Quantitative Trilobite Biostratigraphy of the Middle Cambrian (Wuliuan Stage; Miaolingian Series) and Microfacies Analysis of the Middle Cambrian Stephen Formation, Southern Canadian Rocky Mountains
Date
2021-07-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Carbonate microfacies and trilobite successions were examined in seven sections of the Stephen Formation, southern Canadian Rocky Mountains. Seven microfacies and three ichnofacies are identified, including a new Protopaleodictyon ichnofacies with Protopaleodictyon aitkeni (n. isp.). Palaeoenvironments include ephemeral oolitic shoals, intraclastic/oncoidal tempestites, and quiescent muddy-bottomed mid-shelf within a low-latitude, carbonate platform. Three parasequences were identified in the Narao Member, and five in the Waputik Member. Narao Member parasequences are sub-tidal muddy carbonate, shallowing toward microbial build-ups. Waputik Member parasequences contain green-grey, laminated shale, with sporadic carbonate tempestites, indicating a platform inundated by upwelling cool-dysoxic water. Carbonate production was shut-off, except within localized shoals and build-ups. The stacking pattern indicates slow base-level change with periodic upwelling events. The overlying Eldon Formation re-established carbonate platform deposition associated with a stabilised chemocline. Chemocline perturbation is postulated to affect trilobite biomere extinction at the Narao-Waputik boundary. Fifteen trilobite species, eleven trilobite genera, one orthothecid, one edrioasteroid, and three Burgess Shale organisms (Tuzoia, Haplophrentis carinatus, Margaretia dorus) were identified in the Stephen Formation, which ranges from the uppermost Glossopleura Assemblage Biozone into the Ehmaniella Assemblage Biozone. Four new biozones are established in this interval, including the Glossopleura boccar, Proehmaniella basilica, Ehmaniella waptaensis, and Spencella montanensis interval biozones. A quantitative biostratigraphy using Unitary Association (UA), integrates regional biozones from southwestern USA and western Canada into a unified Miaolingian trilobite succession (582 taxa, 1035 samples, 121 sections, and 48 formations). Seventy-three UA biozones, including 33 previously defined biozones, are delineated from the upper Bonnia-Olenellus to Cedaria assemblage zones. Six new Wuliuan interval biozones (Fieldaspis superba, Albertella bosworthi, Glossopleura boccar, Proehmaniella basilica, Spencella montanensis, and Bathyuriscus adaeus) are established. Nineteen UA zones encompass the top of the upper Bonnia-Olenellus Assemblage Biozone, 11 in the Plagiura-Poliella Assemblage Biozone, 18 in the Albertella Assemblage Biozone, 10 within the Glossopleura Assemblage Biozone, 7 within the Ehmaniella Assemblage Biozone, and 8 in the Bolaspidella and Cedaria biozones. This is the first recognition of temporal equivalence of regional biozones using quantitative biostratigraphic methods. The faunal succession informs biostratigraphic correlation potential pointing to mid-Cambrian intervals that may yield additional high-resolution biozones in the future.
Description
Keywords
Biostratigraphic methods, quantitative biostratigraphy, mid-Cambrian, biomere, microfacies analysis, sequence stratigraphy, global correlation, Burgess Shale
Citation
Morgan, C. A. (2021). Quantitative Trilobite Biostratigraphy of the Middle Cambrian (Wuliuan Stage; Miaolingian Series) and Microfacies Analysis of the Middle Cambrian Stephen Formation, Southern Canadian Rocky Mountains (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.