ABSTRACT

Two selected Long Island Sound beaches were investigated as to erosional and accumulational processes during individual tides. Measured breaker heights were considered as being representative of the hydraulic energies causing these processes. Depth of the erosion and the amount and quality of newly accumulating foreshore sediment were recorded with the help of artificially colored sand, placed in the beach before the beginning of the tides.

A dual lamination developed most frequently over those sedimentation stations which were touched by the breaker zone during the tide. The dual lamination consisted of a lower, coarse-grained, and an upper, finer-grained lamina, several mm thick. The coarse laminae possessed a poorer sorting (_I=up to 2.2) and a more negative skewness (SK_G=-0.68-+0.26) than the fine ones. The depth of the disturbance of the foreshore surface sediments by tidal erosion was found substantially greater than reported from certain British beaches by King.

The "breaker zone step" was found not to be controlled exclusively by the collision of breakers with the backwash current, as described by R. L. Miller, but to develop also in the absence of appreciable breaker activity.

The heavy mineral composition of beach samples was strongly influenced by varying hydraulic conditions and the mixing of adjoining sand bodies. The resulting great variability in the heavy mineral composition over small beach surface areas indicates the problems in the proper evaluation of provenance data: hydraulic factors produce strikingly different heavy mineral assemblages from the same source sediment.