Sedimentary environments and provenance of the Balfour Formation (Beaufort Group) in the area between Bedford and Adelaide, Eastern Cape Province, South Africa

By

Monica E. Oghenekome

A dissertation submitted in fulfillment of the requirements for the degree of

Master of Science

in the Department of Geology,

Faculty of Science and Agriculture,

University of Fort Hare

2012

ABSTRACT

The research examines the sedimentary environments and provenance of the Balfour Formation of the

Beaufort Group (Karoo Supergroup) in the Eastern Cape Province, South Africa. This Formation occurs in the southeastern part of the Karoo Basin. It consists of sedimentary rocks, which are an alternating siltstone, shale and mudstone succession with subordinate interbedded sandstone and subsequently intruded by Karoo dolerite in the form of sills and dykes. Lithostratigraphically, the

Balfour Formation is subdivided into five units namely, from the base to the top, the Oudeberg,

Daggaboersnek, Barberskrans, Elandsberg and Palingkloof Members. The Balfour Formation is overlain by the Katberg Formation.

This study involved field investigations in the vicinity of the towns of Bedford and Adelaide with integrated stratigraphical, sedimentological and petrological studies. A geological map was constructed after field investigations. Lithofacies of the Balfour Formation that were studied are characterised by sandstone facies (Sh, Sm, St, Sr, Sp) and fine-grained sediments (Fl or Fsm) which reflect point-bar, cut-bank, channel and floodplain deposits. Lithologically, the Oudeberg Member consists of sandstone of which some units are internally massive alternating with thin laminated siltstone and mudstone. The Daggaboersnek Member is characterised by regular, generally non- lenticular, overall stratification, in the Barberkrans Member consists of sandstone lithosomes, while the Elandsberg Member is an argillaceous unit, similar to the Daggaboersnek Member. The

Palingkloof Member is composed predominantly of red mudstone that can be used to distinguish the

Balfour Formation from the overlying Katberg Formation, which consists predominantly of sandstone. The stratigraphic sequence displays two fining upward megacycles of sedimentary deposits with change in the sediment supply pattern from low-sinuosity to high-sinuosity river

i

systems which reflect both braid and meandering deposits, respectively. Sedimentary structures in the sandstone units and the provenance of the Balfour Formation indicate that these deposits were produced by rivers flowing from the southeast with minor drift towards the northwest. According to the composition of the sediments and their sequence of deposition the Formation represents a fluvial environment.

Mineralogical and grain size data from the sandstones of the various members of the Balfour

Formation indicate the same source area of granitic, metamorphic and older sedimentary rocks and show no significant petrographic differences. The petrographic and geochemical investigations confirmed the sandstone to be feldspathic litharenite and ultralithofeldspathic sandstone. The palaeocurrent investigation indicates the main provenance to have been situated to the southeast of the Karoo basin. Heavy-mineral concentrations within the sandstones also give an indication that the source had a transitional arc plate tectonic setting.

Keywords: Balfour Formation, sedimentology, lithostratigraphy, sedimentary environment, provenance

ii DECLARATION

I declare that this dissertation is my own work and it is hererby submitted for the degree of Master of

Science at the University of Fort Hare. It has not previously been submitted for any degree or examination at any other University/Faculty and all the sources used or quoted have been acknowledged by complete references.

Signature

Monica E. Oghenekome

Date: December 2012

Place: Alice, South Africa.

iii ACKNOWLEDGEMENTS I am grateful to my supervisor Mr. C.J. Gunter for his consistent guidance, timely responses, valuable suggestions and unfailing encouragement throughout the research period.

My sincere gratitude to Dr. Napoleon Q. Hammond at the South African Council for Geoscience for his unreserved sharing of his research knowledge and fatherly advice.

I am indebted to all the Staff members of the Department of Geology, particularly to:

Dr. O. Gwavava (Head of Department) for his consistent support and guidance throughout my stay at the University;

Mr Luzuko Sigabi for administrative and logistical assistance throughout the study period.

Mrs Vuyokazi Mazomba for helping me in many ways.

Mr Eric Madi, and Mr Sonwabile Rasmeni for their valuable support.

My gratitude to David Katemaunzanga, Velenjani Dube and Sikhulule Sinuka for their valuable support with the field work.

Thanks to my colleagues, George Maneya, Malaza Ntokozo (Tk) and Liuji Yu for their consistent and invaluable encouragement.

My gratitude to Dr. A. Y. Billay of the South African Council for Geoscience, Pretoria, and Mr and Mrs Fatoki for their support with the GIS part of the study. My thanks also goes to Mr. Elijah Nkosi of the South African Council for Geoscience for the technical laboratory services.

Special thanks to the Govan Mbeki Research and Development Institute at the University of Fort Hare for funding my studies.

I am greatly indebted to my spouse Mr Edmund Osikomaya for his patience and dedication in supporting me up to this level as well as his consistent asistance and encouragement.

I am indebted to my parents, brothers and sisters for their consistent and invaluable encouragement.

I would also like to thank all my friends and relatives who offered me their moral and expert advice throughout the research period. My special thanks go to Mr. Ajayi Emmanuel of the Chemistry

iv Department, University of Fort Hare, Lami Babajide, Juwon Dele-oni, Idowu Seriki (Id), Nolon Gcanga and many others who supported me morally and otherwise.

v TABLE OF CONTENTS

ABSTRACT ...... i

DECLARATION ...... iii

ACKNOWLEDGEMENTS...... iv

TABLE OF CONTENTS ...... vi

LIST OF FIGURES ...... x

LIST OF TABLES ...... x

CHAPTER ONE ...... xvi

INTRODUCTION ...... 1 1.1 Background ...... 1

1.2 Research problem ...... 2

1.3 Aims and objectives ...... 3

1.4 Rationale of study...... 3

1.5 Significance of study ...... 4

1.6 Location ...... 4 1.7 Structure of dissertation ...... 7

CHAPTER TWO ...... 8 LITERATURE REVIEW ...... 8 2.1 Introduction ...... 8

2.2 General geology of the Karoo Basin ...... 9

2.3 Tectonic setting of the Karoo Basin ...... 12

2.4 Geology of the Balfour Formation ...... 15

2.5 Stratigraphy of Balfour Formation ...... 16

vi CHAPTER THREE ...... 19 METHODOLOGY...... 18 3.1 Introduction ...... 18

3.2 Desktop study ...... 19

3.2.1 Air photo interpretation ...... 19

3.2.2 GIS and remote sensing ...... 20

3.3 Geological mapping ...... 21

3.3.1 Sedimentary structures ...... 29

3.4 Sedimentary petrography ...... 30 3.4.1 Oudeberg Member ...... 32

3.4.2 Daggaboersnek Member ...... 34

3.4.3 Barberskrans Member ...... 35

3.4.4 Elandsberg Member ...... 36

3.5.5 Palingkloof Member ...... 37

3.5.6 Katberg Formation ...... 37

3.5 Sedimentary textures ...... 39 3.6 Modal analysis ...... 39 3.7 Heavy-mineral analysis ...... 47 3.8 Classification of the sandstone ...... 50

CHAPTER FOUR ...... 53 SANDSTONE GEOCHEMISTRY OF THE BALFOUR FORMATION ...... 53 4.1 Introduction ...... 53 4.2 Major elements ...... 54 4.3 Trace elements ...... 61 4.4 X-ray diffraction ...... 64 4.5 Weathering conditions in the source area ...... 65

vii CHAPTER FIVE ...... 69 STRATIGRAPHY OF THE BALFOUR FORMATION ...... 69 5.1 Introduction ...... 69 5.2 Lithostratigraphy of the Balfour Formation...... 70 5.2.1 Oudeberg Member ...... 73

5.2.2 Daggaboersnek Member ...... 75

5.2.3 Barberskrans Member ...... 76

5.2.4 Elandsberg Member ...... 77

5.2.5 Palingkloof Member ...... 78

5.2.6 Katberg Formation ...... 89

5.3 Areal distribution of lithostratigraphic units ...... 81

CHAPTER SIX ...... 84 SEDIMENTOLOGY OF THE BALFOUR FORMATION...... 84 6.1 Introduction ...... 84 6.2 Lithofacies ...... 84 6.2.1 Oudeberg Facies ...... 85

6.2.2 Daggaboersnek Facies ...... 87

6.2.3 Barberskrans Facies ...... 90

6.2.4 Elandsberg Facies ...... 92

6.2.5 Palingkloof Facies ...... 93

6.2.6 Katberg Facies ...... 93

6.3 Conditions of deposition of the Balfour Formation ...... 95

CHAPTER SEVEN ...... 98 PROVENANCE OF THE BALFOUR FORMATION ...... 98 7.1 Introduction ...... 98 7.2 Sandstone petrography ...... 98 7.3 Sandstone geochemistry ...... 103

viii 7.4 Palaeocurrent pattern analysis ...... 104

CHAPTER EIGHT ...... 109 OVERVIEW ...... 109 8.1 Introduction ...... 109 8.2 Discussion and conclusions ...... 110

CHAPTER NINE ...... 116 RECOMMENDATIONS ...... 116

REFERENCES ...... 117

APPENDIX ...... 132

ix LIST OF FIGURES CHAPTER ONE Figure 1: Geological map of the Karoo Basin, showing the study area and indicating the main lithostratigraphic units of the Karoo Supergroup (Rubidge, 2005)...... 5

Figure 2: Map of the study area in the Bedford and Adelaide district of the Eastern Cape Province. ... 6

CHAPTER TWO

Figure 3: The Karoo Basin in other parts of the world; arrows show the palaeogeographic reconstruction of the palaeo-Pacific plate from south to north (Catuneanu and Elango, 2001)...... 14

Figure 4: Lithostratigraphic subdivision of the Balfour Formation of the Karoo Supergroup, Eastern Cape Province, modified after Catuneanu and Henry (2001), Rubidge (2005) and Tordiffe et al. (1985)...... 17

CHAPTER THREE

Figure 5: Investigative and analytical methods used for the study of the Balfour Formation...... 18

Figure 6: Satellite image of study area showing some of the sample locations (Google Earth, 2010). 20

Figure 7: Existing 1:250 000 3226 (CA-CD) King William‟s Town geological map mainly covering the Balfour Formation and including the study area, (Johnson and Keyser, 1976). The subdivisions of the Balfour Formation are not differentiated...... 23

Figure 8: Sample locations in the vicinity of the towns of Bedford and Adelaide on the various members of the Balfour and of the Katberg Formation, Eastern Cape Province...... 24

Figure 9: Outcrop covered with abundant vegetation. A – Barberskrans Member at Black Hill north of Adelaide (S32°19´42.27" E26°19´48.61"). B – Katberg Formation at Buffelskloof Northwest of Bedford (S32°35´37.29" E26°02´35.63")...... 25

Figure 10: Geological map of the study area around Bedford and Adelaide in the Eastern Cape Province, South Africa...... 26

x Figure 11: A – Normal fault in an outcrop of sandstone of the Oudeberg Member with alternating shale and mudstone. B – Fault zone in sandstone unit of about 5m thick at a road-cutting south of Adelaide. Figures for scale...... 27

Figure 12: A – Flat-bedded sandstone above, overlying siltstone in the Daggaboersnek Member. B – Trough cross-bedding in sandstone of the Daggaboersnek Member along the R63 main road south of Adelaide, at elevation 577m. S32°42´15.59" E 026°18´55.18"S...... 28

Figure 13: A – Planar-laminated sandstone alternating with shale and mudstone along the main road between Adelaide and Cradock. B – Massive bedded sandstone south of Bedford...... 29

Figure 14: A - Ripple marked capping on Oudeberg Member sandstone S32°49´35.9" E026°28´02.0". B - Horizontally laminated sandstone in the Daggaboersnek Member S32°40´32" E026°01´52.7" ... 29

Figure 15: Photomicrograph of Oudeberg sandstone. The red arrow points to an overgrown unstrained quartz grain. Mostly the quartz has intergranular boundaries with culminating texture that can be attributed to the recrystallisation of clay minerals. The plagioclase displays clearly preserved twinning indicating limited alteration...... 33

Figure 16: Photomicrograph of Oudeberg sandstone showing K-feldspar and biotite grains undergoing alteration. The biotite is altered to iron oxide with the matrix containing clay minerals and silica...... 34

Figure 17: Daggaboersnek sandstone containing relatively large feldspar grains which exhibit angular form suggesting a very short travel distance and first cycle detritus. The green arrow points to very small apatite grains and the yellow arrow to monocrystalline quartz grains...... 35

Figure 18: Barberskrans sandstone containing predominantly clear quartz grains which are mostly monocrystalline with undulatory extinction. The white arrows indicate a quartz grains; the blue arrow points to twinned plagioclase. Grains display concavo-convex contacts and have subrounded to subangular shape while the matrix is dominated by fine sediments...... 36

Figure 19: Elandsberg sandstone with quartz grains showing undulose extinction. The matrix contains biotite which is partly altered to iron oxide and clay minerals. A few heavy minerals such as garnet and zircon, are present...... 37

xi Figure 20: Photomicrograph of Katberg sandstone. A few siliciclastic and volcaniclastic fragments (white arrow) are present. The quartz grains display undulose extinction and are angular in shape, while the feldspar is fairly altered, typical of a granitic source. The green arrow points to an apatite grain...... 38

Figure 21: Grain size distribution across the members of the Balfour Formation and of the Katberg Formation...... 44

Figure 22: Tailing train for washing the pulverized samples and collecting the heavy mineral fraction from the tailings...... 48

Figure 23: A – Frantz electromagnetic separator used for separating metallic from the non-metallic heavy minerals. B – Extraction of the heavy minerals using a fume chamber...... 48

Figure 24: Heavy-mineral assemblage from the sandstones of the Balfour Formation...... 49

Figure 25: Zircon grains from sandstones of the Balfour Formation...... 49

Figure 26: Modal data plot of quartz-feldspar-lithic fragments (Q-F-Lt) and triangular classification on the Folk (1974) diagram of different sandstone samples from the Balfour Formation...... 51

Figure 27: Q-F-Lt ternary diagram of Dickinson et al. (1983), indicating the mineral composition of the sandstones in the Balfour and Katberg Formations of the Eastern Cape Province...... 52

CHAPTER FOUR

Figure 28: Quartz content variation amongst sandstone units of the Balfour Formation (after Crook, 1974). The plot indicates that the Oudeberg Member and the overlying Katberg Formation have higher quartz content than the Barberskrans and Elandsberg Members while the Daggaboersnek Member has low quartz content...... 56

Figure 29: Co-variation plot of SiO2 versus Al2O3 of the sandstones in the Balfour Formation. (after Akarish and El-Gohary, 2008). This linear trend of negative correlation confirms the increase in quartz according to SiO2 content in the sandstones of the Balfour and Katberg Formations (Akarish and El-Gohary, 2008 and Osman, 1996)...... 58

xii Figure 30: Discrimination diagram plots of sandstone in the Balfour Formation after Bhatia (1983).

(A) TiO2 versus Fe2O3+MgO and (B) Al2O3/SiO2 versus Fe2O3+MgO; Fields A, B, C and D represent fields for various plate tectonic regimes. A (Oceanic Island Arc), B (Continental Island Arc), C (Active Continental Margin) D (Passive Margin) and sst represents sandstone in the legend...... 59

Figure 31: Geochemical classification of the Balfour sandstones after Herron (1988). The sandstones plot in the litharenite and arkose fields, indicating the consistency of the petrological data...... 60

Figure 32: Bi-variant plot of SiO2 versus Al2O3+K2O+Na2O showing the chemical maturity trend of the Balfour sandstone (after Suttner and Dutta, 1986)...... 60

Figure 33: Discrimination plot of Th/Sc against Zr/Sc ratios (after McLennan et al., 1983). The plot shows concentration of zircon with high Zr/Sc ratio in the trailing edge indicating the dominant heavy mineral in the sandstone to be zircon which is attributable to sedimentary sorting and recycling...... 62

Figure 34: Scatter plot of Zr/Sc versus SiO2 showing zircon concentration and a significant reworking trend in the Balfour Formation and Katberg sandstone (after Cingolani et al.,2003)...... 64

Figure 35: Plot of CIA versus SiO2 for Balfour and Katberg Formation sandstones (after Nesbitt and Young, 1982)...... 67

Figure 36: SiO2 versus CIA (Chemical Index of Alteration) of Balfour sandstones indicating a moderate degree of weathering (after Nesbitt and Young, 1982; Tayor and McLennan, 1985)...... 67

Figure 37: A-CN-K triangle plot of the degree of depiction (after Cingolani et al.,2003), showing the weathering trend and indicating that the sandstone source was of igneous composition...... 68

CHAPTER FIVE

Figure 38: Lithostratigraphic subdivision of the Balfour Formation according to various authors. The Barberskrans and Oudeberg Member are sandstone dominated. Modified after Katemaunzanga (2009)...... 71

Figure 39: Lithostratigraphy of the Karoo Supergroup in the Eastern Cape Province which includes the Balfour Formation (After SACS, 1980)...... 72

xiii Figure 40: Massive arenaceous unit overlain by horizontally laminated sandstone at the top of the Oudeberg Member southeast of Adelaide along the R63 main road to Fort Beaufort...... 74

Figure 41: Ripple-laminated sandstone of the Oudeberg Member reflecting unidirectional current flow...... 74

Figure 42: Typical view of Daggaboersnek Member sandstone alternating with mudstone layers and persisting over a relatively long distance along main road southeast of Adelaide...... 75

Figure 43: Exposure of typical flat bedded and laminated Barberskrans sandstone with some incipient concretionary structures in road-cut beyond One Oak farm to the north of Adelaide (S32°33´26.8" E026°08´34.7")...... 77

Figure 44: Typical exposure of red laminated mudstone of the Palingkloof Member indicated by the white arrow...... 79

Figure 45: Stacked tabular sheets of fine- to medium-grained sandstones with subordinate red and greenish-grey mudstones of the Katberg Formation...... 81

Figure 46: Geological map indicating each of the lithological units of the Balfour Formation in the study area...... 83

CHAPTER SIX

Figure 47: Oudeberg sandstone facies. (A) – Medium-grained sandstone with alternating siltstone and mudstone of approximately 10m thick along the Adelaide road (S32°56´22.0" E026°63´25.9). The facies surface indicated by red dashes shows an erosional surface. The white arrow indicates mud drape, the portion between the white lines shows grey parallel-laminated alternating siltstone and mudstone. (B) – Massively bedded sandstone with an erosional base grading into fine-grained sandstone with some symmetrical ripple forms is at the top...... 86

Figure 48:(A) – Three metres thick massively bedded sandstone in the Oudeberg Member.(B) – Some small nodules formed by contact metamorphic effect of nearby dolerite intrusion near the base of the Oudeberg Member, S32°45´07.5" E026°47´07.0"...... 87

Figure 49: Horizontal and trough cross-bedded sandstone along the R63 main road from Adelaide to Bedford. S32°59´75.0" E026°67´74.3"...... 89 xiv Figure 50: Upper bedding surface of sandstones showing micro cross-lamination traces (Left) and ripple-lamination (Right). These sedimentary structures are the most common palaeocurrent indicators in outcrops in the Balfour Formation, especially in the Daggaboersnek facies...... 89

Figure 51: Barberskrans sandstone facies in roadcut to the north of the town of Bedford with lenticular alternating sandstone–siltstone deposits in a laterally persistent section of a high-sinuosity channel sandstone of the Barberskrans Member, S32°32´28.4" E026°06´59.4" ...... 91

Figure 52: Ripple cross-lamination (Left) and plan view ripple marks (Right) occuring in Barberskrans sandstone...... 91

Figure 53: Sandstone alternating with thin mudstone facies of the Elandsberg Member. The white arrow points to a mudstone unit while the red arrow shows a sandstone-rich unit, S32°32´29.6" E026°07´00.2"...... 92

Figure 54: Argillaceous red mudstone facies of the Palingkloof Member in the study area...... 93

Figure 55: Representative facies of the Katberg Formation. The arrow shows mud drapes and the dashed lines separate channel fill deposits of a braided river system...... 94

Figure 56: Oblique view of a large-scale trough cross-bedded unit of Katberg sandstone. S32°18´58.3" E026°11´13.8". The structure is composed of cross-laminae, nearly parallel to current direction in medium-grained sandstone of the Katberg Formation...... 95

CHAPTER SEVEN

Figure 57: Sandstone modal data plot for the Balfour Formation on the Qm-F-Lt diagram of Dickinson et al. (1983) as also used by Johnson (1991) and Haycock et al. (1997). Qm (Monocrystalline quartz); F (Feldspar); Lt (Lithic fragments)...... 102

Figure 58: Paleocurrent directions of sandstone units in the Balfour Formation. The arrows indicate the vector mean directions...... 107

Figure 59: Summary of palaeocurrent plots of sandstones across the Balfour Formation succession in the study area in the Eastern Cape province...... 108

xv LIST OF TABLES

CHAPTER THREE Table 1: Classification and symbols of grain types. Modified after Johnson (1991)...... 42

Table 2: Grain size parameters for quartz and feldspar grains in the sandstones of the Balfour Formation. The values are sum averages of quartz and feldspar from the total sandstone samples. ... 42

Table 3: Mineral composition of the various sandstones in the Balfour Formation...... 43

Table 4: Mean modal compositions of sandstones from the various members across the Balfour Formation and of Katberg sandstone...... 44

Table 5: Grain size distribution of sandstones in the members of the Balfour Formation and of the Katberg Formation. The grain size values are averages of the individual members from the Balfour sandstones samples...... 45

Table 6: Grain size scale for sediment and sedimentary rocks of Wentworth (1922)...... 46

Table 7: Folk and Ward (1957) sorting based on standard deviation measurement values...... 46

Table 8: Major-element data of sandstone members from the Balfour Formation, Eastern Cape Province, South Africa. Values in oxide weight percent. ODST: Oudeberg sandstone, DGST: Daggaboersnek sandstone, BBST: Barberskrans sandstone, ELST: Elandsberg sandstone: KTST: Katberg sandstone...... 57

Table 9: Trace element data of sandstone members from the Balfour Formation, Eastern Cape Province, South Africa; all concentrations are in parts per million (ppm)...... 63

Table 10: Semi-quantitative XRD estimates of the Balfour sandstone mineralogy in the Eastern Cape Province. Phase abundances expressed in weight percent...... 66

Table 11: Lithofacies description code of the Balfour Formation (modified after Bordy and Catuneanu, 2003 and Bordy et al., 2005)...... 85

Table 12: Summary of the architectural elements of the members in the Balfour Formation ...... 97

xvi Table 13: Summarized palaeocurrent data localities for the members across the Balfour Formation ...... 106

xvii CHAPTER ONE

INTRODUCTION

1.1 Background

The Karoo Basin, which is situated along the southern margin of Gondwana, is known to contain a complete extensive stratigraphic succession that is well exposed with a continuous sedimentological record of Permian–Triassic times. In the southern part, the Karoo depositional environment varied over time from glacial to fluvial. Sequentially, it commenced with the glacial deposits of the Dwyka

Formation, overlain by the post-glacial inland marine deposits of the Ecca Group and followed by the fluvial deposits of the Beaufort Group. The Balfour Formation is part of the sedimentary succession of the Beaufort Group in the Karoo Basin of South Africa which ranges in age from late Permian to earliest Triassic. It is composed of several lithosomes, which have lithologically distinctive stratigraphic units, large enough in scale to be mappable. These lithosomes are masses of rock units with essentially uniform character and have intertonguing relationships with adjacent masses of different lithology (Johnson, 1976). Lithostratigrahically, the Balfour Formation is subdivided into five members viz, the Oudeberg, Daggaboersnek, Barberskrans, Elandsberg and Palingkloof

Members (SACS, 1980; Tordiffe et al., 1985; De-Kock and Kirschvink, 2003; Johnson et al., 2006).

Each of these members was studied sedimentologically as they all play an important part in interpreting the sedimentary environment and provenance.

This research is built upon previous work that already established a sequence stratigraphic framework of the Karoo Supergroup. The work also aligns with the terminology and nomenclature guidelines of the South African Code of Stratigraphic Classification by the South African Committee for

Stratigraphy (SACS), 1980 and the standardised lithostratigraphic guide of Johnson (1987). The 1

South African Code of Stratigraphy is a simplified and condensed document which can be compared to that of the International Subcommission on Stratigraphic Classification (ISSC) which deals primarily with the basic principles and procedures of the stratigraphic guide (Johnson,1987). This work documents the petrology combined with the grain size variation, geochemistry, stratigraphy and with the sediment depositional pattern, and provenance.

1.2 Research problem

The sedimentological record of the Karoo Basin in South Africa has led to geological research in various parts of the Basin. The Balfour Formation, however, has only been studied by a few

(Johnson, 1976; Tordiffe, 1978; Visser and Dukas, 1979; Rubidge et al., 2000; Catuneanu and

Elango, 2001; Katemaunzanga, 2009, and Yu, 2011). There is an absence of integrated analysis of sedimentary and geochemical data of the sandstone in the Balfour Formation. Sedimentological investigation is needed in this part of the Balfour Formation. Petrographic studies which emphasized the heavy minerals of the Balfour Formation to determine its provenance have never been documented. It is hoped that future heavy-mineral analysis of the Karoo Supergroup and its formations will prove to be useful in the determination of the provenance of the various rock types

(Bordy et al., 2004). The King William‟s Town 2632 geological map is the only existing map showing the general geology of the Balfour Formation in the study area but does not differentiate between the various member units, even though these members are officially accepted by SACS

(1980) as subdivisions of the Balfour Formation.

2 1.3 Aims and objectives

This work presents a detailed sedimentological and provenance study of the Balfour Formation in the eastern part of the Karoo Basin in South Africa. It establishes a clear and distinct lithostratigraphic description of the various successions of the Balfour Formation in the area around Bedford and

Adelaide. The distinction of the lithostratigraphic units is based on the lithological composition of the actual rock material. It also analysed the sedimentary environment to interpret its provenance. The geochemical investigation, petrographic study and heavy minerals analysed were also used to aid in the interpretation of the provenance. A geological map was constructed with air photo interpretation and field control, including detailed field investigation of, and depicting the various members within, the Balfour Formation.

1.4 Rationale of study

The Balfour Formation has attracted the attention of researchers for it palaeontological significance.

However, less attention has been given to its sedimentary environments in relation to provenance.

There is little sedimentological and geochemical information in the literature on the Balfour

Formation, hence the research aims to contribute to this aspect of the geology. This work also attempts to determine in detail the sandstone geochemical composition in this area of the Balfour

Formation and relates it to the provenance for the first time. In his studies on the Balfour Formation,

Katemaunzanga, (2009) concentrated on the geochemistry of the argillaceous components of the

Balfour Formation.

3 1.5 Significance of study

The Balfour Formation of the study area is considered to represent a non-marine fluvial environment.

This study was an opportunity to determine the fluvial sequences and provided a basis for the description and interpretation of the sedimentology of the Balfour Formation. There are few studies that have examined the depositional history in relation to the development of the Balfour Formation.

Hence, this study has generally focused in the main on the depositional processes within the Balfour

Formation. It is hoped that the scientific information and the geological map produced could be used as a basis for further research.

1.6 Location

The study area is situated in the southeastern part of the Karoo Basin in South Africa, between longitudes 26°15´ and 26°30´E, and between latitudes 32°30´ and 32°45´S (Fig.1). It represents a total area of approximately 750 km2 with a length of 30km and a width of 25km (Fig.2).

Geographically the area is located in the Eastern Cape Province and incorporates the areas around the towns of Adelaide and Bedford (Fig.2), a region that has not until now been studied for the purposes of an investigation of this nature. The choice of the study area was largely influenced by field observations on the mappability, and hence the potential for spatial discrimination, of the subdivisons of the Balfour Formation within the framework of which sedimemtological and provenance interpretation could be perfomed.

Geographically, the area stretches from west of Adelaide to the farms Waterfall in the north and

Olifantsbeen in the south. It extends from the farm Bell-Vue, west of Bedford, to Buffelskloof to the north and Canary Fontein to the south (Fig.2). Generally, accessibility is fair; the area is transected by the R63 main road from Fort Beaufort to Bedford and beyond (Fig.2), while the other roads are gravel 4 and farm roads. However, some of the area, apart the human settlements and farm land, is covered by thick vegetation and is generally subdivided by fences which limited traverse mapping. The major accessibility challenge was fenced farm lands which made it difficult to gain access as a result of not being able to meet with the owner for obtaining permission to the land.

Study area

Figure 1: Geological map of the Karoo Basin, showing the study area and indicating the main lithostratigraphic units of the Karoo Supergroup (Rubidge, 2005).

5 Study area

Figure 2: Map of the study area in the Bedford and Adelaide districts of the Eastern Cape Province.

6 1.7 Structure of dissertation

This dissertation consists of nine chapters. Chapter One provides a brief introduction on the background of the study. It also defines the research objectives and significance of the project.

Chapter Two consists of literature reviews of the geological and tectonic setting of the Karoo Basin.

This chapter also includes the geology and stratigraphy of the Balfour Formation. Chapter Three is a description of the research methodology, which includes detailed petrographic study. In Chapter

Four, geochemical analysis of the sandstone used for additional understanding of the rock composition of the Balfour Formation and interpretation of the provenance is discussed. Chapter Five consists of stratigraphic and lithostratigraphic description of the Balfour Formation. The sedimentological cycles and processes that lead to the sediment deposition of the Balfour Formation forms the basis for Chapter Six. Chapter Seven considers the provenance which includes interpretation of the source area in relation to the depositional environment. Chapter Eight is an overview of the study on the Balfour Formation and its conclusions. Chapter Nine provides recommendations based on the results of the study.

7 CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction

The Karoo Basin has been studied by many researchers, but previous work focused mostly on the

Beaufort Group in general or on parts of the Balfour Formation. Stratigraphically and sedimentologically, the Balfour Formation has been described by Johnson (1976) in his work on the

Cape and Karoo sequences in the Eastern Cape and, who in a regional context, is considered the pioneer researcher of the Karoo Supergroup in the Eastern Cape Province. Tordiffe (1978) also described the lithological succession in the Balfour Formation based on a hydrogeochemical study of the Karoo sequence in the Eastern Cape Province. The succession of the southern Karoo Basin has been investigated for its geochemistry and mineralogy by Coney et al. (2007) who however, focused on the Permian–Triassic boundary. The Balfour Formation was recognised by Visser and Dukas

(1979) as an upward-fining fluviatile cycle which displays both braided and meandering deposits.

Smith (1995) attributed the change in the fluvial style to low sinuosity for the braided river systems and high sinuosity for the meandering river systems of the Karoo Supergroup. The palaeocurrent pattern and palaeontologic sequence of the Ecca-Beaufort contact were also described by Rubidge et al. (2000) who interpreted the lithofacies within a stratigraphic interval in part of the Balfour

Formation. A report on the sedimentary rocks of all parts of the Karoo Basin was compiled by

Johnson et al. (2006). Other previous research related to the Balfour Formation includes: Keyser and

Smith (1978); SACS (1980); Smith (1980/87, 1993); Stear (1980); Stavrakis (1980); Hiller and

Stavrakis (1984); Rubidge (1995); Catuneanu et al. (1998, 2001) and Gastaldo et al. (2005).

8 The tectonic control of the stratigraphic and sedimentological pattern of the fluvial style of the

Balfour Formation was studied by Catuneanu and Elango (2001), who revealed that the Balfour

Formation accumulated in the foredeep of the Karoo Basin and its stratigraphy is composed of six third-order successions. Johnson (1991) did a petrographic study of the southeastern Cape-Karoo

Basin, including the Balfour Formation, and related the petrography of the sediments to its provenance. Keyser (1966) undertook a stratigraphic description and palaeontologic study of the lower Beaufort which included the Oudeberg Member. Katemaunzanga (2009) described the lithostratigraphy, sedimentology and provenance of the Balfour Formation west of Fort Beaufort and

Yu (2011) qualitatively characterised the fractured rocks within the Balfour Formation in the Eastern

Cape Province. These studies represent the most recent research on the Balfour Formation. Although extensive studies have been done on the Beaufort Group including a few on the Balfour Formation, the information acquired with those studies is not sufficient for a comprehensive interpretation of the sedimentary environments and provenance of this part of the Balfour Formation and for producing a geological map.

2.2 General geology of the Karoo Basin

The Main Karoo Basin contains most of the Karoo Supergroup in South Africa. The word „Karoo‟ is derived from the Khoikhoi word for “dry”. This succession has a total thickness of 12km and covers a land area of approximately 700 000km2 in South Africa (Johnson, 1976; Tankard et al., 1982;

Johnson et al., 1996; Gastaldo et al., 2005; Johnson et al., 2006) which is nearly two thirds of the country‟s total surface area. In the south, the Karoo Supergroup has a maximum thickness of 6–8 km

(Rubidge, 1995). A largely uninterrupted palaeontological wealth of 100 million years from the

Permian to the Jurassic is integral to the Karoo Basin (Rubidge, 1995; Rubidge and Hancox, 1999 in

9 Coney et al., 2007; Rubidge, 2005). Lithostratigraphically, the Karoo Supergroup is subdivided into five main groups of basin fill which include the Dwyka, Ecca, Beaufort, Stormberg and Drakensberg

Groups (Johnson, 1976; SACS, 1980; Smith et al., 1993; Catuneanu et al., 1998 and 2002; Bamford,

2004; Anderson and Worden, 2006). Although SACS (1980) abandoned the use of Stormberg Group in a formal lithostratigraphic scheme for lack of adequate unifying lithologic features, it is used here for the sake of convenience. Apart from the Drakensberg Group which consists of volcanic rocks, these Groups are composed of sedimentary sequences (Catuneanu et al., 1998). The Dwyka and Ecca

Groups were deposited during the transgression of the Karoo Basin by an interior seaway. There was a change from deep marine during the lower Ecca interval to shallow marine (Visser and Loock,

1978), which resulted in regression of the Ecca seaway towards the southeast which led to the formation of a fully non-marine environment resulting in the accumulation of the fluvial Beaufort

Group (Smith, 1990 in Catuneanu et al. 2002; Smith et al., 1993).

Dwyka Group: The Dwyka Group forms the base of the Karoo Supergroup and is considered the beginning of sedimentation of the Karoo Basin in South Africa. It ranges in age from Late

Carboniferous (Moscovian) to Early Permian (Sakmarian) (Johnson et al., 1996; Catuneanu et al.,

1998). It comprises a maximum thickness of between 600 and 750 metres (SACS, 1980; Johnson,

1991). Sediments of the Dwyka were deposited from floating ice in deep-marine water in the south while in the north it was deposited from ground ice (Tordiffe et al., 1985; Visser, 1991; Catueanu et al., 1998). Evidence of floating ice can be seen from the lacustrine facies which contains angular clasts floating in a muddy matrix (Bordy and Catuneanu, 2003) and silt-dominated marine diamictites with dropstones (Visser, 1991). The Dwyka Group is characterised by massive diamictite, stratified diamictite, massive carbonate-rich diamictite, conglomerate, sandstone, mudrock with stones and mudrock facies which cyclically grade upwards into fine-grained clastic rock (Catuneanu et al., 1998;

10 Johnson et al., 2006). The glaciogenic Dwyka Group constitutes the oldest rocks of the Karoo deposition of approximately 330–300 million years (Catuneanu, 2004).

Ecca Group: This Group overlies the Dwyka Group and was formed in a marine environment at a time of transgression of the sea (Catuneanu et al., 2005; Gastaldo et al., 2005). The sediments of the

Ecca Group were deposited as turbidity fan complexes on either the basin floor, the slope or on the shelf of the Karoo Basin (Kingsley, 1977), and which range in age from late Carboniferous to middle

Permian (Johnson et al., 1996; Catuneanu et al., 2005). This Group consists essentially of clastic sediments which include mudstone of various colours, siltstone, sandstone, occasional conglomerate and coal (Johnson et al., 1996; Cairncross et al., 2005). It also consists of distal submarine fans which contain volcanic ash deposits (Johnson et al., 2006). A thickness of approximately 2340 metres is attributed to the Ecca Group (Tordiffe et.al., 1985). It comprises sixteen formations that are characterised by lateral facies changes which can be clearly distinguished. These formations occur widespread within the Karoo Basin (Johnson et al., 2006).

Beaufort Group: The Beaufort Group overlies the Ecca Group and has a maximum cumulative thickness of more than 5000 metres. It covers a total land surface area of approximately 200 000 km2 in South Africa (Smith and Ward, 2001; Catuneanu et al., 2005; Johnson et al., 2006). The sediments of the Beaufort Group range from Middle Permian to Middle Triassic time, (Haycock et al., 1997;

Catuneanu et al., 2005). This Group is predominantly composed of sedimentary rocks that are richly fossiliferous (Hancox and Rubidge, 2001). The Beaufort Group comprises of two main subgroups, the Adelaide Subgroup and Tarkastad Subgroup (SACS,1980; Coney et al., 2007) (Fig. 4). In the eastern part of the Karoo Basin the Adelaide Subgroup comprises the Koonap, Middleton and Balfour

Formations, while in the west, it consists of the Abrahamskraal and Teekloof Formations, and in the north are Volksrust and Normandien Formations (Catuneanu et al., 1998; Johnson et al., 2006). These

11 stratigraphic differences reflect a variety of tectonic activities (Catuneanu et al., 1998). The strata of the Beaufort Group are predominantly alternating mudstones and siltstones with subordinate lenticular and tabular channel sandstone deposited by a variety of fluvial systems. This resulted in fining-upward sequences of fluvial systems which prograded into the Karoo Basin at the time of basin fill (Smith, 1980/87; Rubidge, 1995; Johnson et al., 1996; Smith and Ward, 2001; Caincross et al.,

2005; Catuneanu et al., 2005). The sandstones consist of alternating fine-grained lithofeldspathic arenites while mudstone lithosomes also characterise its fluvial deposits (Johnson, 1976; Tordiffe et.al., 1985; Hancox and Rubidge, 2001; Barath and Dunlevey, 2010). In the Eastern Cape, the

Beaufort succession is composed of alternating thick sand- and mud- dominated formation (Haycock et al., 1997).

2.3 Tectonic setting of the Karoo Basin

Tectonism was the primary control on the development of the Karoo Basin with subsidence mechanisms ranging from flexural in the south in relation to processes of subduction and orogeny along the palaeo-pacific margin and extended to the north (Catuneanu et al., 2005). The tectonic regime during this time was defined by compression and accretion along the southern margin of

Gondwana (Wopfner, 1994/2002 in Catuneanu et. al., 2005). The Karoo Basin was first referred to as a passive margin (Smith, 1995). Subsequently, it was generally referred to as a retroarc-foreland basin

(Dickinson 1974 in Johnson et al., 2006 and Johnson and Beaumont, 1995 in Catuneanu et al., 1998), with fills in front of the Cape Fold Belt situated in southwestern Gondwana (Fig.1). The Cape Fold

Belt once was part of the Pan-Gondwanian Mobile Belt but rifted away, due to supralithospheric loading caused by crustal shortening and thickening through compression, collision and terrain accretion along the southern margin of Gondwana, and subsequently resulting in the tectonic regime

12 of the Basin fill of Karoo sediments (Fig.3) (Johnson et al.,1996; Catuneanu et al., 2005). The Basin developed in response to the late Palaeozoic to early Mesozoic subduction episode of the palaeo-

Pacific plate underneath the Gondwana plate (Lock, 1978 and 1980; Winter, 1984; De Wit et al.,

1988; De Wit and Ransome, 1992 in Catuneanu et al., 1998 and 2002; Pysklywec and Mitrovica,

1999; Catuneanu and Bowker, 2001; Catuneanu and Elango, 2001). Gondwana fragments of the foreland basin today are preserved across the world as the Parana Basin (South America), Karoo

Basin (Southern Africa), Beacon Basin (Antarctica) and Bowen Basin (Australia) (Fig. 3) (Catuneanu et al., 1998; Catuneanu and Elango, 2001; Catuneanu, 2004).

The Karoo Basin responded to eight tectonic events related to the Panthalassan (Palaeo-Pacific) plate beneath Gondwana from the time of deposition of the Dwyka through to the Elliot Formation. These tectonic events produced variation in the depositional sedimentary successions within the Karoo setting (Catuneanu et al., 1998) and indicate changes in climate over time. The fourth tectonic orogenic paroxysm event is assigned to Balfour sedimentation (Catuneanu et al., 1998).

Geometrically, the Karoo sedimentary fills display a wedge shape, which is asymmetrical in nature, reflecting a foreland succession. This shape is basically subdivided into two distal facies: a thick southern sequence which is referred to as a proximal facies (regressive system tract) and a northwards thinning sequence which is referred to as the distal facies (transgressive system tract) (Catuneanu and

Elango, 2001; Hancox et al., 2002) (Fig. 1). The western and southern areas separated by the 24°E meridian represent the proximal facies, while the northeastern area represents the distal facies, which is characterised on the basis of stratigraphic differences in relation to the age of units, provenance, transportation direction and stacking pattern (Catuneanu et al., 1998). The study area is situated on the proximal facies which is correlated with regressive system tracts.

13

Figure 3: The Karoo Basin in other parts of the world; arrows show the palaeogeographic reconstruction of the palaeo-Pacific plate from south to north (Catuneanu and Elango, 2001).

The sediments of the Karoo basin accumulated continuously for 100 million years and range in age from the Late Carboniferous (300 Ma) to the Early Jurassic (190Ma) (Johnson, 1976; Tankard et al.,

1982; Johnson, 1991; Smith et al., 1993; Rubidge, 1995; Johnson et al., 1996; Catuneanu et al.,

1998/2002/2005; Catuneanu and Elango, 2001; Bordy et al., 2004). Within this time span, the Karoo

Basin is seen to contain the thickest stratigraphic megasequence of several deposition episodes

(Catuneanu and Bowker, 2001; Catuneanu and Elango, 2001). The source of the sedimentary fill in the Karoo Basin is related to the mountain belt in the palaeo-Pacific southwestern Gondwana when rifting of the Gondwana supercontinent began, also referred to as the flexural subsidence stage

(Johnson, 1991; Cole, 1992 in Bordy et al., 2005; Duncan et al. 1997 in Catuneanu et al., 1998/2005).

Hence, the Karoo succession is mostly dominated by sedimentary rocks which are composed of sandstone interbedded with shale and mudstone, and is intruded by concordant and conical sills of

14 dolerite as well as near-vertical dykes. Lithostratigraphically, the Karoo Basin succession has an overall fining-upward trend related to the gradual decrease in topographic slope during orogenic loading (Catuneanu and Elango, 2001). The continential deposits of the Karoo Supergroup gave rise to the Beaufort Group (Johnson et al., 1996). The Balfour Formation is also attributed to this continental deposition (Smith, 1995; Ward et al., 2000).

2.4 Geology of the Balfour Formation

The Balfour Formation consists of the upper part of the Adelaide Subgroup of the Beaufort Group

(Fig. 4). Its thickness varies from place to place, with a thickness of 2000 metres attained in the southeast (Johnson et al., 2006), but it reaches a maximum thickness of 2150 metres in the Fort

Beaufort area (Johnson, 1976). A thickness of about 650 metres has been recorded at Graaff-Reinet in the Cape Province (Visser and Dukas, 1979). The name “Balfour Formation” was first proposed by

Johnson in 1976 after the village of Balfour, north of Fort Beaufort, during his research on the stratigraphy of the Cape and Karoo successions in the Eastern Cape Province. Catuneanu and Elango

(2001) contend that accumulation of the sediments of the Balfour Formation took place during flexural subsidence stages of the Karoo Basin (foredeep) when there was a large river and floodplain setting (overfilled phase) of the Karoo system which was controlled by tectonics and climate. Both arid and humid climates are identified within the Balfour Formation (Keyser, 1966; Johnson, 1976;

Smith et al., 1993), but there is no evidence of climate fluctuation within this period of deposition

(Visser and Dukas, 1979; Catuneanu and Elango, 2001).

The depositional environment of the Balfour Formation is related to reducing conditions (Tordiffe et al., 1985). It is characterised by overall fining-upward sequences of predominantly sandstone interbedded with shale and subordinate mudstone at the base, and bounded by subaerial

15 unconformities both at the top and the base (Visser and Dukas, 1979; Catuneanu et al., 1998; Turner,

1999; Catuneanu and Elango, 2001). The sediments range in age from Tatarian (late Permian) to early

Scythian (early Triassic) (Groenewald and Kitching, 1995, Kitching, 1995 in Catuneanu et al., 1998).

2.5 Stratigraphy of Balfour Formation

Various authors, have presented accounts of the stratigraphy of the Balfour Formation but in the

Eastern Cape Province Johnson (1976) was the first to describe its lithostratigraphy within the Karoo

Supergroup. Stratigraphically, the Balfour Formation has undergone one incomplete and two complete fluviatile megacyclic episodes emanating from tectonics (Visser and Dukas, 1979).

The Oudeberg Sandstone Member forms the base of the Balfour Formation (Johnson 1976; Johnson et al., 2006) and is overlain by the argillaceous Daggaboersnek Member, followed by the

Barberskrans Member which again is a predominantly sandstone unit (Johnson, 1976). Then follows the Elandsberg Member which is characterised by dark-grey to greenish grey mudstones, overlain by the red mudstones and shales of the Palingkloof Member. Both the Daggaboersnek and Elandsberg

Members are argillaceous in nature (Tordiffe et al.,1985). The Palingkloof Member has attracted the attention of many researchers due to the presence, within or immediately below it, of the Permian–

Triassic boundary. It marks the top of the Balfour Formation and is in sharp contact with the overlying sandstone-rich Katberg Formation (SACS, 1980; Haycock et al., 1997; Rubidge et al.,

2000; Smith and Ward, 2001; Warren et al., 2006; Coney et al., 2007). Generally, these members are distinguished from each other based on the variation of the sandstone composition and colour.

Although they are formally accepted to be part of the Balfour Formation, they are not represented on the 1:250000 3226 (CA-CD) King William‟s Town geological map of the area.

16

PERIOD SUPER- GROUP SUBGROUP FORMATION MEMBER Enivronment GROUP East of 24°E of deposition Drakensberg Volcanic Jurassic Clarens Aeolian

Elliot Arid-fluvial Triassic Molteno K Burgersdorp TARKASTAD Katberg A Palingkloof F

L B Elandsberg P ADELAIDE Balfour U R E Barberskrans V A E I U Daggaboersnek O A R F Oudeberg L O M O R Middleton Transitional T I (Deltaic) Koonap A

Waterford N E C Fort Brown

C Ripon Deep-shallow A marine Collingham

Whitehill

Prince Albert

Carboniferous Dwyka Floating iceberg marine

Figure 4: Lithostratigraphic subdivision of the Balfour Formation of the Karoo Supergroup, Eastern Cape Province, modified after Catuneanu and Elango (2001), Rubidge (2005) and Tordiffe et al. (1985).

17 CHAPTER THREE

METHODOLOGY

3.1 Introduction

In order to achieve the set objectives, the following approaches were employed for the study. These include desktop studies, geological mapping, laboratory methods and data acquisition analysis and interpretation (Fig. 5). The geological mapping was accompanied by collecting of samples and recording of sedimentary structures, measuring of palaeocurrent directions and field description. The laboratory work involved petrographic studies of the sedimentary rocks by means of optical microscopy and geochemical analyses to determine the mineralogy of the rock and to gain further understanding of the sedimentry environments and the provenance. Field data was evaluated both stratigraphically and sedimentologically. The classification of the sandstones is based on the examination of the mineral composition and the evaluation of the particles which were used to interpret the genesis and depositional environment.

Methodology

Data analysis Desktop study Sedimentary petrography Geological Stratigraphic and mapping sedimentological analysis Modal analysis Aerial photo interpretation Field Sedimentary Interpretation of records Geochemistry sedimentology GIS and remote sensing and provenance

Figure 5: Investigative and analytical methods used for the study of the Balfour Formation.

18 3.2 Desktop study

This included storing of information collected in the field in a computer, recording information on individual stratigraphic units and compiling a geological map. During desktop mapping, Google

Earth satellite images (Fig. 6), the regional digital geological map and aerial photographs of the study area were the major tools utilized with geo-referenced digital topographic maps to produce a geological map of the area with the use of appropriate software. Airphoto interpretation, photomosaics and GIS (Geographical Information System) procedures were part of the desktop study.

The computer software used during the course of the study included Arc-GIS Desktop, Arc-View 3.3 and Quarter GIS 7.1 to provide accurate large-scale maps of the geometry of the members in the

Balfour Formation. Grapher 8.0 and Dplot Software packages were used to plot and analyse the geochemical data. Another function of the desktop computer was also to enable easy stratigraphic interpretation.

3.2.1 Air photo interpretation

This involved the use of photogeological and spectral remote characterised images to aid the understanding of the geology and its spatial variation. A digital mozaic of 1:50 000 scale aerial photographs covering the study area was overlain on topographic maps of the same scale and geological map (Fig. 7) for airphoto interpretation. Satellite images from Google Earth provide high- spectral resolutions of the different lithological units. The aerial photographs allow the vertical aggradation units to be mapped in their outcrop areas. Areal variations in sequence attitude, thickness and the lithologies of the strata exposed at the surface were the main attributes that were mapped on the aerial photographs. Well exposed sandstone units were easily distinguished on the aerial photographs. Tracing these sandstones provides a means for correlating individual stratigraphic

19 sections between outcrops within the members. Mapping was transferred from the aerial photographs to 1:50 000 scale digitised topographic maps of the study area and the final geological map (Fig. 10) was produced with the use of ArcGIS software. The large final geologic map can not be incorporated in the text and has been assigned to a map pocket (Appendix).

Figure 6: Satellite image of study area showing some of the sample locations (Google Earth, 2010).

3.2.2 GIS and remote sensing

GIS is a computer-based tool for mapping and analysing features on the earth while remote sensing is the art and science of marking measurements of the earth using sensors on aeroplanes or satellites 20 (Viet Hoa, 2004). Remote sensing is used to manipulate the data collected in the form of visual images. GIS then integrates the data into a common database operation which includes statistical analysis within the map. This was done in order to allow the link of databases to create a dynamic display that is not possible on traditional spreadsheets. Remote sensing and GIS are applied to obtain accurate information about georeference points of the mapped area investigated through integrating the data with the aerial photography overlain on the 1:50 000 topographical and geological map of the area. GIS Desktop although expensive, is a very good package, which aids the electronic mapping of a study like the present. It has facilitated relatively easy acquisition of topographic information relating to elevations, geological features, roads and rivers. The existing 1:250 000 3226 (CA-CD)

King William‟s Town geological map was consulted (Fig. 7). Data acquired was analysed and used to show the boundary contacts of the various members in the Balfour Formation (Fig. 10).

3.3 Geological mapping

Geological mapping was done by observation and investigation of selected localities in the study area after desktop studies were completed. In the field, the lithologies were identified for each of the members of the Balfour Formation where they were exposed and stratigraphic sections described.

The sedimentary structures were also measured and samples were taken for further study such as petrography, petrology and geochemical analysis.

In the area, outcrops are intermittently exposed both to the northwest and southeast of Adelaide and

Bedford (Fig. 8). A number of field traverses were made to investigate the basal and upper contacts of the individual lithostratigraphic members as suggested by the desktop study. Navigation in the field was generally aided by the use of GPS (Global Positioning System) and GPS waypoints and elevations were recorded. Due to the variable exposure in the outcrop, complete lithostratigraphic

21 sections of the individual members could not be mapped across the entire Formation. Although physical tracing of beds is the only unequivocal method of correlating the continuity of the individual members, it is not without limitation as in places the outcrops are covered by soil or thick vegetation

(Fig. 9) or erosional areas. Other challenges are when beds being traced pinch out or laterally merge with others as is common in non-marine strata. A total of thirty samples were systematically collected and properly labelled in order to obtain a full representation of the selected study area, and to obtain accurate data and viable conclusions. The presence of various primary sedimentary features was recorded for the identification of sedimentary facies and for characterising the depositional environment. Directional data from primary stuctures such as current ripples, cross bedding troughs and channel axis orientations, as well as parting lineations were also recorded in order to interpret the palaeocurrent directions.

22

Figure 7: Existing 1:250 000 3226 (CA-CD) King William‟s Town geological map mainly covering the Balfour Formation and including the study area, (Johnson and Keyser, 1976). The subdivisions of the Balfour Formation are not differentiated.

23

Farms

Figure 8: Sample locations in the vicinity of the towns of Bedford and Adelaide on the various members of the Balfour and of the Katberg Formation, Eastern Cape Province.

24 A B

Figure 9: Outcrop covered with abundant vegetation. A – Barberskrans Member at Black Hill north of Adelaide (S32°19´42.27" E26°19´48.61"). B – Katberg Formation at Buffelskloof Northwest of

Bedford (S32°35´37.29" E26°02´35.63").

The Balfour Formation in the study area exhibits more argillaceous than arenaceous components with the arenaceous units being sandstone lithosomes of varying thickness while the argillaceous ones are mudstone and shale zones. Mapping correlation of the various members is based on lithologic similarity established on the variety of rock properties which include the lithology of the strata, colour and primary sedimentary structures such as bedding and cross-lamination as well as thickness.

The greater the number of properties that can be used to establish the match between strata, the stronger the reliability of the match (Boggs, 2006). Substantial areas to the south and north of

Bedford and Adelaide are occupied by flat-lying sandstone. Dark grey dolerite dykes and sills intruded the sedimentary rocks and several minor fault zones (Fig. 11) occur within the Balfour

Formation. These intrusions vary from a few metres to tens of metres thick and constitute approximately ten percent of the mapped area (Figs 7 and 10). The dolerite intrusions were succesfully mapped with the aid of aerial photographs. Figure 10 shows a reduced version of the

25 geological map of the study area. Some of the contacts between members have been clearly eroded away with conspicuous relief truncating underlying bedding.

Figure 10: Geological map of the study area around Bedford and Adelaide in the Eastern Cape

Province, South Africa.

26 A B

Figure 11: A – Normal fault in an outcrop of sandstone of the Oudeberg Member with alternating shale and mudstone. B – Fault zone in sandstone unit of about 5m thick at a road-cutting south of

Adelaide. Figures for scale.

3.3.1 Sedimentary structures

Sedimentary structures are features in sediments and sedimentary rocks which provide clues to the depositional environment and origin of the rock type (Lapidus, 1987; Raymond, 1995). Such features include primary depositional sedimentary structures and, in addition, erosional, deformation and diagenetic structures, are also important as they reflect the environmental conditions that prevailed at, or after, the time of deposition, as well as the type of transportation processes that took place. The sedimentary structures identified within the rock can be classified into the following (Johnson, 1976):

Internal structures: These are primary structures produced at the same time as the deposition of the sediment. These include planar bedding (Fig. 12a), cross-bedding and trough cross- bedding (Fig. 12b). Planar bedding are differentiated beds that do not contain internal dipping laminae. The planar bedding (Fig. 13a) is the most abundant structure in the sandstone. There is also

27 massive bedding (Fig. 13b) which appears to contain no internal structures. This is be due to the production of large-scale straight crest movement (Tucker, 2001). This bedding type generally ranges from twenty centimetres to two metres in maximum thickness.

External structures: These are penecontemporaneous sedimentary structures or secondary structures such as oscillation ripple marks (symmetrical) and current ripple marks

(asymmetrical), which occurred on the upper surface of sedimentation shortly after deposition (Fig.

14). These ripple marks are related to current-produced structures and are relatively common in the

Balfour Formation, but oscillation ripple marks are rarely observed. In the study area, the ripple marks are most common in the Oudeberg, Daggaboersnek and Barberskrans Members as can be seen along the R63 main road within the Bedford - Adelaide vicinity. In the Daggaboersnek Member distinctly large ripple marks are fairly common, as seen in the Cradock–Adelaide area (Johnson,

1976).

A B

Figure 12: A – Flat-bedded sandstone above, overlying siltstone in the Daggaboersnek Member. B -

Trough cross-bedding in sandstone of the Daggaboersnek Member along the R63 main road south of

Adelaide, at elevation 577m. S32°42´15.59" E 026°18´55.18"S.

28

Figure 13: A – Planar-laminated sandstone alternating with shale and mudstone along the main road between Adelaide and Cradock. B - Massive bedded sandstone south of Bedford.

A B

Figure 14: A – Ripple marked capping on Oudeberg Member sandstone S32°49´35.9" E026°28´02.0". B – Horizontally laminated sandstone in the Daggaboersnek Member S32°40´32" E026°01´52.7"

29 3.4 Sedimentary petrography

Sedimentary petrography is the scientific description and classification of sedimentary rocks in relation to the origin of the sediments and their alteration by diagenetic processes during burial

(Boggs, 2006). It involves studying the rock material for its composition, texture and structure

(Johnson, 1976). Petrographic studies are conducted to determine the composition of the rock and source of the detritus even though the original detrital composition may have been modified by the interaction of physical and chemical processes such as weathering, erosion, transportation processes and palaeoclimate (Johnson, 1976; Liu et al., 2007).

The petrographic studies were done on selected samples collected in the field from which thin sections were made. This entailed petrographic investigation and analysis of the thin sections using a binocular microscope to identify the mineralogical composition and to do a detailed description of the rocks, including the textural relationships within the rocks and their grain size variation. Heavy minerals were also studied for information about the source rock. The main mineral constituents encountered are quartz, feldspar (plagioclase and alkali feldspar), mica (biotite and muscovite), accessory minerals and matrix.

Quartz: It is the most dominant mineral in the sandstone and is regarded as the principal constituent of the rock. The prominent abundance of quartz is due to the fact that it demonstrates strong covalent bonding (Boggs, 2006), chemical stability and its hardness; hence it is more stable and able to survive considerable abrasion during transportation from the source to the depository. A few quartz grains display some degree of roundness acquired during the process of transportation. Monocrystalline

(Qm) and polycrystalline (Qp) quartz are seen to occur throughout the sandstone member sequences in the Balfour Formation. Inclusions are present within both quartz grain types but most commonly in

Qm quartz.

30 Feldspar: Feldspars are the second-most abundant minerals amongst the constituents of the rocks.

There are various types of feldspar with differences in chemical composition and optical properties.

Feldspar groups in the sandstone include the alkali feldspars (K-feldspar) and the plagioclase feldspars. The plagioclase feldspars were clearly distinguished from potassium feldspars by their optical properties such as optic sign and twinning, including the maximum symmetric extinction angle from which the An-content was derived. Oligoclase and andesine, with some microcline, are the most common feldspar minerals occurring throughout the sandstone in the Balfour Formation.

The K-feldspar is less abundant and more altered than plagioclase. This is due to its weak intercrystalline or intergranular bonds which are more easily broken during sediment transportation

(Tucker, 2001). The incipient alteration gives the feldspar a dusty appearance.

Lithic fragments: These are smaller pieces of ancient (probably Precambrian) source rock grains and finer grained material that are not disintegrated to yield individual mineral grains and make up a few percent of the whole rock framework. It could originate from igneous, metamorphic or sedimentary rock. Lithic fragments were not classified in terms of the source type as they were difficult to differentiate due to the very small size of the constituent grains. The most common rock fragments associated with the sandstone are clasts of volcanic and fine-grained rocks (locally derived argillaceous rock fragments) in all the sandstones and occurring in variable proportions throughout the sandstone occurences.

Accessory minerals: These are less abundant minerals in the rocks and include common mica

(biotite and muscovite) and heavy minerals. There is a minor amount of biotite. Indications of oxidised environments that result in the decomposition of biotite to clay minerals and ferric oxide are quite common. Some of the mica is altered to sericite and in some samples the sericitisation seems to

31 be advanced. The mica is present in various amounts in all the samples. There also are some heavy- mineral grains which include zircon, rutile, opaques and garnet.

Matrix minerals: A matrix is clastic or finer grained material with grain sizes of about 0.03mm which fills interstitial spaces and encloses large grains in sedimentary rocks (Lapidus, 1987). It is classified into a primary matrix which is detrital (clay, mica and chlorites) and a secondary matrix which is a chemical precipitate (calcium carbonate). The primary matrix gives indications about the provenance and transportation of the sediment while the secondary matrix reveals information about post-depositional conditions (Raymond, 1995). The matrix in the sandstone is composed mainly of mica (biotite) and fine grains of silica and constitutes approximately 5% to 10% of the sandstone. The dominant presence of biotite is an indication of a reducing condition within the sediment at the time of deposition and a wide range in acidity, while the muscovite is an indication that there was not much of an oxidising environment (Boggs, 2006).

3.4.1 Oudeberg Member

The Oudeberg Member is a sandstone-rich unit interbedded with shale and siltstone. It contains subordinate greenish to grey mudstones (Tordiffe, 1978). The sandstone is composed of quartz and feldspar grains, some rock fragments, as well as heavy minerals (Fig. 15). The grains have concavo– convex contacts and are subrounded to subangular in shape. Texturally, the sandstone is fine to medium grained in size and is moderately sorted with some silica cement. In their study, Visser and

Dukas (1979) also recorded coarse grains. Thin section obervation showed lesser amounts of volcanic fragments and small amounts of heavy minerals, the most common being zircon. Most of the monocrystalline quartz grains are unstrained and some contain common inclusions that suggest a plutonic origin of the sediment (Basu et al., 1975; Potter and Pettijohn, 1977). While most of the

32 plagioclase displays well-developed twin grains with very few being untwinned, the K-feldspar and biotite are highly altered (Figs 15 and 16)

A B

1µm 1µm .

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 15: Photomicrograph of Oudeberg sandstone. The red arrow points to an overgrown unstrained quartz grain. Mostly the quartz has intergranular boundaries with culminating texture that can be attributed to the recrystallisation of clay minerals. The plagioclase displays clearly preserved twinning indicating limited alteration.

Key: Bio = biotite, K-spar = K-feldspar, M-Qtz = monocrystalline quartz, Plag = plagioclase, P-Qtz = polycrystalline quartz, Zr = zircon and Ser = sericite. Horizontal field of view is equal to 41mm for all the images in this section.

33 A B

1µm 1µm

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 16: Photomicrograph of Oudeberg sandstone showing K-feldspar and biotite grains undergoing alteration. The biotite is altered to iron oxide with the matrix containing clay minerals and silica.

3.4.2 Daggaboersnek Member

The Daggaboersnek Member consists of interbedded shale and mudstone with subordinate sandstone units. There are almost equal amounts of quartz and feldspar grains in the sandstone (Fig. 17). Most of the feldspar grains are larger than the quartz grains and the grains are moderately to poorly sorted.

The sandstone samples are characterized by a low rock fragment content and contain more monocrystalline than polycrystalline quartz grains, as well as few heavy minerals. Some of the quartz grains contain inclusions of opaque minerals.

34 A B

1µm 1µm

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 17: Daggaboersnek sandstone containing relatively large feldspar grains and exhibiting angular form suggesting a very short travel distance and first cycle detritus. The green arrow points to very small apatite grains and the yellow arrow to monocrystalline quartz grains.

3.4.3 Barberskrans Member

The Barberskrans Member is distinguished from the underlying and overlying members by its predominance of sandstone. The sandstone is composed mainly of quartz, feldspar and mica with few lithic fragments and zircon grains (Fig. 18). Feldspar grains are highly altered to clay minerals such as sericite and some of the quartz grains are of volcanic derivation.

35 A B

1µm 1µm

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 18: Barberskrans sandstone containing predominantly clear quartz grains which are mostly monocrystalline with undulatory extinction. The white arrows indicate quartz grains; the blue arrow points to twinned plagioclase. Grains display concavo-convex contacts and have subrounded to subangular shape while the matrix is dominated by fine sediments.

3.4.4 Elandsberg Member

The Elandsberg Member comprises alternating sequences of mudrock and subordinate fine- to medium-grained sandstones. The main minerals in the sandstones are quartz, feldspar and mica with a few lithic fragments (Fig. 19). The sandstone also contains some heavy minerals such as garnet and zircon grains. There is a high level of sericitisation amongst the feldspar grains.

36 A B

1µm 1µm

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 19: Elandsberg sandstone with quartz grains showing undulose extinction. The matrix contains biotite which is partly altered to iron oxide and clay minerals. A few heavy minerals such as garnet and zircon, are present.

3.5.5 Palingkloof Member

The Palingkloof Member forms the top of the Balfour Formation and is overlain by the Katberg

Formation (Ward et al., 2005). The Palingkloof Member predominantly comprises red with subordinate greyish mudstones and shale and lacks significant sandstone. A comprehensive description of the Palingkloof Member was given by Katemaunzanga (2009).

3.5.6 Katberg Formation

The Katberg Formation occurs immediately above the Balfour Formation and is present in the study area. It constitutes the lower part of the Tarkastad Subgroup and consists predominantly of sandstone

37 (Johnson et al., 2006) that unconformably overlies the Balfour Formation (Catuneanuet al., 1998)

(Fig. 20). The sandstone is medium grained and consists mainly of quartz, feldspar, rock fragments and matrix. Modal composition of the Katberg Formation, according to Haycock et al.(1997), is 30–

45% quartz, 3–6% chert, 6–11% feldspar and an average of 17.3% lithic fragments. Subsequent authors did not report the presence of chert but identified lithoclasts of volcanic fragments instead.

A B

1µm

1µm

A: PPL (Plane polarised light) B: XPL (Cross-polarised light)

Figure 20: Photomicrograph of Katberg sandstone. A few siliciclastic and volcaniclastic fragments

(white arrow) are present. The quartz grains display undulose extinction and are angular in shape, while the feldspar is fairly altered, typical of a granitic source. The green arrow points to an apatite grain.

Although there are no major distinctive compositional variations of the sandstone across the members of the Balfour Formation, the effect of weathering and sediment transportation has influenced the rock components to varying degrees. Catuneanu and Elango (2001) confirmed that there are no variation trends in the composition of the sandstone, indicating that the associated minerals are lithoclasts, feldspar and quartz. 38 3.5 Sedimentary textures

Texture in a rock is the general character or appearance of a rock as indicated by relationships between its component particles, specifically grain size distribution and arrangement (Lapidus, 1987).

The texture of sedimentary rocks reflects the nature of transport and depositional processes.

Characteristics of the texture can aid in interpreting ancient environmental settings (Boggs, 2006).

This involves the physical texture which is composed of the grain size and shape in the mineral framework. The mineral roundness of the grains was considered through visual comparison with the photographic chart of Powers (1953) which combined the two independent properties of sphericity and roundness. Estimation of sorting was done using the comparison charts of Longiaru (1987). Qm grains are angular to sub-angular, suggesting short distance of transportation. Most of the Qp grains are more angular. Feldspar grains range from largely euhedral to sub-angular while the mica flakes range from large to small in size. Rounded to subrounded grains characterise the heavy-mineral population but some angular to subangular grains are also present. The zircon grains, however, invariably have a strong tendency towards euhedralism.

Generally, the framework grains are medium to fine in size, angular to subangular in shape and moderately to poorly sorted. Texturally, the sandstone is an immature sediment due to the amount of matrix present with poor sorting and angular grains Folk (1951). The analysed petrographic data was plotted on a QFL ternary diagram to interpret the classification and source terrain.

3.6 Modal analysis

Modal analysis involves the quantitative method of statistically analysing the grain size distribution of the various sandstones. The fundamental attribute of grain size distribution is an important property of siliciclastic sedimentary rocks for which the basic descriptive elements and understanding 39 of the processes which resulted in the formation of the sedimentary rock are determined (German,

1967; Griffiths, 1967; Tucker, 2001; Boggs, 2006). It is an essential tool for classifying sedimentary environments (Blott and Pye, 2001) and to determine the provenance of the sandstone (Decker and

Helmold, 1985). This tool is also used to analyse the broad tectonic and depositional history of a group of strata when combined with other petrographic data (Johnson, 1976). The point-counting method of Gazzi-Dickinson (1966), as described by Ingersoll et al. (1984), was applied, in which all grains that are sand sized (coarse to medium grained) were counted. The Gazzi-Dickinson method is referred to as a more appropriate point-counting technique for petrologists than the traditional point- counting method (Decker and Helmold, 1985). A total of 300 grains per thin section was measured and counted. Previous research found a three hundred grain count to be adequate for maximum accuracy of the investigation and satisfactory to obtain reliable percentages of the components present

(Bordy et al., 2004). The abbrevations used during the survey are listed in Table 1 with a brief description, and the counts of the individual components were totaled and recalculated to the percentage values shown in Table 3. The mean modal compositions of each individual member are shown in Table 4.

Grain size analysis involves the use of thin sections under a petrographic microscope with a micrometer eyepiece and dedicated image software connected to the microscope. For modal analsis, a grid (point count spacing) is effectively imposed over the thin section and the composition of the framework (mineral types) under each grid node is recorded. The grid is not actually drawn on the thin section; instead, a point-counting stage is used to move the thin section in precise increments so that each grid point moves exactly under the intersection of the cross-hairs of the microscope. Each grain in the grid that passes under the cross-hair intersection is recorded with the stage counter, identified and measured with the micrometer eyepiece of the microscope. True grain size measurements are recorded with the calibrated eyepiece. Horizontal distance between transects was 40 chosen to be greater than the individual largest grain encountered to ensure that the entire thin section is sampled and that no two transects would intercept the same grain. This interval was between

1.0mm and 1.67mm for the various sandstones analysed. The resultant grid therefore covered the whole thin section so as not to be biased. Grain size measurement in thin section is an attempt to reduce the number of variables influencing particle size (Johnson, 1976). A number of grain size scales have been proposed but the Wentworth scale, which was modified from the Udden-Wentworth scale, was used; it is a geometric scale proposed by Wentworth (1922) (Table 6). The choice of the scale is based on its use of clear, universally recognised terminology and its categorising of the sediment according to grain size classses such as gravel, sand and clay with their numerous subdivisions of measurable size and consistent ratio. Thus, the size fraction ranges from coarse to fine sand. Table 5 shows the grain size distribution in the sandstones of the Balfour Formation Members.

The sediments were characterised by dispersion values (mean, median, mode, standard deviation and sorting coefficient according to Boggs, 2006) of the various member sandstones of the Balfour

Formation, as shown in Table 5. The mean value of the quartz is 2.37 mm and is 2.88 mm for feldspar grains (Table 2) and (Fig. 21). Average values of grain size for the individual members and for the Katberg Formation are used to derived the mean grain size. The mean, median and mode values indicate that the quartz grain size distribution is normal and more symmetrical than that of the feldspar. The grain size parameters suggest that there is not much variation in size of the grains.

Based on the grain size scale, according to the data of Blott and Pye (2001), the sandstone can be classified as moderately to poorly sorted which ranges from 1.40–4.58φ. The sorting can also be measured from the standard deviation value according to Folk and Ward (1957) which confirms the sandstone to be moderately well sorted to poorly sorted (Table 7).

41 Table 1: Classification and symbols of grain types. Modified after Johnson (1991).

Symbols Description

Qm Monocrystalline quartz

Qp Polycrystalline quartz (fine-grained quartzite)

F Total feldspar (alkali feldspar, plagioclase and microcline)

L Lithic fragments

Lt Total lithic fragments (volcaniclastic and siliciclastic)

Acc Accessory minerals (heavy and opaque minerals)

Mx Matrix (all fine-grained interstitial material which cannot be identified)

Table 2: Grain size parameters for quartz and feldspar grains in the sandstones of the Balfour Formation. The values are sum averages of quartz and feldspar from the total sandstone samples.

Statistical parameters Quartz grains Feldspar grains

Mean 2.37 2.88

Standard Error 0.106 0.136

Median 2.25 2.91

Mode 2.32 2.54

Standard Deviation 0.47 0.59

Kurtosis 1.39 2.89

Skewness 0.56 1.02

42 Table 3: Mineral composition of the various sandstones in the Balfour Formation.

Sample Member n Qm Qp F L Mx Acc Qm% F% Lt

%

Kt st-1 Katberg 305 115 16 72 28 17 57 49.8 31.2 19.0

KT st-2 Katberg 300 135 15 70 25 20 35 55.1 28.6 16.3

KT st-3 Katberg 300 143 21 45 21 24 46 62.2 19.6 18.3

KT st-4 Katberg 306 136 20 75 23 20 32 53.5 29.5 16.9

EL st-1 Elandsberg 300 85 25 48 38 29 75 43.4 24.5 32.1

EL st-2 Elandsberg 300 87 27 49 30 30 77 45.1 25.4 29.5

EL st-3 Elandsberg 300 88 23 46 36 28 79 45.6 23.8 30.6

EL st-4 Elandsberg 300 89 25 45 37 30 74 45.4 23.0 31.6

BB-1028 m Barberskrans 300 98 16 82 35 25 44 43.6 36.4 20.0

BB-1079 m Barberskrans 300 100 20 72 54 21 33 40.7 29.3 30.1

BB-1099 m Barberskrans 300 91 25 66 42 22 54 42.5 30.8 25.6

DG st-1 Daggaboersnek 300 118 19 63 40 31 29 49.2 26.3 24.6

DG st-2 Daggaboersnek 300 103 29 46 50 33 39 45.2 20.2 34.6

DG st-3 Daggaboersnek 300 110 30 49 37 36 38 48.7 21.7 29.6

DG st-4 Daggaboersnek 300 103 18 61 47 25 46 45.0 26.6 28.4

Oud-533 m Oudeberg 302 95 15 75 25 35 52 44.2 37.2 18.6

Oud-535 m Oudeberg 300 72 15 65 68 42 38 37.3 29.5 33.2

Oud-582 m Oudeberg 300 96 18 67 50 32 37 41.6 29.0 29.4

Oud-414 m Oudeberg 307 94 19 68 56 34 36 39.7 28.7 31.6 n=number of counts, The last three columns are percentages of Qm, F and Lt (L + Qp).

43 Table 4: Mean modal compositions of sandstones from the various members across the Balfour Formation and of Katberg sandstone.

Member Qm Qp F L Mx others Qm% F% Lt%

Katberg 132.3 18.0 65.5 24.3 20.3 42.5 55.7 27.6 17.8

Elandsberg 87.3 25.0 47.1 35.3 29.3 29.3 36.1 19.5 24.9

Barberskrans 96.3 15.0 73.3 43.7 22.7 43.7 41.2 31.4 25.1

Daggaboersnek 108.5 24.0 54.8 43.5 31.3 38.0 47.0 23.7 29.3

Oudeberg 91.8 16.8 70.1 47.3 35.8 40.8 41.1 31.3 28.6

The mean modal compositions for sandstones from the first three members (Oudeberg,

Daggaboersnek and Barberskrans) are much the same while the Elandsberg values are low and the

Katberg Formation has the highest values (Table 3). Although the lithic fragment content is high it differ significantly from the values as recorded by Johnson (1991) and Katemaunzanga (2009) in this study area.

5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 Mean 1.00 0.50 Quartz 0.00

Feldspar

Oudeberg Oudeberg Oudeberg Oudeberg

Elandsberg Elandsberg Elandsberg Elandsberg

Barberskrans Barberskrans Barberskrans

Daggaboersnek Daggaboersnek Daggaboersnek Daggaboersnek

Katberg Formation Katberg Formation Katberg Formation Katberg Katberg Formation Katberg

Figure 21: Grain size distribution across the members of the Balfour Formation and of the Katberg Formation 44 Table 5: Grain size distribution of sandstones in the members of the Balfour Formation and of the Katberg Formation. The grain size values are averages of the individual members from the Balfour sandstones samples.

Member Sample Grain size Mean of the grain

(Φ) size (Φ)

Katberg Formation KT st-1 2.66 Katberg " KT st-2 3.06

Katberg " KT st-3 3.10

Katberg " KT st-4 4.06 3.22 Elandsberg Member EL st-1 2.55

Elandsberg " EL st-2 2.60

Elandsberg " EL st-3 2.49 Elandsberg " EL st-4 2.93 2.64 Barberskrans Member BB-1028m 2.62 Barberskrans " BB-1079m 2.89 Barberskrans " BB-1099m 2.23 2.58 Daggaboersnek Member DG st-1 2.88 Daggaboersnek " DG st-2 2.42 Daggaboersnek " DG st-3 2.42 Daggaboersnek " DG st-4 2.44 2.54 Oudeberg Member Oud-533m 1.64 Oudeberg " Oud-535m 2.18 Oudeberg " Oud-582m 2.40 Oudeberg " Oud-414m 2.36 2.14

45 Table 6: Grain size scale for sediment and sedimentary rocks of Wentworth (1922).

Table 7: Folk and Ward (1957) sorting based on standard deviation measurement values.

Φ Values Description

Less than 0.35 Very well sorted

0.35–0.5 Well sorted

0.5–0.71 Moderately well sorted

0.71–1.00 Moderately sorted

1.0–2.0 Poorly sorted

46 3.7 Heavy-mineral analysis

Heavy minerals are useful for source rock interpretation because they tend to survive the hazards of weathering, transportation and diagenesis and they occur in a restricted range of provenance types

(Johnson, 1976). They are used to unravel the source of the sediment as well as the depositional environment, although in some cases the heavy minerals do not reflect the mineralogy of the source area because of post-depositional modification. Hence, the analysis concentrated on highly resistant heavy minerals. Heavy minerals were extracted from ten selected sandstone samples and the heavy minerals considered in this study are those with a specific gravity greater than 2.9. These heavy minerals are divided into chemically stable (zircon and rutile) and unstable varieties (magnetite, pyroxenes and amphiboles) (Boggs, 2006). Analysis of the heavy minerals was carried out by first disintegrating the selected samples with a jaw crusher and then sieving and collecting the -80 +170 mesh fraction. The samples were submitted to the Council for Geoscience in Pretoria for the extraction process. This involved washing the sieved samples in a tailings train; the heavy mineral fraction was then separated from the tailings (Fig. 22). Further separation of the magnetic from the non-magnetic heavy minerals was done using a Frantz electromagnetic separator (Fig. 23a). Minerals such as haematite and other iron rich minerals such as biotite were successfully separated. The non- magnetic fraction was then stirred into a heavy liquid (methylene iodide) inside a funnel placed in a fume chamber (Fig. 23b). The Light minerals float on the surface of the heavy liquid and the heavy minerals gradually sink into the stem of the funnel where they were drawn off and separated from the light fraction. The heavy mineral concentrates were then mounted on a glass microscope slide and examined with the optical petrographic microscope in transmitted light. Among the heavy minerals found were opaque minerals (ilmenite, and haematite) and non-opaque minerals such as rutile, garnet, tourmaline and zircon (Fig. 24); they are sporadic in occurrence due to the small amounts present. Of the non opaque population, zircon, rutile and garnet are the most dominant grains because they are 47 highly resistant to weathering. The most stable assemblage consists of zircon (Fig. 25), rutile and tourmaline. This confirmed the report of Bordy et al. (2005) on the high content of heavy minerals including zircon, rutile and opaques in the Balfour sandstone.

A B

Figure 22: Tailing train for washing the pulverized samples and collecting the heavy mineral fraction from the tailings.

A B

Figure 23: A – Frantz electromagnetic separator used for separating metallic from the non-metallic heavy minerals. B – Extraction of the heavy minerals using a fume chamber. 48 1µm

Figure 24: Heavy-mineral assemblage from the sandstones of the Balfour Formation.

Key: G =.garnet, Ru = rutile, Tu = tourmaline and Zr = zircon.The rounding of most of the grains may be due to dissolution and transportation (Diskin et al., 2010).

Figure 25: Zircon grains from sandstones of the Balfour Formation.

49 3.8 Classification of the sandstone

There is no one method accepted by geologists for classifying sedimentary rock, but there are many schemes of classification based upon the following: theoretical principles, emphasis on the mineral composition and others devised empirically for convenience in field and laboratory descriptions.

Finding a classification that is suitable for all types of sandstone and acceptable to most geologists has proven to be an elusive goal (Boggs, 2006). Sandstones are universally best classified on the basis of the proportions of the three end-members, quartz, feldspar and rock fragments that are illustrated in a triangular composition diagram (e.g., Johnson, 1976). Hence, the classification of the Balfour sandstone is based on the method of Folk (1974) (Fig. 26) and Dickinson et al., (1983) (Fig. 27). Folk

(1974) proposed a classification method based on the abundance of quartz, feldspar and rock fragments in a ternary diagram as well as the use of matrix content. Considered one of the best ways of classification and used by most previous researchers, it is based on mineral attributes. Folk‟s classification reveals significant information about provenance with the name of the rock reflecting details of its composition (Raymond, 1995). The main mineralogical constituents of the sandstone classification are monocrystalline quartz, feldspar and lithic fragments. Polycrystalline quartz are considered as lithic or rock fragments. It is universal practice to describe polycrystalline grains as rock fragments. However, polycrystalline quartz could be plotted either as lithic fragments if the purpose of study is on provenance or as quartz grains depending on whether emphasis is on the maturity of the sand (Pettijohn et al., 1987). Matrix and accessory minerals are recognised as minor variables within this conceptual framework. The ternary diagram classification plot was compared with that of Johnson (1991),who modified the diagrams of Dickinson et al.(1983) and Haycock et al.

(1997) (Fig. 27).

50 1 Quartzarenite

2 Subarkose

3 Sublitharenite

4 Arkose

5 Lithic arkose

6 Feldspathic litharenite

7 Litharenite

Figure 26: Modal data plot of quartz-feldspar-lithic fragments (Q-F-Lt) and triangular classification on the Folk (1974) diagram of different sandstone samples from the Balfour Formation.

Key: Qm (Monocrystalline quartz); F (Feldspar); Lt (Lithic fragments). This key also applies to figure 27.

From the plots on the Q-F-Lt ternary diagram it is clear that the total composition of the sandstone within the various members is similar. The mineral composition of the sandstones plots in the area of feldspathic litharenite (Fig. 26) while in the Dickinson et al., (1983) diagram the plots fall in the ultralithofeldspathic field with a few in the lithic and the ultralithic fields (Fig. 27), which indicates that the sandstones have a high content of feldspar, as comfirmed by previous researchers, e.g.

Johnson (1991) plotted the Balfour sandstones in the ultralithofeldspathic field only. Katemaunzanga

(2009) indicated that all the sandstones of the Balfour Formation have less than 15% matrix and are feldspathic litharenites with a few being in the lithic arkose field. Classification based on grain size

51 and matrix content, according to Folk (1974), indicates that the sandstone can be characterised as consisting of fine- to medium-size grains with less than 15% matrix. Texturally, the sandstones can also be referred to as grain-supported arenites (Pettijohn et al., 1987).

1 Ultraquartzose sandstone

2 Quartzose sandstone

3 Subfeldspathic sandstone

4 Sublithic sandstone

5 feldspathic sandstone

6 Lithofeldspathic sandstone

7 Lithic sandstone

8 Ultrafeldspathic sandstone

9-Ultralithofeldspatheic sandtone

10 Ultralithic sandstone

Figure 27: Q-F-Lt ternary diagram of Dickinson et al. (1983), indicating the mineral composition of the sandstones in the Balfour and Katberg Formations of the Eastern Cape Province.

52 CHAPTER FOUR

SANDSTONE GEOCHEMISTRY OF THE BALFOUR FORMATION

4.1 Introduction

The mineralogical composition of the rocks does not completely reflect the depositional source due to post depositional modification of the constituent grains. It is essential therefore that the geochemical characteristics of the various sandstones be understood in order to identify the signatures of the source rocks and to infer the redistribution of elements during and after deposition (Bhatia, 1983).

Geochemical analysis is a valuable tool in the study of sandstone (McLennan et al., 1983). It gives information about the provenance, weathering history of the source rock, geological processes and the tectonic setting (Raymond, 1995; Liu et al., 2007; Rahmani and Suzuki, 2007; Banerjee and

Banerjee, 2010). Sandstone geochemistry of the study area was investigated in selected representative samples from the members of the Balfour Formation using X-ray fluorescence spectrometry (XRF) and X-ray diffraction (XRD). XRF is a highly sensitive technique used to analyse both trace and major elements of rock composition, but cannot generally perform analysis of small spot sized particles; it is typically employed for bulk analysis of larger fractions of geological material. Some geochemical ratios can become altered during weathering through oxidation (Taylor and McLennan,

1985) but, as long as the bulk composition of the rock is not totally altered, such samples are suitable for analysis. XRD is used to determine clay mineralogy and to analyse the whole rock to confirm the petrographic framework. It can also be used to qualitatively determine the mineral phases in the rock sample (Coney, 2005). The rock samples were crushed and sieved at -170 mesh, and pulverised samples were analysed at the South African Council for Geoscience in Pretoria. Analyses of major elements were performed with milled samples (<75 µ fraction) placed in an oven at 100°C for at least one hour to drive off the water contained and roasted at 1000°C for no less than three hours to oxidise 53 Fe2+ and S and to determine the Loss on Ignition (L.O.I). Glass disks were prepared by fusing 1.5g roasted sample and 9g flux consisting of 35% LiBO2 and 64.71% Li2B4O7 at 1000°C. Twelve grams milled sample and three grams Hoechst wax C micropowder was mixed and pressed into a powder briquette by a hydraulic press with applied pressure of 25 tonnes for trace elements analysis. The X-

Ray Diffraction measurements were performed on a BRUKER D8ADVANCE instrument with a

2.2kW Cu long fine focus tube (Cu Kα, λ=1.54190 Å) and 90 position sample changer. The system was equipped with a LynxEye detector with 3.7º active area. Samples were scanned from 2 to 70° 2θ at a speed of 0.02° 2θ step size/0.5 second, and generator settings of 40 kV and 40mA. Phase identification was based on the BRUKER DIFFRACPlus - EVA evaluation program. Routinely, phase concentrations were determined as semi quantitative estimates (with accuracy ±5%) using the RIR

(Reference Intensity Ratio) method and relative peak heights/areas proportions.

The Chemical analysis helped to clarify the compositional details not resolvable with the petrographic microscope (Akarish and El-Gohary, 2008). Geochemical data from the XRF analyses of major and minor element concentrations of the Balfour Formation are represented in Tables 8 and 9 respectively, and the XRD analyses of all the sandstones are given in Table 11. The major- and trace- element analyses of the sandstone were further used for provenance interpretation.

4.2 Major elements

Major-elements undergo some changes during sedimentary processes but provide clues as to the provenance type as well as weathering conditions within the basin setting (Bhatia, 1983). The major- element oxides associated with the sediment composition of the sandstone include silica (SiO2), aluminium oxide (Al2O3), iron oxide (Fe2O3), magnesium oxide (MgO), calcium oxide (CaO), sodium oxide (Na2O) and potassium oxide (K2O). All iron oxides are expressed as Fe2O3. Balfour

54 sandstones are rich in SiO2, ranging from 68.41% to 80.31% upwards in the succession with an interval of a few percent which sequentially begins with the Oudeberg Member (68.41–69.38%) upwards into the Katberg Formation (74.47–80.31%). This is followed in abundance by the values of

Al2O3 (9.62–15.44%). The sandstone also contains very low percentage of titanium oxide (TiO2), manganese oxide (MnO) and magnesium oxide (MgO). Several binary plots of the major oxides were created to illustrate the geochemical variation of the oxides in the Balfour sandstone. Quartz content was determined with the K2O/Na2O ratio (Table 8 and Fig. 28). The value of Fe2O3/TiO2 (Table 8) reveals that this oxide ratio (6.98%) generally is low, but the value of Fe2O3 varies systematically among the various stratigraphic subdivisions and coincides with the colour change of the mudstone to red upward in the succession. There is no significant variation of phosphorus oxide (P2O5) across the various members.

According to Crook (1974), subdivision on the basis of SiO2 content, in conjunction with the relative

K2O/Na2O ratio classes, (quartz-poor, quartz-rich and quartz-intermediate) can be done and each assigned to a plate tectonic setting and provenance. The quartz-poor class is characterized by low

SiO2 content typical of a volcanic provenance and an island arc environment. Quartz-rich population, which has average SiO2 content of 89% and K2O/Na2O of less than one indicates a sedimentary provenance and an inactive continental margin. The quartz-intermediate class is characterized by

SiO2 content ranging from 68% to 74% with K2O/Na2O ratio less than one indicating mixed provenance in an active continental margin or in a microcontinent. Most of the sandstone thus corresponds to the intermediate quartz class (Fig. 28). Plots of Na2O against K2O (Fig. 28) and Al2O3 against SiO2 (Fig. 29) give an indication of the systematic increase in quartz content in the sandstone.

The major element geochemistry of the sandstones can also be used to determine the tectonic setting of the basin by a discrimination tectonic setting plot (Bhatia, 1983). Thus, plots of TiO2 versus

55 Fe2O3+MgO and of Al2O3/SiO2 versus Fe2O3+MgO (Fig. 30) were used to define the tectonic setting of the Balfour Formation after Bhatia (1983), while logarithmic values of Fe2O3/K2O versus logarithmic values of Al2O3/SiO2 after Herron (1988) are utilized to determine the chemical classification of the sandstone (Fig. 31). The schematic Herron (1988) sand classification system is based on geochemical content for sandstone classification and shows the relationship between element composition, mineralogy and rock type. A variant plot of SiO2 against total

(Al2O3+K2O3+Na2O) (Fig. 32) proposed by Suttner and Dutta (1986) is used to identify the maturity of the Balfour sandstones. This plot can also be used as a function of paleoclimate.

Figure 28: Quartz content variation amongst sandstone units of the Balfour Formation (after Crook,

1974). The plot indicates that the Oudeberg Member and the overlying Katberg Formation have higher quartz content than the Barberskrans and Elandsberg Members while the Daggaboersnek

Member has low quartz content.

56 Table 8: Major-element data of sandstone members from the Balfour Formation, Eastern Cape

Province, South Africa. Values in oxide weight percent. ODST: Oudeberg sandstone, DGST:

Daggaboersnek sandstone, BBST: Barberskrans sandstone, ELST: Elandsberg sandstone: KTST:

Katberg sandstone.

Sample ODST: ODST: DGST: DGST: BBST: BBST: ELST: ELST: KTST: KTS: mean 1 2 1 2 1 2 1 2 1 2

Major element

SiO2 69.38 68.41 70.67 70.80 73.33 73.50 70.31 76.20 74.47 80.31 72.74

TiO2 0.53 0.57 0.39 0.49 0.43 0.45 0.59 0.30 0.31 0.32 0.44

Al2O3 14.88 15.33 14.84 15.44 14.49 13.17 14.98 13.29 12.99 9.62 13.90

Fe2O3(t) 3.73 4.54 3.43 2.95 2.75 2.77 3.96 1.89 1.98 2.54 3.05

MnO 0.060 0.063 0.085 0.037 0.040 0.057 0.084 0.032 0.037 0.057 0.06

MgO 1.01 1.40 1.23 0.88 0.60 0.71 1.25 0.42 0.55 0.15 0.82

CaO 2.26 2.17 1.37 1.15 0.87 1.74 1.56 1.32 2.31 3.55 1.83

Na2O 3.63 2.31 4.88 4.88 5.65 3.16 3.34 3.01 3.09 0.91 3.48

K2O 2.50 2.97 1.40 1.71 1.03 2.27 2.72 2.46 2.54 1.38 2.10

P2O5 0.112 0.177 0.093 0.109 0.099 0.105 0.157 0.082 0.082 0.038 0.11

Cr2O3 0.003 0.002 0.002 0.002 <0.001 0.003 0.005 <0.001 <0.001 <0.00 0.00 1

L.O.I. 2.20 1.94 1.58 1.75 1.19 2.28 1.49 1.88 2.29 1.25 1.79

Total 100.30 99.89 99.98 100.19 100.48 100.22 100.44 100.89 100.64 100.12 100.32

SiO2/Al2O3 4.66 4.46 4.76 4.58 5.06 5.36 4.69 5.73 5.73 8.35 5.36

Na2O/K2O 1.45 0.78 3.49 2.85 5.48 1.39 1.23 1.23 1.21 0.66 1.93

Al2O3/SiO2 0.21 0.22 0.21 0.22 0.20 0.18 0.21 0.17 0.17 0.12 0.19

K2O/Na2O 0.69 1.29 0.29 0.35 0.18 0.72 0.82 0.82 0.82 1.52 0.75

Fe2O3+MgO 4.74 5.94 4.66 3.83 3.35 3.48 5.21 2.31 2.52 2.69 3.87

Al2O3+Na2O+K2O 21.01 20.61 21.12 22.03 21.17 18.60 21.04 18.76 18.62 11.90 19.49

Fe2O3/Ti2O 6.99 7.93 8.8 6.06 6.43 6.19 6.69 6.28 6.41 8.02 6.98

CIA 64.00 67.00 66.00 67.00 66.00 65.00 66.00 66.00 62.00 62.00 65.11

57

Figure 29: Co-variation plot of SiO2 versus Al2O3 of the sandstones in the Balfour Formation. (after

Akarish and El-Gohary, 2008). This linear trend of negative correlation confirms the increase in quartz according to SiO2 content in the sandstones of the Balfour and Katberg Formations (Akarish and El-Gohary, 2008 and Osman, 1996).

58 A B

Figure 30: Discrimination diagram plots of sandstone in the Balfour Formation after Bhatia (1983).

(A) TiO2 versus Fe2O3+MgO and (B) Al2O3/SiO2 versus Fe2O3+MgO; Fields A, B,. C and D represent fields for various plate tectonic regimes. A (Oceanic Island Arc), B (Continental Island

Arc), C (Active Continental Margin) D (Passive Margin) and sst represents sandstone in the legend.

The geochemical characteristics of the sandstone in the Balfour Formation show that the geotectonic setting is related to an active continental margin (Fig. 30A) and continental island arc (Fig. 30B).

These continental margin settings are marked by plate convergence and orogenic volcanicity (Bhatia and Crook, 1986). The sediments are mainly derived from either felsic volcanic rock, granitic- gneisses and siliceous volcanics of an uplifted basement (Bhatia, 1983).

59

Figure 31: Geochemical classification of the Balfour sandstones after Herron (1988). The sandstones plot in the litharenite and arkose fields, indicating the consistency of the petrological data.

Figure 32: Bi-variant plot of SiO2 versus Al2O3+K2O+Na2O showing the chemical maturity trend of the Balfour sandstone (after Suttner and Dutta, 1986).

60 The maturity of the sandstone can be partially attributed to the prevailing climate and can be presented as a function thereof (Juboury, 2007). Thus, it shows that the Balfour sandstones are mature and related to the influence of climate. Overall, sandstone in the Katberg Formation is more mature than in the Balfour Formaton.

4.3 Trace elements

Trace elements reflect the signature of the parent materials (Bhatia and Crook, 1986), which makes them relevant for information about provenance and depositional setting (Raymond, 1995) especially also because their distribution is not significantly affected by diagenesis and metamorphism

(McLennan et al., 2001). Various studies have shown that the chemical signature of some trace elements such as chromium (Cr), lanthanum (La), nickel (Ni), niobium (Nb), scandium (Sc), zirconium (Zr), yttrium (Y), thorium (Th) and barium (Ba) is generally preserved throughout weathering and diagenesis of sedimentary source rock. The immobile elements such as cobalt (Co), strontium (Sr), hafnium (Hf), thorium (Th), yttrium (Y), chromium (Cr) and zirconium (Zr) are useful and reliable indicators of geological processes, provenance and tectonic setting (McLennan et al.,

2001; Lui et al., 2007). Elements such as cerium (Ce), neodymium (Nd), lanthanum (La), niobium

(Nb), scandium (Sc), and titanium (Ti) have low mobility during sedimentary processes and low residence time in sea water, they play a similar role as indicators of provenance and tectonic setting

(Holland, 1978). The value of the Sr content is very high, ranging from 249 to 421ppm, in sandstone of the various members (Table 9). Nickel and chromium content is low, which is an indication of depletion. The high Ba, Th and U suggests that the concentration of the trace elements is controlled by clay minerals and mica (McLennan et al., 1983) and which conforms with the petrographic observations. Th/U ratio is often used to define the weathering state under oxidising conditions. This

61 value increases significantly and systematically upwards in the Balfour Formation succession. The fairly high content of Cr may be associated with disseminated magnetite as demonstrated by the

Cr/Ni ratio range of 2.87 to 5.94ppm (Table 9), while the Zr/Th ratio gives an indicates of zircon in the sandstone composition. Thorium and scandium are good indicators of igneous chemical differentiation processes and are transported as terrigenous components during sedimentary processes

(McLennan et al. 1983). Thus, discrimination plots of Th/Sc against Zr/Sc after Mclennan et al.

(1983) (Fig. 33) are used to determine the compositions of the source rock, providing insight into the degree of fractionation thereof. The relative abundance of zircon in the sandstone is also reflected by the high Zr/Sc ratio which ranges from 15.63 to 41.09 ppm and in the plot of Zr/Sc versus SiO2 (Fig.

34) indicates significant reworking and selective sorting during transportation.

Figure 33: Discrimination plot of Th/Sc against Zr/Sc ratios (after McLennan et al., 1983). The plot shows concentration of zircon with high Zr/Sc ratio in the trailing edge indicating the dominant heavy mineral in the sandstone to be zircon which is attributable to sedimentary sorting and recycling.

62 Table 9: Trace element data of sandstone members from the Balfour Formation, Eastern Cape

Province, South Africa; all concentrations are in parts per million (ppm).

63

Figure 34: Scatter plot of Zr/Sc versus SiO2 showing zircon concentration and a significant reworking trend in the Balfour Formation and Katberg sandstone (after Cingolani et al.,2003).

4.4 X-ray diffraction

The dominant mineral constituents in the Balfour sandstone as identified with XRD include quartz, feldspar and clay minerals (Table 10). This conforms with the petrographic investigation finding with quartz being the dominant constituent mineral across the sandstones of the Balfour. The dominant clay minerals include kaolinite/chlorite, zeolite and smectite. Chemical weathering in the source area can be characterised by transformation of plagioclase into clay minerals (illite). Presence of zeolite in the Oudeberg Member at the base of the Balfour Formation and in the Elandsberg Member which constitutes the upper part of the succession as well as in the overlying Katberg Formation is an indication that the metamorphic temperature within the Balfour Formation ranged from 100 to 200°C

(Tucker, 2001). Zeolite is absent from the Daggaboersnek and Barberskrans Members. The

64 decomposition produced by chemical weathering of aluminium silicate minerals such as feldspar and mica minerals results in the presence of kaolinite throughout the sandstones, as confirmed by the petrographic investigation and suggests that alteration of feldspar and mica occurred during diagenetic processes in the sediments.

4.5 Weathering conditions in the source area

Chemical weathering significally affects the composition of siliciclastic sediments, the principal constituent of the sedimentary rock (Fedo et al., 1995 in Lee, 2002). The post-depositional influence in the source area was mainly affected by chemical weathering; hence, information about chemical weathering can provide information about the source rocks. The weathering effects can be evaluated in terms of the molecular percentages of the oxide components using the Chemical Index of

Alteration (CIA) (Cingolani et al., 2003). The CIA value reflects the degree of chemical weathering of the detritus incorporated into the source rock. It is also used as an estimate of the climatic conditions that existed during the formation of sedimentary rocks (Nguema Mve, 2005). Some of the major elements are used to determine the CIA in relation to their molar proportions. The coefficient of reliability of the CIA is when the rock contains less than 75% SiO2 and less than one weight percent CaO (Fedo et al., 1995 in Lee 2002), hence the CIA value of the Balfour sandstone was reliable.

The CIA index of the sandstones was calculated as: CIA=[Al2O3/(Al2O3+CaO+Na2O+K2O)]*100 and its value ranges from 62–67% (Table 8) with an average of 65.11% for the Balfour rocks (sandstone).

The closer the CIA value to 100, the more weathered the source rock (Fedo et al., 1995 in Lee 2002).

Most samples showed values greater than 60, suggesting moderate to high degree of weathering, either from the original source or during transport before deposition. The average value of the CIA,

65 with the SiO2 average value of the content ranging from 68.41% to 80.31% (Fig.35 and 36), suggests

that an older granite source had been weathered. A triangular plot of Al2O3-(CaO+Na2O)-K2O (Fig.

37), also referred to as an A-CN-K diagram, is used to deduce the weathering trend (Nyakairu and

Koeberl, 2001) and the initial stages of weathering (McLennan et al., 1983). However, from the A-

CN-K plot for the Balfour rocks (sandstone), it is apparent that weathering did not proceed to a stage

at which the significant components that made up the rock were removed from its sediments.

Table 10: Semi-quantitative XRD estimates of the Balfour sandstone mineralogy in the Eastern Cape

Province. Phase abundances expressed in weight percent.

Sample ODST: ODST DGST DGST BBST BBST ELST ELST KTST KTST 1 :2 :1 :2 :1 :2 :1 :2 :1 :2

Dolomite ------10

Spinel ------1

Plagioclase 26 20 38 55 21 36 23 30 18 8

Microcline ------2

Quartz 47 56 53 35 59 46 58 49 53 76

Kaolinite/Chlorite 10 2 3 3 7 12 13 1 7 -

Mica 6 2 5 4 6 6 6 4 5 -

Zeolite (Laumontite) 10 11 - - - - - 10 18 -

Smectite 1 8 1 3 6 - - 5 - -

I/S inter-stratification ------2

66

Figure 35: Plot of CIA versus SiO2 for Balfour and Katberg Formation sandstones (after Nesbitt and

Young, 1982).

Figure 36: SiO2 versus CIA (Chemical Index of Alteration) of Balfour sandstones indicating a moderate degree of weathering (after Nesbitt and Young, 1982; Tayor and McLennan, 1985).

67

Figure 37: A-CN-K triangle plot of the degree of depiction (after Cingolani et al.,2003), showing the weathering trend and indicating that the sandstone source was of igneous composition.

68 CHAPTER FIVE

STRATIGRAPHY OF THE BALFOUR FORMATION

5.1 Introduction

This chapter examines and explains the stratigraphy of the sedimentary rocks in the Balfour

Formation with relation to the individual members in the study area. Stratigraphy is the scientific description of strata in relation to the arrangement, distribution, chronological succession, classification and nomenclature of the rock bodies with respect to their properties (Johnson, 1976). It also deals with all the characteristics and attributes of the rocks in the strata and the interpretation of the strata in terms of derivation and geological background (Lapidus, 1987). It involves lithological composition, fossil content, age, origin and history in relation to organic evolution and any other features of the rock investigation (Johnson, 1987). Although there is a wide range of stratigraphic classifications, the most generally used are lithostratigraphy, biostratigraphy, magnetostratigraphy and chronostratigraphy. These stratigraphic classifications have all been applied to the Balfour

Formation (Catuneanu et al., 1998). The general lithostratigraphy of the Balfour Formation has been drawn up with reference to various researchers e.g. Johnson (1976), Visser and Dukas (1979), Smith

(1980; 1987), Rubidge (1995) and Catuneanu and Elango (2001) (Fig. 39). A major objective of the stratigraphic study was to investigate and describe the stratigraphic succession of the Balfour

Formation in greater detail. Information gathered with the investigation and description of the stratigraphic succession was also used to assist with interpretation of the depositional environment and origin of the sedimentary processes. There still is a need for more systematic organisation according to the South African Code of Stratigraphic Nomenclature and Classification. Detailed stratigraphic descriptions were done according to the guidelines of SACS (1980) at a number of localities during the field investigation but some were highly eroded and many parts of stratigraphic 69 successions occur in isolation as a result of which no single continuous stratigraphic succession can be drawn up for the Balfour Formation in the area. Facies and sedimentological interpretation were done with the aid of photographs taken in the field.

5.2 Lithostratigraphy of the Balfour Formation

Lithostratigraphy is the organisation of strata into units based on lithological characteristics and the correlation of these units (Lapidus, 1987). The various lithological units of the rocks are the main physical characteristics used for the lithostratigraphic description in this study. The units in the

Balfour Formation provide clear evidence of lithological variation in both vertical and lateral succession relationships in the strata and reflect environmental changes that occurred during the time of their deposition. The Balfour Formation has a maximum thickness of approximately 2150 metres

(Fig. 39), but since the Karoo is geometrically variable, the thickness varies from one geographical area to the other. The Balfour Formation is attributed to the lithological succession of the sandstone- mudstone ratio decreasing from the base to the top and a gradual decrease in topographic slope during orogenic loading (Catuneanu et al., 1998; Catuneanu and Elango, 2001). However, the Oudeberg-

Daggaboersnek and the Barberskrans-Elandsberg successions constitute the two megacycles. In terms of colour the components of the Balfour Formation consist of greenish-grey sandstone, greyish shale and very subordinate red mudstone. The Balfour Formation was divided by Johnson (1976) into four distinct zones based on lithological variation (Fig. 38). These zones are, listed from the base which is the oldest, to the top, which is the youngest, as follows: Oudeberg (Zone 1), Daggaboersnek (Zone 2)

Barberskrans and Elandsberg (Zone 3) and Palingkloof (Zone 4). Subsequent workers (Tordiffe,

1978; Visser and Dukas, 1979) as well as SACS, (1980) concluded that the five units recognized in

70 the Balfour Formation are separate lithostratigraphic members with the Palingkloof Member being overlain by the Katberg Formation.

Johnson (1976) Tordiffe (1978) Visser and Dukas (1979) SACS(1980)

Katberg Formation Katberg Katberg Formation Katberg Formation Formation

Palingkloof Zone 4 (Palingkloof) Elandsberg Elandsberg mudstone Elandsberg

Zone 3 (Elandsberg and Barberskrans Barberskrans Barberskrans Barberskrans) Boesmanskop mudstone Daggaboersnek Daggaboersnek Zone 2 (Daggaboersnek) Ferndale sandstone/mudstone

Zone 1 (Oudeberg) Oudeberg Oudeberg Oudeberg

Figure 38: Lithostratigraphic subdivision of the Balfour Formation according to various authors. The Barberskrans and Oudeberg Member are sandstone dominated. Modified after Katemaunzanga (2009).

Each of these members was also considered a lithostratigraphic unit by Hancox and Rubidge,(2001).

A lithostratigraphic unit is one which is unified by consisting dominantly of a certain rock type or combination of rock types, or by other distinctive lithological features which include colour, primary structure, mineralogy, geochemistry, etc. (Johnson, 1976). Each of the lithostratigrapic units that make up the Balfour Fromation is systematically described below from oldest to youngest.

71 MAXIMUM SUPERGROUP GROUP SUBGROUP FORMATION MEMBER LITHOLOGY THICKNESS (m)

Drakensberg Basalt, 1400 pyroclastic deposit

Clarens 300 Light grey White Sandstone Elliot Red mudstone 500 Sandstone Molteno Coarse sandstone

Grey & khaki shale 450 Coal measure K Burgersdorp Red mudstone TARKA-STAD Light-greyand red grey 1000 shale, sandstone Katberg Sandstone 900 B A E Palingkloof Red mudstone Light-grey sandstone 50 A Grey shale ADELAIDE Balfour Elandsberg Shale R U Siltstone 700 Sandstone F Barberskrans Light-grey sandstone Khaki shale O 100 O Daggaboersnek Grey shale R Sandstone 1200 Siltstone T Oudeberg Light-grey sandstone 100

O Grey & black shale Middleton Light-grey sandstone 1500 Red mudstone Koonap Grey sandstone 1300 Shale

Waterford Sandstone E Shale 800 C Fort Brown Shale 1500 Sandstone C Ripon Sandstone 1000 Shale A Collingham Grey shale 30 Yellow claystone WhiteHill Black shale 70 Chert Prince Albert Khaki shale 120

Dwyka Elandsvlei Diamictite, Tillite, 750 Shale

Figure 39: Lithostratigraphy of the Karoo Supergroup in the Eastern Cape Province which includes the Balfour Formation (After SACS, 1980).

72 5.2.1 Oudeberg Member

The Oudeberg Member is considered the base of the Balfour Formation and has a maximum thickness of approximately 100 metres (Johnson, 1976) (Fig. 39). This sandstone unit overlies the grey, black and khaki-coloured shales with subordinate sandstone and red mudstone of the Middleton

Formation (Tordiffe, 1978). It is regarded as a single sandstone only unit (Keyser, 1966), which consists predominantly of lenticular sandstone beds that are greenish-grey to light-grey in colour. The sandstones are massively bedded and planar laminated with erosional surfaces (Fig. 40). Massive bedding often grades into rippledrift cross-lamination and flat bedding in these sandstones. These features were also recorded by Tordiffe (1978). A transition across a few metres of thickness, grading from sandstone to siltstone, and finally to dark-grey shale was observed, constituting upward-fining sequences in the study area. The whole succession of the Oudeberg member is being complicated by a fault which causes duplication of strata resulting in a thickness variation of between 100 metres and

150 metres, but individual sandstone units have an average maximum thickness of 7–10 metres. A section with thickness of approximately seven metres is exposed in a road cut southeast of Adelaide along the R63 road to Fort Beaufort. Generally, the surface upon which the sandstones were deposited was undulating with scour channels. In addition, thin dark-green argillaceous units, approximately two metres thick, are often associated with the sandstones; these beds in many cases occur immediately above massively bedded sandstone and the sandstone sheets are overlain with varying intervals by grey siltstone. The sandstones often have an erosional base with channel lag material and disseminated mud flakes generally less than 0.5 centimetres thick (Figs 40 and 41).

73

Figure 40: Massive arenaceous unit overlain by horizontally laminated sandstone at the top of the

Oudeberg Member southeast of Adelaide along the R63 main road to Fort Beaufort.

Figure 41: Ripple-laminated sandstone of the Oudeberg Member reflecting unidirectional current flow.

74 5.2.2 Daggaboersnek Member

The Daggaboersnek Member has a maximum thickness of 1200 metres (Johnson, 1976; SACS,

1980). It is the thickest member in the subdivision of the Balfour Formation (Fig.42) and is characterised by a relatively lower amount of sandstone than shale and mudstones (Johnson, 1976).

Lithologically, it essentially consists of greyish subordinate sandstone alternating with dark-grey shale and mudstone, with the mudstones dominating in the succession. The sandstones are sub-tabular in shape and persist over a relatively long lateral distance of approximately 20 metres (Fig.42) and are characterised by cross-lamination and cross-bedding. These sandstones are also associated with greenish-grey to grey mudstone and are evenly stratified, sometimes displaying wave-ripple marks with regular lithosomes indicating deposition under uniform physical conditions of sedimentation over a given interval of time.

Figure 42: Typical view of Daggaboersnek Member sandstone alternating with mudstone layers and persisting over a relatively long distance along main road southeast of Adelaide.

75 5.2.3 Barberskrans Member

The arenaceous Barberskrans Member overlies the Daggaboersnek Member and is characterised by predominantly fine-grained sandstone with a total thickness ranging from 100 to 190 metres

(Tordiffe, 1978; SACS, 1980). In the field, a thickness of approximately 40 meters was observed on

Regopkloof northeast of Bedford town. A tabular and relatively thick sandstone outcrop of the

Barberskrans Member is found at a road-cutting east of Balfour (Johnson, 1976). The individual sandstones attain a thickness ranging from five to ten metres and are interbedded with thin greenish- grey mudstone, but Tordiffe (1978) recorded an individual average thickness of the sandstone unit ranging between six and twenty metres. The Barberskrans Member sandstone is a lens-shaped, arenaceous unit that can be used as a marker horizon for study by field observation (Johnson, 1976), also in the area mapped. The sandstone was recorded to vary from light-grey to greenish-grey and light brown in colour. This has been attributed to the nature of the clay matrix, redox environmental conditions in the depository as well as diagenetic effects. This colour change can also be seen in exposures along Nico Malan Pass (S32°55´73.6" E026°75´19.5") to the east of the study area. The sandstones are massive in places with some horizontal bedding, but often display tabular and trough cross-bedding (Fig. 43) and some ripple cross-lamination. Some are vertically displaced by dolerite sills. Ripple cross-laminations were seen in some sections and asymmetrical ripples are more dominant on the upper surfaces of the sandstone units.

76

Figure 43: Exposure of typical flat bedded and laminated Barberskrans sandstone with some incipient concretionary structures in road-cut beyond One Oak farm to the north of Adelaide

(S32°33´26.8" E026°08´34.7").

5.2.4 Elandsberg Member

The Elandsberg Member underlies the Palingkloof Member of the Balfour Formation (Coney et al.,

2007). It has an estimated maximum thickness of 700 metres (Johnson et al., 2006) and is a predominantly argillaceous unit. A thickness of 100 metres was observed around Koedoeskloof, along the Endwell road east of Adelaide town. The sandstone units are lenticular in shape and often characterised by trough cross-bedding at the base. Thick flat bedded units of greenish-grey mudstone containing three to five metres thick lenticular sandstone bodies often occur. In places, these outcrops display successions seen to be 20 to 40 metres thick. The mudstones also alternate with thin siltstone

77 and fine sandstone beds (Visser and Dukas, 1979). Generally, in the study area, the sandstone beds display mostly small-scale trough cross-bedding and horizontal bedding.

5.2.5 Palingkloof Member

The Palingkloof Member forms the uppermost part, or top, of the Balfour Formation and underlies the arenaceous Katberg Formation (Haycock et al., 1997; SACS, 1980; Smith and Ward, 2001;

Warren et al., 2006). This thin argillaceous unit that overlies the Elandsberg Member (De Kock and

Kirschvink, 2003) was deposited mainly by suspended load settling (Rubidge et al., 2000). It reaches a maximum thickness of 50 metres and is comprised mainly of red and maroon mudstone with subordinate thin units of sandstone (Smith, 1995; Groenewald, 1996; Warren et al., 2006). In the study area it consists of richly laminated maroon mudstone (Fig. 44) which makes it easily identifiable in the field as opposed to the dark-grey to greenish-grey mudstones of the underlying strata of the Elandsberg Member. The first appearance upwards of red mudstones in the Balfour

Formation marks the base of the Palingkloof Member (Botha and Smith, 2006) with the red colour suggesting prolonged periods of exposure after deposition and resultant oxidation. It is also characterised by the occurrence of subordinate siltstone units with prominent brown-weathering calcareous nodules (De Kock and Kirschvink, 2003). These have been identified as concretions rather than nodules. The concretions are composed of spherical bodies of material similar to that which forms the sandstone matrix, and are cemented by soft carbonate minerals. They grew with irregular shapes due to the restricted enclosing host rock. These concretions appear to be attributable to the action of organic decomposition which created a chemical environment conducive to the precipitation of calcite. The Palingkloof has poor exposure within the study area due to the fine-grained associations but, where observed, it typically displays massive to finely-laminated mudstones and

78 shale. The Palingkloof Member is very rich in fossils, particularly of the dicynodont Lystrosaurus, and therefore attracted the attention of many researchers. The Permo-Triassic (P-T) boundary has been placed within this part of the Karoo succession of South Africa. This P-T boundary has been assigned an elevation of 12–20 metres within the Palingkloof Member by Smith and Ward, (2001) and Collinson et al., (2006). Most authors, however, place the boundary at, or just above, the base of the Palingkloof Member (Smith, 1995; Retallack et al., 2003; Ward et al., 2005). The placement of this boundary is based on the vertebrate biostratigraphy (Gastaldo et al., 2005).

Figure 44: Typical exposure of red laminated mudstone of the Palingkloof Member indicated by the white arrow.

Occasionally, sections of siltstone, rich in numerous clay chip breccia lenses, can be seen. It is also characterised by the occurrence of laminated siltstone interbedded with massive mudstone (Haycock

79 et al., 1997; Smith and Ward, 2001; Gastaldo and Rolerson, 2008). The siltstone varies from dark- grey to olive grey in colour.

5.2.6 Katberg Formation

The Katberg Formation forms the lower part of the Tarkastad Subgroup of the Beaufort Group and overlies the Balfour Formation in the Eastern Cape Province with a preserved thickness of 900 metres

(Johnson, 1976; Catuneanuet al., 1998; Gastaldo et al., 2005). It is considered to be a braided river deposit (Hiller and Stavrakis, 1984; Groenewald, 1989 in Cairncross et al., 2005; Haycock et al.,

1997) that resulted from low-sinuosity river flow. Hiller and Stavrakis, (1984) and Warren et al.,

(2006) report a maximum thickness of 1000 metres. However, the true original thickness is unknown as the stratigraphic top of the Katberg Formation has been removed by erosion. A section of 50 metres is exposed along the Avondale road at Skelmkloof northeast of Bedford town in the study area. It is dominanted by arenaceous lithologies and characterised by stacked tabular sheets of fine-to medium-grained sandstones with subordinate red and greenish-grey mudstones. Large trough cross- bedded units are very common within the planar cross-stratified sandstones in which ripple marks commonly occur (Fig. 45). Extensive intraformational conglomeratic sandstone bodies are also common in the Katberg sandstone (Coney, 2005; Botha and Smith, 2006).

80

Figure 45: Stacked tabular sheets of fine- to medium-grained sandstones with subordinate red and greenish-grey mudstones of the Katberg Formation.

The sandstones of the Katberg Formation vary in colour from olive-green to greenish-grey and are distinguished from those of the Balfour Formation by the great abundance of stacked lenticular, arenaceous units.

5.3 Areal distribution of lithostratigraphic units Identification in the field and on aerial photographs of the various lithostratigraphic units underpins the geological mapping (Fig. 46). Sandstones in each member vary in thickness over a lateral distance of up to several hundred metres. Both outcrop- and microscopic scale differences, effective methods for identifying contacts, were applied to the mapping of the contacts between the various members of the Balfour Formation. This method involved the use of combinations of changes in lithologic properties and stratigraphic changes in architectural style. The lithostratigraphic units are commonly stratified and tabular in form, hence the contact between the different member units is either placed

81 where it is clearly identifiable or where contacts are recognized by a change in geomorphic expression in areas where outcrops are poorly exposed or absent. Tracing of the Palingkloof–Katberg contact within the area was particularly challenging due to lateral interfingering of the facies as well as the variable thickness of the former, it even being absent in places. Hence the stratigraphic assignment of the Palingkloof was based on the high proportion of green-grey sandstone above it and the fact that its red mudstone succession has an approximate maximum thickness of 50 metres in the area. The areal distribution of the various lithostratigraphic units is presented in Figure 46 using auxilliary field observation information and interpolating of the data using satellite images and air photographs. The Oudeberg Member has an areal distribution which extends from Olifantsbeen farm south of Adelaide to Plathus farm in the west and spread to Waterfall Farm in the north. The vicinity of Bedford and Adelaide is underlain by the Daggaboersnek Member. The Barberskrans Member covers a small area northeast of Adelaide to Bell-vue farm north west of Bedford while the

Elandsberg covers a much wider area from northeast of Adelaide to northwest of Bedford. The

Palingkloof Members outcrop in a narrow strip below the Katberg Formation in the northwestern extremity of the study area (Fig.46).

82

Figure 46: Geological map indicating each of the lithological units of the Balfour Formation in the study area.

83 CHAPTER SIX

SEDIMENTOLOGY OFTHE BALFOUR FORMATION

6.1 Introduction

Sedimentological study gives insight into the physical processes by which the sediments were generated and provides a basis for interpreting depositional environmental subdivisions of the various members. Stear, in 1978, was one of the first to study sedimentological aspects of the sandstones of the Balfour Formation and to interpret their features (Stear, 1980). Each of the members is associated with a unique sedimentary facies on a small scale. The term „facies‟ was introduced by Nicolas Steno in 1669 and different geologists have used it in different ways (Tucker, 2001). In this study, a facies is a restricted part of the stratigraphical unit which exhibits characteristics significantly different from other parts of the unit and is ascribed to depositional features which characterise a particular depositional process or set of processes. Individual facies of each of the members are described according to the Miall (1977), Miall (1995), Bordy and Catuneanu (2000) and Bordy et al. (2005)

(Table. 11). Finally, the facies dimensional relationships of the architectural elements compiled, are further used to interpret the depositional environment. These facies relationships are summarized in

Table 12.

6.2 Lithofacies

Cycles of sedimentary strata in the vertical stratigraphic successions display the related depositional processes. Eight types of facies are associated with the sediment deposition (Table 11). The lithofacies of the members are described in terms of the sediment itself, the depositional processes

84 and depositional environment (Tucker, 2001). The lithofacies within the Balfour Formation are discussed below.

Table 11: Lithofacies description code of the Balfour Formation (modified after Bordy and

Catuneanu, 2003 and Bordy et al., 2005).

Facies Facies Sedimentary structures Code

Sm Massive sandstone Massive beds, laminated beds

Horizontally stratified Horizontal lamination. primary current Sh sandstone lineation

St Trough cross-bedded sandstone Massive with faint lamination

Ripple cross-laminated Sr Fine grained with ripple marks sandstone

Solitary, or groups of, planar cross- Sp Planar cross-bedded sandstone beds

Horizontally laminated Fl Fine lamination, very small ripples mudstone and siltstone

Massive with silt and clay Fsm Massive mudstone or siltstone grain-size

6.2.1 Oudeberg Facies

The Oudeberg Member is a greenish-grey sandstone-dominated unit interbedded with siltstone and mudstone. The outcrops are laterally extensive with maximum thickness in excess of 20 metres (Fig.

47). The facies is characterised by massive bedded sandstone with sub-horizontal and sharp external erosion surfaces at the base (Fig. 48A). This massive bedded sandstone appears to be homogeneous with lack of internal structures. Generally, the erosion surfaces occur in asymmetrical channel fills 85 and minor erosional surfaces are seen with the bedding. The strata also contain mud-drapes but in some places the mud-drapes are rare within the unit. The massive bedding is followed by planar bedding (Sp) which is an indication of laminar flow (Fig. 47a). There are a few undulating bedding planes that indicate turbulent flow, associated with irregular or random components of fluid motion during deposition. The mudstones contain nodules with no preferred orientation and shape and some micro cross-lamination at the base (Fig. 48B).

A B

Sp Sh

Sh

Fl Sm

Figure 47: Oudeberg sandstone facies. (A) – Medium-grained sandstone with alternating siltstone and mudstone of approximately 10 metres thick along the Adelaide road (S32°56´22.0"

E026°63´25.9). The facies surface indicated by red dashes shows an erosional surface. The white arrow indicates a mud drape and the portion between the white lines shows grey parallel-laminated alternating siltstone and mudstone. (B) – Massively bedded sandstone with an erosional base grading into fine-grained sandstone with some symmetrical ripple forms at the top.

86 A B

Sm

Figure 48:(A) – Three metres thick massively bedded sandstone in the Oudeberg Member.(B) –

Some small nodules formed by contact metamorphic effect of nearby dolerite intrusion near the base of the Oudeberg Member, S32°45´07.5" E026°47´07.0".

6.2.2 Daggaboersnek Facies

The Daggaboersnek Member is the thickest lithostratigraphic subdivision in the Balfour Formation with a total maximum thickness of 1200 metres. It is characterized by alternating shale and siltstone with very subordinate amounts of greyish sandstone. Individual facies vary from approximantly two metres to ten metres in thickness at different localities. It is mostly dominated by tabular (planar) bedding, with planar cross-bedding (Sp) (Fig. 49) and trough cross-bedding (St). Ripple marks, which are cross-lamination structures, are fairly common in places (Fig. 50), and parting lineation is well developed in the sandstone units. Planar cross-stratification arises from straight-crested dunes

(Bridge, 1984), although they are modified by erosion and deposition. Cross-bedded sandstones can be formed either by filling of scour pits and channels or by deposition on point bars of meandering 87 streams; cross-beds are mostly more than five centimetres thick. Channel fills and point bars are the most conspicious features associated with the sandstone, with their scale varying considerably within this facies. The facies forms the upper part of a fining-upward megacycle of which the Oudeberg facies forms the coarser basal part. Thinly laminated (Fl) rhythmites of alternating mudstone and sandstone units characterise the Daggaboersnek facies and are an indication of distal floodplain deposits (Johnson et al., 2006). Thin sandstone beds comprised of cross-laminated or planar- laminated zones as thin as 10cm are common near the base of this facies. Fine-grained sandstone and siltstone in the Daggaboersnek mostly contain ripple marks that are either symmetrical or asymmetrical, with asymmetrical ripples being the most dominant (Fig. 50). The presence of ripples and cross-lamination is principally a feature of sand-graded sediment (Collinson and Thompson,

1982). Sedimentary structures associated with this facies suggest meandering stream deposits with extensive floodplains (Catuneanu et al., 1998). There are no mud drapes in this facies, hence the presence of the locally derived intraformational conglomerates is an indication of a depositional system in which the streams/rivers often deserted their channels (Bordy and Catuneanu, 2003).

This succession is interpreted as a river deposit, with sharp-based sandstone lenses containing wave ripples and cross-lamination and interbedded with fine-grained siltstone. The type of deposition associated with this facies resulted from both bedload and suspension load processes (Cairncross et al., 2005).

88 St

Fl

Figure 49: Horizontal and trough cross-bedded sandstone along the R63 main road from Adelaide to

Bedford. S32°59´75.0" E026°67´74.3".

Figure 50: Upper bedding surface of sandstones showing micro cross-lamination traces (Left) and ripple-lamination (Right). These sedimentary structures are the most common palaeocurrent indicators in outcrops in the Balfour Formation, especially in the Daggaboersnek facies.

89 6.2.3 Barberskrans Facies

This facies is a thick-bedded fine-grained sandstone unit interbedded with mudstone. It was also described as a multistoried sandstone unit (Johnson, 1976; Katemaunzanga, 2009) which is characterised by lithofacies of well-developed flat-bedded or horizontal stratified sandstone (Fig. 51), also referred to as parallel lamination. On the bedding plane surface one finds ripple cross-lineation and some ripple marks (Fig. 52) which confirm the fluviatile nature of the Barberskrans facies. The flat-bedding is inferred to be a product of lower energy flow conditions or the deposition of sand

(Collinson and Thompson, 1982). There are also some unlaminated beds that are lenticular in vertical sections. Lamination may be destroyed by intense reworking of the sediment by organisms or by physical disruption due to liquefaction and movement of the sediment while it is still in a waterlogged state. Lack of lamination may also imply rapid deposition from suspension, most probably by the deceleration of heavily sediment-laden currents (Boggs, 2006). These facies attain a thickness of several metres. The facies is also associated with thick massive cross-bedded interbeds with thin mudstone in some areas. The dimensions of individual trough sets range from a width of 2.5metres to

10 metres. Large-scale trough cross-beds are present at the base of the sandstone units. This is the result of migration of dunes or megaripples with sinuous crestlines (Collinson, 1978 in Rubidge et al.,

2000). It is a fining-upward cycle where the sandstone is capped with mudstone of facies Fl and Fm.

90

Sh

Sp SP

Sp Fsm m Sr

Figure 51: Barberskrans sandstone facies in roadcut to the north of the town of Bedford with lenticular alternating sandstone–siltstone deposits in a laterally persistent section of a high-sinuosity channel sandstone of the Barberskrans Member,. S32°32´28.4" E026°06´59.4"

Figure 52: Ripple cross-lamination (Left) and plan view ripple marks (Right) occuring in

Barberskrans sandstone.

91 6.2.4 Elandsberg Facies

The Elandsberg Member consists of subordinate thin lenticular sandstone units alternating with mudstone (Fig. 53) and is very similar to the Daggaboersnek Member lower down in the succession.

It is distinguished from the Barberskrans facies by its high content of grey mudstone and abundance of near planar erosion surfaces. The subordinate sandstone occurs as well-developed, massive to ripple-laminated or trough cross-bedded units with very fine to medium grained textures, while mudstones display both massive and finely laminated facies.

Sp Fl

Fl Sp Sp

Figure 53: Sandstone alternating with thin mudstone facies of the Elandsberg Member. The white arrow points to a mudstone unit while the red arrow shows a sandstone-rich unit, S32°32´29.6"

E026°07´00.2".

92 6.2.5 Palingkloof Facies

The Palingkloof Member comprises argillaceous rock that consists predominantly of red-brown to pale-red mudstone and subordinate siltstone (Fig.54). The facies is characterised by flat-laminated mudstone and siltstone, which gives indication of a low-energy fluvial system. The facies also contains subordinate minor amounts of sandstone (Rubidge et al., 2000) which are inferred to have been deposited in a semi-arid climate (Smith, 1995; Groenewald, 1996). The sandstone units often display ripple cross-lamination.

Fl

Fm

Figure 54: Argillaceous red mudstone facies of the Palingkloof Member in the study area.

6.2.6 Katberg Facies

The Katberg Formation is dominated by arenaceous lithologies with subordinate argillaceous layers.

The lithofacies is characterised by horizontal laminae, ripple cross-lamination, planar bedding, and planar and trough cross-bedding (Fig. 55). This facies is characterised a product of fluvial sedimentation (Zielinski and Gozdzik, 2001). The trough and tabular cross-bedded units often are 93 very large scale (Fig. 56) ranging from two to ten metres thick and 10 to 20 metres wide. The dip direction of the cross-beds ranges from 300°–50°. This sandstone facies is interpreted as having resulted from channel infill by a major braided stream system. The horizontally laminated fine- grained sandstone and siltstone units which are composed of the argillaceous layers often are a few decimetres thick.

Sh Sh Sp

Sm

mud drapes

Figure 55: Representative facies of the Katberg Formation. The arrow shows mud drapes and the dashed lines separate channel fill deposits of a braided river system.

In general the facies architecture of vertical profiles of the Balfour Formation is fining-upward, showing a gradual decrease in flow energy. The sandstone architectural assemblage is associated with isolated channel fills and channel bars, but within the sandstones minor scour and fill structures bounded by sharp straight to sub-horizontal and concave-up internal erosional surfaces also occur.

94

Figure 56: Oblique view of a large-scale trough cross-bedded unit of Katberg sandstone.

S32°18´58.3" E026°11´13.8". The structure is composed of cross-laminae, nearly parallel to current direction in medium-grained sandstone of the Katberg Formation.

6.3 Conditions of deposition of the Balfour Formation

Studies of the lithostratigraphy of the Karoo Basin in the Eastern Cape Province by previous investigators (e.g., Johnson, 1976; Tordiffe, 1978; Visser and Dukas, 1979; Rubidge et al., 2000;

Catuneanu and Elango, 2001; Katemaunzanga, 2009) have contributed meaningful interpretation of its sedimentological environment and provenance in the regional reconstruction of the sedimentology of the Balfour Formation. The principal depositional environment of the Balfour Formation in the

Eastern Cape Province can be attributed to a large continental fluvial system. This fluvial succession is dominated by flood-plain deposits where the mudrocks are laterally continuous, with some subordinate sandstone bodies (Smith and Ward, 2001). The sandstone bodies include crevasse splay, levee and point bar deposits. Internal geometries and structures include fluvial cross-bedding, planar beds and ripple marks which characterise it as the product of depositional processes of fluvial systems that prograded into the Karoo basin. The depositional environment of the Balfour Formation varies 95 from a meandering river system to a shallow braided environment. This observation suggests shallow sandy river sedimentation under dry climatic conditions for the latter (Groenewald and Kitching,

1995 in Catuneanu et al., 1998; Groenewald, 1996; Haycock et al., 1997; Hiller and Stavrakis, 1984;

Smith, 1995). The braided environment appears to be less widely distributed in the Balfour Formation and it is mainly found within the overlying Katberg Formation. The presence of ripple marks indicates that shallow water environments were involved, although ripples are not common in the bedforms of all members. It was observed that sandstone units are often separated by hiatuses, which gives an indication of minor interruption in sedimentation. The Balfour Formation consists of fining- upward sequences with erosively-based sandstones formed by lateral accretion at the bottom which grade upward into siltstone or mudstone. Individual alternating sandstone units reach a maximum thickness of two metres and display traction structures such as horizontal lamination (Fl) and small- scale cross-bedded and trough cross-bedded sandstone (St) which demonstrates that the deposition was a fluvial process. The Oudeberg and Barberskrans Members, which are relatively thin, are very persistent and represent pulses of uplift in the source area during the Cape orogenesis, while the

Daggaboersnek, Elandsberg and Palingkloof Members represent deposition associated with inactive tectonic loading.

96 Table 12: Summary of the architectural elements of the members in the Balfour Formation

Member Facies Sedimentary structures Interpretation

Katberg Sm,Sh,Sr,Sp, Channel fill, and point bar. Transverse bedforms or linguoid dunes or Formation St. straight-crested or waning flow deposits. muddrapes

Palingkloof Fl, Fsm Massive, planar and laminated Drape deposit or, less frequently, lower beds. flow regime deposit.

Elandsberg St, Sm,Sr Sandy bedforms, silt and clay Sedimentd eposit or sinuous crested. grain-size class.

Barberskrans St, Sp, Sr Sandy bedforms with silt and Sediment deposits, sinuous crested clay grain-size classes. indicating lower flow regime deposits.

Daggaboersnek St,Sp, Sh,FL Channel fill, point bars and ripple Overbank and/or waning flow deposits in marks. standing water bodies or abandoned water courses at lower flow regime deposit.

Oudeberg Sm, Sp,St, Channel fills, channel bars, and Sedimentary gravity flow from either sandy bed. upper or lower flow regime deposits or deposits from hyperconcentrates. Lag deposits or, less frequently, intraformational breccia at the base of sandstone units.

97 CHAPTER SEVEN

PROVENANCE OF THE BALFOUR FORMATION

7.1 Introduction

The objective of provenance studies is to determine the position and the constituents of the source area, particularly to reconstruct and interpret the predepositional history of the sediments from the initial erosion of parent rock to the final burial of its detritus (Anderson and Worden, 2006; Juboury,

2007; Weltje and Eynatten, 2004). The character of the source area is deduced from properties of its sediment yield (Pettijohn et al., 1987). There is a combination of genetic factors including the petrographic nature of the source rocks, tectonic and climatic conditions in the source area, size dispersion of sediment grains and influence of distributing agents (Boggs, 2006). It involves all factors related to the production and composition of sediment with specific reference to the composition of the parent rocks, including information from mineralogy, geochemistry and palaeocurrent measurements. The mineralogy of the sediment and palaeocurrent data provide the main evidence that can reveal the nature of the lithology and the position of the source area (Johnson,

1976). The combination of petrography and geochemical data of sedimentary rocks can also reveal the source regions, the tectonic setting of sedimentary basins and palaeoclimate conditions

(Jafarzadeh and Hosseini-Barzi, 2008).

7.2 Sandstone petrography

The kinds of siliciclastic minerals and rock fragments preserved in sedimentary rock provide very important evidence on the lithology of the source rock. Clastic detrital components preserve detailed information on the provenance and the pattern in which the sediment was transported, especially

98 where the present geological setting has little or no resemblance to the original setting whence the strata were deposited over a long period of time (Dickinson, 1988). Clastic sedimentary rocks also contain important information for interpretation of both compositional tectonic setting and evolution of continental crust (Liu et al., 2007) which can be linked to the depositional environment. Several attempts have been made by researchers to refine the image of the provenance of the Balfour

Formation, albeit in a regional context. Generally, the rock frameworks are all very similar in terms of mineralogy and grain size throughout the Balfour Formation. There are no petrographic variation trends in the composition of the sandstone sequence of the Balfour Formation indicating that there was no significant change in the source terrane (Catuneanu and Henry, 2001; Coney, 2005). It ranges from medium to fine grained detrital preserves and the major framework of the sandstone used for the provenance interpretation is described below.

Quartz

Quartz, which is a dominant mineralogical component of the sandstone, plays an important role as a provenance indicator. Its abundant occurrence reveals that the sediment was derived mostly from acid igneous rocks, gneisses and older sandstone sedimentary rocks. The abundance of monocrystalline quartz grains that commonly contain inclusions and fewer polycrystalline grains present in all the samples suggest a plutonic origin (Basu et al., 1975). Quartz grains display sweeping patterns of extinction as the stage is rotated between crossed polarizers with the petrographic microscope; this is a further indication that the quartz grains have possibly been derived from plutonic rock (Boggs,

2006).

99 Feldspar

Feldspar is also important as a source rock indicator. The presence of more plagioclase than K- feldspar indicates abundant granite in the source area. Most feldspathic sandstones are derived from granitic-type primary crystalline rocks such as coarse granite or metasomatic rocks (Boggs, 2006).

The Balfour sandstone contains a predominant abundance of plagioclase. The alteration/modification of the feldspar as observed in the petrographic study can be related to more rapid deposition and shorter transportation of the sediments of the Balfour Formation.

Lithic fragments

The rock fragments in the sandstone consist mainly of igneous and volcanic rock types. It is an indication that the source area contains a prominent constitutent of intermediate to felsic volcanics

(Tordiffe, 1978).

Accessory minerals

Heavy minerals are high-density mineral constituents of siliciclastic sediments which are very useful in determining provenance source areas (MacDonald et al., 2009). They are indicators of sediment source rock types as different kinds of source rock yield different suites of heavy minerals (Boggs,

2006).Within the heavy concentrates of the sandstones of the Balfour Formation, the main heavy minerals are apatite, biotite, garnet, epidote, rutile, haematite, tourmaline and zircon with some subordinate opaques such as ilmenite and magnetite, indicating alkaline igneous source rocks. In order of abundance, the heavy mineral assemblage is charaterised predominantly by zircon, followed by garnet (pyrope and almandine according to colour), epidote, staurolite and tourmaline. According to Diskin et al., (2010) the presence of garnet indicates derivation from a sediment source evolving from a region of higher to lower grade metamorphism. The appreciable amounts of abraded zircon,

100 garnet, tourmaline and rutile in the heavy residue of the sandstones suggest derivation from pre- existing arenaceous rocks and the presence of micas are an indication of metamorphic as well as plutonic igneous source rocks (Boggs, 2006). In places the sandstone is very rich in biotite which, according to Tucker, (2001) suggests the source to be nearby older biotite gneisses.

Sediment grain Size

The sediment grain size also plays a vital role in the interpretation of the provenance of the Balfour

Formation. It can be used to determine degrees of weathering and alteration of the minerals as a tool for interpreting the climate and relief of source areas (Tucker, 2001). The amount of physical alteration of the grains, especially the quartz and angular feldspar grains, suggests derivation from a low-relief source rock area, which might have caused the grains to be eroded slowly, and hence to be affected by extensive weathering. Irregular angular size of the quartz grains and roughly equidimensional form in the sandstone suggest a granitic source area (Boggs, 2006). The contribution of quartz grains in large quantities to the sandstone and their angular to subangular shape as well as the moderate amount of feldspar suggest intensive reworking. However, the fine-grained matrix suggests possible material of volcanic origin.

The tectonic discrimination source of the sandstone from all the various members of the Balfour

Formation can be deduced from the ternary diagram plot of the Qm-F-Lt (Monocrystalline Quartz-

Feldspar-Lithic fragments) content (Fig. 57) after Dickinson et al. (1983).

101

Figure 57: Sandstone modal data plot for the Balfour Formation on the Qm-F-Lt diagram of

Dickinson et al. (1983) as also used by Johnson (1991) and Haycock et al. (1997). Qm

(Monocrystalline quartz); F (Feldspar); Lt (Lithic fragments).

The circle shows plots of sandstones from the Balfour Formation while outside the circle are sandstone plots for the Katberg Formation. Most of the sandstones plot in the transitional arc region, a result resembling Johnson‟s (1991) for the Balfour Formation, with a few plotting in the dissected arc area demonstrating uniformity of the sandstone composition throughout the succession. The source of the sediments is seen to suggest either an uplifted terrain of folded and faulted strata from which has been derived recycled detritus of sedimentary and meta-sedimentary origin (Dickson and

Suczek, 1979; Boggs, 2006).

102 7.3 Sandstone geochemistry

The major-element concentrations of the Balfour sandstones reveal relative homogeneity of their source. Generally, the sandstone is enriched in SiO2 which is characteristic of a homogeneous source enriched in silica. Presence of SiO2 in excess of 70% implies that the sandstones are rich in silicate minerals derived from a silica rich provenance. This suggests a highly weathered granite-gneiss or pre-existing sedimentary terrane (Rahmani and Suzuki, 2007). The K2O/Na2O ratio can be used as a chemical provenance indicator. High K2O/Na2O ratio reflects derivation from granites. This can also be inferred from the presence of illite and kaolinite as identified with X-ray diffractometry. The low value of the TiO2 concentrations suggests an igneous origin. Low value of TiO2 compared to the high

Al2O3 value indicates a felsic source.

Most suitable elements for provenance determination include, Ba, Co, Hf, Sc, and Th due to their relatively low mobility during weathering, transportation, diagenesis and metamorphism, while the most useful immobile trace elements include Co, La, Nb, Sc, Th, Ti and Y (Bhatia and Crook, 1986).

The ratio of both incompatible and compatible trace elements is useful for identifying the source rock

(Nyakairu and Koeberl, 2001). Thus, the high Ba/Co ratio which ranges from 40.5 to 183 suggests that the sediment was derived from weathered granitic sources. The enrichment of the following trace elements such as Nb, Hf, Th, Y and Zr in the sandstone suggests a felsic source. Barium concentration is controlled by clay minerals and mica, hence the derivation of the sediments could be from a highly weathered granite-gneiss terrane and/or from a pre-existing sedimentary terrane. Low

Cr and Ni values may suggest very little or insignificant basic input from the source rock. The Cr/Ni ratios vary from 2.87 to 5.94; this indicates that mafic rock is most likely to be more widespread than ultramafic rocks in the source area. Th/U ratio ranges from 0.99 to 1.90, indicating limited weathering or high sediment recycling in the source area.

103 Tectonically, the sediments of the Karoo Basin represent a retro-arc foreland basin setting that were deposited due to the orogenesis in the Cape Fold Belt prior to Gondwana break-up (Johnson, 1991), hence the Karoo is situated behind a magmatic arc and is associated with that fold thrust belt (Cape

Fold Belt). The bulk of the Balfour Formation sediments in the southern foredeep part of the basin was derived from a transitional to dissected arc (fig. 59), although the source of the Beaufort Group sediments, which include the Balfour Formation, has been attributed to Archaean granite (Theron,

1975 in Bordy et al., 2004; Cole, 1992 in Bordy et al., 2005). The sandstones contain very little sedimentary lithic fragments, indicating that the sediments did not have much of a recycled orogen provenance (Rahmani and Suzuki, 2007). Low MgO and relatively low MnO contents also confirm this genetic observation.

Statistically, the average quartz content is 45.9% with proportionately less Qp than Qm respectively and the rocks contain more plagioclase than potassium feldspar; rock fragments indicate igneous and metamorphic sources (Boggs, 2006). The garnet is often fractured, indicating a relatively short transportation distance.

7.4 Palaeocurrent pattern analysis

Palaeocurrent analysis is one of the most powerful tools for obtaining information on the local or regional direction of sediment supply and on the geometry of lithologic units (Miall, 1984). It can also be used to determine the directional variability across a stratigraphic unit and the sinuosity of the palaeochannels (Le Roux, 1992) as well as possible denudation trends and sediment dispersal patterns

(Bordy and Catuneanu, 2003) within the Balfour Formation. It can be used effectively to determine the locality of the provenance of the Balfour Formation and the position of the sediments relative to their source.

104 The palaeocurrent investigation was conducted across the various sandstones members as well as subordinate sandstones in the dominantly argillaceous units of the Balfour Formation (Table. 13).

Ripple marks were mostly present at the tops of the beds and this is an indication that sediment deposition must have taken place below wave base (Johnson,1976). Palaeocurrent directions were measured on current ripples, trough cross-lamination, micro cross-lamination and primary current lamination. Other palaeocurrent indicators, such as groove marks, flute marks and gutter casts were not observed. Symmetrical ripples are most common in the Daggaboersnek Member. The palaeocurrent features were seen in the sandstone rich units. Micro cross-lamination has the tendency to represent local current flow directions since they are generated by less unimodal currents (Bordy et al., 2004). In some areas ripple marks are not present at all, which may be due to erosion or deposition that took place very rapidly during migration. A total of seventy-eight palaeocurrent measurements were recorded in the field, with a minimum of ten palaeocurrent readings per locality in accordance with the requirement determined by Cole and Wipplinger (2001), but due to poor exposure and erosion at one of the outcrops, fewer than ten readings were recorded there, for the calculation of statistical values and palaeocurrent plots of the rose diagrams. The use of rose diagrams is useful for providing a visual perspective of directional variation. It also is one of the most suitable devices for the detection and representation of bimodal (Fig. 58) and polymodal variation patterns

(Fig. 59) as also confirmed by Johnson, (1976). Palaeocurrent measurements reveal unidirectional current patterns (Figs. 58 and 59). The analysis of the palaeocurrent measurements shows some distinct variations of the sediment supply pattern amongst the various lithostratigraphic members of the Balfour Formation. Palaeocurrent data indicate that the bulk of the sediments was derived from a source area situated to the southeast of the Basin and that the major river system transporting the sediment was flowing mainly to the northwest.

105 Table 13: Summarized palaeocurrent data localities for the members across the Balfour Formation

Member Longitude Latitude sedimentary n mean circular standard structures vector(µ°) deviation (°) Oudeberg S32°51´29.8" E026°08´58.1" MXL, PCL 10 327 10.8 Oudeberg S32°50´54.3" E026°21´08.2" MCL 13 303 30.0 Daggaboersnek S32°40´32.0" E026°01´52.7" MXL, PCL 10 325 36.5 Daggaboersnek S32°35´35.5" E026°15´27.8" MCL 10 346 27.4 Daggaboersnek S32°37´24.7" E026°01´19.6" MCL 5 338 9.8 Barberskrans S32°29´13.7" E026°02´15.5" MCL, PLC 10 286 19.8 Barberskrans S32°33´12.3" E026°07´47.0" MCL 10 337 24.5 Elandsberg S32°23´54.8" E026°04´23.2" MXL 10 313 26.1

The palaeoflow measurements give consistent results for individual members but show fairly different patterns from one another. Daggaboersnek Member displays numerous wave ripples oriented NE to NW and this suggests deposition in a fairly extensive inland sea (Johnson et al.,

2006). The vector mean consists of the means of each palaeocurrent variable and the variance. It represents the most satisfactory estimator of central tendency for directional data (Johnson 1976).

106

Barberskrans sandstone Elandsberg sandstone

Oudeberg sandstone Daggaboersnek sandstone

Figure 58: Paleocurrent directions of sandstone units in the Balfour Formation. The arrows indicate the vector mean directions.

107

Figure 59: Summary of palaeocurrent plots of sandstones across the Balfour Formation succession in the study area in the Eastern Cape province.

108 CHAPTER EIGHT

OVERVIEW

8.1 Introduction

This overview is based on all the data collected and observations made during the study. It is central to interpreting the sedimentary environment and provenance of the Balfour Formation, which was one of the main objectives of the investigation. The discussion is also supported by literature reviews from which it was clear that only scant significant work had been undertaken on the Balfour

Formation in the past. Choice of methods used for the study was based on the objectives, the accuracy required and on the available budget. Data obtained with study of the sedimentary rocks, their sedimentary structures and the processes involved, contributed to the knowledge required for interpreting the sedimentary environments and provenance of the Balfour Formation. The nature of the framework grains in the sandstones and the secondary influences such as weathering and transportation processes were considered for interpreting the sedimentary structures. History of the sedimentation was also related to the environments that determined the palaeo-current patterns. The investigation promoted a more detailed understanding of the sedimentary rocks in the Balfour

Formation in terms of their environments of deposition, the spatial relationships of the structures and the sediment distribution processes. Investigation of the framework mineralogy of the sandstone provided first-hand knowledge of the mineralogical composition as well as information on the depositional environments. Some detailed sedimentological descriptions were also undertaken; these include various depositional facies and sedimentary structures.

109 8.2 Discussion and conclusions

Petrographic evidence from the sandstones of the Balfour Formation shows a relatively high quartz contentin conjunction with abundant feldspar grains, while the heavy minerals suggest derivation of the sediment from igneous rocks, gneisses and older sedimentary rocks. It also is an indication that the source was composed of crystalline rocks and contained second- to third-cycle sediments directly derived from older crystalline igneous or metamorphic rocks. A low percentage of lithic fragments is also present which implies that either the source rock was highly weathered or recycling of the grains took place.

The sandstones are comparatively moderately well sorted to poorly sorted throughout the various members and generally show a fining-upward trend. They indicate a progressive decrease with time in the average grain size of the sediment load transported by the river system depositing the Balfour

Formation. The general morphology of the grains ranges from angular to subangular and occasionally subrounded, the latter indicating that sedimentary rocks in the source area had been recycled. Based upon this observation it is deduced that the transportation distance from the provenance was rather short and the major mechanism of transportation was by river systems. This also revealed that the sediments are both physically and chemically immature and indicate signs of reworking. The reworked Karoo sedimentary rocks are believed to have originated from reworking of older Karoo

Supergroup rocks and Cape Fold Belt lithologies (Catuneanu et al., 1998). Poor sorting of the grains is a further indication of the sediment having been transported by a fluviatile system (Boggs, 2006).

Based on detailed petrographic investigation, the sedimentary rocks in the Balfour Formation consist of siliciclastic (terrigeneous clastic) detritus and can be classified as either feldspathic litharenites or ultralithofeldspathic sandstone and a few as lithofeldspathic. Siliciclastic sediments are a reflection of weathering processes in the source area (Tucker, 2001) with the Balfour sediments having originated 110 mainly from a chemical and physical breakdown weathering process of igneous, metamorphic or older sedimentary rocks. There is every indication that the sandstones have been affected by diagenesis which, inter alia, can be seen by the alterationof the feldspars and of quartz overgrowths and the high percentage of matrix.

Petrographic and bulk-rock geochemistry shows that there is little change in the sandstone composition as confirmed by the major- and trace-element concentrations througout the Balfour sandstone succession revealing the relative homogeneity of their source. The most notable feature of the geochemical signature is the high SiO2 content with an average of 72.74%, followed by Al2O3 with an average of 13.90% and low contents of Fe2O3+MgO (3.87%) and TiO2(0.44%), which can be attributed to the high quartz content and correspondingly low content of mafic components which complements the petrographic observations, although SiO2 is also associated with feldspar and clay minerals (Ward et al., 2005). High amounts of Al2O3 reflect the presence of clays and subordinate mica in the sandstone (Banerjee and Banerjee, 2010). The enrichment in Al2O3 is also atributed to the alteration of rock during weathering in the source area resulting in the depletion of alkalis and alkaline earths (Cingoani et al., 2003). Content of K2O is attributed to the presence of common potassium feldspar (orthoclase and microline) and mica with the source of Na2O being principally related to plagioclase feldspar (Banerjee and Banerjee, 2010). The values of K2O are low, ranging from 1.03% to 2.97%, as compared with the high value of Na2O which ranges from 0.91% to 5.65% and confirmed the higher plagioclase than K-feldspar content. Low MgO and high SiO2 content reflect melting of an unusual iron-rich mantle source region (Johnson et al., 2006). Opaque minerals and rutile are the main sources of Ti2O (Juboury, 2007; Banerjee and Banerjee, 2010) and the low value of Ti2O relates to the small amounts of opaque minerals in the sandstone. The small amount of

CaO and Na2O indicates low carbonate components. Iron content is related to the abundance of iron

111 oxides in the heavy minerals and partly to the presence of iron in the clay minerals. Some iron may be contained in calcite cement in sedimentary rock in general. The concentration value of the transition elements which include Cr, Co, N and V are strong indications of a granitic source. Fairly high content of Cr may be associated with disseminated magnetite which is an indication of mafic to ultramafic source rocks (Boggs, 2006) and Ni and Cr content suggesting absence of basic source.

High Sr content is attributed to either low-temperature depositional environments or to the weathering of feldspars, particularly plagioclase. The Th/U ratio is an indication of the intensity of the weathering in the source area and/or sediment recycling (Rahmani and Suzuki, 2007). The ratio of

Zr/Sc increasing substantially with accompanying decrease in the Th/Sc ratio indicates that the sediment was derived from a passive margin region (McLennan et al., 1983). Th/Sc ratio, which ranges between 0.99 and 1.9, suggests that the sediments were homogenised by sedimentary recycling and, with an average of 1.47ppm, reflects input from fairly evolved crustal igneous sources

(Cingolani et al., 2003). The abundance of Ba, Cr, Th and U suggests that the concentrations of the trace elements are controlled by clay minerals and mica (Rahmani and Suzuki, 2007). This further suggests that the derivation of the sediments could have been from a highly weathered granite-gneiss terrane and/or from a pre-existing sedimentary terrane. The presence of zeolite which is diagenetically generated and smectite as well as the presence of other clay minerals may be a result of the decomposition of feldspar and other aluminium silicate minerals, the zeolite possibly being an indication of avolcanic source rock. Smectite values also give an indication that the iron content in the clay minerals is very small, as seen from the results of major-element analyses. Chemical Index of

Alteration values of the sandstone, which range from 62% to 67%, suggest moderately weathered sources and a relatively warm climate. The CIA analysis shows that the source area was subjected to weathering processes, but with low intensity, hence the sandstones were likely derived from a slightly-weathered terrane. Alteration of feldspar and mica to clay minerals, as determined with the 112 geochemical investigation, strongly suggests that the original modal composition was modified during the diagenetic processes. Therefore, the high SiO2 content, the CIA values and low iron oxide concentrations indicate weak structural deformation in the source area (Liu et al., 2007). However, the sandstone plots in the transitional arc area according to the model of Dickinson et al. (1983). The source of the Balfour Formation sediments, therefore, was an uplifted terrane of folded and faulted strata from which had been recycled detritus of sedimentary and metasedimentary origin. This confirms Johnson‟s (1991) classification of the Balfour Formation.

The fining-upward trends of theBalfour Formation succession indicate rapid erosion of a fast-rising orogen (Catuneanu et al., 1998; Rahmani and Suzuki, 2007) and pulse of sedimentation as a result of mountain-building episodes in the Cape Fold Belt (Catuneanu et al., 1998; Catuneanu and Elango,

2001). These fining-upward sequences are repeated throughout the succession and can be traced both laterally and vertically, despite the current fluvial processes having removed parts of the succession leaving erosional gaps in the area. The sandstone ranges in colour from greenish and light greyish to khaki grey with medium to fine-grained stacks of multiple sandstone beds that often are separated by numerous erosion surfaces interbedded with dark shale. Red mudrocks in the Palingkloof Member are due to the presence of finely divided haematite and reflect subaerial deposition under oxidising conditions. The presence of red mudstone also reflects warm conditions with alternation of wet and dry seasons and the Palingkloof is overlain by the light-grey sub-horizontal laminated sandstones of the Katberg Formation. Tordiffe (1978), however, states that red mudstones do not occur in the

Balfour Formation or in the Palingkloof Member for that matter. The greyish colour in argillaceous units reflects deposition in a reducing environment (Reineck and Singh, 1975).

The base of the Balfour Formation is a massive sandstone lithosome of the Oudeberg Member and the Daggaboersnek Member is characterised by regular, generally non-lenticular overall stratification,

113 while the upper part (Barberkrans and Elandsberg Member) again commences with a sandstone lithosome (Barberskrans) which is generally subtabular to moderately lenticular in shape, overlain by the argillaceous Elandsberg Member which generally is lithologically very similar to the

Daggaboersnek Member. The top of this megacycle consists of thin, horizontal, laminated, interbedded mudstone and siltstone indicating deposition from wide, shallow channels of a fluviatile environment. The succession of this member of the Balfour Formation reflects a change from high- sinuosity suspended load dominated deposits to a low-sinuosity bed load dominated system from flood events (Smith, 1995; Groenewald, 1996; Rubidge et al., 2000). From evidence preserved in sedimentary structures, river currents were the major mechanisms involved in the transportation processes of the sediment and its deposition.

Sandstone facies consist mainly of interbedded fine-grained sediment sand is characterised by internal structures such as erosion surfaces, massive bedding, planar and trough cross-bedding, flat- bedding and ripple cross-lamination. On a larger scale, the sandstone morphologies display channel fills and point bars. The lithology and variation of the beds and sedimentary structures are attributed to changes in fluvial system from predominantly braided to meandering, indicating change from low to high kinetic energy. Planar lamination of beds suggests settling from suspension in a low-energy environment (Johnson et al., 2006) and also indicates a change in the fluid velocity from turbulent flow to low fluid velocity which can be related to lacustrine sedimentation, as was suggested by previous researchers. The presence of laminated siltstone within the sandstone suggests that sedimentation from suspension took place, which led to thin sandstone horizons being deposited at the time of flooding when there was fresh fluvial sediment input.

Measurements of penecontemporaneous sedimentary structures show that the sediments were deposited by a very large river system flowing in a northerly and northwesterly direction and that the

114 source area of the sediments was to the southeast. This is an indication that the Cape Fold Belt to the south was the main source of sediments during the time of the Balfour Formation. Following the depositional analysis, it can be concluded that the Balfour Formation was deposited under seasonally warm to humid climatic conditions.

In conclusion, for the first time an integrated study of the sedimentary environments and provenance of the Balfour Formation in the vicinity of Bedford and Adelaide in the Eastern Cape Province of

South Africa (S32°E26°) has been undertaken. This was achieved by comprehensive investigations through geological mapping, sedimentary petrography and geochemistry in relation to the stratigraphy and sedimentology.

There are little textural and no mineralogical differences amongst rocks and in their geochemistry there are no substantial differences across the members; this indicates that the sediments were derived from the same distant source area. The origin and deposition of the sediments of the Balfour

Formation are due to moderate weathering and recycling of older rocks, eroded and transported debris, as well as some soluble constituents to the Balfour Formation in this part of the Karoo Basin from either igneous, metamorphic and older sedimentary rocks.

All indications with the detailed sedimentological study of the sandstone revealed that the depositional system was that of a fluvial environment which is consistent with the results of previous studies on the Balfour Formation. Overall, the Balfour succession reflects change in sinuosity from braided to meandering regimes. The palaeo-environmental investigation also indicates that the

Balfour Formation was deposited in a fluvial environment and the sediment source of origin was to the southeast of the depository.

115 CHAPTER NINE

RECOMMENDATIONS

Further similar studies should be conducted in adjacent areas from which a comprehensive picture of the genesis of the Balfour Formation and a regional geological map of its subdivisions will emerge.

More in-depth studies of the heavy minerals of the Balfour succession should reveal much about its derivation and should be useful for comparison with the rest of the Beaufort Group as well as with the

Ecca Group.

It is clear that the clastic sediments contain important information about the tectonic setting and evolution of the continental crust (Liu et al., 2007). The detrital zircon can be further studied to determine the ages of the clastic sediments and the evolution of the basin.

All available sedimentological methods could not be applied. However, new developments in technologically advanced laboratory procedures can be employed for further research in the area towards sedimentological interpretation; this will aid the generation of more important information that can give further insight into the past. Examples are techniques in scanning electron microscopy for grain morphologies and surface textures for discriminating between conditions of transportation as well as cathodoluminescence for studying luminescence characteristics of minerals to examine the internal structures and obtain valuable information about the conditions during crystal growth.

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