Erosion and stabilisation sequences in relation to base level changes in the El Cautivo badlands, SE Spain

Abstract The complex multiple-age badlands at El Cautivo are cut in upper Miocene marls of the uplifted and dissected Tabernas Basin, Almeria, in semi-arid SE Spain. Previous work identified six episodes of erosion and subsequent stabilisation, with ages ranging from the late Pleistocene to the present day. This paper uses newly-acquired digital elevation models, orthorectified aerial photographs, and field survey data to illustrate the development sequence of a series of gullies which drain into the Rambla de Tabernas. Changing drainage directions and phases of incision and stabilisation are related to the filling and subsequent dissection of the Tabernas lower lake sediments, differential material strengths, changing process mixes on hillslopes and, in more recent times, land-use changes. We propose that the erosional phases differed considerably in both time-span and depth of incision. A long period of stability during the existence of the lake led to extensive pediment development in the area. Subsequent incision into the lake sediments by the Rambla de Tabernas produced a limited amount of localised pediment incision in the tributary catchment. Subsequent aggradation occurred in the lower reaches of gullies when incision by the Rambla de Tabernas reached the underlying bedrock. Following incision through the lip of the lake the Rambla de Tabernas cut rapidly into the bedrock leading to an altered drainage direction in the tributary catchments and the major phase of badland development visible today. Stabilisation of the pediments and some of the north-facing slopes occurred subsequently. Increased sediment loads, caused by climatic shift, a change in land use, or both, gave rise to a later phase of valley fill in the gullies. The modern channels have reduced this fill to isolated terrace benches and there are also localised remnants of a lower, more recent fill. Whilst supporting the general interpretation of the site's development by Alexander et al. [Alexander, R.W., Harvey, A.M., Calvo, A., James, P.A., Cerda, A., 1994. Natural stabilisation mechanisms on badlands slopes: Tabernas, Almeria, Spain. In: Millington, A.C., Pye, K. (eds.), Environmental Change in Drylands: Biogeographical and Geomorphological Perspectives. Wiley, Chichester, pp 85–111.], this re-analysis highlights the importance of changing drainage direction to the pattern of landform development and attempts to assess the magnitude and overall rate of incision.