C/O-stable isotope composition (VPDB) of speleothems from the Makkaronihalle of the Hüttenbläserschacht Cave in Iserlohn shows a clear separation between glacial and interglacial calcites. In contrast to normal speleothems (stalagmites, excentriques, crystals in cave ponds, draperies; δ18O: –4.0 to –6.1 ‰, δ13C: –4.9 to –10.9 ‰), rhombohedral crystal sinter and spherulitic speleoparticles are characterised by lower δ18O (–8.9 to –17.9 ‰) and higher δ13C values (+0.7 to –6.1 ‰). This suggests that these speleogenetic particles were formed in slowly freezing waterpools on ice during the transition from a stadial to an interstadial phase.
Precise 230Th/U-dating shows younger Weichselian ages of 28.6 to 33.0 ka for these speleogenetic particles from north-west Germany. These formation periods indicate freezing conditions overlain by 34 m of hostrock and provide the minimum depth of permafrost penetration for the younger Weichselian in the area of the northern Sauerland (north-west Germany).