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TitleControls on the formation of microbially induced sedimentary structures and biotic recovery in the Lower Triassic of Arctic Canada
AuthorWignal, P B; Bond, D P G; Grasby, S EORCID logo; Pruss, S B; Peakall, J
SourceGeological Society of America Bulletin vol. 123, issue 5-6, 2019 p. 918-930, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190540
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
AreaAxel Heiberg Island; Ellesmere Island
Lat/Long WENS-100.0000 -70.0000 82.0000 78.0000
Subjectssedimentology; geochemistry; paleontology; Nature and Environment; Science and Technology; sedimentary structures; Lower Triassic; sedimentary basins; bedrock geology; lithology; sandstones; siltstones; oxygen geochemistry; geochemical analyses; microorganisms; depositional environment; paleoenvironment; paleoclimates; extinctions, biotic; arctic geology; Sverdrup Basin; Blind Fiord Formation; Permian-Triassic Boundary; Phycosiphon; Phanerozoic; Mesozoic; Triassic
Illustrationslocation maps; stratigraphic columns; stratigraphic charts; photographs; sections; plots; tables
ProgramGEM2: Geo-mapping for Energy and Minerals Western Arctic, High Arctic LIP
Released2019 08 30
AbstractMicrobially induced sedimentary structures (MISS) are reportedly widespread in the Early Triassic and their occurrence is attributed to either the extinction of marine grazers (allowing mat preservation) during the Permo-Triassic mass extinction or the suppression of grazing due to harsh, oxygen-poor conditions in its aftermath. Here we report on the abundant occurrence of MISS in the Lower Triassic Blind Fiord Formation of the Sverdrup Basin, Arctic Canada. Sedimentological analysis shows that mid-shelf settings were dominated by deposition from cohesive sand-mud flows that produced heterolithic, rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks. The absence of storm beds and any other “event beds” points to an unusual climatic regime of humid, quiet conditions characterized by near continuous run off. Geochemical proxies for oxygenation (Mo/Al, Th/U, and pyrite framboid analysis) indicate that lower dysoxic conditions prevailed in the basin for much of the Early Triassic. The resultant lack of bioturbation allowed the development and preservation of MISS, including wrinkle structures and bubble textures. The microbial mats responsible for these structures are envisaged to have thrived, on sandy substrates, within the photic zone, in oxygen-poor conditions. The dysoxic history was punctuated by better-oxygenated phases, which coincide with the loss of MISS. Thus, Permo-Triassic boundary and Griesbachian mudrocks from the deepest-water settings have common benthos and a well-developed, tiered burrow profile dominated by Phycosiphon. The presence of the intense burrowing in the earliest Triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the Permian. The notion that Early Triassic MISS preservation was caused by the extinction of mat grazers is not tenable.
Summary(Plain Language Summary, not published)
This manuscript examines evidence of life after the worst mass extinction in Earth history and test the hypothesis that extensive microbial mats recorded in the rock record are related to extinction of grazers. The paper concludes that instead it was suppression of environments due to extensive anoxia.

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