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- Ghafarpour, Amin, et al.
(author)
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Late Pleistocene Climate and Dust Source From the Mobarakabad Loess–Paleosol Sequence, Northern Foothills of the Alborz Mountains, Northern Iran
- 2021
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In: Frontiers in Earth Science. - : Frontiers Media S.A.. - 2296-6463. ; 9
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Journal article (peer-reviewed)abstract
- Paleoclimatic investigation of loess-paleosol sequences from northern Iran is important for understanding past changes in a region highly sensitive to shifts in precipitation, and along potential routes of past human migration. Here, we present carbon and oxygen isotopic compositions of bulk carbonate (δ13Cbc and δ18Obc, respectively) coupled with particle size distributions of samples from the Mobarakabad section, northern Iran, to study past wind dynamics and hydroclimate. We also present new initial clay-sized Hf-Nd isotope results from key horizons in order to assess general dust sources. Variations of δ13Cbc and δ18Obc values of modern soils compared to paleosols allow reconstruction of late Pleistocene–Holocene climate change in the area. Our results show severe drought during a major eolian deposition phase (EDP) after 34 ka. The thickness and PSD of the C horizon of unit 5 suggest significant shifts in loess sources and depositional environments during this EDP after 34 ka. Indeed, based on our new clay-sized Hf-Nd data, we hypothesize that the loess unit 5 might originate from the young crustal source of the Alborz and Kopet Dagh mountains. In general, the PSD of C horizons in the section is bimodal in the silt fraction and the very small, very fine clay fraction, with a mode at c. 1 μm in the modern soil and paleosols possibly produced by weathering and pedogenic processes. There also appears to be a good correlation between δ13Cbc and δ18Obc values, differentiating phases of loess accumulation and paleosol formation and hence providing quantitative data for reconstructing paleoclimatic conditions in the study area.
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| 3. |
- Költringer, Chiara, et al.
(author)
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Quaternary sediment sources and loess transport pathways in the Black Sea - Caspian Sea region identified by detrital zircon U-Pb geochronology
- 2022
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In: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364. ; 209
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Journal article (peer-reviewed)abstract
- Constraining the controls on the distribution of sediment at a continental scale is a critical step in understandinglong-term landscape and climate evolution. In particular, understanding of the role of rivers in wider sedimentrouting and impacts on aeolian loess formation on a continental scale remains limited. Extensive Quaternaryloess deposits are present on the East European Plain and in the Black Sea - Caspian Sea region and are associatedwith major rivers draining numerous surrounding cratonic and orogenic hinterland areas. Coupled with this,complex changes in local and global sea level have affected the extent and drainage of the Caspian Sea and theBlack Sea, and Quaternary glaciations have impinged on the northern margin of the East European Plain. Thissuggests that sediment routing and loess formation may show complex patterns and controls. Here, we applyU–Pb dating of detrital zircons from fluvial, marine and aeolian (dominantly loess) sedimentary records on theEast European Plain and in the Black Sea - Caspian Sea region. This shows a strong control of large rivers on thedistribution of sediments at a continental scale in the region, through long-distance transport of several 1000 km,sourced from continental and mountain glacier areas prior to marine or atmospheric reworking and trans-portation. Strong spatial variability in zircon U–Pb data from loess deposits on the East European Plain revealsmultiple diverse sources to the different individual loess sections, whereas no significant temporal variability inloess source is detected during the Late Pleistocene of the Lower Volga loess in South Russia. While the sedimentsupply from glacial areas via rivers plays an important role for the provenance of East European Plain loessdeposits, our data indicate that the stark spatial diversity in loess provenance on the East European Plain is oftendriven by the input of multiple local sources. Similar to the loess, marine sediments from different basins of theBlack Sea and the Caspian Sea also show significant spatial variability. This variability is controlled by the ba-thymetry of the seas, leading to sedimentary intermixing by sea currents within, but not between differentseparated sea basins. A direct comparison of marine and aeolian sediments at the same depositional site suggeststhat although loess and marine sediments are both dominantly sourced from river sediments containing fartravelled sedimentary material, local sources play a more important role in many loess deposits.
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