Multiple talus flatirons, variations of scarp retreat rates and the evolution of slopes in Almazلn Basin (semi-arid central Spain)

We studied a group of talus flatirons situated at the foot of structural platforms capped by Miocene limestones in the Almazلn Basin, a southeastern extension of the Tertiary Duero Basin, in northern Spain. This group of talus flatirons exhibits five different stages of slope evolution (S1, S2, S3, S4, and S5). They are concave slopes separated from the limestone scarp by a distance that increases with the age of the slope. We measured their profiles and fitted them to mathematical functions. By extrapolating these functions, we obtained the intersection point with the scarp at every stage. This gives different distances retreated by the scarp during each interval between consecutive stages of slope evolution. Remains of charcoal found in the debris slopes corresponding to stages S1, S3, and S4 have been dated by means of 14C to 1090±40, 3590±40, and 28,550±130 BP, respectively. These values allowed us to calculate the following rates of scarp retreat: 0.5 mm/year during the time interval between stages S4 and S3, and 10.5 mm/year for the interval between S3 and S1. There is a good correlation between the ages of the slope accumulations and cold periods. S3 is correlated with the Middle Bronze Age cold epoch and S4 may correspond to the Heinrich event H3. These correlations seem to confirm that talus flatirons in arid environments are good climatic indicators.