Dear Professor Hamzehpour,

it is a delicate question because of the gradual transition from alluvial- fluvial fan seqeunces into those of playas or ephemeral lakes (playas). Both sedimentary environments evolved under the same morpho-climatic conditions of comparatively high aridity in a distal position relative to the provenance area of the detrital components which should be more or less of the same mineralogical composition. The major criteria to differ both environments from each other are grain size, texture and structure. The closer your soil types evolved towards the fan apex or, in other words, alluvial sediments, the more your intercalating sediments will show unidirectional traction-related features as to their bedding types towards the playa, the closer you move to the basin center of the playa the subsoil sediments will lack such characteristics and floculation and settling of fine-grained or suspended material becomes the most prevailing component over suspended load deposits.

I gave a rather general description of the environments as I miss any further details of your intramountain basin. And there is not anything worse than putting you on a wrong track.  But there are many good textbooks and papers on sedimentology which you should browse in order to refine your distinction. The soil types are in-situ formations which evolve across the  boundary of the lacustrine-alluvial environments and as such the response is only reflected in change of the hydrological system from running through stagnant water bodies in an otherwise aquatically starved or undernourished basin.

Even if you speak of a clay-dominated environment you will see in the micromorphology the differences I referred to above.

I wish you much success

H.G.Dill

Pr Dill made a nice answer; I will just add that looking to diatoms, fossils; malacofauna will help.

Dear Nikoo

You should consider the following facts:

1-    What is the evolution processes (geomorphic or/and pedologic) to evolve the mentioned basin. I mean, has the whole basin evolved with one run of process or some different processes have been taken place in the past of area. This refers to, whether the basin sediments are translocated materials from higher mountains or they are lacustrine sediments, or let say river alluviums, separately or in concordance have formed the basin. If the second, differentiation of these materials should be done first.  

2-    The playa formation mostly, due to its genetic character, is chronologically formed after sedimentation or in rare conditions (in permanent aridity and drought conditions) in concordant with. This is because the playa formation needs specific climatic condition or situation. This is because we do not see playas in all basins.

3-    If the area is evolved with one run, there you cannot detect any differences in sediments's essence, only gradual transitions of sizes.

4-    Playa geoforms are formed by differentiation and construction of different soluble materials in fine textured sediment in due climatic and basin conditions.

In your case when you do not have any salinity in your soil profile, therefore it is not in a playa, your soil point may be on previous lacustrine sediments.

Norair Toomanian

thank you for your answer. the study area has polygenetic soils with several time zeros, mostly due to lake fluctuations. however, at the same time to the lake expansion due to the increased depth and surface area, it seems that rivers in the basin also flooded as the consequence of increased precipitation/decreased evaporation.

as you mentioned, we considered the pedon in the margin of the playa and end of the plain, as of alluvial origin as we couldn't confirm otherwise.

clay mineralogy studies of pedons revealed that illite, chlorite, kaolinate and quartz are common minerals in all pedons, in both pedons developed in playa and plain. in very few Bk and Btk horizons montmorillonite is detected which is probably of pedogenic origin.

If the size of the material and the layering do not show any distinct differences among the horizons, it shows that the sedimentation have the same origin, in this case lacustrine. The playa formation is secondary to this sedimentation and it has its boundary.