Cavern pearls of the Lluis Auroux's Collection: geochemical and mineralogical characterization on caves from the Geoparc Orígens (Catalan Pyrenees)

The unequivocal global warming of the climate system and the clear influence of human activities underscore the urgency of addressing the current challenge of Earth's warming. Not only many ecosystems but the whole Earth System is being affected, and in some cases, knowledge about the impact of climate change remains limited. A good example of this are the cave pearls, which are highly interesting due to their particular geochemical fingerprint and also from the perspective of natural heritage.

The mountain regions of the Catalan Pyrenees are experiencing more pronounced temperature increases than the rest of the territory, which intensifies the impacts of climate change in this area. Regarding precipitation, and as is the case throughout the rest of Catalonia, all projections seem to indicate a significant reduction in the annual number of days with light precipitation (20 fewer days) and an increase in the maximum duration of dry spells (20 more days). In this context, one might wonder how this 'new hydroclimatic variability' is altering the environmental conditions of karst cavities. Frequent observations by speleologists reveal a widespread trend toward drier conditions inside caves. More intense droughts could lead to a reduction in the water level of the gours where the pearls grow, a reduction that could significantly hinder their growth.

Cave pearls, technically known as pisolites or oolites depending on their size, represent a type of speleothem growth that is much less known than stalagmites and stalactites. They form rare, difficult-to-find deposits that are still poorly studied and are located on the floors of certain underground cavities. Unlike other stone formations, they are not attached to the rock due to the vibration of the water in the basin where they are found, a vibration caused by the dripping that sustains it. These are complex processes, highly sensitive to environmental variations. As such, they present a potential vulnerability, yet still unknown, to situations arising from the current climate emergency, drought, and human access. The scientific understanding of this heritage (particularly as a record of climate change) and its dissemination must contribute to preserving them from the current irreversible damage and mass spoliation.

This study aims to carry out a geochemical and mineralogical characterization of cave pearls from 15 cavities located within the Orígens Geopark, in the Catalan Pyrennes (NE Spain). The cavities are made of different lithologies (limestones, conglomerates, and sandstones) and include various geomorphological units. The methodology incorporates elemental and mineralogical analyses at both macro and micro scales using XRF, SEM-EDS, XRD, and Raman Spectroscopy, alongside crystallography, X-ray tomography, and advanced 3D imaging techniques. Innovative approaches to imaging and microanalysis will also be utilized.

Our data and analysis show the high richness and geochemical variability of cave pearls in the Orígens Geopark, with high potential to extract useful information about the impact of climate change on karstic systems.