Formation and evolution of back-barrier perched lakes in rocky coasts: An example of a Holocene system in north-west Spain

Coastal back-barrier perched lakes are freshwater bodies that are elevated over sea-level and are not directly subjected to the inflow of seawater. This study provides a detailed reconstruction of the Doninos back-barrier perched lake that developed at the end of a small river valley in the rocky coast of the north-west Iberian Peninsula during the Holocene transgression. Its sequence stratigraphy was reconstructed based on a core transect across the system, the analyses of its lithofacies and microfossil assemblages, and a high-resolution radiocarbon-based chronology. The Doninos perched lake was formed ca 45kabp. The setting of the perched lake was favoured by Late Holocene sea-level stabilization and the formation of a barrier and back-barrier basin, which was contemporaneous with the high systems tract period. This basin developed over marine and lagoonal sediments deposited between 102kabp and 80kabp, during rapidly rising sea-level characteristic of the transgressive systems track period. At 11kabp, the barrier was breached and the perched lake was partially emptied, causing the erosion of the back-barrier basin sediments and a significant sedimentary hiatus. Both enhanced storminess and human intervention were likely to be responsible for this event. After 1kabp, the barrier reclosed and the present-day lake was reformed, with the water level reaching as high as 5m above mean sea-level. The depositional evolution of the Doninos system serves as a model of coastal back-barrier perched lakes in coastal clastic systems that have developed over gently seaward-dipping rugged substrates at small distances from the shoreline and under conditions of rising sea-level and high sediment supply. A review of estuaries, back-barrier lagoons, pocket beaches and back-barrier perched lakes in the rocky coast of north-west Spain shows that the elevation of the bedrock is the main factor controlling the origin and evolution of these systems.