Timing of Weichselian ice marginal positions in Brandenburg (northeastern Germany) using cosmogenic in situ Be-10

摘要

In the eastern German lowlands, erratic boulders of the Weichselian (Wurn) glaciation have been studied since AD 1775 and moraine sequences since the mid-19(th) century. Yet, no existing geochronological data of terrestrial late Weichselian ice marginal positions from northeastern Germany constrain the age of glacial events. Here, we report six Be-10 ages associated with the Brandenburg, Frankfurt and Pomeranian moraines. Our new data provide the first direct age estimate of the LGM and the deglaciation in the Berlin area. Our results date the retreat from the last glacial maximum advance (Brandenburg phase) to similar to 19 Be-10 kyr. The retreat from the Frankfurt phase is dated to similar to 18 Be-10 kyr and the retreat from the Pomeranian moraines to similar to 16 Be-10 kyr. The age of the Pomeranian moraine is younger than assumed by previous authors. These results are corroborated by a set of Be-10 ages from eastern Europe (RIN-TERKNECHT et al. 2005, 2006a, 2006b, 2007, 2008). Our Be-10 moraine ages imply that the glacial chronostratigraphy, otherwise identified by means of geomorphological, stratigraphical and archaeological evidence in combination with C-14, TL and OSL dating methods, might need to be reinterpreted. The ages of Weichselian ice marginal positions in Brandenburg arc younger than the ages of the Scandinavian Ice Sheet (SIS) moraines in Denmark and northern Germany. We present a potential glacio-dynamic explanation for the observations along the southern margin of the SIS which does not reject already published ages and mapping results but rather reinterprets the correlation between features and thus sheds new light on the late glacial extent of the ice stream in the Baltic Basin.