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The church's pre-romanesque vault of the Santa María del Naranco (Asturias, Spain) is Humanity's Cultural Heritage of the UNESCO. It is composed of travertine, which is used in arches and vaults of some antiques buildings to free weight from their walls. To investigate the location of the stone pit from which the mentioned material could have been extracted an hydrogeologic methodology has been used.
From the geological point of view, the area investigated is placed in the Cantabrian Zone, the outer zone of the Varisca mountain (Julivert, 1971; Pérez Estaún et al., 1988). Within the Paleozoic serie, the Mountain Limestone of the Carboniferous serie and the Moniello formation of the Devónico's constitute the more important aquifer. Others aquifers, although of lower interest, constitute the stretches of karst limestones come from the Rañeces's Group, as well as the sandy levels of the Naranco's Formation, also of the Devonian.
The knowledge previous of aquifer belonging to the Cretacic at the zone and the water proof character of the Paleogen's calcareous strata, it allowed us to discard that the travertino may come from a carbonated spring up belonging to Cretacic. Splitting of hypothesis of the stone pit where the rock of vault of Santa Ma del Naranco's church was extracted, it would be at relatively close surroundings, the springs that drain the carbonated aquifer of the proximate zone have been analyzed. Only one of the all of the water points localized is associated with a travertine, the Sopeña spring that drains the aquifer from Montaña's Limestone, in the nor-west slope of the Naranco.
This spring generated two travertine's great mass that at the present time appears divided in two units, clearly separated for a zone whose morphology seems to indicate that an antique exploitation may have come from stone pit. Disposition of two masses of travertine separated for a clear space suggests the idea that this rocky mass had been exploited in the past and that hole be precisely, the place from where proceeds the rock that today constitutes the Santa Ma Naranco's vault.
The presence of clays in the pores of samples of the vault of Santa Ma del Naranco and of the travertine associated with the Sopeña spring, it was the cause that analysis of U-T isotopes were impossible, so X-Ray Powder Diffraction and Scanning Electron Microscopy + X-ray Dispersive Energy were used to confirm that both samples come from the same rock.
The dimensions of outcrop and the beauty of surroundings along with the possibility to observe at the present time the travertine's genesis, confer to this place an important value like geological heritage, since it increases to be the rock's birthplace that constitutes the Santa Ma del Naranco's vault, important for its value like historic heritage.
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