Unravelling calcrete environmental controls in volcanic islands, Gran Canaria Island, Spain

Abstract

Volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief, climate and vegetation, and lacking carbonate host rocks. This paper discusses the formation of Quaternary calcrete profiles in Gran Canaria volcanic Island, under direct influence of the SAL (Saharian Air Layer). Calcrete profiles are multi-storey and composed of prismatic, massive, laminar, pisolithic, ooid-bearing, sandy mudstones with rhizoliths and brecciated horizons. Host rocks include basalts, siliceous mudstones, volcanic sands and gravels and bioclastic-rich sands. Carbonate is mostly calcite but some dolomite occurs in massive horizons. The main microfabrics include laminated micrite, fine crystalline dolomite, desiccated micrite, micrite-clay groundmass, oriented Mg-rich clays, peloids, spherulites and coated grains. δ 13 C varies from −3.26 to −9.18‰ VPDB and δ 18 O from +0.86 to −3.24‰ VPDB. The 87 Sr/ 86 Sr ratios are between 0.707504 and 0.708860, indicating that calcium was mostly supplied from the CaCO 3-rich aeolian dust coming from the Sahara Desert. Calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils. The correlation trend of δ 13 C and δ 18 O points to a climate control on precipitation, with the heavier isotope values in the horizons containing dolomite. Sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles/horizons. Amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion, whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons. The direction of the winds supplying aeolian dust, and the varied relief, vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island. Our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates.

Carbonate tufas as archives of climate and sedimentary dynamic in volcanic settings, examples from Gran Canaria (Spain)

“…Although this may be evidence to interpret a different water composition for this deposit (Ford & Pedley, 1996; Pentecost, 2005; Pedley, 2009), waters feeding Los Berrazales were not very different from those from Azuaje or Las Temisas, as indicated by the overall geochemical data (SPA‐15, 1975). The geochemical values of tufas and travertines from Gran Canaria Island contrast with those of calcretes from the same Island which indicates a significant provenance of calcium (aeolian dust) and a dominant meteoric/pedogenic CO 2 (Alonso‐Zarza et al ., 2020a).…”

“…1). In addition to tufas and travertines, Gran Canaria also contains a wide variety of Pleistocene calcretes occurring mostly in the eastern and northern areas of the Island (Alonso‐Zarza et al ., 2020a). The studied tufa deposits are Las Temisas tufa (Las Pilas Ravine) in the south‐east sector, Azuaje tufa (Azuaje Ravine) in the north‐east sector, and Los Berrazales tufa (Los Rios Ravine) in the north‐west sector (Fig.…”

Rare earth element resources on Fuerteventura, Canary Islands, Spain: a geochemical and mineralogical approach

“…However, the current arid and deforested conditions have led to extensive erosion of the weathered rock profiles present in different areas of the island. Edaphic calcretes are abundant in Fuerteventura (Alonso-Zarza and Silva, 2002;Huerta et al, 2015), with their primary source of calcium believed to be the Pliocene paleodunes formed by calcarenites, rather than the parent igneous rock itself (Chiquet et al, 1999;Huerta et al, 2015;Alonso-Zarza et al, 2020). Interestingly, the aeolian dust deposits predominantly originate from the Sahara Desert (Goudie and Middleton, 2001;Menéndez et al, 2007;Scheuvens et al, 2013).…”