LATE-PLEISTOCENE AND HOLOCENE GEOMORPHOLOGY OF THE DARKHAD BASIN, MONGOLIA: IMPLICATIONS FOR HUMAN SETTLEMENT PATTERNS

Changing environmental conditions and basin evolution influence archaeological site distribution as the culture and its needs change through time. The Darkhad Basin, located in northern Mongolia, has a geomorphic history that is strongly tied to paleoclimate and changing lake levels. Previous work has documented the Late Pleistocene and Holocene changes of the paleo-lake Darkhad, which occupied large parts of basin. These varying lake levels resulted in upstream changes in the fluvial systems as the drainages responded to the evolving base level. In turn, the formation of new landforms and evolving water sources affected the distribution of human occupation across the landscape. This study focuses on integrating aerial image interpretation, surface geomorphology and archaeological survey, geochronology, and excavations of both geological test pits and archaeological sites to understand the interplay between the formation of Late Pleistocene and Holocene landforms and human occupation.

We focused on two sites near the southwestern end of the basin, Soyo and Bagsgiin Bulan, which record evidence of human occupations spanning from >10 ka to the present. These sites are located on glaciofluvial outwash terraces of different ages that formed after the last glacial maximum (LGM). At both sites, an upper paleosol marks the most recent surface of human occupation, which is now capped by <50-cm-thick aeolian dunes near the river margin, but merges with the present day surface <100 m from the sites. The stratigraphy beneath the sites is broadly similar, with interbedded fine sands and conglomerates interpreted to be glaciofluvial in origin. At Soyo, excavations yielded artifacts indicative of human occupation from multiple levels dating back to >10 ka within an overall more complex stratigraphy. In contrast, at Bagsgiin Bulan, artifacts from excavations of a structure were dated to ~4500 BP. We propose that the widespread terrace surfaces selected for site occupation were formed by paleoclimatic and lake level changes within the basin between the end of the LGM (11-18 ka) and the middle Holocene (4-5 ka), and the surfaces were occupied shortly after their formation.