Micromorphology of the Calcic Soils of the Thar Desert: Implication for Climate Change and Origin of Palygorskite

The Thar desert is known as one of the hottest and most arid regions of the world with a dominance of intense aeolian activity and calcretization of the subsoils. This chapter highlights the application of thin-section investigation and submicroscopy to identify and interpret various pedogenic features of the arid regions and also to assess the origin of palygorskite that occurs commonly in these soils and paleosols of ~30 ka in age. Micromorphology confirmed dominance of weakly developed pedogenic features that are defined by various types of CaCO3 features as powdery to dense and indurated nodules of calcite. The CaCO3 in these soils have also influenced the weathering of the mineral grains within the nodules. Submicroscopy of the calcretes in Bw, Bk, Bss, and BC horizons shows the presence of silt-size palygorskite in the pore spaces of these calcretes. Given the weak pedogenesis and lithological discontinuities, it is interpreted that genesis of the palygorskite in these calcic soils is due to aeolian flux containing the palygorskite silt that was derived from adjoining marine sedimentary rocks. Thus, it is of non-pedogenic origin.