Periodicities of paleoclimate variations in the first high-resolution non-orbitally tuned grain size record of the past 1 Ma from SW Hungary and regional, global correlations
Introduction
Various climatic forcings in the past resulted in different responses at a regional level during the Quaternary (Imbrie et al., 1993, Kageyama et al., 2012, Kohfeld and Harrison, 2000, Schmidt, 2010, Lang and Wolff, 2011, Rapp, 2012). Understanding the leads and lags between proxy archives is crucial to understand feedbacks in Earth’s climate system. Long and high-resolution terrestrial paleoarchives yielding us information on past climatic fluctuations over several glacial-interglacial cycles on the millennial scale are rare. Loess can represent such a semi-continuous terrestrial paleoenvironmental record (Pécsi, 1990, Pye, 1995). The substantial loess deposits of the Middle and Lower Danube Basin in southeastern Europe are the thickest and most complete terrestrial paleoenvironmental records in Europe (Buggle et al., 2009, Buggle et al., 2013, Marković et al., 2011, Marković et al., 2015, Jordanova and Petersen, 1999, Jordanova et al., 2007, Jordanova et al., 2008, Panaiotu et al., 2001, Rădan, 2012, Sümegi et al., 2011, Sümegi et al., 2018). Loess and paleosol sequences (LPS) of the Danube Basin go back 1 Ma (Buggle et al., 2009, Buggle et al., 2013, Jordanova and Petersen, 1999, Jordanova et al., 2007, Jordanova et al., 2008, Marković et al., 2011, Marković et al., 2015, Sümegi et al., 2011, Sümegi et al., 2018). The wealth of studies dealing with the comprehensive analysis of these paleoarchives yielded information on chronology, stratigraphy, geochemistry, paleoecology, as well as environmental magnetic characteristics of these sites on the scale of multiple millennia (Fitzsimmons et al., 2012, Marković et al., 2011, Marković et al., 2015, Sümegi et al., 2011, Sümegi et al., 2018). However, most multiproxy studies published so far from Mid-Danube Basin sites are either low resolution, or use only a single -mainly magnetic susceptibility- proxy or two (e.g. Marković et al., 2011, Marković et al., 2012, Sümegi et al., 2018). Multiproxy studies are mostly restricted to the period of the last glacial cycle (Antoine et al., 2009a, Antoine et al., 2009b, Bokhorst et al., 2011, Novothny et al., 2011, Stevens et al., 2011, Schatz et al., 2011, Schatz et al., 2014, Schatz et al., 2015, Zech et al., 2013) as establishing an independent chronology beyond 300 kyr down to ca. 1 Ma is not without problems as direct luminescence dating is difficult due to technical problems or age is established by correlation to some other global or orbital records (Schmidt et al., 2010, Murray et al., 2014, Thiel et al., 2014, Marković et al., 2015, Obrecht et al., 2016, Wacha and Frechen, 2011, Wacha et al., 2013, Sümegi et al., 2018, Zeeden et al., 2016). Some works use artificial composite sections made via stitching together proxies of two or more adjacent sites with different temporal coverage to attain a full coverage of 700–800 ky (Buggle et al., 2013, Marković et al., 2012, Marković et al., 2015). Others rely on orbitally tuned records to find orbital cycles (Marković et al., 2012, Basarin et al., 2014). Thus, chronological issues related to these studies generally prevent us from undertaking a wide-scale reliable comparison (Sümegi et al., 2018, Zeeden et al., 2018).
Loess grain size is one of the most common proxies used to reconstruct environmental and climatic conditions driving aeolian accumulation in LPS over several glacial/interglacial and millennial timescales (Vandenberghe et al., 1998, Bokhorst et al., 2009, Bokhorst et al., 2011, Újvári et al., 2014, Újvári et al., 2016, Újvári et al., 2014, Schulte et al., 2018, Xiao et al., 1995, Lu and An, 1998, Sun et al., 2006, Ding et al., 2002). Grain size distribution is a function of complex interactions between various factors like wind speed, frequency of storm events, moisture availability in source and sink areas, distance of source areas, type of transport mechanism, sediment availability, mineral composition, vegetation cover in source regions and post-depositional processes (Smalley and Marković, 2014, Stevens et al., 2013, Stevens et al., 2018, Schulte et al., 2018, Újvári et al., 2016). This study presents the first independently dated, high-resolution grain size record of one of the oldest and thickest loess/ paleosol sequence of Hungary, the borehole Udvari 2a. Dating was based on biostratigraphically controlled independent magnetostratigraphic ages beyond 50 ka down to 1.1 Ma. 14C ages helped us to constrain the chronology in the youngest part of the sequence (Sümegi et al., 2018). Spectral and wavelet analysis of grain-size fractions enabled us to unravel regional cycles of past aeolian dynamics spanning the past 1 Ma. Differences between the loess areas are due to different responses of regional climate systems to the global climate and different contributions of dust availability, erosion, tectonic uplift and local environmental conditions, including vegetation cover and soil formation (Smalley and Marković, 2014, Stevens et al., 2013, Stevens et al., 2018, Schulte et al., 2018, Zeeden et al., 2018). Thus, comparison of our grain-size proxy data and results of cycle analysis with other regional (Danube Basin) and extra regional (SW and SE Europe, China) grain size and paleoclimate records is essential to highlight similarities and differences with potential underlying causes.
Section snippets
Location, climate, lithostratigraphy, chronology of the site
The borehole Udvari-2A is found in the central plateau part of the Tolna Hills, SW Hungary (Fig. 1). The climate is temperate (Köppen Bs) with strong oceanic (Köppen Cf) and sub-Mediterranean climatic influences. This site is located at an interface between drier and wetter climates mainly seen in higher temperatures, multiple rainfall peaks and elevated hours of sunshine. The mean annual temperature is around 9–9.5 °C with average annual precipitation reaching 700–750 mm in the western part of
Sampling and sample description
Our sampling was restricted to the upper 86 m of the core (344 samples) corresponding to the last ca. 1 Ma (MIS 1-MIS 27; Sümegi et al., 2018). Samples of ca. 60 g were taken at 25 cm increments. Samples were air dried and their color was determined using the Munsell color chart. Furthermore, the main visual characteristics of the samples was also described.
Grain size measurement
Grain size analyses were performed on an OMEC Easysizer 20 laser wet dispersion particle size analyzer after sample pretreatment. The
Results of grain-size distribution analyses
Particle size follows a multi-modal distribution for all sampled loess horizons as depicted in Fig. 2. This polymodal distribution is typical for loess/paleosol sequences with a pronounced shift to the coarser grain sizes (Antoine et al., 2001, Antoine et al., 2002, Antoine et al., 2009a, Antoine et al., 2009b, Bokhorst et al., 2011, Varga, 2011, Novothny et al., 2011, Machalett et al., 2008). There is a prominent double peak representing the coarse fraction (coarse silt + sand) and a wide tail
Grain-size variations and provenance of the deposited material
Heavy mineral compositional analysis of loess and paleosol samples from the borehole Udvari 2a and the nearby Paks brickyard site exposing LPS of similar ages, revealed significant compositional differences (Thamó-Bozsó et al., 2013, Újvári et al., 2008, 2014). These must be relevant in the grainsize and leachate geochemistry record as well. In the case of Udvari 2a, we see a dominance of chlorite and biotite, just like in many other SW Transdanubian loess/paleosol sequences. However, it is
Conclusions
Results of time series analyses of the three grain-size indices at our site revealed that the 100 kyr cycles are constantly present throughout the past 900 ky. The stepwise change in the climate corresponding to the second phase of the Mid-Pleistocene Transition is also recorded. The 100 kyr cycles are moderately strong between 900 and 650 ky. These cycles are weaker between 360 and 650 ky corresponding to the Mid-Brunhes transition. It also falls into an interval when the development of a
Acknowledgements
Two anonymous reviewers and Jan-Berend Stuut are thanked for their useful comments helping to improve the language and scientific content of the paper. Research has been carried out within the framework of University of Szeged, Interdisciplinary Excellence Centre, Institute of Geography and Earth Sciences, Long Environmental Changes Research Team. Support of the Ministry of Human Capacities, Hungary grant 20391-3/2018/FEKUSTRAT and GINOP-2.3.2-15-2016-00009 ‘ICER’ is acknowledged.
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