Datos geofísicos y evolución sedimentaria de la Depresión de la Janda (Cádiz)

• Autores: Luis de Luque Ripoll, Pablo G. Silva Barroso, Caridad Zazo, José Manuel Recio Espejo, Pedro Carrasco García, José Luis Goy Goy, Manuel Angel Dueñas López, Javier Lario, Cristino José Dabrio González, Francisco Miguel González Hernández, L. Poza
• Localización: Geogaceta, ISSN 0213-683X, Nº. 29, 2000, págs. 69-72
• Idioma: español
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• Resumen

  • La Janda lake is located ¡rito a tectonic graben filled by Pleistocene and Holocene fluvio-marine sediments. Geophysical survey consisting on Electric-logs and seismic refraction profiles aimed to determining the thickness of Quaternary sediments infilling the graben. Nevertheless, the results are significantly distorted by a saline aquifer that occupies most of the sedimentary filling. In any case it is possible to identify an assymetric subsident area reaching up to 300 m depth, characterised by very low apparent resistivities (1.5-2.4 W/m). This thick geoelectrical unit can be preliminary subdivided into 3 different subunits here called A, 67, B2, characterised by resistivity differences. The shallow 4-6 m thick Unit A consists of a thin lacustrine and alluvial day and silts of Holocene age easily recognized in seismic refraction profiles and drill cores. Unit B can be separated in two subunits; Both are saturated in brackish or saline waters; B1 is a 20-40 m thick unit that thins northward and correspond to the Plio-Pleistocene, B2 is a slightly more resistive unit that extends from this depth to 352 m and corresponds to deeply weathered mio-pliocene sandstones. The upper part of Sub-unit 87 correspond to estuarine sands recorded in a previous core which deposition finishes at ca. 3810 cal BP. A sharp normal fault limits the southern part of La Janda assymetric graben