Unpredictable pathways: Subsurface radon and an academic career never envisioned
Friday, November 25 at 12PM (MDT) in Tory 3-36
Abstract:
The Devonian period saw an increase in terrestrial organic matter abundance through the development of tree root networks and forest diversification. The development and deepening of root networks from the Emsian-Eifelian (407-387 Ma) into the Givetian and Frasnian (387-372 Ma) resulted in increased pedogenesis and weathering that would have likely affected the marine realm. Several δ13C(org) excursions are recognized in Frasnian marine shales and carbonates worldwide and are referred to collectively as the punctata Event, named for the corresponding conodont zone. The cause of these excursions has been linked to forest diversification. Trace metal proxies indicate that during this interval, increased soil weathering likely resulted in nearshore upper water column productivity, and bottom water anoxia. What is not well understood is the effect that suspected increased nutrient levels and siltation had on major reef builders, such as stromatoporoids and corals that were thriving during the Frasnian.
The punctata Event has been recognized in the Canadian Rockies and subsurface of the Western Canada Sedimentary Basin (WCSB), which hosts some of the world’s best examples of Devonian reef growth. This study investigates the potential link between the punctata Event and changes in reef-building biota in an extremely well-preserved carbonate platform, known as the Redwater Leduc Formation reef. Most stratigraphically equivalent reefs in the WCSB have experienced significant diagenesis and fabric-destructive dolomitization, but most of the Redwater reef was not affected by this late-stage dolomitization and the fossils preserved in the reef are pristine. The punctata Event is recognized in the stratigraphically equivalent Duvernay shales. Trace metal proxies detected at intervals corresponding to the δ13C(org) excursion punctata Event record reduced oxygen levels in the marine shales at this time, but the adjacent carbonate platforms continued to develop throughout this interval. Changes to reef building organisms have been observed at this interval in the middle to upper Leduc Formation reefs. Framework textures shift from a stromatoporoid framestone, to stromatoporoid-renalcis framestone, and finally to a coral stromatoporoid framestone. Several Megalodon bivalves, considered to possibly be resistant to increased levels of nutrients, have also been recorded at a consistent interval across preserved Leduc Formation platforms. This study investigates whether the punctata Event, signalled by trace metal and isotopic signatures, is linked to the observed changes in reef-building biota and reef structure. The findings of this study aid in developing our understanding of the controls on reef-building organisms and the effects of significant changes in the terrestrial environment on marine ecosystems.