Development and factors controlling tropical carbonate barrier island systems—Bar Al Hikman; mid-late Holocene, Oman

Modern carbonate barrier island systems are crucial coastal geomorphological features increasingly affected by human activities and global environmental change. Predicting their evolution is essential for effective coastal management. In addition, in the subsurface, palaeo-barriers may hold valuable reservoir potential; however, due to complex internal depositional heterogeneities predicting their reservoir behaviour is challenging. This study documents the depositional heterogeneities of mid- to-late Holocene carbonate barrier systems of the Bar Al Hikman Peninsula (Arabian Sea coast, Oman) using satellite imagery, field observations and sea-level reconstructions. Two distinct carbonate barriers were identified: (1) the northern abandoned barrier, characterized by low lateral facies heterogeneity and primarily composed of mollusc-dominated carbonates, and (2) the present-day forming barrier, dominated by coarse coral-rich carbonates and exhibiting high depositional heterogeneities with lateral stacking patterns of beach ridges separating elongated lagoonal depressions. The initiation of these barriers likely began during the last interglacial transgression period. Then, their rapid development coincides with (a) the onset of aridification in Arabia (5500 years bp) and (b) the beginning of the forced regression that followed the mid-Holocene highstand (+2.5 to 3.2 meters above present sea-level; 6000 years bp). These events also triggered a shift in terms of carbonate factory and platform morphology transitioning from a mollusc-dominated ramp system during the transgression (7700 to 5500 years bp) to a coral-dominated partially rimmed system during the forced regression (i.e. patch reefs, since 5500 years ago). Overall, this study provides an example of how millennial-scale shifts in carbonate factories and platform morphology—by altering the rate and spatial distribution of in-situ carbonate production—can significantly influence coastal sediment supply and local hydrodynamic conditions. These factors ultimately play a fundamental role in controlling the development, facies, and morphological characteristics (i.e., depositional heterogeneities) of carbonate barrier island systems.