Search Results (2)

Las Loras UNESCO Global Geopark (UGGp) is geologically diverse, particularly in relation to water-derived features: springs, karst springs, travertine buildings, waterfalls, caves. In this work, the interactions between geology, geomorphology, structures and hydrogeology are analyzed. As a result of this study, a first conceptual model of the hydrogeological functioning at Las Loras UGGp is presented. The most plausible hypothesis is that the system is formed by two superimposed aquifer systems, separated by an aquitard formed by Lower Cretaceous material. The deep lower aquifer formed by the Jurassic limestones only outcrops on the northern and southern edges of the Geopark and in a small arched band to the south of Aguilar de Campoo. It forms a basement subject to intense deformation. The upper aquifer system, formed by outcropping materials from the Upper Cretaceous, is a free aquifer. It is formed by a multilayered aquifer system that is highly compartmentalized, constituting individual moorland and lora units acting as a separate recharge–discharge system. This model explains the base level of the permanent rivers and the abundant springs, important components of the water cycle and representing a contribution to the rich geological heritage of the location. Full article

Banded travertines are important parts of fissure ridge systems, but studies on geochemical characterization of banded travertines are limited. This study investigated the lithofacies and stable carbon and oxygen isotopic features of banded travertines from Xiagei (southwestern China) to examine their formation mechanisms. Petrographic analyses of the banded travertines revealed two lithotypes: thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust. δ¹³C and δ¹⁸O of the Xiagei banded travertines range from 2.82‰ to 4.50‰ V-PDB, and from −25.86‰ to −20.90‰ V-PDB. Parent CO₂ evaluation shows that the Xiagei banded travertines mainly received CO₂ from the decarbonation of marine carbonates, but the contributions of magmatic CO₂ and the dissolution of marine carbonates are also unneglectable. Significantly, the magmatic-derived CO₂ might indicate that the delamination of the lithosphere along with the asthenosphere upwelling could be taking place in the eastern Tibetan plateau. Paleotemperature calculation shows that the Xiagei travertines were precipitated from moderate- to high-temperature hot springs (44.3 to 86.8 °C). Interestingly, the thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust display calculated paleotemperature between 66.6 and 86.8 °C and between 56.6 and 77.7 °C, respectively, reflecting the great role of water temperature in controlling the lithofacies of banded travertines. A comparison between the banded travertines at Xiagei and other areas also shows temperature is a non-negligible factor controlling banded travertine precipitation. However, this does not mean that water temperature is the decisive controlling factor and more studies on banded travertines are still indispensable to disclose the potential factors controlling the factors/processes affecting banded travertine lithofacies. This study provides a good example for understanding the relationship between lithofacies and stable isotopic geochemical characteristics of travertine deposits. Full article