Experimental Study of Cross-Strata Development on an Undulatory Surface and Implications Relative to the Origin of Flaser and Wavy Bedding

Abstract

ABSTRACT Flume experiments were carried out in order to examine the influence of sedimentation surface undulation upon structural and textural development of cross-bedded sedimentation units. The evidence of this study indicates that in addition to flow conditions, the morphology of the sedimentation surface is a significant factor responsible for the mechanics of bedding formation. The relation between the bedding type and the sedimentation surface morphology may be quantitatively expressed by a combination of the symmetry index RSI of sedimentation surface undulation and the parameter A/m, defined as a ratio of mean amplitude (A) of sedimentation surface undulation to mean thickness (m) of the sedimentation unit deposited on this surface. Flaser and wavy bedding are built of couplets of sandy and muddy elements. A single pair of sandy and muddy elements of an individual couplet is known to form by alternate tractional current deposition and slack-water suspension settlement. As a result of the present study, another reasonable mode of origin is proposed. An individual pair of sandy and muddy elements may also develop simultaneously in a bed form migrating on an undulatory sedimentation surface, under unidirectional flow conditions. A sequence of sandy-muddy couplets may develop in response to alternate processes of deposition and erosion of such deposits.