New evidence of glacier advances during Lateglacial Interstadial deciphered from facies evolution in proglacial lacustrine basins of the Maurienne Valley, French Alps

Sedimentological analysis of glaciolacustrine deposit in the French Alps provides an opportunity to elucidate poorly understood glacier fluctuations during the Lateglacial Interstadial. This study focuses on two proglacial lacustrine basins in the Maurienne Valley, Le Verney and Lanslebourg, recording sediment deposition during the Lateglacial. Sedimentological and soft sediment deformation analyses were conducted on these glaciolacustrine sedimentary deposits to constrain the dynamic of the Arc glacier. At Le Verney, the sedimentary succession records the deposition of a proglacial subaquatic fan under supercritical conditions, transitioning to a Gilbert delta-type sedimentation, indicating glacier retreat. Fluid overpressure, shear deformations, and compressional stresses found within Gilbert delta-type sediment marks a subsequent glacier advance. In the Lanslebourg basin, sedimentary deposits display supercritical and subcritical conditions, separated by deposition under a hydraulic jump characteristic of ice contact delta. In this area, glacier advance is recorded by a more proximal condition toward the top of the sedimentary succession, along with a transition to a subglacial condition. These findings reveal glacier advances during the Bølling-Allerød Interstadial, providing the first evidence of glacier re-advances in the French northern Alps during this warming period. This result highlights the complex interactions between local climate, glacier dynamics, and topography.