The Ili river delta: Holocene hydrogeological evolution and human colonization

Abstract

Extensive survey of paleocourses of the Ili delta discovered archaeological findings that, chronologically attributed and systematized, allowed the historical reconstruction of the human occupation of the delta. Until recently the colonization was believed to have begun only during medieval times.We argue it began much earlier at the start of the Bronze Age of Kazakhstan (second half of the III millennium BC) under the impulse of new economical activities based on stockbreeding and bronze metallurgy. The basic method of research consisted in surveys, collection of surface finds and documentation of hydrogeological and climatic data. The correlation between the two types of information gives an idea of the factors that influenced the distribution of habitats, mostly represented by winter camps. Their number and concentration change by epoch, pointing to changes in both cultural proclivities and environmental factors. The understanding of the whole historical process requires background knowledge of the hydrological history of the Ili delta, a complex system involving active distributaries and intermittent or inactive paleo-courses, and showing the anticlockwise rotation of 5 successive deltas. Generally speaking, arid climate phases stabilize the delta, pluvial phases favor changes in various directions. Human colonization concerned the two Holocene deltas preceding the modern one: relict terraces of the Uzunaral delta (8–4 ka BP) and terraces of mild active distributaries of the Bakanas delta (4000–250 BP), subject during the last 4000 years to complex geomorphological and hydrological changes that, when reconstructed and correlated with the distribution of finds, explain the location of habitats and allow the mutual chronological attribution of geological and cultural deposits.