SCANNING ELECTRON-MICROSCOPE EVIDENCE FOR OFFSHORE-ONSHORE SAND TRANSPORT AT FIRE-ISLAND, NEW-YORK, USA

Balancing the sediment budget of the Atlantic shoreline of Long Island has proved to be problematic because more sediment has been found to be moving westward in littoral drift than was estimated to be supplied by wave erosion of the Ronkonkoma terminal moraine at Montauk Point. There is a need for the existence of an additional, possibly offshore source. As part of a larger Atlantic shore study, 11 beach samples fro m Fire Island were compared with samples representing the known glacia l source at Montauk Point, and also with four offshore samples to the south. Comparisons were based upon quartz sand grain surface texture p atterns derived by scanning electron microscope checklist analysis. In itial evidence of an offshore-onshore link was provided by qualitative results examining surface texture variability between samples, illust rated by photographic evidence and written notes. This evidence was co nfirmed consistently during quantitative analysis. In particular, cano nical variate analysis grouped two offshore samples representing depos its of buried glacial to fluvioglacial lobes with beach samples from F ire Island in adjacent onshore locations or slightly downdrift. In add ition, canonical variate analysis and factor analysis using the SPSSX package, together with cluster analysis using the ARTHUR package, depi cted the main factors and texture variables largely responsible for sa mple discrimination. The significance of both the offshore-onshore lin k and the associated factors influencing quartz grain surface texture was revealed by the fact that they are strongly related to each other and to the regional geomorphology.