Multi-Proxy Study of a Holocene Soil Profile from Romania and Its Relevance for Speleothem Based Paleoenvironmental Reconstructions

• Main Authors: Luchiana Faur, Virgil Drăgușin, Daniela Dimofte, Ferenc Lázár Forray, Maria Ilie, Constantin Marin, Cristian Mănăilescu, Ionuț Cornel Mirea, Cristian George Panaiotu, Barbara Soare, Alida Timar-Gabor, Maria Laura Tîrlă
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Minerals
• Subjects: soil; clay minerals; Holocene; stable carbon isotopes; speleothems
• Online Access: https://www.mdpi.com/2075-163X/11/8/873

In this study, we describe a sedimentary deposit situated above Ascunsă Cave (SW Romania) that should be in depositional connection with coeval stalagmites from the cave. We excavated a 2.5 m deep soil profile and took contiguous bulk samples every 5 cm. Soil samples were analyzed for clay mineralogy, grain size, chemical composition, magnetic susceptibility, and stable carbon isotopes. Radiocarbon dating revealed that the soil is of Holocene age, and presents a depositional hiatus between 5.4 and 2.3 thousand years before the present. Due to the open system behavior of soils and mobility of organic matter, a few hundred years of uncertainty should be considered for the duration of this hiatus. The fine fraction is dominated by silt, while the clay mineralogical association is made of illite, chlorite, kaolinite, vermiculite, and illite–vermiculite and illite–chlorite mixed layered minerals. The sediment source of this soil is represented by a nearby mélange complex, as well as by an underlying terra rossa-type soil. As this latter type of soil is widespread in our study area, we performed luminescence dating on two samples from a representative location close to our site and it appears that this type of Mediterranean soil was formed during the Last Interglacial period. δ¹³C variability in soil organic matter and a stalagmite from the cave are comparing well, and could help future studies identify modifications in isotopic fractionation processes within the cave.