Comparative morphosedimentary framework of small subtropical islands offshore Kuwait

Five small islands offshore of the State of Kuwait in the northern Arabian Gulf (Miskan, Awhah, Kubbar, Qaruh, and Umm Al-Maradem) occur in differing structural settings and have evolved in a dynamic environment of shifting fluvial depocenters, fluctuating Holocene sea level, and variable tidal conditions. As a first step in reconstructing the origin and evolution of the islands, bathymetric charts, historical photographs, topographic profiles, and sediment samples were used to investigate their geomorphology and sedimentary environments. The subaerial portion of the islands varies in area from 0.04 to 0.57 km². The plan-shape ellipticity ranges from nearly circular (0.10) to oval-shaped (0.54). The northern two islands (Miskan and Awhah) experience mesotidal conditions and are situated on a shallow platform (<5 m below mean sea level), which is part of a larger Failaka Island structure. In contrast, the three southern sites have a microtidal regime and sit atop small isolated platforms of aggrading perched reef origin, which descend steeply to more than 20–30 m depth within 3 km of the islands. Topographic profiles indicate that island interiors are composed of beach-ridge sets, whereas modern shoreline consists of segments of beachrock platforms alternating with depositional salients and flying spits in areas of longshore transport convergence. The proportion of total shoreline length represented by exposed beachrock varies from 4 to 46%. Beach sediments consist of very coarse to medium sand and variable sorting, primarily due to the degree of attrition of bioclastic material. A simple conceptual model is proposed to describe the general evolutionary trajectory of end-member islands. Both their accretion during the Late Holocene sea-level stillstand and decadal-scale persistence of sediment transport convergence sites (salients) suggest a morphosedimentary stability of the islands in the near future.