Collection: Clay mineral maps for western Victoria - kaolinite, illite and smectite

Clay mineralogy is recognised for its role in carbon turnover and storage, buffering of soil pH and ultimately the chemical behaviour of soils. Although clay mineralogy is important to understand the services delivered by soil, it is rarely measured or observed. General reasons given for not observing these properties include their expense, they are often time consuming and difficult to obtain. This set of clay mineral maps (according to GlobalSoilMap.net specifications) was derived using legacy clay mineral determinations from XRay Diffraction (XRD) in combination with Mid Infra-Red Spectroscopy (MIR) and a spatial inference process (model trees).

Mid-infrared (MIR) spectroscopic models were formulated for clay minerals kaolinite, illite and smectite using partial least squares regression (PLSR) and quantitative XRD determinations. The MIR spectroscopic models were applied to 11,500 samples from western Victoria and harmonized to the GlobalSoilMap specified depth intervals (0-5, 5-15, 15-30, 30-60, 60-100 and 100-200 cm) using equal area splines. The abundance of clay minerals were mapped using model trees and spatial covariates of soil forming factors (climate, terrain, organisms, parent material and soil) to represent processes at the various spatial scales. A 10-fold cross validation procedure was implemented to derive a mean prediction estimate and 90% prediction interval.

Kaolinite was the dominant clay mineral of western Victorian upland terrain and volcanic landscapes. Illite was associated with granitic plutons of southern Victoria and aeolian landscapes in the north. Smectitic clay soils were most common in depressions on the volcanic and sedimentary plains.

All clay mineral abundance (%) maps are produced at a 50 m spatial resolution and include: a) mean prediction; b) lower limit of the 90% prediction interval, and c) upper limit of the 90% prediction interval. The maps are for all GlobalSoilMap.net depth intervals for each clay mineral: kaolinite, illite and smectite. There are currently 54 datasets in this collection.