The Azuaje travertine: an example of aragonite deposition in a recent volcanic setting, N Gran Canaria Island, Spain

Abstract

The Azuaje travertines in the north of Gran Canary Island crop out in the Azuaje Gorge, which is incised into Miocene volcanic breccias of the Roque Nublo Formation. This travertine is interesting because of the scarcity of travertines in the Canary Islands and its close relationship with recent volcanic events. Part of the travertine overlies a lava flow, dated at 2420±40 years BP. The travertine is composed mainly of aragonite in both perched systems on the gorge walls and in gorge bottom deposits parallel to the present stream. Perched systems include deposits from the feeder conduits within the Roque Nublo Formation that spilled out through waterfalls and over barriers. The gorge (valley) bottom system includes barrier and pool deposits. The main laminated facies are composed mostly of large fibrous aragonite crystals, while there are also common micritic and porous microfabrics. Shrubs, coated grains, coated bubbles and rafts are present in many of the deposits. Detailed study of the microfacies shows the presence of sparsely distributed biogenic features. The δ13C values are between +4.0 and +11.0‰, and the δ18O values range between −11.0 and −2.0‰ VPDB. These δ13C values lie within the range of those of thermogene travertines fed by thermal waters that cooled downstream, as indicated by the increase of the carbon and oxygen isotope values in that direction. The common occurrence of fibrous radial fabrics is interpreted to be due to disequilibrium conditions during aragonite precipitation. Disequilibrium was likely caused by rapid CO2 degassing of the thermalwaters that led to a rapid increase in the degree of aragonite saturation. Thus, themorphology of the aragonite crystals and the isotopic composition indicate that the formation of the Azuaje travertine was mostly due to abiogenic processes induced by rapid degassing of thermalwaters, linked to the presence of a recent lava flow within the Gorge. In short, the Azuaje travertine shows the important role of volcanic activity in travertine deposition, in the facies distribution as well as in the geochemical signatures of the deposits, and so can be used as a recent analogue for ancient travertine deposits in volcanic settings