Creating a soil parent material map digitally using a combination of interpretation and statistical techniques

Abstract

In this study, a map of soil parent material is created to support the delineation of soil properties and classes of the Narrabri Shire, NSW. Currently, available information in this study area is geological and lithological maps at a scale of 1:250 000 to 1:1 000 000. These maps are not detailed, and the description in some areas is not accurate. Thus, this study created a new parent material map using information from the geological and lithology information, barest earth satellite imagery, gamma radiometric, topography, prior soil map and digital soil texture maps (clay and sand content). Based on interpretation and parent material observations, 18 parent material classes were delineated in the area. The 18 classes were then modelled using Linear Discriminant Analysis using Digital Elevation Model, slope, topographic wetness index, Gamma potassium (K) and thorium (Th), Ratio K to Th and soil visible and near infrared (NIR) reflectance (created using RGB and NIR bands) as covariates. This modelling process was iterated 50 times, and the most frequently predicted class was assigned to each of the 90 m × 90 m pixels throughout the study area. A map of the frequency of the predicted classes was also created to assess modelling uncertainty. The new parent material map consists of sedimentary residuals (sandstone), volcanic materials (basalt), alluvium and colluvium. The alluvium can be distinguished into six classes according to slope, soil information from satellite images and soil texture. The colluvium consists of three classes with a characteristic of high clay content (smectitic) and brown in colour (kaolinitic). Using similar approaches, such soil parent material or substrate maps could be developed for different regions in Australia. This method generated unique soil parent material classes combining stratigraphy, lithology and geomorphology.