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      TAPHONOMY OF THE LOWER JURASSIC KONSERVAT-LAGERSTÄTTE AT YA HA TINDA (ALBERTA, CANADA) AND ITS SIGNIFICANCE FOR EXCEPTIONAL FOSSIL PRESERVATION DURING OCEANIC ANOXIC EVENTS

      1 , 2 , 2 , 3 , 4 , 2 , 2

      PALAIOS

      Society for Sedimentary Geology

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          ABSTRACT

          Konservat-Lagerstätten provide the most complete snapshots of ancient organisms and communities in the fossil record. In the Mesozoic, these deposits are rarely found in marine facies outside Oceanic Anoxic Event (OAE) intervals, suggesting that OAEs set the stage for exceptional fossil preservation. Although anoxia does not guarantee survival of non-biomineralized tissues or articulated skeletons, other OAE phenomena may promote their conservation. Here, we test this hypothesis with a taphonomic analysis of the Konservat-Lagerstätte in the black shales and siltstones of the Jurassic Fernie Formation at Ya Ha Tinda (Alberta, Canada). This deposit contains crustacean cuticles, coleoid gladii with ink sacs and mantle tissues, and articulated skeletons of fish, crinoids, and ichthyosaurs. The fossils were preserved in the Pliensbachian and Toarcian (Early Jurassic) when euxinic conditions were common in the area, in part, due to the ∼183 Ma Toarcian OAE. Some of the fossils contain carbonaceous material, but the majority consists of apatite minerals, and phosphatic gladii demonstrate that some animals were preserved through secondary phosphate mineralization. Phosphatization generally occurs within phosphate-rich sediment, but oceanic anoxia causes sediment to release phosphorus and prevents animals from colonizing seafloor habitats. Accordingly, we propose that the animals were preserved during brief episodes of bottom water oxia and/or dysoxia, when the environment would have been most favorable to benthic communities and phosphate mineralization. In this setting, phosphatization may have been fueled by phosphate delivery from continental weathering in response to climatic warming, ocean upwelling of eutrophic water, and/or nutrient trapping by anoxia in the basin.

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          Sedimentary pyrite formation: An update

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            Sedimentary pyrite formation

             R. Berner (1970)
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              Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event

              In the Jurassic period, the Early Toarcian oceanic anoxic event (about 183 million years ago) is associated with exceptionally high rates of organic-carbon burial, high palaeotemperatures and significant mass extinction. Heavy carbon-isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon, which is isotopically light. In contrast, examples of light carbon-isotope values from marine organic matter of Early Toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12C versus 13C (refs 1,2,5,6). Here, however, we report carbon-isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic, biospheric and atmospheric carbon reservoirs, and that this occurred despite the enhanced burial of organic carbon. We propose that--as has been suggested for the Late Palaeocene thermal maximum, some 55 million years ago--the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental-margin sediments.
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                Author and article information

                Journal
                PALAIOS
                Society for Sedimentary Geology
                0883-1351
                November 4 2019
                November 4 2019
                November 4 2019
                November 4 2019
                : 34
                : 11
                : 515-541
                Affiliations
                [1 ]Department of Geology, Cornell College, 600 First Street SW, Mount Vernon, Iowa, 52314, USA
                [2 ]Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 2275 Speedway, Austin, Texas, 78712, USA
                [3 ]Department of Geological Sciences, University of Missouri, 101 Geological Sciences Building, Columbia, Missouri, 65211, USA
                [4 ]X-ray Microanalysis Core Facility, University of Missouri, 1 Geological Sciences Building, Columbia, Missouri, 65211, USA
                Article
                10.2110/palo.2019.050
                © 2019

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