Formation Chronology of Arsain Pingo, Darhad Basin, Northern Mongolia

Numerous frost mounds exist on the meander belt and alluvial fan around Arsain Gol River in Darhad basin, northern Mongolia, at the southern fringe of the north‐eastern Eurasian permafrost zone. In this environment, abundant water supply and inter‐permafrost taliks may allow the development of artesian pressure that leads to groundwater upwelling. The aim of this study was to determine the formation chronology of pingos in this region. The Arsain pingo was drilled to a depth of 35 m to determine the stratigraphy, and data were collected on ground‐ice stable isotopic composition, electrical resistivity, ground temperature, and radiocarbon dating and interpreted in conjunction with the chronology of paleo‐lake retreat in the basin. A 10 m thick ice core sandwiched between fine‐grained lacustrine sediments was identified by drilling and electrical resistivity tomography (ERT). Stable isotope values of ice core samples indicated Rayleigh‐type isotope fractionation during the freezing of liquid water. Consequently, closed‐system freezing of artesian groundwater appears to be the driving mechanism of pingo formation. Near‐surface, segregated ground ice formed from the open‐system freezing of meteoric water, concurrent with pingo growth. The lake coverage was extensive until about 10,000 years before present (yr bp), and the growth of the Arsain pingo began after 4500 yr bp, when the paleo‐lake was completely drained. The pingo is not presently growing because of a limited groundwater supply to feed the ice core. Copyright © 2015 John Wiley & Sons, Ltd.