A family of primary sedimentary structures formed by the migration of the slip-faces of rippled bedforms or of bars. It is characterized by inclined laminations (foresets) bounded by planar surfaces (planar or tabular cross-stratification), or by scoop-shaped surfaces (trough cross-stratification). The foresets dip at the angle of repose of the sediment on the ripple slip-face and are oriented in the direction of migration of the ripple (see palaeocurrent analysis). Tabular cross-stratification is produced by the migration of straight-crested, asymmetrical ripples or sand waves. Trough cross-stratification is generated by the migration of linguoid ripples or dunes. The term ‘cross-lamination’ is applied to cross-stratification formed by the migration of ripples; ‘cross-bedding’ is used for cross strata formed by the migration of large-scale forms such as dunes, sand waves, or bars. The term ‘cross set’ is used to define the cross-stratification preserved between any upper and lower bounding surface. Where the original bedform which produced the cross set is preserved and forms the upper bounding surface to the set, the term ‘form set’ is used. A number of cross sets preserved within a single bed are called a ‘coset’.
Subjects: Earth Sciences and Geography.