncontrolled Keywords:Palaeontology
Language:English
Date:1 December 2020
Deposited On:06 May 2020 14:40
Last Modified:29 Jul 2020 15:07
Publisher:Springer
ISSN:1664-2376
OA Status:Hybrid
Publisher DOI:https://doi.org/10.1186/s13358-020-00205-9
Project Information:
  • : FunderSNSF
  • : Grant IDCRSII5_180253
  • : Project TitleQuantifying decamillennial changes in carbon cycling, climatic and biotic responses to Late Permian-Early Triassic volcanism
  • : FunderSNSF
  • : Grant ID200020_160055
  • : Project TitleMid-Early Triassic Extreme Climatic Oscillation (METECO): biotic-abiotic global couplings

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