Browsing by Author "Hedhli, Makram"

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    Devonian to Carboniferous Earth Systems Change in Western Laurentia
    (2019-05-22) Hedhli, Makram; Beauchamp, Benoît; Grasby, Stephen E.; Meyer, Rudi; Henderson, Charles M.; Dutchak, Alexander
    The Devonian to Carboniferous (DC) transition is marked globally by carbonate factories turnover, anoxia, profound unconformities and mass extinctions. Various authors have proposed global mechanisms such as meteorite impact, global climate cooling, anoxia, intensification of upwelling, etc. The DC boundary in western Canada and western United States has recorded this major Earth Systems change. Yet, a holistic study of this subject is non-existent. Sixteen sections across the DC boundary from Famennian to Viséan strata, in Alberta, Montana and Nevada were measured, sampled and analyzed. The DC sequence stratigraphy of western Laurentia was revisited based on microfacies analysis and field observations performed in these sections. The DC anoxia was also studied from five outcrop sections, providing the first coherent understanding of environmental changes along the continental margin of western Laurentia. Sediment provenance was examined based on detrital zircon analysis. Carbonate factories turnover and a depositional change from a Devonian warm-water carbonate ramp to a Carboniferous cool-water carbonate distally-steepened ramp were documented. Microfacies distribution in time was compared with geochemical proxies to emphasize the interaction between the biosphere, oceanography and palaeoclimate at the onset of the Permian-Carboniferous ice-house climatic mode. Two low-order T-R sequences were correlated from Alberta to Nevada. Results from this work provide clarification of the spatial-temporal extent of environmental changes and anoxia across Laurentia. This work demonstrates that these events are unrelated to the Hangenberg event recorded in Europe, as commonly suggested by various authors. Carbonate factories shut down and turnover, influx of westerly-derived sediments that are sourced from the Antler terranes, with northern affinities suggest that the Antler Orogeny, and associated plate tectonic reorganization, were the main contributors to the DC Earth Systems change in western Laurentia, rather than being part of a global event. This study demonstrates that the simple global-event paradigm across the D-C boundary does not adequately explain regional changes in the rock record.