Global Distribution of Barrier Islands in Terms of Tectonic Setting

Measurements of the global abundance of barrier islands indicate that 49% occur along coastlines of trailing continent margins; 24%, along collision plate margins; and, 27%, along coasts of marginal seas. Based on 2619 shelf width measurements, evidence is presented to show that for only trailing margins is shelf gradient related to barrier island abundance. Of those barrier islands situated along trailing margin coasts, 75% occur along Amero-trailing margins (average gradient 0.57 m/km); 19%, along Afro-trailing margins (average gradient 2.4 m/km); and, 6% along Neo-trailing margins (average gradient 5.9 m/km). Because sediments supplying barrier islands today are generated mainly on the inner shelf and shoreface in response to both nearshore processes and to rising sea level, barrier islands occur in greatest abundance where broad, low-relief coastal plains lie adjacent to the inner shelf and where both are comprised of abundant uncon-solidated detritus. Elsewhere, barrier island occurrence is sparse to absent along very low gradient shelves where the coastal plain-continental shelf sedimentary prism is absent. The tectonic setting of the continental margin is fundamental in controlling factors governing barrier island abundance.