Sedimentary redox geochemistry of the Lower Triassic Montney Formation, British Columbia

Publication Year:
2018
Usage 27
Abstract Views 24
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Repository URL:
https://scholarworks.smith.edu/theses/2044
Author(s):
Mwinde, Chiza Ngachize
Tags:
Redox-Geochemistry; Lower Triassic; Iron speciation; Montney formation; Early Triassic recovery; Triassic anoxia; Triassic euxinia; Oxidation-reduction reaction; Geochemistry; Stratigraphic geology-Triassic; Anoxemia; Geochemistry-British Columbia; Iron-Speciation
project description
The end-Permian mass extinction ~252 Mya was the most severe biotic crisis in Earth history, with >90 % of marine species going extinct. It was followed by 5 million years of reduced biodiversity and large perturbations in global biogeochemical cycling. Delayed earth system recovery after the Permian-Triassic mass extinction is often attributed to marine anoxia. However, the extent of marine anoxia and the influence of global versus local drivers remains poorly constrained. To further evaluate the role of redox conditions during the recovery period after the Permian-Triassic mass extinction we conducted geochemical analyses on 395 m of core through the Lower Triassic Montney Formation. Samples were analyzed for pyrite sulfur contents, iron speciation, major and minor elemental compositions, and total organic carbon measurements. These proxies, used as signals of shifting redox conditions, can be used to interpret the depositional environment and correlate to other time-equivalent basins. Additionally, 22 thin sections were prepared to determine mineralogy trends in relation to redox changes. Stratigraphic trends of iron proxies show that the Montney Formation was deposited under persistent anoxic conditions. These geochemical data also suggest that redox conditions shifted towards euxinic conditions at 3 intervals: after the PTB, during the Smithian-Spathian boundary and the at the beginning of Lower Anisian. Occurrences of glauconitic grains near the Permian Triassic boundary and into the Griesbachian also point towards more complex variations in redox conditions associated with the end-Permian mass extinction. The Early Triassic was also a period of recurrent carbon isotope perturbations as observed in Triassic sections across the Tethys ocean. Repeated disturbances to the carbon cycle combined with persistent anoxia and shifts to euxinia may