Controls on aeolian sand sheet formation exemplified by the Lower Triassic of Helgoland

The basal part of the Middle Buntsandstein (Lower Triassic) on Helgoland in the southern North Sea is composed of lacustrine redbeds with thin white beds of aeolian sand sheet origin. The aeolian deposits formed during lake low-stands, and sand sheet formation was caused by a restricted sand supply perhaps in combination with frequent wind changes and high-speed wind events. With time aeolian sedimentation was progressively influenced by brief flood events or by minor lake transgressions. Ultimately the sand sheets were covered by fine-grained lake deposits during a new phase of lake high-stand. Preservation of the aeolian deposits records the overall low-energy of the littoral processes, and early cementation. The aeolian deposits define sedimentary cycles of various thickness, and it is suggested that the cyclicity records Early Triassic orbital climatic forcing.