Hipótesis sobre el origen de la laguna de Medina (Jerez de la Frontera, Cádiz)

Résumé

In this paper we propose a hypothesis for the formation of the closed basin hosting Medina playa-lake, one of the main shallow lakes of Andalusia. The lake is located S of the flood plain of the Guadalete river. It is separated from the alluvial sediments of the river by two narrow ridges, aligned in an E-W direction. Multi-coloured marly rocks, dolomites and gypsum with a Triassic origin make up these hills. At the top of such hills, rounded-pebbles conglomerates with a subbetic origin appear. The conglomerates are interpreted as alluvial deposits (terraces) associated with older stages of deposition of the Guadalete river. These sediments are located more than 40 m above the current level of the river and exhibit fold deformation, oriented roughly WNW-ESE. With the information obtained, it is presumed that the main structure that has generated these hills would be an antiform with a core of Triassic and Miocene sediments. This structure aids the formation of a barrier to the natural runoff flow to the north, remaining the leading cause for the genesis of the endorheic basin that leads to the establishment of the playa-lake.