Caracterización y significado ambiental de los nidos de abejas de las calcretas cuaternarias de Lanzarote y Fuerteventura

Résumé

Thick laminar calcrete profiles are common on the surface of Lanzarote and Fuerteventura. In this paper we study one profile from Lanzarote (Macher profile) and one from Fuerteventura (Teffa profile). The profiles are about 2 m thick. The Macher profile developed on basaltic host rocks and consists of a lower horizon in which white veins of laminated micrite penetrate within cracks and an upper laminar one. The Teffa profile consists from base to top of: massive, laminar, massive and laminar-brecciated horizons. It developed on alluvial fan gravels. The study of the profiles shows the presence ofooids, the complex structure of the laminar horizons and the occurrence of fossil bee nests (Celliforma). Celliforma occurs as ovoid larval cells whose base is more or less rounded, but whose top is flat. The cells are about 3 cm long and 1.5 cm in diameter. Their wall is about 5 mm thick, and is commonly laminated. Celliforma is interpreted as fossil nests of solitary bees. Their presence in the laminar horizons is evidence for the existence of a vegetation cover containing angiosperms. The association of the fossil nests with the calcretes and the microstructures of the calcretes, indicating the active influence of the vegetation cover, suggest that calcretes formed in the relatively more humid periods, in a general context of an arid to semi-arid climate.