A SYNTHESIS OF NEW STRUCTURAL, STRATIGRAPHIC, AND GEOCHRONOLOGIC CONSTRAINTS FROM NORTHEASTERN WASHINGTON WITH IMPLICATIONS FOR NEOPROTEROZOIC SNOWBALL GLACIATIONS

The North American Cordillera records wide-ranging Neoproterozoic glacial sedimentation, however, the nature of and causal trigger for these glaciations are still being understood. A proposed factor for glaciation is the rifting of the hypothesized supercontinent, Rodinia, beginning ~800 Ma. However, uncertainties in Rodinia’s geography and rift history hinder the rigorous evaluation of such a causal mechanism. Here we report new structural, stratigraphic, and geochronologic results from the Shedroof Conglomerate, Leola Volcanics, and Monk Formation of the Windermere Supergroup in eastern Washington. New mapping and field observations support glacial deposition within the Monk Formation, highlight a previously unrecognized major thrust fault, and amend previous interpretations for locations of and displacements along syn-depositional structures. With a refined understanding of regional fault blocks, we present new stratigraphic findings including the varied eruptive dynamics of extensive rift-related Leola Volcanics interfingering with diamictites and a subdivision of the Monk Formation into non-glacial and glacial members. Finally, our U-Pb geochronologic data place radioisotopic constraints on these units, improving correlation with other Cryogenian-Ediacaran units along the Cordilleran margin and elucidating the context for glacial sedimentation.