Mechanisms of flashflood deposit preservation in shallow marine sediments of a hyperarid environment

Abstract

Flashflood deposit preservation was explored on the shallow seafloor in the Gulf of Eilat- Aqaba. Changes to two fine-grained flashflood deposits were tracked throughout the year after their deposition through repeated sediment coring. Resuspension, removal, and vertical mixing of flashflood deposits were investigated by measuring near-bottom water currents, photographing demersal fish activities, and by measuring the depths and magnitudes of bioturbation using fluorescent sediment tracers. Flashflood deposits were generally not identifiable on the seafloor surface within the year after their deposition. Water currents were typically too weak to resuspend sediment, while demersal fish did resuspend sediment when present. Bioturbation was strongest in the upper 2 cm of the seabed. Despite the rapid dissipation of flood layers, lenses of fine sediment persisted in the seabed for years. Deposition within seafloor depressions, and burial by biological mounds and ensuing flashflood deposits are proposed as mechanisms for localized preservation of flood signatures.