TRACKING REDOX CHANGES ON THE FRANKLINIAN MARGIN ACROSS THE SILURIAN-DEVONIAN TRANSITION

The Silurian-Devonian transition represents an important period in Earth history due to the emergence of terrestrial plants and their impacts on the Earth Systems. Increased terrestrial productivity and erosion by plants may have allowed for greater nutrient input into the marine system, causing sub-surface waters to become more reducing due to increased marine productivity and consequent rates of respiration at depth. The burial of organic matter, fueled by this increased nutrient supply, may also have allowed for a hypothesized increase in atmospheric oxygen. To better understand the relationship between environmental change and early plant evolution, the sedimentary geochemistry of the Cape Phillips and Bathurst Island formations located on Bathurst Island, Nunavut, Canada is being investigated.

The Cape Phillips Formation is a fine-grained deep-water basinal unit lying to the west-northwest of a shallow water carbonate platform on the Franklinian passive margin. It is thermally immature in the study area and rich in graptolite fossils, which are indicative of an Upper Ordovician to the Upper Silurian (~458.4 Ma – ~419.2 Ma) age. The Bathurst Island Formation is a graptolite-bearing unit conformably overlying the Cape Phillips Formation that contains slightly coarser sediments derived from the Boothia uplift; graptolites indicate this unit spans from the upper Pridolian to the Lochkovian (~4230.0 Ma - ~410.8 Ma). Previously collected samples from the Twilight Creek and Humphries Hill localities that span from the Mid-Ludlovian to upper Pridolian and upper Pridolian to lower Devonian, respectively, were studied here. Major element and redox-sensitive trace metal concentrations, iron speciation, and total organic carbon (TOC) concentrations will be used to track bottom-water redox conditions on the Franklinian margin across the Silurian-Devonian transition and will be compared to similar data from other published studies. These new data will be compiled with sedimentary geochemical data in the Sedimentary Geochemistry and Paleoenvironments Project (SGP) Phase 2 data release to track global bottom water redox changes from the Ordovician through Carboniferous.