NEW RE-OS AGE AND OS GEOCHEMISTRY FROM THE ROAD RIVER GROUP: TEMPORAL CONSTRAINTS FOR THE REDOX STATE OF PALAEOZOIC OCEANS

The Paleozoic Era (541 to 252 Ma) records intense perturbations to nearly all of Earth’s biogeochemical cycles, numerous biological innovations, and dynamic shifts in plate tectonic configuration, all of which ultimately set the stage for the expansion of life onto land. The Cambrian to Devonian Road River Group is a near-continuous record of deep-water sedimentary rocks deposited on the northwestern margin of Laurentia. These strata illustrate redox characteristics of both earlier Neoproterozoic and later Mesozoic/Cenozoic oceans pointing towards a transitional marine state in the Paleozoic. Although much of the Road River Group is characterized by graptolitic shale, the Lower Devonian strata are mostly unfossiliferous, and well-suited to the Rhenium-Osmium (Re-Os) geochronometer. Robust age controls are critical for refining the age model for this time period, as well as tying this section into global records. Here, we present a new Devonian Re-Os age and preliminary Os isotope chemostratigraphic data from the Road River Group. The data presented here provides an absolute age constraint for this part of the succession and the Os isotope dataset allows us to interrogate observed changes in ocean redox chemistry through the lens of changing continental weathering fluxes.