Pedosedimentary and climatic reconstruction of the last interglacial and early glacial loess–paleosol sequence in South Tadzhikistan

Abstract

The thick loess–paleosol-sequences in Tadzhikistan, which indirectly record the environmental changes from the Upper Pliocene to the present-day, have been extensively described from a chronostratigraphical and archaeological point of view. The genesis of the soil-sedimentary complexes and their implications for palaeoenvironmental reconstruction in Tadzhikistan, however, have been considered only relatively recently [Bronger, A., Winter, R., Derevjanko, O., Aldag, S., 1993. Loess–paleosol sequences in Tadjikistan as a palaeoclimatic record of the Quaternary in Central Asia. Quaternary Proceedings 4, 69–81; Lomov, S.P., Tursina, T.V., Zhou, L.P., 1996. Magnetic susceptibility of soils: Micromorphology and possible reconstructions of climate. In: Soil micromorphology. Studies in Soil Diversity, Diagnostics, Dynamics, 10th International Working Meeting on Soil Micromorphology. Moscow, Russia, July 8–13, 1996, p. 145]. The pedocomplex of Last Interglacial and Early Glacial age (Oxygen Isotope Stage 5) in the Tagidjar and Darai Kalon sections near the town of Khovaling is represented by three major stages of soil formation. The soil characteristics have been micromorphologically analysed. The distinction between primary and secondary carbonates is of major importance to understand the soil forming processes. The relative distribution of needle fibre calcite (NFC), micritic infillings (M), hypocoatings (CHC), coarse calcitic grains (CCG) and calcified root cells (CRC) provides detailed insights into the environmental conditions prior, during and following pedogenesis. The abundance of coprolitic aggregates (CA) and pupal chambers gives a clear indication of the rate of biological activity which prevailed during the last two soil forming stages. Void pseudomorphs after gypsum crystals ( gypsum pseudomorphs) are frequently observed beneath the Cca horizons of the paleosols. Using the present-day climate and soilscape as a reference base, the obtained pedosedimentary events detected in the Tadzhikistan sections provide a detailed palaeoenvironmental record. Indeed, glacial and interglacial climates and soils respond to contemporaneous climatic schemes and soil forming processes, which are still active in the region today. The amount and the seasonal variability of precipitation, mostly, are at the origin of the variable soils formed during glacial and interglacial ages.