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Hanna Bremer:

Geoecology in the Tropics

with a Database on Micromorphology and Geomorphology

2010. 337 pages, 132 figures, 91 tables, 24x17cm, 850 g
Language: English

(Zeitschrift fόr Geomorphologie, Supplementbδnde, Volume 54, Supplementary Issue 1)

ArtNo. ES023105401, paperback, price: 139.00 €

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Synopsis
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Weathering is the true basis of geoecology, as the weathering process breaks down solid rock and liberates substances, that can be transported by water movement in the regolith and at the surface. The governing factors of weathering are the climate, water, surface rock type, relief, soil properties, vegetation and time. Based on 12 studies of various cratonic areas and 20 years worth of laboratory data, a database of more than 1220 regolith, solid rock and crust samples has been established at the Dept of Geography of Univ of Cologne. The data sets comprise twelve field parameters and 20 lab parameters that have up to 10 components each. Lab data were determined by standard analytical methods and include micromorphological parameters. The integrative study of these parameters presented here leads to inferences about the weathering process itself and its intensity and allows statements to be made about geomorphological processes, morphogenesis and water movement.

The data of this comprehensive set were studied in multiple steps: the abundance of primary minerals was estimated on thin sections, yielding information on rock/regolith-type and extent of weathering. More revealing are correlations of individual weathering parameters, such as soil structure and grain size distribution, where most samples are characterized by a high fraction of sand. Most of these are not „sand“ grains but pseudosand — pseudosand, clay and silt particles compounded by iron and/or silica. For the first time, the fraction coarse pore volume was quantified in these tropical samples, and is found to be unusually high. Another key factor are quartz grains, whose shape, rounding, surface structure and morphogenesis has been studied. Intensive solution features and growth of secondary silica indicate a strongly weathered regolith, and pseudomorphs an authochtonous or allochthonous regolith. The extent of newly formed minerals as indicated by XRD, was also recorded by micromorpology as was the crystallisation grade and the growth type. Pseudosand and well crystallized new minerals stabilize both matrix and pore walls.

Integrated analysis highlights the differences between regoliths formed in rain forests and savannas, and many of the latter are found not to have formed under their present climatic conditions, but in wet climates and therefore represent palaeoregoliths. Old regoliths in the rain forest are called 'aged soils' as they most likely formed under similar conditions as today. Correlations created using the database often allowed earlier findings on regolith and soil formation to be confirmed, and in many cases provide insight in new details of tropical weathering processes.

Using exemplary cases of subterraeous transport and river working the author demonstrates, that field oberservations may be supplemented by laboratory data in order to gain a more detailed understanding of geomorphological processes. Slope and plain formation are more pronounced, if palaeoformations are present. High pore volumes enable pore waters and the substances dissolved in it to move rapidly within the regolith. Analysis of coarse pore volume allows conclusions on transport processes, which have a bearing on soil fertility, too. Characteristic for tropical regoliths are three properties: a large pore volume, formation of new minerals, - gibbsite, hematite, SiO2, kaolinite, goethite. Crystallization on the pore margins and within the matrix enhance the mechanical stability of the regolith, which is in agreement the widespread abundance of authochtonous soils, palaeosoils and aged soils. The compounds of fines to pseudosand and pseudsilt result in increased grain sizes, which in turn lead to greater permeability and mechanical stability.

Table of Contents
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Preface

1. Introduction 1

1.1 The Frame of the study 1
1.2 Preceding work 1–2

2. Regolith: the realm of weathering and geoecological processes 3–35

2.1 Introduction 3–5
2.1.1 Concepts for the study of weathering and its position in geoecology 3
2.1.2 Fundamental geomorphological concepts for this study 3–4
2.1.3 The Cologne Regolith Database (CRD) 4–5
2.1.4 Summary 5
2.2 Weathering of minerals – processes and intensity 5–12
2.2.1 Primary minerals 5–12
2.2.1.1 Light minerals 5–7
2.2.1.2 Heavy minerals 7–9
2.2.1.3 Quartz 9–12
2.2.1.4 Rarely occurring minerals 12
2.2.1.5 Summary 12
2.3 Neoformation of minerals 12–23
2.3.1 Introduction 12
2.3.2 Minerals in X-ray-analysis 12–13
2.3.3 Iron minerals 13–14
2.3.4 Calcite 14–15
2.3.5 Aluminium minerals 15–16
2.3.6 Silica 16
2.3.7 Duricrusts and concretions 16–22
2.3.8 Discussion 22
2.3.9 Summary 23
2.3.10 Summary of the weathering of primary and neoformed minerals 23
2.4 Initial stages of weathering 23–26
2.4.1 Chemical and biological processes 23–24
2.4.2 Fissures 24–25
2.4.3 Single grains 25–26
2.4.4 Summary and discussion 26
2.5 The weathering front 26–33
2.5.1 Introduction 26
2.5.2 Forms of the weathering front 27–28
2.5.3 Grus occurences 28–31
2.5.4 Depth of the weathering front 31–33
2.5.5 Summary: The weathering front 33
2.6 Weathering of transported masses 33–35
2.6.1 Weathering of sediments 33–34
2.6.2 Modifications of mineral grains by transport 34–35
2.6.3 Summary: Weathering of transported masses 35

3. Small-scale forms of weathering 36–43

3.1 Introduction 36
3.2 Stable rock surfaces 36
3.3 Solution forms 36–38
3.4 Taut steep walled convex slope forms and slope-parallel sheeting 38–40
3.5 Corestones and penitent rocks 41–43
3.6 Summary 43

4. Characteristics of the regolith in shield regions 44–65

4.1 Introductions and definitions 44
4.2 Indicators of weathering intensity 44–47
4.2.1 Introduction 44
4.2.2 pH values 44–45
4.2.3 Chemical and physicochemical processes 46–47
4.2.4 Summary of indications of weathering intensity 47
4.3 Regolith structures 47–65
4.3.1 Introduction 47
4.3.2 Grain-size 47–51
4.3.2.1 Introduction 47
4.3.2.2 Grain-size in relation to precipitation and bedrock 47–51
4.3.2.3 Grain-size conclusions 51
4.3.3 Pore quantity and quality 51–56
4.3.3.1 Introduction 51
4.3.3.2 Pore volume 51–53
4.3.3.3 Pore forms 53–54,
4.3.3.4 Pore fillings 54–56
4.3.3.5 Summary and conclusions: Pore volume 56
4.3.4 Microtexture of tropical regoliths 56–65
4.3.4.1 Introduction and definitions 56–57
4.3.4.2 Regolith structure components in percentage of volume 58–59
4.3.4.3 Texture forms 59–61
4.3.4.4 Matrix type 61
4.3.4.5 Pseudosand and pseudosilt 61–63
4.3.4.6 Special forms: Compactions and concretions 63–65
4.3.4.7 Summary: The microtextures of tropical regoliths 65
4.4 Summary: Characteristics of tropical regoliths of the shield areas 65

5. Translocation in regolith: processes and forms 66–84

5.1 Subterranean processes: removal, depletion and enrichment 66–79
5.1.1 Introduction 66
5.1.2 Soil water movement 66–69
5.1.3 Subterranean material removal, piping 70–71
5.1.4 Clay horizon and clay displacement 71–72
5.1.5 Spodosol and gley formation 73–75
5.1.6 Iron precipitates 75–78
5.1.7 Bioturbation 78–79
5.1.8 Summary and conclusions 79
5.2 Special forms resulting from turbation in profiles 79–84
5.2.1 Introduction 79
5.2.2 Vertisol formation 80
5.2.3 Stonelines 79–82
5.2.4 Patterned ground 82–84
5.2.5 Summary special forms 84
5.3 Summary and conclusions on translocation 84

6. Time and space as weathering factors: Terminology and fundamentals
85-126

6.1 Introduction 85
6.2 Temporal weathering factors 85–101
6.2.1 Introduction 85
6.2.2 Weathering age and weathering and erosion rates 85–96
6.2.2.1 Measuring soil age and erosion rates 85–87
6.2.2.2 Aged soils, palaeosols and polygenetic soils 87–90
6.2.2.3 Weathering structures of high age and low erosion 90–96
6.2.2.4 Summary and conclusions: The temporal factor in tropical
weathering 96
6.2.3 Climate change 96–99
6.2.4 Morphogenesis and relative regolith age 99–101
6.2.5 Summary and conclusions concerning temporal weathering aspects 101
6.3 Spatial weathering factors 101–111
6.3.1 Introduction 101–103
6.3.2 Definitions and terminology 103–111
6.3.2.1 Introduction 103
6.3.2.2 Zonal soils – palaeosols – aged soils 103–104
6.3.2.3 Classifications 104–105
6.3.2.4 Soil horizon 105–108
6.3.2.5 The standard profile? 108–110
6.3.2.6 Soil mosaic 110
6.3.2.7 Summary and conclusions 111
6.4 Spatial and temporal weathering conditions 111–125
6.4.1 Introduction 111
6.4.2 Geoecological weathering parameters 111–116
6.4.2.1 Subterranean moisture and vegetation 111–113
6.4.2.2 Drainage and discharge 113–116
6.4.2.3 Summary and conclusions on geoecological parameters 116
6.4.3 Zonal differentiation: Soil types 116–117
6.4.4 Regional differentiation 117–123
6.4.4.1 Introduction 117
6.4.4.2 Petrovariance 117–122
6.4.4.2.1 Introduction 117
6.4.4.2.2 Field observations 117–118
6.4.4.2.3 Laboratory studies 118–122,
6.4.4.2.4 Summary and conclusions on petrovariance 122
6.4.4.3 The age of landscape development 122
6.4.4.4 Tectonovariance 122–123
6.4.4.5 Summary and conclusions on regional diff erentiations 123
6.4.5 Local differentiations 123–125
6.4.5.1 Introduction 123
6.4.5.2 The Catena 123–124
6.4.5.3 Divergent weathering 124–125
6.4.5.4 Summary: Local differentiations 125
6.4.6 Summary: Temporal and spatial weathering conditions 125
6.5 Summary and conclusions on time and space in weathering 125–126

7. Methodical considerations regarding weathering 127–140

7.1 Introduction 127
7.2 Quantitative and semi-quantitative weathering analysis 127–128
7.2.1 Introduction 127
7.2.2 Weathering balance and weathering indexes 127–128
7.3 Ergodic principle or ubiquitary versus zonal soils? 128–129
7.4 Pitfalls 129–135
7.4.1 Soil formation in the tropics 129
7.4.2 Deposition structures 129–134
7.4.3 Biological evidence 135
7.4.4 Pitfalls; summary and conclusions 135
7.5 Relief-forming soil 135
7.6 Discontinuities 136–137
7.7 Positive and negative feedback during weathering 137
7.8 Sensitivity and balance 137–138
7.9 Spatial relationships 138–139
7.10 Summary and conclusions 139–140

8. Analyses and results on tropical weathering using the Cologne
Regolith Database – CRD 141–200

8.1 Introduction: Development of laboratory analyses for morphogenesis
and geoecology 141
8.2 Database Parameter: Field Parameter 141–154
8.2.1 Introduction 141–142
8.2.2 Altitude 142
8.2.3 Annual precipitation 142
8.2.4 Geomorphological position 142–145
8.2.5 Gradient 145–146
8.2.6 Wetness 147–148
8.2.7 Parent rock 148–151
8.2.7.1 Introduction 148
8.2.7.2 Distribution of the rocks 148–149
8.2.7.3 Unconsolidated rocks 149–151
8.2.8 Vertical position in the soil 151
8.2.9 Transport 151–153
8.2.10 pH-values 153
8.2.11 Catastrophic events 153–154
8.2.12 Summary and conclusions: Field parameters 154
8.3 Laboratory parameters 154–200
8.3.1 Indicator qualities of the minerals 154–160
8.3.1.1 Introduction 154, 8.3.1.2 Primary minerals 154–156
8.3.1.3 Quartz grain morphology 156–158
8.3.1.4 Secondary quartz 159
8.3.1.5 Summary: Quartz grains as indicators 159–160
8.3.2 Minerals determined by X-ray analysis 160–167
8.3.2.1 Introduction 160–161
8.3.2.2 Quantities of the minerals in precipitation zones 161–164
8.3.2.3 Ratio of smectite to kaolinite 164–165
8.3.2.4 Proportion of clay minerals and the clay fraction 165–167
8.3.3 Summary and conclusions on the indicator quality of individual
minerals 167
8.3.4 Indicator qualities of heavy minerals 167–170
8.3.4.1 Introduction 167
8.3.4.2 Heavy minerals and weathering intensity 168–169
8.3.4.3 Summary and conclusions on the indicator quality of heavy
minerals 170
8.3.4.4 Comparison of the indicator qualities of light and heavy
minerals 170
8.3.5 Microtexture of tropical regoliths 170–174
8.3.5.1 Introduction 170
8.3.5.2 Distribution of different structure and texture forms 171–174
8.3.5.3 Summary and conclusions: texture of tropical regoliths 174
8.3.6 Neoformations 174–182
8.3.6.1 Introduction 174–175
8.3.6.2 Neoformations: Matrix and crystallisations 175–179
8.3.6.3 Pseudomorphs and crystalline pore fillings 179–181
8.3.6.4 Summary and conclusions: Neoformations 182
8.3.7 Grain sizes as indicators 182
8.3.8 Weathering grade 182–189
8.3.8.1 Introduction 182–183
8.3.8.2 Weathering grade of individual para meters and components 183–185
8.3.8.3 Weathering grade as an indicator 185–188
8.3.8.4 Summary and conclusions on weathering grades 188–189
8.3.9 Autochthony – allochthony 189–194
8.3.9.1 Introduction 189
8.3.9.2 Field observations – sampling 190–191
8.3.9.3 Laboratory analyses 191–192
8.3.9.4 Summary of autochthony – allochthony 192–193
8.3.9.5 Stability of the regoliths 193–194
8.3.10 Statistics in the Cologne Database – CRD 194–198
8.3.10.1 Introduction 194
8.3.10.2 Setting up the CRD and statistical possibilities 194–196
8.3.10.3 Feldspar and methods of determination 196–198
8.3.10.4 Summary and conclusions on statistics in CRD 198
8.3.11 Evaluation of the CRD 198–199
8.3.12 Summary: Indicators of weathering 200
8.3.12.1 Indicator qualities of the field and laboratory parameters 200
8.3.12.2 Results of individual parameters 200

9. Integrative work methods: Spatial and temporal classification
in the tropics 201–225

9.1 Introduction 201
9.2 Methods 201–202
9.2.1 Methodical background 201–202
9.2.2 Data collection 202
9.3 Classification of samples 202–204
9.3.1 Introduction 202
9.3.2 From observations of individual samples to conclusions 203–204
9.3.3 Summary: Classification of the samples 204
9.4 Zonal classification of the statistical entries 205–210
9.4.1 Introduction 205
9.4.2 Correlations of laboratory analyses and annual precipitation 205–208
9.4.3 Zonal distribution of weathering grad 208–210
9.4.4 Conclusions and summary 210
9.5 Indicators for recent, ancient and aged regoliths 210–221
9.5.1 Introduction 210
9.5.2 Field observations 211
9.5.3 Laboratory investigations 212–221
9.5.3.1 Recent soils – Palaeosols 212–215
9.5.3.2 Incompatibility 215
9.5.3.3 Summary: Palaeo-regoliths 215
9.5.3.4 Aged and transformed regoliths in rainforests 215–221
9.5.4 Summary recent, aged soils and palaeosols 221
9.6 Geography of weathering 221–225
9.6.1 Introduction 221
9.6.2 Synopsis of regolith characteristics in rainforests and savannas 221–223
9.6.3 Proposals for aging and further formation of soils in zonal concepts
223–225
9.6.4 Summary: Geography of weathering 225
9.7 Summary and conclusions of integrative work methods 225

10. Integrative work methods of weathering and geoecology 226–291

10.1 Introduction 226
10.2 Subterranean processes 226–238
10.2.1 Introduction 226
10.2.2 Field observations 227–231
10.2.2.1 Subterranean removal of material and subsidence 227–229
10.2.2.1.1 Open depressions and forms with fillings 227–229
10.2.2.1.2 Summary and conclusions on subterranean processes with
subsidence 229
10.2.2.2 Subterranean removal and erosion 230–231
10.2.2.2.1 Plane bands and dambos 230–231
10.2.2.2.2 Swales on divides and planar passes 231
10.2.2.2.3 Summary and conclusions on subterranean processes with lowering 231
10.2.3 Laboratory analyses on subterranean removal of material 231–238
10.2.3.1 Distribution of the pores and their impact 231–238
10.2.3.2 Summary on the laboratory analyses of subterranean removal of
material 238
10.2.4 Summary and conclusions on the processes of subterranean
removal of material 238
10.3 Internal migrations: Distribution of different iron formations 238–291
10.3.1 Introduction 238–239
10.3.2 Field observations 239
10.3.3 Laboratory analyses on the migration of iron 240–250
10.3.3.1 Introduction 240, 10.3.3.2 Opaque heavy minerals 241–246,
10.3.3.3 Further iron formations 246–247
10.3.3.4 Soil colour 247–249
10.3.3.5 Distribution and geoecological conditions of different iron
formations 249–250
10.3.3.6 Summary and conclusions: Iron formations 250
10.4 Summary and conclusions: Subterranean processes 250
10.5 Surface transport 250–267
10.5.1 Introduction 250–251
10.5.2 Fluvial processes 251–258
10.5.2.1 Introduction: Sand, an indicator for transport processes 251
10.5.2.2 Field observations 251–255
10.5.2.3 Laboratory investigations of the river sand 255–257
10.5.2.4 Floodplain and fl uvial deposits 257–258
10.5.2.5 Summary and conclusions on fluvial dynamics 258
10.5.3 Planar processes 258–262
10.5.3.1 Field observations 258–259
10.5.3.2 Laboratory investigations 259–262
10.5.3.3 Summary and conclusions on planar processes 262
10.5.4 Aeolian processes and sand 262–263
10.5.5 Slope and valley development 263–267
10.5.6 Summary and conclusions on valley and slope development 267
10.6 Stability of surfaces indicated through morphogenesis 267–274
10.6.1 Introduction 267–269
10.6.2 Morphogenesis in arid areas 270
10.6.3 Morphogenesis in the South American Rainforest 270–273
10.6.4 Summary and conclusions on the stability of surfaces 274
10.7 Statistical analysis of the processes at the surface 274–280
10.7.1 Correlations of individual parameters 274–275
10.7.2 Trask-values, indicators for the variability of the regoliths 276
10.7.3 Geomorphological positions and clay minerals 276–279
10.7.4 Summary of the statistical analysis 279–280
10.8 Summary and conclusions on transport at the surface 279–280
10.9 Transport processes: Hydrological conditions and erosion rates 280–285
10.9.1 Introduction 280
10.9.2 Hydrological conditions 280–283
10.9.3 Transport processes and erosion rates 283–285
10.9.4 Summary and conclusions: Hydrological conditions of transport
processes and erosion rates 285
10.10 Discussion 285–291
10.10.1 Discussion of integrative work methods 285–286
10.10.2 Discussion numerical work methods 286–287
10.10.3 Ubiquitous or zonal weathering from an integrative point of
view 287–288
10.10.4 Integrative considerations for landscape development 289–291
10.10.5 Summary: Integrative work methods and arguments 291
10.11 Conclusions and summary 291

11. Perspectives 292–302

11.1 Introduction 292
11.2 Differences in weathering in the study areas (continents) 292–295
11.3 Th e significance of the regolith for land use potential 295–301
11.3.1 Introduction 295
11.3.2 Soil fertility 296–301
11.3.2.1 Field observations 296–297
11.3.2.2 Laboratory analysis 297–301
11.4 Susceptibility of tropical regoliths 301–302
11.5 Summary of the perspectives 302

12. Summary 303–311

12.1 Summary of contents 303–304
12.2 Individual results 304–311
12.2.1 Zonal diff erences and general findings 304–306
12.2.2 Regolith charcteristics with indicator functions for weathering
processes 306–307
12.2.3 Regolith charcteristics indicative of soil moisture and transport
processes 307–308
12.2.4 Statistical evaluation 308–309
12.2.5 Results of integrative methods for transport processes 309
12.2.6 Results of integrative methods for landscape genesis 310–311
12.2.7 Outlook on applied questions 311
12.3 Main focus 311

Appendix 312–337

Glossary 312–315

The Cologne Database – CRD 316–320

Data sheet 321–323

Literature 324–337