" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico's Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society's imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia's portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia's major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.

PART I CHAPTER 1 T E — , , . . . . . . . . . 15 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Geological change — the answers within, and without. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Man on the Moon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Back to the beginning — from the Big Bang to early Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Impact — the ubiquitous process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The oldest rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Time to cool — birth of the Kaapvaal continent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Old crust in the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Rifting, oceans, volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Mountains, fire and ice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 The unique Bushveld magmatic event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 CHAPTER 2 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 49 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Extinction or survival — our restless Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Meteorite-impact catastrophes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Normal (background) versus mass extinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 A brief look at the impact record in the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 What are the projectiles capable of causing an impact catastrophe?. . . . . . . . . . . . . . . . . . . . . . . 87 What is an impact crater? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 How can we identify impact structures? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Shock metamorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 CHAPTER 3 T A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Tswaing meteorite crater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Does Tswaing have a twin? (Kalkkop Crater, Eastern Cape Province) . . . . . . . . . . . . . . . . . . . . . . . 108 South Africa’ s other Giant Impact Morokweng impact structure, — North West Province . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Our southern African neighbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Testimony of earliest impact catastrophe — Barberton and the Northern Cape Province . . 113 Traces of catastrophe in the Karoo?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6 CHAPTER 4 V : T W . . . 117 The Vredefort Structure revealed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Getting to know the giant: By road through the Vredefort Structure . . . . . . . . . . . . . . . . . . . 120 Traversing the outer parts of the Vredefort Dome (Fochville to Parys) . . . . . . . . . . . . . . . . . . 12 5 The geology of the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PART I CHAPTER 1 T E — , , . . . . . . . . . 15 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Geological change — the answers within, and without. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Man on the Moon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Back to the beginning — from the Big Bang to early Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Impact — the ubiquitous process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The oldest rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Time to cool — birth of the Kaapvaal continent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Old crust in the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Rifting, oceans, volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Mountains, fire and ice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 The unique Bushveld magmatic event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 CHAPTER 2 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 49 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Extinction or survival — our restless Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Meteorite-impact catastrophes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Normal (background) versus mass extinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 A brief look at the impact record in the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 What are the projectiles capable of causing an impact catastrophe?. . . . . . . . . . . . . . . . . . . . . . . 87 What is an impact crater? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 How can we identify impact structures? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Shock metamorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 CHAPTER 3 T A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Tswaing meteorite crater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Does Tswaing have a twin? (Kalkkop Crater, Eastern Cape Province) . . . . . . . . . . . . . . . . . . . . . . . 108 South Africa’ s other Giant Impact Morokweng impact structure, — North West Province . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Our southern African neighbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Testimony of earliest impact catastrophe — Barberton and the Northern Cape Province . . 113 Traces of catastrophe in the Karoo?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6 CHAPTER 4 V : T W . . . 117 The Vredefort Structure revealed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Getting to know the giant: By road through the Vredefort Structure . . . . . . . . . . . . . . . . . . . 120 Traversing the outer parts of the Vredefort Dome (Fochville to Parys) . . . . . . . . . . . . . . . . . . 12 5 The geology of the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico''s Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society''s imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia''s portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia''s major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.

" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico's Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society's imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia's portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia's major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.

" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico's Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society's imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia's portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia's major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.

PART I CHAPTER 1 T E — , , . . . . . . . . . 15 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Geological change — the answers within, and without. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Man on the Moon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Back to the beginning — from the Big Bang to early Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Impact — the ubiquitous process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The oldest rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Time to cool — birth of the Kaapvaal continent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Old crust in the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Rifting, oceans, volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Mountains, fire and ice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 The unique Bushveld magmatic event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 CHAPTER 2 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 49 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Extinction or survival — our restless Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Meteorite-impact catastrophes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Normal (background) versus mass extinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 A brief look at the impact record in the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 What are the projectiles capable of causing an impact catastrophe?. . . . . . . . . . . . . . . . . . . . . . . 87 What is an impact crater? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 How can we identify impact structures? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Shock metamorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 CHAPTER 3 T A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Tswaing meteorite crater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Does Tswaing have a twin? (Kalkkop Crater, Eastern Cape Province) . . . . . . . . . . . . . . . . . . . . . . . 108 South Africa’ s other Giant Impact Morokweng impact structure, — North West Province . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Our southern African neighbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Testimony of earliest impact catastrophe — Barberton and the Northern Cape Province . . 113 Traces of catastrophe in the Karoo?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6 CHAPTER 4 V : T W . . . 117 The Vredefort Structure revealed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Getting to know the giant: By road through the Vredefort Structure . . . . . . . . . . . . . . . . . . . 120 Traversing the outer parts of the Vredefort Dome (Fochville to Parys) . . . . . . . . . . . . . . . . . . 12 5 The geology of the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PART I CHAPTER 1 T E — , , . . . . . . . . . 15 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Geological change — the answers within, and without. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Man on the Moon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Back to the beginning — from the Big Bang to early Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Impact — the ubiquitous process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The oldest rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Time to cool — birth of the Kaapvaal continent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Old crust in the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Rifting, oceans, volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Mountains, fire and ice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 The unique Bushveld magmatic event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 CHAPTER 2 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 49 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Extinction or survival — our restless Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Meteorite-impact catastrophes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Normal (background) versus mass extinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 A brief look at the impact record in the Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 What are the projectiles capable of causing an impact catastrophe?. . . . . . . . . . . . . . . . . . . . . . . 87 What is an impact crater? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 How can we identify impact structures? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Shock metamorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 CHAPTER 3 T A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Tswaing meteorite crater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Does Tswaing have a twin? (Kalkkop Crater, Eastern Cape Province) . . . . . . . . . . . . . . . . . . . . . . . 108 South Africa’ s other Giant Impact Morokweng impact structure, — North West Province . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Our southern African neighbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Testimony of earliest impact catastrophe — Barberton and the Northern Cape Province . . 113 Traces of catastrophe in the Karoo?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6 CHAPTER 4 V : T W . . . 117 The Vredefort Structure revealed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Getting to know the giant: By road through the Vredefort Structure . . . . . . . . . . . . . . . . . . . 120 Traversing the outer parts of the Vredefort Dome (Fochville to Parys) . . . . . . . . . . . . . . . . . . 12 5 The geology of the Vredefort Dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico''s Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society''s imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia''s portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia''s major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.

" . . . bangs have replaced whimpers and the geological record has become much more exciting than it was thought to be. " Derek Ager (1993) The New Catastro­ phism. Cambridge University Press, Cambridge, p xix Scientific and public interest in asteroids, comets, and meteorite impacts has never been more intense than right now. Much of this interest stems from the fervent debates surrounding the causes of the Cretaceous-Tertiary mass extinctions and their possible relationships to a giant bolide impact in Mexico's Yucatan Penin­ sula. Recent spectacular impacts on Jupiter, and several near misses of our own planet by Near-Earth Objects have intensified professional and popular discussion of society's imperative need to understand the process and effects of bolide im­ pacts. In the United States, the scientific community and the public, as well, were startled to learn, in 1994, that the largest impact structure in this country had been detected beneath Virginia's portion of the Chesapeake Bay. Seismic surveys and deep coring revealed a huge crater, 85 kilometers in diameter and more than a kilometer deep, stretching from Yorktown, Virginia, to 15 kilometers out onto the shallow continental shelf. Several of Virginia's major population centers, includ­ ing Norfolk, Hampton, and Newport News, are located on the western rim of the crater, and still experience residual effects of the original collision, 36 million years after the impact took place. Exploration and documentation of the Chesapeake Bay impact structure has proceeded in three phases.