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|Title: ||Soil degradation due to the destruction of crystalline kaolinite and the formation of X-ray amorphous clays accompanying ephemerial saline groundwater discharge.|
|Authors: ||Taylor, GR|
|Issue Date: ||2012|
|Publisher: ||TAYLOR & FRANCIS LTD|
|Citation: ||Taylor, G. R., Day, M., Meredith, K. (2012). Soil degradation due to the destruction of crystalline kaolinite and the formation of X-ray amorphous clays accompanying ephemeral saline groundwater discharge. AUSTRALIAN JOURNAL OF EARTH SCIENCES, 59(1), 135-152.|
|Abstract: ||The discharge of saline groundwater results in the formation of sodic soil scalds in irrigated, dryland and urban environments of southeastern Australia. Sodic soils are dispersive, and this leads to soil erosion and a loss in agricultural productive capacity. These sodic soils commonly show polygonal cracking and pressure ridges indicating the presence of swelling clays. Infrared spectroscopy of scald surfaces and XRD (X-ray diffraction) analyses of the clay fractions of the sodic soils show the presence of amorphous clays, smectite, illite or mixed smectite/illite layer clays. Non-salinised soils adjacent to the salt scalds are commonly predominantly kaolinitic. SEM images and normative EDS mineral analyses of the clay fractions of these soils show that crystalline particles, predominantly of kaolinite, are progressively replaced by poorly crystalline smectite, illite and amorphous material. Normative mineral analyses determined from the bulk soil composition, based on a derived composition of submicron clay particles, show that increased soil salinity correlates with a higher percentage of X-ray amorphous clays of a smectitic composition. By comparison with studies from elsewhere, we propose a mechanism by which kaolinite is transformed into smectite and illite or mixed layer smectite/illite, which proceeds by dissolution and subsequent crystallisation, rather than by solid-state transformation. We propose that the crypto-crystalline or amorphous nature of the clays produced is largely a function of cycles of varying mineral stability produced by alternating periods of saline water discharge and freshwater flushing. The transformation of primary kaolinite to smectite/illite within saline discharge zones explains the spectral changes that allow such saline discharge areas to be mapped with hyperspectral imagery. © 2012, Taylor & Francis Ltd.|
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