Insights into the Phaeozems pedogenesis using total elemental composition analysis. A case study from north-eastern Romania

Phaeozems with very deep mollic topsoil overlying a cambic B horizon occur in a patchy distribution in Eastern Romania, in areas where present climatic conditions are rather favourable for forest soils development. Due to their unusual characteristics, it has been hypothesized that the main factors implied in their development could be related to the prehistoric habitation and climate changes during the Holocene, but this approach was never explored. In this context, an archaeological excavation into an Eneolithic (5000-3500 BCE) settlement located in north-eastern Romania offered the opportunity to investigate pre- and post-Eneolithic development of these soils. Fifty soil samples were collected above and below an Eneolithic dwelling floor, between adjacent dwellings and by off-site sampling. A portable X-ray fluorescence (pXRF) spectrometer was used to scan the soil samples and the total element composition of 18 elements was retained for subsequent statistical analysis. The main objective of this study was to analyse the depth functions of elemental contents in relation to the morphological characteristics of these soils in order to infer the pedogenic pathways of their formation. Results showed increased concentrations of P, Sr, Ca, Cu and Zn above the Eneolithic layer relative to the control soil profile, as a result of both prehistoric and recent anthropogenic activities, but similar trends bellow the dwelling remnants and between adjacent dwellings, which suggest the relict character of the pre-Eneolithic soil. The geogenic elements like Al, Fe, K, Rb, and V are highly correlated, have similar curve shapes in all analysed profiles and generally increase with depth, starting from the pre-Eneolithic land surface. The variability of Ti, Zr and Ti/Zr ratio shows a clear contrast in the upper part of soil profiles and a similarity below the Eneolithic level. Statistical analysis also confirms at least two major phases in the evolution of these soils. The application of the Pettitt test placed most of the elemental changes at the depth were the upper soil welded to the buried Eneolithic soil. Therefore, our study demonstrates the utility of Pettitt test in detecting pedogenic thresholds, besides its traditional use for time series analysis. The characteristics of the pre-Eneolithic soils support the hypothesis that they were already formed in the mid-Holocene, which constituted the prerequisite for the beginnings of human habitation and agriculture in this area. It can be concluded that the successive changes of climate and the land use since the midHolocene until present are likely the main factors that controlled the formation of the upper part of these overthickened soils, resulting in an incipient Luvic Phaeozem, which extended and welded downward to a relict Cambic Chernozem.

Automated summary

The study in Eastern Romania investigated Phaeozems with deep mollic topsoil and cambic B horizon, suggesting that prehistoric human habitation and climate changes during the Holocene played a role in their development. Soil samples from an Eneolithic settlement were analyzed, showing differences in elemental contents above and below the dwelling remnants, indicating two major phases in the evolution of these soils. Results also suggest that climate and land use changes since the mid-Holocene controlled the formation of the overthickened soils.