Palaeowind: geological criteria for direction and strength

Abstract

The practical geological indicators of palaeowind are several scalar properties (bed thickness, grain size and sorting, mineral proportions) and directional structures (dune forms, yardangs and wind furrows, dune cross-bedding, windblow n trees, wind ripples, adhesion ripples, flutes and grooves). These indicators ideally should be sampled so as to minimize geographical bias, and the data assessed so as to afford smoothed paths of sand and dust flow. Because most geological wind-related processes involve a threshold wind speed and proceed nonlinearly, inferred patterns of sand and dust flow may not exactly match patterns of the time-averaged wind direction. The use and potential of palaeowind indicators are well illustrated by w indblown trees (mid Flandrian, southwest Britain) and by dune cross-bedding (Palaeozoic-Mesozoic, U.S.A.).