Quaternary laminar calcretes with bee nests: evidences of small-scale climatic fluctuations, Eastern Canary Islands, Spain

Abstract

Thick laminar calcrete profiles are common on the surface of the eastern Canary Islands of Lanzarote and Fuerteventura. This paper reports the study of one profile from Lanzarote (Macher profile) and one from Fuerteventura (Tef|¨a profile). These profiles are about 2 m thick. The Macher profile is developed on basaltic host rocks and consists of two main horizons: a lower horizon in which white veins of laminated micrite penetrate cracks, and an upper laminar horizon. The Tef|¨a profile is cumulative and consists, from base to top, of massive, laminar, and massive and laminar-brecciated horizons. Highlighted in the study of these profiles are the presence of ooids, the complex structure of the laminar horizons, and the occurrence of fossil bee nests (Celliforma). Ooids consist of a nucleus of clay, micrite and etched grains coated with envelopes of micrite and clay (mainly palygorskite). Organic films favoured both the precipitation of carbonate and the adhesion of clays when the ooids formed in the soil. The laminar horizons consist of a centimetre-scale alternation of massive micrite with varied amounts of ooids and detrital grains with laminated micrite. This alternation indicates the small-scale periods of sedimentation, erosion and soil formation in the upper part of a relatively stable surface. These small-scale alternations may reflect climatic vegetation changes in which arid periods are represented by micrite with ooids, while laminated micrite reflects a better-developed vegetation of the wet periods. Celliforma occur as ovoid larval cells with more or less rounded bases and a flat top. 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 horizon is evidence for the existence of a vegetation cover containing angiosperms.