Structural controls on the development of the drainage system in the Triassic gypsum-rich formations of the western Subbetics (El Pontón stream, Badolatosa, Sevilla)

Abstract

Tectonic processes operating at different spatial-temporal scales condition the geomorphological features that are to be expected in any region. Particularly in areas with the presence of both soluble and light rocks (such as gypsum and/or halite), abundant in the Triassic materials of the External Subbetic and other units with similar lithologies, it is expected that the different rheology of such rocks in an active tectonics setting could generate uplifts resulting in the formation of drainage subsystems that differ from the regional one. In this study, the drainage system of the El Pontón stream (Badolatosa, western Subbetic) is analyzed from hydrological, geomorphological and structural points of view. The morphology of the enclosed valley and the structural features analyzed are coherent with a general uplift of a wider structural unit, the so-called Algodonales - Badolatosa shear zone. Moreover, a geomorphological point of interest, a natural bridge within the valley of the stream, is analyzed. This morphology is related to an anomalously large foliated gypsum block within a gypsum mega -breccia. It is hypothesized that the higher plasticity and cohesion of this block probably favored gravity-driven flow from both sides of the valley, closing up its upper part.