The Role of Permeability and Geological Inheritance in the Slope of Boulder Beaches on Shore Platforms

Abstract

The slope of the underlying impermeable sediment matches that of the coarse beach, suggesting that factors other than hydraulic conductivity influenced the system's development. Radiocarbon dates place the deposition of the underlying cohesive layers at the end of the Early Holocene, when sea level was low. On this coast, sea level reached an elevation close to the present around 3.5 kyr BP. The system's evolution suggests that, with the Holocene Sea level rise, continental sediments were eroded, exposing the rocky shore platform and partially eroding an older boulder beach, which supplied clasts that acted as abrasive tools. To achieve an equilibrium profile, an initial phase likely occurred where clast accumulation and cohesive sediment erosion took place simultaneously. Gravel and sand from fluvial sediment erosion were also incorporated into the new beach through processes such as kinetic sieving and infiltration, resulting in a Holocene coarse beach with a matrix of angular gravels and sands.