Analysis of barrier island surface sediments by scanning electron microscopy

Abstract

The analysis of quartz grain surface microtextures from a sedimentary environment where grain transport and depositional pathways were closely interconnected, allowed insight into subtle microfeature alteration during movement between subenvironments. Four Fire Island (New York) and one Montauk Point (beach) sample were analysed, principally through use of a checklist approach, using 36 common surface features. Beach, overwash, floodtidal delta, dune and inlet grains displayed similar surface features, only the latter two samples displaying distinctive microtextural patterns. The pattern of development of inlet grains was related to the application of higher shear stresses on the grains during transport in the shallow channel. The results from dune grains testify to the effectiveness of aeolian transport mechanisms in rapidly altering existing features. Glacially derived microtextures altered by subsequent subaqueous action were prevalent but whether these glacial microfeatures are derived from the headland region, Montauk Point, or from a closer offshore “glacial lobe” source is not determined. Comparison of offshore lobe and adjacent sediments revealed contrasting surface and morphological differences. Statistical treatment of checklist data in binary form (1,0) using stepwise discriminant analysis proved workable, but more rigorous testing is required to prove its relevance and use in deciphering raw textural data.