The role of neotectonics and climate variability in the Pleistocene-to-Holocene hydrological evolution of the Fuente de Piedra playa lake (southern Iberian Peninsula)

Abstract

Playa lakes that developed in semi-arid regions are sensitive to water input reductions, which may be influenced not only by climate changes and human management, but also by changes in the size of the watershed. We conducted an interdisciplinary study combining structural, geomorphic, sedimentological, mineralogical and hydrological analyses to better understand the evolution of the Fuente de Piedra (FdP) playa lake in southern Spain. By using previously published temperature and precipitation reconstructions, we assessed the potential evapotranspiration and runoff to estimate the maximum lake level during the FdP playa-lake lifespan (>35 ka). Our results indicate that the FdP playa-lake level never exceeded 5 m, although deposits at its north-eastern margin are up to 15 m above the current lake bed at present. These lacustrine deposits are slightly tilted towards the south-west. The electrical conductivity profiles of groundwater on the FdP's shore and in its surroundings reveal a more pronounced interface between brackish water and brine in the northern part of the basin compared to the southern part. This implies that saline water once occupied the northern playa-lake margin in an area that is hardly ever flooded at present. The presence of reworked gypsum in the sedimentary sequence of the southern margin (down to a depth of 14 m) indicates substantial erosion of prior gypsum deposits that are possibly redistributed from northern deposition areas. Altogether, our data suggest a south-westerly displacement of the playa-lake depocentre caused by an uplift of the eastern area and subsidence of the south-western area. This shift is congruent with the combined effect of both the La Nava sinistral–normal fault and the Las Latas dextral–normal fault at the eastern and southern margins of the FdP playa lake. Consequently, the FdP flooded surface mostly remained constant and in equilibrium with climate variables and its watershed along its lifespan. The south-westerly displacement of the flooded surface was provoked by the recent tectonic activity.