Geochemical records from loess sediments provide insights into early hominin influence on the landscape in the Khovaling region of Southern Tajikistan, Central Asia

Abstract

This study presents a multi-proxy investigation of loess-paleosol sequences from the Khovaling Loess Plateau (KLP) in southern Tajikistan to explore long-term human-environment interactions during the Early Paleolithic. This region has been the focus of numerous archaeological projects since Soviet times, as it contains evidence of some of the oldest ([~]0.9 Ma) hominin occupations in Central Asia and is one of the key regions connecting eastern Asia to centers of hominin evolution that lie to the west. Previous archaeological expeditions have discovered rich collections of stone tools from alternating non-pedogenically modified loess and paleosol sequences at the archaeological sites of Karatau, Lakhuti, Obi-Mazar, and Kuldura. We analyzed lipid biomarkers such as n-alkanes, polycyclic aromatic hydrocarbons (PAHs), together with newly generated stable isotopes ({delta}{superscript 1}3C, {delta}{superscript 1}N), magnetic susceptibility, and archaeological assemblages from three sites: Obi-Mazar/Lakhuti (on-site), and non-artifact-bearing strata from Kuldara (near-site) and Khonako-II (off-site), focusing on pedocomplexes (PCs) 4, 5, and 6 and their intercalated loess layers. High odd-over-even predominance (OEP) and average chain lengths (ACL) suggest that soil organic matter is predominantly derived from higher-order terrestrial plants, with better preservation in paleosols compared to loess layers. The inverse correlations of {delta}{superscript 1}3C with TOC and C/N reflect organic matter degradation, while elevated {delta}{superscript 1}N in paleosols suggests enhanced nitrogen cycling under warmer and drier conditions. Magnetic susceptibility and {delta}{superscript 1}3C trends reveal a progressive shift toward open grassland ecosystems since [~]0.8 Ma, with intensified pedogenesis during interglacial stages MIS 11, 13, and 15. The spatial distribution of PAH concentrations and lithic artifact densities further highlights human-environment interactions in the KLP locality. Obi-Mazar exhibits abundant lithic materials and high PAH levels, indicating repeated occupation and frequent burning in a resource-rich riverine setting. Kuldara exhibits moderate PAHs but minimal artifacts, whereas Khonako-II records only a minimal level of signals, reflecting a decrease in human impact with distance from the water source. Together, these findings demonstrate that Early Paleolithic hominins preferentially occupied ecologically stable, pedogenically developed zones during interglacial phases, contributing to localized fire regimes and shaping their landscapes. This study provides a refined paleoenvironmental framework for understanding hominin adaptations in Central Asia during the Pleistocene.