A shallow-water dunefield in a microtidal, wind-dominated strait (Stintino, NW Sardinia, Italy)

Abstract

Abstract This study focuses on the recent evolution of a shallow-water dunefield system off La Pelosa Beach, located in the wind-dominated, microtidal, asymmetrical Asinelli Strait (Stintino, NW Sardinia, Italy). The system comprises four zones defined by a gradual decrease in current strength from the strait centre to more distal parts that form different bedforms. The strait centre (Zone A) is a substrate-carved channel passing downcurrent to a vast sandy shoal characterized by a subaqueous dunefield (Zone B) that is surrounded by a sandwave–ripple carpet (Zone C). The strait margin (Zone D) is dominated by a sandy cusp, the so-called La Pelosa Beach system. The extensive seagrass meadow located on the SE side of the strait-end zone feeds the system with bioclastic-rich sands. This carbonate sedimentary load is ensured by natural seagrass meadow retreats that are possibly boosted by human impact. The sediment transport is modulated by the interaction between two opposite currents triggered by the east-incoming Greco/Levante and NW-incoming Mistral winds. These currents experience a great variability due to multi-annual fluctuations (4–6 years) of the prevailing wind activities. Such cyclicity is responsible for periodic dune migration and and transport from La Pelosa Beach out of the system below the active part of the submerged beach (depth of closure). Bedform formations (ripples, dunes and sandwaves) and migrations within the strait are the result of complex physical processes observed in modern environments but rarely described in rock formations. The presented conceptual model can be used to recognize sediment ‘spillover’ processes on other modern, microtidal, wind-dominated straits, as well as proposing the main criteria for recognizing this strait sedimentary succession in the geological record.