Facies relations in a conglomeratic single-barred nearshore environment on the glaciated Atlantic Coast of eastern Long Island, New York, were determined by examination of 42 can cores, bed-form distributions, and sediment textures.

Two principal subtidal zones are recognized. The shoreface zone (0 to 10 m water depth) is composed of clean fine to coarse sand and consists of the planar parallel to megaripple-laminated upper shoreface facies, the massively bedded longshore trough facies, and the megaripple to parallel-laminated longshore bar facies. The inner shelf zone (> 10 m water depth) is composed predominantly of organic-rich fine sand and consists of the parallel-laminated transitional facies and bioturbated offshore facies. Scattered throughout this zone are coarse sand outcrops of megaripple-laminated inner shelf lag facies.

By deployment of dye tracer and by inspection of bed forms in the longshore trough (during low wave-energy, fair-weather conditions) little evidence of longshore or seaward flow could be found. Landward migration of bar deposits over trough deposits was observed over a 6-week period during fair-weather conditions. A core in the trough facies adjacent to the distinct bar-trough contact revealed an underlying bar facies. An equilibrium model of near-continuous fair-weather landward migration of the bar facies interrupted by high wave-energy pulses of seaward movement of trough sediment is believed to account for the stable position of the longshore bar.

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