First tree-ring chronology from Andronovo archaeological timbers of Bronze Age in Central Asia

Abstract

We crossdated spruce ( Picea schrenkiana) tree rings of archaeological timbers from the Asi-2 settlement and Turgen-1 barrow associated with the Andronovo in the Tian-Shan Mountains, an archaeological culture known for the development of pastoral transhumance in this particular area of the Eurasian steppe, in order to establish a chronological framework for the Bronze Age period of southeastern Kazakhstan. Age of the Asi-2 semi-subterranean house was determined by radiocarbon dating between ca. 1610 and 1490 cal. BC, which places the settlement in the transition between the Middle Bronze Age and Late Bronze Age. Sixty-two percent of tree-ring specimens (20 wood samples) collected from construction timbers of a collapsed roof, entryway and an interior wall of the house were suitable for crossdating. The crossdating success resulted in developing a 121-year tree-ring width chronology of the Asi-2 house and a 101-year tree-ring width chronology of the Turgen-1 barrow. The archaeological tree-ring width series have high mean sensitivity (0.2–0.4) and significant values of interserial correlation that indicate strong common signal in variance of the tree-ring indices. The archaeological timbers from the house and burial mound construction appear to have been cut in a closed-canopy stand of young spruce trees (40, 80 and 100-years old) at this high-elevation locality (2400 m asl). The Ulken tree-ring width record developed from modern spruce subalpine forest growing on a steep slope just 300 m above the archaeological site (2610–2760 m asl) showed a strong negative relationship with April temperature, mainly ( R=−0.61, R 2 adj.=0.37, F (1,59)=35.03 at p<0.000). This is contrary to positive relationship between tree-ring widths and summer temperature that have been previously reported for the Tian-Shan upper tree-lines in the region. This negative relationship could be related to spring moisture stress when the growing season starts in April with mean daily temperature range from 4.4 to 9.9 °C and merely 50 mm of monthly precipitation. Likewise, tree-ring width variability in the archaeological records could be dominated by moisture availability in the area. This provides a framework of archaeological tree rings for modeling migration patterns of ancient cultures in search of pastures and water. The study suggests good dendrochronological potential of archaeological timbers from Andronovo archaeological sites of this region. We discuss peculiarities in application of climatically sensitive spruce tree rings to developing an Andronovo absolute chronology and reconstructing environmental changes for the 2nd millennium BC in Central Asia.