Base de données de recherche des TNO

Régions: South Slave Region

étiquettes: physical sciences, evolutionary processes, cambrian explosion

Objectif(s): To develop new quantitative tools to infer evolutionary processes from the geological record, with a particular focus on the origin of animal ecosystems in the ‘Cambrian explosion’, an event that marked the onset of diverse complex animal life on our planet.

Description du projet: This licence has been issued for the scientific research application No.5298. The aim of this research project is to develop new quantitative tools to infer evolutionary processes from the geological record, with a particular focus on the origin of animal ecosystems in the ‘Cambrian explosion’, an event that marked the onset of diverse complex animal life. Through fieldwork in the June Lake area in the Mackenzie Mountains, the research team will target strata from Ediacaran and Cambrian periods that record some of the earliest animal fossils and geochemical signatures of ancient environments those animals inhabited. The team will obtain and process geochemical and biostratigraphic samples from sections spanning the late Ediacaran and the early Cambrian periods and perform high resolution stratigraphic measurements in the field to provide a robust stratigraphic framework. The team will target carbonates and shales and siltstones to analyse: 1) stable carbonate and organic isotopic ratios of carbon (d13C) for chemostratigraphic correlations; 2) zircons for radiometric dating of the age of the rocks; 3) rhenium-osmium (Re-Os) isotopic rations for high precision dating of the age of the rocks; and 4) a variety of fossil types: organic walled microfossils, small carbonaceous fossils, small shelly fossils, trace fossils. Targeting diverse fossil types, in tandem with chemostratigraphic analyses and geochronology, will help the team better understand biotic changes through this time interval and enable us to correlate with multiple Ediacaran-Cambrian rock successions around the world. These resulting data will be synthesized into a Bayesian framework. This will generate precise stratigraphic correlations between independent geological sections, allowing simultaneous analysis of geochemical, palaeontological, biostratigraphic and sequence stratigraphic information, and the integration of absolute radiometric age estimates. This work will contribute to the formalization of the Cambrian timescale, and will allow statistical tests of the synchroneity of biological and geochemical events – and thus inference about causal links between evolutionary innovations and environmental change during the ‘Cambrian explosion’. The main units of interest are the late Ediacaran Sheepbed, Blueflower, and Risky formations and the early Cambrian Ingta, Backbone Ranges, Vampire, and Sekwi formations. All of these units are exposed in the vicinity of our proposed Campsites 1 (Sekwi Mountain) and 2 (Blueflower Mountain), and Backbone Ranges and Vampire formations are exposed at Campsite 3. The proposed fieldwork will consist of observations of data in the field, i.e. high resolution stratigraphic measurements, and sampling rocks for laboratory analyses in geochemical and palaeontological labs. The team will collect fist-sized samples of carbonate rocks for d13C analyses and small shelly fossil analyses, and c. 100 g (fist-sized) samples of shales/siltstones for the analysis of d13C of the organic carbon, for rhenium-osmium geochronology analyses for dating the age of the rocks, as well as for micropalaeontological analyses (with the focus on small carbonaceous fossils and organic-walled microfossils). Large rock surfaces that contain abundant trace fossils will be extensively imaged, and smaller rocks that contain well preserved age-diagnostic trace fossils may be collected for sectioning in the lab. Several stratigraphic sections (i.e. order of sedimentary rock units that represent different, successive time) will be measured and described near each base camp, with the goal of covering the strata of Ediacaran to Cambrian age. Carbon isotopes from our collected samples will be measured back at Durham University using ThermoScientific MAT 253 and ThermoScientific Delta V Advantage gas-source mass spectrometers for the measurement of stable isotope ratios. Rhenium-Osmium radiometric dating of the age of the rocks will be performed at the Source Rock and Sulfide Geochronology and Geochemistry Laboratory at Durham University. Small shelly and small carbonaceous fossils will be extracted from sampled rocks through digestions in acetic and hydrofluoric acids respectively, using lab facilities at Durham. Microscopy observations of the fossil material will reveal which fossil species are present (taxonomy), as well as palaeobiological and palaeoecological information such as what types of organisms and ecological tiers were present in early animal communities. The fossils data will be incorporated into the framework of the high resolution stratigraphy. The successions of Ediacaran-Cambrian rocks in the Mackenzie Mountains is nearly continuous, in contrast to most contemporary rock units around the world that have gaps in the rocks record (called unconformity). So the June Lake area is a unique place where the team can conduct the detailed measurement and collection, and integration of various types of fossils and geochemical data that reconstruct ancient environments. This will help the team better understand the sequence of evolutionary events in some of early animal life, and it will also help both in correlation with rock units around the globe and in inferring links between evolutionary patterns and the environmental change during the Ediacaran-Cambrian transition. The results from the fieldwork and palaeontological and sedimentological analyses will be published in peer-reviewed journals, as open access whenever possible. Durham University has publishing agreements with a suite of geoscience publications, and the team will use this resource to communicate the science to a wide audience, without paywall barriers. The team will also publish a popular science article on the research topic in open access outlets like Palaeontology Online. Palaeontology Online is a website that publishes reviewed articles on cutting edge palaeontological research aimed for general audiences and acts as an excellent resource for either high school or undergraduate teaching, and making science more accessible to general audiences. The research team will develop short videos on the basics of stratigraphic and palaeontological fieldwork that could be used in classroom, as well as easily digested and shared on social media. On-site visual materials like videos and photographs help in creating a virtual fieldtrip learning experience and are a great resource for teaching science. Short videos from the field were also helpful in geoscience teaching during lockdowns, when other fieldtrip options were unavailable. These popular science article materials and short videos will be shared with the Aurora College and Fort Smith Paul William Kaeser high school. The fieldwork for this study will be conducted from July 27, 2022 to August 07, 2022