Submarginal glaciotectonic deformation of Pleistocene permafrost

Recent advances in our understanding of glacier-permafrost interactions provide an alternative hypothesis to interpret Pleistocene glaciotectonic sequences in regions where permafrost no longer exists. Instead of necessarily forming under unfrozen subglacial conditions, some glaciotectonic sequences may have formed by submarginal deformation of warm, partially-frozen permafrost. An example from North Norfolk, U.K., suggests that an ice sheet during Marine Isotope Stage 12 advanced across permafrost terrain, deforming it beneath the margin. Such a scenario can help explain some features whose formation under unfrozen conditions is problematic, including (1) the substantial thickness of the deforming layer and (2) the preservation of stratified intraclasts. Accordingly, glacial geologists should remain open to the possibility of glacier-permafrost interactions when interpreting glacigenic sequences. Such a re-interpretation could have major implications for reconstructing basal thermal regimes and modeling palaeo-ice sheets.