Two from Donegal: Neoproterozoic glacial episodes on the northeast margin of Laurentia

Two glacial episodes, the Sturtian (ca. 720 Ma) and Marinoan-Varangerian (c a, 590 Ma), characterize many Neoproterozoic successions worldwide. In cont rast, northeast Laurentia is typically considered as containing only the la tter; in Scotland and Ireland this is represented by the Port Askaig Tillit e. Here we present evidence (ice-rafted debris) for a second, younger Neopr oterozoic glacial event in the Dalradian Southern Highland Group of Donegal , Ireland. These deposits overlie strata correlative to ca. 595 Ma rocks in Scotland, making this heretofore unrecognized glacial episode a Marinoan-V arangerian equivalent. In that the Port Askaig occurs similar to 3-5 km str atigraphically below the Southern Highland Group rocks, it is most likely S turtian, not Marinoan-Varangerian, in age. Thus, the Dalradian succession i n the Irish Caledonides contains strata representing both the Sturtian and Marinoan-Varanger glaciations.