International Journal of Speleology (Jan 2021)

On the genesis of aluminum-rich speleothems in a granite cave of NW Spain

  • Jorge Sanjurjo-Sanchez,
  • Carlos Arce Chamorro,
  • Juan Ramón Vidal Romaní,
  • Marcos Vaqueiro-Rodríguez,
  • Victor Barrientos,
  • Joeri Kaal

DOI
https://doi.org/10.5038/1827-806X.50.1.2358
Journal volume & issue
Vol. 50, no. 1
pp. 25 – 40

Abstract

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Granite massifs often contain caves, with dimensions ranging from a few meters up to 1,000 m, also referred to as pseudokarst. The speleothems in such caves are mostly composed of either Si-rich (commonly opal-A) or Al-rich authigenic mineraloids. Whereas the formation and geochemical composition of opal-A biospeleothems have been studied and are fairly well understood, knowledge on the Al-rich analogues is scarce. This work reports for the first time a study on the composition, accretion process, age and growth rate of an Al-rich speleothem type flowstone from the A Trapa Cave System (Galicia, NW Spain), developed in a granite cave. To understand the growth process, trickling water was analyzed and the deposition environment inside the cave was characterized. We found that the speleothems are alternating Si- and Al-rich layered deposits formed between 1,635 ± 75 and 1,243 ± 58 cal BP by percolating water that carries underground mineral grains, dissolved ions, and organic matter from soil and the weathered bedrock above the cave.

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