Provenance of multicycle quartz arenites of Pliocene age at Arcos, southwestern Spain

A typical deposit of multicycle quartz arenites of considerable economic significance located in Arcos (SW Spain) has been studied to establish the provenance of the grains and their stages of sedimentary evolution. The quartz grains were studied by SEM and the composition of the sand determined by modal analysis of the heavy and light minerals. The sources of the silica sands were the Numidic sandstones (known as 'Aljibe') in the Betic Cordilleras, and the late Miocene calcarenites of the Guadalquivir basin. Four phases in the evolution of the Arcos quartzose sands are: (a) the initial surface features, upturned plates; (b) mechanical features (an association of conchoidal fractures and arcuate steps), formed in littoral environments, inherited from the Late Miocene calcarenites; (c) fluviatile features, such as mechanical V's and grooves; and (d) a final stage of chemical features (oriented etch pits, solution pits and hollows, and silica globules), developed in a hot, humid climate. The most important process producing the enrichment of the quartzose sands takes place during erosion-depositional cycles.