Some evolutionary patterns of palaeokarst developed in Pleistocene deposits (Ebro Basin, NE Spain): Improving geohazard awareness in present-day karst

Pleistocene detrital deposits in the central Ebro Basin frequently show deformation features due mainly to karstification in the underlying Neogene evaporites. In 123 cases, estimation of parameters of shape and minimum volume of materials involved was accomplished. Six of them were analysed in more detail to establish the main processes involved in their genesis and the succession of events. All the deformation features in the selected sites are synsedimentary. To achieve the objectives, intense fieldwork was made applying methods of sedimentology and structural geology. Usually, a complex evolutionary pattern was observed, with evidences of dissolution, sagging, collapse, gravity flow, suffosion, and plastic flow. In a schematic way, three main situations, independent of the age of the analysed deposits, can be distinguished: (a) slow subsidence, (b) collapse, and (c) temporal overlapping of both processes. In the first 2 scenarios, basins with smooth or abrupt borders, respectively, were generated on the land surface. In the third one, slow subsidence was followed by a collapse, located in the area of maximum flexure. These patterns are also observed in present-day dolines. Comparison of direct and indirect parameters between paleodolines and present-day dolines indicates a bigger size of the latter, probably caused by the different conditions of observation. This study helps to know the possibilities in the evolution of mantled karst features, to estimate the volume of material affected by karstification and to improve the knowledge of present-day dolines behaviour. Consequently, study of paleodolines must be considered to achieve a better urban planning in active karstic areas. Copyright © 2018 John Wiley & Sons, Ltd.