『Abstract
Weathering intensity largely controls the degree to which primary
minerals are altered to secondary components including clay minerals
and oxides. As weathering intensity increases there are changes
in the hydrological, geochemical and geophysical characteristics
of the regolith. Thus, once calibrated, weathering intensity can
be used to predict a range of regolith properties. A weathering
intensity index (WII) over the Australian continent has been developed
at a 100 m resolution using regression models based on airborne
gamma-ray spectrometry imagery and the Shuttle Radar Topography
Mission (SRTM) elevation data. Airborne gamma-ray spectrometry
measures the concentration of three radioelements - potassium
(K), thorium (Th) and uranium (U) at the Earth's surface. The
total gamma-ray flux (dose) is also calculated based on the weighted
additions of the three radioelements. Regolith accounts for over
85% of the Australian land area and has a major influence in determining
the composition of surface materials and in controlling hydrological
and geomorphological processes. The weathering intensity prediction
is based on the integration of two regression models. The first
uses relief over landscapes with low gamma-ray emissions and the
second incorporates radioelement distributions and relief. The
application of a stepwise forward multiple regression for the
second model generated a weathering intensity index equation of
: WII = 6.751 + -0.851*K + -1.319*Relief + 2.682*Th/K + -2.590*Dose.
The WII has been developed for erosional landscapes but also has
the potential to inform on deposition processes and materials.
The WII correlates well with site based geochemical indices and
existing regolith mapping. Interpretation of the WII from regional
to local scales and its application in providing more reliable
and spatially explicit information on regolith properties are
described.
Keywords: Regolith; Weathering intensity index; Environmental
regression; Gamma-ray spectrometry; Australia』
1. Introduction
1.1. Background - gamma-ray spectrometry
1.2. Distribution of radioelements in the weathered environment
1.2.1. Potassium
1.2.2. Thorium
1.2.3. Uranium
2. Materials and methods
2.1. Study areas, geology and landforms
2.2. Datasets - gamma-ray spectrometry, DEM and geology
2.3. Field classification and measurements
2.4. Regression models and exploratory analysis
2.4.1. Relief based model
2.4.2. Multiple regression correlations and stepwise regression
2.4.3. Combining the regression models
2.5. Prediction accuracy and uncertainly
3. Results
3.1. Regional scale observations
3.1.1. Weipa bauxites
3.1.2. Eastern Australia uplands
3.1.3. Ashburton surface
3.1.4. Victorian Basalts
3.1.5. Darling Plateau
3.1.6. Reynolds Range Central Australia
3.2. Local scale observations
3.2.1. Correlations with existing regolith-landform maps
3.2.2. Hydrological applications and predicting specific soil
attributes
3.2.3. Correlation with field based geochemical weathering indices
3.2.4. Weathering index over depositional landscapes
4. Discussion
4.1. Radioelement trends during weathering
4.2. Weathering intensity index a proxy for regolith thickness
4.3. Applications
4.3.1. Geomorphic studies and pedogenesis
4.3.2. Digital soil mapping and natural resource management
4.3.3. Mineral exploration
4.3.4. The global context
5. Conclusions and future work
Acknowledgements
References