Depósitos arenosos de un delta tipo Gilbert en el Urgoniano de Laga (Bizkaia): Facies y procesos sedimentarios

Abstract

Sand and silt deposits of a fluvial-dominated Gilbert type delta corresponding to an Urgonian mixed platform are described and interpreted. Their outcrop in Laga beach (Bizkaia) allows the recognition of10 sedimentary fades and the construction of a 70 m long and 11.5 m high detailed cross-section, showing the typical tripartite depositional geometry. Topset deposits are horizontally bedded fluvial sandstones with Internal trough cross-stratification. Foreset deposits, up to 28° dip, are composed of interbedded sandstones and fallout siltstones; sandstones were deposited by supercritic flows (chutes-and-pools, antidunes and plane beds) and gravity flows (sand flows, slumps, slides and creep?). Bottomset deposits, up to 5° dip, are composed of fallout siltstones and turbiditic sandstones. The development of the delta was related with active tilting