Neoproterozoic storm deposits in western Yangtze: Implications for the sea conditions during the middle Sturtian glaciation

The Neoproterozoic snowball Earth hypothesis emerged to explain an inferred planetary wide extreme climate change. However, storm deposits requiring open water conditions in the Huangdongzigou Formation, South China, contradict interpretations of a global Cryogenian hard snowball Earth. These deposits accumulated during the middle Sturtian interval (690-675 Ma) on the basis of U-Pb zircon age data from andesitic tuff and coarse siltstones within the formation. Siltstones and mudstones with abundant storm-generated erosional and sedi-mentary structures, such as hummocky and swaley cross-stratification occur through the sedimentary succession, which require the action of oscillating ice-free water flow. Chemical weathering indices and resultant mean annual temperature calculations indicate a warm-humid environment during storm events, with the transition to a cold water depositional environment towards the top of the formation, which is possibly related to the next glacial episode.

Automated summary

The Neoproterozoic snowball Earth hypothesis was proposed to explain a significant global climate change. However, the presence of storm deposits in the Huangdongzigou Formation of South China contradicts the idea of a complete frozen Earth during the Cryogenian period. The age of these deposits, based on U-Pb zircon data, indicates that they were formed during the middle Sturtian interval. Sedimentary structures, such as hummocky and swaley cross-stratification, suggest the presence of oscillating ice-free water flow during storm events.