DEVELOPMENT OF CUSP-RELATED, GRAVEL SIZE AND SHAPE FACIES AT MALIN HEAD, IRELAND

Samples of beach gravels were obtained from foreshore cusp deposits at Portmore Beach, near Malin Head, Republic of Ireland. Axial dimension s (A, B and C) were measured, and the maximum projection sphericity wa s derived, for each of 4360 clasts. Each sample was also categorized a ccording to depositional subenvironment. Principal components analysis and cluster analysis were used to identify potential facies zonation. Results indicate that reworking of the foreshore by incident and edge waves resulted in clast size and shape segregation both parallel and perpendicular to the beach. Patterns of zonation were distinctly diffe rent from those described in earlier facies descriptions, showing a co mplex set of foreshore facies. The distribution of these facies was co ntrolled primarily by location within beach cusp systems. Primary and secondary facies demonstrate alongshore variability of a magnitude com parable to across shore differences. The results have important implic ations for palaeoenvironmental reconstruction, morphosedimentary descr iption and research sampling design, and provide the basis for a conce ptual model of gravel beach cusp facies.