بررسي تكامل خاك ها و تعيين منشا و سن يابي رسوبات سيلتي در لندفرم هاي اطراف مشهد

چكيده انگليسي :

Abstract As an important component of natural ecosystems the identification of soil characteristics is necessary for sustainable land use management On the other hand soils have been extensively used as continental archives of climate change Silt enriched soils and sediments have discontinuously covered the regolithic pediments meta sedimentary rock pediments terraces of Torogh River and some parts of piedmont plain of Binaloud zone in southern Mashhad Despite the importance of the silty deposits for Quaternary landscape evolution and land use management they have received little attention by geologists and soil scientists The objectives of this study were i to determine the distribution characteristics nature and provenance of the silty sediments of southern Mashhad ii to study the morphology mineralogy and micromorphology of silty soils and other soils and sediments to make a qualitative paleoclimate interpretation and iii to conduct a pedochronostratigraphical investigation on silty sediments from southern Mashhad and loess deposits from Kalat e Naderi In this regard the particle size distribution microtexture of quartz grains geochemical properties mineralogy and micromorphology of silty deposits and associated soils and sediments were studied The infrared stimulating luminescence IRSL dating of Robat e Khakestari Tappeh salam and Deh Gheybi sections a and b from southern Mashhad and Kalat e Naderi a and b sections from Kalt e Naderi area were determined Based on particle size distribution abrupt particle size difference between silty deposits and underlying materials the shape and microtexture of quartz grains chemical and geochemical data and geochemical homogeneity of silty deposits from different landforms and geomorphic position silty sediments of the study area seem to be wind blown in origin and are therefore classified as loess The particle size distribution of loess deposits around the study area is more or less identical and shows the dominance of silt fraction more than 70 Silt sized particles in turn are dominated by the coarse silt fraction 35 45 Sub rounded and well rounded quartz grains with bulbous edges pitting and incision as a consequence of aeolian abrasion are most common in the loess deposits Dominance of coarse silt suggests a local origin for loess deposits Similarity in chemical properties particle size distribution mineralogy and geochemical signatures of gypsiferous marls and loess deposits indicate that gypsiferous marls near the loess deposits are the main source of aeolian deposits Four types of palygorskite were distinguished in sediments and soils based on their quantity and morphology 1 A high amount of well grown fibers of palygorskite were detected by XRD and SEM analyses in the marly sediments and also in the lower part of Tappeh Salam section The presence of palygorskite in gypsiferous marls of study area the sediments younger than lower Cetaceous of eastern central and southern Iran as well as those in arid parts of the world is an indication of similarity in Tertiary paleoenvironmental conditions of these areas 2 A relatively high amount of palygorskite detected easily by XRD in Bk and By horizons appears to be the result of illuviation of palygorskite associated with carbonates or gypsum 3 A lesser amount of palygorskite was detected by TEM in the red Btk horizons OIS5 paleosols in loess sections The existence of carbonate nodules covered by clay and silt coating indicates a moist condition after carbonate illuviation and an unstable environment for palygorskite during the last interglacial period 4 A very low quantity of detrital palygorskite was found in unaltered loess deposits originated from gypsiferous marls The dose rate ranges from 3 65 to 4 28 Gy ka Equivalent dose values range from 45 7 2 1 to 782 8 10 2 Gy resulting in IRSL age estimates between 12 5 1 0 and 203 13 ka The most detailed last interglacial glacial loess record is exposed at the Kalat e Naderi sections a wher

كريمي كارويه، عليرضا

بررسي تكامل خاك ها و تعيين منشا و سن يابي رسوبات سيلتي در لندفرم هاي اطراف مشهد

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