The extent of permafrost during the Last Permafrost Maximum (LPM)on the Ordos Plateau, north China

This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM)permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23–19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N.