Abstract
The article presents the results of soil and archaeological study of the pedo-sedimentation sequence formed in the floodplain of the Derkul River (West Kazakhstan). The aim of the study was to reconstruct the stages of the alluvial sedimentogenesis alternating with relatively prolonged spans of soil formation, corresponding to the periods of floodplain agricultural development. It was established that floodplain sediment layer started to form as a result of stream sedimentation in the early Holocene; then this stage was followed by the relatively long-term soil formation period (5.6–3.8 cal. yr BC) resulting in a humus quasi-gleyic soil in the low floodplain (120–200 cm). The last period of soil formation (4.6–3.6 cal. yr BC) the floodplain was developed by man, which is displayed by the identified cultural horizon containing artifacts and having increased phosphorus content. At the end of the Subboreal period the next stage of alluvial sedimentation, started by the changed river hydrology regime, was found to be chronologically separated from the stage of stationary development of the floodplain by settled humans.