PaleoVertisols of the northwest Caucasus: (Micro)morphological, physical, chemical, and isotopic constraints on early to late Pleistocene climate

Physical and chemical properties, macro‐ and micromorphology, clay mineralogy, and stable‐isotope compositions of paleosols within a pedostratigraphic column (PSC) of early to late Pleistocene age, interstratified paleosols, and loess (NW Caucasus, S Russia) were examined to better understand the evolution of the pedogenic environment over this time period, separating the effects of postpedogenic diagenesis. The column includes eight paleosols and six intercalated loessic horizons. Most of paleosols represent Vertisols or vertic intergrades. Vertic features increase in the middle of the PSC, where the paleosols are more clayey in texture and reddish in color. The morphology of carbonate nodules and soft masses, morphology‐ and depth(age)‐related changes in stable C and O isotope compositions, soil color, redoximorphic features, clay mineralogy, and illuviated clay indicate periods of wetter pedoenvironment in the past and suggest the Pleistocene paleosols are polygenetic and were formed with several wet/dry stages under a climate generally similar to the modern environment in the N Caucasus (mean annual temperature approx. 9°C–12°C). Interpretation of the time sequence of climate/environmental change requires careful separation of pedogenic mineral phases from phases altered by later diagenesis. The early Pleistocene period of paleosol formation appeared to be wetter or more humid, resulting in more significant development of vertic features. The terrestrial ecosystem remained dominated by C3 vegetation throughout the formation of the PSC, with four small periods of change towards a greater proportion of C4 plants or increased moisture stress.