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

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.