ABSTRACT

Fourier analysis of quartz grain shapes across the shelf and adjacent beach-littoral system off Long Island reveals a pattern of variation that distinguished: a beach-littoral zone, an inner zone (inner shelf), and an outer zone (mid and outer shelf). The basis of this distinction is the relative proportion of type I (abraded) and type 2 (irregular) sand present.

Irregularly shaped sands (type 2) of glaciofluvial origin (70-100% type 2) off Long Island first became abraded in the beach environment (50% type 2 sand). The inner shelf averages 45 percent type 2 sands (similar to the beach sands). The outer zone (mid and outer shelf) contains the lowest proportions (averaging 15%) of type 2 sand, suggesting a multicycle abrasion history. The boundary between the inner and outer zones is sharp and may represent the seaward limit of dominantly glaciofluvial sediment.

The beach-littoral zone off eastern Long Island has the widest variation in relative proportions of shape types (35-95% type 2 sand). Within this zone two sources of sand are indicated: 1) the partially abraded sands (50% type 2 associated with the beach), and 2) highly irregular glaciofluvial sands (95% type 2) of glaciofluvial substrate underlying the beach facies. The crest of the longshore bar contains samples containing a wide range in proportions of these sand types, implying episodes of both seaward transport onto the bar crest as well as landward transport from a glaciofluvial substrate exposed just seaward of the beach-littoral bar (approximately 10-m water depth)--in a similar fashion as the nearshore zone off Cape Cod, Massachusetts.