Composition and provenance of beach sands in La Graciosa, Lanzarote, Fuerteventura and Gran Canaria Islands (eastern Canary Islands, Spain): a review

Abstract

In this work, a review of petrographic studies in recent decades on 50 sandy beach samples of the eastern Canary Islands (La Graciosa, Lanzarote, Fuerteventura and Gran Canaria) has been carried out in order to know the composition and provenance of the sand grains. The sandy samples are intertidal and most are related to beach-dune systems with coastal desert and arid climates. Thus, these samples contain different proportions of calcareous bioclast, intraclast and volcaniclast grains, with the latter coming from different source areas associated with the building stages of the islands (shield, decline, erosive and rejuvenation). In general, the calcareous bioclasts are mostly fragments of red coralline algae and molluscs, with the appearance of occasional grains of echinoderms, foraminifera and bryozoans. The lithoclasts are essentially fragments of ultramafic and mafic alkaline rocks (basanite and basalt) from the shield and rejuvenation stages and to a lesser extent trachytic-phonolitic felsic rocks from the decline stage, while there are few mafic (olivine, clinopyroxene, Fe-Ti oxide, and amphibole) and felsic (feldspar) mineral grains. The intraclasts are fragments of coastal sedimentary rocks such as beachrocks, eolianites, and paleosols. The abundance percentages depend on geographic and geological factors in each coastal zone. In general, the beaches studied in La Graciosa, Lanzarote and Fuerteventura contain higher percentages of bioclasts than lithoclasts. However, volcaniclasts are more abundant than bioclasts in Gran Canaria, and sand grains of trachytic-phonolitic composition appear only on this island. Finally, urban and semi-urban beaches were found to have fewer bioclasts than natural ones.