Aeolian dynamics in Southeastern Europe during the late pleistocene, based on detailed sedimentological and geochemical investigations on loess

  • Äolische Dynamiken in Südosteuropa während des Spätpleistozäns anhand von detaillierten sedimentologischen und geochemischen Untersuchungen von Löß

Obreht, Igor; Lehmkuhl, Frank (Thesis advisor); Stevens, Thomas (Thesis advisor)

Aachen (2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2017

Abstract

Loess is a valuable archive of past climatic and environmental conditions. Southeastern European thick loess-palaeosol sequences have preserved a quasi-continuous record of glacial-interglacial cycles, reaching as far as the Early Pleistocene. The Middle and Lower Danube Basins are lowland areas with thick loess plateaus comprising several glacial-interglacial cycles. Those areas have been the focus of recent research on the Quaternary in Europe, which has resulted in a better understanding of the Pleistocene palaeoenvironmental and palaeoclimatic signals. However, while some local and regional palaeoclimatic information is available, large-scale forcing mechanisms and the climatic conditions responsible for loess formation have not been revealed. Contrary to the Middle and Lower Danube Basins, the interior of the Balkans is poorly investigated. Lack of information of past climatic and environmental conditions over the Balkans represents an additional barrier to the understanding of large-scale atmospheric circulations over Southeastern Europe. The aim of this dissertation is to reconstruct aeolian dynamics and climatic conditions over Southeastern Europe during the Late Pleistocene. Before the reconstruction of the past climatic conditions, a definition of loess and its evolution through time is given. Loess is usually defined as a wind-blown dust that after deposition undergoes a special process called loessification. The lack in knowledge and understanding of postdepositional processes during loessification make a clear definition of loess difficult. For now, it is proposed to define loess as a mainly aeolian dust deposit that has experienced loessification, resulting in loess-like aggregation. The sections studied for palaeoclimatic reconstruction are located in different regions in Southeastern Europe. The Orlovat section is located in the Middle Danube Basin (Vojvodina, Serbia), the Stalać section is in the Central Balkans (Central Serbia), and the Urluia and Vlasca sections are situated in the Lower Danube region (Dobrogea, Romania). Regional palaeoclimate conditions of these three areas have been reconstructed. It is shown that past climatic and environmental conditions have been very diverse among different regions of Southeastern Europe. The climate evolution was dynamic and different even within smaller regions, such as parts of the southern Middle Danube Basin. The southeast Košava wind, a regional wind of the southern Banat region, had a strong impact on the environmental conditions over the Banat region, particularly during MIS 5 and the Holocene. The sedimentological dynamics were determined by the relative influence of local winds and particularly changes in the source areas.Palaeoclimatic evolution over the Central Balkans was a very dynamic process over the past 350,000 years. Mediterranean-like climate was very prominent during the Middle Pleistocene. However, the influence of Mediterranean climate weakened over time, and was finally replaced by continental climate influence during MIS 5. The reported shift in a dominant atmospheric mode over this area during MIS 5, and associated changes in precipitation, resulted in warmer and more humid conditions over the following glacial cycle when compared to previous glaciations. Such a palaeoclimatic evolution during the Late Pleistocene was characteristic only for the Balkans area, and the climatic conditions in other part of Southeastern Europe were colder and drier. During the Late Pleistocene the Mediterranean-like climate was not present in Southeastern Europe, although the relative influence of the warmer air masses from the south was present in the Central Balkans. Accordingly, climatic influences over the Middle and Lower Danube Basins were associated with the Atlantic and continental climates only. However, the influence of those climates did not equally affect those regions over time. Especially between 40,000 and 27,000 years ago, the Lower Danube Basin was under a stronger influence of continental climate conditions (with especially colder winters). On the contrary, the Middle Danube Basin was under the influence of Atlantic climate and milder climatic conditions. Such opposing trends indicate major large-scale atmospheric changes in Europe during the mentioned time interval. An explanation for the opposing trends and general changes in the European large-scale atmospheric systems is given. During this time interval (late MIS 3 - 40,000 to 27,000 years ago) the intensification of the Siberian High had a crucial influence on European climate causing a general continentalization of major parts of Europe. An area from the Lower Danube Basin to Western Europe experienced a trend of increasing air pressure because of an intensification of the Siberian High, causing the southwards shift of the Westerlies. The Westerlies from the south had been bringing warmer and more humid air masses into the Balkans and the Middle Danube Basin. This highlights the fact that during the limited extent of the Fennoscandian ice sheets the Siberian High played a crucial role in the evolution of prevailing atmospheric circulations and palaeoenvironmental conditions in Europe.Based on presented large-scale atmospheric systems evolution in Europe, this dissertation also provides the climatic and environmental context for the Anatomically Modern Human dispersal into Europe. It is highlighted that with the intensification of the Siberian High during late MIS 3 adverse environmental and climatic conditions prevailed in Eastern European Plains, but the palaeoenvironment in major parts of Europe became an open and fertile steppe able to sustain large herds of herbivores and their hunters. Thus, a possible intensive westwards dispersal of Anatomically Modern Human from western Siberia may have taken place over the Eastern European Plains, especially after the Campanian Ignimbrite/Y-5 tephra deposition.