Abstract

The results of a research study of bed form movement and internal structure will be presented. Detailed measurements were made on a daily basis over neap/spring tidal cycles. Internal structures were inferred from measurements made by divers at a nearshorc subtidal site. These included cross-sectional profiles, recorded at successive slack waters. Sequential profiles were used to determine the positions for box cores at an intertidal site. These were then interpreted in terms of the depositional processes that occurred over known periods of time. In association with these studies, measurements were made of boundary-layer flow, sediment transport, sediment dispersion, and temporal and spatial variation in grain size. Lag cross-correlation techniques were used to quantify form change and bed form migration which, when related to tidal range, give contra-rotating hysteresis loops.

The study of sedimentary structures is fundamental to the geological interpretation of paleoenvironments and the significant sedimentary processes. Despite its importance, insufficient verification of the interpretation of ancient sedimentary sequences has been carried out by studying modern processes. Most of the work that has been undertaken in the marine environment is restricted to the intertidal zone and, despite bed form movement, is limited to single observations. Bed forms with similar sizes to those studied at the nearshore site occur at the shelf edge in water depths of approximately 150 m. Can we distinguish these contrasting environments, including those of the intertidal zone, using traditional stratigraphic criteria?