Sedimentology and stratigraphy in the cave Hamnsundhelleren, western Norway

The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are 14 C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost‐weathered clay and scattered angular blocks. It is 14 C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late‐glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice‐free–ice‐covered cycle have been identified: (i) ice‐free phase (deposition of bones and frost‐weathered blocks); (ii) subaerial ice‐dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice‐dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice‐plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).