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Climatical and Pedological Trends in North- East of Iran during the Holocene

Author:
[ Pashaie ] - Prof. of Soil Science at Gorgan Univ. Iran

Abstract:

In order to understand the climatical and pedological changes in North- East Iran during the Holocene, two different methods have been used. The first one was sedimentological studies in the Atrak- Valley and the second one was pedological studies in the loess sedimentation area of Gorgan - Plain. The sedimentological studies at different river- cuts from Korand to Ghoshe- Tapped village indicate four alternated eolian and pluvial sedimentation periods. The lowest sedimentation layer of all of them is a thick and loose conglomeratic layer of Sangamon- Formation (KS). This means that the climatic changes during the Holocene in this area, started with a Post- Pluvial period, followed by four alternated loess sedimentations with a warm and dry climate, as well as three other much thinner fluvial sediment layers. By pedological investigation in this area, two different profiles were studied, one on Agh- Emam Pass with 1270 meters and another one in the Minoo - Dasht Plain with 150 meters elevation. In comparison with Khage- Galdi section in the Atrak- Valley, we also found four humificated horizons alternated with the loess material layers in Minoo- Dasht profile. The lowest buried horizon of this profile indicated a cool and wet climate, while the others have had a warm and most climatic condition. The lowest humification period occured in 7040 - 6420 B.C during the late -Glacial time. The second and third humification period occured during sub - Boreal in 1250 - 1000 and 820 - 770 B.C. respectively, while the last one developed during Sub- Atlantic time in 370 - 170 B.C. The pedological processrin all of them was melanization. On the other hand, the Agh- Emam profile indicates loess sedimentation periods alternated with two Bir- horizons under tropical climate in the lowest part of this profile.The ages of Bir - horizons in this section do not indicate and probably are older than Late - Glacial time. In later investigations we also found two other profiles in "Gholami" Area located in S. W. Gorgan with 1300 meters elevation and in "Karim ishan" area located near the Agh - Emam area with 470 meters elevation. Gholami profile belong to 7260 B.C. but the age of karim - ishan Profile dose not indicate. Finally we found also a complete section in Neka - River area in west of Gorgan. It is a well develop section with the whole determine climatic changes in this area (tab.2). We hope to be able to determine the ages of Karim - ishan, Agh - Eman and Neka section in later time.

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