The late Neoproterozoic (ca. 700–730 Ma) Mechum River Formation is exposed as a structural inlier within Grenvillian basement in the Blue Ridge province of central Virginia, United States. The southern portion of the Mechum River belt preserves evidence of glaciomarine sedimentation at the margin and basinward of grounding-line fans. Subaqueous glacial till, coarse-grained rhythmites, and dropstones record the incursion of ice into the basin. Marine deposition is evidenced by persistent laminations (cyclopsams) in rhythmically bedded diamictite and possibly by tidally pumped, distal turbidites in laminated mudstones. Glaciomarine sedimentation in the Mechum River Formation may have been coeval with Sturtian-Rapitan glaciations in northwestern Laurentia and Australia, and provides further evidence for a globally cold climate during the late Neoproterozoic.

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