Gavkhoni playa, Iran

The Gavkhoni playa, with an area around 550 km2, is located to the southeast of Esfahan in an intramontane basin in central Iran. Water enters this endorheic basin via the Zayandeh River, an ephemeral river outflow in the north, as well as via some small streams, groundwater discharges and direct precipitation. The weather is cold in winter when temperatures decrease to around -7°C, but in mid-summer the playa floor is hot, and temperatures rise to about +42°C. Annual evaporation (about 3265 mm) exceeds precipitation (about 80 mm).

A few small dunes, covered by gypsiferous marl, occur in the surrounding saline sand flat. A soft, low-relief thin efflorescence of salt crust covers its surface. This salt crust includes a higher proportion of underlying sediment and adhesive aeolian sand and often exhibits an irregular network of puffy surface salts. The puffy ground is temporary and usually changes season to season. A few carbonate mounds (tufa) occur west of the dunes. Acicular gypsum is generally present as wavy layers, interbedded with aeolian sand layers along the eastern side of the dunes. Gypsum layers tend to soft and crumbly and not more than a few centimetres thick.

When the salt surface is exposed, the halite layers become buckled, break into a polygonal crust, and petee structures are formed. The polygonal pattern is interpreted to be the result of fracturing during volume reduction caused by either thermal contraction or desiccation. A net volume increase creates the buckling due to expansion during crystallisation. The continued growth of the halite crystals just beneath the dry surface of the pan causes the lateral extension of the surface crust and leads to disruption of the crust into large polygons rimmed, by pressure ridges that over-ride each other. Pumping of subsurface brine, and subsequent evaporation along the cracks between the polygons, leads to precipitation of spongy efflorescent halite and rare ephemeral bittern salts that can include tachyhydrite.

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Gavhoni playa, Iran
Gavkhoni Figure2-1
Different flats in Gavkhuni playa lake and Zayandehrud River delta, A) Mud flat and delta channel, B) Zayandeh delta and vegetation (f:Phragmites sp.; s: Salicornia sp.), C) Salt pan, D) Sand dune and interdune (after Pakzad et al., 2014)
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