Evidence for currents associated with waves in Late Precambrian shelf deposits from Finnmark, North Norway

Abstract

ABSTRACTAbundant wave ripples with wavelengths of up to 0.3 m, top‐surface granule lags and tabular sand‐stone beds suggest that the interbedded sandstones and siltstones of the Skaergårdnes Formation are shallow marine deposits. A simple orthogonal relationship between crestal trends of wave ripples and trough axes/cross‐bed dip directions indicates that bottom currents and surface waves were closely related, suggesting that wind‐drift currents were responsible for deposition. Interbedding of the tabular sandstones with siltstone is more probably due to the patchy nature of sand cover on the sea floor than to episodic sand derivation from the coast. The top‐surface granule lags indicate local, temporary excess of sand removal over supply, and were probably formed by both wave‐winnowing and non‐depositional megaripple migration. The well developed lags in this and similar ancient sediments suggest that winnowing, leading to bed armouring and sediment bypassing may be an important shallow marine process.