Pleistocene environmental dynamics recorded in the loess of the middle and lower Danube basin

摘要

The substantial loess deposits of the middle and lower Danube basin in southeastern Europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent, yet are also the least well understood. Environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions, which nevertheless reflect oscillations between relatively warm-humid (" interglacial") and cold-dry (" glacial") intervals. This relative environmental stability may have proven important for hominins migrating into and through the region.The loess stratigraphy comprises distinct loess-paleosol sequences, reflecting glacial-interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry. These phases are emphasised by variations in vegetation and malacofauna which respond to climatic change. The loess deposits demonstrate broadly similar sedimentological characteristics across the basin.Danubian loess deposits initiated in response to the tectonic formation of the Pannonian basin, retreat of the large palaeolakes, and increased sediment supply from the Danube. The period from ~1 Ma-500 ka (MIS 27-13) was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively, in response to relatively humid, forested conditions. This period represents the opening of the Danube corridor and provides the backdrop for initial hominin arrival into Europe. After ~500 ka, and particularly after MIS 9, loess accumulation rates increased in response to relatively more steppic, arid, environments. MIS 9 and 13-15 were the most humid phases of the last ~600 ky. The MIS 5 interglacial period was the warmest, and relatively most humid, period preceding the Holocene, and was followed by substantially increased loess accumulation during MIS 4, which may be linked to North Atlantic circulation. The complexity of the MIS 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time. MIS 3 corresponds with the first arrival of anatomically modern humans to Europe. The last glacial maximum and Younger Dryas of MIS 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the North Atlantic, although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota, as may also have been the case for most of the Pleistocene glacial cycles. The Holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial.