Speaker
Mr
Kevin Manchuel
(EDF-DIPNN-DI-TEGG)
Description
Last Glacial fluvial sequences in the Paris Basin show laminated lacustrine deposits OSL and radiocarbon dated to between 24.6 and 16.6 ka in one site and overlying alluvial sandy gravel. A thermokarst origin of the lakes is sup- ported by abundant traces of ground ice, particularly ice wedge pseudomorphs beneath the lacustrine layers and synsedimentary deformation caused by thaw settlement. The features include brittle deformation (normal and reverse faults) resulting from ground subsidence owing to ice melting and ductile deformations caused by slumping of the sediments heaved by the growth of ice-cored mounds. These correspond to lithalsas (or lithalsa plateaus) and/or to open system pingos. At least two generations of thermokarst are recorded and may re?ect the millennial climate variability typical of the Last Glacial. The structures studied in quarries are associated with an undulating topography visible in 5-m DEMs and a spotted pattern in aerial photographs. The search for similar patterns in the Paris Basin indicates that many other potential thermokarst sites exist in the Last Glacial terrace (Fy) of rivers located north of 48N when they cross the lower Cretaceous sands and marls. In some sites, the presence of organic-poor, ?ne-grained deposits presumably of lacustrine origin was con?rmed by borehole data. The site distribution coincides broadly with that already known for ice wedge pseudomorphs. This study provides new evidence of permafrost-induced ground deformations in France and strongly suggests that thermokarst played a signi?cant and probably largely underestimated role in the genesis of Late Pleistocene landscapes.
Primary authors
Mr
Kevin Manchuel
(EDF-DIPNN-DI-TEGG)
Mr
Pascal Bertran
(INRAP-PACEA)
Co-authors
Ms
Deborah Sicilia
(EDF-DIPNN-DI-TEGG)
Mr
Eric Andrieu
(PACEA - Univ. of Sheffield)
Mrs
Marianne Font
(M2C - UMR 6143)
Prof.
Mark Bateman
(Univ. of Sheffield)
