## 6 Discussion and Conclusions
These discontinuity planes act similar to preferential water accumulation areas, in such a way that the action of the winter freeze-thaw cycles becomes more effective and the flakes formation and separation phenomena are more common;
* At the same time, the splitting away of the flakes leaves areas of fresh rock once more exposed to chemical alteration;
* The releasing of Ca\({}^{2+}\) and HCO\({}_{3}\)- by the feldspars carbo-hydrolysis favours a greater development of the bio-induced carbonate crusts. This in turn has an incrusting effect and favours the physical and chemical attack processes towards the interior of the rock. With respect to the rates of weathering, the preservation of rock paintings denotes low rates of weathering, at least in the immediate host rock. Although no data are available in the form of old photographs, for example to quantify the alteration, the existence of hardened rinds lining a large part of the walls of the shelters of alveolar structures on the walls and ceilings of same and biological colonisation are indicative of slow rates of alteration in the shelters [13; 36; 72]. The rates of alteration would vary as a function of the climatic and geographical contexts and the lithological and geomorphic characteristics of the host rock, generally ranging from microns to a few millimetres a year [13; 73; 74]. In the present case, considering both art sites, climate is the most important controlling factor in the rates of alteration as indicated previously. However, considering each shelter separately, the major influence of other local factors can be observed, both in the types and rates of alteration. In this way, it may be stated that in shelters 24 (facing W) and the Cueva del Arco, given that they have a greater effect of natural light, the rates of alteration (in particular, biotic) are relatively greater. On the other hand, in the case of the Cueva del Tajo de las Figuras, the biotic alteration through micro-organisms is restricted, given its nature of a more enclosed shelter. For shelter 17, its closeness to floor level causes the alteration in the lower part to accelerate with regard to the rest of the shelter due to the greater degree of humidity [32]. It is necessary to note that these relatively low rates of alteration correspond to the more recent evolution of the shelters, at least that which is clearly later than the time that the paintings were executed (Epi-Palaeolithic-Neolithic). The genesis of rock shelters probably dates from the humid and glacial cold stages of the Quaternary, when mechanical alteration processes (freeze-thaw cycles) were predominant and the rates of alteration were considerably greater. The alteration features found in the different shelters mainly correspond to natural physical and chemical phenomena. For this reason, corrective measures are difficult to apply without producing unforeseen consequences. Presently, the state of conservation of the paintings is not bad. Natural weathering processes can be considerably accelerated by both anthropic and animal activity. Anthropic action can be direct (wetting and rubbing against the paintings, lighting of fires) or indirect (removal of blocks of sandstone from the ceilings of the shelters). Large animals can produce alteration by different actions (rubbing, defecation, building of nests, etc.) which are particularly harmful for this type of artwork. Conceptualisation, J.C.C. and S.S.-M.; Investigation, J.C.C., S.S.-M. and E.S.-R.; Writing-original draft, J.C.C., S.S.-M. and E.S.-R. All authors have read and agreed to the published version of the manuscript. This study forms part of the research agreement \"Study and diagnosis of the archaeological groups and deposits of the Autonomous Community of Andalusia in their geomorphological, biological and climatic contexts\" financed by the Culture Council, Junta of Andalusia (Spain). Not applicable. The authors declare no conflict of interest.