Improving archaeological site analysis: a rampart in the middle Orkhon Valley investigated with combined geoscience techniques

Abstract

The Orkhon Valley in the Central Mongolia was included in the World Heritage list in 2004. It hosts multiple archaeological sites from Palaeolithic to recent times, which can contribute to the reconstruction of settlement history in this part of the Eurasian Steppe landscape. Almost 100 archaeological sites from prehistoric and historic times including ramparts and khirigsuurs were investigated in five field campaigns from 2008 to 2010 in the middle and upper Orkhon Valley. One site, MOR-2 (Dörvölzhin), proved especially difficult to date due to the lack of sufficient archaeological surface finds, and its role within a manifold of walled enclosures from different times in the study area remained unclear. Therefore, different techniques of archaeology, geophysics and geoarchaeology were combined at MOR-2 in order to determine a comprehensive picture about its timing, archaeological meaning, and environmental history. Information on topographical setting and morphometry of the rampart was gathered by an octocopter equipped with a high-resolution range finder camera. We achieved a high-resolution DEM that allowed us to map the rampart in detail and this served as a base map for all other investigations. SQUID magnetometry, ground-penetrating radar, and electric resistivity measurements (capacitive coupled geoelectrics) were subsequently used to detect archaeological remains and to characterize the sediment distribution of the inner part of the enclosure and the ramparts themselves. The data show that the construction of the walls is similar to well-known Uighur neighbouring sites. Man-made sub-surface structures or bigger finds could not be detected. Sediment cores were drilled in a nearby meander, covering 3000 years BP. The analysis of the strata in terms of elemental composition (P, N, Mn, Fe, etc) revealed an increase of organic content in Medieval times, whereas the allochthonous filling of the back water must have started around the beginning of the 6th century AD. Using geophysical, archaeological and geological observations, we assume a dating in the Turk/Uighur period (6th–9th century AD) and a re-use under Mongolian reign (12th–17th century AD). This would mean that this site is the furthermost walled structure in the peri-urban area of Khar Balgas. However, the specific usage of this walled enclosure remains unclear and needs further analysis.