Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tThe majority of the results points to extensive thermalcontraction cracking during Marine Isotope Stage (MIS)2 (Late Pleni-Weichselian–Lateglacial), peaking around15,000 and 20,000 years ago (Fig. 2). A few data evensuggest the possibility of earlier phases of wedge growth(during MIS 3 or Middle Pleni-Weichselian and MIS 6 orSaalian) (Fig. 3).Figure 2. Vertical cross-section of a complex wedge comprisinga relict sand wedge (AAL4) which dissects an older compositewedgepseudomorph (AAL3), Low-Belgium. Numbers refer to theOSL ages (Buylaert et al., accepted).Figure 3. Schematic cross-section of Quaternary depositsshowing different wedge levels. Grey wedges indicate wedgeswith a composite infilling. OSL dates are also indicated (in kyr:kiloyear).and contraction of the frozen soil due to the lack of aninsulating boundary layer (Murton & Kolstrup 2003). Asa consequence, it cannot be excluded that wedges grew athigher mean annual air temperatures (MAAT ≤ -3°C) thanpreviously suggested (e.g., MAAT ≤ -6°C in Huijzer &Vandenberghe 1998).Finally, OSL dating of the aeolian wedge fillings providesdirect age estimates for these cold-climate soil processes.ReferencesBuylaert, J.-P., Ghysels, G., Murray, A.S., Vandenberghe, D.,De Corte, F., Heyse, I. & Van den haute, P. Accepted.Optical dating of relict sand wedges and compositewedgepseudomorphs in Flanders (Belgium).Boreas.De Moor, G., Heyse, I. & De Grootte, V. 1978. An outcrop ofEemian and Weichselian deposits at Beernem (N.W.Belgium). Bulletin de la Société belge de Géologie87: 27-36.Ghysels, G. 2008. Bijdrage tot de Studie van de Kenmerken,de Genese en de Datering van Periglaciale PolygonaleWigstructuren in België. Unpublished PhD Thesis,University of Ghent, 266 & 357.Ghysels, G. & Heyse, I. 2006. Composite-wedgepseudomorphs in Flanders, Belgium. Permafrostand Periglacial Processes 17: 145-161, doi:10.1002/ppp.552.Heyse, I. 1983. Cryoturbation types in eolian Würm Late Glacialsediments in Flanders, Belgium. Polarforshung 53: 87-95.Heyse, I. 2000. Fossil periglacial remnants in the Beernem-Mouton excavation in Flanders (Belgium). BiuletynPeryglacjalny 39: 53-68.Huijzer, B. & Vandenberghe, J. 1998. Climatic reconstructionof the Weichselian Pleniglacial in northwestern andcentral Europe. Journal of Quaternary Science 13:391-417.Murton, J.B. 1996. Morphology and palaeoenvironmentalsignificance of Quaternary sand veins, sand wedges,and composite wedges, Tuktoyaktuk Coastlands,western Arctic Canada. Journal of SedimentaryResearch 66: 17-25.Murton, J.B. & French, H.M. 1993. Thaw modification offrost-fissure wedges, Richards Island, PleistoceneMackenzie Delta, Western Arctic Canada. Journal ofQuaternary Science 8: 185-196.Murton, J.B. & Kolstrup, E. 2003. Ice-wedge casts asindicators of palaeotemperatures: precise proxy orwishful thinking? Progress in Physical Geography27: 155-170.Murton, J.B., Worsley, P. & Gozdzik, J.S. 2000. Sand veinsand wedges in cold aeoilan environments. QuaternaryScience Reviews 19: 899-922.Vandenberghe, J. & Pissart, A. 1993. Permafrost changesin Europe during the Last Glacial. Permafrost andPeriglacial Processes 4: 121-135.86