Tara Johnson, “Estimating Flow Direction in Near Glacial Deposits in the Ansilta Formation, Argentina Using Anisotropy of Magnetic Susceptibility”
Mentor: Julie Bowles, Geosciences
Poster #78

Deposited during the late Paleozoic ice age about 315 million years ago, the sedimentary depositional environment of the Ansilta Formation in northwest Argentina is still being determined. Originally thought to be sub-glacial deposits, newer research suggests these deposits were emplaced by debris flows, mass transport events, and/or slumps not directly associated with glaciers. Magnetic methods could help make this distinction by measuring the alignment of individual sediment grains that may have different orientations depending on the type of depositional process. Understanding this environment can provide information on the local position of the ice sheet and glacial environment around 315 million years ago. Using the field samples collected in 2019, rock cores from 11 different sites were subdivided in preparation for testing. This research aimed to determine flow direction through anisotropy of magnetic susceptibility (AMS) techniques. This method determines the maximum, intermediate, and minimum directions of magnetic susceptibility and can be interpreted to represent the sedimentary fabric or the physical orientation of the grains. Once corrected for post-depositional tilting of the sediment layers, AMS data from the majority of sites sampled display a consistent flow direction to the west-southwest. In addition, three distinctly patterned clusters in the data may represent different flow regimes. This data mostly supports the hypothesis that the Ansilta Formation sediments were deposited by debris flows.