Sedimentology, mineralogy, and geochemistry of the Late Quaternary Meyghan Playa sediments, NE Arak, Iran: palaeoclimate
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ORIGINAL PAPER
Sedimentology, mineralogy, and geochemistry of the Late Quaternary Meyghan Playa sediments, NE Arak, Iran: palaeoclimate implications Leila Abdi 1 & Hossain Rahimpour-Bonab 1 & Mohsen Mirmohammad-Makki 2 & Johann Probst 2 & Saeed Rezaeian Langeroudi 3 Received: 29 September 2017 / Accepted: 11 September 2018 # Saudi Society for Geosciences 2018
Abstract Playas are shallow ephemeral lakes that form in arid and semi-arid regions. Iran has a large number of playas such as Meyghan Playa, which is located in the northeast of Arak city that borders the central Iran and Sanandaj-Sirjan zones. This study aims to investigate the mineralogical, sedimentological, and geochemical characteristics of the playa sediments. In order to determine the palaeoenvironment, we carried out X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) studies. Meyghan Playa sediments consist of very fine-grained sediments and contain both evaporite and clastic minerals. The evaporite minerals include calcite, gypsum, halite, glauberite, and thenardite, whereas clastic minerals are quartz and clay. The calcite abundance decreases from the margin to the central portion of the playa but gypsum and halite abundances show an increasing trend from the margin to the center. This observation is consistent with the general zonation of other playas. Variations of calcite and gypsum concentration profiles present increasing and decreasing trends with depth, which could be ascribed to the changes in climatic factors. These factors include brine chemical modifications owing to changes in evaporation and precipitation rates and variations in relative abundance of anions-cations or in the rate of clastic and evaporite minerals due to variations in the freshwater influx (climatic changes) with time. A decrease in calcite and increase in sulfate minerals (especially gypsum) with depth is probably due to the higher water level and rainfall, a more humid climate, and salinity variations. Keywords Mineralogy . Geochemistry . Palaeoclimate . Playa . Meyghan . Iran
Introduction Playas are shallow ephemeral lakes that form in arid and semiarid regions. These inland basins generally occur in the lowest part of an internally drained desert following seasonal or episodic storm events (Reeves 1978; Shaw and Thomas 1989), wherever evaporation exceeds precipitation rate in a hydrologically closed basin (Hammer 1986; Mungoma 1990;
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12517-018-3918-3) contains supplementary material, which is available to authorized users. * Leila Abdi [email protected]; [email protected] 1
School of Geology, University College of Science, University of Tehran, Tehran, Iran
2
Humboldt University, Berlin, Germany
3
Department of Geology, Teacher training University, Tehran, Iran
Williams 1991; Seaman et al. 1991). Playa lake deposits and evaporites are sensitive indicators of local climate and may contain sedimentological and geochemical
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