GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 237-7
Presentation Time: 9:40 AM


FRECHEN, Manfred1, RAHIMZADEH, Neda1, KEHL, Martin2 and KHORMALI, Farhad3, (1)Geochronology, Leibniz Institute for Applied Geophysics (LIAG), Stilleweg 2, Hannover, 30655, Germany, (2)Institute of Geography, University of Cologne, Albertus Magnus Platz, Köln, 50923, Germany, (3)Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, 49138-15739, Iran (Islamic Republic of)

Radiometric methods such as optically stimulated luminescence (OSL) and radiocarbon dating have been successfully applied to establish more reliable chronological frameworks to better constrain (quantitative) reconstructions of past climate and environmental change as well as landscape reconstructions. The loess regions along the southern Caspian Lowlands and in the Basin of Persepolis are among the southernmost one of the Northern Hemisphere representing important spatial links between Southeast Europe and Central Asia. These loess records reflect numerous cycles of climate change and landscape evolution during the last interglacial / glacial cycle including periods of more arid and/or more humid conditions. The dust and sand accumulation rates depend on the availability of sediment from the near-by Caspian Sea and thus triggered by sea-level changes. Spectacular landscapes and sections show high resolution records of dust accumulation and soil formation including the determination of past dust accumulation rates, timing of warm-moist and cold-dry events and even the timing of a volcanic eruption, as determined by OSL. The partly three-dimensional shape of the exposures owing to the active extraction of sediments for brick production give insights into the former landscape and its evolution.

The accumulation and formation of dunes in the very northern part of Golestan Province strongly depends on climate conditions and sediment availability and hence on se-level changes. These landforms can provide valuable information about paleoatmospheric circulation and wind activity, coastal evolution, paleoclimate and sea level changes. Several isolated dunes developed south of the Atrak River and north of the Gorgan River, on the flat lowlands, which spread between the Caspian Sea (West), the Koppeh Dagh and Alborz Mountains (East and South) and Karakum desert (North). The formation times of these dunes have been determined in detail by OSL dating (Rahimzadeh et al., under review), and contradict to the previous suggestions that loess and dunes are synchronous deposits in this area. Based on the spatial organization, direction and sediment analysis, the formation of dunes in the study area was likely related to the fluctuation of the Caspian Sea, and indicates a period of quick regression during the early Holocene.