Paleosols Of Archaeological Sites In The Sochi Black Sea Coast

Abstract

The paper provides the distinctive characteristics of several paleosols of the Sochi Black Sea coast of Russia. The authors explored two paleoalluvial soils (Histosoils (Folic)) in the open archaeological pits of ancient encampments (aged 8.3 and 24.5 thousand years) and the middle argic horizon Acrisols (Clayic) buried under the foundation of an ancient fortress (at the age of about 1600 years). Traditional soil methods were employed to reveal the morphological, chemical, microbiological properties of paleosols. Mass-spectrometry and atomic emission analyses with inductively coupled plasma enabled examination of their content for 61 chemical element. Comparison of paleoalluvial soils with their modern analogs revealed: 1) a reduced content of humus (1.4 times on average) and actual soil acidity (pHaq changed from 7.3 to 7.8 on average); 2) a decreased species richness of prokaryote microbiome (the index of operational taxonomic units was reduced 1.7 times on average) and a stable inhibition of a species of the Thermoleophilia class, Gaiellaceae family; 3) an increased content of some elements (Ca, Zn, Ba, Cu, Sr 3.0, 2.9, 1.8, 1.8, 1.7 times on average, respectively); 4) an increased content of exchangeable phosphorus (2.3 times on average), an additional source of which was bone remains of ancient animals hunted by humans. It is unique that the effect of rare earth element fractionation in organomineral horizons of paleoalluvial soils manifested itself as a positive europium anomaly (Er/Er*=1.3–1.1). All the examined paleosols showed lower contents of the rare earth elements group (REE) versus modern soils, due to the specific formation of their complex compounds. REEs are more active than other microelements in forming organic complex compounds with the nonspecific acids, which are released by living roots and generated during fresh plant litter decomposition. Hence, serving as ligands, REEs are accumulated in the complex compounds in modern soils. In paleosols their content is decreased.