1. Regolith-landform mapping: principles and application in WA Richard Langford

2. What is regolith?
Material, whether cemented or unconsolidated, that overlies unweathered bedrock
Formed by weathering and/or other geomorphic processes including erosion, transport, sedimentation, and chemical deposition
Obscures geological structures and lithologies
Blankets, to depths of hundreds of metres, potential mineral deposits
Hosts a variety of derivative mineral deposits ranging from placers to chemical precipitates

3. Why map regolith? Record information Provide derivative maps
type, variation
regolith-landscape maps
Provide derivative maps
engineering geology, regolith geochemistry, etc
Visualize regolith data
aid understanding of relationships
Regolith research
mostly based on mapping

4. Landscape-based mapping
Soil mapping
Morphological mapping
Geomorphological mapping
Regolith-landform mapping
Numerical land systems mapping
Land capability mapping
Land resource studies
Land evaluation frameworks
Engineering geological mapping

5. Soil mapping Soil classification versus mapping units
Classification does not indicate how soils are associated in the landscape
Purity of mapping units
Soils closely related to position in the landscape — catena/toposequence concept
Prediction based on position in the landscape
Allows mapping from aerial photos using landforms as basis for subdivision
Scale independent — essential link is relationship between soil types and landforms

6. Catena concept 1
Particular slope forms are associated with particular soil sequences
“ a unit of mapping convenience a grouping of soils which while they fall wide apart in a natural system of classification on account of fundamental and morphological differences, are yet linked in their occurrence by conditions of topography and are repeated in the same relationships to each other wherever the same conditions are met with” (G. Milne)

7. Catena concept 2
Differences between soils of a catena are generally related to differences in their position in the landscape and their drainage characteristics
Important factors include slope steepness, and slope processes such as surface wash, solution, and mass movements
Underlying rock is the parent material only in upland soils
Rest of catena developed in transported material

8. Morphological mapping
Based on the recognition of breaks and changes of slope, rates of change of slope, and slope form lines
Indicates form and steepness of landscapes
plan and profile convexity and concavity
slope categories
Essential building block for all geological mapping
basis of field mapping training in BGS

9. Geomorphological mapping
Uses morphological map as its foundation
Adds information related to landscape processes
Fieldwork needed to determine regolith-landform relationships
Examples:
RED scheme of Anand & Smith, based on assumptions about the former landscape
soil maps using catenas for soil-landscape
land system maps, similar to regolith-landscape maps

10. Regolith-landform mapping
Basis for both soil and land systems maps
Unit boundaries based on landforms
Map polygons described in terms of regolith types and landforms
Models of landscape evolution constrain the predictions about regolith-landform relationships
Regional models will not predict the location of specific regolith materials, but allow prediction of regolith-landform associations (land systems)
Local models will predict the location of specific regolith materials

11. Land system maps 1
Recurring pattern of topography, soils and vegetation
Underlying geology, landforms, soil, hydrology and vegetation
Used to predict land properties in unknown areas
Similar result to regolith-landscape maps
AGSO (GA) regolith-terrain maps
recurring landscape elements and their associated underlying regolith packages
landform area characterized by similar landform and regolith attributes

12. Land system maps 2 Map units are not the same as bedrock units
Method is not new, but unfamiliar
Method is scale-independent
Models of landscape evolution are useful for predicting materials, vegetation, rock, and landform characteristics
Has proved effective for rapid terrain classification of many areas
Based on the principle that changes in the landform characteristics can be expected to affect the soil and land cover characteristics of an area
Adopted soil catena/toposequence concept

13. Regolith stratigraphy
Bedrock mapping techniques inappropriate
Inappropriate to give formal rock unit names
Law of superposition does not apply
Nature of regolith reflects the evolution of the landform on which it occurs
Correlation of land surfaces is difficult
Cannot naturally be placed in time stratigraphy
Lithostratigraphic units for transported regolith only
Placing in situ regolith in a stratigraphy is illogical

14. Process-Material-Landform
Assess each unit
Compromise
Dominance
Basis of map code
Landform
Material

15. Examples Howatharra King of the West and White Flag Lakes Kalgoorlie
use of landform in mapping
mapping rock and regolith together
simple codes for a simple situation
King of the West and White Flag Lakes
problems with spectral properties
direct observation of landform and material
codes from space or on the ground?
Kalgoorlie
portraying a simple interpretation
can the codes be made to work?

16. Howatharra landform & geology 1
Double scarp
Newmarracarra Limestone
Regionally m AHD

17. Howatharra landform & geology 2

18. Howatharra landform & geology 3
Importance of landform
mappable features eg breaks in slope
topography
eg talus slopes and footslopes
Importance of weathering
fresh or ferruginized limestone and shale
Rock or regolith?
process - fluvial and marine (rock) or weathering?
material - limestone, weathered rock, residual sand and gravel, colluvium
landform - plateau and escarpment
Jd, Jc, Rf, Rz, Ct, Cf

19. King of the West & White Flag Lakes
Decorrelation stretch 457 RGB
terrain units
compositional variability
see Tapley & Gozzard 1992
Ratios 5/7 4/7 4/2 RGB
mapping landforms
5/7 clay & vegetation 4/7 clay vs iron 4/2 ferrous vs ferric iron
Direct observation
process
material
landform

20. King of the West & White Flag Lakes

21. King of the West & White Flag Lakes
King of the West Lake
process - fluvial or valley fill
material - fluvial
landform - remnant terrace
At or Vt
White Flag Lake
process - distal colluvial
material - fluvial or colluvial
landform - fan Cf

22. Inverted topography 1

23. Inverted topography 2

24. Inverted movie (please wait 20s)

25. Inverted topography 3 Is the regolith now rock? A or R?
process - fluvial and residual
material - fluvial and valley fill sand and gravel over completely weathered bedrock or residual soil
landform - hillcrest
A or R?
a landform code of A is misleading
ignoring the fluvial origin is misleading
which parameter gets the guernsey?
Appropriate map codes demonstrate understanding and complement, not supplement, the description

26. Landform as a surrogate
Pros
faster and more efficient than fieldwork
continuous coverage
represents spatial relationships well
can be applied in other areas
Cons
need field validation of correlation
good for thin cover, but not subsurface variations
genesis or age not related to landform

27. Summary 1
At regional scales, regolith-landform maps are similar to land system maps
At local scales, regolith-landform maps are more like soils maps
At both scales landforms provide the basis for mapping
Not enough to describe landforms
Essential to understand geomorphological principles behind regolith and landform development

28. Summary 2 Regolith-landform mapping
Provides a basis for predicting the distribution of regolith materials
Allows comparison between areas
Provides the foundation for a series of thematic maps useful in land use planning, such as land system maps
Establishes exploration methods for an area