بررسي رسوب شناسي برخي از لسهاي استان گلستان از نظر ويژگيهاي بافت شناسي مطالعه موردي: مقاطع قپان عليا و جنوب گرگان

An Investigation of the Sedimentology of Some of Golestan Province Loesses from View Point of Texture Properties Case Study: High Ghapan and Southern Gorgan Sections

Loess sediments among of the most widespread forms of eolian glacial sediments. These sediments are usually yellow but grizzly with approximately 70 to 90 percent of their formation consisting of silt materials. Iran loesses are mainly located in northeast regions. The purpose of this research is to investigate sedimentological properties of loesses in Ghapan (semiarid climate) and Naharkhoran valley (humid climate) regions in Golestan province. Loesses in mentioned sections were described based on soil taxonomy and from non-developed horizons of parent materials (C horizon). Grain granulometry at the 2 stages of measuring sand components, with the help of wet sieve, and also, a determination of silt and clay components, with the help of pipette method, where completed. The gained conclusions indicated that, in studied sediments median and mean diameters stand between 4 to 11 and 3 to 8 microns respectively. Also in these sediments, sorting, skewness and kurtosis are very poorly differented, fine skewed and platy kurtic respectively. These sediments are not equable, the fine grains being abundant and sedimentation having occurred in quiet environments. The main part of inequality is related to particles with the medium size. The statistic conclusions indicate that the sediments found in Ghapan as compared with the ones found in southern Gorgan are significantly different in median and mean diameters, but these sediments are similar from the view point of skewness and kurtosis. Ghapan region loesses are coarser and with a better sorting. A comparison of the studied loesses sedimentary properties with those in a few other countriesʹ loesses indicated that there nearly exists a harmony between them from sorting and skewness aspects, but from the view points of median and mean diameters and kurtosis they are different. Weak sorting and granulometry curve bimodality, in these sediments, indicate that Iran loesses are of 2 origins of different distances. Also, the finer being of southern Gorgan section sediments as compared with Ghapan section, shows that, north and northeast winds ( northeast -southwest) play an important role in forming Iran northeast loesses