| Title | Controls on the formation of microbially induced sedimentary structures and biotic recovery in the Lower Triassic of Arctic Canada |
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| Author | Wignal, P B; Bond, D P G; Grasby, S E ; Pruss, S B; Peakall, J |
| Source | Geological Society of America Bulletin vol. 123, issue 5-6, 2019 p. 918-930, https://doi.org/10.1130/B35229.1  Open Access |
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| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20190540 |
| Publisher | Geological Society of America |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Northwest Territories |
| Area | Axel Heiberg Island; Ellesmere Island |
| Lat/Long WENS | -100.0000 -70.0000 82.0000 78.0000 |
| Subjects | sedimentology; 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 |
| Illustrations | location maps; stratigraphic columns; stratigraphic charts; photographs; sections; plots; tables |
| Program | GEM2: Geo-mapping for Energy and Minerals Western Arctic, High Arctic LIP |
| Released | 2019 08 30 |
| Abstract | Microbially 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. |
| GEOSCAN ID | 321814 |
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