SEDIMENTARY MODELS FOR COAL FOru·ffiTION IN THE KLIP RIVER COALFIELD by Angus

309 Pages·2013·9.81 MB·English

SEDIMENTARY MODELS FOR COAL FOru·ffiTION IN THE KLIP RIVER COALFIELD
by
Angus David Mackay Christie
A thesis submitted in partial fulfilment of the requirements for the degree of
Doctor of Philosophy in the Departnent of Geology, University of Natal, Durban.
Durban 1988
PREFACE
This thesis represents original work by the author and has not been
submitted in part, or in whole to any other university. Where use is made of
the work of others it is acknowledged in the text.
The research was conducted in the Department of Geology and Applied Geology,
Universi ty of Natal, Durban, under the supervision of
Professor R. Tavener-Smi th .
IN MEMORY OF MY FATHER,
DAVID ALEXANDER CHRISTIE
ACKNOWLEDGEMENTS
I wish to express my appreciation to the following individuals and
organisations who contributed to the successful completion of this study:
1. National Geoscience Programme (NGP) for financing the project.
2. Professor R. Tavener-Smith, my supervisor and NGP Co-ordinator, for his
assistance and constructive criticism.
3. The Chief Director, Geological Survey, for adopting this study as an
official project and providing secretarial and drafting facilities.
4. Trans-Natal Coal Corporation, ISCOR, Arncoal, Rand Mines and Goldfields for
providing access to confidential exploration borehole logs and reports.
This study would not have been possible without the co-operation of these
companies.
5. Trans-Natal Coal Corporation for providing accommodation at Northfield
Colliery during the initial stages of this study.
6. Mr R.P. Randel, ISCOR and Dr H.U. Bantz, Trans-Natal Coal Corporation, for
their willing assistance, advice and friendship throughout the duration of
this project.
7. Dr T.R. Mason, University of Natal, Durban for his practical advice
regarding systematic nomenclature of trace fossils, and the interest he
showed in all aspects of the study.
8. My colleagues, Dave Roberts and Alan Smith, for helpful discussions and
advice.
9. My parents-in-law for their support and assistance.
10. My wife Janet, and children Sarah and Matthew, for their love, support and
understanding.
ABSTRACT
The primary objective of this study was to establish sedimentary models for
peat formation in the southern part of the Klip River coalfield during Ecca
(Permian) times and to assess palaeoenvironmental controls on coal seam
behaviour and distribution. In order to achieve this approximately 2 400
borehole logs and 25 field sections were collected.
The coal-bearing Vryheid Formation records early to late Permian
fluvio-deltaic sedimentation within the northeastern main Karoo basin. Three
informal lithostratigraphic subdivisions, based on the investigations of
Blignaut and Furter (1940, 1952), are proposed: the Lower zone, Coal zone and
Upper zone.
An examination of the structural framework and history of the northeastern
Karoo basin reveals that the southern and western boundaries of the Klip River
coalfield are defined by zones of rapid basement subsidence the Tuge la and
Oannhauser Troughs respectively. There is some doubt as to the locality of the
source area to the rivers emptying into the Ecca sea. Ryan (1967) postulated
the "Eastern Highlands" situated off the present southeast African coast, but
it is contended that the Swaziland area, situated no more than 200 to 300 km to
the northeast of the Klip River coalfield, constituted a more plausible source
area.
The Lower zone represents sedimentation along a westerly to southeasterly
prograding coastline dominated by high-constructive lobate or braid deltas, but
also showing significant influence by wave processes. The Coal zone, which
varies in thickness from 35 to 60 m, represents a major phase of coastal
progradation and braided-river deposition on extensive alluvial plains.
Significant coal seams formed only during periods of fluvial inactivity, the
duration of which was dependent on source-area processes.
Coal seam geometry and behaviour in the Klip River coalfield were not
influenced by the depositional environments of associated clastic sediments.
The following factors were found to have of profound influence in determining
the extent, distribution and rate of peat accumulation:
1. Platform stability and temporal and spatial variations therein.
2. The absence or presence of penecontemporaneous clastic sedimentation.
3. Ouration of periods of peat formation.
4. Lithology and topographic expression of clastic sediments underlying
peat-forming swamps.
The peat-forming phase of the Vryheid Formation was terminated by an
extensive transgression brought about by an eustatic rise in basin water-level
and/or an increased rate of platform subsidence.
CONTENTS
CHAPTER 1: INTRODUCTION ••••••.•••••••••.••••••••••.••••••••••.••• 1
1.1 GEOLOGICAL SETTING AND GEOGRAPHy...... . ............... 1
1.2 AIMS AND APPROACH •..•••••••••.•.•••••••••••••••••..•.• 5
CHAPTER 2: PREVIOUS INVESTIGATIONS ••••....••••.....•.••••.••.•••• 10
2.1 STRATIGRAPHIC AND SEDIMENTOLOGICAL INVESTIGATIONS ••••• 10
2.2 STRATIGRAPHIC SUBDIVISION OF THE VRYHEID FORMATION ...• 13
CHAPTER 3: TRACE FOSSILS ••••••••.••••••••••.••••••••••••••••••••• 17
3.1 INTRODUCTION ....••.•••••..••••......•••.••••••••••.••. 17
3.2 SYSTEMATIC ICHNOLOGy.................................. 18
Ichnogenus SIPHONICHNUS Stanistreet et al., 1980 ..•••• 18
Ichnospecies SIPHONICHNUS ECCAENSIS Stanistreet •••••••
et al., 1980 •......•••••••...•••••.•..••••••••.••••• 18
Ichnogenus SKOLITHOS Haldeman, 1840 20
Ichnogenus TIGILLITES Rouault, 1850 21
Ichnogenus DIPLOCRATERION Torell, 1870 •••••••••..•.••• 21
Ichnospecies DIPLOCRATERION POLYUPSILON Smith, 1893 ••• 21
Ichnogenus HELMINTHOPSIS Heer, 1877 •••••.••••.••.••••• 23
Ichnogenus NEREITES Macleay, 1839 •.••••••••••.•••••••. 23
Ichnogenus SCOLICIA de Quatrefages, 1849 •••••••..•.••• 26
Ichnogenus PLANOLITES Nicholson, 1873 •....•••••••..••• 26
Ichnogenus PALAEOPHYCUS Hall, 1847 ••••••.•••••••.•.••• 28
...................
Ichnogenus SPIRODESMOS Andree, 1920 29
3.3 ENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS •..•••..••• 31
3.4 TRACE FOSSIL ASSOCIATIONS ••••.••••••..••.••••••••.•••• 38
..........................
3.4.1 Siphonichnus (S) Association
38
3.4.2 Siphonichnus (F) Association ..........................
40
3.4.3 Spirodesmos Association ...............................
40
3.5 CONCLUSION ............................................
41
CHAPTER 4: SEDIMENTARY FACIES ....................................
42
4.1 FACIES CONCEPT ... .. ...................................
42
4.2 FACIES DESCRIPTIONS AND INTERPRETATIONS •••••.••••••••• 44
4.2.1 The Conglomerate Facies (C) ••••••••••.•••••••..•••••.• 45
Facies Cm: Massive or crudely-bedded conglomerate ••••• 46
Facies Ci: Massive or crudely-bedded intraformational
conglomerate .•••••••••••••••••••••••••••••• 46
4.2.2 The Sandstone Facies (S) ••••••..••••••••••••••••••••.• 46
Facies St: Trough cross-stratified sandstone 46
Facies Sp: Planar cross-stratified sandstone 49
Facies Sx: Cross-stratified sandstone ••••••.•••••••••• 51
Facies Sf: Flat stratified sandstone •••.•.•..•••••.•.• 51
Facies Sr: Ripple cross-laminated sandstone ••••••••••• 53
Facies Smr: Megarippled sandstone 54
Facies Sfl: Flaser-bedded sandstone ••••••••••••••••••• 54
Facies Sm: Massive sandstone ••..•••••••••.•••••••••••• 56
Facies Sb: Bioturbated sandstone •••••••.•••••••••••••• 57
4.2.3 The Fine-Grained Facies (F) •••••...•••••••.••••••••.•• 57
Facies Fm: Massive mudrock •••••••••••••••••••••••.•••• 58
Facies Ff and Fr: Laminated mudrock ••..••••••••..••••• 58
Facies Fb: Bioturbated mudrock •••••••••••••••••••••••• 59
4.2.4 The Heterolithic Facies ••••••••..••.•••••••.•••••••••• 59
Facies Fl: Lenticular-bedded sandstone and mudrock •••• 59
Facies AI: Alternating sandstone and mudrock ••••.•.••• 60
Facies W: Wavy-bedded sandstone and mudrock ••••••••••• 62
4.2.5 The Organochemical Facies ••...••••••.•..•••••.•••••••• 63
Facies C: Coal........................................ 63
4.2.6 Soft-Sediment Deformation ••••.••••••••••••••••••.••••• 64
Facies Sd and Fb: Penecontemporaneously deformed
sandstone and mudrock •.••••••••••••••••••••• 64
CHAPTER 5: SEDIMENTARY MODELS •••••••••••••••••••••.•••••••••••••• 65
5.1 INTRODUCTION ••.•••••••••••.•••..•.••..•....••••••••••• 65
5.2 FLUVIAL FACIES ASSOCIATION ••••••••••••••••••••••••..•• 68
5.2.1 Channel Subassociation •••••••••••••••••...••••••••••.. 68
Description •••••••...•••••••••..••••••..•••••••••..••• 68
Discussion •.•••••••...•...•••.•••••••...•••••••.••.••• 73
5.2.2 Interchannel Subassociation •••..•••••••••••••••••••••• 76
Description ••••...•••••••••••••••....•••••••••••..•••• 76
Discussion 77
5.2.3 Depositional Model ••....••••• 78
5.3 DELTAIC FACIES ASSOCIATION 80
5.3.1 Prodelta Subassociation 80
Description •••••..•••••••••••••••••••••••.•••••••...•• 80
Discussion 82
5.3.2 Distal Distributary Mouth Bar Subassociation •••••••••• 83
Description ••••.••••••••••.••••••••••••••••••.•••••••. 83
Discussion 84
5.3.3 Proximal Distributary Mouth Bar Subassociation 91
Description 91
Discussion ...................................................................................... 92
5.3.4 The Delta Plain .............................................................................. 94
5.3.4.1 Distributary Channel Subassociation 94
Description ...................................................................................... 94
Discussion ........................................................................................ 97
5.3.4.2 Giant Cross-Bed Subassociation ................................................ 100
Description ...................................................................................... 100
Discussion ........................................................................................ 104
5.3.4.3 Embayment Subassociation ............................................................ 108
Description ......................................................................................
108
Discussion ........................................................................................
113
5.3.5 Model for Deltaic Deposition ....................................................
117
Vertical facies associations ....................................................
117
Thickness of deltaic sequences ................................................
118
Distributary mouth processes ....................................................
119
The influence of waves ..........................................................
119
...............................................
Summary
120
5.4 WAVE-DOMINATED COASTLINES ••••••..••••••••.•••••••••••• 121
5.4.1 Delta-Associated Coastlines ...••••.••••••••••••••••••• 121
Description .•••••.•••••••••••••.•••••••••••••••••.•••• 121
Discussion •...•••••••..••••....•.••••••••••••••••..••• 126
5.4.2 Lateral-Accretion Coastlines •••.•••••••••••••••••••••• 133
Description ••...••.••••••.•••••••.•••.•.•....••••••••• 133
Discussion ••••••••••••••••••••••••••••.••••••••••.•••• 140
CHAPTER 6: STRUCTURAL FRAMEWORK AND PALAEOGEOGRAPHY OF THE
NORTHEASTERN KAROO BASIN 148
6.1 STRUCTURAL ELEMENTS AND HISTORY OF THE KAROO BASIN •••• 148
6.2 CLIMATE ••••••••••••••••••••••••••.•••••••••.•••••••••• 156
6.3 PROVENANCE AND PALAEODRAINAGE ....•••••••••••••••••••.. 157
CHAPTER 7 : THE LOWER ZONE •••••••••••••••••••••••••••••••••••••••• 165
7.1 STRATIGRAPHY AND DEPOSITIONAL SETTING ..•.••••••••••••• 165
7.1.1 The Lower Component 165
...................................
7.1.2 The Upper Component 171
7.2 CYCLICITY AND CONTROLS ON SEDIMENTATION ••••••••.•••••• 172
7.3 DEPOSITIONAL MODEL •••••••••••••••••••••••••••••••••••• 178
CHAPTER 8: PEAT-FORMING ENVIRONMENTS - PHYSICAL AND CHEMICAL
CONSIDERATIONS •••••••••.•••••.••••••••••••••••••••••.• 179
8.1 INTRODUCTION •••••••••.•••••••••••••••••••••••••••••••• 179
8.2 TERMINOLOGY •.•.•••••••.•••••••.•..•••••••.•.•.••••.••• 179
8.3 THE INFLUENCE OF TECTONIC SETTING, BASEMENT RELIEF AND
......................................
SUBSIDENCE RATES 185
8.4 THE INFLUENCE OF CLIMATE AND FLORA ON COAL TYPE ••••••• 186
8.5 CHEMISTRY OF THE PEAT ENVIRONMENT •.••.•.•••••••••••••• 188
8.6 THE ORIGIN OF MINERAL MATTER IN COALS ••••••••••••••••••• 190
8.7 PEAT ACCUMULATION AND COMPACTION RATES •.•••••.•••••••••• 191
8.8 PEAT ACCUHULATION IN RELATION TO CLASTIC DEPOSITIONAL
MODELS ••..•.••.....••••••••••••••••••••••••••....•••...• 191