Deformaciones cuaternarias en la terraza fluvial de la Laguna de Medina (Río Guadalete, Jerez de la Frontera)

Abstract

The deposit of the +50 m fluvial terrace of the Guadalete river, near Medina Lake, shows diapiric deformations of intrusive type, dueto the ascent of Triassic marls. The presence of lithic tools within the fluvial deposits allows the dating of the terrace as middle Pleistocene. The structural analysis presents two possible episodes of deformation, one in the early upper Pleistocene and the other throughout this period. The general structure may be defined as an aproximately E-W antiform, with a greater vertical ascent eastwards. Such an ascent originated ductile structures mainly, accompanied by several minor faults and fractures, most of them compatible with the general diapiric structure. The initial marls diapiric elevation was of the domal type, with an absolute rise of about 20-25 m The so created reliefbrought about the development of a debris slope deposit, which triggered renewed intrusive processes, due to a disequilibrium of loads. Finally, during the upper Pleistocene-Holocene times, the Medina Lake showed the present configuration, southwards this terrace, as a consequence of a renewed karst sinking in Triassic gypsums. Such karstic processes had just started in the middle Pleistocene.