Loess sequences in southern Tajikistan, central Asia are characterized by the occurrence of alternating loess and pedocomplexes, a feature which is similar to that in the Loess Plateau of north-central China. Previous studies of Tajik loess revealed that below the third pedocomplex (PC3), the loess units and pedocomplexes have distinctly lower magnetic susceptibility than the upper part. No conclusive consensus has been reached on the paleoclimatic interpretation of such a pattern. Here, results of a systematic mineral magnetic study in combination with spectrophotometric measurements on selected samples from Darai Kalon loess section in the southern Tajikistan, central Asia are presented. The mineral magnetic properties suggest increasing concentrations of the ferromagnetic minerals as well as the superparamagnetic and single domain magnetic grains, together with the decreasing hard magnetic components (i.e. contents of hematite or goethite), from the lower part to the upper part of the sequence, which would point to enhanced pedogenesis through time. Such paleoclimate inference is supported by the higher content of hematite in the lower part of the sequence on the assumption that higher temperature and lower precipitation favor the formation of hematite. In this case, the dry climate in the lower part leads to weak pedogenesis. Therefore, there are less superparamagnetic and single domain magnetic grains, which are responsible for the reduced magnetic susceptibility in the lower part. However, the upwards decreasing goethite content revealed by the measurements of diffuse reflectance spectrophotometric data suggests a change towards a drying climate, as formation of goethite requires wet conditions. In this case, the lower magnetic susceptibility below the PC3 may be manifestation of dissolution of superparamagnetic and single domain magnetic grains due to a prevailing humid environment. While the high field (up to 2 Tesla) isothermal remanence shows that the upper part has a lower content of hematite-dominated hard magnetic components, the poor correlation between redness (a*) and the content of hematite in the upper part indicates the strong influence of the matrix effect in the diffuse reflectance spectrophotometric data. Hence, there exists a major uncertainty in the interpretation of the spectrophotometric result of hematite. The overall good negative correlation between the content of goethite and magnetic susceptibility may be interpreted as indicating a trend of drying climate from the lower part to the upper part of the sequence. Such an interpretation is compatible with previous palynological and geochemical studies in the region. This study highlights the complication in the paleoclimate interpretation of the magnetic susceptibility and even mineral magnetic data for loess-pedocomplex sequence in southern Tajikistan. It calls for caution in the application of the models based on the magnetic investigations of Chinese loess and indicates the need of the use of the multiple proxies.
