A geoquímica isotópica de espeleotemas na compreensão da dinâmica climática holocénica na região do Monumento Natural Cuevas de Fuentes de León, Estremadura, Espanha

A petrographic and isotopic study of a stalagmite from Los Postes cave, located at the Natural Monument “Cuevas de Fuentes de León”, Spain, was carried out in order to assess Holocene climate changes in the landscape of this area. The stalagmite consists of calcite, but also contains small clasts of quartz, plagioclase, zircon, “terra rossa”, limestone, iron oxides and hydroxides and clay minerals. In the stalagmite, columnar textures tend to yield the lowest δ¹⁸O and δ¹³C values, reflecting relatively slow but constant drip rates. On the other hand, layers with columnar microcrystalline and radial-acicular textures show the highest δ¹⁸O and δ¹³C values and are related to decreasing drip rates. Layers formed by aggregates of detrital materials, cemented with micrite, are associated to low drip rates or even dryness periods. Nevertheless, detrital components should have entered in the system due to seasonal torrentional transport processes. The δ¹⁸O and δ¹³C values co-vary, ranging from -5.17 ‰ to -2.57 ‰ and from -9.34 ‰ and -4.95 ‰, respectively. The petrographic and isotopic data point to a outset of a more dry and warm period beginning at ca. 2,6 ka BP, with δ¹⁸O and δ¹³C values higher than -3.75 ‰ and -6.80 ‰, respectively, which could led to a predominance of C4 plants over C3.