Seminar – Thursday, October 1, 2026 – Resolving the paradox of conflicting glacial chronologies: Reconstructing the pattern of deglaciation of the Magellan cordilleran ice dome (53-54°S) during the Last glacial – Interglacial transition

Summary: Raised shorelines and associated lacustrine sediments in the central Strait of Magellan (southern Patagonia) have been interpreted as products of extended glacier margins impounding a large proglacial lake and preventing drainage to the Pacific and Southern Oceans during the Late glacial. The lowest lake level has been dated to between c. 15.0 and 12.0 cal ka BP but a growing body of glacial geological evidence points towards an earlier retreat of the Magellan cordilleran ice dome, insufficient to dam lakes after c. 17.0-16.0 cal ka BP. We critically re-evaluate the extant evidence for the c. 15.0-12.0 cal ka BP lake while providing new evidence for its existence. We also confirm the rapid and widespread retreat of the Magellan ice fields to the inner fjords of the Fuegian archipelago by c. 17.0-16.0 cal ka BP. To resolve the apparent paradox between these two lines of evidence we propose that glacial isostatic adjustment led to a topographic barrier to lake drainage rather than an ice dam. Rapid isostatic recovery following the early deglaciation after c. 17.0 cal ka BP led to elevation of the present shallow south-western coastal margin of the Fuegian archipelago. Final drainage was probably caused by neotectonic subsidence of the same margin along the boundary of the South American – Scotia tectonic plates at c. 12.0 cal ka BP.