Date of Award:

5-1980

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Soil Science and Biometeorology

Committee Chair(s)

Alvin R. Southard

Committee

Alvin R. Southard

Committee

Raymond W. Miller

Committee

Gaylen L. Ashcroft

Committee

Reuel E. Lamborn

Abstract

Characteristics and genesis of five pedons representing some of the soils of the central Alborz mountain northeast of Tehran were investigated. The present climate of the area is similar to the Mediterranean climate. The parent materials for the soils under study have apparently been derived from the Ecocene Alborz Green Beds (a thinly bedded light green mudstone), the Pliocene Hezardareh Formation (a poorly-cemented conglomerate) and Recent alluvium and colluvium. Pedons 2 and 4 are located at lower elevations (plain and river terraces) on 1 to 2 percent slopes. Pedons 3 and 5 are located at higher elevations (hills that surround the valley) on steep slopes of 60 to 75 percent.

According to the results obtained from the physical, chemical, mineralogical, and micromorphological analyses, the pedons have been classified as Xeric Torriorthent--loamy-skeletal, mixed, thermic (pedon 1); Vertic Xerochrept--fine, mixed, thermic (pedon 2); Xerollic Calciorthid--loamy-skeletal, mixed, thermic (pedon 3); Xerollic Calciorthid--fine, mixed, thermic (pedon 4); and Argic Calciorthid--clayey-skeletal, mixed thermic (pedon 5).

The studies on the genesis of the soils were summarized as follows:

1. Wind deposition has affected the top layer of the eroded surfaces of the five pedons. The process has incorporated silt and very fine sand materials into these layers.

2. The differences in landform stability, and consequently, the various degree of the influence of the erosion-deposition processes, are believed to be responsible for the differences in the horizon differentiation of the pedons. The steepness of sloper rather than age of the landform was responsible for the present morphology of the pedons.

3. Pedons 1 to 4 are Recent in age but the control section of pedon 5 reflects an age of Pleistocene or older and, therefore, a wetter climate than at present.

4. The clay mineralogy and the texture of the control section of the pedons reflect the greater influence of the parent materials than any other factor of pedogenesis.

It was suggested that for the Aridisols with moisture regimes bordering on Xeric, the required electrical conductivity of more than 2 millimhos per centimeter be eliminated from the differentiating criteria in Soil Taxonomy.

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