Structure, generation and preservation of upward fining, braided stream cycles in the Old Red Sandstone of Scotland

Abstract

ABSTRACTA sequence of upward fining cycles contain braid bar structures in the coarse member. Bars, medially placed in the stream are recognised either by radiating large foresets or by identifying bar tail sediments with converging dips to their foresets. Lateral bars are recognised by the growth of major sandstone sheets oblique to the direction of channel trend and over slough mudstone. The fine member contains structures which indicate a direction of flow in the same direction as the channel, suggesting that only the unlevéed part of the floodplain is preserved.The direction of transport for the Old Red Sandstone sediments is perpendicular to the direction of bar accretion. This is accounted for by assuming the section dealt with to be on the NNW margin of a cone which builds outward to the NE, and where the river building the cone swings from one side to the other. An upward increase in cycle thickness within the section is possibly the result of an increase in the size of the cone and the consequent amalgamation of the coarse members.