Early Triassic environmental dynamics and microbial development during the Smithian–Spathian transition (Lower Weber Canyon, Utah, USA)

Abstract : The Early Triassic biotic recovery following the end-Permian mass extinction is well documented in the Smithian–Spathian Thaynes Group of the western USA basin. This sedimentary succession is commonly interpreted as recording harsh conditions of various shallow marine environments where microbial structures flourished. However, recent studies questioned the relevance of the classical view of long-lasting deleterious post-crisis conditions and suggested a rapid diversification of some marine ecosystems during the Early Triassic. Using field and microfacies analyses, we investigate a well-preserved Early Triassic marine sedimentary succes- sion in Lower Weber Canyon (Utah, USA). The identification of microbial structures and their depositional set- tings provide insights on factors controlling their morphologies and distribution. The Lower Weber Canyon sediments record the vertical evolution of depositional environments from a middle Smithian microbial and dolosiliciclastic peritidal system to a late Smithian-early Spathian bioclastic, muddy mid ramp. The microbial de- posits are interpreted as Microbially Induced Sedimentary Structures (MISS) that developed either (1) in a subtidal mid ramp where microbial wrinkles and chips are associated with megaripples characterizing hydrody- namic conditions of lower flow regime, or (2) in protected areas of inter- to subtidal inner ramp where they formed laminae and domal structures. Integrated with other published data, our investigations highlight that the distribution of these microbial structures was influenced by the combined effects of bathymetry, hydrody- namic conditions, lithology of the substrat physico-chemical characteristics of the depositional environment and by the regional relative sea-level fluctuations. Thus, we suggest that local environmental factors and basin dynamics primarily controlled the modalities of microbial development and preservation during the Early Triassic in the western USA basin.
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Sedimentary Geology, Elsevier, 2018, 363, pp.136 - 151. 〈10.1016/j.sedgeo.2017.11.009〉
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Soumis le : lundi 27 novembre 2017 - 15:42:44
Dernière modification le : mardi 16 janvier 2018 - 16:12:22

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Anne-Sabine Grosjean, Emmanuel Vennin, Nicolas Olivier, Gwénaël Caravaca, Christophe Thomazo, et al.. Early Triassic environmental dynamics and microbial development during the Smithian–Spathian transition (Lower Weber Canyon, Utah, USA). Sedimentary Geology, Elsevier, 2018, 363, pp.136 - 151. 〈10.1016/j.sedgeo.2017.11.009〉. 〈hal-01649555〉

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