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How to cite this thesis

Surname, Initial(s). (2012). Title of the thesis or dissertation (Doctoral Thesis / Master’s Dissertation). Johannesburg: University of Johannesburg. Available from: http://hdl.handle.net/102000/0002 (Accessed: 22 August 2017). CASE STUDIES OF SPELEOGENESIS IN THE CRADLE OF HUMANKIND

UNESCO WORLD HERITAGE SITE AND THE WEST RAND EXPANSE, SOUTH

AFRICA: TECTONIC CONTROLS AND THEIR PALAEOPROTEROZOIC

COMPONENTS

by

Pedro Boshoff

Dissertation

Submitted in fulfillment of the requirements for the degree

MAGISTER SCIENTIAE

in

GEOLOGY

in the

FACULTY OF SCIENCE

at the

UNIVERSITY OF JOHANNESBURG

Supervisor: Prof. J.D. Kramers

Co-supervisor: Dr. H.S. van Niekerk

April 2019

Abstract

This study concerns itself with a comparison of tectonic structural control components for speleogenic propagation in the Cradle of Humankind UNESCO world heritage site 40 km

NW of Johannesburg, and in the Far West Rand. From the Cradle of Humankind area, the

Rising Star system situated at S26o 00.951′ E27o 44.071′ and Bats cave at S26o 02.008′; E27o

44.089′ were selected as they show the typical collective morphology and structural overprint of the majority of caves found in the area-showing cave genesis within this region to have been predominantly influenced by lithological, layer parallel controls interacting with cross- cutting fracture systems reflecting an NW to SE directed extensional far-field stress.

Armageddon Pot situated at 26o 23.517′ E27o 43.562′ in the vicinity of Westonaria, taken as an example of speleogenesis in the Far West Rand, is a massively developed linear cavity measuring ±2600 m in explored length and ±257m in depth. Its cave entrance is located at the bottom of a 50 m deep sinkhole that formed in the 1990’s due to stoping, gradually weakening the roof until it was structurally compromised.

Armageddon Pot is situated along the southern margins of the Panvlakte/Witpoortjie horst domain. Its chief initiating structural control is a normal fault striking east to west and dipping at ±75o north to south. This structure appears clearly linked with the broader structural characteristics of the Panvlakte/Witpoortjie horst block domain (a succession of elevated crustal blocks of Witwatersrand Supergroup units), that in turn has a direct causal relationship with deep-seated Witwatersrand tectonics.

This normal fault, as Armageddon’s chief linear structural control, is transverse (crossed) by older Pre-genetic (sub-horizontal) offset shear zones and numerous interleaved micro-shears.

Along these offset shear zones, massive cataclasite bodies occur that enclose compressional as well as extensional structures. This has not been observed before in caves within the CoH

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or elsewhere within the Transvaal Supergroup carbonate lithologies. Thus, speleogenic controls in this cave is entirely dissimilar from those in the CoH.

A single sample of sericite for 40Ar/39Ar dating, collected within Armageddon Pot from a schistose horizon set between the contact of the lowermost Pretoria Group (Timeball Hill

Formation), and the underlying uppermost Frisco Formation of the Malmani Group yielded ages bracketed between 2046.6 ± 8.4 and 2061.1 ± 8.4 Ma, encompassing the intrusion age of the Bushveld Igneous Complex (BIC). Ages in this range of 2046.6 ± 8.4 Ma-2056.0 ± 8.4 were also obtained from strata-parallel shear zones within the Monte Christo Formation in

Rising Star cave.

Eight further samples taken from select sub-horizontal thrust-sense shear zones in the sidewall of Armageddon Pot ±250 m east of the entrance yielded a significantly older date set ranging from 2080-2140 Ma.

A sample from the lowermost major sub-horizontal shear zone in Armageddon Pot, at the contact between the upper Frisco and Eccles Formations, yielded duplicate ages of 2021.2 ±

8.8 and 2025.5 ± 7.9 Ma, identical to the age of the Vredefort impact event at 2025 Ma. No dateable samples could be taken from the normal fault that is the main control for the speleogenic propagation of Armageddon Pot, due to hanging and footwall weathering having removed the original contact surfaces.

The oldest dates recovered, those close to 2140 Ma, are interpreted as defining a minimum age for the expansion of the Malmani basin during basin subsidence and relaxation, with the younger ‘tail’ down to 2028 Ma reflecting partial recrystallization of sericite during later shear events. Although interesting, the direct involvement of the earliest shearing in the speleogenic development of Armageddon Pot seems improbable.

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The BIC age range bracket at 2046.6 ± 8.4-2061.1 ± 8.4 can be understood if the shear zone at the contact between the Timeball Hill and Frisco Formation is interpreted as a detachment fault (décollement) associated with the elevation of the Johannesburg Dome in response to the downwarping of rock units to the north of it, in which the BIC magmas intruded. This interpretation is strongly supported by similar structures within the Cradle of Humankind found in several caves (e.g. Knocking shop, Villa Louse, aka site 105, Rising Star and van

Rooy’s cave) bordering the Johannesburg Dome, with samples from Rising Star yielding an identical 40Ar/39Ar date range. The role of these structures role in the speleogenic propagation of Armageddon Pot as well as most caves within the Cradle of Humankind is important, as these structures are frequently permeable and function as conduits for acid rich meteoric water influx, channelling it into major fault zones where dissolution commenced.

In spite of being yielded by just one sample, the Vredefort impact age may be significant. The occurrence of cataclasites points to a rapid event. It seems conceivable that during impact and compression Panvlakte/Witpoortjie horst thrust faults were accentuated then reverted to a normal fault during rebound and crater rim collapse.

The structural speleogenic controls for Armageddon Pot can thus probably be attributed to at least three tectonic events. Phreatic saturation dissolution probably commenced during

African and post-African surface 1 times with the possibility of this converting to a largely vadose environment during the post-African surface 2 erosion cycles with the cave opening to the surface via a massive sinkhole formed recently.

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Acknowledgments

First and foremost a heartfelt word of thanks to my two promoters, Prof. J. Kramers and Dr.

H. van Niekerk for affording me the opportunity to have concluded this research under their patronage and supervision.

In specific: to Prof. Jan Kramers whom I fondly refer to as ‘father time’ for his profound knowledge on geo-chronological dating techniques. Herewith a special word of thanks for providing me with financial assistance and for being a strict and scrupulous critic.

Mr Rudi Burger, the owner of the properties where Armageddon Pot is located for him allowing me unhindered access to the cave as well as his interest in the project.

A word of thanks to Prof. L. R. Berger, the University of the Witwatersrand, the municipality of Krugersdorp and numerous landowners who gave me unhindered access to the Rising Star cave system, Bats cave and several other caves within the CoH.

All my friends from the caving community and in specific the members from SEC (SASA) with whom I have been spelunking for many years and with whose support and active participation this research project would never have come to fruition. In specific, to Steven

Joseph Tucker, a caver and explorer par excellence who mapped out Armageddon cave in part for the purpose of this dissertation.

A special mention of John Dickey for his outstanding and safe rigging of Armageddon caves dizzying entrance and the pits. Many a safe abseil as well as zip line and tyrolean work, were

(are) done on his sound rigging.

A special thanks to VCA (Vietnam Caving Association), a small but energetic caving group in Vietnam for allowing me to cave with them in what certainly is the toughest environment I have been in, and the most beautiful caves I have explored.

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A special word of thanks to Prof. Georgy Andreii Coppachenko, Lomonosov Moscow State

University, for his assistance with the mathematical equations and the many conversations we had on Skype.

Last but not least, to my external examiners for being strict, but fair in their marking of this thesis.

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Dedications

As an agnostic to a God, I can never hope to fathom or delineate-yet constantly marvel at the works of His Hands.

To my mother for giving unto me this life and her unwavering support in my research endeavours in spite of her sometimes finding my trogloxenic behaviour unsettling.

To Nguyen Thi Bich Ngoc (Nhim), who at time of writing were my Vietnamese fiancé; your help and support, and many Skype conversations often carried the day when I was exhausted and ready to throw in the towel.

To the ancient African cave-guide at the Sterkfontein caves for striking a chord with a young inquisitive mind that started a lifelong fascination with caves and ‘ape-man’ after my father took us there during a Sunday outing circa 1972.

To Prof. Francis Thackeray, a soft-spoken man of gentle disposition, a peacemaker, that similarly encouraged and supported me during trying times.

To the late Prof. T. C. Partridge who taught me much about the evolution of the African surfaces and with whom I have done extensive fieldwork in the Makapans valley, often under strenuous conditions.

To the late Prof P. V. Tobias; a small man in stature, but a giant in the field of palaeo- anthropology.

In specific, to Prof. L. R. Berger, a colleague and an exceptionally gifted scientist who maintained his belief and faith in me when others often considered me only an eccentric.

To my sisters, Elmarie and Louise for simply being there, also to Ruaan and Tinkie for the many cups of coffee they brought me when I spent weekends writing this thesis.

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Index

PP

Chapter 1: Introduction ...... 1

Background ...... 1

1.2. Location of the study area ...... 3

1.3. Summary of geological setting and previous work...... 5

1.4. Exploration history of Armageddon Pot ...... 12

1.5. Motivation and scope of this study ...... 13

Chapter 2: Methodology ...... 15

2.1. Cave exploration ...... 15

2.2. Interpretation of satellite data ...... 15

2.3. Collection of structural data ...... 16

2.4. 40 Ar/39Ar radiometric dating ...... 16

2.5. Comparative work ...... 17

2.6. Modelling ...... 18

Chapter 3: Regional geological and geographical setting ...... 19

3.1. Stratigraphic context ...... 19

3.1.1. Study area ‘A’ the ‘Cradle of Humankind’ (CoH) ...... 19

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3.1.2. Study area ‘B’ the Far West Rand...... 22

3.2. Topography ...... 24

3.2.1. Study area ‘A’ the ‘Cradle of Humankind’ (CoH) ...... 24

3.2.2. Study area ‘B’ the Far West Rand...... 26

3.3. Regional geological background ...... 28

3.4. Landscape evolution and drainage ...... 31

3.4.1. Landscape evolution ...... 31

3.4.2. Drainage ...... 32

Chapter 4: Cave formation processes ...... 35

4.1. Introduction ...... 35

4.2. Dissolution physics and chemistry ...... 39

4.2.1. Types of Chemical Weathering ...... 39

4.2.1.1. Acid Reactions ...... 39

4.2.1.2. Hydrolysis ...... 40

4.2.1.3. Hydration ...... 40

4.2.1.4. Oxidation ...... 41

4.3 Factors influencing rock disintegration ...... 41

4.3.1. Mineral Composition ...... 41

4.3.2. Soil/Vegetation Cover/ bacterial interaction ...... 41

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4.3.3. Relief ...... 42

5.1. Carbonate Rock Solubility ...... 42

5.1.1. Carbonic acid ...... 43

5.1.2. Solution of Limestone on the Surface ...... 44

5.1.3. Dissolution in the phreatic and vadose environment ...... 45

5.1.4. Effect of temperature ...... 46

5.1.5 Effect of pressure ...... 46

5.1.6. Carbonate (CaCO3) deposition ...... 46

6.1. Structural controls ...... 47

6.1.1. The speleogenic interface between rock and water...... 47

6.1.2. Faults ...... 49

6.1.3 Fractures ...... 50

6.1.4. Joints ...... 51

6.1.4.1. Joint genesis ...... 52

6.1.5. Joints commonly encountered as speleogenic controls...... 52

6.1.5.1. Non-systematic joints ...... 52

6.1.5.2. Systematic joints ...... 53

6.1.5.3. Columnar joints ...... 54

6.1.6. Joint origins ...... 54

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Chapter 5: Examples of dissolution caves in the Cradle of Humankind ...... 56

5.1. Introduction ...... 56

5.2. Westminster/Rising Star cave system ...... 56

5.2.1. Locality ...... 56

5.2.2. Background ...... 57

5.2.3. Topography ...... 58

5.2.4. Geology ...... 59

5.2.5 Structural controls ...... 61

5.2.6. Speleogenic sequencing ...... 63

5.3. Bats cave ...... 65

5.3.1. Locality ...... 65

5.3.2. Background ...... 65

5.3.3 Topography ...... 66

5.3.4. Geology ...... 66

5.3.5. Structural controls ...... 67

5.3.6. Speleogenic sequencing ...... 68

5.4. Similarities between Bats and Rising star ...... 71

5.5. Causal relationships ...... 72

Chapter 6: Armageddon Pot ...... 76

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6.1. Description ...... 76

6.2. Geology ...... 84

6.2.1. Context ...... 84

6.2.2. General type description ...... 84

6.2.3. Structural features ...... 86

6.2.4. Thrust and shear zone orientations ...... 107

6.2.5. Joint set orientations ...... 111

Chapter 7: 40Ar/39Ar dating ...... 114

7.1. Introduction ...... 114

7.2. Results ...... 114

Chapter 8: Discussion ...... 129

8.1. Introduction ...... 129

8.2. The Vredefort impact structure ...... 129

8.3. Reasons for implicating the Vredefort impact event ...... 130

8.3.1. Proximity ...... 130

8.3.2. Impact as probable or major agent for inserting speleogenic structural controls ...... 131

8.3.3. Impact amplitude ...... 133

8.3.4. Explosive force: a comparison ...... 134

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8.3.5. Explosion yield examples ...... 135

8.3.6. Impact kinetics and energy ...... 136

8.3.7. Initial effects of impact ...... 137

8.3.8. Shockwave propagation ...... 138

8.4. Structural features seen in Armageddon Pot that can be attributed to the Vredefort

Impact and speleogenic controls ...... 141

8.5. The Bushveld Igneous Complex ...... 143

8.5.1. Introduction ...... 143

8.5.2. Reasons for implicating the Bushveld Igneous Complex ...... 144

8.6. The Johannesburg dome ...... 146

8.6.1. Basic geology ...... 146

8.6.2. Reasons for implicating the Johannesburg dome ...... 147

8.6.3. The Johannesburg dome’s structural contribution to Armageddon Pot and caves in the

CoH ...... 149

8.7. Tectonic episodes predating the Bushveld Igneous Complex ...... 150

8.7.1. Palaeoproterozoic extensional far-field stress and the relaxation of the Malmani basin

...... 150

8.7.2. Deep-seated Witwatersrand tectonics and the forming of the Panvlakte horst set...... 150

8.7.3. Other possible contenders ...... 151

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8.7.3.1. The Vryburg arch ...... 151

8.7.3.2.. The Transvaalide thrust and fold belt ...... 152

8.7.3.3. The Etosha-Griqualand-Transvaal Axis ...... 153

8.8. A model of the events leading up to the formation of Armageddon Pot ...... 154

8.8.1. Introduction ...... 154

8.8.2. Phase 1: Foundation ...... 154

8.8.3. Phase 2: Forming of the Panvlakte horst set ...... 155

8.8.4. Phase 3: Deposition of the Rooihoogte and Timeball Hill Formation and insertion of interleaved micro-shears ...... 156

8.8.5. Phase 4: Downwarping of the Bushveld Igneous Complex ...... 158

8.8.6. Phase 5: Vredefort impact ...... 159

8.8.6.1. Stage 1: Compression phase ...... 159

8.8.6.2. Stage 2: Rebound ...... 160

8.8.7. Phase 6: Phreatic immersion and non-acid dissolution ...... 162

8.8.8. Phase 7: African surfaces ...... 162

8.8.9. Phase 8: Stoping...... 164

8.8.10. Phase 9: Sinkhole forming and the opening of cave system to the surface ...... 165

8.9. Comparative observations between the CoH and the Far West Rand ...... 166

Conclusion ...... 172

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Figures

Fig 1: Showing the map situation covering the general area of study, also including the more defined areas of study (After maps of South Africa: https://images.search.yahoo.com) ...... 3

Fig 2: A Google Earth satellite image of the areas of study showing the Johannesburg dome

(A) separating the two regions, The Far West Rand (B), The Cradle of Humankind (C), the

Pretoria Group (D), the Bushveld Igneous Complex (E), the Pilanesberg Complex (F) and the northern faces of the Vredefort impact crater (G) (Google Earth image)...... 4

Fig 3 A and B: A simplified diagram demonstrating the basic structural anatomy of the Far

West Rand including the Panvlakte horst domain (After Osburne et al., 2014) with B showing the lithologies involved with Armageddon pot as indicated on the stratigraphy column

(Transvaal Supergroup and Witwatersrand Supergroup)...... 6

Fig 4: Digital terrain model showing the known fossil sites within the Cradle of Humankind and a fraction of the known caves within the dolomitic region north of the Johannesburg dome (After Dirks and Berger, 2013) ...... 11

Fig 5: A stratigraphic column of the formations and members of the Transvaal Supergroup carbonate lithologies within the CoH and the Far West Rand (The succeeding Pretoria Group is excluded) ...... 23

Fig 6: A geological map of the area of study, Study ‘A’ is within the CoH and ‘B’, the locality where Armageddon Pot is found (Far West Rand) (After maps of South Africa: https://images.search.yahoo.com) ...... 24

Fig 7: Position of the Transvaal and Griqualand West basins in South Africa in relation to the Vryburg arch (After Johnson, 2006) ...... 29

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Fig 8: Detailed stratigraphy of the areas of interest (After stratigraphy of the Transvaal

Supergroup: https://images.search.yahoo.com) ...... 30

Fig 9: Indicating the position of the Etosha-Griqualand-Transvaal axis (After Nyblade and

Robinson, 1994) ...... 33

Fig 10: The northerly drainage (Limpopo basin) of South Africa ‘A’ and the south-western drainage (Vaal-Orange River) basin ‘B’ of South Africa (After the drainage basins of South

Africa: https://images.search.yahoo.com) ...... 34

Fig 11 A and B: Demonstrating the mechanism through which epigenetic and hypogene speleogenesis occurs (After how do caves form: https://images.search.yahoo.com) ...... 35

Fig 12 A and B: Westminster/Rising Star cave system survey and structural composition ...... 64

Fig 13: Rising Star/Westminster cave’s fault (yellow) and joint sets (blue) strike orientation.

Red semi-circles indicate range variables ...... 65

Fig: 14 A and B: Showing the survey of Bats cave and its comparative joint and fracture orientations ...... 70

Fig 15: Rose diagram of Bats cave’s fault (yellow) and joint sets (blue) strike orientation. Red semi-circles indicate range variables ...... 71

Fig 16: Rose diagram demonstrating the similar joint and fault strike orientations found both within the Rising Star cave system and Bats cave. Red semi-circles indicate range variables .. 72

Fig 17: Demonstrating the linear morphology and depth extend of Armageddon pot, also indicating points of interest ...... 76

Fig 18: Armageddon Pot is only accessible via a deep rotund-shaped sinkhole developed in shale 50m deep to first landing (No: 1 on Google earth image, Fig 43) ...... 77

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Fig 19 A: The entrance to the cave at the bottom of the sinkhole along a talus slope approximating ±35o to the bottom of the entrance chamber at ±107 m from surface. The two cavers provide scale (No: 2 on Google earth image, Fig 43) ...... 77

Fig 19 B: Looking at the entrance from a position halfway up the collapse cone ‘heartbreak hill’-so called for being steep, arduous to climb and slippery. In spite of powerful portable

LED lights, the enormity of this chamber makes it difficult to illuminate or to scale it properly (No: 3 on Google earth image, Fig 43) ...... 78

Fig 20: Skirting around the first pit on a safety line and on a ledge. The caver provides scale

(No: 4 on Google Earth image, Fig 43) ...... 80

Fig: 21: The cable traverse (zip line) over pit two. The caver provides scale (No. 5 on Google earth image, Fig 43)...... 81

Fig 22: A selection of the type formations commonly encountered in Armageddon Pot: A and

B, iron oxide, C, D and F, aragonite and F, manganese oxide flowstone (No: 6 on Google

Earth image, Fig 43) ...... 83

Fig 23: A view from the top section of the sinkhole The car provides scale. (No: 7 on Google

Earth image, Fig 43) ...... 85

Fig: 24: Demonstrating the stratigraphic sequence of the Sinkhole entrance series of

Armageddon Pot ...... 86

Fig 25: The décollement and its delineation set between the lowermost Pretoria Group and uppermost Frisco Formation, Malmani basin dolostone lithologies (No: 8 on Google earth image, Fig 43) ...... 87

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Fig 26: Compression structure and micro fault displacement within a micro-shear band,

(Hammer provides scale) (No: 9 on Google earth image, Fig 43) ...... 88

Fig 27: Boudinage structures, indicative of extension dynamics (Compass provides scale) ..... 89

Fig 28: Boudinage structures within Armageddon Pot attaining considerable dimensions (No:

10 on Google image, Fig 43) ...... 89

Fig 29: Diagram showing the hanging and footwall offset value measured along the main normal fault by correlating thrust and shears ...... 90

Fig 30: Stereonet representation (D) of the strike and acute dip direction/trend and dip/plunge of the normal fault directing Armageddon Pot’s linear extent as reflected by the rose diagrams (A, B and C) above and field data table below (Table 1)...... 92

Fig 31 A, B, C and D: A selection of cataclasite clasts to illustrate the variation encountered in Armageddon Pot. Scale bars and compass provide scale (No: 11 on Google earth image,

Fig 43) ...... 95

Fig 32 A and B: Demonstrating the size range and morphologies of somewhat cohesive cataclastic chert bands seen in Armageddon Pothole (No: 12 on Google earth image, Fig 43) 96

Fig 33: A flower structure exhibiting several compression characteristics (No 13: on Google earth image, Fig 43) ...... 97

Fig 34: A, B, C and Stereonet diagram D: showing the plane great circles (orange) and pole

(red and blue) positions represented by the rose diagrams above ...... 99

Fig 35 A, B, C and Stereonet diagram D: showing the plane great circles (lavender) and pole

(blue) positions throw specifics of the flower structure’s thrust directions as represented by the rose diagrams above ...... 101

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Fig. 36: A massive compression, ramp and thrust structure, indicative of a massive high energy, high-velocity compressional event (No: 14 on Google earth image, Fig 43) ...... 103

Fig 37: Rose diagram A, B, C and Stereonet diagram D: showing the plane great circles

(blue) and pole (green) positions major thrust trends as represented by the data below (table

5) ...... 105

Fig 38: The lithology of the ‘upper’ chamber of Armageddon Pot (dip not indicated) ...... 106

Fig 39 A and B: Showing a selection of thrusts seen in Armageddon Pot along the Frisco and

Eccles Formation contact (No: 15 on Google earth image, Fig 43) ...... 108

Fig 40 A, B, C and Stereonet diagram D: compilation showing the plane great circles

(burgundy) and pole (yellow) directional trends of the macro and micro thrusts cutting across the main controlling fault controlling Armageddon pots linear extent as represented by the rose diagrams above ...... 110

Fig 41: Rose diagram demonstrating the joint strike trends measured in Armageddon Pot .... 112

Fig 42: Survey superimposed over Google Earth imagery indicating the localities where the photos in this chapter were taken ...... 113

Fig 43 A and B: 40Ar/39Ar age spectra from duplicate runs of a sample taken from the lowermost thrust zone in Armageddon Pot, separating the Frisco and Eccles Formations showing a Vredefort age range ...... 116

Fig 44 A-F: 40Ar/39Ar age spectra from samples taken from strata-Parallel shear zones in

Rising Star cave and Armageddon Pot, reflecting a Bushveld Igneous Complex age ...... 120

Fig 45 A-H: 40Ar/39Ar age spectra from 8 samples taken from small thrusts reflecting varying ages all distinctly older than that of the Bushveld Igneous Complex ...... 124

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Fig 46: Showing the formations and the localities from which sampling was done for

40Ar/39Ar dating within the Rising Star cave system ...... 127

Fig 47: Showing the formations and the localities from which sampling was done for

40Ar/39Ar dating within Armageddon Pot ...... 127

Fig 48: A compilation of the total age data recovered from Armageddon Pot (series 1) and

Rising Star (series 2) demonstrating three distinct date clusters ...... 128

Fig 49: Demonstrating the position of Armageddon Pot in the context of the Vredefort impact’s crater dimensions (Internet image) ...... 130

Fig 50: The stratigraphic setting of the Transvaal basin at the onset of deep-seated

Witwatersrand tectonics ...... 155

Fig 51: The forming of the Panvlakte/Witpoortjie horst set due to deep-seated Witwatersrand tectonics ...... 156

Fig 52 A and B and C: The pre-Vredefort impact insertion of interleaved micro shears within the Frisco Formation due to rifting expansion and then the Deposition of the Pretoria Group due to thermal subsidence ...... 157

Fig 53 A and B: The isostatic uplift of the Johannesburg dome and the forming of detachment faults along its flanks: These acted as conduits for water, allowing dissolution within older fault systems where they intersected ...... 158

Fig 54 A and B: Demonstrating the effects of compression and rebound brought by the

Vredefort impact on the main thrust zones of the Panvlakte/Witpoortjie horst set separation 161

Fig 55: Phreatic immersion and non-acid (undersaturation) dissolution ...... 162

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Fig 56: Vadose dissolution and forming of speleothems: lowering of the water table relates to the deepening thalweg gradient of the African surfaces ...... 164

Fig 57: Stoping (structural collapse of the roof due to non-phreatic support) ...... 165

Fig 58: The last stage: Sinkhole forming, connecting the cave to surface ...... 166

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Tables

Table 1: The controlling fault strike measurements of Armageddon Pot ...... 92

Table 2 A and B: The cataclasite clast, size range and type cataclasitic matrixes seen in

Armageddon Pot ...... 94

Table 3 A: The strike, dip direction/trend and dip/plunge angle field measurements of the flower structure’s downthrow segment as represented in the rose diagrams A, B C and stereonet diagram D (Fig 34) above ...... 99

Tables 3 B: The strike, dip direction/trend and dip/plunge angle measurements of the flower structure’s thrust throw portion...... 101

Table 4: The strike, dip direction/trend and dip/plunge angle measurements of the major thrust structure ...... 105

Table 5: Demonstrating the similarities between the footwall thrust and micro-thrusts dip direction, the flower structure (Fig 33) and the thrust (Fig 34) directional specifics to be strikingly similar ...... 111

Table 6 A, B, C, and D: The Vredefort impact event specifics (After Moser, 1997) ...... 138

Table 7: The above diagram represents the magnitude of earthquakes, from minor to the most severe (After: USGS Internet earthquake awareness program) ...... 140

Table 8 A and B: Demonstrating the extent, volumetrics and ages of the various provinces and groups of the Bushveld Igneous Complex (After Eales and Cawthorn, 1996) ...... 146

References...... 177

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Appendix: Table of argon isotope data, 40Ar/39Ar ages, Ca/K and Cl/K ratios of individual heating steps.

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Chapter 1: Introduction

1.1. Background

Recently a cave called ‘Klipgat’, named ‘Armageddon Pot’ by SEC/SASA (Speleological

Exploration Club/South African Speleological Association) members was initially accessed for recreational purposes. However, it soon became clear that this cave exhibited morphologies differing from those anticipated. Certain structural characteristics and rock types not before observed or described in other caves situated within the Transvaal

Supergroup dolomitic lithologies raised apposite questions on structural geology and its connection to speleogenesis.

The field observations made during the exploration and surveying of Armageddon Pot suggest that fundamental geological differences exist between the primary speleogenic controls of this cave and those seen in the caves of the Cradle of Humankind (CoH). In the

CoH speleogenic placement and propagation is largely controlled by lithology layer-parallel controls interacting with cross-cutting fracture systems of Palaeoproterozoic origin and NW to SE directed extensional far-field stress as indicated by the orientation of networks of intensely developed joint grid systems superimposed over older faults and fractures (Dirks and Berger, 2013; personal observations, author).

Work done by other fieldworkers on the speleogenic character of the CoH (Barber and

Berger, 2002; Boshoff et al., 1990; Clarke and Partridge, 2010; Martini and Kavalieris, 1976;

Martini, 1980; Martini et al., 2003) concur and in general comply with Dirks and Berger’s

(2013) findings regarding the structural controls acting as chief speleogenic controls within the CoH as presently pointed out above. Their work also ties in well with what is generally

1 known from studies abroad on the mechanics of speleogenesis (Bauer, 1971; Jackson, 1982;

Jennings, 1971; Marker, 1980; Moon and Dardis, 1988).

This seems in stark contrast with what has been observed in Armageddon Pot where a seemingly steep dipping normal fault (formerly a thrust fault) cut by low angle offset thrusts and micro shears as well as numerous compression and extension structures set in a cataclasite rock matrix suggest a structural or causal relationship with tectonic or neo-tectonic events other than those accepted for the CoH.

2

1.2. Location of the study area

Fig 1: Showing the map situation covering the general area of study, also including the more defined areas of study (After maps of South Africa: https://images.search.yahoo.com).

3

Fig 2: A Google Earth satellite image of the areas of study showing the Johannesburg dome

(A) separating the two regions, The Far West Rand (B), The Cradle of Humankind (C), the

Pretoria Group (D), the Bushveld Igneous Complex (E), the Pilanesberg Complex (F) and the northern faces of the Vredefort impact crater (G) (Google Earth image).

(Fig 1) represents the basic locations (map situation) of the research areas in context to South

Africa as a whole, whereas (Fig 1), lower map, shows more precisely the research areas placement in context to Gauteng province, South Africa. (Fig 2) represents a Google Earth satellite image of the areas of study, including the Johannesburg dome (A, yellow circle) separating the two regions, The Far West Rand (B, green rectangle), The Cradle of

Humankind (C, red square), the Pretoria Group (D), the Bushveld Igneous Complex (E), the

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Pilanesberg Complex (F) and the northern faces of the Vredefort impact crater (G) (distance scale estimated).

1.3. Summary of geological setting and previous work

The first area of interest (the Far West Rand) (Fig 2) comprises a portion of the entire

Transvaal Supergroup dolostone lithologies located to the SSW of the Johannesburg dome and Witwatersrand Supergroup lithologies. To the NW of the Johannesburg dome the second area of interest (the Cradle of Humankind) (Fig 2), also comprising a portion of the entire

Transvaal Supergroup dolostone lithologies is again contained between the Johannesburg dome and basil Witwatersrand Supergroup lithologies and to the north bordered by Pretoria

Group Lithologies.

Armageddon Pot as chief subject of this study is situated on the southern margin of the

Panvlakte/Witpoortjie horst domain located on the farm Jagtfontein 344 IQ ±11 km SE of the town of Westonaria in the North-West Province of South Africa (Fig 2, within the green square, B).

The Panvlakte/Witpoortjie horst block forms an integral component of the geology of the Far

West Rand area (McCarthy et al., 1986). The macro-structure of the Far West Rand is characterized by older north-trending faults (Far West Rand and Panvlakte) and younger east- trending dextral wrench faults (Waterpan and Wrench). This faulting, initiated by residual mantle plume activity (Manzi et al., 2013) has resulted in the development of structural blocks dominated by the Far West Rand (or Witpoortjie) and Panvlakte horst blocks that are superimposed over broad folding associated with the SE plunging Far West Rand syncline.

5

The northerly limb of the syncline dips to the SSW and the southern limb to the ENE (Bjinse et al., 2010; Osburne et al., 2014) (Fig 3).

A

B

Fig 3 A and B: A simplified diagram demonstrating the basic structural anatomy of the Far

West Rand including the Panvlakte horst domain (After Osburne et al., 2014) with B showing the lithologies involved with Armageddon pot as indicated on the stratigraphy column

(Transvaal Supergroup and Witwatersrand Supergroup).

6

The second area of direct interest comprises the same Transvaal Supergroup dolostone lithologies as those seen within the primary area of study embracing the area NNW of

Krugersdorp, Gauteng province. More specific, between the Sterkfontein caves area

(Sterkfontein valley) and Centurion to the east where the area describes an arcuate belt situated between the Johannesburg dome and the Bushveld Igneous Complex (BIC). The area under direct study known as the Cradle of Humankind (CoH) is mostly contained between the

R563 and the R512 located on the 2527DC Hekpoort and 2527DD Broederstroom 1:50 000 topographic maps.

The dolostone lithologies found within both areas of study, in essence, comprise the same lithological characteristics as they form parts of a single depositional event. The reason for their separation, however, can be found in the elevation of the Johannesburg dome whereby the overlying dolostones have been elevated over a brachy-anticlinal basement dome with later denudation removing a substantial portion of this elevated landscape, thereby separating the two areas into distinctive regions, each developing unique post-depositional structural and landscape characteristics (Martini, 1980; personal communications, Martini, 1984).

In general, the Transvaal Supergroup carbonate lithologies of the Chuniespoort Group,

Malmani Sub-Group, were deposited in the Neo-Archaean to earliest Palaeo-Proterozoic at around 2.6-2.2 Ma as an intra-cratonic epeiric shallow marine platform succession (Eriksson and Truswell, 1974; Eriksson et al., 1975; Eriksson and Alterman, 1998; Eriksson and

Reczko, 1995; Eriksson et al., 2001; Eriksson et al., 2006).

In understanding aspects pertaining to the dolostones, exhaustive research projects and numerous scientific papers dealing with numerous aspects of the dolostone lithologies of the

7

Transvaal Supergroup have been published. This resulted in much of the Transvaal basins geology being well understood. However, mentioning all the work done will comprise a protracted list not necessarily supporting the purpose of this study, but mentioning a few applicable studies seems more appropriate.

More generally, Button (1973) undertook a regional study of the stratigraphy and development of the Transvaal Basin in the East and North-East Transvaal. Eriksson and colleagues in (Eriksson and Truswell 1974; Eriksson et al., 1975; Eriksson and Reczko, 1995;

Eriksson et al., 2001; Eriksson et al., 2006) have done exhaustive research on the Transvaal basin sequences. Visser (1984) compiled the explanation for the 1:1000 000 scale geological map in which the stratigraphy of all major lithologies, including those of the Transvaal basin has been discussed in some detail. Mendelsohn and Potgieter (1986) described in detail the pre-dolostone sequences of the Witwatersrand and their stratigraphic relationship with the dolomitics. Stanistreet et al., (1986), Dankert and Hein (2010) and Manzi et al., (2013) embarked on exhaustive studies of the structural anatomy of the Witwatersrand gold bearing fields. Snyman (1996) discussed the stratigraphy and basin development of the Transvaal

Supergroup in detail and with a view to make it presentable for lecturing purposes. MacRae

(1999) treats the subject from a paleontological viewpoint and points out the evolution of life- forms found within the basin and the regional development aspects of the Malmani basin.

Poujol and Anhaeusser (2001) and Robbs et al., (2006) concerned themselves with Archaean granitoid intrusions and the development of the Johannesburg dome whilst in reference to specifically the geology of the CoH in regarding the region’s geological dynamics, Wilkinson

(1973) addresses the evolution of the Sterkfontein cave system as a karst form, but does not elucidate on the cave in a regional geological context. Martini (1980), Martini and Kavalieris

(1976) and Martini et al., (2003) contributed to an understanding of the karst developments of

8 the region in context to speleogenesis. Brain (1981) did a comprehensive study on the taphonomy dynamics of the region’s fossil assemblages found in association with cave breccias, explaining in detail the derivation of these and the mechanisms by which deposition occurred. Boshoff et al., (1990) contributed to an understanding of the geology of the Lincoln cave system adjacent to the Sterkfontein caves demonstrating the two cave systems to be components of a single (syngenetic) speleogenic event. Partridge et al., (1999) and Clark

(1994) addressed the problems around Sterkfontein’s stratigraphy and the dating of Stw 573

(‘little foot’), a complete early australopithecine skeleton discovered during 1997 by S.

Molefe and R. Clark in the Silberberg grotto, Sterkfontein caves. Martini et al., (2003) again contributed in particular to an understanding of the speleogenesis of the Sterkfontein caves.

Regarding the question of caves and speleogenesis in the context to landscape developments,

Dirks et al., (2010) on Malapa and Dirks and Berger (2013) made a significant contribution to the relationship between landscape erosion rates, the forming of existing caves and their weathering sequence as integral components of a transient landscape. Their research provides constraints on the evolution of the landscape of the CoH since the Pliocene. Their aim was to better understand the distribution of hominid fossil sites in the CoH and to determine a link between tectonic processes controlling the landscape and the evolution and distribution of hominins that occupied the landscape.

In reference to specifically the geology of the Far West Rand, Brink and Partridge (1965) did considerable work on the development and morphology of the karst terrains of the Transvaal with special reference to sinkholes and subsidence’s on the Far West Rand. Beukes (1986) and Beukes et al., 2000) deals extensively with the mineralization of the Transvaal sequence and the Post-Gondwana African land surfaces and their pedogenic ferromanganese deposits along the Far West Rand. Partridge (1980) and Partridge and Maud (1987, 2000) address the

9 landscape evolution of the region during the Mesozoic. Moon and Dardis (1988) dealt with

Southern African geomorphology and specifically karst forming and karst processes, notably that seen in the wider Cradle area and along the Far West Rand. Kavalieris et al (1977) and

Martini et al (1991) contributed specifically to an understanding of the geology of certain caves found along the Far West Rand expanse. In an MSc dissertation, Van Niekerk (1997) discussed components of the evolution of the region’s palaeo-land surfaces. Apart from mapping and the formal description of the caves found along the Far West Rand expanse in

SASA/SEC and CROSA bulletins, little is known about their geology as they have not been researched in detail or placed within the context of their associated regional geology. These caves are in many cases not easily accessible and as a result, no concerted effort seems to have been made in studying their contextual geology. The general consensus accepted the notion that these caves formed as a result of conventional dissolution type speleogenesis and therefore never evoked intense interest apart from recreational spelunking. However, Martini et al (1991), Boshoff and Bischoff (personal communications, 1986) speculated that the original speleogenic control for a portion of the caves found along the Far West Rand may be partially accredited to impact-induced structural processes, but no substantial proof for this hypothesis has been established.

On an ongoing basis, SASA (South African Speleological Association) now SEC

(Speleological Exploration Club) and CROSA (Cave research organization of South Africa) are exploring and mapping out numerous caves found along the Far West Rand, and areas north of the Rand anticline and caves found within the CoH, and in doing so generate articles pertaining (unreferenced SASA/SEC and CROSA bulletins). These articles, however informal often contain detailed and credible scaled maps of caves being explored that can be used for scientific study and reference.

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At the time of writing an extensive and exhaustive undertaking was launched by L. R. Berger following the hominid discoveries at the Rising Star cave system and site 105 whereby

Boshoff and colleagues were tasked to locate or re-visit every cave and possible fossil site found within the region in the hope of locating more hominid-bearing fossil sites. Currently, in excess of a thousand caves, fossil sites and sites of geological and historical interest have been located awaiting further investigation (personal communications, Tucker, 2017) (Fig 4).

Fig 4: Digital terrain model showing the known fossil sites within the Cradle of Humankind and a fraction of the known caves within the dolomitic region north of the Johannesburg dome (After Dirks and Berger, 2013).

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1.4. Exploration history of Armageddon Pot

On the 12th February 1991 at or around 4 am in the morning the local farmer, Mr. R. Kruger heard a loud rumble and experienced tremors. The next day one of the farm workers reported the appearance of a gaping sinkhole on the side of a maize field in close proximity to Mr.

Kruger’s house. Upon inspection, Mr. Kruger decided it best to evacuate his house in favor of a new residence as the sinkhole’s proximity at ±175 m from his house was of great concern.

During the 1990s members of SASA/SEC accessed the sinkhole. The sinkhole entered into through a slightly oblong-shaped steep-sided shaft with an initial surface diameter of ±14 m was found to bell out to ±60 m towards the first landing at ±50 m depth with a slope approaching ±35o to the deepest point at ±65 m. However, at that point in time, no visible opening into a cave was seen and it was believed that this sinkhole, like many others in the vicinity, was a dead-end, not leading into the open cave.

After the initial reconnaissance of the sinkhole, returning to Armageddon Pot in 2012 Gerrie

Pretorius was the first to descend into the sinkhole to test the possibility of a dig towards the deepest point of the sinkhole that could lead to gaining access to an open cave. However, running out of rope he was forced to ascend and exploration was postponed. Returning on a later date Steven Tucker was the first to successfully abseil to the bottom. On landing, he immediately noticed a gaping entrance leading down a steep talus slope where a seemingly recent landslide opened a gaping hole into what appeared to be an open cave. Whilst waiting for the other team Members’ arrival Steven entered the cave and at once discovered a capacious chamber. The other SASA/SEC team members comprising: Linden Mazilis, John and Selena Dickey, Irene Kruger and Sharon Reynolds followed him into the cave. Dave

Ingold, Collin Redmayne-Smith, and Horst Muller stayed on the surface as a back-up and in

12 case of an emergency. Since then and over numerous visits since 2012 the cave is being explored and surveyed by members of SASA/SEC

During the ensuing exploration of the system, it was initially thought that this cave’s development simply followed along a seemingly singular normal fault line exhibiting a predominantly WNW to ESE strike trend. However, upon noticing several structures incongruent with fault and joint bound speleogenic propagation, interest peaked. Curiosity was amplified when it was noticed that large sections of the cave walls comprised thrust and compression structures. In places, whole sections included cataclasite rock that has been wholly or partially formed by the progressive fracturing and comminution of existing rock in a process known as cataclasis, a process occurring in response to regional shock metamorphism (Bradlower et al., 1998; Farndon, 1992; Fischer, 1986; Kearey, 2001).

The occurrence of boudinage structures and seemingly cross-cutting thrusts and interleaved micro shears seen on the opposing sides of the cave walls were found to be correlatable along strike and at a hanging/footwall offset value of ±12 m (Fig 30). This phenomenon was never before noted or observed in other caves found in the Far West Rand expanse, the Cradle of

Humankind, or within the Malmani dolostone lithologies in general. It appeared that the speleogenic morphology of Armageddon Pot might be unique to the region, adding to the speleogenic variability of caves found in the Malmani dolostones.

1.5. Motivation and scope of this study

Armageddon Pot presents speleogenic characteristics different from those observed in the

Cradle of Humankind. In the case of Armageddon Pot, cataclasite horizons along a normal fault in association with shear and thrust zones and the presence of compressive and

13 extension (boudinage) structures cutting across cave strike suggest dynamics different from

‘normative’ tectonic/neo-tectonic faulting generally associated with dissolution speleogenesis. Furthering interest, Armageddon Pot seems to have an affinity with the

Panvlakte/Witpoortjie horst block. It appears that speleogenic transmission may be related to the derivation and broader structural anatomy of the Panvlakte/Witpoortjie horst block. This also suggests a direct causal relationship with factors or influences responsible for the creation of, or the modifying of this already anomalous structural entity.

Based on the above, it became clear that an in-depth study of Armageddon Pot was warranted, also including a comparison with cave systems in the Cradle of Humankind. Cave exploration, observation, and field mapping have been the primary tools in studying and modeling the geology of Armageddon Pot. This has been supplemented by overlaying cave surveys on Google Earth satellite imagery of the region’s in question in order to determine fault and joint block strike trends-as well as determining the orientation of thrust orientation measurements taken.

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Chapter 2: Methodology

2.1. Cave exploration

The initial exploration of Armageddon Pot came about during recreational caving events. This stimulated the formal exploration. Initially, exploration only included visual inspections made during a number of succeeding visits to the cave. During the initial exploration, a basic line survey was completed using a Leica disto D3a laser rangefinder and clinometer for inclines less than 45o and a Suunto Tandem compass and clinometer in defining the length, and strike of the cave. The core survey team comprised John Dickey

(Exploration leader and SEC Chairman), Steven Tucker, Gerrie Pretorius, and Rick Hunter.

During subsequent visits, most Members of SASA/SEC continuously assisted them

At the date of writing, surveying and exploration of the cave are ongoing with an explored length along strike approaching 2.1 km (line of sight) and vertical depth approaching ±260 m

(820ft). This, so far recorded, makes Armageddon Pot the deepest known ‘dry’ cave in South

Africa (Unpublished SASA/SEC survey data). During 2014-2016, a penetrable explored length of 2.6 km was established and a relatively detailed line survey completed. However, the sheer size of the system and difficulty in negotiating a challenging terrain makes this an arduous task and it is foreseeable that this project may continue for some time into the future that may result in extensions added and alterations made to the final survey. When work is completed, it is hoped to encompass all data, including structural measurements, and other related specifics into a high definition survey.

2.2. Interpretation of satellite data

Much use was made of Google Earth imagery and aerial (stereoscope) photo blocks in correlating the caves’ position to known regional structures. This was then correlated with geological maps delineating the extent of both the Panvlakte/Witpoortjie horst block as well

15 as the Foch thrust, which are known to have a causal relationship with the Vredefort impact event (Ngobo, 2003).

2.3. Collection of structural data

It was decided to approach the definition of structural types and characteristics seen within these caves in a purely descriptive way, before moving on to interpretation and testing of hypothesis. Structural data collected comprised taking numerous compass strike and clinometer dip measurements of observed thrust zones and compression structures as well as determining slip distance between the hanging and footwall of what appears to be a normal fault that seems to determine the linear extent of the cave system.

2.4. 40 Ar/39Ar radiometric dating

40Ar/39Ar dating of sericite from schistose rocks sampled at select localities was carried out and used in determining date ranges for specific structures. Sericite in these samples is too fine-grained to be separated by hand picking, and a two-staged settling method was used.

Sample fragments were crushed inside plastic bags with a hammer, placed in bottles with 500 ml of sterile water and subjected to ultrasonic agitation for three hours to disassociate small grains. After shaking and allowing settling for 20 minutes, the water with the suspended matter was decanted into a second bottle. This second bottle was then left standing for one hour, leaving grains <5 µm still in suspension. After decanting this suspension the settled material, mainly sericite between 5 and 20 µm, was dried and used for analysis.

Approximately 2 mg per sample was wrapped in aluminum foil for irradiation.

40Ar/39Ar dating was carried out in the noble gas laboratory of the SPECTRUM analytical facility at the University of Johannesburg, as described by Makhubela et al., (2017) following

16 earlier work (Stoenner, et al., 1965; Phillips et al., 1998; 1999, Renne, et al., 2001; Sanna, et al., 2011). Irradiation was done in the SAFARI 1 nuclear reactor at Pelindaba, Pretoria, operated by NTP®, a subsidiary of the Nuclear Energy Corporation of South Africa

(NECSA). With the reactor running at 20 MW, the samples were irradiated for 20 hours

(Phillips et al., 1999). Stepwise heating (mostly 12-16 steps) was done by a defocused beam from a SPECTRON® continuous Nd-YAG 1064 nm laser, capable of producing up to 9W in

Too mode. The argon isotopes measured in seven cycles using a Johnston electron multiplier detector operated in analogue mode (Kossert and Günther, 2004). The total 40K decay constant value used is (5.554 ±0.014) × 10-10 yr-1 (Renne et al., 2010). Fluence monitors placed at the bottom and top of the stack were: Hb3GR amphibole (1080.4 ±1.1 Ma, Renne et al., 2010), McClure Mountain amphibole (MMhb, 523.1 ±1 Ma, Renne et al., 1998), and Fish

Canyon sanidine (FCs, 28.201 ±0.046 Ma, Kuiper et al., 2008). Measurements, run regressions, corrections and age calculations were done using software developed in-house, which includes full error propagation (including uncertainties of the decay constant and J- values) by Monte Carlo simulations. The full analytical data set and further details are given in (Appendix: Table of argon isotope data, 40Ar/39Ar ages, Ca/K and Cl/K ratios of individual heating steps).

2.5. Comparative work

The interpretation of the above was done in comparison with select caves found within the

Cradle of Humankind known to have been controlled by lithology layer-parallel controls interacting with cross-cutting fracture systems of Palaeoproterozoic origin and an NW to SE directed extensional far-field stress (Dirks and Berger, 2013) in testing the hypothesis that

Armageddon Pot’s speleogenic initiation and subsequent progression are fundamentally different from these.

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2.6. Modeling

All of the available data are interpreted and used to construct a model for the controls on the origin and evolution of Armageddon Pot. anxious

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Chapter 3: Regional geological and geographical setting

3.1. Stratigraphic context

3.1.1. Study area ‘A’ the ‘Cradle of Humankind’ (CoH)

According to Visser (1984), in the wider CoH the Malmani Sub-Group is represented by five formations, the basal Oaktree followed by the Monte Christo, Lyttelton, Eccles, and the uppermost Frisco Formations. The total thickness this Sub-Group attains here is approximately 2100 m and little variation exists within the isopach values of individual formations (SACS, 1980).

The basal Oaktree Formation consists of dark-grey, largely chert free dolostone that contains large stromatolite domes, shale marker beds, the convolute chert marker and a tuffite unit

(Eriksson et al., 1975).

The succeeding Monte Christo Formation has been divided into the following members according to Obbes (2000). The lowermost Rietfontein Member consists of dark dolostone characterized by waves and current ripples as well as numerous oolite beds. On aerial and ortho-photographs this has a streaky appearance is coarse textured and shows well-defined bedding traces.

The Mooiplaatz Member comprises dolostone dark grey in color with more chert bands than the underlying Rietfontein Member. Stromatolites, ripple marks, and oolite beds characterize it. It has a streaky appearance, light tone and well-defined bedding traces on aerial photos.

The upper chert is the base of a laterally continuous silicified chert breccia.

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The Rietspruit Member comprises three chert-poor, color-banded dolostone units and three chert-in-shale breccia horizons. On aerial photos, it has a dark tone and smooth texture, with bedding traces being poorly visible. The upper contact is the base of a chert breccia.

Crocodile River Member: Overlying the chert breccia this member contains stromatolites, and wave rippled dark-grey dolostone units containing öoliths. On aerial photos, well-defined bedding traces are seen. The upper contact is below a prominent laterally continuous chert-in- shale breccia.

The overlying Lyttelton Formation consists of dark-grey dolostone with more chert in its lower part than in the central section. The dolostones in this formation weather to a chocolate-brown color. Megadomal stromatolites are common whilst columnar stromatolites and cross-bedded arenitic dolostone (dolarenite) also occur. In aerial photos, the Lyttelton

Formation is characterized by a dark tone and poor bedding traces. The contact between the

Lyttelton Formation and the overlying Eccles Formation is gradational and defined by a marked increase in chert content.

The Eccles Formation outcrops as the prominent Schurweberg and consists of light-grey interbedded chert and dolostone that weathers to what is referred to as a “bread and butter” appearance. On aerial photos, the Eccles Formation is easily defined by means of a sharp topographic contrast with the more subdued topography of the Lyttelton Formation. The

Eccles Formation also exhibits well-defined bedding traces and near the top, a chert-in- breccia occurs overlain by a dark grey chert poor dolostone. The uppermost part of the Eccles

Formation consists of a silicified chert breccia known as the Leeuwenkloof Member (Giant chert breccia).

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The uppermost dolomitic formation of the Malmani Sub-Group, the Frisco Formation, consists of chert-poor dark-grey dolostone that weathers to a dark brown color and shows ill- defined bedding traces on aerial photographs. It further exhibits stromatolites, gas escape structures, and horizontally laminated dolarenite. In the lower portion, tuffite and shale beds occur and the upper contact with the Pretoria Group is characterized by the Rooihoogte

Formation.

The Rooihoogte Formation consists of variable thickness of weathering breccias with a siliceous-ferruginous matrix and residual chert clasts. It occurs as a prominent capping on some topographic high-lying areas. This formation may be the silicified weathering product of the underlying carbonate rocks formed on a palaeo-karst terrain (Eriksson and Truswell,

1974; Eriksson et al., 1975; Eriksson and Alterman, 1998; Eriksson et al., 2001, 2006 in

Johnson et al., 2006 (eds).

Caves in the study area do not seem to be limited to only one formation, but seem to be distributed over all the formations present as their placement is not dependant on stratigraphy characteristics, but rather on cross-cutting structures transgressing all formations. The same applies to Study area ‘B’ as here caves also occur within all the carbonate formations present with some, such as Armageddon Pot encompassing at least two formations, the Frisco and

Lyttelton.

The Pretoria Group overlies the Chuniespoort Group unconformably and buried a palaeo- karst landscape developed on dolostone that was exposed during a depositional hiatus lasting at least eighty million years. The Pretoria Group was deposited after renewed subsidence and is composed of a predominantly alternating sequence of mudrock and sandstone formations

21 with subordinate conglomerates, diamictites and carbonate rocks as well as significant basaltic-andesitic volcanic belonging to the Hekpoort Formation (Eriksson and Truswell,

1974; Eriksson et al., 1975; Eriksson and Alterman, 1998; Eriksson et al., 1995; Eriksson and

Reczko, 1995; Ericksson et al., 2001, 2006).

Fragments of Karoo Supergroup sediments are encountered sporadically and their placement may be attributed to Palaeo valley fills and karst features. This sequence is completed by cave breccias and alluvium of Tertiary origins with the former found within weathered karst forms such as caves and the latter found mostly along the existing drainage networks (Dirks and

Berger. 2013, personal communications, Dirks, 2013).

3.1.2. Study area ‘B’ the Far West Rand

Here carbonates of the Transvaal Supergroup comprise the basal Oaktree and overlying

Monte Christo, Lyttelton, Eccles and Frisco Formation with the Deutschland Formation

(similar to the CoH) absent. The lithology characteristics are the same as seen within the

CoH.

To the NW and west, the dolostones are bordered in what appears to be an arcuate trend by basement granitoid, volcanoclastic rocks of the Ventersdorp Supergroup and Witwatersrand

Supergroup, all present in fragmentary outcrops. To the north and NE of Westonaria, positioned around the Johannesburg basement dome (along with the Witwatersrand plateau) exposures of Ventersdorp Supergroup and Witwatersrand Supergroup lithologies border the dolostones of the Malmani Sub-Group. Around the town of Westonaria pockets of deltaic clastics of the Karoo Supergroup can be found preserved in Palaeo dolines (Marker, 1974,

22

Rubidge, 1995). These are mainly thin diamictites of the Dwyka Formation overlain by, in some places coaliferous sediments of the Ecca Group (Visser, 1984).

To the east, towards the city of Alberton, distal sedimentary and volcanoclastic lithologies of the Karoo Supergroup overlie the dolostones of the Transvaal Supergroup. To the south the area is bordered by the prominent Gatsrand ridge that is formed by Pretoria Group sediment lithologies and forms one of a number of conspicuous cuesta-like arcuate rings associated with the Vredefort impact event (Bischoff, 1988; Brink et al., 1997; Brink et al., 1999; Brink et al., 2000 a, 2000 b). A small igneous complex, the Losberg complex, containing mafic and ultramafic rocks and considered an outlier of the Bushveld Igneous Complex, is located in proximity to Potchefstroom and is situated within the perimeters of the Potchefstroom synclinorium (not indicated in the stratigraphic column) (Boshoff, 2010) (Fig. 5 and 6).

Fig 5: A stratigraphic column of the formations and members of the Transvaal Supergroup carbonate lithologies within the CoH and the Far West Rand (The succeeding Pretoria Group is excluded).

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Fig 6: A geological map of the area of study, Study ‘A’ is within the CoH and ‘B’, the locality where Armageddon Pot is found (Far West Rand) (After maps of South Africa: https://images.search.yahoo.com).

3.2. Topography

3.2.1. Study area ‘A’ the ‘Cradle of Humankind’ (CoH)

This area covers approximately 500 km2 and is located on the 1: 250 000 scale geological map sheets 2626 Far West Rand and 2526 Rustenburg as well as on the 1: 50 000 scale topographic map sheets 2627 BA Randfontein, 2527 DC Hekpoort, 2527 DD Broederstroom,

2528 CC Centurion and 2627 BB Roodepoort.

Topographically, the area known as ‘Cradle of Humankind’ (CoH) belongs to the Middle and

Upper Bush field region with the present thalweg depth at ±1431m (Carruthers, 2007). The regional northerly dip appears to have had a definitive role in the landscape evolution of the region, which took place in the wake of a southwards retreating scarp, forming the southern perimeter of the Limpopo basin (Partridge, 1980, Partridge and Maud, 1987, 2000). Drainage is uniform to the north draining into the Hartebeestpoort gorge, now dammed (Carruthers,

24

2007). The topography is also strongly influenced and regulated by neotectonics and differing weathering characteristics suggested by (Dirks and Berger, 2013; Dirks et al., 2010).

To the south and adjacent to the Johannesburg dome the lowermost Orange Grove quartzites and shales of the Witwatersrand Supergroup form a pronounced escarpment. Directly to the north thereof the Black Reef including the basal Oaktree Formation of the Transvaal

Supergroup is located and has no distinctive profile that forms a low relief landscape.

The overlying Monte Christo Formation and its subdivisions can be described as follows. The lowermost Rietfontein Member exhibits a moderate relief, is coarse textured and has well- defined bedding traces on aerial and ortho-photographs. The Mooiplaats Member has a prominent relief, light tone and well-defined bedding traces on aerial photos. The upper chert is the base of a laterally continuous silicified chert breccia The Rietspruit Member comprises three chert-poor, color-banded dolostone units and three chert-in-shale breccias. On aerial photos, it has a dark tone, low relief, smooth texture, and poor bedding traces. The upper contact is the base of a chert breccia whilst the Crocodile River Member exhibits a prominent topographic expression.

The succeeding Lyttelton Formation is characterized by a relatively subdued topography whereas the subsequent Eccles Formation outcrops as the prominent Schurweberg. Near the top of the Eccles Formation, a chert-in-breccia occurs overlain by a dark grey chert poor dolostone whilst the uppermost part of the Eccles Formation consists of a pronounced silicified chert breccia known as the Leeuwenkloof Member (giant chert breccia) that express as pronounced caps. The final carbonate formation, the Frisco is characterized by a subdued topography. The succeeding Rooihoogte Formation consists of variable thickness of

25 weathering breccias with a siliceous-ferruginous matrix and residual chert clasts and occurs as a prominent capping on some topographic high-lying areas (SACS, 1980).

To the north, downwarping of the Bushveld Igneous Complex (BIC), isostatic uplift of The

Johannesburg dome and differential weathering characteristics of the Pretoria Groups composite formations developed pronounced cuesta topography, colloquially known as

Bankenveld (Carruthers, 2007).

In terms of vegetation, the CoH is characterized by patchworks of dense and sparse

(predominantly Acacia) woodland forests encroached upon, and in places wholly replaced by open savannah. In places, gully and hardwood forest prevails in protected gullies. Wetland type flora and fringe, dense riverine forests exist in places in close association with perennial drainage networks (Carruthers, 2007; Personal observations, author).

3.2.2. Study area ‘B’ the Far West Rand

The mapping area covers an area of approximately 1000 km2 and is located on the 1: 250 000 scale geological map sheets 2626 Far West Rand and 2526 Rustenburg, and on the 1: 50 000 scale topographic map sheets 2627 AC Rysmierbult 2627 AD Carletonville, 2627 BB

Roodepoort, 2627 CA Potchefstroom, 2627 CB Klipdrif, 2627 CC Skandinawiedrif, 2627 BC

Westonaria and 2627 CD Parys.

Study area ‘B’ is situated along the Far West-Rand expanse or West-Wits line positioned on the older African and post-African surfaces (van Niekerk, 1997) to form part of the Highveld situated to the south of the mentioned escarpment line at ±1663 m. In response to the westwards tipping of the continent, contour altitude decreases towards the west and south.

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However, lithology dip values within the region vary considerably. Along the southern perimeters of the Johannesburg dome, they seem to exhibit a strong southerly dip.

To the south of the Johannesburg granitoid-greenstone dome and the main subject of study the prominent Gatsrand ridge formed by Pretoria Group sediment lithologies forming one of a number of conspicuous cuesta-like arcuate rings associated with the Vredefort impact event exhibits strong dip variation along strike developed along a strongly developed arcuate trend, all pointing towards the Vredefort impact event epicentre.

To the west of the CoH and over the scarp the area is characterized by a well-defined pedi and peneplanated post-African surface platforms with little topographic expression (van

Niekerk, 1997). Here the dolostones exhibit lesser dip values and in caves like Boons located on the 1:50 000 2627 AA Mathopestad topographic map at co-ordinates S26o 5.874′ E27o

7.839′ and Koster cave, also known as Nick’s cave, located on the 1:50 000 2626 Gamogopa topographic map at co-ordinates S26o 2.552′ E26o 42.475’ map. In both cases dip values <

12o have been measured.

Due to the long erosion history of this region resulting in peneplanation and the development of thick Terra Rossa lithological boundaries are difficult to distinguish on aerial photos.

In terms of vegetation, the area is almost entirely covered by extensive grasslands (Savannah) with sparse tree coverage, whilst just north of Carletonville an extensive wetland and deflation pans can be found as part of the Vaal-Orange river basin.

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3.3. Regional geological background

For the purpose of this thesis the area of study is divided into a northerly section north and north-east of Krugersdorp referred to as study area ‘A’ whilst study area ‘B’ is located to the south-west of the Johannesburg dome and as mentioned concentrated around an area south of

Carletonville and Westonaria, North-West Province (Fig. 1 and 2).

Study area ‘A’ lies in an arcuate belt limited in extent by the Bushveld Igneous Complex to the north and the Johannesburg granitoid-greenstone dome to the south. All geological formations in this region demonstrate a predominantly EW strike and northerly dip angles varying from 17-25o (personal observations, author). To the north, the CoH dolostone series is overlain by deep marine clastics of the Pretoria Group forming a well-developed cuesta landscape comprising shale and quartzite formations intercalated by minor volcanics which likewise strikes EW and dip to the north with similar dip angles varying from 17-25o. Of significance, a major volcanics Member, the Hekpoort Andesite Formation also forms a composite of the Pretoria Group and likewise dips underneath the Bushveld Igneous Complex due north.

The basement underlying the areas of interest is the Halfway House Palaeo-Meso-Archaean

Kaapvaal craton granite greenstone units of Swazian age (Snyman, 1996). The first supra- crustal unit to be deposited was the Dominion Group, followed by the Witwatersrand

Supergroup (Fig 8). Following this, copious amounts of lava poured onto the crust during the

Ventersdorp rifting event, most likely due to mantle plume activity (Manzi et al., 2013).

Incomplete rifting failed to rupture the continent and instead it stabilized around ±2650 Ma

(McCarthy, 2009).

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During subsequent subsidence, relaxation and extension of the Kaapvaal craton a third, graben bound rift developed between the northerly Thabazimbi-Murchison line and the southerly Sugarbush fault. This was to become the Transvaal basin, initially comprising three separate structural proto basins, the Kanye-(Botswana), Griqualand-West and Wolkberg basins (Eriksson and Truswell, 1974; Eriksson et al., 1975; Eriksson and Alterman, 1998;

Eriksson and Reczko, 1995; Eriksson et al., 2001; Eriksson et al., 2000; Eriksson et al.,

2006).

The Transvaal Supergroup carbonates are exposed in two geographically separate areas: the

Transvaal basin, where it circumscribes the Bushveld Igneous Complex, and the Griqualand

West basin at the western Kaapvaal craton margin, that extends into southern Botswana beneath Kalahari cover as the Kanye basin. A broad basement high separates the two basins, referred to as the Vryburg arch (Johnson et al., 2006) (Fig 7).

Fig 7: Position of the Transvaal and Griqualand West basins in South Africa in relation to the Vryburg arch (After Johnson, 2006).

29

Fig 8: Detailed stratigraphy of the areas of interest (After stratigraphy of the

Transvaal Supergroup: https://images.search.yahoo.com).

Transvaal Supergroup sedimentation in the Transvaal basin was initiated by the deposition of the quartzites of the Black Reef Formation which overlies all pre-basinal successions across the preserved basins along an unconformity. A transgressive black shale formation forming the base of the Chuniespoort Group overlies the Black Reef quartzite. The Chuniespoort

Group further includes the Lower Malmani Sub-Group, consisting of stromatolitic dolostone with chert intercalations, and the upper Malmani Sub-Group comprising the Penge (Banded

Iron Formation) and Duitschland Formation (absent in the study area) (SACS,1980).

Differentiation between the formations of the Malmani Sub-Group is made on the basis of the presence or lack of interbedded chert and shale, the variety of stromatolite structures and low

30 angle unconformities within the Sub-Group. The interbedded mudrocks and sandstones, as well as cherts and shale breccias in the Malmani Sub-Group, are believed to represent significant disconformities and a carbonate ramp depositional model has been proposed with supra-tidal, intertidal and subtidal to shallow basinal facies occurring.

Age constraints from dated volcanics and detrital zircon grains for all three of the preserved proto-basins, the Kanye-(Botswana), Griqualand-West and Wolkberg basins indicate that deposition of the entire Transvaal Supergroup took place between 2658 ±1 Ma and 2224 ±21

Ma with the carbonate succession forming over a period of 120 million years between 2643 and 2520 Ma (Fig 8). At the fullest extent of its development, this composite basin is thought to have covered an area in excess of 600 000 km2 (Beukes, 1986; Button, 1973; Eriksson, and

Truswell, 1974; Eriksson et al., 2001, 2006).

3.4. Landscape evolution and drainage

3.4.1. Landscape evolution

Over both study areas, large portions of the Transvaal basins sediments have been eroded away. This cycle of erosion began shortly after the breakup of Gondwanaland around ±180

Ma (McCarthy, 2009; van Niekerk, 1997). Remnants of the original Gondwana Cretaceous surface can still be seen in portions of the Lesotho highlands (Moon and Dardis, 1988; Moore et al., 2009; Partridge and Maud, 1987, 2000). As much as 2-3 km (vertical) was removed by erosion in the Southern African interior, which was largely pedi and peneplained to result in the African and post-African surfaces (van Niekerk, 1997).

Subsequent epeirogenetic uplift resulted in an accentuated scarp (Drakensberg scarp) fringing the South African interior. In the Highveld extensive chemical weathering occurred at this

31 time, resulting in the formation of a deep pedogenic weathering profile over the region-the so-called Waterval saprolites (van Niekerk, 1997). Renewed uplift and tilting to the west at

±30 Ma resulted in the generation of the Post-African 1 surface characterized by valley incision. In the West Wits expanse, this was later filled in by the West Wits ferruginous silty mudstone (Partridge, 1980; Partridge and Maud, 1987; van Niekerk, 1997).

Following the deposition of the West wits ferruginous silty mudstone (Pre 2.5 Ma) a podzolic soil profile was superimposed as a result of pedogenesis under a savannah woodland landscape and with slow erosion. Mineral leaching indicates humid conditions (van Niekerk,

1997). At ±2.5 Ma renewed uplift again interrupted the region’s erosion stasis, leading to the

(less severe) post-African 2 weathering cycle. At this time the interior of Africa became progressively more arid resulting in the encroachment of Kalahari sand and dust over the region. These combined factors resulted in the forming of the post African 2 surface. In more recent times and up to the present this was followed by the pedogenic reworking of Kalahari sediments during more humid times resulting in the formation of the Hutton soils and a thin humic soil cover supporting a savannah type C4 grassland (personal communications, van

Niekerk, 2016) whilst ongoing isostatic repair dynamics led to a continuation of valley incision at a slower rate.

3.4.2. Drainage

South Africa exhibits an asymmetric drainage flow pattern (Goudie, 2005) due to an epeirogenic uplift with an (anticlinal) flexure axis called the Etosha-Griqualand-Transvaal

(EGT) axis (Tankard et al., 1983; Moore, 1988; Moore and Larkin, 2001; Moore et al., 2009;

Watts, 2001). (Fig: 9 and 10). This flexure axis is associated with tensional dynamics in the lithosphere responding to plate tectonics. This assisted in the asymmetric development of the

32 river flow patterns noted over Gauteng’s south-western (old southern Transvaal) region, creating a watershed. In response, the respective African surfaces underwent erosion by river systems flowing both to the SW (to the Atlantic), and to the north (to the Limpopo River and into the Indian Ocean) (Nyblade, 2003; Partridge, 1980; Partridge and Maud, 1987).

Fig 9: Indicating the position of the Etosha-Griqualand-Transvaal axis (After Nyblade and

Robinson, 1994).

The south-western Highveld erosion platform associated with the African, post-African 1 and

2 weathering surfaces was less intense than seen over the CoH resulting in the formation of a low relief landscape (van Niekerk, 1997). On the Northern system, i.e. in the CoH, erosion was more intense with the development of an escarpment incising the Highveld. It is thought that the more pronounced erosion over the CoH was mainly the result of an increase in the thalweg gradient of the African Surface by tilting of the peneplain with the present scarp forming the southern borderline of the Limpopo basin (Partridge, 1980; Martini et al., 2003)

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(Fig.10). However, Dirks and Berger (2013) invoke neo-tectonics here with the reactivation of old fracture systems as the cause of the region’s accentuated erosion levels.

Fig 10: The northerly drainage (Limpopo basin) of South Africa ‘A’ and the south-western drainage (Vaal-Orange River) basin ‘B’ of South Africa (After the drainage basins of South

Africa: https://images.search.yahoo.com).

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Chapter 4: Cave formation processes

4.1. Introduction

Although dissolution within carbonate rocks is by far the most prevalent mechanism for cave formation, speleogenesis can also occur in other rock types such as gypsum and halite deposits (Gunning, 2004).

The two main types are epigenetic caves, a cave formed by the action of surface waters descending into the ground via authigenic or allogenic transport dissolving rock, whilst the second type, hypogene caves are formed by hydrothermal water rising from below (Fig 11, A and B), dissolving the rock, usually as a result of the mixing of waters with different pH values (Bauer, 1971; Jackson, 1982; Garrels and Christ, 1965, Langmuir, 1997).

..

A: Epigenetic B: Hypogene

Fig 11 A and B: Demonstrating the mechanism through which epigenetic and hypogene speleogenesis occurs (After how do caves form: https://images.search.yahoo.com).

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However, there are numerous additional mechanisms by which caves can be formed. Caves have been classed by Gunning (2004) into the following varieties with some exhibiting either an epigenetic or hypogene character or both:

Primary caves: Lava tubes are formed through volcanic activity and are the most commonly occurring primary caves. As mafic or ultra-mafic lavas flow under gravity, the surface crusts over whilst the inner portions remain fluid draining away, leaving a hollow tube. The longest lava tube named Kazumura is found in Hawaii and measures 65.5 km in length going down to a depth from the surface to 1101 m. Another example is caves formed in gneiss or granite where the removal of unconsolidated materials along a shear zone formed an elongate passage, or in between joints forming complex non-systematic passages amongst boulders.

Caves like these are not common but have been observed where shearing acted as speleogenic control within gneiss whilst ‘boulder caves’ are relatively common along scree slopes.

Sea caves or littoral caves: Sea caves are found along coasts around the world. These are called littoral caves and are formed when planes of weakness in the country rock are being exploited by wave action. These caves often develop along faults or bedding plane.

Exemplary examples of these can be seen in the vicinity of Mosselbay, Western Cape where folded quartzites of the Cape Supergroup provided the ideal environment for generating littoral caves (personal observations, author).

Erosion caves: These caves form entirely by erosion by flowing streams carrying abrasive materials. These can form in any type of rock, including granites. Generally, there must be a zone of weakness to guide the water, such as fractures, a fault or joints. A subtype of this type

36 of erosion cavitation is wind or aeolian caves carved by wind-borne particles. Many caves initially formed by dissolution are subsequently enlarged by means of erosion.

Locally a cave named Mogoto located in quartzites of the Pretoria Group formed along a bedding plane and in response to abrasion. This unique cave is situated in close proximity to the Makapansgat lime works outside Mokopane (Potgietersrus) Limpopo province and measures 1.6 km in length (Unreferenced SASA data).

Glacier caves: these caves are formed by melting ice and flowing water under glaciers. The morphology of these cavities is influenced by the slow flow of the ice, which tends to collapse the cave again in time.

Fracture caves: These caves are formed when layers of suitable minerals such as gypsum dissolve from between less soluble rock causing fracturing and block collapse.

Talus caves: these caves are formed by openings that have remained within a scree slope often found on a pediment slope. These unstable deposits may be subject to frequent alteration due to gravity slippage, rock falls or landslides.

Anchialine caves: these caves form in response to the effects of the alternating (pH) and chemical composition of fresh and saline water. The openings to these caves are often sub- marine features. Strictly spoken, they should be classed within dissolution speleogenesis with special reference made to the cause of dissolution, that of rapidly alternating water chemistry and the dissolution effects thereof on the country rock.

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Caves are found in the following configurations:

Branchwork caves: These caves resemble surface dendritic stream patterns, they are made up of passages that join downstream as tributaries and are the most common of cave patterns.

They normally form near sinkholes where groundwater recharge occurs. Each passage or branch is fed by a separate recharge source and converges into other higher order branches downstream.

Angular network or box work caves: these caves form when cross-cutting open unloading joint blocks or fracture systems are being developed into cave systems by dissolution. These fractures/extensional unloading Joint blocks networks form high, narrow, straight passages that persist in widespread closed loops. This configuration is most commonly observed within the CoH.

Anastomotic caves: these caves largely resemble surface braided streams with their passages separating and then meeting further down the drainage. They usually form along bedding structures and only rarely cross into upper or lower beds. This kind of cave seems to largely define the type cave systems of the Cango Valley, Western Cape.

Spongework caves: These caves are formed as dissolution cavities are joined by mixing of chemically diverse water. The cavities form a pattern that is three-dimensional and random.

Ramiform caves: These caves form irregular large rooms, galleries, and passages. These randomized three-dimensional rooms form from rising hypogene hydrothermal sulfide enriched brine that erodes the carbonate rock.

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4.2. Dissolution physics and chemistry

The dissolution of rocks associated with caves most commonly associates with chemical disbanding, and as such a short introduction is needed to explain chemical weathering, and how that interacts with carbonate rocks (in as far as speleogenesis is concerned).

4.2.1. Types of Chemical Weathering

There are three basic types of chemical reactions that cause four types of chemical weathering of rocks. The first two, dissolution and hydrolysis are caused by reactions with acids. Hydration is the absorption of water. Oxidation is a reaction with oxygen (Bauer, 1971;

Langmuir, 1997; Summers and Bennet, 2003; Gunning, 2004). All of these apply to speleogenesis.

4.2.1.1. Acid Reactions

In its most rudimentary form acids are chemical compounds that produce H+ ions when dissolved in water. The stronger the acid, the more H+ ions they produce. Acids react with any rock mineral that has other positive ions, like Ca++, Na+, or K+ by taking their place- which alters the chemical composition of the mineral and disrupts its atomic structure – thereby cause destabilization and disbanding (Guch, 2006). As stated, the most important natural acid concerned with carbonate dissolution is carbonic acid (H2CO3), which forms when carbon dioxide is taken up in water.

However, in itself, limestone and dolostone are not soluble. But if an acid, in this case, carbonic acid is introduced, hydrogen ions (H+) react with the carbonate to form hydrogen carbonate (HCO3-) ions, which are soluble in water. With the addition of more acid, two hydrogen ions will react with a carbonate to form carbonic acid (H2CO3), which in time

39 dissipate in gaseous form or is driven off in a water medium. Carbon dioxide (CO2) being dissipated into the atmosphere is frequently noted in caves where often heavy carbon dioxide

(CO2) traps or sinks can pose a threat and a condition known as hypercapnia can become life- threatening.

4.2.1.2. Hydrolysis

In hydrolysis, silicate and carbonate minerals transform into new minerals, principally clay, which have a sheet-like structure similar to mica whereby both the chemical composition and crystalline structure become completely different (Drever, 1997). This is frequently seen in the caves of the CoH and along the Far West Rand where hydrolysis converted once solid dolostone into clay wad.

4.2.1.3. Hydration

The term ‘hydration’ refers to the absorption of water. The H+ and OH-ions of water incorporate themselves into the atomic structure of a mineral to form a new version of it called a hydrate. If the original mineral had a chemical formula of X, the new suite of minerals will have chemical formulas of (XnH2O). For example, anhydrite (CaSO4) exposed to water hydrates into gypsum (CaSO4 2H2O). Examples of this can be seen in sheets or loose powdery assemblages of gypsum seen in numerous caves along the Far West Rand-having resulted from the hydration of anhydrite. Particularly massive deposits of this mineral have been observed in a cave called West Driefontein at co-ordinates S26o 22.782′ E27o27.584′ situated on the premises of the West Driefontein Goldmine, Westonaria, North West province.

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4.2.1.4. Oxidation

Oxidation occurs where oxygen from the atmosphere reacts with metal elements in the rocks to form oxides. The most common metal involved is iron. It reacts with oxygen to form iron oxide minerals such as hematite (Fe2O3) or, if water is present which it often is, hydration occurs in conjunction to form limonite (Fe2O3 nH2O). Oxide minerals tend to be structurally weak and easily crumble or is simply washed away leaving cavities. Numerous examples of oxidized iron (limonite) can be seen in numerous caves and often forms the red, brown or yellow earths in caves and streaks on cave walls, often discoloring speleothems. In

Armageddon unique complete speleothems are formed from goethite and limonite. In one spectacular case, a cave in Mpumalanga, known as Mbobomongkulu (big hole, in Zulu) at

o o co-ordinates S25 32.358′ E30 39.905′ exhibits bright green copper oxide (CuO2) streaks against a back wall in a large terminal chamber, probably originating from the supergene leach zone of a localized copper deposit (probably hydrothermal veinlets) higher up in the dolostone lithology from where it arrived in the oxide zone, the cave (personal communications, Martini, 1984).

4.3 Factors influencing rock disintegration

4.3.1. Mineral Composition

Rocks composed of minerals farther out of equilibrium with the surrounding conditions will undergo faster chemical weathering (Hamblin, et al., 1980). Minerals with more positive ions for acid to attack will also weather faster than minerals without.

4.3.2. Soil/Vegetation Cover/ bacterial interaction

Plant roots grow into the joints of rocks creating cracks (mechanical weathering) which allow more water to seep through and increase chemical reaction. Plants also give off more carbon

41 dioxide, creating a higher concentration in soil than the surrounding air, hence Makondos, shaft-like entry points into subterranean chambers where once a tree stood as can be seen demonstrated at Swartkrans situated in the CoH and Makapansgat, close to Mokopane,

Limpopo province. The involvement of soil bacteria accentuate the process by generating or assisting in the manufacture of carbonic acid whereas climate and atmospheric conditions like temperature and rainfall affect the rate of chemical reactions as can be seen in the caves of

Vietnam where tropical jungle producing high levels of carbonic acid, excessive atmospheric humidity and high rainfall combined with a pure (soft) limestone develops caves of spectacular dimensions (personal observations, author).

4.3.3. Relief

Slope processes like hillside or gully erosion, landslides or slumps result in the exposure of more of the rock’s surface to chemical weathering. This is also a common means by which caves, as noted in the CoH is being exposed to the surface (Dirks and Berger, 2013).

5.1. Carbonate Rock Solubility

The key question regarding solution speleogenesis revolves around the dissolvability of the carbonate host rock. Most quantitative work has been carried out on calcite and limestone, rather than on dolostone. While dissolution is generally seen to proceed more slowly in dolostone than in calcite, saturation is not normally reached for magnesium: there are no dolostone (and certainly no magnesite) speleothems in caves and no Mg-rich residues form in solution cavities in dolostone. Below I review work on the dissolution of limestone, considering that it yields some insights into the formation of caves in dolostone as well.

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G5.1.1. Carbonic acid

The acid most commonly responsible for dissolution is Carbonic acid (H2CO3). Carbonic acid is generated when carbon dioxide is being taken up into water through equilibrium with the atmosphere. Water is a nucleophile whilst carbon dioxide is an electrophile. Nucleophiles react with electrophiles. In this case, the water oxygen nucleophile attaches to the highly electrophilic carbon of (CO2) yielding (H2CO3), which weakly dissociates (Fauer, 1998).

H2O + CO2 <-- > H2CO3 (Equation 1)

+ - H2CO3 <-- > H + HCO3 (Equation 2)

Atmospheric carbon dioxide is a major contributor to the formation of carbonic acid in the environment. The partial pressure for carbon dioxide in the atmosphere is 0.03% of the atmospheric pressure at the surface of Earth (1 bar or atmosphere = 0.0003 bar of carbon dioxide). In addition, plants deliver carbon dioxide to the soil, particularly indirectly, as decaying organic matter is oxidized by bacterial action, but also directly through respiration.

These processes combine with the cracking of rocks by roots to the formation of Makondos

(tubular vertical or near vertical shafts formed around where plant roots once penetrated rock) with notable examples seen at Swartkrans at co-ordinates S26o 1.043′ E27o 43.416′ and

Makapansgat (lime works) at co-ordinates S24o 8.355′ 29o 11.369′ as well as in several other caves within the CoH where in fact, a few caves within the CoH are only accessible through a

Makondo.

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5.1.2. The solution of Limestone on the Surface

Acids react with all rock minerals that have other positive ions, like Ca++, Mg++, Na+, or K+.

During the dissolution of a carbonate mineral, a molecule of H2CO3 is effectively converted

- into two HCO3 ions:

++ CaCO3 + H2CO3 <-- > Ca + 2HCO3- (Equation 3)

The overall equilibrium constant for calcium bicarbonate at ambient temperatures is,

++ -5 [Ca ] [HCO3-]2/[H2CO3] = 4.4 x 10 . (Equation 4)

The (H2CO3) concentration in water is dependent on its (CO2) concentration, which in turn depends linearly on the (CO2) partial pressure in the associated air:

[CO2]aq/[CO2]air = 0.034 (Equation 5)

o The hydration equilibrium constant (at 25 C) of carbonic acid (H2CO3) is

[H2CO3]/[CO2] = 1.70×10−3 (Equation 6)

- If it is assumed that (HCO3 ) forms only from the dissolution of calcium carbonate, then the calcium concentration in the solution is proportional to the cube root of the partial pressure of

(CO2) in the air. For instance, at the surface, a cubic meter of water (1000 kg = 1000 liters) could dissolve 0.48 moles of calcium (19 grams) or 48 grams of limestone. In a warm rainy climate with 1 meter of precipitation per year, this could dissolve 48 grams of limestone per square meter per year or about 18 cm3. This equals .0018 cm of material removed from the surface per square meter, or 1.8 cm per 1000 years, or 18 meters per million years.

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5.1.3. Dissolution in the phreatic and vadose environment

In ‘conventional’ dissolution speleogenesis as commonly observed in the caves of the CoH as well as globally, water is the main dissolution agent (Bauer, 1971; Jackson, 1982; Guch

2006; Wilkinson, 1973; Martini and Kavalieris, 1976; Marker, 1980; Jennings, 1971; Moore and Sullivan, 1978; Farndon, 1992; Langmuir, 1997; Martini et al., 2003; Holland 2007;

Leyland, 2008). Pure water, however, cannot act as a dissolving agent. Two distinct chemical environments below the surface enable the dissolution of carbonates (Bauer, 1971; Garrels and Christ, 1965; Hem, 1985; Holland, 2007; Langmuir, 1997; Moore and Sullivan, 1978;

Summers and Bennet, 2003):

Water takes up carbon dioxide from ambient air. This occurs within the vadose environment, where dissolution occurs by slow gravity seepage of water with a high CO2 content along pre-existing conduits or/and often through imbibition-the absorption of a fluid by a granular rock through capillary action. Soil gas can have much higher CO2 content than the atmosphere, due to the bacterial oxidation of organic matter. In alpine caves, this is a major factor in carbonate dissolution and seems the same in the CoH (personal communications,

Kramers, 2017). In this way, massive volumes of carbonate rock can be dissolved.

In the second instance, water itself becomes the dissolution agent as water undersaturated in calcium bicarbonate can assimilate an appreciable amount of calcium carbonate (Garrels and

Christ, 1965; Hem, 1985; Guch, 2006; Leyland, 2008). Within a phreatic environment, dissolution is most effective just below the water table as the mixing of water volumes with different pH values creates a constantly undersaturated situation in respect to calcium bicarbonate (Bauer, 1971; Langmuir, 1997). This seems to be the leading process by which dissolution occurs within a phreatic environment (Krauskopf and Bird, 1995).

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5.1.4. Effect of temperature

Counter to the typical increase of mineral solubility with increasing temperature observed for most minerals, all carbonate minerals are more soluble in cold dissolution. For example, the

o o -8.02 -8.63 (Ksp) for calcite at 0 C and at 50 C is 10 and 10 respectively (Garrels and Christ,

1965). These values represent a four-fold difference in calcite solubility caused by temperature alone. The reason is that the dissolution reaction for carbonate minerals is exothermic, which results in higher temperatures favoring the solid phase over dissolved ions

(Garrels and Christ, 1965). In addition to an increase in solubility products with decreasing temperature, carbon dioxide is more soluble at lower temperatures, further favoring carbonate mineral dissolution in cooler environments.

5.1.5 Effect of pressure

The increased partial pressure of carbon dioxide (CO2) near the surface of the earth increases the amount of carbon dioxide (CO2) that dissolves, therefore, increasing carbonic acid concentration-and, therefore, intensifies the solubility of carbonate minerals. Pressure alone does not affect the solubility of calcite as much as the effect of temperature. Nonetheless, where pressure applies its effect alone can increase calcite solubility about two-fold providing the conditions for uptake remains within a cold environment (Krauskopf and Bird, 1995). In as far as speleogenesis is concerned; this may apply to phreatic environments where temperature stability and depth may play a significant role.

5.1.6. Carbonate (CaCO3) deposition

The degassing of carbon dioxide from water drives equation (3) to the left. This leads to the precipitation of calcite and the formation of stalagmites, stalactites, and other speleothems.

Although the original thoughts on calcite deposition invoked calcium oversaturation by

46 evaporation, the process appears to be chiefly due to either a temperature increase, or a decrease in the partial pressure of (CO) in the ambient air, or both, as water enters a cave.

Water that has percolated through the soil and rock fractures have in many cases equilibrated with soil gas having an elevated (CO2) partial pressure due to vegetation and microbial action as mentioned above, or with soil gas trapped in capillaries and pockets, pressurized by a water column. Both lead to such water being oversaturated in (CO2) relative to the air in the cave.

6.1. Structural controls

Dissolution speleogenesis is not a random process but controlled and initially contained within definable chemical perimeters and structures determined by extraneous factors. Some problems are encountered if caves are considered to have formed purely by dissolution or abrasion. If dissolution per se was the only prerequisite for speleogenesis without being directed along structured pathways, neither epigenetic nor hypogene speleogenesis would likely occur. The more likely scenario would have been a landscape simply pedi and peneplanated by surface karst processes. It is a well-known fact that faults, fractures, and various joint block types are principle pathways for dissolution speleogenesis (Bauer, 1971;

Martini and Kavalieris, 1976; Moore and Sullivan, 1978; Brain, 1981; Farndon, 1992; Davis and Reynolds 1996; Dirks and Berger, 2013; Engelder and Geiser 1980; Fischer, 1986;

Martini et al., 2003; Clark and Partridge, 2010; Dirks et al., 2012).

6.1.1. The speleogenic interface between rock and water

Although carbonate rock is susceptible to dissolution the conditions for its solubility are specific (Bauer, 1971; Dirks et al., 2012; Dirks and Berger, 2013; Moore and Sullivan, 1978).

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The initial control on subterranean speleogenesis is thus given by the original fractures, faults and/or Joints along which the circulation of groundwater can be channeled, and their degree of permeability. However, due to solid carbonate rock’s low porosity, micro-fractures will not transmit water in sufficient quantities to allow for significant dissolution, and dissolution conduits would not be expected to form unless circulation is possible. Conduits facilitating circulation need to be of a specific minimum dimension or diameter. (Bauer, 1971; Brink and

Partridge, 1965; Moore and Sullivan, 1978; Roberts, 1995).

Owing to the low porosity of dolostones, dissolution occurs chiefly along a two-dimensional plane. The first dissolution interface (karstification) is found on the surface. The karstification of a landscape may result in a variety of large or small scale features both on the surface and beneath. On exposed surfaces, small features may include flutes, runnels, clints, and grikes, collectively called karren or lapiez-these being ribbed and fluted rock due to surface dissolution and etched, fluted and pitted rock pinnacles.

Medium-sized surface features may include sinkholes or dolines (closed basins), vertical shafts, disappearing streams, and reappearing springs. Large-scale features may include limestone pavements, poljes, and blind valleys. Poljes having steep and often perpendicular walls and a more or less flat floor and blind valleys or steephead valley is a deep narrow, flat- bottomed valley with an abrupt end (Bauer, 1971).

Mature karst landscapes, where more bedrock has been removed than remains, may result in karst towers or haystack/egg-box landscapes as seen in China and Vietnam (personal observations, author). Beneath the surface, complex underground drainage systems (such as karst aquifers) and extensive caves and cavern systems may form.

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The second dimension of karst dissolution manifests at depth as epigenetic or hypogene cavities generated along faults, fractures and open (extensional) joint networks and often along bedding planes or lithology boundaries (Davis, 1930; Bauer, 1971; Brain, 1981;

Martini and Kavalieris, 1976; Moore and Sullivan, 1978; Farndon, 1992; Martini et al., 2003;

Clark and Partridge, 2010; Dirks et al., 2012; Dirks and Berger, 2013). These distinct interfaces often occur in a syngenetic relationship so that both surface and subsurface boundaries often form components of an integrated system forming a specific cave or karst region’s speleogenic profile.

6.1.2. Faults

In geology, a fault, or fault line, is a planar rock fracture which shows evidence of relative movement, also defined as a fracture in rock where one side slides laterally past the other

(Press and Sievers, 1982, 1993; Sievers, 1994; McKnight and Darrel, 2000; Marshak, 2001).

These are the most conspicuous structural entities along which dissolution speleogenesis occurs, and have proven to be a major universal contributor towards determining a cave’s linear development and extent (Bauer, 1971; Moore and Sullivan, 1978).

Caves may form along all known faults types with two primary fault types in evidence, these being seismic and non-seismic. Seismic; whereby slippage along fault axis associates with forceful movement causing a severe seismic response. The second; non-seismic, whereby slippage along the fault axis occurs via creep (Fischer, 1986).

Faults can be transpressional or transtensional. In the case of a transpressional fault limited permeability is predicted depending on the irregularity of the fault plane. In a transtensional fault, there may not be much void space along the fault. The importance however of faults for

49 speleogenesis is given by the large extent of these structures, compared to fractures and joints. Faults play a major role as speleogenic control within the CoH as can be seen within

Sterkfontein where a strongly developed strike-slip (transverse) fault determined to a large extent the caves linear extension. Other noteworthy examples are the caves found on the

Bolts properties where caves are clearly aligned along a fault line evidenced by fault breccia cropping out on the surface along strike. Here also, in places strike-slip (transverse) faulting caused folding, resulting in saddle reef formation, in turn accommodating dissolution.

6.1.3 Fractures

In geology, a fracture is a planar feature, which shows no slippage along its opposing contacts. Speleogenic propagation along a static planar fracture can exhibit a similar distribution pattern as that seen along a fault line and is one of the most prevalent structural controls for both epigenetic and hypogene speleogenesis (Beazly, 1980).

Fractures are caused by irreversible strain within the rock matrix wherein the material breaks.

As such, materials can be divided into two classes that depend on their relative behavior under stress. The first, A: being brittle having a small or large region of elastic behaviour but only a small region of ductile behaviour before they fracture; whereas B: ductile materials have a small region of elastic behaviour and a large region of ductile behaviour before they fracture (Engelder and Geiser, 1980; Fischer, 1986). The importance of fractures in speleogenic propagation also seems to depend on void space-allowing penetration. Here fractures aligned along strike with anticlinal folds or having seemed more likely to allow substantial penetration. Numerous caves are seen within the CoH with an example, Tristians cave located on the 1:50 000 2627 BA Randfontein topographic map at co-ordinates S26o

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2.381’ E27o 42.482’ and portions of Bats cave are developed along fractures and not fault lines as no vertical or horizontal movement have been noted as would be the case with a fault.

6.1.4. Joints

The second principal structures along which speleogenesis propagate are joints (Bauer, 1971;

Jackson, 1982; Roberts, 1995). Their genesis, however, may be attributed to a number of varying factors and as such, it is necessary to explain the nature of these structures in some detail and the mechanisms along which they emerge.

In geology, the term joint (similar to fracture) refers to a planar feature in rock where there has been no lateral movement in the plane (up, down or sideways) of one side relative to the other (Gunning, 2004; Holmes and Holmes, 2004; Jennings, 1971; Martini and Kavalieris,

1976; Fischer, 1986). In some cases it may be difficult to distinguish between joints and fractures, the main distinction is that joints generally occur as blocks, with each joint block consisting of numbers of joints crisscrossing one another at various angled orientations.

In addition, joints normally have a regular spacing related to either the mechanical properties of the individual rock or the thickness of the layer involved whilst fractures tend to be singular extended linear features. Joints occur in sets, an overall greater permeability is given for them than for single fractures. In particular, because joint blocks usually contain a tensional component (Ladeira and Price, 1981; Roberts, 1995).

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6.1.4.1. Joint genesis

Similar to the generation of fractures, joints form in solid, hard rock that is stretched such that its brittle strength is exceeded (the point at which it breaks). When this happens the rock fractures in a plane parallel to the maximum principal stress and perpendicular to the minimum principal stress, the direction in which the rock is being stretched. This leads to the development of a single sub-parallel joint block. Continued deformation may lead to the development of one or more further joint blocks. The presence of the first block strongly affects the stress orientation in the rock layer, causing subsequent blocks to often form at a high angle to the first block called oblique joints. Joint blocks are commonly observed to have relatively constant spacing with the spacing roughly proportional to the thickness of the layer (Engelder and Geiser, 1980; Ladeira and Price, 1981; Roberts, 1995).

6.1.5. Joints commonly encountered as speleogenic controls

Joints are classified either by the processes responsible for their formation or by their geometry. The geometry of joints refers to the orientation of joints as either plotted on stereo- nets or rose-diagrams observed in rock exposures. In terms of geometry, three major types of joints are recognized, non-systematic, systematic and columnar joints (Engelder and Geiser,

1980).

6.1.5.1. Non-systematic joints

Non-systematic joints are joints that are so irregular in form, spacing, and orientation that they cannot be readily grouped into distinctive, through-going joint blocks.

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6.1.5.2. Systematic joints

Systematic joints are planar, Parallel, joints that can be traced for some distance, and occur at regularly, evenly spaced distances on the order of centimeters, meters, tens of meters, or even hundreds of meters. As a result, they occur as families of joints that form recognizable joint blocks (Ladeira and Price, 1981; Roberts, 1995).

Typically, exposures or outcrops within a given area or region of study contains two or more blocks of systematic joints, each with its own distinctive properties such as orientation and spacing, that intersect to form well-defined joint systems as can often be seen in the ‘grid- iron’ pattern joints follow in numerous dissolution caves as seen in the CoH but especially significant in caves like Rising Star, Bats, and van Rooyes.

Based upon the angle at which joint blocks of systematic joints intersect to form a joint system, systematic joints can be subdivided into conjugate and orthogonal joint blocks. The angles at which joint blocks within a joint system commonly intersect are called the dihedral angles. When the dihedral angles are nearly 90° within a joint system, the joint blocks are known as orthogonal joint blocks. When the dihedral angles are from 30 to 60° within a joint system, the joint blocks are known as conjugate joint blocks (Engelder and Geiser, 1980).

Within region’s that have experienced tectonic deformation, systematic joints are typically associated with either layered or bedded strata that have been folded into anticlines or synclines as can be seen in the dolostone quarry, Fouries farm, CoH at co-ordinates S26o

1.654′ E27o 42.915′. Such joints can be classified according to their orientation with respect to the axial planes of the folds as they often commonly form in a predictable pattern with

53 respect to the hinge trends of folded strata based upon their orientation to the axial planes and axes of folds (Engelder and Geiser, 1980).

6.1.5.3. Columnar joints

Cooling joints are columnar joints that result from the cooling of either lava from the exposed surface of a lava lake or flood basalt flow or the sides of a tabular igneous, typically basaltic, intrusion. They exhibit a pattern of joints that join together at triple junctions either at or about 120° angles. They split a rock body into long, prisms or columns that are typically hexagonal, although 3, 4, 5 and 7-sided columns are relatively common. They form as a result of a cooling front that moves from some surface, either the exposed surface of a lava lake or flood basalt flow or the sides of a tabular igneous intrusion into either lava of the lake or lava flow or magma of a dike or sill Goehring (2013). However, in relationship to speleogenesis they normally do not interact as, presently mentioned these types of joints associated with igneous rocks normally not associated with dissolution.

6.1.6. Joint origins

On the basis of their origin, joints have been divided into a number of different types that include tectonic, hydraulic, exfoliation, unloading (release), and cooling joints Goehring

(2013). It should be kept in mind that different joints in the same outcrop may have formed at different times and for different reasons. The joint types associated with speleogenesis, however, is most commonly tectonic/neo-tectonic, hydraulic and unloading (expansion joints) and will be discussed briefly below.

Unloading joints, also known as tension or extension joints are most commonly formed when uplift and erosion removes the overlying rocks, thereby reducing the compressive load and

54 allowing the rock to expand laterally (Roberts, 1995). Joints related to uplift and erosion unloading have orientations reflecting the principle stresses during the uplift and care needs to be taken when attempting to understand past tectonic stresses. Unloading joint systems superimposed over older faults are commonly encountered within the caves of the CoH, as well as some along the Far West Rand, such as seen within Crystal and Apocalypse. (Martini et al., 2003).

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Chapter 5: Examples of dissolution caves in the Cradle of Humankind

5.1. Introduction

In this Chapter, the combined effects of both chemical disbanding and the structural directions along which dissolution speleogenesis occurs are demonstrated. Two cave systems within the CoH are described as these are representative of the most common cave type found within the CoH.

The chosen examples, Bats, and the Rising Star cave systems, represent, in general, the most common cave configuration (boxwork, chapter 4, this thesis) found within the CoH, also demonstrating the most common underlying structural controls directing speleogenic propagation and therefore serve as suitable comparative material demonstrating the mechanisms and structural controls along which far and close approximation stress field tectonic/neo-tectonic related fault, fracture, and joint block systems transmit to speleogenesis within the CoH.

5.2. Westminster/Rising Star cave system

5.2.1. Locality

Using Sterkfontein caves as a point of reference at co-ordinates S26o 00.951′ E27o 44.071′ the

Westminster/Rising Star cave system can be located to the WSW at 257oTn and 2.15 km distance (ground primitive). The cave is found on the farm Swartkrans 172 IQ positioned on the 1:50 000 2627 BA Randfontein topographic map at co-ordinates S26o 01.201′ E27o

42.769′.

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5.2.2. Background

Like most caves in the area, the cave was mined for its calcite formations in the 1930s.

However, miners could not access the back reaches of the cave system and this remained largely unexplored and intact. This cave, known by SASA/SEC since the early 1980s, has been visited regularly for recreational purposes. Mapping of this cave is ongoing as new sections are still being discovered. This is a complex system with portions of the cave only accessible to small bodied cavers and cavers competent in high-risk climbing work.

This cave deserves special mention as it was here that on the 13th October 2013, Steven

Tucker, Rick Hunter and the author made a remarkable discovery yielding specimens of significance, later to be described as belonging to a new hominid species named Homo

Naledi (Berger et al., 2015).

The fossils are found in association with an as of yet unfamiliar sub-surface palaeo-karst fill presenting with an unusual taphonomy situation (Berger et al., 2015). At the date of writing the Rising Star/Westminster system (which represents a small portion of the regional karst) has yielded the highest number of hominid fossil specimens (>1500 identifiable skeletal components) among other comparable deposits clustered in the Sterkfontein/Kromdraai areA

All indications are that the initially discovered localized deposit will yield an unprecedented number of hominid fossil specimens with the possibility that dissemination of materials from the original area of deposition may have caused a trap, or nick point deposits throughout the system and perhaps adjacent dissected segments of what may have been a singular extensive cave system. As such this cluster of caves may provide substantial numbers of hominid fossil specimens for a generous period of time into the future.

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This thought was underlined when on the 2nd July 2014 the same team discovered hominid remains belonging to either A robustus or a transitional form of A Africanus (personal communications, Berger, 2013) in an adjacent cave named Villa Louise 1/site No: 105. The initial discovery at site 105 was enhanced when on the 22nd August 2014 L. R. Berger identified further finds made by the team as belonging to a partial australopithecine skeleton and unrelated cranium. Since then several more finds have been made making this a seemingly particularly rich hominid fossil bearing site.

5.2.3. Topography

The Rising Star/Westminster system is located on the side of a small hill at 1484 m. To the

SE and south, the flat bottom of the Sterkfontein valley at 1466 m has been incised by a stream (Wilkinson, 1973). This entrenchment of the present Blaauwbankspruit drainage system developed in response to a recent isostasy-related uplift event deepening the region’s thalweg gradient (Martini et al., 2003). The most recent incisions are excavating what appears to be a former wetland terrain overlain by at least two distinctive gravel terraces on both sides of the present Blaauwbank stream course (Clarke and Partridge, 2010).

To the west, the topography rises gently over an undulating landscape forming part of a soft scarp intercepting the older post-African landscape platforms at ±9 km distance and at ±1574 m. To the north, the scenery continues to comprise undulating country but abruptly develops pronounced cuesta topography as soon as the Pretoria Group quartzites are encountered. To the SE a pronounced scarp comprising Witwatersrand Supergroup lithologies (Orange Grove quartzite) can be seen forming the southern margin of the Limpopo basin.

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5.2.4. Geology

The Rising Star/Westminster cave system is located in a chert-rich dolostone matrix typical of the karst of the Transvaal basin and is wholly developed in the basal-most neo-Archaean-

Palaeo-Proterozoic carbonate lithologies of the Transvaal Supergroup, Chuniespoort Group,

Malmani Sub-Group dated at 2.3-2.6 Ma (Ericksson and Alterman, 1998).

The system straddles the boundary between the basal Oaktree and succeeding Monte Christo

Formation (marked by a prominent chert horizon) and can be classified as a typical three- dimensional multi-leveled at present hyper-phreatic (vadose) karst dissolution cavity set along a maze of fissure passages placed at right angles (Boxwork cave, chapter 4, this thesis).

The dolostone lithologies exhibit a generally SW dip, in contrast to the generally northerly dip observed elsewhere in the CoH. This drastic shift in dip seems to be the function of folding (personal communications, Dirks, 2014).

In confirmation, the country rock exhibits a series of low intensity (undulating) anticlinal folds followed by synclinal folds (as observed within an open quarry 700 m to the south of the cave) also having a roughly EW strike.

The Rising Star/Westminster system is developed over a restricted surface area of ±250 m x

200 m whilst the combined length of all (known) surveyed passages within this area amounts to ±3.2 km (unreferenced SASA data). The system occurring at 1482 m above mean sea level extends over a vertical height of ±30 m following the general northerly dip of the local strata at an average 17o following along and under a prominent chert horizon defining the roof of the cave system. However, the present indications are that this chert layer is continuous and impenetrable thereby intensifying the mystery regarding the influx origins of the Naledi

59 chamber’s fossil assemblage whereby it is presently assumed that they (H naledi) used the present entrance series as only access point/s (personal communications, Berger, 2013).

However, measured against personal observations, author made in numerous caves in the vicinity it’s the author’s opinion that this chert layer could be breached in places allowing for an interconnecting shaft-like entrance/s into the present system from a higher superimposed, now eroded and removed system. This could have allowed access into an area in close approximation to the present point of deposition, whereby the present area of deposition served as a later receptacle derived by seasonal flooding (flushing) of the cave. This observation by the author seems to be supported by surface features such as sinks and depressions along a prominent east-west striking fault line where remnant speleothems and numerous on surface breccia pockets are observable-strongly indicative of the presence of a once structurally related interconnected superimposed roofed system.

All the present openings to the subterranean chambers, apart from the southernmost main entrance are found within the Oaktree Formation, whilst the weathered remnants of previously higher (supposedly) interconnected chamber/s (evidenced by remnant speleothems and breccia pockets on surface) are located along the Monte Christo/Oaktree Formation’s contact (personal observations, author). The present cave entrances are encountered along a small SSE to NNW running ridge, seemingly the exposed portion of a low-frequency synclinal fold having a roughly south to north strike direction. Just above the cave entrances and to the west, the area encounters a flattened, slightly concave topography believed to be part of the previously mentioned open synclinal fold.

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Surrounding caves such as Yomtoff (Meaning “a good day” in Hebrew), Assassination and

Villa Louise-also known as site 105-and other unnamed small caves found in direct proximity, and as mentioned, the surface remnants of a previously higher existing speleogenic interface seemingly form component parts of a single extended cave network dissected by the erosion dynamics of a transitory landscape.

The rationale behind the supposition that these smaller caves once were integral portions of a single speleogenic event is found in their close proximity, and when plotting out their joint orientations on stereonet definite strike direction trends are correlatable. Also, their close approximation to a major ENE-WSW striking dextral fault turning WNW also lends credibility to the probability that they all relate to a single speleogenic event with the area where this cluster of caves are found being located within the perimeter of a tension release radius (aura) around said fault. This making it probable that they form part of a single joint cluster-forming one of the main structural components of the Rising Star ‘cluster’.

Of interest is to notice that however signs of flooding within Rising Star cave are prevalent, presently no long-standing water is found in Rising Star, but located at ±40 m below the surface in Yomtov cave to the east and directly adjacent to the Rising Star System. This seems to be a function of rapid drainage through-flow within these systems only halted or retarded by the present water-table depth determined by the present thalweg gradient depth.

5.2.5 Structural controls

The entire system is located within an open fold with the first dominant cave control being a major regional WSW striking steeply dipping strike-slip (wrench) fault system having a horizontal dextral displacement of ±20 m and associated anastomosing splay fractures. The

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Rising Star/Westminster fault and associated linear anastomosing fracture system can be traced with relative ease on the surface as their exact placement can be detected by obvious angular fault breccias and a number of fossiliferous remnant karst fills ‘dotted’ along strike.

Fault movement and strike direction were determined by elongate and boudinage stromatolite structures on surface aligning along the same strike direction as the main fault-indicative of the forces applied in forming some of the key structures responsible for this cave’s morphological characteristics (personal observations, author, personal communications,

Dirks, 2014).

A second equally important structural component characterized by a mylonitic horizon is found at the southern-most entrance forming the roof of the biggest single chamber of the system comprising a clear WSW striking shear zone having an NNW oriented shear sense.

The presence of this presently mentioned shear zone has been interpreted as either relating to far-field stress tectonics, a suspected orogenic episode, compressive tectonics associated with the Bushveld, expansion of the Malmani basin, the Vredefort impact event or detachment faulting along the flanks of the Johannesburg dome (personal observations, author).

The third most important structural control is a series of tightly spaced extension Joints forming a complex network at both conjugate and orthogonal angles. As such these are divided into 13 distinct joint plane trends demonstrating a predominantly SEE SE SSE SSW

SW WSW and lesser ENE and WNW strike trends (Fig 12. A, B and Fig 13).

The joint system seen in the Rising Star system follows a predictable pattern where the surrounding rock fractured in a plane Parallel to the maximum principal stress and

62 perpendicular to the minimum principal stress-the direction in which the rock was being stretched (personal observations, author). This observation complies with what has been described as a common characteristic along which speleogenic propagation often advances globally (Bauer, 1971, Roberts, 1995). An ENE to WSW trending major fault turning WNW and fracture trend leading to the development of a single sub-parallel joint block with continued deformation subsequently leading to the forming of further joint blocks indicate this.

5.2.6. Speleogenic sequencing

From field remnants, it seems clear that the present system is an integral portion of a once extensive stacked speleogenic sequence, the upper elevated section of which has been largely removed. In both cases, initial dissolution took place within a phreatic environment carried on into a hyper-phreatic environment as evidenced by ‘cave popcorn’ (a speleogenic formation forming in response to oversaturation precipitation within a phreatic environment whereby CaCO3 is directly precipitated from solution (chapter 4, this thesis).

In response to uplift followed by a deepening of the region’s thalweg gradient, the uppermost

(now eroded) system drained, however leaving the present system within a phreatic interface as is commonly seen in a number of caves in the CoH. Further uplift, as indicated by the forming of at least two isostatic repair related terraces (Clark and Partridge, 2010) then drained the lower system. At this point, the present system acquired a semi-vadose character where acid related dissolution and precipitation of speleothems took precedence over the supra-phreatic zone, with intermittent periods of renewed phreatic immersion (probably due to high rainfall cycles)-partially re-dissolving speleothems as is witnessed in several places in the cave. Further deepening of the region’s thalweg gradient then completely drained the

63 present system, which then acquired an entirely (permanent) vadose character, as evidenced by massive speleothems in places not showing any signs of re-dissolution. In due course the cave was intercepted by surface via continuous back-etching of the terraces mentioned, possibly removing a sizeable portion of the present system previously existing to the NE.

The reason for the limited volumetric extent of cave chambers can probably be found in the rapid lowering of the water table due to neo-tectonics arresting or slowing phreatic dissolution whilst a limited tension relief radius dictated the cave’s perimeter in which joints were permitted to expand sufficiently to permit speleogenic propagation (chapter 4, this thesis).

A B

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Fig 12 A and B: Westminster/Rising Star cave system survey and structural composition.

Fig 13: Rising Star/Westminster cave’s fault (yellow) and joint sets (blue) strike orientation. Red semi-circles indicate range variables.

5.3. Bats cave

5.3.1. Locality

Using Sterkfontein caves as a point of reference, Bats cave can be located to the south of

Sterkfontein at 178oTn and 2.01 km distance (ground primitive). The cave is situated on the farm Honingklip 178 IQ positioned on the 1:50 000 2627 BA Randfontein topographic map at co-ordinates S26o 02.008′ E27o 44.089′.

5.3.2. Background

Bats cave, named for the large numbers of bats that once occupied it, has been extensively mined for calcite and phosphate deposits during the 1930s as most caves in the vicinity have been. It has been surveyed in detail by SASA/SEC in the mid-1980s. In its basic configuration, it agrees with most fault and joint controlled systems commonly seen in the area Although the cave contain sparse fossil breccias similar in composition as those seen at

65 numerous other caves in the vicinity, there appears to be the possibility of again discovering a similar taphonomy environment as seen at Rising Star, as these caves are in close proximity with the chance that this cave, like Rising Star, could have lent itself to similar influx.

5.3.3 Topography

Bats cave is located on the side of a small hill at 1519 m and 65-70 m above the Sterkfontein valley with the Blaauwbank River flowing ENE. To the north, the scenery comprises undulating country dissected by gullies. Bats cave is situated in close proximity to the southern margins of the Limpopo basin escarpment separating two natural regions: the

Highveld at 1500-1600 m towards the south and east and the Bushveld to the north at 1000-

1100 m. The areas topography becomes more pronounced (hilly) to the north in response to lithology characteristics within the Malmani dolostones, becoming well pronounced

(mountainous) within the Pretoria Group where topography characteristics express as Cuesta

(Bankenveld) topography.

5.3.4. Geology

Similar to the Rising Star/Westminster’s cave system, Bats cave is developed in a cherty dolostone matrix, typical of the karst of the Transvaal basin and is wholly developed in the basalmost Neo-Archaean-Palaeo-Proterozoic carbonate lithologies of the Transvaal

Supergroup, Chuniespoort Group, Malmani Sub-Group dated at 2.3-2.6 Ma.

Bats cave is wholly developed in the bottom-most Oaktree Formation and, similar to the

Rising Star/Westminster system, can be classified as a typical three-dimensional supra- phreatic karst dissolution cavity comprising a maze of fissure passages characterized by joint

66 sets set at mostly at right and oblique angles (dependant on the effects of peripheral and far stress field influences).

Inside the cave, the Oaktree Formation dolostone exhibits a variable 17-25O northerly dip along strike. A prominent shale marker, in places up to 30 cm thick, traverses the cave system and forms a prominent horizon in the cave where it frequently crops out along passages, also forming the roof of the biggest chamber situated towards the eastern portion of the system causing the cave to be developed in a strata-bound fashion (personal observations, author).

5.3.5. Structural controls

The structural controls and strike directions of three predominantly major ENE to WSW trending fractures seem the main directions along which Bats cave acquired its linear expanse whilst associated (superimposed) joint blocks observed in the system are strikingly similar in orientation and types to those seen in the Rising Star/Westminster system. The northerly section of Bats cave seems to be developed within a synclinal fold adjacent to an anticlinal fold-postulated as being part of a regional fold trend in response to slumping associated with detachment faulting along the northerly slopes of The Johannesburg dome (personal observations, author). This configuration led to the formation of a ‘saddle reef’ type tensional zone-later exploited during uplift and surface denudation in regulating and superimposing jointing (personal communications, Kramers, 2015).

Surveyed joints demonstrate thirteen distinct strike directions with a predominantly ESE, SE,

SSE, SSW, SW, WSW and lesser ENE strike trends prevailing whilst the faults plotted within the cave has a strongly ENE and WNW strike trend. This lends Bats cave a similar floor plan geometry as the Rising Star/Westminster Cave system (Fig 14 A and B, 15 and 16).

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In terms of geometry, two major types of joints, non-systematic Joint blocks and systematic joint blocks comprising orthogonal joint blocks (with dihedral angles being nearly 90°) and conjugate joint blocks (with dihedral angles varying from 30 to 60°) have been identified, likely reacting to the same stress inputs affecting the Rising Star/Westminster system.

5.3.6. Speleogenic sequencing

Initiated as a fully phreatic system advancing into a later vadose realm, due to rapid uplift and draining, dissolution advanced along the mentioned structures with the cave developed over a restricted surface area of ±90 m x 170 m with the combined length of all passages within this area amounting to 4.41 km (survey data, SASA). The reason for the limited extent of the cave agrees with the reasons given for the Rising Star system with the exception here that the caves more volumetric dimensions and passage sizes can be attributed to the Cave could simply have been within the phreatic realm for longer through flow. The system extends over a height of about 25-30 m and the dry part of it is limited downwards by the water-table, appearing as a single static sump found within Cannabis Passage at ±30 m (western portion of the cave-survey being the deepest point of the dry cave. The sump has been explored by

SASA divers during the 1980s adding another 50 m of passage length whilst dropping approx. 7 m at an incline of approx 4o before coming to an abrupt end (personal observation).

The present investigation confirmed that the cave is part of a single but formerly multi- leveled speleogenic system similar to Rising Star whereby the former upper levels were deroofed, only leaving a rough surface outline identifiable by weathered cave residual in the form of sparse weathered calcite formations. Of the present three natural entrances, two occur at intersecting joints whilst the third is a steep-sided round sinkhole that developed in response to roof stoping.

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A number of discarded ex situ breccia fragments, originating from on surface pockets and holding some fossil material, attest to a period when this cave, similar to Sterkfontein

(Member 4) housed a higher chamber that acted as a bone receptacle-likely brought in by predators or scavengers (Brain, 1981). The reason why this chamber was almost wholly removed is postulated to be in response to the more rapid erosion of the chert free Oaktree

Formation. This seems in contrast to Sterkfontein where the upper section of the cave including the fossil chamber is developed within the chert rich Monte Christo Formation resisting erosion due to its higher intercalated chert layers (Martini et al., 2003).

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A B

Fig: 14 A and B: Showing the survey of Bats cave and its comparative joint and fracture orientations.

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Fig 15: Rose diagram of Bats cave’s fault (yellow) and joint sets (blue) strike orientation. Red semi-circles indicate range variables.

5.4. Similarities between Bats and Rising star

Both the Rising Star system and Bats cave demonstrate a strikingly similar joint grid plan in

as far as joint orientation and types are concerned (Fig 16). This configuration agrees well

with the majority of caves in the area, including Sterkfontein. This strongly suggests the

overwhelming effect of perhaps a singular tectonic event taking precedence over other

contenders, that to a large extent might have reduced the effect of former tectonic or neo-

tectonic events that may also have inserted directive speleogenic control within the CoH.

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Fig 16: Rose diagram demonstrating the similar joint and fault strike orientations found both within the Rising Star cave system and Bats cave. Red semi-circles indicate range variables.

5.5. Causal relationships

Applicable to both the Rising Star cave system and Bats:

In respect to speleogenics, the CoH had a complex and involved tectonic history. According to Dirks et al., (2010), cave genesis within the region was influenced by lithological, layer

Parallel controls interacting with crosscutting fracture systems of Palaeoproterozoic origin and an NW to SE directed extensional far-field stress related to the expansion of the Malmani basin at a time when the African erosion surface was still intact. This relationship with speleogenesis seems well demonstrated by caves such as e.g., Malapa at co-ordinates S25o

53.699′ E27o 48.090′ (Berger et al., 2010; Dirks et al., 2010; Dirks et al., 2013), Rising Star

(personal communications, Dirks, 2014), Villa Louisa at co-ordinates 26o 1.329′ 27o 42.715′, van Rooys at co-ordinates 26o 0.377′ E27o 44.208′ and Knocking shop at co-ordinates 26o

2.551′ E27o 42.114′ (personal observations, author).

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Within the CoH dominant east to west striking dextral wrench faults are present with an often crosscutting extension or detachment faults present acting as conduits for meteoric or connate ground waters. The mentioned fault and fracture trends were corroborated with other worker’s findings when, for the purposes of this dissertation, the author taking bearings of and compared fault, fracture and joint trends of several caves in the vicinity found them to be congruent with the work done by Berger et al., (2010), Dirks et al., (2010) and Dirks et al.,

(2013).

The debate regarding the exact origins or cause to the mentioned NW to SE directed extensional far-field stress and fault systems seem to favor the regional tectonic effects of the relaxation of the Malmani basin (personal communications, Dirks, 2014). The broadly north verging cleavages and folds in the quartzites and slates of the Black Reef formation along the northerly margins of the Witwatersrand basin and the Johannesburg dome, based on their geometry, favors the influence of the Vredefort impact event (Alexandre et al., 2006).

However, Gibson et al., (1999) documented similar folds and cleavages as well as bedding-

Parallel shears, thrusts and tectonic lineation is in the overlying Chuniespoort Group and raised the possibility that an orogenic event named here the Transvaalite fold-and-thrust belt was involved. This apparently occurred between the intrusion of the Bushveld Igneous

Complex and the Vredefort impact and was involved in regulating some, if not most of the

Cradles tectonic history (Alexandre et al., 2006).

Downwarping of the Bushveld Igneous Complex exercised a marked tectonic and epeirogenic effect on the region by elevating and tilting all Transvaal Supergroup carbonate lithologies within the CoH, including those belonging to the Pretoria Group to the north

(Carruthers, 2007). Dip and elevation were accentuated by the syngenetic isostatic counter

73 elevation of The Johannesburg dome (personal communications, Viljoen, 2000). This apparently caused the reactivation of older Transvaal Basin expansion faults by converting them to detachment faults along its flanks (personal communications, Kramers, 2015). In fostering this rationale it was noticed that often planar ‘thrust’ faults observed in numerous caves found along the fringes of the Johannesburg dome recurrently exhibit slickensided surfaces along fault planes that gives a sense of movement away from the Johannesburg dome. Within the CoH, this sense of movement trends north and NNW in approximation to

Sterkfontein whilst in Armageddon Pot the décollement there noticed exhibits a southerly sense of movement. Of importance is to notice that caves further afield, away from the perimeter zone do not exhibit these conspicuous features, giving imputes to the consideration that these faults may either be uniquely formed detachment faults or reactivated expansion faults.

Supporting this supposition is the age range recovered from two of these fault zones, Samples taken from Rising Star and Armageddon Pot (Chapter 7 this thesis) both reflects a Bushveld

Igneous Complex range.

These, often low-angle detachment faults seem too often transverse older established faults and fractures associated with far-field stress as described by Berger et al., (2010), Dirks et al.,

(2010) and Dirks et al., (2013) are seemingly key speleogenic controls. This is especially noticeable in locations where low frequency anti-and synclinal folding (supposedly caused by gravity slippage) as seen with the Rising Star system provided sufficient extension to allow for the penetration of meteoric waters (chapter 3, this thesis) permitting dissolution beyond a surface interface.

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Of certain tectonic influence is the expansion of the Limpopo basin over the region with its present southern margin marked as a prominent escarpment south of the Sterkfontein caves.

This had as affect the development of tectonic unloading joint blocks superimposing over existing fault lines, fracture trends, lithological, layer Parallel shears as well as open (syn and anticlinal) folds to came together in augmenting speleogenic propagation (personal observation).

In addition, east to west striking fracture lines within the CoH often accommodated pathways for Pilanesberg related syenite and Karoo aged dolerite feeder dykes, with these features being conspicuous on aerial photos. The relationship between these and speleogenic propagation lies in the role they played in phreatic enlargement of some caves in the CoH by creating compartments arresting through flow. Examples thereof can be seen in Wonder cave where dolerite dykes are known to exist to the south and east of the cave (downslope) arresting through flow. This had as affect the retention of groundwater allowing for extensive phreatic dissolution so that today the cave comprise one massive chamber, the third biggest in

South Africa. Another example can be seen in Sterkfontein caves itself. A dolerite sill is known to underplate the caves (personal communications, Martini, 1984) and this has as effect a retarded through flow whereby the cave still retains, in part, a phreatic portion.

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Chapter 6: Armageddon Pot

6.1. Description

Armageddon Pot is a massively NW to SE developed single chambered fissure-like linear developed cavity (Fig 17).

Fig 17: Demonstrating the linear morphology and depth extent of Armageddon pot, also

indicating points of interest.

The cave is only accessible via a deep rotund-shaped sinkhole (Fig 18) measuring approximately ±14 m across at surface, belling out to ±30 m towards the first landing at ±50 m (Fig 17, C) where a talus slope (Fig 19 A and B) approaching ±45o to a point into the first chamber at ±90 m depth from surface from where a capacious cave system is entered (Fig 17, point E).

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G

E______W

Fig 18: Armageddon Pot is only accessible via a deep rotund-shaped sinkhole developed in shale 50m deep to first landing (No: 1 on Google earth image, Fig 42).

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Fig 19 A: The entrance to the cave at the bottom of the sinkhole along a talus slope approximating ±35o to the bottom of the entrance chamber at ±107 m from surface. The two cavers provide scale (No: 2 on Google earth image, Fig 42).

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Fig 19 B: Looking at the entrance from a position halfway up the collapse cone ‘heartbreak hill’-so called for being steep, arduous to climb and slippery. In spite of powerful portable

LED lights, the enormity of this chamber makes it difficult to illuminate or to scale it properly (No: 3 on Google earth image, Fig 42).

Upon entering the cave down the presently mentioned talus slope at ±70 m depth, to the right facing east, a series of step-like drops of various depths are encountered that can only be accessed by abseiling (Fig 17, point D). At present these are being explored and mapped and the deepest point here has not been reached yet as the area in places is superlatively unstable and dangerous, evidently forming parts of the sinkhole collapse (Fig 17, point C).

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To the left of the talus slope facing west, there seems to be a section leading around the talus slope to perhaps the eastern aspect of this cave (Fig 17, point F). This area becomes progressively unstable and extremely perilous as loose rock fall; evidently, sinkhole related collapsed material prohibits further exploration.

The upper main section of the cave, developed within the Frisco Formation is a massive tunnel-like chamber striking on average 295o SE-NW measuring at its widest point ±136 m in width and at ±40 m in height (Fig 17, point G).

At ±364 m meters from the entrance and at ±180 m depth from the surface the ‘upper chamber’ abruptly enters into the lower section of the cave through a boulder choke at ±403 m from the entrance and at ±160 m depth (Fig 17, point H). From this point on, still following the same strike direction the system narrows down considerably exhibiting variable width variables along strike with some sections considerable, though never again as capacious as the ‘upper chamber’ with the dolostones exhibiting a marked increase in closely spaced chert intercalations. However, when looking up at the roof and over the boulder choke it is clear that the cave is a single linear entity as open space, and the ceiling at roughly the same height as the ‘main chamber’ continuous throughout the cave.

From this point on, shortly after the boulder choke one need to traverse a pit of ±10 m across and of uncertain depth (Fig 17, point I). This is done by skirting along and around the pit on a chert ledge whilst being tethered to a safety line (Fig. 20).

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Fig 20: Skirting around the first pit on a safety line and on a ledge. The caver provides scale

(No: 4 on Google Earth image, Fig 42).

From this point on the cave starts to descend gradually until a significant pit at ±476 m from the entrance and at ±200 m depth from surface ±30 m across and ±40 m deep, a deep pothole is encountered (Fig 17, point J). This is traversed via a zip line. From this point on the cave descends further to yet another deep pit at ±591 m from the entrance and at ±230 m depth from the surface with approximately similar dimensions as the first, similarly traversed on a zip line (Fig 17, point K) (Fig 21).

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Fig 21: The cable traverse (zip line) over pit two. The caver provides scale (No: 5 on Google earth image, Fig 42).

Following this, the cave floor plateaus out entering a massive chamber measuring ±30 m across with a relatively flat floor (Fig 17, point L). The floor of the cave comprises mud and deep mud cracks, evident from recent times when this part of the cave was still phreatic. The cave now follows along this spacious chamber where at ±1255 m from the entrance it suddenly pinches out again. At ±1415 m from the entrance a large chamber is again entered and at ±1489 m from the entrance, this chamber splits in two where the right-hand passage ends after about ±71 m (Fig 17, point M). The left-hand series now follows an upwards incline following along a fracture for ±136 m before breaking into another large chamber.

Here a tunnel leading off to the left follows a developed joint for ±51 m before terminating.

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Returning to the entrance of this tunnel another large chamber is entered continuing for ±207 m where again it splits into a right and left-hand series. Before getting to the split a small oblique fracture line on the left leads to a small tunnel running Parallel with the main tunnel but it terminates rapidly at both ends. Returning to the main tunnel and to the split the right- hand series then follows along a large chamber for ±150 m but then terminates whilst the left- hand series continued for another ±55 m and then split into a short right and left-hand series.

The cave evidently continues beyond this point, but here from entrance at1800 m line of site at 116.63oTn, but following the cave’s contours at ±2600 m from the entrance, a high mud wall for now stopped further exploration as the wall demands specialized climbing equipment

(Fig 17, point N).

Speleothems occur almost exclusively in only the ‘upper chamber’, and within the Frisco

Formation. Speleothems are of a peculiar nature and comprise dripstone formations containing iron oxide (FeO2). Other formations noticed comprise floor flowstone formations containing manganese oxide (MnO2). Aragonite crystals are abundantly present with some needles observed being up to 2 cm in length in places (Fig 22, A-F).

Of interest is to notice that amongst the aragonites a habit called floss ferri or "flowers of iron"-a branching, clumpy habit forming delicate tree, coral or worm-like formations and a steep pyramidal habit forming clusters of sharp spiked crystals referred to as "church steeple" habit (Gunning, 2004) can be observed.

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A B

C D

E F Fig 22: A selection of the type formations commonly encountered in Armageddon Pot: A and

B, iron oxide, C, D and F, aragonite and F, manganese oxide flowstone (No: 6 on Google

Earth image, Fig 42).

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6.2. Geology

6.2.1. Context

Armageddon Pot is a massively developed NW to SE striking cave system developed within the intra-cratonic Transvaal Basin dolomitic lithologies, Transvaal Supergroup, Chuniespoort

Group, Malmani Sub-Group uppermost dolostones of late Archaean age (Button 1973). The bulk of the cave developed within the uppermost Frisco and Eccles Formations with the possibility of the cave transversing lower lithologies.

Here the dolostone lithology, similar to the CoH, consists essentially of shallow marine stromatolitic dolostone with a variable amount of chert. The dolostone mineral is typically rich in Fe and Mn (up to 3% combined) and along the Far West Rand, the dolostone lithologies reach a combined thickness of 1450 m (Eriksson and Truswell, 1974). Based on the abundance of chert, the Sub-Group has been similarly subdivided into 6 Formations

(Chapter 3, this thesis).

6.2.2. General type description

Armageddon Pot seemingly represents a predominantly supra-phreatic dissolution type cave having cycled through a fully phreatic stage at a point when both the post-African 1 and 2 surfaces over the region was intact, with portions of the cave (upper section) reverting to a supra-phreatic environment, as isostatic uplift commenced and peneplanation progressed coupled with a time when a deepening of the region’s thalweg developed in response to the development of the Etosha-Griqualand-Transvaal axis dividing South Africa in distinctive north and southerly drainage networks (Chapter 2, this thesis).

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The sinkhole profile comprises an initial pedogenic horizon consisting of, from top to bottom a thin ±1 m thick humus rich dark brown soil of recent origin followed by the ±3 m thick

Hutton soils-a reddish well oxidised sandy loam horizon, followed by an post-African 2 surface palaeosol horizon characterized by alluvium clastics (van Niekerk, personal communication) where it overlies the Pretoria Group clastic Timeball Hill Formation along an angled unconformity, with the Pretoria Group exhibiting a dip value of ±25o N (Fig 23).

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Fig 23: A view from the top section of the sinkhole The car provides scale. (No: 7 on

Google Earth image, Fig 42).

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Fig: 24: Demonstrating the stratigraphic sequence of the Sinkhole entrance series of

Armageddon Pot.

The dolomitic portion of the cave is developed within the upper chert poor Frisco and chert- rich Eccles Formations with the possibility of it traversing deeper lithologies (Fig 24).

However, this cannot be ascertained at present as roof fall debris (scree) forming an undulating and unstable floor section chokes the system so that at present only the mentioned two formations can be observed.

6.2.3. Structural features

Arriving at the bottom of the sinkhole it was perceived that the contact between the Pretoria

Group and the underlying dolostone lithologies is set along a décollement recognized by schistose shale and mylonitic clay-smear bands (Fig 25) (red dotted lines) This overlies the underlying dolostones resting on a thin fault gouge lens comprising incohesive, clay-rich fine-to ultrafine-grained cataclasite possessing a planar fabric containing <30% visible fragments (Yellow dotted line).

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Fig 25: The décollement and its delineation set between the lowermost Pretoria Group and uppermost Frisco Formation, Malmani basin dolostone lithologies (No: 8 on Google earth image, Fig 42).

In confirmation to the composition of this layer, numerous slickensided shale fragments litter the collapse talus slope. These suggest considerable movement along a shear zone and their provenance as being parts of the observed décollement seems probable.

In proximity to the upper dolostone contact with the Pretoria Group shale, Timeball Hill

Formation numerous highly mylonitic/schistose intertwining ‘veinlets’ distributed within a

±3.5 m thick band cut across dip. Individual veins and veinlets vary in thickness from a few

87 mm to several cms and exhibit the same dip value as the presently mentioned upper décollement.

Within this zone, compression and boudinage structures can be commonly observed (Fig 26,

27 and 28) Fig 26 demonstrates the shortening of a seemingly older shear whilst also displacing a fracture (A and B). Here shortening and ‘bundling’ of the micro-shear can be seen (point C) as well as micro thrusting (point D) whilst the dolomitic partition above the shear contains cataclasite (point E), all indicative of a compressive shock event.

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Fig 26: Compression structure and micro fault displacement within a micro-shear band, (Hammer provides scale) (No: 9 on Google earth image, Fig 42).

In opposition, (Fig 27) shows an extension structure. In this photo, clear boudinaging can be observed (within the black dotted demarcations). These structures are also commonly

88 observed within the upper chamber Frisco Formation with in places boudinage structures attaining considerable dimensions with some measuring up to 3m in length and 2.5 m in height (Fig 28, points A, B, and C). These structures are frequently accompanied by lenticular lenses of fine-grained fault gouge occurring either above or below boudinage structures (Fig

28: point D).

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Fig 27: Boudinage structures, indicative of extension dynamics (Compass provides scale).

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Fig 28: Boudinage structures within Armageddon Pot attaining considerable dimensions (No: 10 on Google image, Fig 42).

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Descending into the ‘upper’ chamber situated predominantly within the chert free Frisco

Formation it is perceived that this area has been extensively affected by shearing/thrusting with shear/thrusts correlatable along a considerable offset value of ±12 m along the opposing hanging and footwalls of the upper chamber (Fig 29).

Fig 29: Diagram showing the hanging and footwall offset value measured along the main normal fault by correlating thrust and shears.

This strongly indicates the presence of a normal fault having cut across the mentioned shear/thrust region along a ±295o SE-NW strike line (measured from five points as the survey team advanced deeper into the cave). The fault line furthermore follows an acute dip direction trend averaging 191.5o and a dip plunge averaging 74.5o as reflected by the stereonet plane circle (red) and pole (yellow) colors (Fig 30 and Table 1).

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A. Strike B. Dip direction

C. Dip plunge

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D

Fig 30: Stereonet representation (D) of the strike and acute dip direction/trend and dip/plunge of the normal fault directing Armageddon Pot’s linear extent as reflected by the rose diagrams (A, B and C) above and field data table below (Table 1).

Armageddon Pot fault orientation Strike Dip direction/trend Dip/plunge 290 200 77 280 190 75 290 200 74 275 185 72 281 191 77 Average 283.2o 191.5o 74.5o

Table 1: The controlling fault strike measurements of Armageddon Pot.

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The second most pertinent feature, entering deeper into the cave and lower down the cave wall profile it was noticed that sections of the side walls of the main chamber, developed within the Frisco Formation, in places comprise almost entirely of massive cataclasite. This was noticed to outcrop along the full length of the upper section and in places up to the roof, often also including the roof.

The cataclasite observed in Armageddon Pot has no planar fabric and is mostly incohesive and characterized by generally rounded and angular clasts and smaller dolomitic fragments in a finer-grained matrix of similar composition. It has been formed by the progressive fracturing of mineral grains and aggregates, a process known as cataclasis. The fracturing continued until distribution of clast sizes was developed that allowed the sliding of clasts past each other, without high enough frictional stresses to further fracture the rock significantly.

From then on deformation was accommodated by continued sliding and rolling of fragments, a deformation mechanism known as cataclastic flow associated with shock metamorphism

(Jefferies et al., 2006).

The size of the clasts seen in Armageddon exhibits considerable size ranges from smalls (2-

10 cm), medium (25-40 cm) to large (60-100 cm) whilst the encompassing matrix (depending on locality) are proto-cataclisitic (up to 50% of total volume), meso-cataclasitic (50-90% of total volume) and ultra-cataclasitic (>90% of total volume) (Table 1 and Fig. 31 A, B, C and

D). These three ranges are commonly observed, are often intermixed so that no definitive areas can be accredited to any preference in size or cataclisitic matrix percentage as defined by Woodcock and Mort (2008) and Kearey (2001).

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This random distribution of clast size and matrix percentages as observed throughout the upper section of Armageddon Pot is postulated as being resultant from a high speed, high shock, high brisance event not preferring or targeting a specific horizon within the Frisco

Formation, but rather the collective result of an even, wide fronted unbiased shock front choosing the path of least resistance-much as seen in the dispersion pattern of the humidity halo after conventional explosives are detonated indicating the uniform nature of the detonation shock (overpressure) front (providing the shock front is not deflected or re- directed) (Boshoff and Teitge, 1987).

Cataclasite clasts Average size diameter Small 2-10 cm Medium 25-30 cm Large 60->100 cm A.

Cataclasite classification Cataclasite matrix % Proto-cataclisitic 50% Meso-cataclasitic 50-90% Ultra-cataclasitic 90% B. Table 2 A and B: The cataclasite clast, size range and type cataclasitic matrixes seen in

Armageddon Pot.

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A. B.

C. D.

Fig 31 A, B, C and D: A selection of cataclasite clasts to illustrate the variation encountered in Armageddon Pot. Scale bars and compass provide scale (No: 11 on Google earth image,

Fig 42).

In places, angular somewhat cohesive fragments are distinguishable where broken and disjointed chert bands form the majority of clasts encompassed or encapsulated by a dolostone matrix. Again individual sizes vary from small to large, also within the same size range as the above (Fig 32 A and B).

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A.

B. W______E

Fig 32 A and B: Demonstrating the size range and morphologies of somewhat cohesive cataclastic chert bands seen in Armageddon Pothole (No: 12 on Google earth image, Fig 42).

Of certain importance, a massive structure with a triangular configuration can be observed approximately 150 m into the main upper chamber (Fig 33). However, on closer examination, it can be seen that it is portion to a massive downthrown block developed along a normal fault (G, yellow arrow) riding against an opposing syngenetic developed thrust (B, blue

96 arrow), but also demonstrating again, syngenetic perpendicular movement along strike (A, red arrow) giving this structure a three-directional sense of movement.

Unfortunately, the structure could not be approached for direct structural measurements as access to it demanded highly specialized climbing equipment. Thus, an evaluation of its structural characteristics, dip and strike values could only be made from various vantage points across a deep gully and estimated. However, realistic measurement correlations with features in the opposing southerly footwall clearly related to this structure could be made and from this, this structures dimension could be calculated.

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Fig 33: A flower structure exhibiting several compression characteristics (No 13: on Google earth image, Fig 42).

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The ‘triangular’ footwall structure exhibits a dip direction/trend averaging 36o and a dip/plunge averaging 41o, also a strike trend averaging 306.25o (33) with (Fig 34, rose diagram A, B, and C and stereonet diagram D indicating the structural plane great circle

(orange) and pole positions (red and blue) of this portion of the structure as represented by field data (Table 3). In addition, the downthrown (footwall) block experienced compression from an SSW originated pressure force at 200o (C) causing secondary fracturing developing a semi-detached downthrow segment (E) and ‘driven in’ chevron structures (D) indicating the direction of force flow.

A. Strike. B. Strike dip direction/trend.

B. Strike dip/ plunge direction.

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D

Fig 34: A, B, C and Stereonet diagram D: showing the plane great circles (orange) and pole

(red and blue) positions represented by the rose diagrams above.

Flower structure downthrow segment directional measurements Dip Strike direction/trend Dip/plunge 306 36 negative 41 308 38 negative 40 305 35 negative 42 306 36 negative 41 Average 306.25o 36o negative 41o

Table 3 A: The strike, dip direction/trend and dip/plunge angle field measurements of the flower structure’s downthrow segment as represented in the rose diagrams A, B C and stereonet diagram D (Fig 34) above.

In opposition, the hanging wall (B) experienced elevation (thrusting) along a thrust strike averaging 306.24o, a thrust direction of average 216o and a throw angle (positive) averaging

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41o. (Fig 33, B and F, Fig 35 A rose diagram A, B and C and stereonet diagram D indicating the structural plane great circle (lavender) and pole positions (blue) of this portion of the structure as represented by field data (Table 3). In addition, downwards traversing fracture lines (H) within the footwall attest to the effects of sudden compression. Also, within the hanging wall features (J) a compressional structure (K) appears to be shatter cones, also attesting to the effects of a sudden high-value compressive shock event.

A. Strike. B. Throw angle.

C. Throw direction.

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C

Fig 35 A, B, C and Stereonet diagram D: showing the plane great circles (lavender) and pole

(blue) positions throw specifics of the flower structure’s thrust directions as represented by the rose diagrams above.

Flower structure throw directional measurements Strike Thrust throw direction/trend Thrust throw angle: positive 306 216 positive 41 308 218 positive 40 305 215 positive 42 306 216 positive 41 Average 306.25o 216o positive 41o

Tables 3 B: The strike, dip direction/trend and dip/plunge angle measurements of the flower structure’s thrust throw portion.

This structure thus having demonstrated syngenetic movement along three planes of movement consequently complies with the definition of a flower structure being a structure produced by local changes in a strike-slip fault system where faults have opposed dip, leading

101 to alternate zones of elevated and depressed blocks arising from local zones of transpression, the compression associated with movement along a curved strike-slip fault, and transtension with tension associated with movement along a curved strike-slip fault (Kearey, 2001).

A third structure and perhaps the most telling can be seen approximately 270m into the main chamber (Fig 36). This structure comprise a major compression/ramping structure where severe shock loading resulted in intense shattering, buckling (O), displacement (N and I.-blue arrow) and ramping/thrusting (L, red and P, the yellow arrow indicates ramp/thrust travel) and the compartmentalizing of individual chert layers (A, B, C, D, E, F, G, H, I, J, and K) producing uneven (irregular) and splintery fracturing developed along a curvature with a dip value of ±9o towards the southern bottom aspects of the structure to ±50o towards the apex

(personal observations, author).

In opposition and in response to intense shock loading the progressive fracturing of the dolostone partitions between the chert layers reduced the dolostone to a matrix comprising fine-grained aggregates and mineral grains with some mylonite. Within the dolostone partitions, this fracturing continued until distribution of clast sizes was developed that allowed the sliding of clasts past each other, without high enough frictional stresses to further fracture the rock significantly. From then on deformation was accommodated by continued sliding and rolling of fragments, a deformation mechanism known as cataclastic flow associated with shock metamorphism (Jefferies et al., 2006). This process could only have been achieved during a directional high velocity, high brisance compressive shock event traversing the area, forcing the features presently mentioned. The only suitable candidate for this structure’s genesis seems to be the Vredefort impact event.

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The entire structure demonstrates considerable elevation values with a ballpark maximum elevation point of ±20-25 m. This distance of elevation has been suggested by having a measured layer thickness of the original chert band where this could be approached and then to multiply that thickness to the point of maximum elevation seen on photos. The main thrust platform (L) also follows along an upwards trending curve with curvature values starting at the bottom southern aspects of the structure at ±9o with curvature values measured at the top

(northern aspects) of the structure also approaching 50o. (Figure 36, rose diagram A, B and C and stereonet diagram D indicating the structural plane great circle (blue) and pole positions

(green) of this portion of the structure as represented by field data, (Table 5).

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Fig. 36: A massive compression, ramp and thrust structure, indicative of a massive high energy, high-velocity compressional event (No: 14 on Google earth image, Fig 42).

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Of equal interest is to notice, similar to the presently mentioned flower structure, when the strike and dip values of this structure were measured it was found to comply in orientation with those given for the mentioned micro-thrust structures yielding a Vredefort date range.

The conclusions drawn was that this structure, due to its morphology characteristics as well as dip and strike values likely and similarly relates to the compressional shock effect of the

Vredefort impact event.

A. Thrust strike. B. Thrust direction.

C. Thrust angle variables.

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D.

Fig 37: Rose diagram A, B, C and Stereonet diagram D: showing the plane great circles

(blue) and pole (green) positions major thrust trends as represented by the data below (table

5).

Major thrust structure Strike dip direction/ trend Dip/plunge 280 190 9 280 190 12 280 190 16 285 195 19 290 200 20 290 200 28 290 200 30 292 202 40 295 205 42 297 207 50 Average 287.9o 197.9o 26.6o

Table 4: The strike, dip direction/trend and dip/plunge angle measurements of the major thrust structure.

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Of specific interest; entering into the lower section of the cave traversing the Frisco/Eccles

Formation boundary another major thrust zone developed (Fig 38 and 39). This thrust again demonstrates a strong south to north vergeance (according to preserved in situ slickensided surfaces in places) and seems to have utilized the contact between the two mentioned formations as a mobilization platform as indicated by a fine-grained mylonitic layer along the contact. This is followed by an intermittent layer of unaltered chert rich Eccles Formation in turn followed by a substantial strongly schistose thrust horizon. This again is followed by an undisturbed portion of Eccles Formation followed by a cataclasis thrust horizon accompanied by a series of closely spaced medium thickness (<10 cm) to micro shear zones (<5 cm). From this point on one passes through a thick rubble and boulder choke and into the remainder of the Eccles Formation that seems largely undisturbed apart from the mentioned cross-cutting fault.

Fig 38: The lithology of the ‘upper’ chamber of Armageddon Pot (dip not indicated).

Passing through a boulder choke and into the underlying Eccles Formation none of the above- mentioned structures is observable and the cave’s morphology alters dramatically. From this point on the cave follows along a deep steep-sided canyon regulated by the same normal fault

106 noted in the ‘upper chamber’ with inter-lithology marker horizons, in this case, prominent chert horizons correlatable along strike demonstrating a similar displacement as seen within the upper portion of the cave.

Here the cave’s sidewalls comprise almost entirely of ‘stacked’ chert bands having collapsed on top of one another in response to the intercalated dolostones being removed within evidently a long-standing phreatic environment clearly indicated by dehydrated dolostone partitions between chert layers whereas in places lower down in the sequence still hydrated decalcified MnO2 and FeO2 wad (mud) are encountered demonstrating that up to recently this portion of the cave was phreatic. This is also borne out by thick wad clay covering the floor in flat chambers as is also is the lack of any speleothems in this part of the cave.

This trend continues with the lower section altering in chamber dimensions only, but retaining the same wall morphology so that it seems that major structural alterations such as those observed in the ‘upper’ chamber and within the Frisco seem limited to the uppermost portion of the Eccles only and along the contact with the Frisco Formation. This seems the case with the overlying Pretoria Group, Timeball Hill Formation as well that seems largely unaffected apart from the mentioned décollement and the Eccles Formation similarly being displaced by the mentioned normal fault.

6.2.4. Thrust and shear zone orientations

Within Armageddon Pot thirty-two thrust orientation measurements were done to determine strike and dip values. These are represented in stereonet format (Fig 42) and as can be seen, shear zones measured demonstrate a strong NNE to SSE strike trend with the thrusts demonstrating the same direction of dip at a moderate dip value of 30o.

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A. B. E______W

Fig 39 A and B: Showing a selection of thrusts seen in Armageddon Pot along the Frisco and

Eccles Formation contact (No: 15 on Google earth image, Fig 42).

(Figure 38 A and B) is a selection of some of the thrust horizons found in proximity to the contact between the lower Frisco and upper Eccles Formations with (Fig 34 A, point A) representing the thrust, point B, a cataclasitic slide plain, points C and D, direction of thrust and point E strongly developed slickensided mylonitic schist between this thrust and the overlying dolostone (personal observations, author). Fig 34, B, point A representing the thrust, point B, the direction of thrust, point C, strongly developed slickensided mylonitic schist slide plane resting above thrust presently described in (Fig 34: A), seen here as point D.

When correlating Armageddon Pot’s survey as superimposed on Google earth images (Fig

42) and when compared to the measurement bearings taken on site (Fig 39 A, B, C, and D) it can be seen that the rose diagrams dip plunge, dip direction and the strereonet’s plane pole positions (yellow) and plane great circles (burgendy) direction values, as indicated also by

(Table 6) strongly support the notion of an SSW origin for the force/s responsible for the genesis of the presently mentioned thrusts, also, demonstrating a point of crossing near or in approximation to the area believed to be the Vredefort impact epicenter. This lends strong

108 support to the notion that at least a number of the observed thrusts may be Vredefort related. or at least, reactivated older thrusts. (personal observation).

A. Strike B. Dip angle

C. Dip direction.

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D.

Fig 40 A, B, C and Stereonet diagram D: compilation showing the plane great circles

(burgundy) and pole (yellow) directional trends of the macro and micro thrusts cutting across the main controlling fault controlling Armageddon pots linear extent as represented by the rose diagrams above.

110 footwall thrust and micro-thrusts structural characteristics Strike Dip direction/trend Dip/plunge 287 197 19 287 197 19 287 197 20 288 198 21 288 198 22 288 198 22 289 199 25 289 199 25 289 199 25 289 199 26 289 199 27 289 199 28 290 200 28 290 200 28 290 200 30 290 200 30 290 200 30 290 200 30 291 201 31 291 201 32 Average 289.05o 199.05o 25.9o

Table 5: Demonstrating the similarities between the footwall thrust and micro-thrusts dip direction, the flower structure (Fig 33) and the thrust (Fig 34) directional specifics to be strikingly similar.

6.2.5. Joint set orientations

Numerous major joint has been measured in determining joint orientation to determine whether a specific joint direction predominated or whether joint set orientations were random. It was found that although joint sets within Armageddon could be classified as belonging to all joint set types (Chapter 3, this thesis) there seem to be a strong NW to SE and SW to NE joint and lesser well-pronounced ENE to WSW and SSE to NWN groupings,

111 strongly suggesting the influence of a south-westerly extension force (Fig 40). This again has been contributed to the partial influence of the Vredefort impact believed to have contributed to the surveyed joint sets orientations.

Fig 41: Rose diagram demonstrating the joint strike trends measured in Armageddon Pot.

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Fig 42: Survey superimposed over Google Earth imagery indicating the localities where the photos in this chapter were taken.

Photo 1. (Fig 18) page 77 Photo 12. (Fig 32) page 96

Photo 2. (Fig 19 A and B) page 77 and 78 Photo 13. (Fig 33) page 97

Photo 3. (Fig 20) page 80 Photo 14. (Fig 36) page 103

Photo 5. (Fig 21) page 81 Photo 15. (Fig 38) page 108

Photo 6. (Fig 22) page 83

Photo 7. (Fig 23) page 85

Photo 8. (Fig 25) page 87

Photo 9. (Fig 26) page 88

Photo 10. Fig (27/28) page 89

Photo 11. (Fig 31 A-D) page 95

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Chapter 7: 40Ar/39Ar dating

7.1. Introduction

The age of the Malmani Subgroup is bracketed between 2100-2600 Ma (Snyman, 1996) and the structural features found in Armageddon Pot as well as in caves in the CoH area could thus in principle be related to a number of known tectonic events that occurred over the extended time-span of its existence. The following seems the most apposite. (1). Tectonics associated with the intrusion of the Bushveld Igneous Complex (now very precisely dated at

2054 ±0.8 Ma (Zeh et al., 2015). (2). Compressional tectonics of the Transvaalide orogeny postulated by Alexandre et al (2006) who suggested dates of±2041 or±2150 Ma for this event on the basis of 40 Ar/39Ar dates on sericite in shear zones. (3) The Vredefort Impact event, dated at 2023 ±3 Ma by zircon U-Pb (Kamo et al., 1996) and (4), and later, possibly quite young events that are undated but referred to as Neotectonics (Dirks and Berger, 2013).

On shear zones within the Malmani Subgroup, particularly within shale horizons, fine- grained sericite occurs as a fabric forming mineral, or at least well aligned with the foliation.

Since this indicates that the sericite crystallized or recrystallized during the respective tectonic event, a number of samples were taken from shear zones in Armageddon Pot as well as in the Rising Star cave for 40Ar/39Ar dating of these sericites.

7.2. Results

The results are shown as age spectra against cumulative 39Ar in (Fig 41 A and B, Fig 42 A-G and Fig 43 A-H) (with gas release at progressively higher temperatures from left to right) and summarized in a complete step data graph (Fig 46).

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Without exception, the age spectra are characterized by young apparent ages in low- temperature steps and staircase patterns up to smaller or larger plateaus, or near-plateaus.

Considering the fine grain size of the sericite analyzed, effects of 39Ar loss by recoil, and/or

40Ar loss by recoil-related damage (Dong et al., 1995; Hall et al., 1997; Hall, 2014) cannot be ruled out. The former can lead to apparent ages that are too high, and typical hump-shaped spectra in samples that are not monomineralic. In monomineralic samples such as those analyzed here, recoiled 39Ar is likely to be re-implanted into adjacent grains (e.g. Dong et al.,

1995) so that the average apparent age is not affected. Loss of 40Ar during irradiation, due to lattice damage caused by the recoil of 39Ar and other nuclides formed, causes apparent ages that are too young such as observed in the low-temperature steps. This is a common feature in samples with a fine-grained fraction (Hall, 2014). In general, age plateaus that appear towards the higher temperature side of the spectrum are considered to be reliable. Normally, an age plateau is considered a valid one if it represents more than 60% of the total 39Ar released

(McDougall and Harrison, 1999). With the present samples this is often not the case, therefore duplicates, and many samples were analyzed to obtain confidence in the results.

The dated sericite samples define three age clusters (Fig 41 A and B, Fig 42 A-F: and Fig

43A-H) showing the 40Ar/39Ar age spectra of the samples (following pages).

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Cumulative39Ar Fraction A: PB6_8_1 (Armageddon Pot)

Cumulative39Ar Fraction B: PB6_8_2 (Armageddon Pot)

Fig 43 A and B: 40Ar/39Ar age spectra from duplicate runs of a sample taken from the lowermost thrust zone in Armageddon Pot, separating the Frisco and Eccles Formations showing a Vredefort age range.

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Cumulative39Ar Fraction A: PB3_5_1 (Rising Star)

Cumulative39Ar Fraction B: PB4_6_1 (Rising Star)

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Cumulative39Ar Fraction C: PB_RS_11_2 (Rising Star)

D: PB9_10_1 (Rising Star)

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Cumulative39Ar Fraction E: PB_5_7_1 (Armageddon Pot)

Cumulative39Ar Fraction F: PB_A_9_9_1 (Armageddon Pot)

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Cumulative39Ar Fraction G: PB8_9_1 (Armageddon Pot)

Fig 44 A-F: 40Ar/39Ar age spectra from samples taken from strata-Parallel shear zones in

Rising Star cave and Armageddon Pot, reflecting a Bushveld Igneous Complex age.

A: PB-A-1_1_2 (Armageddon Pot)

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Cumulative39Ar Fraction B: PB-A-2_2-2 (Armageddon Pot)

Cumulative39Ar Fraction C: PB-A-3_3-2 (Armageddon Pot)

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D: PB-A-4-4-2 (Armageddon Pot)

Cumulative39Ar Fraction E: PB-A-6_6_2 (Armageddon Pot)

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Cumulative39Ar Fraction F: PB-A_8_8_1 (Armageddon Pot)

Cumulative39Ar Fraction G: PB_10_10_2 (Armageddon Pot)

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Cumulative39Ar Fraction H: PB_5_5_1 (Armageddon Pot)

Fig 45 A-H: 40Ar/39Ar age spectra from 8 samples taken from small thrusts reflecting varying ages all distinctly older than that of the Bushveld Igneous Complex.

The 40Ar/39Ar dates obtained fall into three distinct Groups: (1). Ages identical to that of the

Vredefort impact at ages ranging from 2021.2 ±8.8 and 2025.5 ±7.9 (PB6_8_2 and

PB6_8_1). (2). Ages overlapping within the intrusion age of the Bushveld Igneous Complex bracketed between 2046.6 ±8.4 – 2061.1 ±8.4 Ma (PB3_5_1, PB4_6_1, PB_RS_11_2,

PB9_10_1, PB_5_7_1, PB_A_9_9_1 and PB8_9_1) and (3), ages substantially older than the

Bushveld Igneous Complex ranging from 2080 to 2140 Ma spanning 60 Million years (PB-

A-1_1_2, PB-A-2_2-2, PB-A-3_3-2, PB-A-4-4-2, PB-A-6_6_2, PB-A_8_8_1 and

PB_10_10_2).

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A thermo-chronological interpretation, following which the dates obtained would in part represent cooling ages, appears to be not applicable to these data First, the whole range of ages is yielded by samples taken at less than 2 km distance from each other and in a depth range less than 150m in extent, and second, the occurrence of fine-grained sericite is typical of low-grade metamorphism, not exceeding±400˚C, whereas the first order estimate for the closure temperature of the K-Ar system in muscovite is around 550˚C (Villa, 1998). The conclusion is that the dates represent ages of crystallization and/or re-crystallization of sericite, which is most likely identical to the age or shearing in the respective shear zones.

On the first sample run, samples were taken from the main shear zone (‘décollement’) situated between the topmost of the Malmani dolostones (Formation) and the Pretoria Group

(Timeball Hill Formation). The conviction was that all the dates within Armageddon Pot would be the same, all reflecting a Vredefort impact event date range and therefore only one site locality was selected for sampling. However, the results indicating a Bushveld age range from 2046.6 ±8.4 – 2061.1 ±8.4 Ma came as a revelation (Fig 37 A-F, 45 and 46). After deliberation and consultation, the concept that this structure represented a detachment fault that developed along the flanks of a rising Johannesburg dome in isostatic response to the downwarping of the Bushveld Igneous Complex was considered. A point of interest: Similar shears are observable within several gold mines in the vicinity (with specific reference to

West-drie gold mine) (personal communications, Combrink, 2017). These have the same slide orientation and dip as that seen along the Pretoria Group/Malmani contact in

Armageddon Pot, giving the impression that these may also represent (syngenetic) detachment faults also associated with gravity slippage along the flanks of the Johannesburg dome.

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To test this supposition it was decided to sample similar structures noticed in caves on the northerly side of the Johannesburg dome and within the CoH. The result thereof was that the dates recovered from the shear zones found within the CoH, in specific the Rising Star cave system, was of a similar date range (Fig: 37 A-D, 44 and 46). The morphology characteristics on both sides were congruent, except, within the CoH similar shear zones dipped NNW in opposition to a southerly dip in the case of Armageddon Pot. This fortifying the postulate that these features rightfully represent detachment faults (shears).

Based on these findings it was then decided to sample deeper within Armageddon Pot to determine whether this date was universal across the entire cave profile, or whether date variables existed. The second sample run, executed by Herman van Niekerk and the author targeted micro shear zones located towards the top and middle portion of the Frisco

Formation as well as a major subhorizontal shear zone at the contact between the lowermost

Frisco and uppermost Eccles Formations. Within the lower Eccles Formation, no such structures were observable as they are either very difficult to distinguish, or absent. If absent the reason would probably be because of the high-density intercalated chert layers acting at structural stabilizers, preventing interleaved micro shearing (personal opinion).

The samples from towards the top and middle section were sampled first. All except one reflected dates that far surpassed the Bushveld age ranges, yielding dates from 2080 to 2140

Ma, reflecting a 60 Million yr date range (Fig: 42. A-H, 45 and 46).

Lastly, the lowermost major subhorizontal shear zone in Armageddon Pot, at the contact between the lowermost Frisco and uppermost Eccles Formations was sampled, though one

126 sample only. This sample analyzed in duplicate yielded a Vredefort age of 2021.2 ±8.8 and

2025.5 ±7.9 Ma respectively (Fig: 41: A and B, 45 and 46).

Fig 46: Showing the formations and the localities from which sampling was done for

40Ar/39Ar dating within the Rising Star cave system.

Fig 47: Showing the formations and the localities from which sampling was done for

40Ar/39Ar dating within Armageddon Pot.

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. Fig 48: A compilation of the total age data recovered from Armageddon Pot (series 1) and

Rising Star (series 2) demonstrating three distinct date clusters.

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Chapter 8: Discussion

8.1. Introduction

From the above, it seems that at least three major periods of tectonics played a part in creating the structures observed within Armageddon Pot. When correlating the dates recovered the three following events stand out as the most likely candidates. These are: From youngest to oldest.

A The Vredefort impact event dated at 2023 ±3 Ma by zircon U-Pb (Kamo et al., 1996) (Fig:

39).

B. The downwarping of the Bushveld Igneous Complex and the isostatic elevation of the

Johannesburg dome bracketed between 2046.6 ±8.4 – 2061.1 ±8.4 Ma (Fig 39).

C. Various possible tectonic episodes predating the Bushveld Igneous Complex intrusion, indicated by the age range 2080 – 2140 Ma (Coertze et al.,1978) (Fig 39).

8.2. The Vredefort impact structure

The Vredefort impact is a ring structure which is elongated toward the SE where it is covered by both Dwyka tillite and the Ecca Group of the Karoo Supergroup. This unique structure is a well-studied and explained phenomenon accepted as a meteorite impact crater (Bischoff,

1988, Brink et al., 1997, 1999, 2000a, 2000b, Gibson and Reimold, 2008, Johnson et al.,

2006; Jahn and Riller, 2009, 2015) and not a volcanic diatreme (Truswell, 1977). The

Vredefort crater’s original diameter of ±100 km immediately the following impact was enlarged to ±250-300 km after rebound and crater rim collapse (Gibson and Reimold, 2008).

In further confirmation of its impact origin a correlation between pseudo-tachylite, shatter cones and the occurrence of coesite and stishovite as resultant of impact metamorphosis has been made (Gibson and Reimolds, 2008). Further, structures such as the Foch Thrust-

Potchefstroom fault system and the Katdoornbosch-Witpoortjie ring thrust have been shown

129 to be concomitant with shock displacement (Brink et al., 1997; Brink et al., 1999; Brink et al., 2000b).

8.3. Reasons for implicating the Vredefort impact event

8.3.1. Proximity

Following impact, the Vredefort bolide left a crater approximately (>100 km across that enlarged to (250-300 km after rim collapse (McCarthy et al.,1986, 1990). Armageddon Pots present locality is situated at ±75 km at 16o NE of the estimated impact epicenter, therefore, its position would be well within the diameter of the original crater rim and well within the range where impact would have exerted definitive structural effects such as faulting, fracturing and thrusting (Jahn and Riller, 2009, 2015) creating cataclasite matrixes in the process (Fig. 40).

Fig 49: Demonstrating the position of Armageddon Pot in the context of the Vredefort impact’s crater dimensions (Internet image).

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8.3.2. Impact as probable or major agent for inserting speleogenic structural controls

Currently, ±186 impact structures are definitively recognized on earth and therefore impacting earth by bolides is per se, not an atypical phenomenon. The recognition that on rare occasion and in singular events impact played a significant role as an initiator for speleogenic propagation is therefore not entirely pioneering. The association between impact and speleogenic propagation is known from the United States of America, Mexico, and

Europe (Baier, 2007; Bradlower et al.,1998; Milan 2006). This situation regarding Africa may now demonstrate the role of impact in creating speleogenic pathways, though rare, to be a global phenomenon.

It is known that the caves and cenotes found in proximity to the Chicxulub crater on the

Mexican peninsula relate to impact (personal communications, Lampini, 2000). Here thrust faulting arranged around impact epicenter and situated well within the impact zone’s structural disruption sphere has created the pathways for later dissolution speleogenesis.

These cave systems, accessible through numerous cenotes extend for several tens of kilometers following the same roughly arcuate trend as the crater rim, and therefore a causal relationship between impact and speleogenesis could be established (Bradlower et al., 1998).

A second incident where impact relates to speleogenesis is with the Flynn Creek impact crater, the United States of America Milan (2006) states ‘We have discovered that impact cratering, one of the dominant surface-modifying forces on Mars and elsewhere in the solar system, can also exert control over cave passage development and the location of subsurface microclimates. Such is the case at the Flynn Creek crater, a 3.8 km diameter complex crater that formed in Ordovician-aged rocks of what is now Jackson County, Tennessee. Flynn

Creek target rocks (to within 1500' of the crater rim) contain 5.5 x the concentration (1 cave/2.38 km2) of known dissolution caves found elsewhere in the county (1 cave/13.14

131 km2). Nine of the caves are concentrated along the crater rim, while one formed in the central uplift’.

‘With lowering of the regional base level, cave development first occurred at Flynn Creek at the highest elevations of limestone/dolostone exposure in target rocks, namely along the crater rim. Similar to other non-impact related caves, many at Flynn Creek developed preferentially according to the strike and dip of the crater rim. However, others formed along extensional fractures in the fold axes of anticlines and along major faults where compression of the crater rim and wall collapse, respectively, occurred’.

The third case, the Nӧrdlinger Ries Kessel Meteorite impact site is a large circular depression situated in western Bavaria, Germany, located north of the Danube in the district of Donau-

Ries. The depression interpreted as an impact structure formed during the Miocene between

±14.3-14.5 Ma (Baier, 2007). The original crater rim had an estimated diameter of 24 km with the present crater floor being approximately 100-150 m below the eroded remains of the crater rim. Recent computer modeling of the impact event indicates that the impactor probably had a diameter of ±1.5 km impacting the target area at an angle of ±30 – 50o. The impact velocity is thought of as being around 20 km/s (45 000 km per hour) delivering 2.4 x

1021 joules-the equivalent of 1.8 million Hiroshima bombs (Baier, 2007). The impact caused the formation fractures. These open fractures align in a radial and circular pattern, and clearly formed during impact rebound (Zipfell, personal communications, 2014). Being situated in predominantly graphitic non-carbonate rock type their relationship with a unique or innovative type of speleogenic event has therefore never attracted attention or in this context recognized. However, would this impact have occurred elsewhere in Europe where limestone predominates, the situation could have been similar to the Chicxulub Mexico event. The

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South African situation, therefore, may not be unique, but in as far as Africa is concerned so far seemingly exclusive.

8.3.3. Impact amplitude

The rationale that the Vredefort impact had a major role in the speleogenic initiation of

Armageddon Pot is further based on the following:

If the shock amplitude delivered by the Vredefort event could be compared with known measured amplitudes it can be seen that first, a shock wave of this severity has never officially been recorded, but if possible would have been utterly destructive bringing about both topographic and sub-surface structural alterations out to a distance far beyond its initial crater rim diameter of (>100 km) enlarged to (250 – 300 km) after rim collapse as suggested by (Bischoff, 1988; Brink et al., 2000 a & b, 1997; Gibson and Reimold, 2008; McCarthy et al.,1986, 1990).

The impact penetrated into Kaapvaal craton basement granitics folding all lithologies back in a series of overturned folds. The impact also accelerated crustal material outward, activating thrusts zones such as the Foch and Witpoortjie thrust zones as well as re-activating or accentuating older structural units such as the Panvlakte/Witpoortjie horst block set (Manzi et al.,2013), the Black Reef Décollement Zone (BRDZ) and the Potchefstroom-Master Bedding

Plane Fault (PMBF).

This also resulted in the forming of at least two concentric anticlines and an annular syncline

(Bischoff, 1988; Brink et al., 1997; Brink et al., 1999; Brink et al., 2000 A and B; Gibson and Reimold, 2008). On a more local scale the forming of pseudo-tachylite, chocolate

133 boudinage, shatter cones, cataclasite and the presence of stishovite and coesite (Bischoff,

1988; personal communications, Martini, 1984) also attests to impact intensity.

8.3.4. Explosive force: a comparison

The following demonstrates possible or probable explosive force, impact kinetics and dynamics and the likely quantity of (J) energy released by the Vredefort impact in demonstrating the likeness that this impact expended sufficient force to have exerted a definitive role in creating some of the disruptive structures noticed within Armageddon Pot.

To gain an understanding of the energy (Joules) output the Vredefort impact event could have generated a substance capable of generating a comparable force ha to be used as analogue. As such the most convenient material known capable of producing similar joules values- providing sufficient quantities could be provided would be conventional explosives. As such

TNT (Trinitrotoluene) is the explosive of choice.

Although TNT is not the most energetic of conventional explosives (Pure nitro-glycerine for instance, per equal volume, has more than 60% more energy density, approximately 7.5

MJ/kg, compared to 4.7 MJ/kg for TNT (Lenz, 1976, Boshoff and Teitge, 1987). TNTs velocity of detonation (VOD) at ±6900 m/s as standard provides a credible measure (analog) in dealing with mass/volume and shock wave propagation calculations. As such the kiloton and megaton energy (joules) output of TNT equivalent method is now the universally accepted standard in quantifying the energy released during the detonation of nuclear weapons. This now is also applied in measuring the joules delivery of geological phenomenon e.g. earthquakes, volcanic eruptions and asteroid impacts in giving a sense of destructiveness (Boshoff en Teitge, 1987).

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The metric tonne of TNT delivers 4.184 GJ of energy. However, the measured pure heat output of a gram of TNT is only 2724 J (personal communications, Coppachenko,2014).

This, however, is not the imperative value for explosive blast effect calculations. Of more significance for calculating the possible destructive force output of the Vredefort impact event is the VOD (velocity of detonation) of TNT delivering a high brisance, high-velocity shock wave.

8.3.5. Explosion yield examples

To achieve a sense of destruction wrought by the Vredefort impact: conventional bombs (as those dropped from bombers in World War 2) yielded TNT equivalent ranges from less than

1 to 11 tonnes, delivering 17.5 and 192.5 GJ respectively. A 1985 United States conventional explosion utilizing 4,400 tonnes of ammonium nitrate/ fuel oil-(ANFO) explosives believed to be the largest planned detonation of conventional explosives in history delivered a 4 kiloton TNT equivalent explosion producing a 17 TJ nuclear explosion simulant (personal communications, Coppachenko, 2014).

The ‘Little Boy’ atomic bomb dropped on Hiroshima, Japan on August 6, 1945, exploded with an energy output of ±15 kilotons of TNT equivalent producing 63 TJ. During the Cold

War, the United States developed hydrogen bombs with a maximum theoretical yield of 25 megatons of TNT theoretically capable of yielding 104 PJ.

The nuclear weapons currently in the arsenal of the United States range in yield from 0.3 KT-

1.2 MT TNT equivalents capable of yielding 1.3 TJ and 5.0 PJ respectively. In opposition the former Soviet Union (USSR) developed a prototype weapon (Tsar Bomba) challenging the

West by stating, ‘Kuz kina mat’-interpreted as-We will show you, which was tested at 50 MT

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TNT equivalent yielding 212 PJ and a maximum theoretical yield of 100 MT TNT equivalent yielding 424 PJ (personal communications, Coppachenko, 2014).

8.3.6. Impact kinetics and energy

Given a bolide measuring 1.6 km in diameter with the average density of granite at 2.88.g cm-3, impacting Earth at 19 km/s, physics, and computer modeling demonstrates that this impact will be capable of producing the explosive power yield of ±240 000 MT of TNT equivalents, producing 1.0 PJ. This is 20 million times the yield of the bomb dropped on

Hiroshima, Japan at 50 MT, and 3600 times higher than the most powerful hydrogen bomb ever tested. In calculating the joules delivered by the Vredefort event, the above specifics have been used as a benchmark for calculating the possible yield of the Vredefort impact.

From available computer programs, the author calculated that the Vredefort bolide estimated

. o at 10 km diameter with a density of 2.88 g cm-3 entering at an approximate 45 (prograde) angle would have collided with earth at a likely velocity of 19 km/s (68400 km/h). From this realistic yet conservative estimates inferences could be computed regarding the Vredefort’s possible energy deliverance range on impact by applying Newton’s second law of motion where, F = ma-whereas the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector A, of that object.

It has therefore been calculated that the Vredefort impact likely delivered ±6.309573e+19 J

(6.3 quadrillions) J of energy or 80-100 GPa (Gibson and Reimolds, 2008) on impact. This equates to the detonation of 1.508024e+10-4.76879 least+14 Tonne or approximately 40-44 exatonne of TNT (personal communications, Coppachenko, 2014).

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8.3.7. Initial effects of impact

The initial impact excavated a 100 km diameter crater 40 km deep vaporizing 70 cubic kilometers (70 km3) of rock (Gibson and Reimolds, 2008; McKenzie, 2014). This likely generated a radial propagating shock wave likely traversing the region at ~ 6900 m/s or 6.9 km/s (using the velocity of detonation (VOD) of TNT) initiating a probable compressive (P) shock wave and secondary (S), Love and Rayleigh wave probably ranging between a magnitude of 10 to 13 on the Richter scale.

The Vredefort impact event at a Richter scale magnitude of 10 would, therefore, have produced 31.6 times the energy amplitude released by the most powerful earthquakes recorded and at a Richter scale magnitude of 13, 31554.5 times the energy amplitude delivered at 10. If unimpeded (taking the velocity of detonation of TNT at 6900m/s as benchmark) the radial outwards propagating shockwave generated by impact would have for example, covered the distance from Pretoria to Cape Town at ±1600 kilometres in ±0.065

Hours, or ±3.9 minutes, or 234 seconds (personal communications, Nguyen, 2017).

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The following represents the (conservative) variables calculated for impact

Parameter Value Size estimate 10 km across Density (calculated for a stony meteorite) 2.88.g cm-3 Projectile velocity 68400 km/h Trajectory angle ±40o – 45o Projectile density 3000 kg/m3 Target density 2750 kg/m3

A Projectile and target specifics

Parameter Value Break-up altitude 55.825 Ft Kinetic energy 2.84 x 1023 J Impact energy 6.309573e+19 J Impact Richter scale magnitude 10

B. Energy deliverance at impact

Parameter Value Impact crater radius 100 km Peak thermal radiation 14 – 15000 K Irradiation duration 1.71 x 103 s

C. Fireball (thermal) effects during impact

Parameter Value Crater depth 35 – 40 km Crater diameter 85 – 100 km Crater diameter following crater rim collapse 270-300 km

D. Crater dimensions

Table 6 A, B, C, and D: The Vredefort impact event specifics (After Moser, 1997).

8.3.8. Shockwave propagation

Considering the calculated Joules output of the Vredefort event on impact, it is certain this would have generated a shock wave equal in nature to that generated by fault-induced earthquakes (Richter, 1935; Lamb and Sington, 1998; Reitherman, 2012). As such the nature

138 and sequencing of shock waves associated with such an event needs to be briefly discussed as this will aid in an understanding as to why and how an impact of that magnitude could have assisted in establishing Armageddon Pots structural controls.

Shock waves following an earthquake, or in this case impact comprises the initial primary (P) wave, also known as compressional waves. This is experienced as sudden and violent shock waves radiating outwards from the epicenter of movement (in this case impact). This, as is the case with fault induced quaking would likely have been followed by a secondary (S) waves moving rock particles up and down or side to side perpendicular to the direction the wave is traveling in (the direction the wave is traveling).

In addition, directly following in the wake of the (P) wave the initial tremor would likely have been accompanied by surface waves:

The first, Love wave is the fastest surface wave and moves the ground from side to side.

Confined to the surface Love waves produce exclusively horizontal motion. The second surface wave known as the Rayleigh wave propagates across the ground in the same fashion a wave propagates across a body of water. Because it rolls it moves the ground up and down but also side to side in the same direction the wave is traveling. Most of the shaking felt by an earthquake is due to the Rayleigh wave which can be much larger than the other waves.

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Richter scale magnitude Mercalli scale intensity 1.0-3.0 I 3.0-3.9 II-III 4.0-4.9 IV-V 5.0-5.9 VI-VII 6.0-6.9 VII-IX 7.0 and higher VIII or higher

Table 7: The above diagram represents the magnitude of earthquakes, from minor to the most severe (After: USGS Internet earthquake awareness program).

The following explains the severity of the quakes as described above.

I. Not felt except by a very few under especially favorable conditions.

II. Felt only by a few persons at rest, especially on upper floors of buildings.

III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motorcars may rock slightly. The

Vibrations are similar to the passing of a truck. The duration can be estimated.

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. The Sensation is like heavy truck striking a building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone. Many awakened. Some dishes, windows breaking. Unstable objects overturned. Pendulum clocks may stop.

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage is slight.

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VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys breaking.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. The damage is great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage is great in substantial buildings, with partial collapse.

Buildings shifted off foundations.

X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.

XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.

XII. Damage total. Lines of sight and level are distorted. Objects are being thrown into the air. The following gives an explanation of the severity of the quakes as described above. This intensity earthquake may create thrusts, new faults or reactivate older faults (After USGS,

Magnitude/Intensity Comparison, USGS Internet earthquake awareness program).

8.4. Structural features seen in Armageddon Pot that can be attributed to the Vredefort

Impact and speleogenic controls

From the above, the Vredefort impact’s contribution to Armageddon Pot’s speleogenesis can be found in the following:

The cataclasites seen within Armageddon are clearly formed through fracturing and comminution of existing rock in a process known as cataclasis, often found in response to

141 regional shock metamorphism (Kearey, 2001). Considering the above, the candidate most likely responsible as cause to, is the Vredefort impact event.

Although dateable sericite could not be recovered from the cataclasites themselves, the rationale that the cataclasites were formed by impact metamorphism is based on the fact that, as mentioned, Armageddon Pot at ±73 km NE from impact epicenter is well within the impact’s crater perimeter at 85-100 km. Furthermore, Armageddon Pot falls south of the

Foch and Witpoortjie thrust line known to be directly affiliated to the Vredefort impact thus showing Armageddon Pot to be well within the shock aura-perimeter of the Vredefort impact event, and therefore its shock metamorphism influence sphere. The rationale based on these facts, therefore, seems sensible.

Although the generation of cataclasites had little to do with the cave’s speleogenic initiation per se, it reflects on the kinetic effects of a passing high brisance shock front well capable of reactivating and elevating (enhancing) pre-impact thrust fault systems associated with the structural anatomy of the Panvlakte horst block system, that during rebound (extension), seemingly reversed, converting into an normal fault (as indicated by off-throw values) with possible hanging and footwall disassociation thereby creating a natal cavity. Although hypothetical, this postulate is not irrational if one includes the possible effects of post-impact rebound and rim collapse.

Answering the question as to why only the upper chamber contains cataclasite and why the

Vredefort dates recovered are located seemingly only within the bottom low angle imbricate thrust zone (along with the contact with the Frisco and Eccles Formation), the following explanation is offered. The Eccles Formation is particularly rich in intercalated chert bands

142 making for intensely fortified structural integrity and support, whilst the overlying Frisco

Formation is relatively chert poor, lending itself to structural failure in a high brisance

(shattering) event. As with conventional explosives, overpressure chooses the path of least resistance.

In the case of Armageddon Pot this could have had the effect of deflecting a massive rapid propagating shock wave off the Eccles, and up into the Frisco Formation causing the forming of a thrust (hence the Vredefort date from this horizon) with displacement along the

Eccles/Frisco boundary-as well as the forming of cataclasite and compression structures during impact, and extension structures (boudinage) during rebound, whilst in opposition the lower Eccles-because of structural integrity due to the abundant presence of chert bands, remained largely unaltered and intact.

The physical size of the upper chamber though is more the function of phreatic dissolution and the chemistry associated with undersaturation dissolution (Chapter 4, this thesis). This also played a significant role within the Eccles Formation, but again the chert layers present retarded the same dimensions of expansion as seen within the upper chamber as chert comprising predominantly silica (SiO2) is not susceptible to dissolution, but only to mechanical (brittle) failure.

8.5. The Bushveld Igneous Complex

8.5.1. Introduction

The Bushveld igneous province in South Africa has its most southern outcrop at 77 km due north of Armageddon Pot. A huge volume of mafic magma intruded the floor rocks of the

Transvaal Supergroup lithologies in a very short time interval at 2054 ±0.8 Ma (Zeh et al.,

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2015), creating the largest layered igneous complex on Earth. Presently the complex measures from south to north, ±126 km and from east-west, ±417 km and attains a depth of up to 9 km in places (Snyman, 1997). It, however, is clear that the complex would have covered a much larger area also attaining greater depths following intrusion. However, it can only be roughly surmised how much surface was removed following in the wake of the

African Superswell activated expansion of the Limpopo basin over the region (Partridge,

1980). A conservative estimate of the volume would be ±half a million cubic kilometers although the precise volume cannot be calculated because of erosion. It is also not possible to estimate the amount of basaltic materials that intruded as sills and dykes underplating the crust. (Hugh, 2001) calculated that between 0.7-1 million km3 were produced within 1-3 Ma which would have required magma generation rates between 1 and 0.3x106 km3 per Ma respectively. If the estimates for the magma volumes of 384x106 km3 for the Rustenburg layered suite and 200x106 km3 for Molopo farms are included then a cumulative volume of lava in access of 1 to 15x106 km3 was generated. This compares favorably with similar volumes given for the Deccan Traps, India, and the North Atlantic Tertiary Provinces.

8.5.2. Reasons for implicating the Bushveld Igneous Complex

The Bushveld Igneous Complex was not directly involved in creating structures later to control speleogenic propagation along the Far West Rand per se but likely exercised an indirect influence. When considering the volumes, extent and mass calculated for the

Bushveld Igneous Complex (Table 5 A and B) it can be envisaged how crustal thickening and downwarping affected the surrounding geology. This have specific reference to an isostatic response within the lithosphere, causing other structures such as the adjacent Johannesburg dome to elevate (personal communications, Viljoen, 2000) that in turn had direct structural implications for the Far West Rand expanse. The extent and volumetric specifics are listed

144 below to illustrate this, and the observed inward dip of the main Bushveld Igneous Complex can serve as evidence that downwarping of the Transvaal basin lithologies indeed occurred.

One consequence was the isostatic counter elevation of the Johannesburg dome, and its subsequent structural effects on the strata overlying it. The relatively large number of sericite dates from Armageddon as well as Rising Star bracketing the BIC age is striking, it must be emphasized here that these dates do not reflect direct heating by the Bushveld magma (they are found over a wide area, and very remote from any contact metamorphic features associated with the BIC). Instead, as recorded above they are clearly associated with the shear zone that is now interpreted as décollement horizons, as discussed below.

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Conservative estimate of total volume x103 Arial Extent Maximum thickness km3 50 000-100 000 km2 although it may have Rooiberg Group originally extended <200 Volcanic Province 000 km2 Up to 3 km 384-350 Rustenburg Layered Suite 65 000 km2 Up to 9 km 150-400 Bushveld Granite Suite and granophyres 30 000 km2 Up to 3 km 180 Satellite intrusions-Molopo farms 12 000 km2 Up to 3 km 30 Total 710-1060

A

Lithostratigraphic unit Age (Ma ±95%) Loskop Formation Rhyolite 2057.2 ±3.8 Makhutso granite 2053.4 ±3.9 Nebo Granite 2054.2 ±2.82 Lebowa granite suite Steelpoort Park Granite 2057.5 ±4.2 Critical Zone (SHRIMP) 2054.4 ±2.8 Rustenburg layered suite Critical zone (IDTIMS) 2054.5 ±1.5 Rashoop granophyre Suite Rooikoppies Porphyry 2061.8 ±5.5 Rooiberg Group Kwaggasnek Formation 2057.3 ±2.8 Molopo farms 2044 ±24 Mashaneng complex 2054 ±24 Satellite intrusions Uitkomst complex 2044 ±8

B Table 8 A and B: Demonstrating the extent, volumetrics and ages of the various provinces and groups of the Bushveld Igneous Complex (After Eales and Cawthorn, 1996).

8.6. The Johannesburg dome

8.6.1. Basic geology

The Johannesburg dome measuring ±50 km east to west and 30 km north to south comprise a domical window consisting of a variety of mid-Archaean granitoid rocks intruded into mafic- ultra-mafic greenstone remnants located in the central part of the Kaapvaal craton (Visser,

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1984). Trondjemitic gneiss sampled on the NW part of the dome yielded an age of 3340 ±3

Ma (Visser, 1984) representing the oldest granitoid phase recognized so far. This implies that the greenstone remnants scattered throughout the dome are older than 3.34Ga. The basement is overlain in the south by rocks of the West Rand Group of the Witwatersrand Supergroup, and in the north and west directly by the Black Reef quartzite and Chuniespoort Group of the

Transvaal Supergroup carbonates. All of these strata dip away from the center of the dome.

8.6.2. Reasons for implicating the Johannesburg dome

In considering the possible effects of tectonics around the Johannesburg dome on controls for speleogenesis in the region, it is assumed here that the Bushveld Igneous Complex and the

Johannesburg dome seemingly acted in syngenetic isostatic concert. During the isostatic elevation of the Johannesburg dome, in response to the downwarping effect of the Bushveld

Igneous Complex, the dolostone lithologies overlying the dome were elevated to initially form a brachy-anticlinal dome. It is considered a logical consequence that at some point tensional dynamics caused by gravity generated slumping, resulting in mild open folds with as well as numerous detachment faults developing along its flanks. Observed faults of this nature are generally strata-conformable and mostly have a moderate dip angle of ±12-17o. In the vicinity of Armageddon Pot the dip is to the SSE. In contrast, in the the CoH, in the vicinity of Rising Star it is ±17o NNW. At van Rooys cave, situated on the 1:50 000 2627 BA

Randfontein map at co-ordinates S26o 0.377’ E27o 44.208’, a major detachment fault outcropping on surface and underground within the cave has a roughly E to W strike and dips due north at ±55o.

Within the Cradle of Humankind and in addition to the Rising Star system some of these detachment fault sheets can also be seen within both Knocking shop cave, also situated on the

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1:50 000 2627 BA Randfontein map at co-ordinates S26o 2.551′ E27o 42.114′ (forming the ceiling of the main chamber) as well as within site 105, also known as Villa Louise, again located on the 1:50 000 2627 BA Randfontein map at co-ordinates S26o 1.329′ E27o 42.715′.

Here they all have a dip of ±17o NNW.

A similar dip angle of ±17o was also observed and confirmed within in situ materials found within the aforementioned décollement at the bottom of the sinkhole entrance into

Armageddon. In confirmation, In situ slickensided surfaces clearly exhibit striations, slickenfibres, and steps indicating an SW downslope trend in the direction of movement. This trend was also confirmed when applying a tactile test. It was found that the slickensided surfaces felt smooth to the touch when moving in the direction of movement and rough in the opposing direction. Sites were measured and recorded, all demonstrating an SW slide trend.

As mentioned above, the set of 40Ar/39Ar sericite ages bracketing the BIC age support the notion that many of the strata-Parallel shear zones within the Malmani dolostone are décollement zones caused by uplift of the Johannesburg dome, in turn in response to the BIC intrusion. The elevation of the Johannesburg dome as an isostatic counter to the downwarping of the Bushveld Igneous Complex had as a further consequence some folding of lithologies along its flanks due to gravity slippage (detachment faulting). It seems that in this fashion some of the older faults, perhaps related to the expansion of the Malmani basin could have been utilized (reactivated) as detachment faults (personal communications, Gibson, Hein, and

Viljoen, 2015).

Relating to this and applicable to Armageddon Pot, between the Pretoria Group and the dolostones a clear mylonitic zone is prominent. This ‘thrust’ sheet, although known has never been described (personal communications, Dirks, 2015). The interpretation of this sheet put

148 forward here is that it represents not a thrust, but perhaps a Malmani era expansion fault re- organized as a detachment fault associated with the up-doming of the Johannesburg dome.

Thus, not all of these fault sheets can be seen as relating to detachment faulting and only those in close approximation to the dome’s flanks should be considered in this context.

Similar features found further afield associate with either thrust associated with Palaeo-

Proterozoic far-field stresses, a proposed period of Palaeo-orogeny or with the relaxation of the Malmani basin (personal communications, Dirks, 2015). This is reflected by the set of pre-BIC 40Ar/39Ar sericite ages found.

8.6.3. The Johannesburg dome’s structural contribution to Armageddon Pot and caves in the

CoH

As discussed above, the elevation of the Johannesburg dome had resulted in the forming of down gradient (dipping) detachment faults (shear zones). These could have acted as conduits where they cut across established fault lines, allowing seepage into the aquaclude (as un- fractured dolostone is not porous), to produce an aqueduct. This simultaneously allowed for saturation dissolution within the phreatic zone to commence (at the right depth, temperature and pressure values, (chapter 4, this thesis). As such, the elevation of the Johannesburg dome and the creation of detachment faults along its flanks would have created the initial direct pathways for meteoric or connate water influx into an open fault system to effect later amplification.

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8.7. Tectonic episodes predating the Bushveld Igneous Complex

8.7.1. Palaeoproterozoic extensional far-field stress and the relaxation of the Malmani basin

Dirks (personal communications, Dirks, 2015) as well as Gibson (personal communications,

Gibson, 2015) are of the opinion that many of the low angled thrusts seen within the CoH as well as those seen along the Far West Rand are normal extensional faults created by a

Palaeoproterozoic extensional far-field stress field with an NW to SW orientation. The thought is that these extensional Palaeoproterozoic tectonics opening (extending) the

Kaapvaal craton had a regional effect, leading to normal (extensional) fault and fracture systems across much of the Transvaal Basin.

In addition to both the Vredefort event and Bushveld ages, the set of pre-BIC 40Ar/39Ar sericite ages dates obtained from shear zones in Armageddon Pot possibly point to age ranges congruent with the expansion period of the Malmani basin (personal communications, Dirks,

2015). The rather large range of pre-BIC ages found (2080-2140 Ma (Fig: 38) need not be interpreted as indicating prolonged tectonic activity. In view of the disturbed nature of some of the age spectra, and the evidence for a distinct BIC-aged episode a possible overprint, it is more likely that this set of dates reflects a variable mixture of sericite crystallized in one or more episodes at 2140 Ma or older, and sericite recrystallized during the BIC-induced event.

Unlike the latter, an earlier basin extensional event may have been regional, affecting the entire Malmani basin.

8.7.2. Deep-seated Witwatersrand tectonics and the forming of the Panvlakte horst set

The Panvlakte/Witpoortjie horst block forms an integral component of the geology of the Far

West Rand area The macro-structure of the Far West Rand is characterized by older north- trending faults (Far West Rand and Panvlakte) and younger east trending dextral wrench

150 faults (Waterpan and Wrench). This faulting, initiated by residual mantle plume activity

(Manzi et al.,2013) has resulted in the development of structural blocks dominated by the Far

West Rand (or Witpoortjie) and Panvlakte horst blocks that are superimposed over broad folding associated with the SE plunging Far West Rand syncline. The northerly limb of the syncline dips to the south-SW and the southern limb to the ENE (Osburne et al., 2014;

Stanistreet et al., 1986).) (Chapter 1, this thesis).

As a speleogenic contributor this period in time probably played a critical role. During the elevation of the Panvlakte horst set, the fault system along which later speleogenic propagation would commence was established. Although there is no direct geo-chronological evidence to support this, I propose below (Section 8.8) that reactivation of major faults related to the Panvlakte/Witpoortjie horst set during the Vredefort impact event created the main structural control for the propagation of Armageddon Pot. This seems not unique to

Armageddon Pot only, but to adjacent cave systems within the perimeters of the

Panvlakte/Witpoortjie horst block system as well (personal observations, author).

8.7.3. Other possible contenders

8.7.3.1. The Vryburg arch

As presently mentioned (Chapter 3, this thesis), the Transvaal Supergroup is developed in three unconformity-bounded sequences that are preserved and exposed in two geographically separate areas-the Transvaal basin, where it circumscribes the Bushveld Igneous Complex and the Griqualand West basin at the western Kaapvaal margin that extends into southern

Botswana beneath Kalahari cover as the Kanye basin. A broad basement high separates the two basins, referred to as the Vryburg arch (Eriksson et al., 1975; Eriksson and Truswell,

1974; Eriksson and Alterman, 1998; Eriksson and Reczko, 1995; Eriksson et al., 2001;

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Eriksson et al., 2006). It can, therefore, be foreseen that during the genesis of this basement how considerable associated stresses would have accompanied its derivation-that probably had far-reaching structural effects on the surrounding lithologies out to, and perhaps beyond the CoH. Of interest is to note that major fault lines in the CoH can be plotted pointing towards a western point of origin, the direction expected if the Vryburg arch, in fact, is responsible for at least some of the major faults seen in the CoH.

However, any structural influence pertaining to speleogenic controls along the Far West Rand is inferred, as no clear markers exist. Therefore, the Vryburg arch as having had a major role to play in inserting speleogenic controls along the Far West Rand, for now, is being speculative only.

8.7.3.2.. The Transvaalide thrust and fold belt

Some researchers favour an orogenic episode between the intrusion of the Bushveld Igneous

Complex at 2054 ±0.8 Ma (Zeh et al., 2015) and the following Vredefort impact event at

2023 ±3 Ma (Kamo et al., 1996) referred to as the Transvaalide fold-and-thrust belt. This event is seen as chief in inserting the structural character of the CoH (Alexandre et al., 2006)- and perhaps the Far West Rand expanse.

If this postulate could be validated the dynamics associated with orogeny would likely have contributed substantially to stress-induced faulting, fracturing and folding seen within the region. As such this would have had a substantial and direct influence on the region’s stress field dynamics and therefore, most likely, the region’s speleogenic controls, and should, if this postulate can be substantiated, be included in understanding the region’s regional but also local speleogenic dynamics.

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However, dates returned from materials sampled in Armageddon Pot and Rising Star cave do not reflect an intermediate date set between the Bushveld Igneous Complex and the Vredefort impact event. Until more confirmative work has been concluded regarding the apparent or suspected orogenic events influence in the region and its possible effect or influence on speleogenesis within the Wider CoH, or along the Far West Rand, its effect regarding remains highly speculative.

8.7.3.3. The Etosha-Griqualand-Transvaal Axis

The Etosha-Griqualand-Transvaal axis is a three-pronged southwards migrating axis of epeirogenic uplift due to lithosphere flexure generated in response to the African Superswell

(Holmes and Meadows, 2012; Moore and Larkin, 2001; Nyblade and Robinson, 1994;

Nyblade, 2003; Partridge, 1980; Partridge and Maud, 1987, 2000). Just south of the CoH the

Etosha-Griqualand-Transvaal Axis forms a major watershed regulating river system flow to both the south-west in the direction of the Atlantic, and to the N to the Indian Ocean

(Limpopo basin) (Martini et al., 2003; Moore and Larkin, 2001; Moore et al., 2009).

Apart from activating the Etosha-Griqualand-Transvaal Axis the African Superswell event also activated isostatic repair-aiding in the development and expansion of the Limpopo basin.

This basin’s southerly margin seen as a prominent escarpment to the south also forms the southern and westerly border of the Cradle of Humankind. In accordance with the dynamics of unloading and the effects, this has on the forming of open joint blocks it can be foreseen how this could have interacted with speleogenesis.

In as far as tensional dynamics is concerned and how this relates to the tectonics of the Far

West Rand with specific reference to tectonic influences pertaining to speleogenics definitive

153 markers to confirm or suggest any significant influence has not been established. Therefore, at present any correlation between the Etosha-Griqualand-Transvaal Axis and its effects on speleogenic controls may be incidental and for now only speculative.

8.8. A model of the events leading up to the formation of Armageddon Pot

8.8.1. Introduction

The following gives a likely sequential account of the events thought to have led to the formation of Armageddon Pot. This sequence has been proposed after all factors and other tectonic events that could have created speleogenic pathways in the vicinity have been considered. The 40Ar/39Ar radiometric data dates and tectonic events that are bracketed within the reflected dates are taken into account (Chapter 7, this thesis).

The major structural foundations to Armageddon Pot have seemingly been inserted by three major palaeo-tectonic events of pre-Bushveld, Bushveld and Vredefort age. However, although an open natal fracture could have been created during the insertion of the main linear control structure and subsequent thrust and inversion, phreatic and supra-phreatic

(vadose) amplifications likely only commenced during post-African 1 and 2 weathering

(denudation and epeirogenic) cycles, when the correct speleogenic depth interface and the conditions for phreatic and later vadose (supra-phreatic) enlargement was arrived at (chapter

4, this thesis).

The following sequence has been proposed:

8.8.2. Phase 1: Foundation

The following (Fig 51) demonstrates the basic lithological sequence of the Far West Rand expanse at the onset of deep Witwatersrand tectonics. At this point in time, it seems that the

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Pretoria Group was not yet deposited as none of the interleaved shears noted within the dolostones (Frisco Formation) was detected within the Pretoria Group.

Fig 50: The stratigraphic setting of the Transvaal basin at the onset of deep-seated

Witwatersrand tectonics.

8.8.3. Phase 2: Forming of the Panvlakte horst set

The tectonic evolution of the Witwatersrand is complex and the exact time frame during which the Panvlakte horst set developed is not precisely known as it seemingly occurred over a considerable period of time. However, it can be surmised that it had to be prior to the deposition of the Pretoria Group bracketed between 2224-2050 Ma as the forming of the erosion platform (peneplain) on which the Rooihoogte Formation deposited seems to be regional and deposited on an undisturbed planar platform throughout the Transvaal basin

(Catuneanu and Ericksson. 2004) (Fig 52). As such the Panvlakte horsts were ‘shaved’ off in accepting a peneplain surface (Fig 53, A).

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Fig 51: The forming of the Panvlakte/Witpoortjie horst set due to deep-seated Witwatersrand tectonics.

8.8.4. Phase 3: Deposition of the Rooihoogte and Timeball Hill Formation and insertion of interleaved micro-shears

Following the deposition of the top-most Frisco Formation of the Malmani dolostone sequence (in other localities the Penge Formation) a period of stasis and denudation known as the 80 million years ‘gap’ (Fig 6) commenced allowing for the forming of a weathering cap, the Rooihoogte Formation. Following this, at around 2300-2050 Ma, a period of thermal and extensional subsidence commenced whereby the Pretoria Group was deposited (Catuneanu and Ericksson. 2004) (Fig 53, C).

The ages recovered from the interleaved micro-shears within the dolomitic Frisco Formation yielded a radiometric date varying between 2140-2080 Ma (Chapter 4, this thesis), falling between the oldest and youngest dates given for the Pretoria Group bracketed at 2224-2050

Ma (Bartman, 2014; Catuneanu and Eriksson, 2000). The reflected dates for the micro-shears seen within the Frisco Formation strongly support the notion that they were generated

156 throughout the deposition of the Pretoria Group, from the earliest to the latest and for the reasons mentioned.

A

B

C

Fig 52 A and B and C: The pre-Vredefort impact insertion of interleaved micro shears within the Frisco Formation due to rifting expansion and then the Deposition of the Pretoria Group due to thermal subsidence.

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8.8.5. Phase 4: Downwarping of the Bushveld Igneous Complex

At±2054 ±0.8 Ma (Zeh et al., 2015), and to the north the Bushveld Igneous Complex intruded, causing considerable downwarping. In isostatic response, the Johannesburg dome, a domical window of basement granitoids was elevated (Fig 54, A and B). This caused brachy- anticlinal folding and tilting of overlying strata at17-24o and the development of detachment faults (possibly older shear zones) to be reactivated along its flanks (field observations, author). Subsequently, this accentuated landscape was to be peneplained by the African, Post

African 1 and Post African 2 erosion cycles (Fig 54, B).

A

B

Fig 53 A and B: The isostatic uplift of the Johannesburg dome and the forming of detachment faults along its flanks: These acted as conduits for water, allowing dissolution within older fault systems where they intersected.

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8.8.6. Phase 5: Vredefort impact

The Vredefort impact event at 2023 ±3 Ma (Kamo et al., 1996) caused older thrust faults to be reactivated thereby accentuating (elevating) the Panvlakte horst set whilst also inserting numerous shock induced cataclasite and compressional structures, in particular, within the upper Frisco Formation, leaving the lower Eccles largely unaffected as it is speculated that perhaps the strong chert layering within the Eccles redirected the impact shock up and into the chert free Frisco Formation due to its tilt angle and structural rigidity acting as a ricochet platform, thereby compounding extensive compaction and fracturing within the upper Frisco.

The impact event can be subdivided into:

1). Compressional phase

2). Rebound

8.8.6.1. Stage 1: Compression phase

It is construed that immediately following impact a radial (P) compression shock wave with a probable Richter scale magnitude of higher than 10 traversed the region, possibly propagating at >6900 meters per second (If the VOD of TNT is used as a measuring stick, Chapter 8, this thesis). This had various structural effects on the surrounding country rock depending on the host rocks composition, characteristics and previous tectonic history in managing shock propagation (of this magnitude) (Chapter 5, this thesis).

In the vicinity of Armageddon Pot, research indicates that following the pre-impact Panvlakte horst block was elevated and accentuated (ramped-up) along pre-existing fault delineations to now also intersect the Pretoria Group. This was seemingly accompanied by the creation of massive cataclasites and compression structures within the Frisco Formation (Fig 55, A).

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However, no marked deformation has been noted within the Eccles Formation. The lower part of the cave situated within the Eccles Formation seems to have resisted or averted marked deformation (Chapter 6, this thesis).

8.8.6.2. Stage 2: Rebound

Following compression, it is surmised that rebound caused the former thrust (caused by compression) to reverse and perhaps in doing so the hanging and footwall contact separated creating an immediate void (Field observations) (Fig 55, B). The evidence for rebound seems to be found in offset values of correlatable strata and the forming of boudinage structures within the mentioned schistose bands as well as other massive boudinage structures noticed within the Frisco Formation (Fig: 26).

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A

B

Fig 54 A and B: Demonstrating the effects of compression and rebound brought by the

Vredefort impact on the main thrust zones of the Panvlakte/Witpoortjie horst set separation.

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8.8.7. Phase 6: Phreatic immersion and non-acid dissolution

Following this phase and at the then depth interface it seems likely that the freshly formed

(open fracture line) was immersed. Whether at that point due to factors mentioned (Chapter 4, this thesis) phreatic amplification commenced is unclear. However, the thought is that true amplifications only commenced during, and in concert with the development of the African, post-African 1 and 2 surfaces as perhaps only then the area where Armageddon would have come into a feasible epigenetic horizon allowing dissolution (Fig, 56) (Chapter 4, this thesis).

Fig 55: Phreatic immersion and non-acid (undersaturation) dissolution.

8.8.8. Phase 7: African surfaces

Following Post-Cretaceous continental break-up, uplift and tilting of a newly formed sub-continent to the south-west the interior was both pene-and pediplained to produce the African surface whereby as much as 2-3 km of the original Gondwana Cretaceous surface was eroded (Moore et al., 2009;

Partridge and Maud, 1987, 2000; van Niekerk, 1997). Following initial uplift at ±65 Ma renewed uplift and further tilting during the early Miocene at ±30 Ma succeeded by a major late Miocene to early Pliocene uplift and tilting at ±5 Ma (de Wit, 2004; Hugh, 2001; Partridge, 1980; Partridge and

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Maud, 1987, 2000; McCarthy and Rubidge, 2001; McCarthy, 2009; Moon and Dardis, 1988; Moore and Larkin, 2001).

These cycles would have brought Armageddon Pots speleogenic horizon within an epigenetic interface depth. It is probable that during African and post-African 1 times, Armageddon was wholly phreatic, but following further uplift, and following a deepening thalweg gradient the upper section was drained to accept a supra-phreatic countenance allowing for the formation of various speleothems (Fig 57).

The lower section of Armageddon Pot (mostly within the Eccles Formation) remained largely within the phreatic zone. This area seemingly only recently became vadose – probably mainly in response to mining activities when water was drained from the aquifer to prevent flooding in the gold mines

(Kleywegt and Pike, 1982). Overzealous pumping by agricultural interest and local households for domestic use also created a dewatering cone and in combination, these two factors contributed largely to the region being dewatered - adding significantly to the forming of sinkholes in the region.

In support of this area being within a phreatic environment until relatively recent times: speleothems are lacking and thick wad and hydrated agglomerate packages are frequently encountered. Dolostone fractions are also deeply eroded between chert intercalations so that often it seems the entire sections of the sidewall seem to comprise of only ‘pancaked’ chert slabs.

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Fig 56: Vadose dissolution and forming of speleothems: lowering of the water table relates to the deepening thalweg gradient of the African surfaces.

8.8.9. Phase 8: Stoping

The growing dimensional aspects of the upper chamber are caused to structural instability, especially within an already weak roof section in response to joint development, fracturing and fragmenting so that the roof component of the cave has a low structural integrity. This had as effect the steady collapse of roof materials in a process known as stoping (Fig, 58).

As the width of the fracture/dissolution line develops and the cave enlarges the roof, or sections thereof simply disintegrate along stress fractures and joints. This process is exacerbated by the fact that since this region became vadose, phreatic support no longer applies. In this manner, the upper section’s floor is covered by ‘scree’. The same can be said for the ‘lower’ chamber but here scree seems to be more limited in size, possibly regulated by the general width measurements of the passage with the roof overhead being more stable and the bigger roof fall trapped higher up (personal observations, author).

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Fig 57: Stoping (structural collapse of the roof due to non-phreatic support).

8.8.10. Phase 9: Sinkhole forming and the opening of cave system to the surface.

It is doubtful whether the dewatering of the Far West Rand goldfields by mining activities as described by Kleywegt and Pike (1982) is responsible for the forming of the sinkhole leading into Armageddon Pot. In this case, the sinkhole collapse is more likely the culmination of a natural and long on-going process whereby the roof of the ‘main chamber’ was sufficiently weakened to facilitate a catastrophic collapse (Fig, 59). The following seems to be the cause:

Over-extension of the upper chamber by dissolution and stoping whereby the structural integrity and carry or supporting the ability of the roof was compromised. This was accentuated in the vicinity of the sinkhole where the ‘main chamber’s’ roof consisted mainly of shale. Gs poor bonding ability and plasticity further aided by surface hydration (adding significant weight) added to an already stressed situation-leading to catastrophic collapse.

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Fig 58: The last stage: Sinkhole forming, connecting the cave to surface.

8.9. Comparative observations between the CoH and the Far West Rand

Of interest is to note that of all the caves found along the Far West Rand, as far as is known at the time of writing, only Armageddon Pot cave exhibits the morphologies and structures noted. This does not mean that Armageddon Pot is, therefore, the only cave in the vicinity of the Far West Rand-with specific references to the Panvlakte/Witpoortjie horst domain that possess the characteristics presently mentioned, and therefore there is the possibility that should other caves in the direct vicinity of Armageddon Pot become accessible, the same structural characteristics may be present.

Fostering this thought, numerous large sinkholes are found within the vicinity of

Armageddon Pot and within the perimeters of the Panvlakte/Witpoortjie horst structural domain. This indicates that similar caves or satellite systems are likely to be present exhibiting the same characteristics and likely having the same causal relationships with past tectonic events as Armageddon Pot.

The reason why these caves have not been discovered or opened to surface can be found (in respect to the Panvlakte horst domain) in that the overlying terra rossa regolith (still covering these systems) are thick, comprising a thin cover of recent soils followed by the Hutton soils

166

(Aeolian), post-African 2 surface weathering produce (alluvium) and the shales of the

Pretoria Group Timeball Hill Formation to a depth of ±50 m before encountering the dolostones of the Malmani basin. In other places along the Far West Rand caves are often overlain by a thick dolomitic weathering cap comprising decomposed dolostone and chert clasts. Cases, where cave entrances associate with dolostone outcrops on the surface are also known such as at Apocalypse Cave located at co-ordinates S26o15.900′ E27o19.150′.

Therefore, a variety of entrance morphologies can be seen along the Far West Rand – as can also be seen in the CoH.

Also, often, where sinkholes develop they are either dolines or choke up with debris and scree, not permitting full access to subterranean systems (as was initially the case with

Armageddon Pot).

If in due time some existing sinkholes in the vicinity of Armageddon Pot, and found within the perimeter of the Panvlakte/Witpoortjie horst structural domain provide access to open cave, an investigation of these systems will augment our knowledge and perhaps reveal more, or other structures not seen in Armageddon Pot pertaining to the region’s past speleogenic relationship with past tectonic events.

In respects, to fossil-bearing sites as those commonly found in the CoH the possibility does exist, but to date, no such fossil sites have been located, possibly for the following reason:

Most entrances in the vicinity and along the Far West Rand have only recently developed a large number of these in response to dewatering due to mining activity. A second reason can be found in, especially the older cave systems like Crystal at co-ordinates S26o27.828′

E27o11.204′, Chaos at co-ordinates S26o 28.587' E27o 11.215' and Apocalypse. Their

167 entrances do not permit easy access to any animals utilizing caves as shelters, dens or lairs as often these caves can only be accessed via steep-sided or vertical shafts, most in access of 25 m deep. However, the one animal (skeletal remains) commonly found in these older caves are baboons – Papio ursinus, the common cape chacma baboon. Some have been found as deep as 200 m into the caves. However, the condition of the skeletons suggests them to have died there in the not too distant past.

In places where some sediment influx occurred, these are mostly small deposits derived from in close approximation alluvium, found mostly in the entrance series, unconsolidated and unlithified, some containing sparse skeletal components of recent origin.

The region should not be discounted in the search for Cainozoic fossil deposits as if these exist may yield fossils much older than those found within the CoH, as the various African surfaces (considerably older than the Limpopo basin surface found in the CoH) have been extensively developed in the region with the possibility of some past cave systems or remnants thereof containing fossil breccia, as is the case with Boons (Weltevreden cave) located at co-ordinates S26o 5.872' E27o 7.836' and situated near the small town of Boons,

North West Province.

Apart from marked structural differences between the Far West Rand and the CoH influencing speleogenesis, marked differences also exist between the causal relationships of these respected regions with past tectonic events. Of pertinence, regarding Armageddon Pot are the Panvlakte/Witpoortjie horst domain and its relationship with deep-seated

Witwatersrand tectonics, the elevation of the Johannesburg dome and the Vredefort impact

168 event imprinting in unique ways each their influence on the linear (major) fault system

(reversed thrust) along which Armageddon Pots speleogenic augmentation developed.

From a structural point, whereas Armageddon Pot developed along a singular linear E-west striking reversed thrust (fault line), the caves in the CoH’s placement and propagation is largely controlled by Lithology layer-parallel controls interacting with cross-cutting fracture systems of Palaeoproterozoic origin and an NW to SE directed extensional far-field stress as indicated by the orientation of networks of intensely developed joint grid systems superimposed over older faults and fractures (Dirks and Berger, 2013).

In opposition with the Far West Rand, the regolith cover in the CoH is largely removed with only sparse cover over most of the dolostone lithologies. Cave exposure here also seems to be regulated by the weathering back of hill slopes and gullies as part of a highly transient (fast weathering) landscape whilst along the Far West Rand exposure is mostly achieved by slow planar peneplanation and sudden drastic sinkhole collapse (through a thick weathering regolith) due to structural failure, in some cases owing to dewatering (personal observations, author).

Furthermore, the CoH is further away from ‘ground zero’ of the Vredefort impact, no large faults similar to the Panvlakte-Witpoortjie system exist to be reactivated by the Impact, so no likelihood of the development of large caves like Armageddon Pot.

Only a few examples of relatively large sinkholes like the one on the Nash properties at co- ordinates S25o 53.674′ E27′ 48.991′ and those found around at co-ordinates S25o 56.461′

E27o 46.308′ are found in the CoH. The reason seems to lie with a number of factors:

169

If any capacious systems as seen along the Far West Rand existed in the CoH, this speleogenic interface seems to have been largely removed by the isostatic responsive retreat of the southern margin of the Limpopo basin (to be seen as an escarpment) over the region.

This observation seems strongly supported by numerous dissected systems and flowstone remnants found on the surface (personal observations, author).

Successive periods of isostatic related uplift (Van Niekerk, 1997) further assisted in removing this speleogenic interface. As such new caves developing in synchronization with the region’s deepening thalweg and dynamic service denudation are perhaps considerably younger than those found within the Far West Rand, being exposed to surface perhaps no longer ago than five million years (Partridge, 1973).

The innate stability of cave systems in the CoH is, therefore, a function of their relatively small dimensions (having rapidly cycled through the phreatic and vadose cycles in response to numerous periods of uplift). This is in opposition of caves in the Far West Rand having had a deeper speleogenic interface depth and being exposed to extended periods of stable phreatic non-acid dissolution-allowing significant enhancement to develop. This observation seems to be supported by the considerable dimensions of Wondergrot at co-ordinates S25o

58.223′ E27o 46.288′ in the CoH where this cave has been exposed to unusually long phreatic immersion due to a major dolerite dyke forming the western margin of the Sterkfontein aquifer compartment-causing extended periods of water retention.

However, there are some similarities: There seems to be one shared denominator between the

Far West Rand and the CoH responsible for inserting structures for speleogenic propagation-

The Vredefort impact event. This postulate may be feasible as the original impact crater

170 diameter of ±100 km (Bischoff, 1988; Brink et al., 1999; Gibson and Reimold, 2008; Brink et al 2000a and b) would have encompassed the CoH. However, surface traces of the crater rim have since been erased by the peneplanation dynamics of the African, post-African 1 and 2 surfaces, and the expansion of the southern margin of the Limpopo basin over the CoH.

However, this did not erase the structural entities as pointed out by Gibson (1999) postulated as relating to the Vredefort impact event at ±2023 ±3 Ma (Kamo et al., 1996).

Some researcher’s favours another possible major role player for inserting the speleogenic structural character of the CoH-an orogenic episode between the intrusion of the Bushveld

Igneous Complex at 2054 ±0.8 Ma (Zeh et al., 2015) and the following Vredefort impact event at 2023 ±3 Ma (Kamo et al., 1996) referred to as the Transvaalide fold-and-thrust belt

(Alexandre et al., 2006). However feasible, no dates have been recovered from Armageddon

Pot supporting the influence of this event in as far as Armageddon Pot is concerned.

A major shared control for speleogenesis noticed in Armageddon has also been seen in the

CoH, also fulfilling a similar role. These are detachment faults coming off the flanks of the

Johannesburg dome. They are seemingly all of the similar antiquity as suggested by 39Ar/40Ar dating and acted as conduits for water into pre-existing faults and fractures, allowing dissolution.

171

Conclusion

This thesis concerned itself with a comparison between the structural controls for speleogenic propagation between two adjacent but geographically different areas, that of the Cradle of

Humankind (CoH) and the Far West Rand - with specific reference to the Panvlakte horst domain where, within a very large cave called Armageddon Pot, structural controls different from those seen within the Cradle of Humankind was noticed.

Cave genesis within the CoH was mostly influenced by lithological, layer-parallel controls interacting with cross-cutting fracture systems and an NW to SE directed extensional far-field stress. At later intervals and due to denudation cycles and overburden weight reduction

(related to the expansion of the Limpopo basin) intensely developed joint grid systems were superimposed over existing faults and fractures. Along these structures dissolution speleogenesis advanced, arguably first within a non-acid undersaturation dissolution phreatic environment, then later within a supra-phreatic (vadose) acid driven dissolution environment as the cave systems drained due to the region’s deepening thalweg gradient. Cave systems in the CoH are small, rarely exceeding 500m in extent.

Layer-parallel shear zones occur in many caves found in the CoH. In the Rising Star cave, sericite from four of these dated by 40Ar/39Ar, yielded apparent ages between 2046.6 ±8.3 and

2056 ±8.4 Ma, within the error of the Bushveld Igneous Complex (BIC) intrusion age.

Downwarping of the BIC evidently exercised a marked effect on the region. Isostatic uplift of the Johannesburg dome, in response to this downwarping, probably caused reactivation of older Transvaal basin expansion faults, converting them into detachment faults along its

172 flanks. These low-angle detachment faults appear to have been key speleogenic controls as they transported meteoric and or connate waters into fault systems where these were intercepted.

In comparison, it was immediately noticed that structures and rock types saw within

Armageddon Pot appeared conspicuously different from those seen in the CoH. Here a single linear normal fault, the main structural control of speleogenesis, seemingly offset low angled imbricate thrusts and interleaved micro-shears. In addition, compression and extension structures included within a cataclasite matrix marking large portions of Armageddon Pot’s sidewalls have never been observed in caves within the CoH, and therefore could not be explained against the structural controls recognized in the CoH.

The presence of cataclasites within Armageddon Pot and the particular orientation of associated shear zones and the main controlling fault favoured a causal relationship with the

Vredefort impact at ±2025 MA However, 40Ar/39Ar sericite dates from distinct thrust and shear horizons yielded three distinct date clusters: (1) falling within the accepted age given for the Vredefort impact event (2021.2 ±8.8 and 2025.5 ±7.9 Ma), (2) the BIC (ages between

2046.6 ±8.4 – 2061.1 ±8.4 Ma) and (3) appreciably older than the BIC (ages between 2080 to

2140 Ma).

Armageddon Pot’s structural character formed an integral structural component with that of the broader Panvlakte horst domain that in turn had a causal relationship with deep-seated

Witwatersrand tectonics. Realizing this, this explained the predominantly linear configuration of Armageddon Pot as part of a Panvlakte horst domain related thrust fault forming the structural control along which Armageddon Pot linear configuration developed.

173

The pre-BIC dates were yielded by interleaved micro shear zones distributed throughout the upper levels of the cave. They have been interpreted as being related to the expansion

(relaxation) of the Malmani basin with the considerable date range assigned to partial re- crystallization in either or both of the younger episodes. Their importance as contributing to the overall structural controls or speleogenic enlargement of Armageddon seems unlikely.

The BIC ages relate to a schistose zone located between the lowermost Pretoria Group

(Timeball hill Member) and uppermost portions of the Malmani dolostones (Frisco

Formation). This south dipping zone was interpreted as being a detachment fault

(décollement) developed in response to the elevation of the Johannesburg dome, analogous to similar structures seen within the CoH and dated in the Rising Star cave.

The Vredefort age was obtained from a low angle imbricate thrust zone observed between the

Frisco and Eccles Formations, associated with cataclasites. It is suggested that during the impact compression phase, the formation of these thrusts and cataclasites, as well as the reactivation of older (Panvlakte) thrusts occurred. From the correlatable southern dipping offset values of shear and thrust zones, it seems likely that, during the rebound stage of impact, that older Panvlakte thrusts were reactivated and reversed, with the possibility of hanging and footwall separation taking place possibly creating an immediate cavity. Even if this is so, the subsequent cave enlargement was due to normative dynamics of dissolution chemistry.

Armageddon Pot’s geology and the caves within the CoH share some commonalities and overlap with at least one structural causing denominator-the BIC, via the Johannesburg Dome uplift, responsible for some structural controls. However, sufficient differences exist in

174 structural characteristics of Armageddon Pot and the caves within the CoH to be placed within region specific speleogenic models.

175

Afterthought

Apart from elucidating on the speleogenic profiles for the CoH and the Far West Rand with specific reference to Armageddon Pot’s causal relationships with certain tectonic events, the value of this research also lies in cautioning researchers against prejudice, assumption and preconceived ideas based on what the researcher ‘wants to see’. To authenticate research, setting it apart from pseudo-science, the researcher needs to consider all options and possibilities and from this arrive at the more likely situation, and acknowledge, no matter how inconvenient the factual, to accept that one’s original hypothesis regarding sometimes need considerable alteration. In that lays the value of progressive science.

176

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Appendix: Table of argon isotope data, 40Ar/39Ar ages, Ca/K and Cl/K ratios of individual heating steps

Sample: PB6_8_1 Irradiation position: 8 (Z=6.4 mm) J-value: 0.008610 +/- 0.000017 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.42E-07 6.15E-03 1.8E-05 4.55E-05 5.2E-06 1.95E+00 1.4E-02 2.95E-02 9.6E-04 160.4 0.6 1.1 1563.4 9.8 0 3.75E+00 5.1E-02 3.71E-03 1.4E-04 2 1.37E-06 4.92E-03 7.1E-06 1.94E-05 8.6E-07 1.54E+00 7.1E-03 1.78E-02 2.4E-04 202.0 0.3 4.9 1816.1 7.8 0 2.96E+00 3.7E-02 2.23E-03 5.5E-05 3 2.75E-06 4.57E-03 3.9E-06 1.05E-05 5.6E-07 1.16E+00 4.8E-03 1.64E-02 1.8E-04 218.3 0.2 9.1 1906.1 8.0 0 2.23E+00 2.7E-02 2.05E-03 4.8E-05 4 4.00E-06 4.41E-03 4.3E-06 6.97E-06 2.9E-07 9.91E-01 3.1E-03 1.50E-02 1.9E-04 226.4 0.2 12.7 1949.1 8.3 0 1.91E+00 2.3E-02 1.89E-03 4.5E-05 5 5.07E-06 4.31E-03 4.2E-06 3.82E-06 2.6E-07 8.49E-01 3.1E-03 1.53E-02 1.8E-04 231.8 0.2 15.7 1976.9 8.3 0 1.63E+00 2.0E-02 1.92E-03 4.6E-05 6 5.00E-06 4.24E-03 3.1E-06 3.75E-06 3.2E-07 6.58E-01 2.6E-03 1.54E-02 1.4E-04 235.7 0.2 15.3 1997.5 8.2 0 1.27E+00 1.5E-02 1.93E-03 4.3E-05 7 3.22E-06 4.19E-03 5.4E-06 4.01E-06 3.2E-07 5.12E-01 2.6E-03 1.54E-02 1.7E-04 238.2 0.3 9.7 2010.1 8.9 0 9.85E-01 1.2E-02 1.93E-03 4.5E-05 8 4.67E-06 4.15E-03 2.2E-06 2.89E-06 2.7E-07 3.94E-01 2.8E-03 1.76E-02 1.4E-04 240.9 0.1 14.0 2023.6 8.9 1 7.58E-01 1.0E-02 2.21E-03 4.9E-05 9 4.06E-06 4.14E-03 3.7E-06 1.47E-06 3.4E-07 3.07E-01 1.8E-03 1.78E-02 1.1E-04 241.7 0.2 12.1 2027.6 8.6 1 5.91E-01 7.6E-03 2.24E-03 4.8E-05 10 1.61E-06 4.13E-03 5.3E-06 9.05E-06 1.1E-06 2.07E-01 2.6E-03 2.55E-02 4.5E-04 241.2 0.3 4.8 2025.3 9.0 1 3.97E-01 6.7E-03 3.20E-03 8.7E-05 11 1.73E-07 4.18E-03 1.9E-05 1.10E-05 1.7E-04 4.80E-01 1.9E-02 7.86E-02 2.5E-03 238.6 1.2 0.5 2012.1 15.1 0 9.24E-01 3.7E-02 9.86E-03 3.7E-04 12 2.83E-08 4.12E-03 5.4E-05 1.53E-04 4.8E-05 1.55E+00 1.0E-01 3.09E-01 2.2E-02 231.8 4.3 0.1 1977.0 48.0 0 2.98E+00 2.0E-01 3.87E-02 2.8E-03 13 1.61E-08 4.12E-03 9.4E-05 -2.15E-04 9.6E-05 0.00E+00 0.0E+00 1.29E-01 2.2E-02 258.2 6.7 0.0 2108.7 67.0 0 0.00E+00 0.0E+00 1.62E-02 2.8E-03 14 9.09E-09 5.15E-03 1.5E-04 -1.66E-04 6.1E-03 7.94E-01 1.8E-01 1.68E-01 4.5E-02 203.8 9.4 0.0 1826.1 109.5 0 1.53E+00 3.4E-01 2.11E-02 5.6E-03 15 8.45E-09 5.08E-03 1.5E-04 -4.52E-05 2.0E-04 6.10E-01 3.0E-01 2.09E-01 3.1E-02 199.4 8.9 0.0 1800.9 103.0 0 1.17E+00 5.8E-01 2.62E-02 4.0E-03 16 3.18E-09 4.90E-03 2.8E-04 9.90E-05 1.4E-03 0.00E+00 0.0E+00 6.14E-02 1.2E-01 198.1 27.8 0.0 1793.5 329.3 0 0.00E+00 0.0E+00 7.71E-03 1.5E-02 Weighted averages of included steps: 3.31E-01 1.5E-03 1.89E-02 9.9E-05 241.2 0.1 30.8 2025.5 8.5 6.36E-01 7.9E-03 2.37E-03 5.1E-05

Sample: PB6_8_2 Irradiation position: 8 (Z=6.4 mm) J-value: 0.008610 +/- 0.000017 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 9.72E-08 7.37E-03 3.2E-05 9.90E-05 7.4E-06 2.41E+00 2.1E-02 2.86E-02 1.3E-03 131.7 0.7 0.4 1365.6 11.1 0 4.63E+00 6.7E-02 3.59E-03 1.8E-04 2 6.46E-07 5.40E-03 1.0E-05 3.07E-05 1.8E-06 1.84E+00 1.2E-02 1.96E-02 5.2E-04 183.5 0.3 2.0 1707.6 8.0 0 3.54E+00 4.7E-02 2.46E-03 8.3E-05 3 2.01E-06 4.91E-03 4.4E-06 1.74E-05 4.9E-07 1.44E+00 3.5E-03 1.69E-02 2.7E-04 202.7 0.2 5.7 1819.6 8.0 0 2.77E+00 3.3E-02 2.12E-03 5.5E-05 4 3.63E-06 4.59E-03 3.7E-06 8.98E-06 4.8E-07 1.27E+00 3.1E-03 1.53E-02 2.3E-04 217.2 0.2 9.7 1899.6 7.9 0 2.44E+00 2.9E-02 1.92E-03 4.9E-05 5 5.59E-06 4.39E-03 3.0E-06 4.83E-06 2.6E-07 9.95E-01 3.3E-03 1.49E-02 1.5E-04 227.3 0.2 14.3 1953.8 7.7 0 1.91E+00 2.3E-02 1.87E-03 4.3E-05 6 6.90E-06 4.28E-03 3.2E-06 3.52E-06 2.1E-07 7.15E-01 1.8E-03 1.45E-02 8.5E-05 233.6 0.2 17.1 1986.4 8.6 0 1.37E+00 1.6E-02 1.81E-03 3.9E-05 7 7.19E-06 4.21E-03 2.5E-06 3.08E-06 1.9E-07 5.41E-01 2.0E-03 1.49E-02 1.3E-04 237.2 0.1 17.6 2005.1 7.7 0 1.04E+00 1.3E-02 1.87E-03 4.2E-05 8 4.86E-06 4.17E-03 2.7E-06 2.39E-06 3.2E-07 3.95E-01 1.9E-03 1.65E-02 1.2E-04 239.6 0.2 11.8 2017.0 8.2 1 7.60E-01 9.5E-03 2.07E-03 4.5E-05 9 3.87E-06 4.15E-03 3.4E-06 2.23E-06 2.7E-07 3.03E-01 9.2E-04 1.83E-02 1.8E-04 240.8 0.2 9.3 2023.2 8.4 1 5.83E-01 7.0E-03 2.30E-03 5.3E-05 10 3.77E-06 4.14E-03 3.3E-06 2.53E-06 2.8E-07 2.14E-01 1.2E-03 1.97E-02 2.8E-04 241.2 0.2 9.1 2025.0 8.3 1 4.11E-01 5.3E-03 2.47E-03 6.2E-05 11 1.10E-06 4.16E-03 6.2E-06 4.90E-06 1.3E-06 1.62E-01 2.5E-03 3.41E-02 4.0E-04 240.0 0.4 2.7 2019.3 8.9 1 3.11E-01 6.0E-03 4.27E-03 1.0E-04 12 4.73E-08 4.24E-03 5.2E-05 1.08E-04 1.3E-05 1.21E+00 4.2E-02 2.63E-01 9.1E-03 228.5 3.1 0.1 1959.7 32.4 0 2.32E+00 8.4E-02 3.30E-02 1.3E-03 13 2.72E-08 3.59E-03 5.1E-05 4.37E-05 1.4E-03 4.48E-01 7.9E-02 4.11E-01 1.2E-02 275.1 4.5 0.1 2188.6 41.3 0 8.62E-01 1.5E-01 5.15E-02 1.8E-03 14 1.90E-08 3.32E-03 6.0E-05 -5.15E-05 4.5E-04 2.94E-01 9.1E-02 4.43E-01 1.9E-02 305.5 6.1 0.0 2323.4 53.4 0 5.66E-01 1.7E-01 5.55E-02 2.6E-03 15 6.65E-09 3.24E-03 1.5E-04 -1.61E-04 7.4E-04 0.00E+00 0.0E+00 1.81E-01 4.5E-02 323.4 17.0 0.0 2398.1 143.9 0 0.00E+00 0.0E+00 2.26E-02 5.6E-03

Weighted averages of included steps: 3.00E-01 8.4E-04 1.93E-02 1.1E-04 240.4 0.1 32.9 2021.2 7.9 5.77E-01 6.8E-03 2.42E-03 5.2E-05 1 Page

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Sample: PB3_5_1 Irradiation position: 5 (Z=4.0 mm) J-value: 0.008631 +/- 0.000018 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 1.02E-06 4.67E-03 9.0E-06 1.65E-05 7.0E-07 0.00E+00 0.0E+00 1.56E-02 2.3E-04 213.0 0.4 1.0 1880.2 9.1 0 0.00E+00 0.0E+00 1.95E-03 6.4E-05 2 3.13E-06 4.34E-03 6.0E-06 6.25E-06 2.4E-07 3.20E-04 5.0E-04 1.38E-02 1.5E-04 230.0 0.3 2.9 1970.7 8.5 0 6.16E-04 9.5E-04 1.74E-03 5.4E-05 3 6.47E-06 4.21E-03 4.1E-06 2.83E-06 1.4E-07 0.00E+00 0.0E+00 1.32E-02 7.9E-05 237.5 0.2 5.7 2009.6 8.7 0 0.00E+00 0.0E+00 1.66E-03 4.9E-05 4 1.11E-05 4.14E-03 5.0E-06 1.68E-06 7.4E-08 4.98E-04 2.1E-04 1.28E-02 1.2E-04 241.7 0.3 9.7 2030.8 8.6 0 9.57E-04 4.0E-04 1.61E-03 4.9E-05 5 1.34E-05 4.09E-03 4.4E-06 1.10E-06 6.7E-08 6.15E-04 1.5E-04 1.27E-02 6.2E-05 244.3 0.3 11.6 2043.5 9.0 0 1.18E-03 2.9E-04 1.59E-03 4.7E-05 6 1.15E-05 4.08E-03 5.1E-06 1.09E-06 8.9E-08 1.10E-03 1.8E-04 1.25E-02 9.7E-05 244.9 0.3 9.9 2046.7 8.9 0 2.12E-03 3.4E-04 1.57E-03 4.7E-05 7 1.16E-05 4.08E-03 4.3E-06 9.91E-07 1.0E-07 1.28E-03 1.9E-04 1.26E-02 8.7E-05 245.3 0.2 9.9 2048.8 9.4 0 2.46E-03 3.8E-04 1.58E-03 4.7E-05 8 1.45E-05 4.05E-03 4.3E-06 8.97E-07 1.3E-07 1.61E-03 1.8E-04 1.25E-02 5.5E-05 247.0 0.3 12.4 2057.0 9.1 1 3.09E-03 3.5E-04 1.57E-03 4.6E-05 9 1.57E-05 4.05E-03 3.4E-06 3.88E-07 7.2E-08 1.12E-03 1.4E-04 1.25E-02 8.1E-05 246.7 0.2 13.5 2056.0 9.4 1 2.16E-03 2.7E-04 1.57E-03 4.7E-05 10 1.07E-05 4.05E-03 3.7E-06 6.23E-07 1.1E-07 9.93E-04 2.1E-04 1.26E-02 8.6E-05 246.8 0.2 9.2 2056.0 8.9 1 1.91E-03 4.1E-04 1.58E-03 4.7E-05 11 7.80E-06 4.04E-03 3.9E-06 7.95E-07 1.4E-07 3.88E-04 2.2E-04 1.27E-02 1.2E-04 247.2 0.2 6.7 2058.1 8.9 1 7.46E-04 4.2E-04 1.59E-03 4.9E-05 12 3.96E-06 4.07E-03 2.9E-06 1.30E-06 2.2E-07 4.69E-04 4.9E-04 1.28E-02 1.5E-04 245.4 0.2 3.4 2049.5 8.4 1 9.02E-04 9.5E-04 1.60E-03 5.0E-05 13 3.48E-06 4.06E-03 3.8E-06 7.10E-07 2.8E-06 1.50E-03 4.2E-04 1.28E-02 1.4E-04 246.4 0.2 3.0 2054.2 8.5 1 2.88E-03 8.2E-04 1.61E-03 5.0E-05 14 5.68E-07 4.05E-03 1.0E-05 3.08E-06 1.6E-05 0.00E+00 0.0E+00 1.34E-02 5.8E-04 246.4 0.7 0.5 2054.3 11.1 0 0.00E+00 0.0E+00 1.68E-03 8.8E-05 15 5.78E-07 4.07E-03 1.1E-05 8.76E-06 1.6E-06 7.89E-03 3.4E-03 1.42E-02 8.0E-04 245.4 0.7 0.5 2049.0 10.9 0 1.52E-02 6.6E-03 1.78E-03 1.1E-04 16 1.42E-07 4.11E-03 2.3E-05 1.91E-05 5.9E-06 5.29E-02 1.2E-02 1.51E-02 1.7E-03 241.8 1.3 0.1 2031.2 15.4 0 1.02E-01 2.4E-02 1.89E-03 2.2E-04 17 4.65E-08 4.08E-03 3.4E-05 -2.38E-05 4.4E-05 0.00E+00 0.0E+00 1.14E-02 5.0E-03 247.0 2.2 0.0 2057.5 22.3 0 0.00E+00 0.0E+00 1.43E-03 6.3E-04 Weighted averages of included steps: 1.10E-03 9.2E-05 1.26E-02 3.7E-05 246.7 0.1 48.1 2056.0 8.4 2.11E-03 1.8E-04 1.58E-03 4.6E-05

Sample: PB4_6_1 Irradiation position: 6 (Z=4.8 mm) J-value: 0.008624 +/- 0.000017 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 9.81E-07 4.90E-03 7.5E-06 1.37E-05 7.0E-07 1.74E-03 1.4E-03 1.43E-02 1.9E-04 203.3 0.3 1.2 1825.2 8.6 0 3.35E-03 2.7E-03 1.79E-03 3.1E-04 2 2.60E-06 4.32E-03 3.9E-06 4.05E-06 2.0E-07 3.14E-04 6.0E-04 1.29E-02 1.8E-04 231.0 0.2 2.7 1975.1 7.9 0 6.04E-04 1.2E-03 1.62E-03 2.8E-04 3 4.68E-06 4.19E-03 5.2E-06 2.19E-06 2.2E-07 0.00E+00 0.0E+00 1.24E-02 1.3E-04 238.8 0.3 4.7 2014.9 8.7 0 0.00E+00 0.0E+00 1.55E-03 2.7E-04 4 6.11E-06 4.13E-03 5.1E-06 1.55E-06 1.6E-07 0.00E+00 0.0E+00 1.28E-02 9.5E-05 242.0 0.3 6.1 2031.3 8.8 0 0.00E+00 0.0E+00 1.61E-03 2.8E-04 5 9.81E-06 4.10E-03 4.6E-06 1.08E-06 9.0E-08 0.00E+00 0.0E+00 1.26E-02 9.2E-05 243.7 0.3 9.7 2039.6 8.7 1 0.00E+00 0.0E+00 1.58E-03 2.7E-04 6 9.08E-06 4.09E-03 4.1E-06 1.28E-06 1.3E-07 4.23E-05 2.2E-04 1.26E-02 1.4E-04 244.4 0.2 8.9 2043.2 8.6 1 8.13E-05 4.2E-04 1.58E-03 2.7E-04 7 1.19E-05 4.08E-03 3.2E-06 1.18E-06 1.1E-07 5.65E-04 1.7E-04 1.25E-02 3.9E-05 245.0 0.2 11.7 2046.1 8.7 1 1.09E-03 3.6E-04 1.57E-03 2.7E-04 8 1.37E-05 4.07E-03 3.0E-06 1.15E-06 5.9E-08 6.73E-04 1.3E-04 1.24E-02 1.2E-04 245.7 0.2 13.4 2049.6 9.1 1 1.29E-03 3.1E-04 1.56E-03 2.7E-04 9 1.26E-05 4.06E-03 3.0E-06 6.63E-07 1.0E-07 0.00E+00 0.0E+00 1.23E-02 9.5E-05 246.2 0.2 12.2 2052.5 8.6 1 0.00E+00 0.0E+00 1.55E-03 2.7E-04 10 1.04E-05 4.05E-03 3.5E-06 1.55E-06 1.0E-07 2.45E-04 2.1E-04 1.25E-02 7.3E-05 246.6 0.2 10.2 2054.1 8.8 1 4.72E-04 4.1E-04 1.56E-03 2.7E-04 11 9.29E-06 4.06E-03 2.5E-06 9.40E-07 1.1E-07 7.29E-04 2.6E-04 1.26E-02 1.1E-04 246.5 0.2 9.0 2053.9 8.8 1 1.40E-03 5.4E-04 1.57E-03 2.7E-04 12 5.55E-06 4.04E-03 3.2E-06 1.40E-06 1.6E-07 0.00E+00 0.0E+00 1.26E-02 1.2E-04 247.2 0.2 5.4 2057.3 8.4 1 0.00E+00 0.0E+00 1.58E-03 2.7E-04 13 2.84E-06 4.03E-03 3.8E-06 5.53E-07 9.9E-07 0.00E+00 0.0E+00 1.29E-02 2.6E-04 247.9 0.2 2.7 2060.5 8.8 1 0.00E+00 0.0E+00 1.61E-03 2.8E-04 14 9.69E-07 4.10E-03 5.5E-06 2.43E-06 1.3E-06 0.00E+00 0.0E+00 1.36E-02 2.2E-04 244.0 0.3 1.0 2041.1 9.1 0 0.00E+00 0.0E+00 1.70E-03 3.0E-04 15 9.37E-07 4.10E-03 7.2E-06 1.21E-05 9.3E-07 2.10E-03 1.1E-03 1.34E-02 3.5E-04 242.9 0.5 0.9 2036.0 9.9 0 4.04E-03 2.1E-03 1.68E-03 2.9E-04 16 2.63E-07 4.13E-03 1.7E-05 2.28E-05 3.1E-06 4.60E-02 5.6E-03 1.54E-02 9.3E-04 240.4 1.0 0.3 2023.0 13.8 0 8.84E-02 1.8E-02 1.93E-03 3.5E-04 Weighted averages of included steps: 4.71E-04 8.5E-05 1.25E-02 3.6E-05 245.7 0.1 83.3 2049.6 8.3 9.06E-04 2.2E-04 1.57E-03 2.7E-04 2 Page

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Sample: PB-RS_11_2 Irradiation position: 11 (Z=8.8 mm) J-value: 0.008588 +/- 0.000017 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 5.96E-07 4.43E-03 8.9E-06 2.66E-05 1.3E-06 1.85E+00 8.4E-03 1.41E-02 3.8E-04 223.9 0.5 0.6 1932.7 9.7 0 3.55E+00 5.6E-01 1.77E-03 3.1E-04 2 1.62E-06 4.35E-03 6.3E-06 1.47E-05 4.4E-07 1.87E+00 6.6E-03 1.42E-02 2.5E-04 228.9 0.3 1.6 1959.3 8.6 0 3.59E+00 5.6E-01 1.78E-03 3.1E-04 3 3.53E-06 4.24E-03 5.8E-06 9.76E-06 3.2E-07 1.43E+00 5.4E-03 1.30E-02 1.7E-04 235.0 0.3 3.5 1990.7 8.9 0 2.75E+00 4.3E-01 1.64E-03 2.8E-04 4 5.61E-06 4.19E-03 3.5E-06 5.93E-06 4.0E-07 1.26E+00 2.6E-03 1.31E-02 1.4E-04 238.5 0.2 5.5 2008.3 8.5 0 2.42E+00 3.8E-01 1.64E-03 2.8E-04 5 8.77E-06 4.14E-03 3.6E-06 5.05E-06 1.8E-07 1.08E+00 1.7E-03 1.29E-02 1.2E-04 241.1 0.2 8.5 2021.9 8.9 0 2.08E+00 3.3E-01 1.61E-03 2.8E-04 6 1.01E-05 4.11E-03 3.4E-06 3.77E-06 1.8E-07 8.65E-01 1.8E-03 1.31E-02 7.6E-05 243.2 0.2 9.7 2032.1 9.1 0 1.66E+00 2.6E-01 1.65E-03 2.8E-04 7 1.28E-05 4.10E-03 2.8E-06 3.03E-06 1.4E-07 7.75E-01 1.5E-03 1.27E-02 6.8E-05 243.9 0.2 12.2 2035.5 8.7 0 1.49E+00 2.3E-01 1.60E-03 2.8E-04 8 1.13E-05 4.07E-03 2.1E-06 2.86E-06 1.7E-07 6.34E-01 1.2E-03 1.29E-02 6.8E-05 245.6 0.1 10.7 2044.4 8.7 0 1.22E+00 1.9E-01 1.61E-03 2.8E-04 9 1.19E-05 4.06E-03 3.1E-06 1.70E-06 1.2E-07 4.62E-01 1.2E-03 1.27E-02 1.2E-04 246.1 0.2 11.2 2046.6 9.0 1 8.88E-01 1.4E-01 1.59E-03 2.8E-04 10 1.03E-05 4.05E-03 2.8E-06 1.89E-06 9.8E-08 3.38E-01 1.4E-03 1.28E-02 9.6E-05 247.1 0.2 9.7 2051.5 8.7 1 6.51E-01 1.0E-01 1.60E-03 2.8E-04 11 1.06E-05 4.04E-03 1.9E-06 2.09E-06 1.4E-07 2.56E-01 1.0E-03 1.26E-02 1.1E-04 247.2 0.1 9.9 2052.1 8.0 1 4.92E-01 7.7E-02 1.58E-03 2.7E-04 12 8.65E-06 4.04E-03 3.9E-06 3.19E-06 1.7E-07 2.10E-01 9.5E-04 1.28E-02 1.1E-04 247.4 0.2 8.1 2053.1 8.8 1 4.04E-01 6.3E-02 1.60E-03 2.8E-04 13 4.43E-06 4.03E-03 4.2E-06 6.36E-06 2.5E-07 2.16E-01 1.3E-03 1.30E-02 1.7E-04 247.4 0.3 4.2 2053.3 8.8 1 4.15E-01 6.5E-02 1.63E-03 2.8E-04 14 2.42E-06 4.03E-03 6.0E-06 1.54E-05 4.6E-07 1.77E-01 1.8E-03 1.35E-02 2.3E-04 247.2 0.4 2.3 2052.0 9.3 1 3.39E-01 5.3E-02 1.69E-03 2.9E-04 15 9.82E-07 4.04E-03 7.1E-06 4.79E-05 1.2E-06 1.71E-01 3.5E-03 1.40E-02 4.4E-04 243.9 0.5 0.9 2035.6 9.4 0 3.29E-01 5.2E-02 1.76E-03 3.1E-04 16 7.74E-07 3.95E-03 7.6E-06 1.35E-04 1.9E-06 1.76E-01 3.7E-03 1.49E-02 3.6E-04 242.8 0.5 0.7 2030.3 9.0 0 3.39E-01 5.4E-02 1.87E-03 3.3E-04 17 5.34E-07 3.94E-03 1.2E-05 1.27E-04 2.4E-06 1.08E-01 4.5E-03 1.36E-02 4.1E-04 244.1 0.8 0.5 2036.6 11.0 0 2.07E-01 3.4E-02 1.70E-03 3.0E-04 18 2.20E-07 3.84E-03 1.7E-05 2.08E-04 5.0E-06 5.00E-02 1.2E-02 1.25E-02 7.8E-04 244.3 1.2 0.2 2037.8 13.3 0 9.61E-02 2.7E-02 1.56E-03 2.9E-04 Weighted averages of included steps: 5.42E-01 4.4E-04 1.29E-02 3.3E-05 245.3 0.1 56.1 2050.4 9.0 1.04E+00 1.6E-01 1.61E-03 2.8E-04

Sample: PB9_10_1 Irradiation position: 10 (Z=8.0 mm) J-value: 0.008595 +/- 0.000017 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 6.08E-07 5.62E-03 1.2E-05 1.56E-05 1.0E-06 1.37E-02 2.3E-03 1.89E-02 3.9E-04 177.2 0.4 1.1 1667.8 8.3 0 2.64E-02 6.1E-03 2.37E-03 4.1E-04 2 1.99E-06 4.64E-03 7.6E-06 4.86E-06 4.0E-07 3.79E-03 1.0E-03 1.42E-02 2.0E-04 215.4 0.3 2.9 1887.9 8.3 0 7.30E-03 2.3E-03 1.78E-03 3.1E-04 3 3.64E-06 4.43E-03 5.8E-06 2.87E-06 2.1E-07 3.97E-04 5.1E-04 1.37E-02 1.4E-04 225.6 0.3 5.1 1942.6 8.8 0 7.64E-04 9.9E-04 1.72E-03 3.0E-04 4 6.62E-06 4.36E-03 5.5E-06 2.69E-06 1.3E-07 2.35E-03 1.8E-04 1.37E-02 6.8E-05 229.2 0.3 9.2 1961.8 8.4 0 4.52E-03 7.9E-04 1.72E-03 3.0E-04 5 1.12E-05 4.27E-03 4.2E-06 1.22E-06 7.1E-08 2.34E-03 1.9E-04 1.34E-02 1.1E-04 234.3 0.2 15.2 1988.1 8.1 0 4.51E-03 8.0E-04 1.69E-03 2.9E-04 6 8.17E-06 4.20E-03 3.7E-06 1.30E-06 6.0E-08 3.01E-03 2.5E-04 1.35E-02 8.7E-05 238.1 0.2 10.9 2007.5 8.7 0 5.78E-03 1.0E-03 1.69E-03 2.9E-04 7 1.09E-05 4.13E-03 3.8E-06 1.16E-06 1.3E-07 2.52E-03 1.5E-04 1.33E-02 7.6E-05 242.3 0.2 14.3 2028.5 8.0 0 4.86E-03 8.1E-04 1.67E-03 2.9E-04 8 1.10E-05 4.08E-03 2.1E-06 1.12E-06 1.4E-07 2.95E-03 1.9E-04 1.33E-02 6.4E-05 245.0 0.1 14.3 2042.0 8.3 1 5.67E-03 9.6E-04 1.66E-03 2.9E-04 9 7.69E-06 4.07E-03 3.7E-06 8.20E-07 1.3E-07 2.03E-03 3.1E-04 1.34E-02 1.6E-04 245.5 0.2 10.0 2044.6 8.6 1 3.91E-03 8.5E-04 1.68E-03 2.9E-04 10 5.91E-06 4.06E-03 4.0E-06 1.47E-06 1.5E-07 2.61E-03 3.3E-04 1.36E-02 1.1E-04 246.3 0.2 7.6 2048.9 8.5 1 5.03E-03 1.0E-03 1.70E-03 2.9E-04 11 4.19E-06 4.05E-03 3.2E-06 2.02E-06 1.6E-07 2.46E-03 4.3E-04 1.36E-02 1.0E-04 246.7 0.2 5.4 2050.8 8.3 1 4.72E-03 1.1E-03 1.71E-03 3.0E-04 12 2.18E-06 4.01E-03 2.6E-06 3.02E-06 3.8E-07 3.41E-03 6.5E-04 1.44E-02 1.9E-04 249.2 0.2 2.8 2063.2 8.6 0 6.57E-03 1.6E-03 1.80E-03 3.1E-04 13 5.19E-07 4.03E-03 7.1E-06 1.10E-05 9.4E-07 5.04E-06 3.2E-03 1.61E-02 5.5E-04 247.2 0.5 0.7 2053.0 9.9 0 9.69E-06 6.2E-03 2.02E-03 3.6E-04 14 2.28E-07 4.07E-03 1.5E-05 1.92E-05 1.9E-06 1.34E-02 5.3E-03 1.88E-02 9.4E-04 244.4 0.9 0.3 2039.0 12.4 0 2.57E-02 1.1E-02 2.36E-03 4.3E-04 15 1.78E-07 4.04E-03 1.2E-05 3.40E-05 2.3E-06 0.00E+00 0.0E+00 1.85E-02 9.8E-04 244.7 0.8 0.2 2040.9 11.8 0 0.00E+00 0.0E+00 2.32E-03 4.2E-04 Weighted averages of included steps: 2.60E-03 1.1E-04 1.34E-02 4.1E-05 244.9 0.1 37.3 2046.6 8.4 4.99E-03 8.1E-04 1.68E-03 2.9E-04 3 Page

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Sample: PB5_7_1 Irradiation position: 7 (Z=6.5 mm) J-value: 0.008617 +/- 0.000017 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 1.51E-06 5.01E-03 6.6E-06 1.33E-05 6.0E-07 2.19E-02 1.3E-03 1.98E-02 3.3E-04 198.7 0.3 2.4 1798.0 8.3 0 4.21E-02 2.6E-03 2.48E-03 6.6E-05 2 2.15E-06 4.42E-03 5.8E-06 6.75E-06 3.9E-07 2.47E-03 6.8E-04 1.38E-02 3.2E-04 225.6 0.3 3.0 1945.8 8.1 0 4.75E-03 1.3E-03 1.73E-03 5.4E-05 3 4.11E-06 4.36E-03 5.1E-06 3.79E-06 1.9E-07 1.89E-03 5.7E-04 1.30E-02 2.3E-04 229.0 0.3 5.6 1963.5 8.4 0 3.63E-03 1.1E-03 1.63E-03 4.5E-05 4 6.78E-06 4.23E-03 3.6E-06 2.41E-06 1.6E-07 2.55E-03 3.6E-04 1.27E-02 8.6E-05 236.1 0.2 9.0 2000.4 8.4 0 4.91E-03 6.9E-04 1.59E-03 3.5E-05 5 8.75E-06 4.18E-03 2.7E-06 1.24E-06 1.4E-07 1.52E-03 2.0E-04 1.27E-02 1.1E-04 239.0 0.2 11.5 2015.2 8.2 0 2.92E-03 3.8E-04 1.59E-03 3.5E-05 6 9.26E-06 4.15E-03 2.8E-06 1.32E-06 1.2E-07 1.94E-03 2.6E-04 1.25E-02 1.1E-04 240.7 0.2 12.1 2023.7 8.3 0 3.73E-03 4.9E-04 1.57E-03 3.5E-05 7 1.08E-05 4.11E-03 2.7E-06 9.72E-07 9.9E-08 2.14E-03 2.2E-04 1.26E-02 1.4E-04 243.4 0.1 14.0 2037.1 8.6 0 4.11E-03 4.2E-04 1.58E-03 3.7E-05 8 9.20E-06 4.09E-03 2.4E-06 1.27E-06 1.3E-07 1.85E-03 2.6E-04 1.26E-02 9.8E-05 244.5 0.2 11.8 2042.7 8.9 1 3.56E-03 5.0E-04 1.58E-03 3.5E-05 9 7.56E-06 4.09E-03 2.7E-06 7.09E-07 1.3E-07 4.63E-04 1.6E-04 1.24E-02 1.1E-04 244.7 0.2 9.7 2043.7 8.5 1 8.90E-04 3.1E-04 1.56E-03 3.5E-05 10 7.39E-06 4.05E-03 1.6E-06 6.21E-07 1.8E-07 1.11E-03 2.8E-04 1.24E-02 8.7E-05 246.9 0.1 9.4 2054.9 8.5 1 2.13E-03 5.4E-04 1.55E-03 3.4E-05 11 6.20E-06 4.05E-03 2.9E-06 2.12E-07 5.7E-06 1.25E-03 2.8E-04 1.28E-02 1.7E-04 246.9 0.2 7.9 2054.6 8.9 1 2.40E-03 5.5E-04 1.61E-03 3.9E-05 12 2.24E-06 4.05E-03 4.9E-06 1.95E-06 3.2E-07 0.00E+00 0.0E+00 1.28E-02 2.8E-04 247.1 0.3 2.8 2055.6 8.8 1 0.00E+00 0.0E+00 1.60E-03 4.8E-05 13 2.46E-07 4.12E-03 1.3E-05 1.36E-05 4.2E-06 4.91E-02 8.6E-03 1.38E-02 1.1E-03 241.5 0.8 0.3 2027.9 11.8 0 9.45E-02 1.7E-02 1.73E-03 1.4E-04 14 3.81E-07 4.12E-03 9.2E-06 1.09E-05 2.0E-06 2.33E-02 5.4E-03 1.45E-02 6.7E-04 241.7 0.6 0.5 2028.9 10.3 0 4.48E-02 1.0E-02 1.82E-03 9.1E-05 15 5.86E-08 4.31E-03 3.5E-05 8.06E-05 1.5E-05 1.42E-01 4.0E-02 2.13E-02 2.6E-03 226.5 2.3 0.1 1950.7 26.1 0 2.74E-01 7.6E-02 2.68E-03 3.4E-04 16 2.31E-08 4.23E-03 6.9E-05 1.65E-04 4.2E-05 2.72E-01 7.7E-02 1.99E-02 5.0E-03 224.7 4.5 0.0 1940.9 49.2 0 5.23E-01 1.5E-01 2.50E-03 6.3E-04 Weighted averages of included steps: 1.20E-03 1.3E-04 1.26E-02 5.7E-05 245.7 0.1 41.6 2048.8 8.5 2.31E-03 2.4E-04 1.57E-03 3.3E-05

Sample: PB-A-9_9_1 Irradiation position: 9 (Z=7.2 mm) J-value: 0.007782 +/- 0.000020 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 4.56E-07 4.29E-03 1.1E-05 4.24E-05 1.5E-06 1.65E-02 4.9E-03 1.40E-02 4.0E-04 230.3 0.6 1.5 1852.8 12.4 0 3.27E-02 9.7E-03 1.64E-03 5.1E-05 2 1.70E-06 3.85E-03 5.6E-06 1.50E-05 6.3E-07 3.09E-02 1.7E-03 1.27E-02 3.0E-04 258.7 0.4 4.9 1990.4 11.7 0 6.12E-02 3.5E-03 1.49E-03 4.0E-05 3 2.71E-06 3.73E-03 4.3E-06 7.64E-06 2.6E-07 5.04E-02 1.5E-03 1.34E-02 1.9E-04 267.2 0.3 7.6 2029.8 12.0 0 9.99E-02 3.1E-03 1.57E-03 3.0E-05 4 2.80E-06 3.70E-03 6.2E-06 5.52E-06 4.7E-07 1.98E-02 2.6E-03 1.25E-02 2.7E-04 270.0 0.4 7.8 2042.3 12.4 1 3.92E-02 5.2E-03 1.47E-03 3.6E-05 5 3.89E-06 3.70E-03 4.8E-06 2.94E-06 3.6E-07 1.56E-02 1.3E-03 1.32E-02 1.9E-04 270.2 0.3 10.7 2043.2 12.5 1 3.10E-02 2.5E-03 1.55E-03 2.9E-05 6 2.45E-06 3.67E-03 5.2E-06 5.75E-06 5.2E-07 4.37E-02 3.1E-03 1.33E-02 2.5E-04 272.0 0.4 6.7 2051.5 11.6 1 8.66E-02 6.2E-03 1.56E-03 3.5E-05 7 4.06E-06 3.66E-03 6.0E-06 2.48E-06 3.3E-07 1.16E-02 1.6E-03 1.32E-02 1.9E-04 272.9 0.4 11.1 2055.4 12.2 1 2.29E-02 3.1E-03 1.54E-03 3.0E-05 8 3.90E-06 3.65E-03 3.8E-06 2.04E-06 2.3E-07 1.41E-02 1.0E-03 1.32E-02 1.7E-04 273.6 0.3 10.6 2058.8 11.9 1 2.79E-02 2.1E-03 1.55E-03 2.8E-05 9 2.92E-06 3.67E-03 1.5E-05 1.56E-06 3.0E-07 4.89E-03 1.4E-03 1.31E-02 2.3E-04 272.2 1.2 8.0 2052.5 15.8 1 9.69E-03 2.8E-03 1.54E-03 3.3E-05 10 3.64E-06 3.64E-03 3.4E-06 1.09E-06 2.9E-07 8.89E-03 1.1E-03 1.31E-02 1.7E-04 274.4 0.3 9.9 2062.2 12.6 1 1.76E-02 2.2E-03 1.54E-03 2.8E-05 11 3.19E-06 3.65E-03 5.3E-06 3.77E-06 3.1E-07 4.22E-02 1.3E-03 1.34E-02 1.6E-04 273.4 0.4 8.6 2057.9 12.6 1 8.36E-02 2.5E-03 1.57E-03 2.7E-05 12 2.56E-06 3.68E-03 3.3E-06 2.12E-06 2.9E-07 2.07E-02 1.6E-03 1.39E-02 3.3E-04 271.5 0.3 7.0 2049.2 11.6 1 4.11E-02 3.1E-03 1.63E-03 4.4E-05 13 1.06E-06 3.67E-03 5.4E-06 3.37E-06 8.8E-07 1.78E-02 3.6E-03 1.45E-02 4.4E-04 271.9 0.4 2.9 2050.9 12.7 1 3.53E-02 7.2E-03 1.70E-03 5.6E-05 14 4.13E-07 3.68E-03 1.4E-05 7.07E-06 2.3E-06 5.30E-02 7.5E-03 1.92E-02 8.7E-04 271.4 1.1 1.1 2049.0 15.7 0 1.05E-01 1.5E-02 2.25E-03 1.1E-04 15 4.11E-07 3.65E-03 1.1E-05 3.89E-06 3.1E-06 1.02E-02 7.0E-03 1.96E-02 8.4E-04 273.3 0.9 1.1 2057.5 14.1 0 2.03E-02 1.4E-02 2.30E-03 1.0E-04 16 1.39E-07 3.70E-03 2.4E-05 6.95E-06 3.9E-04 4.82E-03 2.8E-02 2.92E-02 1.5E-03 270.1 1.8 0.4 2042.8 20.6 0 9.56E-03 5.5E-02 3.42E-03 1.8E-04 Weighted averages of included steps: 1.90E-02 5.5E-04 1.32E-02 6.7E-05 272.3 0.2 83.4 2052.9 11.4 3.76E-02 1.1E-03 1.55E-03 2.1E-05

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Sample: PB8_9_1 Irradiation position: 9 (Z=7.2 mm) J-value:0.008602 +/- 0.000017 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.65E-07 6.19E-03 1.5E-05 4.43E-05 1.7E-06 4.93E-02 4.2E-03 2.89E-02 5.1E-04 159.4 0.4 0.8 1555.9 8.6 0 9.49E-02 1.7E-02 3.63E-03 6.3E-04 2 1.40E-06 5.14E-03 5.3E-06 1.86E-05 2.7E-07 2.44E-02 8.7E-04 1.66E-02 2.2E-04 193.7 0.2 3.5 1767.0 7.3 0 4.70E-02 7.6E-03 2.08E-03 3.6E-04 3 2.85E-06 4.61E-03 3.9E-06 1.15E-05 1.9E-07 2.23E-02 4.2E-04 1.53E-02 1.7E-04 216.2 0.2 6.4 1893.6 8.0 0 4.29E-02 6.8E-03 1.92E-03 3.3E-04 4 4.16E-06 4.38E-03 5.0E-06 8.32E-06 2.8E-07 1.54E-02 5.5E-04 1.47E-02 2.0E-04 227.7 0.2 8.9 1954.7 8.5 0 2.96E-02 4.8E-03 1.84E-03 3.2E-04 5 5.59E-06 4.23E-03 4.3E-06 4.61E-06 1.6E-07 1.08E-02 3.7E-04 1.42E-02 1.1E-04 236.1 0.2 11.5 1998.5 8.4 0 2.07E-02 3.3E-03 1.78E-03 3.1E-04 6 6.73E-06 4.11E-03 3.7E-06 4.35E-06 2.4E-07 1.04E-02 6.1E-04 1.36E-02 1.3E-04 242.9 0.2 13.4 2033.0 8.5 1 2.01E-02 3.4E-03 1.71E-03 3.0E-04 7 7.80E-06 4.04E-03 2.6E-06 4.10E-06 1.9E-07 8.61E-03 2.9E-04 1.31E-02 8.7E-05 247.1 0.1 15.3 2053.9 8.7 1 1.66E-02 2.7E-03 1.65E-03 2.9E-04 8 7.63E-06 3.97E-03 2.3E-06 4.14E-06 1.8E-07 8.20E-03 1.8E-04 1.31E-02 1.4E-04 251.5 0.2 14.7 2075.2 9.1 1 1.58E-02 2.5E-03 1.64E-03 2.8E-04 9 5.78E-06 3.95E-03 2.8E-06 6.17E-06 7.7E-08 7.70E-03 4.6E-04 1.35E-02 1.3E-04 252.4 0.2 11.1 2079.7 8.7 1 1.48E-02 2.5E-03 1.69E-03 2.9E-04 10 3.14E-06 3.97E-03 4.1E-06 1.01E-05 2.7E-07 7.17E-03 5.6E-04 1.38E-02 2.0E-04 251.2 0.3 6.1 2074.2 9.0 1 1.38E-02 2.4E-03 1.73E-03 3.0E-04 11 2.61E-06 3.99E-03 3.4E-06 1.92E-05 3.3E-07 1.23E-02 6.3E-04 1.40E-02 1.8E-04 249.2 0.2 5.1 2064.1 9.0 1 2.36E-02 3.9E-03 1.76E-03 3.0E-04 12 8.91E-07 3.96E-03 6.3E-06 9.33E-05 1.4E-06 1.65E-02 1.6E-03 1.76E-02 2.5E-04 245.8 0.4 1.7 2047.2 9.3 1 3.18E-02 5.9E-03 2.20E-03 3.8E-04 13 3.01E-07 3.89E-03 7.3E-06 2.24E-04 2.0E-06 5.85E-02 3.8E-03 2.28E-02 6.7E-04 240.1 0.5 0.6 2018.5 9.9 0 1.13E-01 1.9E-02 2.86E-03 5.0E-04 14 4.61E-07 3.82E-03 7.3E-06 2.44E-04 2.1E-06 3.31E-02 3.2E-03 2.51E-02 2.2E-04 242.7 0.6 0.9 2031.7 10.2 0 6.36E-02 1.2E-02 3.15E-03 5.4E-04 15 6.69E-08 8.08E-04 1.3E-05 2.89E-03 2.0E-05 8.41E-01 9.3E-02 1.26E-01 4.1E-03 169.5 30.4 0.0 1620.5 394.4 0 1.62E+00 3.1E-01 1.58E-02 2.8E-03 16 4.05E-08 1.30E-03 2.1E-05 2.68E-03 3.2E-05 1.16E+00 1.2E-01 2.54E-01 8.0E-03 154.2 16.4 0.0 1521.4 224.6 0 2.23E+00 4.2E-01 3.18E-02 5.6E-03 Weighted averages of included steps: 9.08E-03 1.8E-04 1.35E-02 4.9E-05 248.6 0.1 67.5 2061.1 8.4 1.75E-02 2.8E-03 1.69E-03 2.9E-04

Sample: PB-A-1_1_2 Irradiation position: 1 (Z=0.8 mm) J-value: 0.007803 +/- 0.000023 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.51E-06 3.69E-03 1.2E-05 7.23E-06 3.9E-07 6.21E-03 8.0E-04 1.38E-02 1.6E-04 270.4 0.9 8.1 2047.8 14.7 0 1.23E-02 1.6E-03 1.62E-03 2.8E-05 2 2.83E-06 3.57E-03 8.3E-06 3.43E-06 3.1E-07 2.18E-03 1.1E-03 1.39E-02 1.9E-04 279.8 0.6 8.9 2089.6 14.1 1 4.33E-03 2.2E-03 1.63E-03 3.0E-05 3 4.14E-06 3.54E-03 7.8E-06 2.56E-06 2.1E-07 4.92E-03 8.0E-04 1.36E-02 2.1E-04 282.2 0.6 13.0 2100.4 13.7 1 9.74E-03 1.6E-03 1.60E-03 3.2E-05 4 4.09E-06 3.52E-03 7.0E-06 2.58E-06 1.5E-07 6.14E-03 8.1E-04 1.36E-02 2.1E-04 284.0 0.5 12.7 2108.4 13.4 1 1.22E-02 1.6E-03 1.59E-03 3.2E-05 5 5.34E-06 3.56E-03 7.0E-06 1.24E-06 2.3E-07 3.87E-03 7.0E-04 1.37E-02 1.2E-04 281.2 0.5 16.6 2095.8 12.5 1 7.67E-03 1.4E-03 1.60E-03 2.4E-05 6 3.62E-06 3.50E-03 7.4E-06 1.02E-06 3.1E-07 2.37E-03 1.2E-03 1.37E-02 2.9E-04 285.6 0.6 11.2 2115.3 13.0 1 4.69E-03 2.4E-03 1.60E-03 4.0E-05 7 1.56E-06 3.53E-03 5.1E-06 2.02E-06 4.3E-07 0.00E+00 0.0E+00 1.37E-02 2.8E-04 283.3 0.4 4.9 2105.3 12.6 1 0.00E+00 0.0E+00 1.60E-03 3.9E-05 8 3.35E-06 3.51E-03 5.7E-06 1.06E-06 2.4E-07 3.96E-03 7.7E-04 1.39E-02 1.7E-04 284.5 0.5 10.5 2110.4 13.1 1 7.85E-03 1.5E-03 1.63E-03 2.9E-05 9 3.59E-06 3.52E-03 6.8E-06 1.04E-06 2.9E-07 3.75E-03 9.0E-04 1.42E-02 1.5E-04 284.0 0.6 11.3 2108.3 13.2 1 7.43E-03 1.8E-03 1.67E-03 2.7E-05 10 5.68E-07 3.62E-03 8.5E-06 5.31E-06 1.3E-06 7.35E-03 5.5E-03 1.59E-02 6.1E-04 275.4 0.6 1.8 2070.3 13.0 0 1.46E-02 1.1E-02 1.87E-03 7.5E-05 11 2.06E-07 3.72E-03 2.0E-05 1.97E-05 2.1E-06 0.00E+00 0.0E+00 1.90E-02 8.2E-04 266.9 1.5 0.7 2032.0 17.8 0 0.00E+00 0.0E+00 2.23E-03 1.0E-04 12 6.92E-08 3.83E-03 2.9E-05 4.20E-05 4.0E-06 3.93E-03 2.8E-02 3.58E-02 2.7E-03 257.6 2.0 0.2 1988.9 22.8 0 7.79E-03 5.6E-02 4.19E-03 3.2E-04 13 2.40E-08 4.02E-03 8.2E-05 1.40E-04 2.8E-05 4.37E-01 1.2E-01 4.62E-02 7.1E-03 238.3 5.6 0.1 1896.1 55.8 0 8.66E-01 2.4E-01 5.41E-03 8.3E-04 Weighted averages of included steps: 3.99E-03 3.4E-04 1.38E-02 7.4E-05 283.0 0.2 89.1 2103.9 11.2 7.91E-03 6.7E-04 1.61E-03 2.2E-05

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Sample: PB-A-2_2-2 Irradiation position: 2 (Z=1.6 mm) J-value: 0.007801 +/- 0.000020 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 8.42E-07 3.83E-03 9.0E-06 1.02E-05 2.5E-06 0.00E+00 0.0E+00 1.36E-02 5.4E-04 260.0 0.6 2.5 1999.4 12.9 0 0.00E+00 0.0E+00 1.59E-03 6.6E-05 2 1.55E-06 3.64E-03 6.3E-06 2.27E-06 2.7E-04 0.00E+00 0.0E+00 1.38E-02 1.2E-03 274.6 0.5 4.4 2066.3 12.3 0 0.00E+00 0.0E+00 1.62E-03 1.4E-04 3 2.44E-06 3.62E-03 4.3E-06 2.69E-06 5.3E-07 0.00E+00 0.0E+00 1.35E-02 2.8E-04 276.3 0.3 6.9 2074.0 12.3 0 0.00E+00 0.0E+00 1.58E-03 3.8E-05 4 2.06E-06 3.56E-03 6.1E-06 2.76E-06 3.4E-07 0.00E+00 0.0E+00 1.30E-02 2.1E-04 280.5 0.4 5.7 2092.5 12.7 0 0.00E+00 0.0E+00 1.53E-03 3.1E-05 5 1.31E-06 3.59E-03 6.0E-06 4.72E-06 5.0E-07 0.00E+00 0.0E+00 1.42E-02 2.8E-04 278.5 0.5 3.7 2083.6 12.9 0 0.00E+00 0.0E+00 1.67E-03 3.9E-05 6 3.24E-06 3.54E-03 5.1E-06 2.31E-06 2.0E-07 0.00E+00 0.0E+00 1.32E-02 1.8E-04 282.2 0.4 8.8 2099.9 11.9 1 0.00E+00 0.0E+00 1.55E-03 2.8E-05 7 3.62E-06 3.51E-03 6.7E-06 1.92E-06 2.4E-07 0.00E+00 0.0E+00 1.37E-02 1.8E-04 284.7 0.5 9.8 2111.1 12.7 1 0.00E+00 0.0E+00 1.61E-03 2.9E-05 8 4.58E-06 3.51E-03 8.0E-06 1.69E-06 2.0E-07 0.00E+00 0.0E+00 1.35E-02 1.8E-04 284.9 0.7 12.4 2111.6 13.4 1 0.00E+00 0.0E+00 1.58E-03 2.9E-05 9 3.94E-06 3.51E-03 4.2E-06 -1.97E-08 1.5E-07 0.00E+00 0.0E+00 1.35E-02 1.6E-04 284.8 0.3 10.6 2111.2 12.6 1 0.00E+00 0.0E+00 1.59E-03 2.7E-05 10 5.43E-06 3.50E-03 4.7E-06 -2.90E-07 3.4E-06 0.00E+00 0.0E+00 1.37E-02 1.7E-04 285.5 0.4 14.6 2114.6 13.1 1 0.00E+00 0.0E+00 1.60E-03 2.8E-05 11 3.09E-06 3.53E-03 5.5E-06 -7.63E-08 3.7E-07 0.00E+00 0.0E+00 1.37E-02 2.1E-04 283.3 0.4 8.3 2104.9 12.9 1 0.00E+00 0.0E+00 1.61E-03 3.2E-05 12 2.61E-06 3.53E-03 4.6E-06 -2.31E-07 9.2E-06 0.00E+00 0.0E+00 1.40E-02 2.3E-04 283.3 0.4 7.0 2104.8 12.0 1 0.00E+00 0.0E+00 1.65E-03 3.4E-05 13 1.29E-06 3.61E-03 6.8E-06 1.33E-06 4.8E-06 0.00E+00 0.0E+00 1.42E-02 3.2E-04 276.7 0.5 3.5 2075.5 13.2 0 0.00E+00 0.0E+00 1.67E-03 4.3E-05 14 4.83E-07 3.66E-03 9.5E-06 4.28E-06 1.5E-06 0.00E+00 0.0E+00 1.52E-02 5.5E-04 272.9 0.7 1.3 2058.7 14.2 0 0.00E+00 0.0E+00 1.78E-03 6.8E-05 15 1.06E-07 3.79E-03 6.8E-05 2.73E-05 5.6E-06 1.74E-02 2.5E-02 2.09E-02 1.9E-03 261.8 2.2 0.3 2007.9 23.1 0 3.44E-02 5.0E-02 2.46E-03 2.3E-04 16 2.72E-08 3.84E-03 5.9E-05 3.63E-05 1.8E-04 2.57E-01 1.1E-01 3.44E-02 5.9E-03 257.3 4.2 0.1 1986.9 42.5 0 5.10E-01 2.1E-01 4.04E-03 7.0E-04 Weighted averages of included steps: 0.00E+00 0.0E+00 1.36E-02 6.7E-05 284.2 0.2 71.5 2108.7 11.9 0.00E+00 0.0E+00 1.60E-03 2.1E-05

Sample: PB-A-3_3-2 Irradiation position: 3 (Z=2.4 mm) J-value: 0.007798 +/- 0.000020 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 5.51E-08 4.63E-03 3.2E-05 4.23E-05 6.7E-06 0.00E+00 0.0E+00 1.54E-02 2.3E-03 213.3 1.6 0.2 1768.0 19.8 0 0.00E+00 0.0E+00 1.80E-03 2.7E-04 2 7.88E-07 3.79E-03 7.4E-06 8.31E-06 7.3E-07 0.00E+00 0.0E+00 1.38E-02 5.4E-04 263.0 0.5 2.9 2012.9 12.1 0 0.00E+00 0.0E+00 1.62E-03 6.6E-05 3 1.14E-06 3.70E-03 7.1E-06 5.11E-06 6.0E-07 9.36E-04 1.8E-03 1.35E-02 3.0E-04 270.2 0.5 4.1 2045.9 12.6 0 1.86E-03 3.5E-03 1.58E-03 4.0E-05 4 1.29E-06 3.66E-03 6.8E-06 4.88E-06 3.6E-07 5.69E-03 2.2E-03 1.36E-02 3.4E-04 272.7 0.5 4.6 2057.3 12.6 0 1.13E-02 4.4E-03 1.59E-03 4.4E-05 5 1.86E-06 3.66E-03 6.0E-06 3.31E-06 3.3E-07 8.35E-04 1.5E-03 1.35E-02 2.5E-04 273.2 0.4 5.7 2059.6 12.8 0 1.65E-03 3.0E-03 1.59E-03 3.5E-05 6 2.63E-06 3.55E-03 7.7E-06 2.57E-06 3.1E-07 1.14E-03 1.1E-03 1.34E-02 2.4E-04 281.4 0.6 7.7 2095.9 12.5 1 2.26E-03 2.1E-03 1.58E-03 3.4E-05 7 2.29E-06 3.58E-03 9.0E-06 2.17E-06 4.2E-06 0.00E+00 0.0E+00 1.35E-02 1.4E-04 279.4 0.7 6.9 2087.3 13.1 1 0.00E+00 0.0E+00 1.58E-03 2.6E-05 8 3.12E-06 3.54E-03 7.8E-06 2.10E-06 2.9E-07 1.81E-03 1.0E-03 1.31E-02 2.0E-04 282.2 0.7 9.2 2099.4 13.2 1 3.58E-03 2.1E-03 1.54E-03 3.1E-05 9 5.39E-06 3.51E-03 4.5E-06 9.12E-07 1.4E-07 2.69E-03 6.7E-04 1.34E-02 1.6E-04 285.2 0.4 15.6 2112.6 12.6 1 5.33E-03 1.3E-03 1.57E-03 2.7E-05 10 6.93E-06 3.51E-03 6.5E-06 7.40E-07 1.7E-07 5.65E-03 6.1E-04 1.34E-02 1.3E-04 284.8 0.5 20.1 2110.8 13.5 1 1.12E-02 1.2E-03 1.57E-03 2.5E-05 11 3.85E-06 3.51E-03 7.1E-06 7.44E-07 3.1E-05 3.26E-03 1.6E-03 1.38E-02 2.3E-04 284.7 0.6 11.1 2110.5 13.3 1 6.46E-03 3.2E-03 1.62E-03 3.4E-05 12 1.59E-06 3.59E-03 8.2E-06 2.61E-06 6.1E-07 0.00E+00 0.0E+00 1.36E-02 3.7E-04 278.0 0.7 4.7 2081.1 12.6 0 0.00E+00 0.0E+00 1.60E-03 4.7E-05 13 1.83E-06 3.58E-03 8.0E-06 2.24E-06 6.7E-07 0.00E+00 0.0E+00 1.44E-02 3.9E-04 279.2 0.6 5.4 2086.2 13.5 0 0.00E+00 0.0E+00 1.69E-03 5.0E-05 14 4.03E-07 3.65E-03 1.1E-05 6.73E-06 3.8E-06 0.00E+00 0.0E+00 1.88E-02 1.4E-03 273.1 0.9 1.2 2058.9 14.9 0 0.00E+00 0.0E+00 2.21E-03 1.7E-04 15 1.28E-07 3.72E-03 2.0E-05 1.40E-05 5.5E-06 0.00E+00 0.0E+00 2.65E-02 1.7E-03 267.8 1.6 0.4 2035.1 18.2 0 0.00E+00 0.0E+00 3.10E-03 2.1E-04 16 2.35E-08 3.81E-03 8.5E-05 -3.86E-05 4.5E-04 0.00E+00 0.0E+00 3.89E-02 3.1E-02 265.2 7.2 0.1 2023.3 69.6 0 0.00E+00 0.0E+00 4.57E-03 3.6E-03 Weighted averages of included steps: 3.41E-03 4.0E-04 1.34E-02 7.2E-05 283.6 0.2 70.7 2105.8 11.9 6.76E-03 8.0E-04 1.58E-03 2.1E-05

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Sample: PB-A-4_4-2 Irradiation position: 4 (Z=3.2 mm) J-value: 0.007796 +/- 0.000022 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.18E-07 4.31E-03 2.1E-05 2.67E-05 2.4E-06 0.00E+00 0.0E+00 1.47E-02 1.0E-03 230.2 1.2 0.8 1854.5 16.8 0 0.00E+00 0.0E+00 1.72E-03 1.2E-04 2 8.67E-07 3.96E-03 9.9E-06 1.12E-05 1.4E-06 8.80E-03 4.4E-03 1.41E-02 5.4E-04 251.7 0.6 2.8 1959.5 13.2 0 1.74E-02 8.6E-03 1.66E-03 6.7E-05 3 1.14E-06 3.81E-03 6.2E-06 9.70E-06 6.3E-07 7.33E-03 2.5E-03 1.44E-02 2.2E-04 261.7 0.4 3.6 2006.8 12.4 0 1.45E-02 4.9E-03 1.69E-03 3.4E-05 4 1.97E-06 3.65E-03 5.3E-06 6.19E-06 3.2E-07 1.65E-02 1.5E-03 1.38E-02 2.0E-04 273.6 0.4 5.9 2060.7 12.3 0 3.26E-02 3.1E-03 1.62E-03 3.1E-05 5 1.32E-06 3.60E-03 8.1E-06 3.30E-06 1.2E-06 7.78E-03 2.3E-03 1.39E-02 3.6E-04 277.2 0.6 3.9 2076.9 13.1 0 1.54E-02 4.6E-03 1.63E-03 4.6E-05 6 2.45E-06 3.54E-03 3.5E-06 3.47E-06 4.1E-07 1.61E-02 2.1E-03 1.39E-02 3.2E-04 282.6 0.3 7.0 2100.8 12.1 0 3.19E-02 4.2E-03 1.63E-03 4.2E-05 7 4.08E-06 3.45E-03 4.5E-06 2.39E-06 2.6E-07 1.07E-02 1.2E-03 1.33E-02 2.3E-04 290.0 0.3 11.5 2132.9 12.2 1 2.11E-02 2.4E-03 1.56E-03 3.3E-05 8 5.08E-06 3.45E-03 5.7E-06 2.42E-06 2.1E-07 1.35E-02 8.4E-04 1.35E-02 1.2E-04 289.7 0.5 14.3 2132.0 13.4 1 2.67E-02 1.7E-03 1.58E-03 2.4E-05 9 4.49E-06 3.41E-03 3.5E-06 8.64E-07 2.9E-07 5.41E-03 1.2E-03 1.37E-02 1.8E-04 293.4 0.3 12.4 2147.8 12.8 1 1.07E-02 2.4E-03 1.61E-03 2.9E-05 10 5.05E-06 3.42E-03 5.8E-06 7.82E-07 2.6E-07 6.76E-03 1.3E-03 1.35E-02 1.9E-04 292.4 0.5 14.0 2143.4 12.7 1 1.34E-02 2.7E-03 1.58E-03 3.0E-05 11 3.08E-06 3.44E-03 5.6E-06 5.08E-07 2.1E-05 5.29E-03 1.0E-03 1.34E-02 2.2E-04 290.3 0.5 8.6 2134.5 12.3 1 1.05E-02 2.0E-03 1.57E-03 3.2E-05 12 2.39E-06 3.52E-03 4.0E-06 1.48E-06 4.6E-07 5.41E-05 1.8E-03 1.37E-02 3.0E-04 284.2 0.3 6.8 2108.0 11.4 0 1.07E-04 3.6E-03 1.61E-03 4.0E-05 13 1.45E-06 3.60E-03 4.9E-06 6.52E-07 7.3E-05 0.00E+00 0.0E+00 1.40E-02 3.8E-04 277.7 0.4 4.2 2079.2 12.7 0 0.00E+00 0.0E+00 1.64E-03 4.9E-05 14 7.26E-07 3.63E-03 6.8E-06 5.00E-06 8.8E-06 0.00E+00 0.0E+00 1.55E-02 7.2E-04 274.9 0.6 2.1 2066.7 12.7 0 0.00E+00 0.0E+00 1.81E-03 8.8E-05 15 2.63E-07 3.67E-03 1.7E-05 6.23E-06 2.7E-06 0.00E+00 0.0E+00 1.72E-02 1.1E-03 272.1 1.3 0.8 2054.0 16.3 0 0.00E+00 0.0E+00 2.02E-03 1.3E-04 16 1.72E-07 3.72E-03 2.4E-05 8.23E-06 5.9E-05 0.00E+00 0.0E+00 1.69E-02 1.5E-03 267.9 1.7 0.5 2034.9 18.9 0 0.00E+00 0.0E+00 1.98E-03 1.7E-04 Weighted averages of included steps: 8.59E-03 5.4E-04 1.35E-02 8.3E-05 291.2 0.2 60.9 2138.4 11.9 1.70E-02 1.1E-03 1.58E-03 2.2E-05

Sample: PB-A-6_6_2 Irradiation position: 6 (Z=4.8 mm) J-value: 0.007789 +/- 0.000022 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.93E-08 6.84E-03 5.9E-05 1.16E-04 2.5E-05 2.13E-02 4.3E-02 1.64E-02 2.9E-03 141.2 1.7 0.2 1338.6 23.9 0 4.21E-02 8.5E-02 1.93E-03 3.4E-04 2 3.99E-07 5.57E-03 1.1E-05 2.39E-05 1.4E-06 0.00E+00 0.0E+00 2.04E-02 6.8E-04 178.2 0.4 1.9 1571.1 9.9 0 0.00E+00 0.0E+00 2.40E-03 8.5E-05 3 1.38E-06 4.62E-03 6.6E-06 1.10E-05 4.5E-07 3.84E-03 2.1E-03 1.82E-02 2.2E-04 215.9 0.3 5.6 1780.0 11.3 0 7.61E-03 4.1E-03 2.14E-03 3.7E-05 4 1.79E-06 3.99E-03 6.1E-06 5.98E-06 4.6E-07 0.00E+00 0.0E+00 1.61E-02 2.2E-04 250.0 0.4 5.2 1950.8 12.0 0 0.00E+00 0.0E+00 1.89E-03 3.5E-05 5 2.12E-06 3.74E-03 5.5E-06 2.84E-06 3.1E-07 0.00E+00 0.0E+00 1.54E-02 2.9E-04 267.2 0.4 5.9 2031.1 11.9 0 0.00E+00 0.0E+00 1.81E-03 4.1E-05 6 3.27E-06 3.55E-03 6.5E-06 3.97E-06 2.2E-07 2.91E-02 1.6E-03 1.48E-02 2.1E-04 281.0 0.5 8.4 2092.7 12.2 0 5.77E-02 3.1E-03 1.74E-03 3.3E-05 7 3.16E-06 3.49E-03 5.4E-06 1.84E-06 2.5E-07 1.67E-03 8.9E-04 1.43E-02 2.3E-04 286.3 0.4 8.0 2115.8 11.7 1 3.30E-03 1.8E-03 1.68E-03 3.4E-05 8 3.47E-06 3.48E-03 4.7E-06 1.40E-06 4.2E-07 3.44E-03 1.4E-03 1.37E-02 2.2E-04 287.3 0.4 8.7 2120.3 13.0 1 6.81E-03 2.9E-03 1.60E-03 3.2E-05 9 2.96E-06 3.48E-03 4.3E-06 3.50E-07 1.1E-05 0.00E+00 0.0E+00 1.41E-02 2.5E-04 287.7 0.4 7.4 2122.2 12.4 1 0.00E+00 0.0E+00 1.65E-03 3.5E-05 10 3.01E-06 3.49E-03 8.6E-06 -1.44E-08 1.7E-08 0.00E+00 0.0E+00 1.40E-02 2.3E-04 286.9 0.7 7.6 2118.7 13.1 1 0.00E+00 0.0E+00 1.64E-03 3.4E-05 11 2.86E-06 3.48E-03 5.7E-06 8.35E-08 7.8E-07 0.00E+00 0.0E+00 1.37E-02 1.7E-04 287.0 0.5 7.2 2118.9 12.4 1 0.00E+00 0.0E+00 1.61E-03 2.9E-05 12 3.88E-06 3.47E-03 3.6E-06 2.61E-07 9.6E-06 0.00E+00 0.0E+00 1.39E-02 2.8E-04 287.9 0.3 9.7 2122.8 12.5 1 0.00E+00 0.0E+00 1.63E-03 3.9E-05 13 2.66E-06 3.46E-03 5.3E-06 6.10E-07 6.3E-07 0.00E+00 0.0E+00 1.39E-02 3.1E-04 289.0 0.5 6.6 2127.8 12.6 1 0.00E+00 0.0E+00 1.63E-03 4.2E-05 14 2.73E-06 3.57E-03 1.9E-05 1.56E-06 2.5E-07 0.00E+00 0.0E+00 1.43E-02 2.2E-04 279.8 1.5 7.0 2087.5 17.4 1 0.00E+00 0.0E+00 1.68E-03 3.3E-05 15 1.56E-06 3.68E-03 9.9E-06 2.67E-06 5.3E-07 0.00E+00 0.0E+00 1.48E-02 3.1E-04 271.2 0.8 4.1 2049.1 13.7 0 0.00E+00 0.0E+00 1.74E-03 4.2E-05 16 1.00E-06 3.75E-03 8.1E-06 8.76E-06 1.3E-06 3.52E-03 7.0E-03 1.56E-02 6.4E-04 265.7 0.6 2.7 2024.1 13.2 0 6.98E-03 1.4E-02 1.82E-03 7.9E-05 17 6.09E-07 3.83E-03 7.7E-06 8.23E-06 1.5E-06 0.00E+00 0.0E+00 1.50E-02 7.6E-04 260.8 0.5 1.7 2001.3 12.5 0 0.00E+00 0.0E+00 1.76E-03 9.2E-05

18 3.38E-07 3.98E-03 1.5E-05 1.40E-05 1.9E-06 0.00E+00 0.0E+00 1.64E-02 7.2E-04 250.4 1.0 1.0 1952.5 14.8 0 0.00E+00 0.0E+00 1.92E-03 8.7E-05 7 Weighted averages of included steps: 2.59E-03 8.5E-04 1.40E-02 8.7E-05 286.6 0.2 62.4 2117.1 12.3 5.13E-03 1.7E-03 1.64E-03 2.3E-05 Page

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Sample: PB-A-8_8_1 Irradiation position: 8 (Z=6.4 mm) J-value: 0.007784 +/- 0.000020 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.26E-07 3.81E-03 1.7E-05 1.92E-05 2.3E-06 1.17E-01 1.4E-02 2.05E-02 6.7E-04 260.8 1.3 0.8 2000.7 16.3 0 2.33E-01 2.7E-02 2.40E-03 8.4E-05 2 6.36E-07 3.66E-03 1.1E-05 1.00E-05 1.7E-06 1.24E-01 8.9E-03 1.65E-02 6.6E-04 272.1 0.8 2.2 2052.2 13.5 0 2.45E-01 1.8E-02 1.94E-03 8.1E-05 3 1.05E-06 3.63E-03 5.6E-06 8.10E-06 7.6E-07 9.45E-02 4.8E-03 1.52E-02 3.7E-04 274.8 0.4 3.6 2064.6 12.4 0 1.87E-01 9.5E-03 1.78E-03 4.9E-05 4 1.34E-06 3.62E-03 1.1E-05 1.10E-05 6.9E-07 9.87E-02 6.2E-03 1.47E-02 5.1E-04 275.1 0.8 4.6 2065.7 13.7 0 1.96E-01 1.2E-02 1.72E-03 6.3E-05 5 1.80E-06 3.60E-03 5.8E-06 8.96E-06 5.4E-07 1.35E-01 3.7E-03 1.43E-02 3.8E-04 276.9 0.4 5.0 2073.9 12.8 1 2.67E-01 7.5E-03 1.67E-03 4.9E-05 6 1.89E-06 3.62E-03 5.0E-06 6.56E-06 5.7E-07 1.25E-01 2.9E-03 1.46E-02 3.6E-04 276.0 0.4 5.3 2069.6 11.7 1 2.47E-01 6.0E-03 1.71E-03 4.8E-05 7 2.44E-06 3.61E-03 4.5E-06 5.46E-06 3.3E-07 1.15E-01 2.8E-03 1.41E-02 2.3E-04 276.3 0.3 6.8 2071.3 12.1 1 2.27E-01 5.7E-03 1.65E-03 3.4E-05 8 5.09E-06 3.59E-03 5.7E-06 3.48E-06 1.5E-07 8.50E-02 1.9E-03 1.38E-02 1.9E-04 277.9 0.5 14.1 2078.5 12.4 1 1.68E-01 3.9E-03 1.62E-03 3.0E-05 9 6.36E-06 3.60E-03 3.9E-06 1.50E-06 2.0E-07 5.39E-02 1.4E-03 1.34E-02 1.1E-04 277.9 0.3 17.7 2078.5 12.4 1 1.07E-01 2.9E-03 1.58E-03 2.4E-05 10 5.53E-06 3.58E-03 4.2E-06 1.37E-06 2.3E-07 4.11E-02 9.9E-04 1.36E-02 1.2E-04 279.3 0.3 15.2 2084.6 12.9 1 8.14E-02 2.0E-03 1.60E-03 2.4E-05 11 3.90E-06 3.57E-03 5.3E-06 1.29E-06 4.1E-07 2.91E-02 1.4E-03 1.36E-02 2.3E-04 280.2 0.4 10.7 2088.5 12.8 1 5.77E-02 2.8E-03 1.60E-03 3.4E-05 12 2.90E-06 3.57E-03 4.0E-06 1.07E-06 4.0E-07 2.18E-02 1.9E-03 1.38E-02 2.7E-04 280.3 0.3 8.0 2089.1 11.9 1 4.32E-02 3.7E-03 1.62E-03 3.7E-05 13 1.46E-06 3.53E-03 6.2E-06 1.98E-06 6.2E-07 6.56E-03 3.3E-03 1.50E-02 2.7E-04 283.0 0.5 4.0 2100.9 13.2 0 1.30E-02 6.5E-03 1.76E-03 3.9E-05 14 4.30E-07 3.55E-03 9.8E-06 5.10E-06 1.8E-06 2.28E-02 6.9E-03 2.00E-02 7.4E-04 281.3 0.8 1.2 2093.4 14.6 0 4.51E-02 1.4E-02 2.34E-03 9.2E-05 15 1.93E-07 3.56E-03 2.1E-05 -5.07E-06 1.7E-04 0.00E+00 0.0E+00 2.89E-02 1.6E-03 281.3 1.7 0.5 2093.3 19.1 0 0.00E+00 0.0E+00 3.39E-03 1.9E-04 16 8.16E-08 3.66E-03 2.9E-05 1.85E-05 9.2E-06 0.00E+00 0.0E+00 3.40E-02 2.5E-03 272.0 2.1 0.2 2051.8 23.3 0 0.00E+00 0.0E+00 3.99E-03 3.0E-04 Weighted averages of included steps: 6.50E-02 6.8E-04 1.38E-02 7.0E-05 278.4 0.1 82.8 2080.5 11.9 1.29E-01 1.5E-03 1.62E-03 2.2E-05

Sample: PB-A-10_10_2 Irradiation position: 10 (Z=8.0 mm) J-value: 0.007779 +/- 0.000022 Corrected for fractionation, 39Ar, 36Ar(Ca) and 40Ar(K) ------Radiogenic ------40 39 40 36 40 37 39 38 39 40 39 39 Step# μmol Ar Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar/ Ar ± 1SE Ar*/ Ar ± 1SE % Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.23E-07 3.84E-03 1.7E-05 2.08E-05 1.3E-03 3.61E-02 2.7E-02 1.39E-02 4.7E-03 259.0 1.4 0.7 1991.5 16.8 0 7.16E-02 5.3E-02 1.63E-03 5.5E-04 2 7.24E-07 3.68E-03 7.7E-06 1.49E-05 1.5E-06 5.48E-02 8.6E-03 1.52E-02 9.3E-04 270.4 0.6 2.3 2044.0 12.7 0 1.09E-01 1.7E-02 1.78E-03 1.1E-04 3 1.17E-06 3.62E-03 6.6E-06 8.21E-06 1.4E-06 6.95E-02 4.4E-03 1.42E-02 3.8E-04 275.8 0.5 3.6 2067.9 12.9 0 1.38E-01 8.8E-03 1.67E-03 4.9E-05 4 1.01E-06 3.61E-03 9.7E-06 8.30E-06 7.8E-07 5.69E-02 6.5E-03 1.34E-02 4.9E-04 276.2 0.7 3.1 2069.7 13.5 0 1.13E-01 1.3E-02 1.58E-03 6.1E-05 5 1.60E-06 3.60E-03 7.6E-06 6.47E-06 5.0E-07 4.86E-02 3.5E-03 1.31E-02 3.0E-04 276.9 0.6 5.0 2072.9 12.7 1 9.62E-02 7.0E-03 1.54E-03 4.0E-05 6 1.82E-06 3.58E-03 7.0E-06 5.12E-06 6.3E-07 4.81E-02 2.5E-03 1.27E-02 3.0E-04 278.6 0.6 5.1 2080.3 12.6 1 9.54E-02 5.0E-03 1.49E-03 4.0E-05 7 2.84E-06 3.54E-03 7.9E-06 5.26E-06 5.0E-07 7.16E-02 2.1E-03 1.30E-02 1.8E-04 281.9 0.6 7.9 2095.1 13.3 1 1.42E-01 4.2E-03 1.53E-03 2.9E-05 8 3.08E-06 3.60E-03 7.5E-06 5.02E-06 3.2E-07 4.74E-02 1.5E-03 1.27E-02 3.0E-04 277.2 0.6 8.7 2074.5 13.6 1 9.40E-02 2.9E-03 1.49E-03 4.0E-05 9 3.84E-06 3.56E-03 5.6E-06 3.07E-06 3.2E-07 4.67E-02 1.8E-03 1.28E-02 2.6E-04 280.3 0.5 10.8 2088.2 13.4 1 9.25E-02 3.7E-03 1.51E-03 3.5E-05 10 3.88E-06 3.59E-03 5.7E-06 4.10E-06 4.0E-07 6.07E-02 1.6E-03 1.33E-02 3.0E-04 278.2 0.4 11.0 2078.6 12.7 1 1.20E-01 3.2E-03 1.56E-03 4.0E-05 11 3.24E-06 3.58E-03 6.7E-06 5.72E-06 3.1E-07 5.65E-02 1.2E-03 1.31E-02 2.0E-04 279.1 0.5 9.1 2082.6 13.0 1 1.12E-01 2.5E-03 1.54E-03 3.0E-05 12 4.53E-06 3.55E-03 6.5E-06 4.63E-06 2.6E-07 4.85E-02 1.2E-03 1.32E-02 2.0E-04 281.2 0.5 12.6 2091.9 12.7 1 9.61E-02 2.5E-03 1.54E-03 3.0E-05 13 3.97E-06 3.56E-03 4.9E-06 6.44E-06 3.2E-07 2.97E-02 1.0E-03 1.32E-02 2.1E-04 280.7 0.4 11.1 2089.7 12.7 1 5.88E-02 2.1E-03 1.55E-03 3.1E-05 14 3.23E-06 3.57E-03 5.7E-06 1.36E-05 3.8E-07 4.87E-02 1.2E-03 1.36E-02 2.3E-04 278.6 0.5 9.1 2080.6 12.9 1 9.65E-02 2.5E-03 1.59E-03 3.3E-05 Weighted averages of included steps: 5.02E-02 5.1E-04 1.31E-02 7.7E-05 279.5 0.2 90.2 2084.4 12.7 9.94E-02 1.2E-03 1.54E-03 2.1E-05

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Sample: PB-A-5_5-1 Irradiation position: 5 (Z=4.0 mm) J-value: 0.007794 +/- 0.000021 39 36 40 Corrected for fractionation, Ar, Ar(Ca) and Ar(K) ------Radiogenic ------Step# μmol 40Ar 39Ar/40Ar ± 1SE 36Ar/40Ar ± 1SE 37Ar/39Ar ± 1SE 38Ar/39Ar ± 1SE 40Ar*/39Ar ± 1SE %39Ar Age Ma ± 95% Incl. Ca/K ± 2SE Cl/K ±2SE 1 2.78E-08 5.96E-03 4.2E-05 4.36E-05 1.9E-04 0.00E+00 0.0E+00 9.65E-03 6.0E-03 165.5 1.6 0.2 1495.4 21.3 0 0.00E+00 0.0E+00 1.13E-03 7.0E-04 2 8.68E-07 4.00E-03 9.2E-06 9.80E-06 5.0E-07 1.44E-02 2.6E-03 1.63E-02 5.9E-04 249.2 0.6 4.7 1947.7 12.5 0 2.85E-02 5.2E-03 1.91E-03 7.3E-05 3 1.30E-06 3.78E-03 7.6E-06 7.75E-06 6.9E-07 1.12E-02 3.1E-03 1.55E-02 3.0E-04 264.1 0.5 6.6 2017.6 13.0 0 2.21E-02 6.1E-03 1.82E-03 4.2E-05 4 1.28E-06 3.71E-03 6.1E-06 5.81E-06 3.5E-07 1.45E-02 2.3E-03 1.52E-02 3.4E-04 268.8 0.4 6.4 2038.8 12.9 0 2.88E-02 4.6E-03 1.78E-03 4.5E-05 5 2.12E-06 3.62E-03 4.7E-06 3.14E-06 4.3E-07 8.94E-03 1.3E-03 1.48E-02 2.2E-04 276.3 0.4 8.7 2072.5 12.3 0 1.77E-02 2.5E-03 1.73E-03 3.4E-05 6 2.84E-06 3.51E-03 6.9E-06 1.89E-06 2.7E-07 7.83E-03 1.4E-03 1.40E-02 2.5E-04 284.7 0.6 11.3 2109.7 13.1 1 1.55E-02 2.7E-03 1.64E-03 3.6E-05 7 3.11E-06 3.45E-03 8.2E-06 1.38E-06 3.1E-07 1.19E-02 1.3E-03 1.33E-02 3.2E-04 289.5 0.6 12.1 2130.6 13.0 1 2.36E-02 2.7E-03 1.57E-03 4.2E-05 8 3.08E-06 3.44E-03 7.2E-06 8.21E-07 2.6E-06 8.75E-03 1.9E-03 1.34E-02 1.6E-04 290.3 0.6 11.9 2134.1 13.4 1 1.73E-02 3.7E-03 1.57E-03 2.7E-05 9 3.57E-06 3.45E-03 5.1E-06 2.65E-07 1.5E-06 8.78E-03 1.4E-03 1.33E-02 1.5E-04 289.8 0.4 13.8 2132.0 13.0 1 1.74E-02 2.7E-03 1.56E-03 2.6E-05 10 3.23E-06 3.51E-03 7.4E-06 6.24E-07 1.8E-05 7.37E-03 1.8E-03 1.36E-02 2.6E-04 284.7 0.6 12.8 2109.6 13.5 1 1.46E-02 3.5E-03 1.60E-03 3.7E-05 11 2.06E-06 3.56E-03 6.4E-06 8.60E-07 1.1E-06 1.08E-03 1.9E-03 1.41E-02 3.5E-04 281.1 0.5 8.1 2093.9 12.2 1 2.14E-03 3.7E-03 1.65E-03 4.6E-05 12 4.60E-07 3.67E-03 8.8E-06 3.29E-06 9.4E-06 0.00E+00 0.0E+00 1.46E-02 6.5E-04 272.3 0.7 1.9 2054.9 13.2 0 0.00E+00 0.0E+00 1.72E-03 7.9E-05 13 1.69E-07 3.73E-03 2.1E-05 1.62E-05 3.3E-06 0.00E+00 0.0E+00 1.47E-02 1.3E-03 266.7 1.6 0.7 2029.2 19.1 0 0.00E+00 0.0E+00 1.72E-03 1.5E-04 14 1.33E-07 3.84E-03 2.0E-05 1.81E-05 6.4E-06 5.99E-02 2.8E-02 1.92E-02 1.8E-03 259.0 1.5 0.6 1993.8 17.9 0 1.19E-01 5.6E-02 2.25E-03 2.2E-04 15 4.07E-08 3.83E-03 3.3E-05 4.58E-05 2.5E-05 1.91E-01 5.9E-02 2.37E-02 4.2E-03 257.3 2.7 0.2 1985.9 27.9 0 3.78E-01 1.2E-01 2.78E-03 5.0E-04 Weighted averages of included steps: 8.02E-03 6.4E-04 1.36E-02 1.0E-04 287.1 0.2 70.1 2120.1 12.2 1.59E-02 1.3E-03 1.59E-03 2.3E-05

Temperatures range from c. 600 C for step 1 to fusion (c. 1300 C) at the last 2 to 3 steps Constants used: Heating time: 5 Min. for each step. Atmospheric argon ratios: 40 36 Exponential fractionation factor: -0.298 ( Ar/ Ar)A 298.56 ± 0.31 Lee et al., 2006 38 36 All values regressed to time of gas inlet into mass spectrometer. ( Ar/ Ar)A 0.1885 ± 0.0003 Lee et al., 2006 Blank measurements carried out after 3 or 4 step measurements using exactly same protocol. Interfering isotope production ratios: 40 39 37 Typical Ar blank level at gas-in time: 1E-10 μMol ( Ar/ Ar)Ca (8.6 ± 0.1)E-4 Own calibrations of position B2W in Safari1 reactor 36 37 Measured signals were blank corrected, using blank time functions, before regression. ( Ar/ Ar)Ca (2.8 ± 1.1)E-4 Own calibrations of position B2W in Safari1 reactor 40 39 Ca/K factor: 1.922 ± 0.022 ( Ar/ Ar)K 0.0426 ± 0.0041 Own calibrations of position B2W in Safari1 reactor Cl/K factor: 0.125 ± 0.003 Both from measurements on McClure Mountains hornblende Decay constants:

40 K total (5.541 ± 0.014)E-10 a-1 Kossert and Günther 2004

39Ar 0.00258 ± 0.00003 a-1 Stoenner et al. (1965)

37Ar Renne and Norman (2001) 0.01975 ± 0.0005 day-1

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