Northern Iranian loess and its palaeoclimatic implication
Soil Sciences
Palaeontology
Final Report Abstract
For a long time, loess deposits of Northern Iran have attracted scientific interest, but detailed sedimentological and palaeopedological investigations were not carried out. Preliminary studies gave general accounts on the nature and age of these deposits and indicated that they provide detailed records of dust accumulation and soil formation which will be crucial for large-scale stratigraphic correlation within the loess belt of southern Eurasia and for climate and palaeoenvironmental reconstructions for West Asia. In addition, it has been argued that dune sands in the Turkmen plain have accumulated concomitantly with loess. This project aimed at improving our knowledge on the formation of these deposits, on the timing of dust accumulation and soil formation, on diachronic and spatial variation of loess facies, and on the nature of palaeosols. We conducted a high-resolution sampling and measurement approach involving the use of luminescence dating, geochemistry, mineralogy, rock and palaeomagnetics, stable isotope analyses and organic matter characterisation including biomarkers. In a pioneering study, we also tested detection of ancient microbial communities from loess and palaeosols. Finally, the assumed contemporaneity of loess and dune formation was scrutinized. Six new profiles were prepared in the field, sampled and analysed. They were located along a transect from the nowadays more humid southwestern to the drier north-eastern part of the study area, which covering loess occurrences along the northern foothills of Alborz Mountains (FAM) and loess in the socalled Iranian Loess Plateau (ILP). Loess in these areas shows large differences in lithologic properties and intensity and number of palaeosols. Pedostratigraphy and luminescence dating provide clear evidence that the major climate cycles of the northern hemisphere are well represented in the loess deposits of the FAM by strongly developed palaeosols formed during marine isotope stages (MIS) 5e, 5c and 5a of the last Interglacial and Early Last Glacial. Several weakly developed palaeosols formed afterwards reflecting climate fluctuation during the Last Pleniglacial. These palaeosols can be correlated over the selected exposures as well but probably reflect features of regional climate change, possibly related to water level fluctuations of the Caspian Sea. Loess deposits studied in the ILP accumulated at high rates but contain several hiatuses indicating proximity to the dust source and a complex history of dust accumulation and erosion. Weakly developed palaeosols suggest comparatively dry climate conditions during interstadial and interglacials in the ILP. Ongoing research is now focussing on the area in between FAM and ILP, and first results are very promising, because both high rates of dust accumulation and better preservation of the sequences, i.e. less hiatuses, are apparent. Being located in the potential source area of dust, the dunes of the Turkmen plain were of special interest for our loess investigations. We were able to set up a first reliable chronology for sand accumulation in the plain. Luminescence data clearly show that the main phase of dune formation was the Early Holocene, hence after the loess deposits have formed. It is very likely, that dune formation is very much affected by Sea level fluctuations. Overall our knowledge on Iranian loess has very much improved in the course of the project and related research. We also took a major step in using microbial communities as markers of past environmental change. Northern Iranian loess thus represents an outstanding archive of past climate and environmental change in West Asia. It comprises detailed proxy records for the last and penultimate glacial/interglacial cycles, which indicate major correlation with the northern hemispheric cyclicity. Furthermore, local factors of palaeoenvironmental change such as fluctuations of the water level of the Caspian Sea affecting the extent of the dust deflation area and regional humidity may have played a significant role for the formation of loess-palaeosol sequences in Northern Iran.
Publications
- (2020) Loess records of environmental change. Quaternary International 552 1–3
Kehl, Martin; Khormali, Farhad; Frechen, Manfred
(See online at https://doi.org/10.1016/j.quaint.2020.07.029) - (2016): The loess-soil sequence at Toshan (Northern Iran): insights into late Pleistocene climate change based on high-resolution records of grain-size, sediment color and carbonate content. Quaternary International 399, 122-135
Vlaminck, S., Kehl, M., Lauer, T., Shahriari, A., Sharifi, J., Eckmeier, E., Lehndorff, E., Khormali, F., Frechen, M.
(See online at https://doi.org/10.1016/j.quaint.2015.04.028) - (2017): Biomarkers in modern and buried soils of steppe and forest ecosystems of Northern Iran. Quaternary International 429, 62-73
Shahriari, A., Khormali, F., Bläsing, M., Vlaminck, S., Kehl, M., Frechen, M., Karimi, A., Lehndorff, E.
(See online at https://doi.org/10.1016/j.quaint.2016.02.048) - (2017): Grain-size distribution of Pleistocene loess deposits in northern Iran and its palaeoclimatic implications. Quaternary International 429, 41-51
Wang, X., Wei, H., Khormali, F., Taheri, M., Kehl, M., Frechen, M., Chen, F.
(See online at https://doi.org/10.1016/j.quaint.2016.01.058) - (2017): Loess, dunes and palaeosols in the South Caspian Basin, Northern Iran. Excursion guide to LoessFest2017, Gorgan, 54 pp.
Kehl, M., Khormali, F., Frechen, M., Ghafarpour, A., Kiani, F., Pourmasoumi, M., Rahimzadeh, N., Taheri, M., Vlaminck, S.
- (2017): Luminescence-chronology of the loess palaeosol sequence Toshan, Northern Iran – A highly resolved climate archive for the last glacial-interglacial cycle. Quaternary International, 429, 3-12
Lauer, T., Frechen, M., Vlaminck, S., Kehl, M., Lehndorff, E., Shahriari, A., Khormali, F.
(See online at https://doi.org/10.1016/j.quaint.2015.03.045) - (2017): Micromorphology of the Lower Pleistocene Loess in the Iranian Loess Plateau, and its paleoclimatic implications. Quaternary International 429, 31-40
Taheri, M., Khormali, F., Wang, X., Amini, A., Wei, H., Kehl, M., Frechen, M., Chen, F.
(See online at https://doi.org/10.1016/j.quaint.2016.01.063) - (2017): The Agh Band loess-palaeosol sequence - a terrestrial archive for climatic shifts during the last and penultimate glacial - interglacial cycles in a semiarid region in Northern Iran. Quaternary International, 429, 13-30
Lauer, T., Vlaminck, S., Frechen, M., Rolf, C., Kehl, M., Sharifi, J., Khormali, F.
(See online at https://doi.org/10.1016/j.quaint.2016.01.062) - 2017. Loess, soils and climate change in Iran and vicinity. Quaternary International 429, Part B, Pages 1-128
Kehl, M., Khormali, F., Lehndorff, E., Frechen, M., eds.
- (2018): Late Pleistocene dust dynamics and pedogenesis in Southern Eurasia – detailed insights from the loess profile Toshan (NE Iran). Quaternary Science Reviews 180, 75-95
Vlaminck, S., Kehl, M., Rolf, C., Franz, S.O., Lauer, T., Lehndorff, E., Frechen, M., Khormali, F.
(See online at https://doi.org/10.1016/j.quascirev.2017.11.010) - (2018): Paleosols and past climate change. In: Roozitalab, M.H., Siadat, H., Farshad, A. (eds.): The Soils of Iran, Springer, World Soils Book Series, p. 149-162
Kehl, M., Khormali, F.
(See online at https://doi.org/10.1007/978-3-319-69048-3_8) - 2019. Investigating soil magnetic properties with pedogenic variation along a precipitation gradient in loess-derived soils of the Golestan province, northern Iran. Quaternary International
Sharifigarmdareh, J., Khormali, F., Scheidt, S., Rolf, C., Kehl, M., Frechen, M.
(See online at https://doi.org/10.1016/j.quaint.2019.11.022) - 2019. Pedogenic carbonates archive modern and past precipitation change – a transect study from soils and loesspaleosol sequences from Northern Iran. Quaternary International
Khormali, F., Shahriari, A., Ghafarpour, A., Kehl, M., Lehndorff, E., Frechen, M.
(See online at https://doi.org/10.1016/j.quaint.2019.12.011) - 2019. Timing and development of sand dunes in the Golestan Province, Northern Iran—implications for the Late-Pleistocene history of the Caspian Sea. Aeolian Research
Rahimzadeh, N., Gribenski, N., Tsukamoto, S., Kehl, M., Pint, A., Kiani, F., Frechen, M.
(See online at https://doi.org/10.1016/j.aeolia.2019.07.004) - Clay mineralogy and geochemistry of the Lower Pleistocene Loess in the Iranian Loess Plateau (Agh Band section) and implications for its provenance and paleoclimate change. Quaternary International
Taheri, M., Khormali, F., Wang, X., Amini, A., Landi, A., Wei, H., Kehl, M., Chen, F.
(See online at https://doi.org/10.1016/j.quaint.2019.09.011)
