Gilleaudeau to examine lower Mississippian black shales
Whereas oxygenated environments are plentiful in the modern ocean, studying contemporaneous uranium isotope behavior under a range of low-oxygen conditions is difficult given the paucity modern anoxic basins. For example, it is not possible to simultaneously test uranium isotope fractionation under oxic, sulfidic, and iron-rich (ferruginous) marine conditions using modern analogues.
For this project, the researchers propose a novel "ancient analogue" approach for understanding uranium isotope behavior. Iron speciation and trace metal data indicate that coeval Lower Mississippian (Tournaisian) shales of the Appalachian Basin were deposited across a strong redox gradient, from oxic conditions proximal to the clastic wedge, to ferruginous conditions in the basin trough, to sulfidic conditions towards the basin-bounding sill. In addition, coeval shale of the Williston Basin (Upper Bakken Formation) was deposited under hypersulfidic conditions as evidenced by zinc and vanadium hyper-enrichment. Taken together, these deposits represent the perfect test case for uranium isotope behavior because a full range of redox conditions—oxic, ferruginous, sulfidic, and hypersulfidic—are recorded in coeval marine units.
Gilleaudeau and his collaborators will employ two undergraduate students to analyze 160 Tournaisian shale samples for uranium isotopes.
The researchers will receive $55,000 from the American Chemical Society for this project. Funding will begin in September 2020 and will end in late August 2022.
Provided by George Mason University