Recurrent emplacement of non-glacial diamictite during the late Paleozoic ice age

Most ice-age diamictites were emplaced in basinal settings by non-subglacial processes. Nonetheless, the occurrence of diamictite in rock successions is widely employed to estimate ice extent and delimit glacial growth-decay cycles that serve as background for paleoclimate modeling. We report a cyclic diamictite-mudstone succession from the Bashkirian-Moscovian Campo do Tenente Formation in southern Brazil to investigate the timing of diamictite emplacement with respect to glaciation. Glacial cycles can be recognized, in which mudstones with ice-rafted debris record deposition in a marine-influenced water body during intervals of maximum ice advance. Diamictites, on the other hand, lack striated and faceted clasts, have deformed blocks of sandstones, and are enveloped by IRD-free mudstones. They are interpreted as non-glacial mass-transport deposits derived from delta collapse during intervals of maximum ice retreat, in which dispersed gravel derives from block assimilation and not from ice rafting.