Frost-shattered debris facies of Younger Dryas age in the coastal sedimentary successions in western Norway: palaeoenvironmental implications

The occurrences of a characteristic facies of in situ frost-shattered debris have been studied in the late Quaternary (late and post-Weichselian) coastal deposits in the Møre-Romsdal district of western Norway. The sedimentary successions represent gravelly beaches, coarse-grained glaciofluvial deltas and colluvial-fan deltas. The majority of these occurrences correspond to the Younger Dryas relative sea level, and the associated facies indicate that the process of intense frost-shattering of debris occurred within an altitudinal range of ca. 2 m around the mean sea level. The process implies permafrost conditions, ground temperatures falling below −5°C, climatic seasonality, and a relatively high water-saturation level in the shoreline deposits (presumably due to the spring-summer meltwater discharges). The study further indicates a rapid change to warmer climatic conditions at the end of the Younger Dryas chronozone. There are also a few higher-altitude occurrences of the frost-shattered debris facies, corresponding to the relative sea-level stand at around 12,000 yr B.P., which imply a cold climate with permafrost conditions in the Older Dryas chronozone.