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Alpine valley, like Oldest Dryas
The Oldest Dryas[a] is a biostratigraphic subdivision layer corresponding to an abrupt cooling event, or stadial, which occurred during the last glacial retreat. The time period to which the layer corresponds varies between regions, but it is generally dated as starting at 18.5-17 kaBP and ending 15-14 kaBP. As with the Younger and OlderDryas events, the stratigraphic layer is marked by abundance of the pollen and other remains of Dryas octopetala, an indicator species that colonizes arctic-alpine regions.
In the Alps, the Oldest Dryas corresponds to the Gschnitz stadial of the Würm glaciation. The term was originally defined specifically for terrestrial records in the region of Scandinavia, but has come to be used both for ice core stratigraphy in areas across the world, and to refer to the time period itself and its associated temporary reversal of the glacial retreat.
The bears would not have returned north except in pursuit of food. The tundra must already have been well populated. It is likely that the species hunted by humans at Lake Neuchâtel in Switzerland by the end of the period were present during it. Here are other animals present:
^The standard sequence between about 18,500 and 11,700 years ago is Oldest Dryas (cold), then Bølling oscillation (warming), then Older Dryas (cold), then Allerød oscillation (warming), then Younger Dryas (cold). A few experts (confusingly) use the terms Old or Older instead of Oldest and Middle or Medium instead of Older.
^Clark, P. U.; Shakun, J. D.; Baker, P. A.; Bartlein, P. J.; Brewer, S.; Brook, E.; Carlson, A. E.; Cheng, H.; Kaufman, D. S.; Liu, Z.; Marchitto, T. M.; Mix, A. C.; Morrill, C.; Otto-Bliesner, B. L.; Pahnke, K.; Russell, J. M.; Whitlock, C.; Adkins, J. F.; Blois, J. L.; Clark, J.; Colman, S. M.; Curry, W. B.; Flower, B. P.; He, F.; Johnson, T. C.; Lynch-Stieglitz, J.; Markgraf, V.; McManus, J.; Mitrovica, J. X.; Moreno, P. I.; Williams, J. W. (13 February 2012). "Global climate evolution during the last deglaciation"(PDF). Proceedings of the National Academy of Sciences. 109 (19): E1134-E1142. doi:10.1073/pnas.1116619109. PMC3358890. PMID22331892. Retrieved 2019.
^Roberts, Neil (2014). The holocene : an environmental history (3rd ed.). Oxford: John Wiley & sons, Ltd. p. 98. ISBN978-1-4051-5521-2.