We redefine the extent of former glaciers in the northern Jura Mountains through the study of endo-karst deposits. Sedimentary deposits (pebbly debris flows, laminated clays, and allochthonous limestone blocks) and chemical deposits (speleothems) were identified and studied using three complementary approaches: (i) detailed geomorphological mapping, (ii) petrographic analysis, and (iii) U/Th-dating. In addition, a surface geomorphological analysis made it possible to calculate the minimum erosion time required for the formation of the sinkhole linked to the underground study site.
The study site is the Dolois Chamber, an underground site upstream of the Verneau karst network (Doubs Department, France). The combined results aided in reconstructing the chronology of the various events affecting the study site, including 1) formation of the Baume-des-Crêtes paleo-sinkhole a few hundred thousand years (during Marine Isotope Stage (MIS) 8); 2) invasion by a pebbly debris flow, probably linked to a mid-Pleistocene glacial periods (MIS 8 or 6); 3) hydrological dysfunction, including significant flooding and deposition of laminated clays; 4) capture of the paleo-sinkhole by the Biefs-Bousset active sinkhole approximately 10 kyr (MIS 2); and 5) a recent return to water level variations of approximately 10 m during flooding. Furthermore, our results show that the extent of the ice cap in the Jura Mountains during the mid-Pleistocene (MIS 8-6) probably did not reach beyond the topographic high of the Salinois Fault Zone at the plateau margin.
Reference: Vivier, M., Jaillet, S., Husson, E., Pons-Branchu, E., Charlier, J.-B., 2025. New evidence of mid- Pleistocene glaciations in the French Jura Mountains using debris-flow deposits and U/Th-dating of speleothems (Verneau karst network). International Journal of Speleology, 54(2), ijs2558. https://doi.org/10.5038/1827-806X.ijs2558