Tracing environmental changes and paleoclimate using the micromorphology of soils and desert varnish in central Iran

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.