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 (43-47000 yr BP). Angular blocks, bones and clay above this are C-14 dated to the Alesund Interstadial (28-38000 yr BP). Another stadial laminated clay following the Alesund Interstadial includes a p alaeomagnetic excursion correlated with Lake Mungo (28000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-we athered clay and scattered angular blocks. It is C-14 dated to 24500 y r BP on bones mixed into the Alesund Interstadial. The Hamnsund Inters tadial 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-fre e phase (deposition of bones and frost-weathered blocks); (ii) subaeri al ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, dep osition of till, debris flows and laminated clay); (d) ice-plugged pha se (cave is plugged by frozen lake water and/or glacial ice, no deposi tion).