Past Environment and Sediment Dynamics in the Black Sea-Caspian Sea Region from Southern Russian Loess Sequences

Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 2046

Past environment and sediment dynamics in the Black Sea-Caspian Sea region from Southern Russian loess sequences

CHIARA AMALIA KÖLTRINGER

ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-513-1218-7 UPPSALA urn:nbn:se:uu:diva-440947 2021 Dissertation presented at Uppsala University to be publicly examined in Hambergsalen with online live transmission, Geocentrum, Villavägen 16, Uppsala, Friday, 11 June 2021 at 09:00 for the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty examiner: Dr. Kathryn Fitzsimmons (Max-Planck-Institut).

Abstract Költringer, C. A. 2021. Past environment and sediment dynamics in the Black Sea-Caspian Sea region from Southern Russian loess sequences. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 2046. 70 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-1218-7.

Loess deposits are excellent past climate and environment archives and contain records of aeolian mineral dust accumulation. Loess deposits stretch across Eurasia and sequences along the Lower Volga in the Northern Caspian lowland in the South East European Plain represent a key link between European and Asian loess. They were deposited during phases of Caspian Sea sea-level low stands in the Late Quaternary and are confined by deposits of marine sediments from transgressive phases. These sea-level fluctuations of the Caspian Sea and their driving factors are not well resolved, and one obstacle is the lack of palaeoclimate information during phases of sea-level low stands. In contrast to the marine sediments, the continental deposits are understudied and the origin and formation of the material is debated. As a consequence, loess along the Lower Volga is often left out from palaeoclimate reconstructions in the region. This thesis aims to resolve the origin, formation and post-depositional modification of this loess and determines its aeolian origin. Provenance analyses show that Lower Volga loess particles were formed due to glacial grinding and were transported over long distances via rivers prior to near-source aeolian deposition, where the loess experienced phases of pedogenic and cryogenic reworking. While no temporal changes in material supply can be identified for Lower Volga loess, a remarkable spatial variability is seen in dust sources over the wider East European Plain and in the South Caspian Sea region. This variability is linked to material input from multiple local sources, while the larger material supply to the region has broadly similar provenance and derives mainly from areas of continental and mountain glaciation, transported via rivers prior to aeolian deflation. This thesis explores the potential of Lower Volga loess for palaeoclimate reconstructions in Eurasia, and shows a generally cold and arid climate in the Northern Caspian lowland during the Late Quaternary Caspian Sea regression, with strong dusty winds, punctuated by slightly more humid and/or warmer periods. The thesis shows that enviromagnetic methods are suitable for palaeoclimate reconstructions from such cold climate loess, as long as several methods are applied in combination and interpreted appropriately. It also provides information about the magnetic fabric of Lower Volga loess. The findings of this thesis in broader implication show that the Caspian Sea level is only secondarily influenced by local-regional climate variation and that Quaternary Northern Hemisphere glaciation is the primary controller via river discharge to the Caspian Sea.

Chiara Amalia Költringer, Department of Earth Sciences, LUVAL, Villav. 16, Uppsala University, SE-75236 Uppsala, Sweden.

ISSN 1651-6214 ISBN 978-91-513-1218-7 urn:nbn:se:uu:diva-440947 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-440947)

For those who cannot

“People must know the past to understand the present, and to face the future” - Nellie L. McClung

List of Papers

This thesis is based on the following papers, which are referred to in the text by their Roman numerals.

I Költringer, C., Stevens, T., Bradák, B., Almqvist, B., Kurbanov, R., Snowball I., Yarovaya S. (2020) Enviromagnetic study of Late Quaternary environmental evolution in Lower Volga loess sequences, Russia. Quaternary Research, 1-25. https://doi.org/10.1017/qua.2020.73 II Költringer, C., Bradák, B., Stevens, T., Almqvist, B., Banak, A., Lindner, M., Kurbanov, R., Snowball I., Palaeoenvironmental implications from Lower Volga loess - joint magnetic fabric and multi-proxy analyses. Quaternary Science Reviews, (under review, 2nd round) III Költringer, C., Stevens, T., Lindner, M., Baykal, Y., Ghafar- pour, A., Khormali, F., Taratunina, N., Kurbanov, R., Quaternary sediment sources and loess transport pathways in the Black Sea- Caspian Sea region identified by detrital zircon U-Pb geochronology. Earth-Science Reviews, (submitted)

Reprints were made with permission from the respective publishers.

Additional Papers

In addition, the author has contributed to the following papers, which are related to but not included in the thesis

I Hällberg, L.P., Stevens, T., Almqvist, B., Snowball, I., Wiers, S., Költringer, C., Lu, H., Zhang, H., Lin, Z. (2020) Magnetic susceptibility parameters as proxies for desert sediment provenance. Aeolian Research, Volume 46, https://doi.org/10.1016/j.aeolia.2020.100615. II Bradák, B., Seto, Y., Stevens, T., Újvári, G., Fehér, K., Költringer, C. (2021) Magnetic susceptibility in the European Loess Belt: new and existing models of magnetic enhancement in loess. Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 569, https://doi.org/10.1016/j.palaeo.2021.110329

Contents

Introduction ...... 11 Sediment cycling, climate controls, and climate records ...... 11 Atmospheric mineral dust and climate ...... 15 Loess ...... 17 Loess as a palaeoclimate archive ...... 19 The northern Caspian Sea region and Lower Volga loess ...... 22 Aim of the thesis ...... 28 Study sites ...... 30 Methods ...... 32 Environmental magnetism ...... 32 Geochemistry as proxy for weathering ...... 36 Grain shape and surface analysis ...... 37 Detrital zircon U-Pb dating ...... 39 Modern wind data analysis ...... 40 Main findings ...... 42 Lower Volga loess characterization (Paper I and II) ...... 42 The applicability of enviromagnetic parameters for climate reconstruction in cool climate loess deposits (Paper I and II) ...... 42 Palaeoclimate evolution in the Lower Volga region during the Late Pleistocene (Paper I and II) ...... 44 Detrital zircons as a provenance tracer on the East European Plain (Paper III) ...... 45 Lower Volga loess provenance and transport (Paper II and III) ...... 45 Sediment routing and spatial variation of loess deposits in the Black Sea-Caspian Sea region (Paper III) ...... 47 Broader implications (Paper I, II and III) ...... 49 Conclusion & Future Perspective ...... 51 Summary in Swedish ...... 54 Acknowledgements ...... 57 References ...... 61

Abbreviations

MIS Marine Isotope Stage ka Thousand years Ma Million years EEP East European Plain LVL Lower Volga loess SA Srednyaya Akhtuba RG Raigorod/Raygorod LN Leninsk χ magnetic susceptibility (mass corrected; m3 kg−1)

χfd frequency dependence of magnetic susceptibility (%)

κT temperature dependence of magnetic susceptibility (volume corrected; SI) Mrs saturated remanent magnetization Ms saturated induced magnetization Bc coercivity SP superparamagnetic SD single domain MD multi domain ARM Anhysteretic Remanent Magnetization IRM Isothermal Remanent Magnetization KDE Kernel Density Estimation OSL optically stimulated luminescence

Introduction

“Of the paths you take in life make sure a few of them are dirt” – John Muir

Sediment cycling, climate controls, and climate records The Earth System comprises the lithosphere, hydrosphere, atmosphere and bi- osphere, which are all strongly connected to each other and within which land, water, air, and life interact. This connection is greatly influenced by the processes and substages of the rock cycle: the formation, weathering and erosion, transportation, deposition and lithification, burial, and melting of rocks of the lithosphere. This cycle is crucial for the development of Earth surface landscapes, climate, environments, and the long-term change of these systems. Sediments are a key part of the rock cycle and their study, and the analysis of their response to Earth surface processes such as weathering and erosion, transport and deposition, play an important role in understandings these processes, their interactions, and implications. The nature of sedimentary deposits can reflect weathering and erosion in source areas as well as the mode of transportation and its pathways, deposition processes, and sediment recycling. Un- derstanding of where and how material gets eroded, transported and deposited and which process agents are active (e.g. water, ice, wind etc.), is essential to link this geomorphic work with changes and forcing of other systems, most crucially climate. Sedimentary deposition and preservation at any scale is dependent on the supply of material, transport pathways, a suitable sink and its exposure to subsequent erosion. All these processes are controlled by several factors and their spatial and temporal changes, e.g. source-rock type, topography and vegetation, which themselves are driven by tectonics and climate. For a more extensive elaboration see e.g. Bridge and Demicco (2008).

Despite climate having a major control on the sedimentary cycle, the reverse is also the case, and temperature and precipitation over the Earth’s surface are greatly influenced by the distribution of surface material and the formation of relief and topography. Due to this reciprocal interaction between the sedimentary cycle and climate, sedimentary deposits have great potential of preserving evidence for climate variation and the interactions between landscape

11 processes and climate. One critical aspect for the utilization of sediments and sedimentary rocks as a joint archive for past environment and landscape evolution, is to understand how land is denuded and how sediment is stored en route to sedimentary basins. This source to sink transfer is critical to address, as constraining lags in the cycling of sedimentary material is central to interpretation of rock archives of erosion on land in terms of past climate, tectonic and landscape evolution. Abundant sediment supply is associated with mountain ranges, continental ice sheets and large rivers, and during erosion, transport, and deposition of these sediments, information about the composition of the atmosphere, its temperature, precipitation and wind patterns, global ice volume, and sea-level stands can be recorded (Bradley, 1999). This coupling is complex and manifold. All components of the global geosystem influence each other and while capturing the effect of one changing parameter on another together with the consequences on climate change is complicated, the study of sediment archives can help to understand these interactions and to predict the natural response to changing climate factors also for the future (Arimoto, 2001).

To assess these climate-controlled processes, it is crucial to understand palaeoclimate records from sedimentary archives. There have been a great deal of studies concerning how glacial, fluvial, lacustrine, marine and aeolian processes are associated with certain climate conditions and variability during the most recent geological Period, the Quaternary (2.58 Ma-present), and in turn how important a detailed characterization of these sediment deposits, their provenance and transport pathways can be for the understanding of sediment dynamics and environmental conditions in the past (e.g. Knox, 1983, 1996; Gregory et al., 1996; Benito et al., 1998; Blum and Törnqvist, 2000; Maher et al., 2010; Li et al., 2020; Krijgsman et al., 2019). As a result, the Quaternary is extensively investigated by the means of a broad variety of provenance and palaeoenvironmental proxies. The Quaternary is characterized by alternating cold glacial and warmer interglacial stages, which lead to the advance and retreat of continental ice sheets and mountain glaciers in both hemispheres, affecting river dynamics, sea-level stands, atmospheric circulation patterns, sedimentary cycling, aridity and dustiness in a chain of implications (e.g. Sun et al., 2007; Kislov and Toropov, 2006; Svendsen et al., 2004; Bird et al., 2015; Stevens et al., 2007; Buggle et al., 2009).

Due to this coupling, the shift between glacial and interglacial stages is reflected in deep-sea cores containing fossil foraminifera shells made of calcium carbonate (CaCO3). This CaCO3 records changes in ice volume and temperature via oxygen isotope composition (δ18O). During cold glacial periods, the sea water is relatively enriched in the heavier isotope 18O, while the lighter isotope 16O is preferentially stored in glacier ice. Because of this stable oxygen isotope fractionation, the relatively more abundant 18O in the ocean is

12 incorporated into the CaCO3 shells of marine organisms such as foraminifera to a greater extent than 16O. During warmer interglacial phases and the melting of glaciers, more 16O becomes available in the oceans and relatively less 18O gets incorporated into the shells of foraminifera compared to glacial phases. This process leads to a characteristic pattern in the benthic foraminifera oxygen isotope ratios during the Quaternary (Fig. 1). These alternating glacial and interglacial periods are numbered as so-called Marine Isotope Stages (MIS), with the youngest stage (the present one) having the lowest number (MIS 1), increasing with time. Stages of even numbers represent glacial phases and odd numbered stages represent interglacial intervals (Emiliani, 1955; Shackleton, 1969). A combination of oxygen isotope data from various deep-sea cores is used to create so-called ‘stacks’ and thus a representative global dataset and basis for age models as well as correlation with less continuous Quaternary sediment sequences (e.g. LR04 stack from 57 globally distributed deep-sea cores; Lisiecki and Raymo, 2005; Fig. 1).

Furthermore, palaeomagnetic studies on the same deep-sea cores allow the establishment of a geomagnetic timescale and correlation with the MIS chronostratigraphy (e.g. Channell et al., 1997). Natural material containing remanent magnetic particles can record the Earth’s magnetic field at times of its formation through the particles’ alignment, allowing its reconstruction through time. The natural magnetic field of the Earth (also referred to as geomagnetic field) extends through the Earth’s mantle and crust out into space and can be modelled in a simplified way as a dipole, which is currently slightly tilted (11 °) to the Earth’s spin axis. At present, the magnetic field lines are pointing vertically towards the Earth’s Geographic North Pole and this situation is referred to as normal polarity. However, the geomagnetic field is not stationary and can fully reverse on geological timescales so that the Geomag- netic North Pole becomes the Geomagnetic South Pole during phases of reverse polarity (e.g. Laj and Channell, 2015). Magnetic stratigraphy was first used by Matuyama (1929), who attributed reverse magnetization in rocks, i.e. magnetization antiparallel to the normal geomagnetic field, to phases of reverse geomagnetic polarity. With this observation, the cornerstone for the development of geomagnetic polarity timescales was set and with age-control via absolute dating techniques (e.g. 40Ar/39Ar) the Pleistocene was subdivided into different polarity zones based on the measurements of magnetic remanence (Cox et al., 1963; McDougall and Tarling, 1963a; b; 1964). Following this pioneering work, palaeomagnetic records have also been stacked for global validity (e.g. Channell et al. 2016; Fig. 1).

14 Fig. 1: Global chronostratigraphical correlation table of stacked deep-sea palaeomagnetic and oceanic drilling record (MIS), and records from the Chinese Loess Se- quence for the last 2.7 million years (Cohen and Gibbard, 2020; modified with permission, the unmodified chart is available online at data.mendely.com). L stands for loess and S for palaeosol horizons in the magnetic susceptibility curve of the Chi- nese Loess Sequence (Ding et al. 2005). Note how palaeosol horizons are reflected by higher magnetic susceptibility than loess units and widely correlate to lower 18O records of the MIS (LR04 benthic isotope stack; Lisiecki and Raymo, 2005) reflecting interglacial phases. The palaeomagnetic record represents a compilation of Laj and Channell (2007).

While the isotopic record of deep-sea cores represents the benchmark record of global Pleistocene climate, glacial cycles are also reflected in continuous terrestrial sedimentary deposits, such as loess sequences. Atmospheric mineral dust (clay to silt sized mineral and rock fragment particles) and its depositional sedimentary product loess are important members in the coupled climate and sedimentary systems. Dust directly drives and responds to climate change and loess/dust deposits can be used to trace sediment provenance and changes in long term sediment cycling and storage, and can also be used to analyse past climate via a range of climate proxy methods. The climatostrati- graphic importance of loess archives was ultimately established through the correlation of Central European loess-palaeosol sequences with deep sea sediments via magnetostratigraphy and thus, with Pleistocene glacial cycles (Kukla, 1970; 1975; 1977). This correlation showed that glacial-interglacial cycles in loess sequences were recorded by repeated alternation of loess and palaeosol horizons. This link is often also reflected in the magnetic susceptibility record of loess-palaeosol sequences, which therefore was proposed as stratigraphic tool in combination with magnetostratigraphy from studies on Chinese loess deposits (Kukla et al., 1988; Fig. 1).

Proceeding from here, this thesis focusses on the wind-blown dust sediment loess and its importance as part of the sedimentary cycle, climate and environment, and linked to this, the use of magnetic susceptibility as palaeoclimate tool in loess is reviewed.

Atmospheric mineral dust and climate Loess sediments are formed from the deposition (and alteration) of atmospheric dominantly silt to clay-sized mineral and rock fragment particles, col- lectively called mineral dust (e.g. Schaetzl et al., 2018). This mineral dust is transported in suspension in the Earth’s atmosphere and as such, plays an important role in the climate system by influencing incoming solar radiation, al- bedo, cloud formation, primary productivity, and biogeochemical cycles. In turn, the amount and circulation of atmospheric dust is controlled by climate

15 changes as well (e.g. Arimoto, 2001; Maher et al., 2010; Choobari et al., 2004; Harrison et al., 2001; Fig.2). This interaction of local and global climate with atmospheric dust makes the material an intensively studied subject, particularly in recent times where climate change and its consequences for nature and humanity have become a greater discussed topic than ever (e.g. Schepanski et al., 2009). Examination of wide scale movement of dust material and its distribution is crucial to understand how much material has been transported for how long and the pathways of this transport. With this knowledge, the potential impact of atmospheric dust on the Earth System can be better simulated (Albani et al., 2015).

Fig 2. Dust-climate-landscape connection (after Schepanski et al., 2009).

Most studies on dust and climate are conducted based on recent and current observations. However, understanding the role of dust in the climate system requires observations extending far back beyond these records because climate and dust variability have been significantly different and more extensive in the recent geological past. Palaeodust deposits, like for example preserved in ice cores, deep-sea sediments, peat bogs, or as loess sequences, represent valuable natural palaeoclimate and dust archives and can be used to demon- strate how dust and climate are linked in complex ways. Palaeoclimate records stored in these palaeodust deposits are not only crucial to reconstruct past climate and its variability in the past, but also to understand the driving forces

16 behind certain environmental conditions as well as dust emission and loading and their interaction with other global systems. An example for excellent paleoclimate archives from aeolian dust are loess sequences.

Loess Loess is a wind-blown sediment, which is generally light brown-yellowish in appearance, metastable open-structured and well sorted. The dominant grain size of loess is silt (2-63 μm), with subordinate sand (>63 μm) and clay (<2 μm) fractions. The proportion of these grain size fractions in loess is site dependent and can yield information about e.g. aridity, wind speed, source prox- imity. Around 6-10% of the Earth’s continental surface are covered by loess today, which forms homogeneous, massive sequences without internal bed- ding or stratification, up to several tens and even hundreds of meters thickness (e.g. Pye, 1995; Li et al., 2020). This extensive spatial distribution of loess deposits is most concentrated in areas of temperate, continental climate, which were not covered by ice sheets and glaciers during the Quaternary (e.g. Muhs and Bettis, 2003). The formation of loess deposits is often associated with cold and dry, gusty climate, during which silt material accumulates through aeolian deposition. However, considerable debate exists over the origin of the cold- climate related silt material of loess (e.g., Smalley et al., 2009, 2011). In addition to the now widely accepted definition of loess as a product of the accumulation (and modification in classical sensu strictu definitions) of wind- blown dust (e.g. Pye, 1995; Muhs, 2013), alternative theories propose the in- situ formation of the material, mainly due to pedogenic or cryogenic weathering and reworking of the underlying substrate, with no aeolian transport in- volved (Berg, 1916). While this latter theory is now widely discredited, it still finds some supporters, especially for some loess deposits on the East European and Siberian plains in the area of the former USSR. Based on the aeolian theory of loess formation, four stages are proposed for the material on its way from source to sink: production, transportation, deflation and deposition (e.g. Smalley, 1966; Fig. 3). In this chain of processes, the main supply for fine- grained material is seen in glacial grinding by mountain glaciers or continental ice sheets (e.g. Hardcastle, 1890; Smalley 1966), and its transportation is explained as a matter of multiple steps, often involving a stage of river transport prior to final aeolian transport to deposition as loess (Fig. 3). This highlights the importance of rivers in the distribution of aeolian sediments, such as loess, as well as the fundamental role of rivers in eroding and moving large volumes of sediment to areas where it can easily be deflated and subsequently trapped and deposited (Smalley et al., 2009). This river-loess model is also supported by the numerous locations where loess deposits are found along large rivers, and implies that final loess transport only occurs over a short distance by wind from relatively close by (single to hundreds of km) deflation zones. In

17 contrast, it implies that rivers are fundamental to the much wider distribution of sedimentary material from source regions, potentially over several thou- sands of km, and that even in loess deposits the last step of aeolian transport plays a minor role in wider scale sediment distribution. Areas for deflation are often unconsolidated, poorly vegetated fluvial deposits of low clay content in semi-arid and arid regions, and with abundant sediment supply. Alluvial plat- forms, floodplains, and alluvial fans of such character can act as sources to wind-blown deposits. In respect to this river-loess model, and considering that there might be temporal sediment sinks, such as desert basins, on the multi- step pathway of material to loess deposits, three general modes of pathways are described (Li et al., 2020, Fig. 3):

(1) Continental glacier provenance-river transport mode: The main production of the material is linked to continental ice sheets and this material then gets transported by rivers from glacial out-wash areas to alluvial plains and similar deposits for deflation. No large temporary sinks exist between the river and the loess deposit.

(2) Mountain provenance-river transport mode: High-altitude areas represent the place of production, mainly via mountain glaciation, from where rivers transport the material to immediate lower elevation zones of deflation. This mode also includes no large temporary sinks along the pathway to loess deposition area.

(3) Mountain provenance-river transport-desert transition mode: The source material production takes mainly place in high altitude areas. Rivers act as transport agent to lower altitudes and into desert basins, from where the material subsequently gets deflated and further deposited as loess. Here, a large temporary terrestrial sink (e.g. a desert area) exists along the long-distance wind transport pathway from the fluvial to the loess deposit.

Thus, loess is therefore a product of many potential sediment pathways, and as a result of this, loess has the unique potential to not only record the climate in the area of loess deposition itself, but it is also sensitive to environmental changes in the source regions and along its transport pathways, making analyses of loess provenance as important as climate reconstructions at its deposits.

Fig. 3. Schematic multi-step sequences leading to the formation of loess deposits via different transport pathway modes. Note the possibility of mixed pathways and sources to loess deposits.

Loess as a palaeoclimate archive Loess represents an excellent climate archive for the Quaternary and is especially important for the reconstruction of palaeoenvironmental conditions in semi-arid to arid regions, where other long-term palaeoarchives might be rare. Extensive deposits are found in semi-arid regions of China, Central Asian countries and Russia for example, and in these areas few other long-term archives are preserved. As a palaeoclimate archive, loess comprises terrestrial records of both past environmental change and near-source aeolian mineral dust (Muhs, 2013). Loess sequences also have the great potential of recording syn-depositional environmental conditions (conditions at transport and deposition), as well as the post-depositional effect of climate on the deposits. The latter is often expressed in form of pedogenic horizons and palaeosols, which form due to the weathering and alteration of the loess. While loess deposition signals cold and arid periods, classical for Quaternary glacial stages, palaeosols generally indicate a shift to milder conditions and decreased dust input, which can generally be correlated with interglacial stages (Fig. 1). An- other post depositional climate indicator is cryogenesis and the formation of frost related features, such as e.g. ice wedges, which modify loess sediments and stratigraphy under permafrost conditions.

A multitude of methods exists for the stratigraphic characterization of loess sequences and to identify such syn- and post-depositional processes; among

19 them environmental magnetism, grain size and geochemistry. These stratigraphic tools are of great importance for the reconstruction of palaeoclimatic and -environmental conditions and their changes, particularly at a local and regional scale. Loess as a climate record, however, can also store information of continental and even global importance and while the wide scale comparison of palaeoclimate proxies from different loess sites can reveal such relationships (e.g. magnetic susceptibility; Fig. 1), particularly also loess provenance analyses are useful for understanding wider climate forcing and several coupled processes of the Earth and climate system. Through their recorded provenance history, loess deposits can reveal information on how loess source and sink areas are formed, help discriminate between distant and near loess sources, and enable the identification of the potential mixing of various dust sources. Also, a temporal change in contributing sources driven by tectonic and/or environmental conditions can be addressed via provenance studies.

As a result of these many investigation possibilities, loess deposits have gained research attention all over the world. Particularly well-investigated are the extensive deposits in East Asia, most notably on the Chinese Loess Plat- eau. Many advances in loess research and in the application and use of different palaeoclimate (e.g. environmental magnetism), chronostratigraphic (e.g. luminescence), and provenance proxies (e.g. detrital zircons) come from studies on Chinese loess (e.g. Chen et al., 1997; Nie et al., 2015; Porter, 2001; Stevens et al., 2018). European loess has also experienced remarkable research interest, pioneered by Fink and Kukla through their magnetostrati- graphic correlation of loess stratigraphy with MIS stratigraphy (Kukla, 1975, 1977; Fink and Kukla, 1977). While European sections are well described by means of numerous palaeoclimate proxies, targeted provenance work is still in its infancy (e.g. Ujvári et al., 2012). European, Russian, Central and East Asian loess deposits together form the vast Eurasian loess belt, and play an important role for the reconstruction of Quaternary palaeoclimate in Eurasia and its dust history. The Lower Volga region in the northern Caspian Sea area of southern Russia, represents an understudied area of probable loess deposition in middle of this Eurasian loess belt, representing somewhat of a missing link towards a full understanding of Eurasian loess and climate evolution (Fig. 4).

Fig.4. Loess distribution (grey shaded areas) in Europe including the East European Plain (from Smalley et al., 2009). Note the occurrence of loess deposits in relation to the extent of the last Glacial Northern Hemisphere Ice Sheet at 18 ka (after Hughes, 2010), mountain glaciation (after Lehmkuhl et al., 2020) and large rivers. Note also the influence of sea-level oscillation on loess deposition and preservation in the Cas- pian Sea region. The Caspian Sea surface extent during the “Great Khvalynian” transgression and the Atelian regression is shown after Dolukhanov (2009) in dark blue lines. Note the possible interaction between Black Sea and Caspian Sea during times of sea-level high stand via the Manych depression and Azov Sea. The red circle indicates the location of the three Lower Volga loess sites studied for this thesis.

The specific aims of this thesis are described below, but in general, the thesis sets out to provide new information on the origin and formation of these continental silt deposits in the Lower Volga region, in order to test whether this understudied, yet debated material can be defined as aeolian loess (Fig. 5). If these silt deposits of the Lower Volga sequences can be confirmed to be wind-blown, this material has great potential to contribute to a better understanding of past climate conditions, and their evolution and wider forcing in the region, as well as of sediment provenance and pathways. As such, the thesis then attempts to understand past climate and sediment routing from Lower Volga deposits.

21 The northern Caspian Sea region and Lower Volga loess The Caspian Sea is the world largest inland water body unconnected to any ocean. The level of its water surface at present lies at 27 m below global sea- level. Its formation as a land-locked sea dates back to about 3 Ma ago when the beginning of a series of tectonic uplift and glacio-eustatic sea-level fluctuations lead to its separation from the Black Sea (Krijgsman et al., 2019). Rus- sia borders the Caspian Sea in the south-eastern part of the East European Plain (EEP). A major part of the Russian Caspian Sea coast is captured by the estuary of the Volga River, which drains into the Caspian Sea forming a large delta. The Volga currently supplies the biggest part of fresh water input to the Caspian Sea, more than 80%. Its catchment area covers 1.4 million km2, most parts of which lie in the EEP (Kroonenberg et al., 1997; Dumont, 1998). South of the city of Volgograd the Volga River starts to significantly change from a single channel large river towards a braided multi-channel system forming a wetland area of several tens of km in extent (Fig. 6). This area extends around the main branch of the Volga and its major side branch, the Akhtuba River, often called the Volga-Akhtuba floodplain. The region surrounded by lowland plains is generally known as the Lower Volga region and more regionally as Northern Caspian lowland (Fig. 6).

The environment of the Northern Caspian lowland at present is dominated by a dry continental climate with grass steppe vegetation, average annual temperatures of around 8 °C, and average annual precipitation of 300-400 mm in the upper part of the Lower Volga region (Sirotenko and Abashina, 1992). Pal- aeogeographically, the Northern Caspian lowland represents a part of the Late Pleistocene Northern Caspian sub-basin, which has been affected by Caspian Sea sea-level fluctuations several times during the Late Pleistocene, leading to tens of meters differences in water stand (e.g. Shkatova, 2010). The effect of these transgression and regression phases can be clearly seen in the landscape and deposits of the flat northern coastline of the Caspian Sea and the present-day Lower Volga region, namely in the form of large marine terraces (Yanina, 2014). During the Late Pleistocene, two major Caspian Sea transgressions took place: the Khazarian (~MIS 5, e.g. Shkatova, 2010; 10 to 5 m below global sea-level) and the Khvalynian transgressions (~MIS 2, e.g. Kurbanov et al., 2020; 50 m above global sea-level). These are separated by the Atelian phase of regression (~MIS 4 and 3; e.g. Tudryn et al., 2013). Table 1 summarizes the different phases and features of this late Quaternary variability in Caspian Sea sea-level. The ‘Great’ Khvalynian, as it is also called due to its considerable spatial extent, represents the most extensive phase of transgression in the history of Caspian Sea evolution during the Late Pleistocene. The sea-level rose up to 50 m above global sea-level (Yanina, 2014), which shifted the location of the estuary of the Volga River into the Caspian Sea considerably further north than where the city of Volgograd is located today

22 (Fig. 4). With the neighboring Manych depression at an altitude of 27 m above global sea-level, interaction between the Caspian Sea and the Black Sea, as well as further discharge to the global ocean over the Bosporus strait, occurred during such phases of sea-level high stand. Relicts of both the Khazarian and the Khvalynian transgressions can be found along all Caspian Sea shorelines (Yanina, 2014).

While these transgressive phases are represented by thick marine deposits of different facies, alternating terrestrial silt and sands are preserved from the intervening regressive Atelian phase (Svitoch, 1991; Svitoch and Yanina, 1997). The Atelian is described as major regression, during which the water level of the Caspian Sea decreased to 120-140 m below global sea-level. This led to the exposure of Caspian Sea shelf in many places (Fig. 4). Deep river incision into these newly exposed surfaces and accumulation of continental sedimentary material was the consequence of this sea-level drop (Fedorov, 1978; Rychagov, 1997; Fig. 5). The base of the Atelian deposits, as described for the Lower Volga region, is formed by the terrestrial Akhtuba deposits. Cracks and wedges, associated with cryogenesis, can be found at the lower boundary of these deposits at many sites and indicate periglacial conditions during Akhtuba deposits deposition (Goretskiy, 1958). The Atelian sediments overlying the Akhtuba deposits are often loosely and variously described in literature even though their thickness can reach up to 20 m (Fig. 5). In the Lower Volga region, they are often referred to as (sandy) loam and loess-like material (e.g. Moskvitin, 1962; Goretskiy, 1966; Sedaykin, 1988). The occurrence of some stunted freshwater and continental mollusks within the Atelian continental deposits, as well as remains of mammals of the Upper Paleolithic fauna (35-10 ka ago; Yanina, 2014), suggest deposition during a cold climate, in accordance with the occurrence of periglacial features. The Atelian as a whole is generally correlated with MIS 4-3, which is likely a period of regional cold and arid conditions in the Northern Caspian Sea region. However, some climate variation is indicated by the occurrence of up to four palaeosol horizons in the Atelian deposits, and pollen records indicate a shift towards warmer climate in the upper part of the sedimentary succession (Yanina, 2014; Lebedeva et al., 2018). Apart from these general climate indicators, the sub- aerially accumulated, continental material of the Northern Caspian lowland has gained little research attention in the literature, very much in contrast to the marine deposits, which are extensively studied in terms of their palaeoenvironmental significance and for understanding of Caspian Sea sea-level history (e.g. Fedorov, 1978; Svitoch and Yanina, 1997). Furthermore, generally, most research from the Northern Caspian Sea region is published in Russian- language journals, leaving an even more incomplete picture of palaeoenvironmental conditions and their implications in the region to non-Russian speaking scientists. In any case, most of our understanding of past changes in this region comes from studies conducted on the transgressive deposits. One of the

23 reasons why the sub-aerial Atelian deposits are seldom considered in palaeoclimate reconstructions might be because of their much-debated origin and transport, as well as lack of understanding of their post-depositional modification. Lower Volga sub aerial deposits have been argued to be derived from both in-situ production as well as an aeolian loess origin. In-situ formation has been suggested based on cryogenic weathering processes (e.g. Kolomoitsev, 1985) or slope processes (e.g. Lavrushin et al., 2014). However, more recent studies have tended to refer to the material as aeolian Lower Volga loess (e.g. Tudryn, 2013; Lebedeva et al., 2018). This conflict is essential to resolve if progress is to be made in the use of these deposits as past environment and climate archives, and for reconstruction of sediment routing.

24 Probable Sea- level stand Characteristic Event Substage Features References time (a.g.s.l.) sediment

Late Khvalynian Yanina (2014); Chocolate Clay; Relict shoreline Khvalynian Coastal with features; e.g. Rychagov Enotaevka MIS 2 50 m Transgression abundant marine Khvalynian (1997); e.g. Tudryn et al. Early Khvalynian fauna fauna (2016) Akhtuba Sands, cracks and Svitoch (1991); Atelian -120 to -140 Atelian sandy wedges, mol- Svitoch and Ya- MIS 4/MIS 3 Regression m loam/loam (lo- lusks and mam- nina (1997); ess/loess like) mal fossils Yanina (2014) Varuschenko et al. (1987); Coastal with Khazarian Khazarian Yanina (2014) Late Khazarian MIS 5 -10 to -5m abundant marine Transgression fauna Tudryn et al. fauna (2013); Shkatova (2010) Table 1: Caspian Sea sea-level evolution during the Late Pleistocene (a.g.s.l. = above global sea-level) 25

In any case, the alternation of continental loess and marine material is unique to the Lower Volga region and changing depositional environments are recorded in both the continental material, likely transported by wind and/or the Volga River, and the marine sediments deposited by the Caspian Sea.

Fig. 5. Natural outcrops of the continental and marine deposits of the Late Pleisto- cene in the Lower Volga along incised gullies and rivers, note the development of pedogenic horizons within the loess sequences and the deposition of marine sands and dark marine clays from the Khvalynian transgression on top of the subaerial Atelian sediments: a and b. Leninsk, c. Srednyaya Akhtuba, d. Raigorod/Raygorod.

Despite the clear sedimentary evidence for Caspian Sea sea-level changes out- lined above, the details and causes of these changes remain to be completely understood. In particular, the causes of sea-level fluctuations are poorly known, and may be linked to local or regional climate, river dynamics, glaciation of the northern EEP, or links to other water bodies. The last glacial climate over the EEP was characterized by cool and arid conditions, drier in its south and milder during interstadials (e.g. Dodonov et al., 2006; Liang et al., 2016; Buggle et al., 2009). Due to its independence from eustatic sea-level, the Caspian Sea is likely to be highly sensitive to variations in this prevailing climate, for example via surface runoff, precipitation, evaporation, and Cas- pian Sea outflow (Panin and Matlakhova, 2015; Soulet et al.,2013; Mangerud et al., 2004; Ollivier et al., 2015; Tudryn et al., 2016; Yanina et al., 2017). However, the extent to which these parameters and resultant sea-level oscillations are related to Northern Hemisphere glaciation in the EEP and the Sibe- rian Plain, and/or rather regional climate changes, is not yet well established.

26 A connection to glacial cyclicity is suggested for the Late Pleistocene evolution of the Caspian Sea and is extensively studied, particularly in regard to the large Khvalynian transgression. This sea-level rise took place during glacial phases and cold climate, which contrasts with the commonly expected occurrence of transgressions during phases of warming and glacial retreat (Chepalyga, 1984; Varuschenko et al., 1987; Velichko et al., 1987; Kar- pychev, 1993). The Volga River likely plays a crucial role in understanding this paradox. Increased precipitation and/or lower evaporation in the EEP coupled with glacial discharge of the Fennoscandian Ice Sheet (increased during phases of its decay and annual melting) might have greatly enhanced the Volga’s discharge into the Caspian Sea during transgression phases. The actual source(s) of and reason(s) for increased water input to the Caspian Sea during cold transgressive phases remain to be understood completely, although it is likely that the EEP represents the main source for any additional water supply (Yanko-Hombach and Kislov, 2018). However, similar events are also hypothesized for rivers draining the Siberian Plain into the Caspian Sea (Kvasov, 1979; Grosswald, 1998; Mangerud et al., 2001, Sidorchuk et al., 2009). In addition to this increased water input, local factors such as decreased evaporation over the Caspian Sea itself, or changes in its outflow, might play a role in the occurrence of transgressive phases during cold climate (Kislov et al., 2014). The understanding of the implications of sea-level changes of the Caspian Sea is further complicated due to proposed interaction of the Caspian Sea and Black Sea during major transgressive phases via the Manych depression (e.g., Mangerud et al., 2001; Leonov et al., 2002; Fig. 4). This uncertainty is ongoing and consideration of the stratigraphic evidence for changing sea- level, and analysis of continental Atelian deposits as palaeoclimate archives, can substantially add to this discussion (e.g., Mamedov, 1997; Dolukhanov et al., 2009; Yanina, 2012).

27 Aim of the thesis

“A journey of a thousand miles begins with a single step” – Laozi

The general motivation for this thesis lies in the need to understand the complexity of the several environmental systems and depositional environments in the Lower Volga region and their link to climate and its variability during the Late Quaternary. In particular, a number of unresolved questions require more investigation and paleoenvironmental studies:

1. What drives Caspian Sea sea-level oscillations and how are they connected with Northern Hemisphere glaciations and regional and global climate? 2. How were the continental deposits in the Lower Volga region formed and what can they tell us about wide scale sediment routing and cycling? 3. What climate records can be derived from the Lower Volga continental deposits, located as they are at a key point of the Eurasian loess belt?

This thesis aims to directly address these key questions. It does so via a series of approaches, including enviromagnetic, geochemical, and providence techniques, designed to first test the origin of continental deposits in the Lower Volga region and then use these deposits to attempt palaeoenvironmental, and sediment transport and routing reconstructions.

While mineral magnetic parameters are widely applied as palaeoclimate proxies in loess deposits (e.g. Maher, 1998), the uniqueness of Lower Volga loess (LVL) sequences, accumulated during a phase of cool regression and subsequently covered by a marine transgression, requires that enviromagnetic parameters are thoroughly tested for their use in climate reconstruction from these and other sediments in such and similar settings. As such, one objective of the thesis was to critically review the use of commonly applied enviromagnetic parameters and their applicability in different climatic and depositional settings and, if possible, provide models for interpretation of similar deposits

28 (Paper I and II). The continental silt (arguably loess deposits) along the Lower Volga and their properties in comparison to other classical loess deposits are then described and characterized by means of environmental magnetism together with stratigraphy, geochemical analyses, and grain size and shape (Paper I). Palaeoenvironmental reconstructions from the LVL are then addressed via two approaches: 1) the use of these climate proxies from three sites along the Lower Volga River to characterize climate variability during the deposition of continental sediments (Paper I and II) and 2) through use of provenance analyses aimed at defining a broader spatial understanding of driving forces behind sediment production, transport, and deposition in the EEP and in the Caspian Sea region more widely and particularly for LVL (Pa- per II and III). In this regard, the thesis also aims to test the applicability of detrital zircon U-Pb ages in sediment provenance studies in the EEP (Paper III).

While addressing these large-scale questions would have given enough material for four separate research articles, we decided to combine more techniques and methods into the single papers and discuss a larger, often multi-proxy dataset, in each of them to address the complexity of the situation more effec- tively and make the interpretations in each paper stronger. Particularly for paper III we complemented a very large original dataset with published data to considerably add to existing knowledge about a wide area stretching from the northern EEP all the way to central Asian deserts and mountain ranges south of the Caspian Sea, providing by far the most comprehensive detrital zircon U-Pb analysis of sediment sources in the region.

29 Study sites

“New places always help us look at life differently” – Joan Bauer

For this thesis, three late Pleistocene sites along the upper braided fluvial system of the Lower Volga River in the Northern Caspian lowland, southern Rus- sia, are used as reference sites for Late Quaternary palaeoclimate reconstructions in the region and on a larger continental scale (Figs. 4 and 5). The site Srednyaya Akhtuba (SA) is located 30 km east of the city of Volgograd on the east bank side of the Akhtuba River, the main side river within the braided Lower Volga system (48.7004° N, 44.8937° E, WGS 84). 30 km further east, on the same river bank side, the site Leninsk (LN) represents a natural outcrop in a dry gully (48.7213° N, 45.1592° E, WGS 84), and the section Raigorod (also Raygorod; RG) lies directly on the west bank of the Volga River’s main branch, 30 km south of Srednyaya Akhtuba (48.4313° N, 44.9665° E, WGS 84) (Fig. 6). All sections show alternating sequences of different marine and continental sediments and therefore well represent alternations between various depositional environments during their deposition. A major part of each section is comprised by loess. A detailed stratigraphic description of the three sections is given in paper I.

Fig. 6. Map showing the location of the three Lower Volga sites Srednyaya Akh- tuba, Leninsk and Raigorod (marked with stars) in the Volga-Akhtuba floodplain. The map detail in the lower right corner shows the location of the Volga-Akhtuba floodplain in the Northern Caspian lowland (after Kurbanov et al., 2020; based on National Geographic World Map, Esri).

31 Methods

“What we see depends mainly on what we look for” – John Lubbock

For this thesis a combination of several different techniques and methods is used to address the topics listed above.

Environmental magnetism Mineral magnetic methods play an important role in the reconstruction of pal- aeoenvironments from loess sites because the type, amount, size, and character of magnetic mineral particles are highly sensitive to environmental changes and can give information about syn-, and post-depositional processes such as weathering, soil formation, and source change (e.g. Thompson and Oldfield, 1986; Maher, 1998; 2011; Hällberg et al., 2020). For this reason, and following the pioneering work of Kukla in magnetostratigraphy combined with magnetic susceptibility as stratigraphic tool, basic environmental magnetic analyses have become somewhat routine in the studies of loess sequences. The most established and commonly applied of these methods are low field magnetic susceptibility (χ, mass corrected and given in m3 kg−1) and frequency dependent magnetic susceptibility (χfd, %) (e.g. Schaetzl et al., 2018 and references therein).

Magnetic susceptibility describes the response of a material to a magnetic field, more specifically the degree of magnetization induced in a material. In natural material such as loess, it is primarily the mixture of the contained minerals and their magnetic properties, which control the response to the applied magnetic field. According to their magnetic behaviour, different types of magnetic minerals are distinguished in natural materials: ferromagnetic, ferrimagnetic, canted-antiferromagnetic, paramagnetic and diamagnetic minerals. Fer- romagnetic minerals (e.g. pure iron, nickel, chromium) exhibit strong positive susceptibility and are rare in natural environmental samples, while ferrimag- netism represents the most important category of magnetic behaviour in natural material. Ferrimagnetic minerals show strong positive magnetic response, capability of magnetic remanence, and commonly contain iron. The most

32 important representatives in loess are e.g. magnetite and maghemite. These minerals can be inherited from the source rock or formed due to weathering and possibly biogenic processes. Such secondary formed iron oxides are typically of fine-grained character (superparamagnetic; SP, or single-domain; SD), while inherited particles are generally larger (multidomain; MD). While canted-antiferromagnetic minerals exhibit moderate positive susceptibility (e.g. hematite), paramagnetic minerals show weak positive magnetic susceptibility (e.g. biotite), and diamagnetic minerals exhibit weak negative susceptibility (e.g. organic matter, quartz, feldspars, carbonate).

The measured χ of a bulk material reflects the sum of all magnetic contributors (ferri-, canted-antiferro-, para-, and diamagnetic; e.g. Evans and Heller, 2003), which means that enhancement of χ in loess can indicate the removal of diamagnetic minerals (e.g. due to dissolution of calcium carbonate), but more importantly, signal the formation of secondary ferrimagnetic minerals due to weathering, or alternatively, the increased input of coarser detrital ferrimagnetic minerals. This leads to two different main models being proposed for the control of the χ signal in loess. Following up on magnetic enhancement studies on contemporary soils (e.g. Tite and Linington, 1975), the most commonly known pedogenic enhancement model has been established from studies on Chinese loess (Heller and Evans, 1995). It describes the enhancement of χ due to pedogenic formation of ultrafine SP grains during warm and moist climate periods (Liu et al., 2004). Alternatively, the wind-vigour model suggests that a higher χ signal is caused by coarser and denser MD iron oxide particle input through stronger winds during cooler periods (Evans, 2001). This model applies for example for Siberian loess sites, where increases in χ are shown to be primarily driven by wind dynamics leading to a coarsening of particles and increased detrital magnetite input (Evans and Heller, 2003). While low field χ measurements at one frequency reflect the contribution of all magnetic minerals state to the signal regardless their domain and therefore, the general composition of the loess, measurements at two different frequencies allow the calculation of χfd, which has been used as an indicator of pedogenesis in loess sequences. The applicability of this proxy is based on the sensitivity of χfd to ultrafine SP particles (Forster et al., 1994) and the formation of ultrafine- grained iron-oxides (e.g. magnetite, maghemite and hematite) during pedogenesis (Liu et al., 2007; Maher, 2011). Keeping the two models for χ interpretation in mind, this would mean that χ and χfd either show a correlating or non-/anticorrelating relationship dependent on whether χ is driven by fine grained secondary formed ferrimagnetic minerals or primary coarser particles. While this seems to be true for the areas where these commonly accepted models were established, there are cases, in which χ and χfd signals do not show the expected straightforward relationship and none of the models can serve as full explanation (Bradák et al., 2021). This shows that the interpretation of magnetic susceptibility in loess research is complex, despite its reputation as

33 straight forward standard magnetic palaeoenvironmental proxy (e.g. Schaetzl et al., 2018 and references therein). A reliable interpretation of its signal requires additional enviromagnetic analyses, despite the majority of studies seldom going beyond χ and χfd. A great complement to χfd in cases where its signal is not distinctive for the discrimination between loess and pedogenic affected horizons, is temperature dependent magnetic susceptibility (κT). Here, magnetic susceptibility is measured at different temperatures. In contrast to χ and χfd, κT not only indicates the type of magnetic contributors but can also give information about the actual magnetic mineral content of a sample, since the magnetic properties of minerals are temperature dependent and can be diagnostic if a defined Curie, or Néel temperature exists, for example. κT can therefore be a useful method for the identification of pedogenesis or the applicability of the enhancement model in loess sequences.

As mentioned before, also the determination of a material’s magnetic domain state can be diagnostic for its formation conditions (Forster and Heller, 1997). While κT can give some information on the domain state (and indirectly grain size) of certain minerals, a more unambiguous determination of domain state (and inferred grain size) is achieved by the use of magnetic parameters from magnetic hysteresis measurements and Anhysteretic Remanent Magnetization (ARM) experiments. These experiments are relevant to the ferrimagnetic content of a material due to the ability of ferrimagnetic minerals to retain magnetic remanence. For magnetic hysteresis experiments, a sample becomes remag- netized along the direction of an applied large magnetic field, which is called isothermal remanent magnetization (IRM). Increasing the applied field, increases the IRM until it reaches saturation (Mrs). Just in the same way, also the induced magnetization of the sample increases until it is saturated, which results in the saturated magnetisation (Ms). Mrs is grain size dependent while Ms is not, so the ratio between the two can provide information about magnetic grain size. The magnetic “hardness” or coercivity (Bc) of a mineral describes the magnetic field that is needed to drive mineral magnetization from saturated to a demagnetized state. These three parameters from hysteresis experiments can be utilised in combination for magnetic grain size estimation through using the parameter specific sensitivity to grain size, domain state and mineralogy. Similar information can be derived also from ARM measurements. ARM is imparted by placing a sample in an alternating field with a superimposed direct current and allows the determination of χARM, which shows different behaviour than χ according to the grain size of the magnetic mineral, and as such, can also be utilized in combination with the other parameters to estimate the mineral magnetic grain size of a sample.

For the enviromagnetic study of Lower Volga loess a combination of these described magnetic methods was applied in paper I. High resolution bulk samples were taken from the entire sections of SA and RG, and from the loess

34 sequence of LN for χ and χfd measurements. Representative pilot samples from all three LVL sites were chosen for κT, ARM and hysteresis analyses. A detailed description of the sampling at the three sections and the laboratory pro- cedure is presented in paper I.

Another way of using magnetic susceptibility is by measuring its anisotropy. Anisotropy of Magnetic Susceptibility (AMS) describes the variability in magnetization in different directions within a sample. AMS in rocks or bulk samples, as in the case of sediments (e.g. loess), derives from the preferred orientation of its anisotropic magnetic particles or grains, which define a magnetic fabric. AMS is described as an ellipsoid of magnetic susceptibility with three principal axes, κmax≥κint≥κmin, where κmax/κint defines the magnetic linea- tion and κint/κmin the magnetic foliation. Dependent on the ratios of these principal axes the AMS ellipsoid can reflect oblate, prolate or triaxial shape. The degree of anisotropy is given by κmax/κmin (Tarling and Hrouda, 1993). In prin- ciple, two controls on the magnetic fabric are distinguished: the orientation of crystallographic axes of magnetic particles and the orientation according to their shape (magnetocrystalline AMS versus shape AMS; Tarling and Hrouda, 1993). For the latter, shape preferred orientation can be caused by the shape of individual grains or of grain clusters, known as distribution anisotropy (Hargraves et al. 1991). The AMS of an environmental material is often controlled by its ferrimagnetic contributors (e.g. magnetite). However, when the ferrimagnetic component is very small or can be considered isotropic, the paramagnetic (and sometimes diamagnetic) minerals have a significant influence on the magnetic fabric. In the case of sediments, the alignment and orientation of magnetic particles within a sample can be influenced by several factors such as processes at deposition. Thus, the AMS of sediments potentially allows reconstruction of the type and orientation of transport, flow energy and post- sedimentary processes (Tarling and Hrouda, 1993). The presence of a current during deposition can cause the alignment of elongated grains parallel to the transport direction, which leads to a flow-aligned magnetic fabric (Fig. 7). In the case of loess, the presence of such flow-aligned magnetic fabric can be used for the reconstruction of palaeowind directions as long as the primary sedimentary magnetic fabric remains preserved (Lagroix and Banerjee, 2004a, 2002; Zhu et al., 2004). Surface processes in loess, such as pedogenesis and cryogenesis, can cause the disturbance of the primary magnetic fabric and the development of a secondary magnetic fabric. Secondary magnetic fabric therefore serves as an indicator for reworking and redeposition, and their driving environmental conditions.

Oriented samples for AMS analyses were collected from the loess at Leninsk site. Details about the sampling and measurement of the total of 107 samples can be found in paper II.

Fig. 7. Alignment of elongated magnetic grains on a surface by a transport current, leading to a flow-aligned sedimentary magnetic fabric, with κmax defining the linea- tion

Geochemistry as proxy for weathering The application of geochemical analyses for measurement of weathering in sediments such as loess is based on the differences in solubility and mobility of some elements compared to others in different environments. To identify weathering affected horizons in loess sequences, the elemental or oxide composition of samples from different stratigraphic depths needs to be compared. To do so, different weathering ratios, chemical proxies and indices have been proposed. These different indices are applicable in different environments and are underpinned by different sets of assumptions over weathering effects (Buggle et al., 2011). The most commonly used elements in weathering ratios and indices include Ca, Sr, Na, Mg, and K because of their high mobility in weathering environments, which leads to their removal and relative depletion in comparison to non-soluble, immobile (or less mobile) elements such as e.g. Rb and Ba. However, since K-feldspar is somewhat more weathering resistant

36 than other silicate minerals, K is often less depleted than other mobile elements (Nesbitt and Young 1984, 1989). Nonetheless, as chemical weathering proceeds, K-feldspars are also affected and degrade together with other feldspars to clay minerals. This process leads to a relative enrichment of Al2O3, which is a dominant constituent of clay minerals. As such, in many of the published weathering indices applies as a general rule, the higher the Al2O3 content in comparison to other elements, the more pronounced the inferred siliciclastic weathering.

In paper II the Chemical Index of Alteration (CIA; Nesbitt and Young, 1982) was used to assess the occurrence of weathering and its intensity in addition to the analyses of selected major and trace elements in element ratios. Details about these used element ratios and the calculation of the CIA can be found in paper II. In total 18 samples from different stratigraphic depths of the loess sequence at LN were analysed via X-ray fluorescence (XRF). The sampling resolution and the laboratory preparation and analyses of the samples are discussed in the paper.

Grain shape and surface analysis The shape of detrital grains and their surface features can be highly distinctive for different processes during sediment cycling. A very effective method for the optical analysis of such features on single grains is scanning electron microscopy (SEM), and recording photographs from SEM represents an integral part of sedimentological research. Via high-resolution imaging of single grains, their shape, surface morphology, and microtexture (micron-sized features on the surface of the grains) can be studied. These features are indicative for processes of grain formation, transportation, and deposition and can serve as “fingerprints” for the pathway of formation to deposition experienced by each grain (Vos et al., 2014 and references therein). For example, rounded grain shapes can be indicative for aeolian transport, while dominating angular shapes point towards glacially forced breaking of the grains. The assessment of different kinds of fractures, percussion marks, striation, edging, or similar features on the grain surface complement the observations of grain shape in this approach. Table 2 gives a more detailed summary of different observed grain shapes and surface features and how this can be used to infer a grain’s sedimentary history.

Thirteen samples from the loess sequence of LN and one sand sample from the Palaeo-Volga River were studied under the SEM for paper II. Details of the sampling resolution, preparation and analysis are given in the paper.

37 38

Mechanical Roundness Conchoidal fractures Other surface features Angular outline Subangular outline Rounded outline µm) (<10 Small Medium (10-100 µm) Large (>100 µm) Arcuate steps Straight steps Meandering ridges Flat cleavage surfaces Graded arcs cracks V–shaped percussion Straight/curved scratches Upturned plates marks Crescentic percussion Bulbous edges Abrasion fatigue Parallel striations tures Imbricated grinding fea-

formation and transport mode

Fluvial S-C C C R-A R-C R-S R-C R-C R R-C R-D S-A R-C R-S R-S R R R R Marine R-S C C-A R-A R-C R R-C R-C R R-C R-S S-A R-A R-S R-S R R R R Aeolian R R-C A C S R S-C S C S C-A R-S R-S A C-A A C-A R R Glacial A R R A A A A A S C R S C S R R C A C Table 2. Environmental interpretation of mechanically caused grain features (after Vos et al., 2014). A=abundant (>75% of grains), C=common (50-75%), S=sparse (5-50%), R=rare (<5%). Note that microtextures of chemical origin are not considered in this table.

Detrital zircon U-Pb dating To properly constrain the provenance of sedimentary material from multiple complex source areas requires a technique that targets different types of source rock and transport histories (Tyrrell et al., 2012). While the majority of sediment provenance work is conducted on bulk/whole rock samples, single-grain approaches are becoming increasingly popular. Single-grain provenance trac- ers can be very source diagnostic in instances where multiple dust sources to loess deposits are expected as multiple individual grains can be traced back to single sources (Stevens et al., 2010). One of the most widely used and power- ful of these single grain techniques is detrital zircon U-Pb geochronology (e.g. Stevens et al., 2010; Újvári et al., 2012).

The mineral zircon (ZrSiO4) can be used to determine the formation age of igneous rocks and the occurrence of high P-T metamorphic events. It is one of the most abundant accessory minerals in most rocks, particularly felsic igneous rocks and their metamorphic equivalents and sedimentary products, and forms at high temperatures in silicic melts in the Earth’s crust. Its widespread use for U-Pb geochronology is based on the fact that its crystal structure is favourable to incorporate U but not Pb on formation. U-Pb geochronology makes use of the radioisotopic decay series of the radiogenic isotopes of U to the stable daughter isotopes of Pb, as well as of their known rates of radioactive decay. There are two separate decay series of U with half-lives covering the entire geological timescale of the Earth: 238U to 206Pb and 235U to 207Pb. This makes U-Pb dating an appropriate chronological tool for rocks of any age, with the exception of the most recent time periods. These two decay systems are linked to each other via the constant ratio of 238U to 235U (Hiess et al. 2012). For U-Pb geochronology, the amount of the radiogenic stable isotopes 206Pb and 207Pb in a mineral (e.g. zircon as ideal candidate) are measured relative to the amount of their parent radioisotopes. Since these Pb isotopes should form solely due to radioactive decay after mineral crystallization, the age of the mineral bearing rock can be determined based on the decay constants of the decay series isotopes (Parrish, 2013). This relationship can be complicated through the loss of Pb via radiation damage and additional age components formed in the analysed minerals, such as e.g. metamorphic rims overgrowing magmatic zircon cores. However, if these features are also specifically analysed, this allows to estimate not only the magmatic mineral formation age but also the age of potential metamorphic events. A common approach in this is the application of the Concordia diagram and its modifications (Wetherill, 1956; Tera and Wasserburg, 1972), in order to check for differences between U-Pb ages based on the two decay series. This approach is widespread in the literature, leading to large volumes of data that can be utilised in provenance studies seeking to characterise primary source rocks.

39 Due to its high resistance to erosion, transport and even metamorphism, zircons can survive several phases of geological cycling without being broken down (Morton and Hallsworth, 2007). This particular property also makes zircon extremely suitable for provenance studies. Detrital zircons reflect the potentially diagnostic formation ages of crustal proto-sources to sedimentary deposits and are used to trace back the origin of sediments and sedimentary rocks. To do so, most commonly the detrital zircon age distribution of the sediment is visually compared to potential source material. Kernel Density Estimation (KDE) is often discussed to be the most suitable way for such visualisation (Vermeesch, 2012). For a statistically robust provenance analysis a minimum number of ~117 grains is required to cover the main age populations in a sample, and a larger number decreases the risk of missing significant age fractions (Vermeesch, 2004) and even allows the comparison of their relative abundance. However, zircon U-Pb dating is not without limitations, e.g. zircon sources may not always be representative of those of the main sediment body, and zircon fertility in source rocks exerts a key control over detrital zircon assemblages (Sláma and Košler, 2012). Furthermore, in some situations, zircon U-Pb ages may not be able to discriminate possible dust sources due to overlapping age fractions and the impact of recycling can make age distributions hard to interpret if understanding of zircon age distributions in potential source sediment is not well constrained. It is therefore important to assess how suitable detrital zircon geochronology is for provenance analyses in a certain area prior to its interpretation. In the EEP the different timing of tectonic events in surrounding protosource areas leads to expected differences in ages of zircons derived from these rocks, and suggests that the detrital zircon U-Pb geochronology technique might be a useful, diagnostic tool to understand provenance and sedimentary dispersal systems in the area.

For paper III a total of 24 samples from loess and other sedimentary material from the EEP and the southern Caspian Sea region were analysed for high-n (n=~300) single grain detrital zircon U-Pb dating. The sampling location and the underlying strategy as well as laboratory details are described in the paper. In addition, paper III provides an extensive review and comparison of published detrital zircon data in the area. This dataset represents the most detailed U-Pb provenance dataset for Quaternary sediments over such a wide area to date, and allows for analysis of wide-scale sediment transport and origins.

Modern wind data analysis While weather and climate records of the present are quite complete, historical records of the Earth’s climate are not as reliable. Global observation stations were less abundant in the past and also more unevenly distributed than today. To overcome this problem and create a global picture of the climate during

40 the past decades close to reality, climate reanalysis as schematic approach combines historical weather observations with the present-day weather model and hence produces datasets for a comprehensive historical record of the Earth’s modern climate and its changing.

In paper II modelled wind data from the past 30 years in the northern Black Sea–Caspian Sea region, as well as at the LVL sites, were compared with reconstructed palaeowinds. These modern wind data were obtained from the reanalysis ERA5 with horizontal resolution of 31 km (Hersbach et al., 2020). Wind speed and wind direction were calculated from the zonal respectively meridional wind speed (u- and v component) measured at 10 m and 100 m height during winter (December, January, February) and summer (June, July, August).

41 Main findings

“A miracle constantly repeated becomes a process of nature” – Lyman Abbott

Lower Volga loess characterization (Paper I and II) The findings of all papers included in this thesis strongly suggest that the subaerial, terrestrial Atelian deposits in the Northern Caspian lowland are true aeolian loess. Previous studies (e.g. Lebedeva et al., 2018) have implied this, however, this is the first time that these sediments are actually characterized and classified based on numerous, combined analytical techniques. In our case, we did this by means of the sedimentary and magnetic properties of the material.

To summarise, based on the combination of the stratigraphic characterization and a detailed enviromagnetic investigation of the three LVL sites, paper I shows that the loess in the Lower Volga region displays classic characteristics typical to loess and its magnetic properties are comparable to other loess deposits all over the world. The aeolian origin of the Lower Volga loess is reinforced by the magnetic fabric analyses in paper II, which show that several horizons at Leninsk preserved primary aeolian magnetic fabric. In addition, grain shape and grain surface features indicate aeolian transport too.

The applicability of enviromagnetic parameters for climate reconstruction in cool climate loess deposits (Paper I and II) As shown in paper I, the magnetic properties of Lower Volga loess are within the range of what is typically observed from loess deposits around the world, but while enviromagnetic methods are widely used for palaeoclimate reconstructions from loess, most interpretations are based on models that were established from magnetic studies in areas of relatively humid and warm climate, mostly the monsoon-dominated Chinese Loess Plateau (e.g. Heller and

42 Evans, 1995). The most common approach is based on the pedogenic magnetic enhancement model and palaeoprecipitation estimations are often based on this prerequisite. However, it is known that this model in many cases does not apply for other loess regions, particularly in a different dominating climate, and that its application might lead to deficient palaeoclimate conclusions. Even though the wind-vigour model was introduced as an alternative model for magnetic enhancement from studies in cool, continental loess areas (e.g. Siberia), our multi-enviromagnetic proxy study on LVL shows that there is not always a sharp boundary between these two models and more factors than previously known might define the relationship between χfd and χ.

Paper I and paper II show that χ and χfd can be used as indicators even for weak pedogenesis under cool and dry climate, but require complementing with other enviromagnetic proxies for a reliable interpretation since a straight forward relationship between these two parameters might be complicated by post-pedogenic hydromorphic conditions or cryogenic reworking. While similar has been proposed from other enviromagnetic loess studies in cold areas (e.g. Babanin et al., 1995; Nawrocki et al., 1996; Taylor et al., 2014), our study is one of the few where such hypotheses are backed up with a large range of different magnetic analyses, including the study of magnetic fabric. In paper I, κT experiments reveal the presence of pedogenic SP maghemite in horizons for which χfd gives indistinctive evidence for pedogenic enhancement, while magnetic grain size determination by ARM and magnetic hysteresis experiments indicates coarse grained MD magnetite. This observation implies that the relationship between χ and χfd cannot always be explained with one of the common models alone, which do not consider the co-existence of SP, SD and MD ferrimagnetic grains and thus expect either correlation or non/anti-correlation of χ and χfd. For the Lower Volga loess, this is clearly not the case and shows that both SP and MD ferrimagnetic particles might be controlling the magnetic signal, and that particularly in cool and dry loess areas several magnetic parameters are required to fully understand the past environmental implications. Proceeding from this, the palaeorainfall analyses in paper I suggest that in areas where no strong pedogenic magnetic enhancement is given, palaeoprecipitation can be estimated more reliably by using methods based on several independent parameters such as from ARM and magnetic hysteresis experiments combined with χ, rather than χfd alone.

In addition to these findings of paper I, the AMS analyses in paper II demon- strate that magnetic fabric can reveal processes of reworking. Previous studies have put forward a connection between disturbed primary sedimentary magnetic fabric and pedogenesis (Matasova et al. 2001;, Zhu et al., 2004; Bradák et al., 2011) but the development of a particular magnetic fabric in connection with frost action and cryogenesis has seldom been observed and discussed (e.g. Lagroix and Banerjee, 2004b). The magnetic fabric of loess at LN

43 suggests that certain horizons were affected by pedogenesis or frost action. These findings give new insights to the formation of magnetic fabric in loess in cold environments and allow a better understanding of how primary magnetic fabric can be reworked and overwritten.

Considering the unique depositional setting in the Lower Volga region, where loess is covered by sediment laid down during a marine transgression, which is not known from anywhere else in the world, the discussion in paper I also suggests that the marine transgression had no detectable influence on the magnetic properties of loess under the given circumstances.

Palaeoclimate evolution in the Lower Volga region during the Late Pleistocene (Paper I and II) The setting and environment at the LVL sites do not impair the use of enviromagnetic methods for palaeoclimate analyses if applied and interpreted cor- rectly, as discussed above. As such, the findings of paper I and paper II reveal from enviromagnetic methods, together with sedimentological and geochemical proxies, that the climate in the Northern Caspian lowland during Atelian loess deposition was generally cool and dry. Palaeoprecipitation and palaeowind reconstructions, together with the observation of bioturbation and organic remains in the loess in the Lower Volga region, suggest a similar environment in the Late Pleistocene to today and that Atelian loess deposition took place in a semi-arid, continental steppe environment with annual precipitation of < 300 mm under prevailing westerly/north-westerly winds. While there is a strong apparent similarity between modern wintertime conditions in the Lower Volga region and our reconstructed Late Pleistocene climate, the Atelian period was cooler and dustier than today, as the amount of loess deposition and its intensive cryogenic reworking indicate. Furthermore, the enviromagnetic results of paper I and II suggest that MIS 4 was the coldest phase of the last glaciation in the region with stronger wind intensities than during the other stages and as such, are in line with studies from the neighbouring Azov Sea region (Liang et al., 2016). This is revealed by the χfd data from LVL discussed in paper I, which point towards cool and arid conditions during the MIS 4 of the Atelian regression, while the combination of the χfd, magnetic hysteresis, ARM, κT, AMS, and geochemical data indicate the occurrence of weak pedogenesis in the loess during potentially more humid and warmer periods during MIS 5 and MIS 3 (Paper II). At least three shifts towards more moist/warm environmental conditions can be determined from the LVL deposits associated with MIS 5 and MIS 3, but these probably were not concur- rent with significant changes in wind direction or strength. The evidence for cryogenesis from all MI stages of LVL deposition and the fact that

44 pedogenesis is only weakly developed, shows that the Atelian regression in the Northern Caspian lowland coincided with generally cold and arid climatic conditions punctuated by only slightly increased humidity and/or temperatures during its early stage (Late MIS 5) and later phase (MIS 3).

Detrital zircons as a provenance tracer in the East European Plain (Paper III) Detrital zircon ages can be highly source diagnostic for sedimentary rocks and sediments, such as loess, and while there can be some limitations in their use as provenance tracer, particularly in areas where the ages of different potential proto-sources are similar or a complex metamorphic history exists, the findings of paper III show that the method is suitable to unravel the provenance of sediments of different types in the EEP and to track their transport pathways. The analyses of high-n detrital zircon U-Pb ages of these sediments in respect to the geological history of the EEP and surrounding geological units show that important tectonic events in the area, such as the formation of the cratonic blocks of the East European Craton and their assemblage, as well as the orogeneses of e.g. the Ural and Caucasus mountains, can be well differen- tiated based on their ages. Even related orogenic phases show differing peaks; e.g. the Variscan phase of orogeny in the Urals is reflected by ages of 360 Ma, while Variscan ages in the Caucasus are 300 Ma old, which allows the discrimination of these sources. As such, the geological setting of and around the EEP makes detrital zircon geochronology a suitable, source diagnostic provenance tool for its sedimentary cover (Paper III).

Lower Volga loess provenance and transport (Paper II and III) Having confirmed the aeolian origin of the Atelian silt material in the Northern Caspian lowland and reconstructed the climatic and environmental conditions at times of its deposition (Paper I and II), leaves the question about the source(s) of LVL and its transport pathways. This is of great importance in understanding the Quaternary palaeoclimate of Eurasia, namely, the controlling environmental factors on dust production, atmospheric conditions, and dust circulation, and climate coupled processes of deposition. Through the analysis of grain shape and grain surface features in paper II, glacial grinding with subsequent multi-step fluvial and aeolian transport is determined for the formation of the LVL material and its distribution. The findings of paper II suggest the production of large amounts of loose and fine-grained sedimentary material by the Fennoscandian Ice Sheet and mountain glaciation and its

45 transportation from pro-glacial outwash plains in the northern EEP to the south via the Volga River and converging rivers. This implies that the final step of transportation and deposition to the LVL sites is carried out by wind from near-source Volga alluvium and this is confirmed by the provenance study via detrital zircon U-Pb ages of Lower Volga loess in paper III. The zircon age distribution of the three loess sites SA, LN, and RG are very similar and indicate the same source for all three locations. The analysis of detrital zircons from different stratigraphic depths, i.e. different depositional age, suggest no major change in provenance during the phase of loess deposition. A slight variability in the contributing sources is indicated for the shifts from MIS 5 to MIS 4 and the transition from MIS 3 to MIS 2. Nevertheless, for all three LVL sequences, and throughout the phase of loess deposition, the Volga River is the main supplying source and small temporal changes in zircon age distribution are explained with potential changes in the drainage and course of the Volga River (Fig. 8). The Volga’s detrital zircon U-Pb signal indicates the transport of material from the East European Craton and its sedimentary cover in the northern EEP where material was reworked by the Fennoscandian Ice Sheet, together with sediments from the Ural Mountains, reworked through mountain glaciation. As such, paper II and III allow the association of Lower Volga loess production to glacial processes, mainly by the Fennoscandian Ice Sheet, and its long-distance transport to large rivers, ultimately the Volga River, with discharge control by continental as well as mountain glaciation. Aeolian processes are important for short-distance transport and appear mainly as a function of regional and local winds.

Fig. 8. KDE plots with underlain histogram of detrital zircon U-Pb ages from LVL and Palaeo-Volga sediment. The rug plot on the x-axis shows each analysed zircon grain as black dash. Note the similar zircon age distribution of the two sediments (Paper III).

Sediment routing and spatial variation of loess deposits in the Black Sea-Caspian Sea region (Paper III) The combined findings of paper II and III reveal the provenance history of LVL. Its comparison to other loess sites in the EEP and in the Southern Cas- pian Sea region based on the detrital zircon U-Pb provenance data in paper III, allows the attribution of at least four loess provinces in the EEP and one loess province in the north of Iran. These loess provinces are the Southwest EEP province, the South EEP province, the North Caucasus province, the Southeast EEP province, and the Southeast Caspian province. In addition, there are loess sites that could not be clearly assigned to any of these provinces, leaving the potential that there are even more loess provinces left to distinguish. The presence of these several loess provinces reveals a

47 remarkable spatial variability in loess provenance in the area and thus, the presence of multiple diverse dust sources and transport pathways. However, all loess provinces show a strong connection to rivers. Such a connection is already indicated by the location of the provinces along the large rivers of the EEP such as the Volga, the Don, and the Dnieper and their tributaries (Fig. 9), and is reinforced by the detrital zircon age patterns at their loess sites. These reveal that the larger mass of material to the loess often has similar sources and is contributed by the large EEP rivers. For the Southwest EEP province, the South EEP province and the Southeast EEP province, this common source material comes from the cratonic blocks in the EEP and their sedimentary cover and is distributed by the Volga, the Don and the Dnieper as main agents prior to aeolian deflation. The previously mentioned LVL sites lie in the Southeast EEP province (Fig. 9). Despite this wider overall control of rivers on a major proportion of loess sediment, in contrast, the remarkable variation in loess source, even between closely located sites and loess provinces, seems to be linked to aeolian material input from multiple local sources from surrounding tectonic basement and orogens. This material is not necessarily glacial or far travelled and, in some cases, also without any obvious river connection. The specific proto- and secondary sedimentary sources to the sites in different loess provinces are discussed in paper III. While these sources could be very well resolved for all loess provinces north of the Black Sea and the Caspian Sea, the provenance and dispersion of loess in the Southeast Caspian province requires further investigation. Our working hypothesis is that long distance transported fluvial sediment from the Central Asian Pamir Mountains might play a role in material supply to the region together with local tectonic units.

In addition to these provenance findings for loess, paper III shows that, similar to the continental deposits, also the marine sediments are controlled by large rivers, which drain into the Black Sea and the Caspian Sea. In contrast to the loess, input of multiple sources does not seem to play a significant role for marine sediments though. Instead they widely reflect the geology of the catchments of rivers, which feed the sea closest to where the marine sediment is deposited.

The great spatial variability in zircon ages found in paper III reveals that sedimentary sinks in the Black Sea-Caspian Sea region are sourced from a range of places and by different transport pathways, which are mainly driven by the formation of large amounts of sedimentary material by the Fennoscandian Ice Sheet and mountain glaciers, and that the distribution of this material over a wide scale and long timescales is mostly undertaken via rivers prior to near source aeolian transport for loess and transport via sea currents within sea basins for marine sediments.

Fig. 9. Estimated loess provinces of the EEP and in the South Caspian Sea region classified based on the detrital zircon age provenance signal of their loess sites (yellow shade). The red circle signals the location of the Lower Volga loess sites in the Southeast EEP (Paper III).

Broader implications (Paper I, II and III) The combination of the findings of the three papers allows consideration of the wider aim of the thesis: to gain a broader understanding of loess formation, transportation and cycling in a cold continental-permafrost climate and under the effect of different continental and marine environments, and also to disen- tangle the complex climate and environment implications in the EEP, bridging Europe and Asia. Each of the three papers contributes to this puzzle and one combined finding reveals that the Fennoscandian Ice Sheet and hydrographic changes in the north of the EEP represent the main control on loess formation and distribution, on the continental environment in the region, and on Caspian Sea sea-level history. The palaeoclimate reconstructions in paper I, including palaeoprecipitation estimations, indicate that the rise of the Caspian Sea sea- level at the end of the Atelian is only secondarily influenced by local-regional climate variation and it therefore ought to be controlled mainly by increased water input from the East European and Siberian plains. In paper II, the comparison of reconstructed and modern-day atmospheric conditions suggests the control of the continental glaciation on atmospheric circulation. The Fen- noscandian Ice Sheet might have influenced large atmospheric circulations by forcing westerly winds further south and might have contributed to the temperature- and pressure-controlled formation of global teleconnections, which are coupled to precipitation and temperature changes in different areas on the Eurasian continent as discussed in paper II in the context of previous studies

49 (e.g. Schaffernicht et al., 2020). Similar to the modern wind data analyses, which clearly show the influence of seas and local topography on wind direction and wind speed in the EEP and in the Black Sea-Caspian Sea region, this is assumed to have also been the case during the Late Pleistocene. Topo- graphic highs deflect wind directions and change wind speeds over a wide area. Valleys and topographic depressions are characterized by lower wind speeds, while seas and flat uplands experience higher wind speeds. Mountain- ous regions with high relief instead, represent a particular case where wind directions and wind speeds are driven in a more complex way. The wind data analyses show also that the topographic control on wind direction is stronger at higher wind speeds (Paper II). Finally, paper III reveals that large amounts of sediment from the northern EEP was transported south via large rivers, in- dicating that the Fennoscandian Ice Sheet had a crucial role in sediment production during the Pleistocene, but also on its distribution by controlling the discharge of these rivers. As such, it could be proven that loess on the EEP widely fits the suggested models for loess formation, which imply ice sheet and glacier production of the material and its long-distance transportation via rivers prior to near source wind transport. However, despite the potential control of the Quaternary continental glaciation on rivers, the findings of paper III also indicate that the catchments and courses of the palaeo rivers were widely the same as the ones of the modern rivers, apart from some anthropo- genic influences on the modern systems.

50 Conclusion & Future Perspective

“Life is the art of drawing suffi- cient conclusions from insuffi- cient premises” – Samuel Butler

This thesis has provided information on the aeolian origin of the loess at the Lower Volga sites and as such has also shown that this continental material represents a climate archive with great potential to contribute to a better understanding of past climate conditions and their evolution in the area (Paper I and II). Proceeding from there, this thesis has started to explore this potential.

This thesis provides not only a first detailed magnetic analysis of Lower Volga loess, but also revises the applicability of different mineral magnetic proxies and their interpretation (Paper I). The thesis shows that χ and χfd are not the straight forward magnetic palaeoenvironmental proxies as is widely believed by loess researchers and recommends their combined use with other enviromagnetic methods. The findings of paper I suggest the possibility of transi- tional cases between the two commonly applied interpretation models of pedogenic magnetic enhancement and wind vigour, and that these models might not be universally applicable. This thesis also provides a new summary and discussion of reworked magnetic fabric in sediment deposits of cool climate and can as such serve as an aid for the identification of cryogenesis from magnetic fabric studies (Paper II).

In addition to the assessment of mineral magnetic methods and their applicability for sediment deposits in cool climates, this thesis has provided new information on the palaeoenvironment and palaeoclimate in the Northern Cas- pian Sea region and in the EEP. Its findings reinforce that the Atelian was a cold and dry period with dusty westerly winds and that conditions were more humid and potentially warmer during phases of late MIS 5 and MIS 3, ena- bling pedogenesis to take place. In addition to periods of milder climate, also generally less strong winds than during late MIS 5 and MIS 4 are indicated for MIS 3. However, cold climate conditions prevailed during all stages of the Atelian and cryogenesis affected their deposits. The generally reconstructed environment of the Atelian in the Lower Volga region is similar to the current

51 semi-arid steppe, although the climate was cooler, windier, and dustier (Paper I and II).

These palaeoclimate reconstructions for the different stages of the Atelian regression are based on the chronology of SA, for which high-resolution optically stimulated luminescence dating (OSL) of the loess sequence was per- formed in a Master thesis at Aarhus University by Højsager (2019), as well as published OSL ages of the marine deposits are provided by Kurbanov et al. (2020) and Yanina et al. (2017). This chronostratigraphy of SA also allows the establishment of chronostratigraphic relationships at RG and LN via the correlation of stratigraphic units and erosional features, pedogenic and cryogenic horizons, and these correlations have been verified by the few published ages from the two sections (Kurbanov et al., 2018; Yanina et al., 2017). How- ever, an even more detailed picture of the past climate and its evolution in the Lower Volga region than is provided in this thesis would require a reliable absolute chronostratigraphy also for RG and LN. While the establishment of such a chronology based on high resolution OSL ages is currently in progress for LN and RG (Költringer et al., in prep.; Kurbanov et al., in prep.), the palaeoclimate reconstructions in this thesis are based on the preliminary chronostratigraphy resultant from few available ages and stratigraphic correlations. These studies in preparation are needed to determine the timing of environmental changes in the region more precisely and to constrain climatic shifts to time periods bounded by absolute ages. After construction of a detailed chronostratigraphy for all three loess sites in the Lower Volga region, the palaeoclimate findings of this thesis can also be complemented by more palaeoclimate proxies, such as e.g. grain size, micromorphology, and more detailed geochemical proxies (Költringer et al., in prep.). Furthermore, a higher resolution AMS study, also from other loess sites, would strengthen the palaeowind reconstructions for the area.

In addition to these palaeoclimate reconstructions from the Lower Volga sites, this thesis has provided the first provenance analyses of Lower Volga loess and reveals glacial origin and continuous dust supply from a Volga source throughout the Late Pleistocene (Paper II and III). Furthermore, in this thesis, a large-scale reconstruction of Quaternary sediment sources, pathway systems, and sinks is established for the EEP and southern Caspian Sea region for the first time (Paper III). Most striking is the richness of sources and different pathways, even within a rather small spatial extent. This indicates that while the larger mass of material to loess deposits is provided by big rivers, loess deposition in the EEP is not only controlled by one large dust source but by various areas for dust deflation, comprised of local and regional detritus, which are distinguishable via their zircon populations. More generally, these findings underpin the importance of rivers for loess formation and reinforce suggestions that for loess deposits aeolian transport generally takes place as a

52 last step and over rather short distances after long-distance river transport, and that this also applies for the EEP. However, the findings of this thesis also show that areas for dust deflation are not necessarily connected to rivers and thus the formation and reworking of loess sources is not always glacial or fluvial.

While the provenance of sediments on the EEP and their pathways of distribution could be identified successfully with the zircon U-Pb dataset collected in this thesis, analyses of more reference material from the area south of the Caucasus, the Southern Caspian Sea region, and from Central Asia are needed to verify the working hypotheses for sediment provenance and pathways in this region. This thesis therefore suggests a need for a more detailed and targeted provenance study for Iranian loess, Karakum Desert sand, and South Caspian Sea marine sand (Paper III). We suggest the comparison of the zircon data from this thesis with more samples from e.g. across the Iranian Loess Plateau, and from Armenian and Central Asian loess deposits. If such additional detrital zircon age data showed that this area comprises a complex geological set-up, for which zircon provenance tracing does not represent a suitable tool, we would suggest to apply additional single grain methods or isotope geochemistry for a targeted provenance study (e.g. Morton, 1991; Garzanti, 2016; Morton, 1985; Újvári et al., 2012; 2013; Han et al., 2019).

Another remarkable insight from the provenance study in this thesis is that in the Black Sea and the Caspian Sea no sedimentary mixing between the individual topographic basins of each sea seems to occur (Paper III).

53 Summary in Swedish

“Perhaps the best test of a man’s intelligence is his capac- ity for making a summary” – Lytton Strachey

Löss är ett vindburet sediment med dominerande siltkornstorlek (2-63 μm), som vanligtvis ackumuleras under faser av kallt och torrt klimat. Dess bildning förknippas i stor utsträckning med produktionen av siltformade bergfragment i glaciala miljöer av kontinentala issköldar eller bergsglaciärer. Fördelningen av materialet över långa sträckor (upp till flera 1000 km) sker via floder medan det sista stadiet av transport, från deflationszoner nära källan till lössavlag- ringen, utförs av vind. Även om denna idé om lössbildning och flerstegstrans- port är allmänt accepterad, finns alternativa teorier som föreslår in situ bildning av löss på grund av markbildande processer eller frostverkan i ursprungs- materialet utan transport via vind. Sådana teorier om in situ-lössbildning fin- ner stöd särskilt bland forskare från det tidigare Sovjetunionen.

Löss avlagringar representerar utmärkta klimatarkiv för Kvartär, den senaste perioden i jordens geologiska historia, och är särskilt viktigt för rekonstrukt- ionen av paleomiljöförhållanden i halvtorra till torra regioner, där andra lång- variga paleoarkiv kan vara sällsynta. Löss-sekvenser kan registrera syn-depositionella miljöförhållanden, som förhållanden vid transport och avsättning, såväl som den post-depositionella effekten av klimatet på avsättningarna, men är också känslig för miljöförändringar i källregionerna och längs dess trans- portvägar. Detta gör paleoklimat- och härkomststudier av lössavlagringar viktiga för förståelsen av tidigare klimatförändringar, landskapsutveckling och sedimentcykling.

Av denna anledning undersöks lössdepåer i Centralasien, särskilt den kine- siska lössplatån, och i Europa. Dessa avlagringar bildar tillsammans med ryska lössavlagringar det stora eurasiska lössbältet och spelar en viktig roll för återskapande av det kvartära paleoklimatet i Eurasien och dess stofthistoria. En underskattad nyckelplats för lössavlagring, som förbinder europeisk och asiatisk löss, ligger längs Volga-flodens nedre delar i norra Kaspiska låglandet på den ryska delen av den sydöstra europeiska slätten. Där finns lössekvenser från sen Kvartär som deponerats under faser av Kaspiska havets

54 lågvattenstånd och begränsas av marina avlagringar från transgressiva faser. Ursprunget, bildandet och modifieringen av denna löss efter avsättning är kon- troversiell och debatterad utifrån de två motstridiga teorierna om lössbildning. Som en konsekvens utesluts löss längs Nedre Volga från palokoklimatrekon- struktioner i regionen. Fluktuationerna i Kaspiska havets havsnivån och dess drivande faktorer är svårförklarligt. Ett hinder för att förstå förändringar i Kaspiska havsnivån utgörs av bristen på paleoklimatinformation under faser med låg havsnivå.

Detta doktorsarbete syftade till att lösa ursprunget, bildandet och modifieringen av löss från Nedre Volga och att använda denna kunskap för att bidra till en bättre förståelse av klimatförhållanden och deras utveckling regionalt såväl som eurasiskt. Dess sedimentära och miljömagnetiska egenskaper visar att Nedre Volga-löss representerar äkta eoliska avlagringar. Tillsammans med analysen av kornform och ytegenskaper avslöjade resultat också att dess par- tiklar bildades på grund av glacial malning och transporterades över långa sträckor via floder före den eoliska avsättningen nära källan, där lössjordarna upplevde faser av pedogen och kryogen modifiering. Proveniensanalys via U- Pb geokronologi av zirkon visade att inga tidsmässiga förändringar i materi- altillförsel inträffade för löss från Nedre Volga, men avslöjade en anmärk- ningsvärd rumslig variation av stoftkällor på Östeuropeiska slätten och i södra Kaspiska havet. Avhandlingen diskuterar att denna variation är kopplad till intransport av material från flera lokala källor från omgivande urberggrund och bergskedjor, medan den större materialtillförseln till lössplatser på den östeuropeiska slätten ofta har liknande källor och härrör huvudsakligen från kontinentala och bergsglaciala zoner och är transporteras via floder före eolisk vindtransport.

Utifrån dessa resultat började denna avhandling att förverkliga potentialen i Nedre Volga-löss för paleoklimatrekonstruktioner i Eurasien för att möjlig- göra en rekonstruktion av ett i allmänhet kallt och torrt klimat i norra Kaspiska låglandet präglat av starka dammiga vindar, följt av ett något mer fuktigare och /eller varmare klimat under Kaspiska havets regressionsfas under sen Kvartär. I ett vidare perspektiv tyder dessa resultat på att Kaspiska havets nivå endast påverkas sekundärt av lokalregionala klimatvariationer och att glaci- eringen av norra halvklotet under Kvartär var den huvudsakliga drivande fak- torn genom flodutsläpp till Kaspiska havet.

Bortsett från dessa viktiga ämnen om eurasiskt klimat och sedimentcykling, behandlar detta doktorsarbete också frågan om användbarheten av mineral- magnetiska parametrar som paleoklimatproxyer från lössavlagringar i kallt klimat, som ombildats genom pedogenes och frostcykler och som var påverkat av en marin transgression och därmed täcktes med havsvatten under flera tu- sen år. Denna avhandling granskar kritiskt användningen av vanligt använda

55 miljömagnetiska parametrar och deras tillämplighet i olika klimat- och depo- neringsmodeller och föreslår att miljömagnetiska metoder är lämpliga för re- konstruktioner av kalla paleoklimat i sådana och liknande miljöer om flera metoder används i kombination och deras resultat tolkas på lämpligt sätt. Dessutom tillhandahåller denna avhandling information om den magnetiska anisotropin av sediment som deponerats och ombildats under kalla klimatför- hållanden.

56 Acknowledgements

“As soon as I saw you, I knew an adventure was going to hap- pen” – Winnie the Pooh

I owe my thanks to many people, who have accompanied me on this dusty journey. If all we are is dust in the wind, and you read my thesis, then you know how important every single particle is for the whole lot. In this sense, you all are part of this thesis and I want to use this section to express my gratitude:

To my main supervisor Thomas Stevens, thanks for introducing me to this bizarre world of loess research. I am grateful for the many things I learned and the challenges there were to master. Thanks for these shared years of my PhD studies and everything it came with; for your guidance in paper writing and the many experiences. To be acknowledged here is also the funding of the Swedish Research Council (VR grant 2017-03888). To my co-supervisor Bjarne Almqvist, thanks for leading my first steps into the jungle of magnetic research and to bushwhack a path on which I can con- tinue walking. To my second co-supervisor Ian Snowball, thanks for your support in critical times. To LUVAL, the program I was affiliated to during my PhD, for financial support, and to everyone within this program; thanks for the friendly environment at work, which was also provided by everyone else at Geocentrum. To my external advisor Balázs Bradák, your supervision was crucial for the development of the magnetic papers. I am really grateful for the time you put into these papers. I learned a lot from working with you, it was simply bril- liant. To Roger Kurbanov, my collaborator on Russian side, who faced this project like a true pirate. Without you, my PhD on Russian loess would not have been possible, regardless of that ‘tomorrow’ never comes. Thanks for bringing me to Lower Volga and Lower Volga to me.

To all my co-authors for your contribution to the here included manuscripts. To Petter, thanks for including me in your work.

57 To Sofya, for the shared time in the lab in Uppsala and Moscow and for having been my rescue anchor in all Moscow experiences throughout. To my Russian colleagues for their support in the field and their help surviving the Russian daily-life adventure: Vladimir, Natasha, Sveta, Dasha, Lisa, Ni- kita, to name only a few. To the many inspiring researchers that I had the pleasure to meet and to interact with during my scientific education and career, beginning with my super- visors at Salzburg University, this would make a long list. Thanks to Tamara Yanina, Marina Lebedeva, Fahard Khormali, Jan-Pieter Buylaert, and Gabór Újvári. Thanks for your friendly and approachable attitude.

To all my friends and colleagues in Uppsala, thanks to you, Sweden has not only been a place to conduct research but become my home. Each and every single one of you was there for me at one point or the other when I needed you, in my professional as well as my personal life, even if it was unknowingly by just dropping a word or a message, giving a smile or a hug in the right moment. Thank you all!

To Yunus, for being my fellow PhD campaigner in loess research and for all the discussions and shared time in the office, the lab, the field, and on conferences. To Bryan and to Steffen, for being around and ready to help if it were neces- sary. To Christoffer, not only for being a great office mate but also for your big help with the climate data and its plotting. The modern wind data analysis chapter in this thesis is dedicated to you. To Kristina, to Saba, to Claudia, and to Eduardo, for your friendship far beyond Geocentrum. To Chris and Audrey, for how much you made me feel welcome when I first arrived to Uppsala and for your supportive friendship throughout the years. To George, to Elisa, and to Faranak, thanks for the unexpected: the unexpected love, empathy, spontaneity, fun, folly and this wonderful caring friends-family you gave me. To Alizée, thanks for your caring friendship and the many shared unique ad- ventures. To Gabriele and Giorgia for your magical ability of turning every straining experience into a fun story, our laughter won’t be forgotten. To Lucia and Hector, Masoud, Emma, Elena, Boris, Amanda, Laora, Cardi, Amit, Sergey, and many more of you, also you, who have left Uppsala for years meanwhile but made it a lively and cozy place as long as you were around. To Stig and Christina, for your lovely neighborhood in Stenhagen.

58 During these past years of my PhD, I did not only get to know Sweden but also to travel a lot. Field trips, lab work and conferences brought me to many new places in the world. How lucky was I, no matter how remote, unknown, and exotic these places were for me, to find wonderful people, who welcomed me not any less than a long-term friend even if I was an almost stranger to them. I will be forever grateful to Maryeh and her family, to Azamat and Bekzhod and their friends and families, to Sonya and Sveta; all of you have not only made my life so much easier by naturally taking care of me, you have also taught me a lot. Thanks for welcoming me in your countries, for sharing your culture and traditions and for helping in widening my horizon.

To all my friends at home and around the world, who are bridging the distance by taking the effort of staying in touch, coming to see me, and offering me a place to stay any time.

To Martin, my academic sidekick. Little did I know when I randomly sat next to you in our very first Geology lecture more than 10 years ago and still, you are the first one to share findings in our field, curiosities, questions, and challenges with. Research would not be the same without you, thanks for sharing this experience of PhD studies, for the many hours of discussions, for all your interest and motivation, for not getting tired to help, thanks for all your time. To all my colleagues from my Geology studies in Salzburg, you were the perfect crew of science nerds, outdoor enthusiasts and crazy party people, who made me stick to this field. To Dani and to Tabea, of all friends, you must have seen the most colours and versions of Chiara through all these years, thanks for appreciating every single one of them and for staying in my life despite the distance, the ways too rare meetings and the different turns our lives have taken. To Berni, to Tanja, to Mietsch, and to Verena, thanks to you guys Salzburg is still a home. Thanks for not getting tired of seeing me in Uppsala, Verena, for all your caring about my life and experiences here and around the world, and your ready support in whichever situation. To Peter, for your unfailing good mood and initiative. To Wanessa, no words needed, you certainly know how I feel just as usual. Don’t cry for me Argentina. To Seli and Fred, danke für die Jahrzehnte der Freundschaft. Solange ich an dieser Doktorarbeit gearbeitet habe, konnte ich mir sicher sein, dass zumindest Fred sie mit Interesse lesen würde. Danke für den Ansporn.

I have come a long way in the past 20 years and this is thanks to my family. I am so lucky to have places to come home to and people who make it hard to part from:

59 My parents, you put the cornerstone for me to become the person I am today. You offered me the best start in life and the best education I could have ever whished for. Thanks for all your diverse interests you shared and passed on to me and without which I wouldn’t be doing what I do today. Thanks for en- couraging me to explore the world, not least a reason why finding a home abroad was a fun and exciting, and not at all frightening challenge to take. My brother Julian, you have been a model and inspiration for my studies for the longest time. Thanks for helping making maths and physics easier under- standable during my undergraduates and all the other support in daily life you give as a matter of course. Thanks to you and Cathi for providing a shelter and more, a home any time. Thanks for keeping me alive in the memories of my adorable nieces, and to Raffaela, Felicitas and Antonia for your bubbly love and the puerile joy you spread, and for how much you trust me and accept me as family despite the rare meetings. My sister Fiona, my partner in crime. Thanks for swinging through life together, for dancing also in between songs and even off-beat with me, regardless what and who is around, but also for pulling me back into rhythm when needed. You have not only seen all my colours of emotion, by taking your share, you made every moment so much more intense, lively, bearable, shap- ing, memorable. Lofer-Oma and Lofer-Opa, I am the luckiest ever having been blessed with such wonderful grandparents. Thanks for your unconditioned love, for your sacrifices, for everything you teach me. You are both so wise and special in your own way and such a big and important part of my life and for who I am. You are home to me. My grandfather Abtenauer-Opa, thanks for appreciating everything I took up on, for saluting my work and for not missing to tell me how proud you were. The story of how you made your life and what you achieved, makes you a person to always look upon to. I miss you. My uncle Peter and all you, my dear Stabsn.

I am really grateful that you all are only one call away and ready to help where you can. Special thanks to Mama, Oma and Opa, who could not be stopped from pampering me during my hours in home office despite their own hard- ship, you are true models of consideration and resilience. Danke Mama für alles was du für mich tust. Thanks to Fiona for designing the cover of this thesis: aquarelle of Leninsk gully on the front and `Dance in the Data Dust´ on the back.

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