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TitleLoss of the sedimentary mixed layer as a result of the end-Permian extinction
AuthorHofmann, R; Buatois, L A; MacNaughton, R BORCID logo; Mángano, M G
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 428, 2015 p. 1-11,
Alt SeriesEarth Sciences Sector, Contribution Series 20130348
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
Subjectspaleontology; sedimentology; Nature and Environment; extinctions, biotic; bioturbation; marine ecology; marine sediments; marine organisms; marine environments; ecosystems; fossil assemblages; fossil distribution; Lower Triassic; trace fossils; sedimentation; sulphur; oxidation; Griesbachian; Smithian; Spathian; Animals; Mesozoic; Triassic; Paleozoic; Permian
Illustrationsphotographs; schematic representations
ProgramGEM: Geo-mapping for Energy and Minerals Yukon Sedimentary Basins
ProgramCentral Foreland NATMAP Project
AbstractThe end-Permian mass extinction resulted in the most dramatic degradation of marine bottom communities during the Phanerozoic. One result of this extinction was the long-recognized, extreme reduction in bioturbation of the Early Triassic seafloor. Several lines of evidence (i.e., preferential preservation of epifaunal and very shallow-tier infaunal trace fossils; paucity of mid- and deep-tier trace fossils; absence of mottled bioturbation textures; dominance of cohesive substrates; widespread occurrence of microbially induced sedimentary structures in open-marine environments; ecological composition of Early Triassic communities) show that the reduction in bioturbation was so extreme that the sedimentary mixed layer was eradicated at an interregional scale for the only time since it was established in the early Palaeozoic. The consequences of this for ecosystem function and geochemical cycling must have been profound and yet they have received little consideration. Biogenic mixing of sediments is fundamental to geochemical cycling in extant marine ecosystems, and it also governs ecologically limiting factors such as nutrient fluxes, benthic primary production, and availability of ecospace. The collapse of biogenic sediment mixing during the Early Triassic must have affected geochemical properties of sediments and the seawater, as reflected in the geologic record of the sulphur cycle. Additionally, many of the proxies traditionally used to infer Early Triassic seawater anoxia may rather reflect poor sediment oxygenation arising from the extinction of bioturbators. Because of its impact on seawater and sediment chemistry, the loss of the mixed layer may have been an important, but hitherto little-considered constraint on the recovery from the end-Permian mass extinction.
Summary(Plain Language Summary, not published)
The end of the Permian Period of earth history (approximately 252 million years ago) witnessed the most profound mass extinction in Earth's history. It wiped out 95% of marine species and greatly reduced the complexity of ecosystems. This manuscript examines the record of marine animal burrowing preserved in rocks dating from several million years before and after the extinction. Post-extinction deposits show that the event wiped out the "mixed layer" in which animals actively churn the top several centimetres to decimetres of the marine sediment column. It took several million years for the mixed layer to recover. The rate of sediment mixing is a key control on oxygen concentration in sediment, and influences the biomass of organisms, the rate of organic matter decomposition, chemical cycling, and regeneration of nutrients. We argue that the devastation of the mixed layer contributed to the sluggish recovery from the extinction.

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