Natural and anthropogenic effects on the elemental compositions of surficial sediments across Tajikistan, Central Asia

Abstract

The elemental compositions of surficial sediments are conducive to understanding various environmental conditions and surface processes. Tajikistan is situated in Central Asia. The eastern region of Tajikistan locating on higher-altitude Pamir Plateau has a dry and cold climate, whereas the western part has a contrasting natural environment and most populations live in this region. To investigate the effects of natural and anthropogenic processes on the elemental compositions of surficial sediments across Tajikistan, this study examines the major, trace and rare earth elements (REEs), and grain size distributions of various types of surficial sediments (e.g., topsoil, fluvial, lake sediments, loess deposit, and bedrock sample). We find that most of the topsoil and fluvial sediments show spatially homogeneous elemental compositions in Tajikistan. The source bedrocks of these various sediments are primarily felsic. Although the sediments in the western region display slightly higher chemical weathering intensity, the sediments across Tajikistan have experienced the overall incipient chemical weathering intensity and weak sorting process. In comparison with topsoil and fluvial sediments, elemental compositions of lake sediments are complex due to the differential proportions of terrigenous detritus with physical and chemical weathering of the bedrock in the catchment. The surficial sediments in western Tajikistan show higher Cd concentrations. The good correlations between Cd, lithogenic element Ti and Chemical Index of Alteration (CIA) suggest that Cd is largely derived from the underlying bedrock and positively correlated with the slightly higher chemical weathering intensity in this region. In addition, anthropogenic input likely contributes to the unusual Cd contamination of the sediments in the western Tajikistan where industrialization has been well-developed.