Climate, fire, and vegetation history from loess-palaeosol sequences in Southern Tajikistan, Central Asia during early Palaeolithic: Reconstruction using organic biomarkers and stable isotopes

We reconstruct palaeoenvironmental conditions with multi-proxy records from loess-palaeosol settings in Tajikistan, Central Asia. Landscape conditions in this area are poorly characterised, ambiguous, and difficult to determine, which confounds models of human dispersal out of Africa. This region has been the focus of Russian-Tajik archaeological projects since the 1970s, as it contains evidence of some of the earliest (~600-400 ka) hominin occupations in Central Asia and has yielded numerous Lower Palaeolithic artifacts. In the present study, fire and vegetation biomarkers and stable isotopes have been used to reconstruct fire and vegetation histories in loess-palaeosol samples of early Palaeolithic sites in the vicinities of the Obi-Mazar River in the Khovaling district of southern Tajikistan. Samples from four loess-palaeosol documented profiles were analysed for linear chain alkanes (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs) together with soil stable isotopes (δ¹³C, δ¹⁵N). The fluctuations in the values of n-alkane derived indices showed vegetation changes in concert with glacial-interglacial variability. The δ¹³C values fell between -20‰ and -25‰ (vs. PDB) and revealed mixed input of C₃ and C₄ plant organic matter into loess-palaeosol sediments, while δ¹⁵N values varied between 3.5‰ and 6.5‰ (vs. AIR) indicating high litter content and tree abundance. The fluctuations in total PAH abundance and increased low to high molecular weight ratio values revealed fire activity and lower temperature burning events during interglacial periods relative to glacial periods.  Moreover, the strong positive correlation between PAHs and deposits that hosted the densest artifact assemblages signals early hominin use of fire in the catchment during MIS 11, 13, and 15. Therefore, our study demonstrates substantial hominin influences on the environment dating to over 500 ka indicating human-ecological processes far predate the modern era.