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étiquettes: physical sciences, geology, paleontology, stratigraphy, fossil coral reefs

Objectif(s): To examine the settlement, development and decline of the fossil corals as a response to environmental conditions in the Liard region during Mississippian to early Pennsylvanian times (358.9 to 314.6 million years ago).

Description du projet: The principal aim of this project is to examine the settlement, development and decline of the fossil corals as a response to environmental conditions in the Liard region during Mississippian to early Pennsylvanian times (358.9 to 314.6 million years ago). The study will be conducted against the background of the world-wide expansion of corals in the Viséan age (346.7 - 330.9 million years ago) and their decline in numbers and species diversity at the end of the Serpukhovian age (323.2 Ma). The particular objectives include a study of post-mortem changes to the corals, taxonomy (naming of fossils), stratigraphy (study of layered sedimentary rocks), study of depositional environments, and establishment of the geographic distribution of the corals. Determining the depositional environments will involve evaluating the ancient sedimentation conditions and settings including water depth, sea-surface temperature, bottom conditions and processes, and the sources (provenance) and amounts of sand and silt. In the field area, two or more stratigraphic sections through the Banff, Flett, Golata and Mattson formations will be measured and described. The section measurement will involve determining the thicknesses of packages of layered sedimentary rock at outcrops. The most important section is at Jackfish Gap, there the team will measure the thickness of the Flett, Golata, and Mattson formations. The research team plan to measure other stratigraphic sections including the ones at Bluefish and Jackfish mountains. By measuring the sections, samples and basic stratigraphic and sedimentologic data will be obtained. Measurement of several sections will permit the team to evaluate regional and vertical lithological and paleoenvironmental trends. For section measurement, tape measures and 1.5 m long telescopic poles (Jacob staves) divided into 10 cm intervals will be used. As the sections are measured, they will be sampled for fossils (mainly corals, brachiopods, and microfossils called conodonts) and representative rock samples (mainly fist size and smaller) for geochemistry and petrographic work (study of rock with microscopes). Sampling will have a negligible impact on the environment because only hand-held equipment will be used, trenches will not be excavated, and no holes will be drilled. In Calgary and Poland, the best fossil corals collected in the field will be identified and described. At the Institute of Geology in Poznan, thin sections and serial peals will be made from the corals and the Principal Investigator (PI) will examine and describe them. The Geological Survey of Canada-Calgary will also study some of the corals. Technicians at the Geological Survey of Canada-Calgary and the Institute of Geology in Poznan Poland will extract the conodonts from their enclosing limestone using acetic acid and heavy liquids (solution of sodium polytungstate). Scanning electron microscope images of conodonts will be taken at the Institute of Geology in Poznan with the use of a Hitachi S-3700N equipment and at the University of Calgary. At the Geological Survey of Canada and the Institute of Geology in Poznan, thin sections from representative limestone and sandstone samples will be made to facilitate their identification and determine their clast composition and textures. The thin-section analyses of limestone will be used to determine environments of deposition. The sources (provenance) of the sand in sandstone from the Yohin, Banff, Flett, and Mattson formations will be evaluated by the study of detrital zircon grains and quantitative microscope analysis of grain types within thin sections. Detrital zircons will be extracted from pulverized sandstone samples at the Geological Survey of Canada and submitted for radiometric dating at the University Of Calgary Department Of Geology and Geophysics and the Institute of Geology in Poznan. The stable carbon and oxygen isotopes (d13C and d18O) trends will be analyzed within the measured sections using brachiopod shells and powder derived from systematically collected limestone samples. The isotopic analyses will be obtained at the Isotope Dating and Environment Research Laboratory in Warsaw. Resulting graphs showing trends in isotope values (d13Ccarbonate and d18Ocarbonate) will be compared with available Carboniferous isotope curves from other parts of the world. The resulting graphs will be treated as records of changes of sea-surface temperature and rates of carbon sequestration. Results of the project will be published in widely available geological journals. The research team also plan to communicate the results at scientific conferences. As for the talks for communities in the NWT – if people in local communities are interested in the work, the team could give a summary presentation at a meeting of the tribal councils in Fort Liard and Fort Simpson. Geological aspects of the region that are of specific interest to First Nations People could also be discussed. Presentations about geology and fossils in the local schools are also possible if First Nations are interested. The fieldwork for this study will be conducted from July 13, 2018 to August 15, 2018.