Disentangling Sedimentary Pathways for the Pleniglacial Lower Danube Loess Based on Geochemical Signatures

Abstract

The source of aeolian sediments such as loess has been investigated since decades. Reliable knowledge on potential dust sources is crucial to understand past climatic and environmental conditions accompanying the dispersal of early modern humans (EMH) into Europe. Provenance studies are usually performed on small sample sets and most established methods are expensive and time-consuming. Here, we present the results of high-resolution geochemical analyses performed on five loess-palaeosol sequences from the Lower Danube Basin (LDB), a region, despite its importance as a trajectory for EMH, largely underrepresented in loess provenance studies. We compare our results with geochemical data of loess-palaeosol sequences from Austria, Hungary, Serbia, and Ukraine. Based on published literature, we thus evaluate five plausible sedimentary pathways for the LDB loess: 1) the Danube alluvium (DA) pathway, which constrains the transport and re-deposition of detrital material by the Danube and its tributaries; 2) the Carpathian Bending (CB) pathway, where sediment is mainly transported from the Cretaceous to Neogene flysch of the Eastern Carpathian Bending; 3) the Eastern Carpathian (EC) pathway, in which sediment is eroded from the flysch of the Outer Eastern Carpathians, transported by rivers, and deflated by northwesterly to westerly winds; 4) the glaciofluvial (GF) pathway, where dust is deflated from glacial outwash plains in nowadays Ukraine, and 5) the Black Sea (BS) pathway, where dust originates from the exposed shelf of the Black Sea. Based on geochemical data, we consider the DA pathway to be the major sediment trajectory for loess in the LDB. Especially the sequences located close to the Danube and the Dobrogea show similarities to sites in Central and Northeast Hungary as well as Northern Serbia. For the northeastern part of the LDB, we demonstrate that dust input is mainly sourced from primary material from the Eastern Carpathians. Mineralogical estimations and geochemical data render the CB pathway as an additional substantial source of detrital material for the loess of this area. We consider the influence of the GF pathway in the LDB as negligible, whereas some minor influences of the BS pathway cannot be ruled out based on geochemical data.

Danubian loess shows dominance of proximal sediment sources and negligible inputs from the Sahara

“…3 top panel) suggests a shared origin of negrained material. Additionally, the relation to the Danube sample points to the Danube's alluvial material as a source, supporting previous suggestions based on other methods 15,17,25,[56][57][58] . The overall similarities between loess sites (e.g.…”

Last glacial loess dynamics in the Southern Caucasus (NE-Armenia) and the phenomenon of missing loess deposition during MIS-2

“…6 ). Instead, compatible elements such as Ni and Cr together with conservative element ratios such as Zr/Ti and Al/Ti may help to identify tephras and dust provenance changes along the profile 29 , 46 , 48 . The major tephra layer suggests rather a rhyolithic character with minima in compatible elements and maximum in Zr (Fig.…”

“…3 ) shows even higher MS-values that may suggest a changed dust source during that period. Referring to the Al/Ti ratio that is regarded as an indication of grain-size and provenance changes 29 , stronger deviations from the Grain Size Index (GSI) curve solely appear in the range of the upper Eemian soil P-1/S3 and the loessic material at the base of the L-2 complex (Fig. 6 , depth of 7 and 11 m) that may point to a provenance change and/or higher tephritic input.…”

“…In particular, loess sedimentation intensified during the Last Glacial Maximum (LGM) (26–19 ka) in line with the coldest part of the last glacial cycle as well as peaking global ice volume 27 . Accordingly, aside from the availability and proximity of dust sources as controlling parameter 28 , 29 , periods of enhanced loess sedimentation are often related to environmental conditions including strongly reduced precipitation and moisture availability, diminished vegetation cover, and higher wind speeds 23 , 30 , 31 .…”

Pleniglacial dynamics in an oceanic central European loess landscape

“…4). The slightly vertical point distribution within the upper cluster of the A-CN-K ternary diagram, a feature which indicates hydraulic sorting (Pötter et al, 2021;Ohta, 2004), also points to reworking. Unit II was frequently overprinted by harsh, periglacial conditions, as indicated by a multitude of small, centimetre-scale ice-wedge casts permeating several layers of the package.…”