干旱区生态环境知识资源中心

The inland lake/playa of Meyghan is a closed basin in the Sanandaj-Sirjan tectonic zone of Iran, containing largest mineable sodium sulfate deposit of the Middle East. The Late Pleistocene-Holocene sediments of this lake/playa were studied for sedimentological and mineralogical characteristics, brine evolution path and the record of climatic variations in the area. Minerals of this lake/playa are mainly evaporites along with some fine-grained clastic components. Evaporite minerals include calcite, gypsum, halite, glauberite, thernadite, polyhalite, natron along with minor volumes of bassanite and sylvite. Gypsum and halite abundances show increasing trend from margin to the center forming a Bull’s-eye pattern. Main clastic components are fine-grained quartz, muscovite, clay minerals, calcite and organic matters. Clay minerals are the most dominant clastic minerals in these sediments. In the surface sediments of Meyghan lake/playa, illite and chlorite abundances reduce from the margin to the center which is contrary to the general patterns of clay distribution in other playas. Inflowing water with low percentage of ions and Na-(Ca)-(Mg)-SO4-Cl-(CO3) type evolve into a brine with high ions concentration during the geochemical evolution and mineral deposition. Finally, geochemical evolution resulted in a Na-SO4-Cl type brine. While clastic components (calcite, quartz and so on) show increasing trend with depth, evaporites abundances show opposite trends. Furthermore, the average grain size of sediments increases with depth indicating higher energy in the past. Typical sedimentary structures of lake/playa environment that are present include efflorescent salt crusts composed of halite, tepees, polygonal structures as the most common sedimentological features of this basin as well as Puffy Grounds. In conclusion, sedimentary records of this lake/playa represent important climatic changes in the area from relatively more humid cold climate in the Late Pleistocene to semi-arid warm climate in the Holocene, with higher evaporation rate.