Onset of intense permafrost conditions in Northern Eurasia at ~2.55 Ma seen in a cryogenic weathering record from Lake El'gygytgyn

Abstract. Physical weathering in permafrost landscapes contrasts to mid- and low latitude physical weathering in the way that quartz is less stable in freeze–thaw (F/T) cycles and breaks down to silt sized grains. F/T weathering also produces a distinct single quartz grain micromorphology such as microcracks and brittle textures of the surface. Both of these sediment-mineralogical features have been used for identifying intense permafrost conditions (i.e. intense F/T dynamics) around Lake El'gygytgyn in NE Eurasia using a Pliocene–Pleistocene sediment record from the centre of the lake. This lake provides the longest terrestrial palaeoenvironmental archive in the Arctic and has been a sediment trap for 3.6 Ma. Detritic material marked by F/T weathering becomes distinctive ~2.55 Ma ago and has been accumulating since then in the lake basin. This time marker coincides with the establishment of a perennial lake ice cover and corresponds with pollen assemblages indicating a significant cooling during that time. It matches fairly well the timing of the Plio-/Pleistocene cooling known from other marine and terrestrial evidence.

The onset of intense quartz weathering is regarded as a first order age assessment for the beginning of persistent Quaternary permafrost conditions and which deepened into the ground since then in settings of high continentality in the non-glaciated NE Eurasian Arctic.