Very large cryoturbation structures of Last Permafrost Maximum age at the foot of the Qilian Mountains (NE Tibet Plateau, China)

Unusually large cryoturbation structures (4-4.5 m amplitude), developed in channel gravels and overbank fine-grained deposits of a river terrace on the NE Tibet Plateau, China, were formed by loadcasting as late Pleistocene-age permafrost degraded. It is suggested that the oversaturation and liquefaction of the thawed sediments could have been achieved only if the amount of ice in the upper 4-4.5 m of terrace sediments had been very high. The structures, dated at around 26-20 ka by OSL, point to the presence of a massive icy layer existing within a permafrost body during the Last Permafrost Maximum.