Features and evolution of slip structures in badlands areas (SE Spain)

•Slips are minor forms located on subvertical walls of semi-arid badlands areas.•We call them slips because they begin as muddy laminar run-off on host rocks.•These morphologies depend on the features of the original colloidal suspensions.•Slip formation requires weather conditions different to the present.•Their development can suppose a distinctive fingerprint of different badlands.

Slips are little known mud-coated structures several centimeters thick, produced by gravity-driven flows on free vertical surfaces. We have differentiated a sequence formed by three main morphologies: mud drips, slips and pseudo-stalactites. This study, located in the badlands of the Guadix and Baza basins (SE Spain), suggests that formation of muddy morphologies on subvertical walls is determined by the physico-chemical characteristics of colloidal suspensions (slurries) related to rainy periods and does not indicate any substrate decay. Multiple braided microchannels, internally structured like irregular book pages, are commonly found, each formed by mudflows during rainy episodes. These morphologies constitute a temporary sink of fine erosive materials. They consist of scarcely sorted mixtures of heterogeneous matter of a detrital-cohesive nature, with low clay contents, which inherit the features of the parent materials. The current semiarid environmental conditions appear to favor conservation rather than development. The differences observed in the slips of the Guadix and Baza basins can be determined by the different geomorphological evolution of the two basins and, to a lesser extent, by the properties of the slurries that fed the slips.