Timing and development of sand dunes in the Golestan Province, northern Iran—Implications for the Late-Pleistocene history of the Caspian Sea

doi:10.1016/j.aeolia.2019.07.004

Aeolian Research

Volume 41, December 2019, 100538

https://doi.org/10.1016/j.aeolia.2019.07.004 Get rights and content

Abstract

The Golestan Province, in northern Iran, presents a rich record of aeolian deposits, including thick loess-palaeosol sequences and prominent sand dunes. While the loess chronology in this area is relatively well constrained, the formation time of the dunes remains largely overlooked, despite their potential to provide valuable information in terms of palaeoclimate conditions and Caspian Sea level changes. In this study, we provide the first reconstruction of dune evolution in Golestan Province, based on geomorphic and sedimentological investigations, high resolution granulometric and microfossil analyses, and luminescence dating. Luminescence analysis includes quartz post-infrared pulsed optically stimulated luminescence (Post-IR pulsed OSL) and K-feldspar post-IR infrared stimulated luminescence (pIRIR) measurements. Luminescence ages indicate that the studied dunes accreted within a few thousand years ranging from 10.6 ± 1.6 ka to 8.4 ± 1.4 ka, during the Holocene. Based on the geomorphological evidence and geographical setting, the dunes observed in the Caspian lowland are of parabolic type, which would reflect arid to semi-arid palaeoenvironmental conditions with sparse vegetation and predominance of easterly winds at the time of dune formation. Grain size distribution analysis and sedimentological investigations indicate a clear influence of the Caspian coast environment on the dunes development, in addition to probable sediment input from nearby fluvial systems. The spatial and temporal distribution pattern of the studied dunes reflects a quick regression of the Caspian Sea during the Early Holocene, probably following the so-called Mangyshlak regression.

Introduction

Dune formation is primarily controlled by the supply and availability of sediments transportable by the wind, and by the capacity of the wind to transport sediments. These controlling factors are in turn strongly dependent of environmental conditions such as vegetation, topography, hydrological and tectonic settings and regional/local climate conditions (Lancaster, 2008, Kocurek and Lancaster, 1999). Therefore, dunes or aeolian deposits in general, can provide valuable information about palaeoatmospheric circulation, palaeoclimate and landscape evolution (e.g. Porat and Bota, 2008). Aeolian sediments are widespread in Golestan Province, located in the northern part of Iran, southeast of the Caspian Sea (Fig. 1a). Loess deposits dominate in the eastern part of the province, and are part of the Eurasian loess belt (Karimi et al., 2009). Recent studies focusing on loess-palaeosol sequences in this area indicate that thick loess sequences accumulated during the Middle and Late Pleistocene (from ~220 ka to ~16 ka; Lauer et al., 2017a), in association with regional climate changes, from dry and cold to more humid and warm conditions (Frechen et al., 2009, Lauer et al., 2017b). Wang et al., 2016, Wang et al., 2017 furthermore demonstrated that loess deposits in northern Iran are desert loess, composed of local dust transported over short distances by near surface winds from the nearby Caspian lowland and Karakum Desert. In addition to the loess deposits, several isolated dunes have been developed in the lowland of the Gorgan Plain (Fig. 1a). However, the processes and formation time of these dune deposits remain unknown, despite their potential to provide valuable information about palaeoenvironmental conditions in the region, e.g. the Caspian Sea evolution. Establishing a chronological framework for the dunes would also permit to check their potential relationship with other aeolian deposits present in the area such as loess. In this paper, we aim to improve our understanding of sand dune formation in Golestan Province, based on the detailed study of five prominent dune deposits. In addition to investigate the sediments structure and composition of these deposits, we reconstruct their evolution based on 16 luminescence ages. This method enables to determine the time elapsed since the last exposure of mineral grains (quartz or feldspar) to sunlight (Aitken, 1998) and has been demonstrated to be well suited for dating aeolian deposits from coastal environments (Kunz et al., 2010, Stone, 2013). Based upon the reconstructed evolution of the studied dunes in Golestan Province, we then discuss the implications in terms of Caspian Sea level fluctuations and palaeoclimate changes.

Section snippets

Geographical context

The Gorgan Plain, northern Iran, is part of the larger Aralo-Caspian depression which experienced strong subsidence during the Middle Pleistocene (Cromerian Stage; Degens and Paluska, 1979, Kehl, 2010), resulting in the gentle inclination of the plain to the west (average slope of ~0.6%). The Gorgan Plain is bordered by the Caspian Sea in the west, the Turkmen Steppe and the Karakum Desert in the north, and two mountain ranges with mean elevation above 3000 m a.s.l. in the south and the east,

Geomorphological mapping

Detailed geomorphological mapping was conducted in the Caspian lowland area, with a focus on aeolian deposits. Morphometric analysis and preliminary onscreen mapping of aeolian landforms was carried out under ArcMap GIS, using satellite imageries (Google Earth) and digital elevation model (SRTM, resolution 30 m) data, combined with field-based observations. Dune deposits were identified based on sedimentary and geomorphic criteria, and can be described as sediment bodies mainly composed of sand

Dune geomorphology

The Gorgan Plain contains sand dunes up to 45 m high (Fig. 3, Fig. 4). Studied dunes vary in height from 5 m (Aq Qala) to 44 m (Aji Gol) and are from several kilometers to tens of kilometers long (e.g. ~12 km for Aji Gol dune). These dune deposits are generally characterized by a crescent to wavy planar-shape with a general NNW-SSE orientation, roughly parallel to the shoreline of the Caspian Sea, and with horns dominantly pointing landward, to the NNE. However, the Aq Qala 1 and Aq Qala 2 do

Dune evolution and palaeoenvironmental context

The morphology, orientation and sedimentology of dunes can provide valuable information about the palaeoenvironmental conditions associated with their formation (Pontee et al., 1998). While dune deposits in the Golestan province could clearly be identified and mapped, the determination of their genetic type is challenging. An interpretation based on the sole planar view shape remains equivocal, as the observed crescent to wavy planar-morphology of the dunes could correspond to both barchan and

Conclusions

We present a palaeoenvironmental reconstruction of sand dunes accumulated in the Gorgan Plain, northern Iran, by combining for the first time luminescence dating with results of detailed granulometric and sedimentological investigations.

Based on their morphology and their geographical setting, e.g., coastal zone and the presence of associated intra-dune lakes, the studied dunes are interpreted to be of parabolic type, implying deposition by dominant easterly winds at the time of the dunes

Acknowledgements

The present study was funded by the German Research Foundation (DFG; FR877/26-2) and Iranian Ministry of Science, Research and Technology (MSRT). Additional support for sample processing was provided by the Leibniz Institute for Applied Geophysics (LIAG). Especially we thank: Sabine Mogwitz for the preparation of the luminescence samples, Petra Posimowski for gamma spectrometry measurements and Sonja Riemenschneider for grain size measurements. We are especially grateful to two anonymous

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Timing and development of sand dunes in the Golestan Province, northern Iran—Implications for the Late-Pleistocene history of the Caspian Sea

Abstract

Introduction

Section snippets

Geographical context

Geomorphological mapping

Dune geomorphology

Dune evolution and palaeoenvironmental context

Conclusions

Acknowledgements

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Quat. Int.

Radiat. Meas.

Radiat. Meas.

Quat. Geochronol.

Sediment. Geol.

Radiat. Meas.

Radiat. Meas.

Palaeogeogr. Palaeoclimatol. Palaeoecol.

Quat. Int.

Quat. Int.

Mar. Geol.

Geoderma

Quat. Int.

Iran. Quat. Int.

Quat. Int.

Quat. Int.

Quat. Sci. Rev.

Quat. Sci. Rev.

Quat. Sci. Rev.

Quat. Geochronol.

Radiat. Meas.

Quat. Int.

Radiat. Meas.

Quat. Sci. Rev.

Oceanol. Acta

Quat. Sci. Rev.

Radiat. Meas.

Quat. Geochronol.

Quat. Int.

Geomorphology

J. Afr. Earth Sci.

Sediment. Geol.

Radiat. Meas.

Quat. Int.

Earth Sci. Rev.

J. South Am. Earth Sci.

Quat. Int.

Quat. Sci. Rev.

Sediment. Geol.

Quat. Int.

Radiat. Meas.

Glob. Planet. Change

Quat. Int.

An Introduction to Optical Dating

An active fault zone in the western Kopeh Dagh (Iran)

Aust. J. Earth Sci.