چکیده:
Soil and desert varnish are powerful records capable of saving invaluable data regarding environmental factors and processes during their formation stages. The present research was carried out to identify the environmental variations and paleoclimate reconstruction in the central deserts of Iran using soil and varnish micromorphological characteristics. Mantled pediment, alluvial fan, and alluvial plain landforms were selected. A minimum of one representative pedon was described and sampled on each geomorphic surface, amounting to a total of eight pedons. Varnished rocks were further collected from all geomorphic surfaces and studied by petrography microscope. Clay (coatings and micro layers) , calcite (nodules, coatings, quasicoatings, and infillings) , anhydrite (nodules) , halite (coatings) pedofeatures, clay coating-calcite infilling, and anhydrite nodule-clay coating compound pedofeatures were investigated in the thin sections of the soil. Lenticular, vermiform, and platy gypsum crystals were identified as nodules and interlocked plates. Desert varnishes (100-600 µm) were different from host rocks as far as color, texture, and formative components are concerned. According to micromorphological evidence, the area probably experienced two different climates. Coatings and infillings of clay in soils and rock crevices were developed in an environment with more available humidity. Evaporite minerals were formed in soils and clay coatings on rock surfaces in the following period with less available moisture. The study results showed that micromorphology could be a necessary and useful tool in pedology and paleopedology investigations.
خلاصه ماشینی:
The micromorphology of desert varnish formed on different geomorphic surfaces in the Jiroft area, central Iran, was investigated in the present research.
/ Desert 24-2 (2019) 331-353 (View the image of this page) a Structure: grade (1- weak); size (m- medium); type (abk- angular blocky, sg- single grain, m- massive) b Concentrations: quantity (f- few, c- common, m- many); size (1- fine, 2- medium, 3- coarse, 4- very coarse); shape (I- irregular, PE- pendular, P- platy); kind (FDC- finely disseminated carbonates, FDS- finely disseminated salts, CAM- carbonate masses, CBM- clay bodies, GYM- gypsum masses, CAX- calcite crystals, GYX- gypsum crystals); location (MAT- in the matrix (not associated with peds/pores), TOT- throughout, BRF- on bottom of rock fragments) c CCE: calcium carbonate equivalent d Gy: gypsum e An: anhydrite f SAR: sodium adsorption ratio g ng: negligible Undeveloped soils (pedons 5, 6, and 7) with the same horizons and classifications (Typic Torrifluvents) were formed on different geomorphic surfaces of alluvial fan (Figs.
Formation of argillic horizon and clay coatings in the soils of arid and semi-arid environments (such as the area of the present research) with low SAR (Table 2) is an index of a paleoclimate with more available humidity in the past, further reported by many studies (Ayoubi et al.
Furthermore, clay coatings in soils (with high SAR) and on the rock surfaces were formed during the arid periods while orange/dark microlamination of desert varnish was observed.