The last glacial cycle in western Norway—extensive MIS 5d glaciation, multiple glacial advances and LGM glacial advance phases

We have investigated fine‐grained marine sediments buried under delta sediments and multiple till beds in a tributary valley in western Norway. The marine bed contains bivalves, foraminifera and terrestrial plant material. The fauna and flora are rather poor, but the presence of molluscan species Mytilus edulis and Arctica islandica suggests that Atlantic waters reached the coastal areas at the time of deposition. The age range of radiocarbon dates from about 25 to 50 ka BP conflicts with previous studies from the area and is considered as minimum ages only. This conclusion is supported by amino acid epimerization values in molluscs from the radiocarbon‐dated unit, indicating that it should be correlated with an Early Weichselian, MIS 5c interstadial. The marine unit and overlying delta succession are situated on the outer coast up to 56 m above present sea level, suggesting that they were deposited during a high sea‐level stand following retreat of an extensive MIS 5d glaciation. A compiled Weichselian glaciation curve shows five major glacial advances extending to the outermost coast or beyond. These advances seem to correspond to periods with North Atlantic sea surface cooling. Three till units on top of the delta are interpreted to represent glacier advance prior to the Last Glacial Maximum (LGM) and during the subsequent deglaciation. Clast fabrics in the lower till and orientation of clastic dikes show an upvalley component opposite to LGM maximum ice‐flow direction. This indicates that initial glacier advance was by fjord glaciers extending to the outer coast while there was limited glacier extent in coastal mountain areas. This interpretation favours fast ice flow along the fjords and major supply of ice from interior mountain areas. Glacier growth in coastal mountains led to merging with fjord glaciers, reorientation of the ice‐flow direction and ultimately maximum glacier extent. Empirical data on ice‐sheet growth are extremely rare and may have been overlooked in many stratigraphic records. Such data are vital for understanding behaviour of ice sheets and in a wider sense, the climate system.