Upper Old Red Sandstone sedimentation near the unconformity at Arbroath

Abstract

Coastal exposures near Arbroath provide information about local sedimentation patterns of the Upper Old Red Sandstone (Late Devonian) and the relationship between these patterns and the underlying unconformity. Bluck's analyses of the morphology and internal structures of gravel and sand river bars have been used to interpret the conglomerates as the major components of river bars that formed on the edges of frequently shifting river channels. Sands accumulated as bar tails and also in overbank areas that seem to have formed preferentially in ‘shadow zones’ protected from channel action close to hillocks of bed-rock. Locally breccias accumulated near these hillocks and plugged steep-sided gullies that formed in the overbank areas. These gullies appear to reflect arid conditions and there are other features of the Upper Old Red Sandstone that support this conclusion.