Sedimentology and hydrodynamic implications of a coarse grained hurricane sequence in a carbonate reef setting

Storms and associated surges are major coast-shaping processes. Nevertheless, no typical sequences for storm surge deposits in different coastal settings have been established. This study interprets a coarse-grained hurricane ridge deposit on the island of Bonaire, Netherlands Antilles. The sequence was deposited during Hurricane Lenny in November 1999. Insight is gained into the hydrodynamics of surge flow by interpreting textural trends, particle imbrication, and deposit geometry. Vertical textural variations, caused by time-dependent hydrodynamic changes, were used to subdivide the deposit into depositional units that correspond to different stages of the surge, such as setup, peak, and return flow. Particle size and imbrication trends and geometry of the units reflect landward bed-load transport of components during the setup, a nondirectional flow with sediment falling out of suspension during the peak, and a seaward bed-load transport during the return flow. Formation of a ridge during setup affected the texture of the return flow unit. Changing angles of imbrication reflect alternating flow velocities during each phase. Normal grading during setup and inverse grading during return flow are caused by decelerating and accelerating flow, respectively. Hence, the interpreted deposit seems to represent the first described complete hurricane surge sequence from a carbonate environment.