Compositional and mineralogical variations in a Neoproterozoic glacially influenced succession, Mirbat area, south Oman: Implications for paleoweathering conditions

During the late Neoproterozoic Era the Earth is believed to have experienced some of the most severe climatic oscillations in geological history. The Mirbat Group in southern Oman comprises a continuous succession of sedimentary rocks containing two Neoproterozoic (Cryogenian) glacial intervals separated by ∼1 km of non-glacial marine deposits. We show that variations in the major element and mineralogical compositions of mudstones from glacial (Ayn Formation) and non-glacial (Arkahawl and Marsham Formations) intervals in the Mirbat Group are best explained in terms of the effects of chemical paleoweathering of contemporary land surfaces. Chemical weathering was at very low levels during deposition of the glacigenic Ayn Formation, whereas intense chemical weathering is recorded in the ∼1 km thick, non-glacial Arkahawl and Marsham Formations. Paleoweathering variations are corroborated by sedimentological evidence of paleoenvironments and attributed to climatic changes from dry and cool during glaciations to humid and warm during the long non-glacial interlude.