Playa-Lakes and Yardangs in the Bujaraloz-Sástago Endorheic Area, Central Ebro Basin

Abstract

The Bujaraloz-Sástago endorheic area occurs on an exhumed structural platform in the central sector of the Ebro Cenozoic Basin, essentially underlain by subhorizontally lying gypsiferous and mudstone units with some limestones. The dominantly flat topography of this structural surface is interrupted by around 150 closed depressions, some of which host playa-lakes of outstanding ecological and geomorphological value. The origin of the depressions is related to subsurface dissolution of the gypsiferous bedrock and aeolian deflation caused by the strong local wind, called Cierzo. The leeward side of the largest playas displays yardangs carved on bedrock and unconsolidated Holocene lake terrace deposits. These are the only yardangs documented in Europe so far. Modern and relict lunette dunes also occur on the downwind margin of some playa-lakes. Lacustrine terraces preserved on the margins of the largest basins record alternating periods of aggradation and excavation, attributable to more humid and drier periods, respectively. The available radiocarbon dates from the most extensive terrace, allow us to infer deepening of the largest playa (La Playa) by wind erosion of 6 m over the last 2 ka, yielding an average lowering rate of ca. 3 mm/year. This figure compares well with those calculated in several arid regions of the world, mainly using yardangs carved in Holocene lake deposits.