Loess accumulation during the last glacial maximum: Evidence from Urluia, southeastern Romania

摘要

The Eastern European loess steppe represents one of the most substantial landform types on the continent, yet the impact on this region of the last glacial maximum (LGM), the coldest climatic episode during the last full glacial cycle, is relatively poorly understood. This is in part due to the comparatively small number of sites which have been reliably dated, and in part due to the need to better elucidate depositional models for loess environments at both local and regional scales. Here we present a high-frequency age-depth profile for the last 40 ky from a loess deposit at Urluia in southeastern Romania, using fine-grained quartz optically stimulated luminescence (OSL) dating and environmental magnetism analyses. Loess accumulation at the site for this period is well constrained by a clearly identifiable tephra deposit corresponding to the ca. 39 ka Campanian Ignimbrite. We show that the tephra is directly overlain by a relatively thin layer of loess corresponding to marine isotope stage (MIS) 3, which is partially overprinted by a weakly developed paleosol. The sequence is dominated by a 6-8 m package of primary loess of LGM age. The eight OSL samples from this package group together around a mean age of 21.6 ± 1.5 ka, and suggest rapid and substantial deposition during this phase. The uppermost part of the section indicates significantly reduced loess accumulation, during the deglacial period into the Holocene, less than 2 m in total thickness. The rapid accumulation of loess during the LGM at Urluia is consistent with increased sedimentation at other loess profiles in the Lower Danube basin, although the variable thickness of these deposits across the catchment highlights the need to more explicitly investigate depositional models for loess. The Urluia record complements emerging data which suggests that the Lower Danube loess steppe was cold, dry and windy during the LGM, yet experienced milder climates than comparable latitudes further west and north, and did not undergo periglacial activity.