DESERT PAVEMENTS AND THE FORMATION PROCESSES OF THE EARLIEST ARCHAEOLOGICAL SITES IN THE ATACAMA DESERT, CHILE

We investigated site formation and modification of surficial and shallow Paleoindian sites (ca. 13-11.5 cal. ka) located in the hyperarid core of the Atacama Desert. Sites occur primarily on inactive Pleistocene to Pliocene alluvial terraces, in and beneath desert pavements, a sparsely studied context for archaeological sites. Our research reveals that desert pavements in the region are unusual and poorly developed: clast densities in pavements average ~30% and clast size averages 5-7 mm, regardless of surface age and of human disturbance; and vesicular A horizons are scarce and patchy even in the oldest terrace. This is very different compared to mature pavements in other deserts, where clast densities are >80%, and A horizons can be thick and rich in vesicles. When comparing natural pavements and those altered by pre-Hispanic humans, however, subsurface disturbance of the vesicular horizons and soils rich in thenardite (Na₂SO₄) is extensive. Additionally, the highest density of archaeological materials, particularly lithic artifacts, is on the surface, indicating that artifacts are being pushed upwards, possibly due to earthquakes and salt expansion and contraction, thus regenerating the pavements after site abandonment. But, features such as wooden posts and prepared fireplaces dug into the cemented Byz horizons remained in situ and engulfed in salts. We believe that the uniquely arid and salt-rich conditions of the Atacama slow and inhibit the process of both pavement formation and healing.