Luminescence age and palaeoenvironmental implications of a late Pleistocene ground wedge on the Northeastern Tibetan Plateau

• Published in: Permafrost and Periglacial Processes
• Main Authors: Porter, Stephen C., Singhvi, Ashok, Zhisheng, An, Zhongping, Lai
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2001
• Subjects: Arctic; Bajada; Gravier; Coin de glace; Ice; permafrost; Permafrost and Periglacial Processes; wedge*; pergélisol
• Online Access: http://dx.doi.org/10.1002/ppp.386; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fppp.386; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppp.386

Abstract A periglacial ground wedge in bajada gravel near the northern base of the Qinghai Nan Shan underlies loess of late‐ and postglacial age. The composition and structure of the wedge fill are consistent with an ice‐wedge origin, implying former permafrost and relatively moist conditions at this locality. A luminescence date of 15,100±1600 years from the wedge fill marks the end of ice‐wedge activity, which is inferred to have been during the last glaciation. The present mean annual air temperature (MAAT) (−0.7 °C) is too high to produce frost cracking and ice‐wedge formation, but snowline depression of ca. 700–800 m in the adjacent mountains is consistent with a reduction in MAAT of at least 3.8 °C during the last glacial maximum. Such a temperature depression would reduce MAAT to values equivalent to Arctic regions now experiencing active ice‐wedge growth. The absence of loess of full‐glacial age and the presence of a weakly developed palaeosol atop the bajada gravel imply a stable, cold land surface. Qinghai Lake, although reduced in size at that time, likely raised local humidity to levels that favoured ice‐wedge growth in this low‐altitude sector (ca. 3000–3400 m) of the Tibetan Plateau. Copyright © 2001 John Wiley & Sons, Ltd. Résumé Près de la base septentrionale de Qinghai Nan Shan, un coin périglaciaire a été observé dans le gravier d'une bahada recouverte de loess tardi‐ et postglaciaire. La composition et la structure du remplissage du coin peuvent s'expliquer par le développement d'un coin de glace, ce qui implique l'existence autrefois d'un pergélisol et de conditions relativement humides. Une date de 15.100 +/− 1600 ans a été obtenue par luminescence pour le remplissage cette date marquerait la fin de l'activité du coin de glace qui serait, de ce fait, apparu pendant la dernière glaciation. De nos jours, la température moyenne annuelle de l'air (MAAT) est de −0.7 °C, température trop élevée pour produire la fissuration par le gel et la formation d'un coin de glace toutefois, ...