Loess accumulation during the last glacial maximum: Evidence from Urluia, southeastern Romania
Introduction
The Last Glacial Maximum (LGM) is globally recognised as the coldest climatic episode during the last full glacial cycle, and took place from approximately 26.5–19 ka, peaking towards 20 ka (Clark et al., 2009). The LGM is broadly characterised by a global sea-surface temperature minimum (Barrows and Juggins, 2005, Clark et al., 2009, Waelbroeck et al., 2009); maximum ice sheet extent in both polar regions (CLIMAP, 1976, CLIMAP, 1981, Svendsen et al., 2004, Golledge et al., 2012); worldwide sea level decrease of approximately 120 m (Yokoyama et al., 2000, Lambeck and Chappell, 2001, Siddall et al., 2003); the most recent major glacial advances in high altitude regions (Barrows et al., 2002, Ivy-Ochs et al., 2006, Blard et al., 2007, Zech et al., 2008, Barrows et al., 2011, Ehlers et al., 2011, Owen et al., 2012); and the intensification of aeolian activity both in deserts (Fitzsimmons et al., 2007, Singhvi et al., 2010, Roskin et al., 2011, Tripaldi et al., 2011), and in the semi-arid loess steppe downstream and downwind of major glaciated zones (Liu and Ding, 1998, Roberts et al., 2003, Antoine et al., 2009b).
In Europe, the LGM-age, so-called late Weichselian (or Würmian) Glaciation experienced temperature reduction of 5–10 °C (Strandberg et al., 2011), and a possible decrease in precipitation of up to 60% (Peyron et al., 1998, Heyman et al., 2013). These conditions triggered considerable changes in both landscapes and ecosystems across the continent (Fig. 1). The European LGM saw southward expansion of the British–Irish and Scandinavian ice sheets as far as approximately 52°N (Svendsen et al., 2004), substantial glacial advances in the highlands of the Alps, Pyrenees, Carpathians and Balkans (Reuther et al., 2007, Delmas et al., 2008, Ivy-Ochs et al., 2008, Kuhlemann et al., 2009, Hughes et al., 2011, Makos et al., 2012), and the southerly expansion of the zone of periglacial permafrost activity to 45°N in western Europe (Renssen and Vandenberghe, 2003, Bertran and Fabre, 2005) and into the Pannonian Basin of Hungary (Kovács et al., 2007, Fábián et al., 2009). This occurred in conjunction with a proposed southward expansion of tundra and boreal forest conditions (Frenzel, 1992, Svenning et al., 2008), and the coeval retreat of more temperate floral and faunal species into hypothesised climate refugia such as southern and eastern Europe (Bennett et al., 1991, Willis et al., 2000, Willis and van Andel, 2004). However, while substantial work has been undertaken to characterise LGM changes in Europe across the western, central and southern parts of the continent (Allen et al., 1999, Frechen et al., 2003, Sima et al., 2009, Antoine et al., 2009b), comparatively little attention has been given to the effects of this significant cold phase on the extensive loess steppe of eastern Europe.
The eastern European loess steppe extends from lower Austria, across the Danube River and Pannonian basins to the Romanian and Bulgarian Black Sea coast (Haase et al., 2007). Geomorphologically, it represents one of the most substantial landscape zones in Europe, and forms a broadly continuous zone ranging across the Russian Plain into central Asia and China. The eastern European loess deposits represent some of the most comprehensive terrestrial palaeoenvironmental records on the continent, extending to at least 1 Ma (Markovič et al., 2011). The eastern European loess archives correlate not only regionally (Markovič et al., 2008, Fitzsimmons et al., 2012) but also across Eurasia into China (Fitzsimmons et al., 2012, Markovič et al., 2012, Buggle et al., 2013). The relatively continuous loess deposits have remained uninterrupted by direct glaciation and periglacial conditions throughout their history, but nevertheless reflect oscillations between relatively cold-dry (glacial loess) and warm-humid (interglacial paleosols) phases (Fitzsimmons et al., 2012). Recent intensification of scientific investigation in the region has seen valuable longer-term reconstruction of palaeoclimatic and palaeoenvironmental change (e.g. Jordanova et al., 2008, Buggle et al., 2009, Markovič et al., 2009, Markovič et al., 2011). However, at this stage, relatively little is explicitly known about the impact of LGM cold conditions in eastern Europe. Several estimates of LGM temperatures in the Pannonian Basin is Hungary suggest cooling of mean annual temperatures in the range of 2–9 °C (Varsányi et al., 2011, Kovács et al., 2012). It has been proposed that the cooler phase of Marine Isotope Stage (MIS) 2, corresponding to the uppermost L1L1 stratigraphic unit in the loess (Markovič et al., 2008), saw the highest rates of loess accumulation over the last million years (Frechen et al., 1997, Fuchs et al., 2008, Újvári et al., 2010), associated with cold, dry, windy conditions (Haesaerts et al., 2003, Antoine et al., 2009a, Stevens et al., 2011). Malacological evidence from Hungarian (Sümegi and Krolopp, 2002, Sümegi et al., 2011) and Serbian (Markovič et al., 2004, Markovič et al., 2006) loess likewise suggests an intensification of cold, steppic conditions during MIS 2, although conditions may have been comparatively warmer than further west, resulting in the establishment of refugia for thermophilic flora and fauna as far north as Hungary (Willis et al., 2000). As yet, however, there exist very few LGM age estimates from the L1L1 loess. Consequently, it has not been possible to directly assess loess accumulation rates during the LGM compared with rates during MIS 3, early MIS 2 and the Holocene.
In this paper we present a high-frequency age–depth profile from a loess deposit at Urluia, southeastern Romania, extending from the MIS 3-age L1S1 paleosol complex to the present S0 Holocene soil, in order to reconstruct LGM conditions in the eastern European loess steppe. A tephra deposit, confirmed to derive from the Campanian Ignimbrite (CI) eruption (39.28 ± 0.11 ka; De Vivo et al., 2001), underlies this sequence (Fitzsimmons et al., 2013) and provides a known-age, maximum constraint for our study. Our chronology is established by direct dating of the fine-grained quartz component using optically stimulated luminescence (OSL) dating, which measures when sediments were last exposed to sunlight (Aitken, 1998). Environmental variations down the sequence are qualified for intensity using environmental magnetism (Hambach et al., 2008). Environmental magnetism in loess is based on the principle of enhancement of magnetic minerals derived from silicate minerals through pedogenesis; variations are therefore climatically controlled, and reflect glacial–interglacial and stadial–interstadial contrasts (Hambach et al., 2008). The two methods combined, targeting the L1L1 stratigraphic unit, provide us with the first direct assessment of environmental conditions and loess accumulation rates in the eastern European loess steppe during MIS 2, and specifically the LGM. The results have implications for depositional models in loess during periods of particularly high accumulation rates.
Section snippets
Regional setting
The loess deposits of the middle and lower Danube River basin represent the most substantial terrestrial recorders of palaeoenvironmental change on the European continent (Markovič et al., 2008, Fitzsimmons et al., 2012). The loess deposits are derived primarily from aeolian transport of fluvial silts associated with glaciers in the Danube catchment headwaters (Smalley and Leach, 1978, Buggle et al., 2008, Újvári et al., 2008), with minor further-travelled contributions from the Russian Plain
Methods
The profile at Urluia was cleaned and logged at six subsections (Fig. 2B), with the aim of documenting sedimentary characteristics and soil development. Two of these subsections (5 and 6) include the exposure of CI tephra and have been described previously (Fitzsimmons et al., 2013).
Sediment samples for environmental magnetism analyses were collected from the cleaned sections at intervals either of 10 cm or 5 cm (see Table S1, Supplementary Information). A total of 222 samples were collected
Stratigraphy and environmental magnetism
This paper investigates the chronostratigraphy of the loess deposit overlying the CI tephra at the Urluia site. The stratigraphy and magnetic susceptibility results are summarised in Fig. 3, and show that the majority of the post-CI deposit is dominated by primary beige-coloured loess deposits corresponding to the L1L1 unit, as defined by the eastern European loess stratigraphic scheme (Markovič et al., 2008, Fitzsimmons et al., 2013). A weakly developed soil and underlying primary loess are
Reviewing the depositional model for loess accumulation in the Lower Danube basin
The rapid accumulation of loess over the LGM period at Urluia is consistent with increased sedimentation rates at this time at loess profiles elsewhere in the Lower Danube basin, at Süttő (Novothny et al., 2009), Surduk (Fuchs et al., 2008) and Crvenka (Stevens et al., 2011). However, the fact that accumulation rates do not increase at other loess sites in the region, irrespective of aspect relative to the alluvial source and prevailing wind direction, such as at Stari Slankamen (Schmidt et al,
Conclusions
The loess profile at Urluia, southeastern Romania, exposes one of the most substantial deposits of post-40 ka loess in the Lower Danube basin. The presence of the known-age, ca. 39 ka CI tephra provides an excellent upper limit for the investigation of LGM loess accumulation. In this study we provide a high-frequency age–depth profile for this upper part of the sequence, using fine-grain quartz OSL and magnetic susceptibility measurements. Dating measurements were undertaken independently on
Acknowledgements
Research for the Lower Danube Survey for Palaeolithic Sites (LoDanS) project was funded by the Max Planck Institute for Evolutionary Anthropology (MPI-EVA). The authors thank Professor J.-J. Hublin and Dr. S. McPherron (MPI-EVA) for their support. Thanks to Dr S. McPherron (MPI-EVA) for help with the surveying by total station and to R. Ioviţă for making sense of those data. Thanks to S. Albert (MPI-EVA) for assistance with OSL sample preparation. We wish to thank R. Ioviţă, A. Doboş and A.
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2021, Quaternary Science ReviewsCitation Excerpt :During the last glacial period the Danube region is thought to have predominantly experienced mostly steppic, continental climates (Marković et al., 2018b; Zech et al., 2013), with conditions too dry to sustain short-term pedogenesis (Marković et al., 2015). This resulted in “classic” loess profiles, comprising thick glacial loess units, separated by well-developed interglacial palaeosols and, at some sites, weakly developed interstadial palaeosols (Buggle et al., 2009; Fitzsimmons and Hambach, 2014; Fuchs et al., 2008; Marković et al., 2009; Vasiliniuc et al., 2011). These classic loess-palaeosol sequences are typically located in a plateau setting and can be linked to large-scale, orbitally driven climate changes (Zeeden et al., 2018b).