Soil–geomorphology relationships in Sirjan playa, south central Iran

To study the soil–geomorphology relationships and the effect of past and present climate on soil formation, 10 representative pedons on different landforms, including rock pediment, mantled pediment, piedmont plain, playa margin and playa, were studied. Non-saline clay flat, saline clay flat with and without puffy grounds, wet zone, and salt crust were among the geomorphic surfaces observed in Sirjan playa. Soil moisture varies from mesic (on rock and mantled pediments) to aridic regimes (on piedmont plain, playa margins, playa and mantled pediment). Soil temperature regime in the area is mesic except on playa surfaces and mantled pediment which are thermic. Results of the study showed that soil salinity increased from the rock pediment to playa surfaces. The maximum EC of 314 dS/m was observed in the puffy ground clay flat. Kaolinite, illite, smectite, chlorite and palygorskite clay minerals were identified using XRD analysis. Coatings and infillings of CaCO3 were observed in pediment and gypsum lenticels and interlocked plates were found on piedmont plain and playa. Clay coatings and infillings in the piedmont plain suggest the presence of a more humid paleoclimate in the history of the area.

► A close relationship was found between geomorphology and soil properties.
► Piedmont plains are the peripheries of old Sirjan Lake.
► Argillic horizons in the arid area studied showed evidence of a more humid paleoclimate.
► Petrocalcic horizons in the playa margin geomorphic surface were found for the first time.