The channels in Storebælt, Denmark: implications of new radiocarbon ages

The brackish water Baltic Sea and the more saline Kattegat in the north are connected by three straits, Lillebælt, Storebælt and Øresund. Storebælt (the Great Belt) is the deepest and widest of the straits. The strait is characterised by deeply incised channels that are partly filled by sediments. The water depth in major parts of Storebælt is about 20 m, though in some areas the channels are more than 50 m deep. The formation of the channels has been subject to discussion. Andersen (1927) suggested that the channels formed due to strong currents that are still active today or by fluvial erosion during the so-called continental period (Fastlandstiden) in the Early Holocene. At this time, the relative sea level in the region was lower than at present and a huge lake, the Ancylus Lake, which occupied the Baltic Basin, may have drained via Storebælt. Andersen dismissed the idea that the channels were formed by subglacial erosion by meltwater during the last deglaciation. More Recently, Mathiassen (1997) interpreted some of the deposits in the channels as late glacial, a viewpoint followed by Bennike et al. (2004). However, the age of the late glacial deposits in the channels are poorly constrained. The first studies of sediment cores from Storebælt were carried out by Krog (1973), Winn (1974) and Mathiassen (1997), but these studies concentrated on the Holocene development from mires to lakes to brackish and marine environments. Wiberg-Larsen et al. (2001) documented the presence of Early Holocene river deposits. Here we report on some new ages of macrofossils from late glacial deposits in the Storebælt channels