Preface 4
Acknowledgements 6
Contents 7
Contributors 9
1 Introduction 11
1.1 Background 11
1.2 Barents Sea Geology 14
1.3 Mjlnir Impact at Volgian/Ryazanian Boundary 20
1.4 The Investigation History of Mjlnir 22
1.5 The Search for Oil and Gas in the Barents Sea 28
1.6 Future Mjlnir Studies 29
1.7 Etymology 32
2 Geological Framework 33
2.1 Plate Tectonic Evolution of the Arctic 33
2.2 Mesozoic Stratigraphy and Depositional Environments of the Arctic 34
2.2.1 Geological and Palaeogeographical Setting 36
2.2.1.1 Cretaceous Palaeogeographic Setting 36
2.2.1.2 The Barents Sea in Time and Space 37
2.2.2 Svalbard 38
2.2.3 Barents Sea 44
2.2.4 Greenland 46
2.2.5 Siberia 50
2.2.6 Late Jurassic and Early Cretaceous Depositional Configuration 52
3 Impact Structure and Morphology 56
3.1 Seismic Reflection Database 56
3.2 Shallow Structure 61
3.2.1 Main Features 61
3.2.2 Detailed Seismic Correlation to Nearby Shallow Boreholes 65
3.2.2.1 Borehole 7430/10-U-01 65
3.2.2.2 Borehole 7329/03-U-01 70
3.2.2.3 Impact Timing as Revealed from Seismic Correlation 72
3.2.3 Impact-Induced Deformation 73
3.2.4 Near-Field Erosional Features 75
3.2.4.1 Resurge Gullies 75
3.2.4.2 Crater Rim 77
3.3 Deep Structure 78
3.3.1 Impact-Induced Disturbance 78
3.3.1.1 Seismic Reflectivity Patterns 78
3.3.1.2 Shape and Dimensions 81
4 Impact Geophysics and Modelling 83
4.1 Features Related to the Cratering Process 83
4.1.1 Excavated Crater and Breccia 83
4.1.2 Impact Melts 89
4.1.3 Gravitational Collapse 90
4.1.4 Structural Uplift 91
4.2 Impact into a Marine Sedimentary Basin 93
4.3 Impact Crater Modelling 97
4.3.1 Potential Field Data 97
4.3.2 Marine Gravity Anomalies and Modelling 99
4.3.3 Marine Magnetic Anomalies and Modelling 105
4.3.4 Traveltime/Velocity Anomalies and Modelling 107
4.4 Modelled Porosity Anomalies 109
4.4.1 Density-Derived Porosity Anomaly 110
4.4.2 Velocity-Derived Porosity Anomaly 112
4.4.3 Postimpact Deformation-Derived Porosity Anomaly 112
4.4.4 Porosity Anomaly and Pore Space Volume 114
4.4.5 Porosity Anomaly and Hydrocarbon Potential 115
4.5 Potential Non-impact Origin 118
4.5.1 Clay Diapir 119
4.5.2 Salt Diapir 119
4.5.3 Igneous Feature 122
4.6 Alternative Interpretation of Mjlnir Crater Dimensions Based on Regional Gravity and Aero-magnetic Profiles and Modelling 122
4.6.1 The Mj酶lnir Aero-magnetic Anomaly 123
4.6.2 The Mj酶lnir Regional Free-Air Gravity Anomaly 125
4.6.3 Alternative Interpretation of Mj酶lnir Crater Dimensions 126
4.7 Impact-Induced Changes in Physical Properties 131
4.8 Mjlnir as an Oblique Impact Event 133
4.8.1 Elongated Crater Diameter 133
4.8.2 Seismic Disturbance Asymmetry 134
4.8.3 Peak-Ring Character 136
4.8.4 Offsets in Brecciation and Structural Uplift 137
4.8.5 Impact Direction and Angle 138
4.8.6 Mj酶lnir Impact Obliquity Constrains Models for Near-Field Perturbations 141
4.8.6.1 Nature and Distribution of Proximal Ejecta 142
4.8.6.2 Tsunami-Wave Distribution 143
5 Impact Cratering and Post-impact Sedimentation 146
5.1 Introduction 146
5.2 The Mjlnir Crater Core (7329/03-U-01) 147
5.2.1 The Ragnarok Formation 147
5.2.2 Ragnarok Formation, Unit I 152
5.2.3 Ragnarok Formation, Unit II 154
5.2.4 Hekkingen Formation 163
5.2.5 Klippfisk Formation 164
5.2.6 Spectral Gamma Results 166
5.2.7 Paleontology of the Ragnarok Formation 166
5.2.8 Paleontology of the Hekkingen Formation 168
5.2.9 Magnetic Properties and Densities of the Mj酶lnir Crater Core (7329/03-U-01) 169
5.3 The Mjlnir Impact Event in a Sequence Stratigraphical Framework 169
5.4 The Evidence for Impact Crater Formation 174
5.4.1 The Crater: Its Structure and Shape 174
5.4.2 Fracturing and Conglomerates 175
5.4.3 Mineralogical Evidence of Impact Cratering 175
5.4.4 Geochemistry 177
5.4.5 Paleontological Evidence of Impact Cratering 180
6 Ejecta Geology 182
6.1 The Identification of Ejecta Beds 182
6.1.1 Introduction 182
6.1.2 The Ragnarok Formation and Sindre Bed 183
6.1.3 The Discoveries of Large Amounts of Soot in Mj酶lnir Related Sediments 189
6.2 The Stratigraphical Distribution of the Ejecta Beds 197
6.2.1 Borehole 7430/10-U-01 198
6.2.2 Borehole 7018/05-U-01 200
6.2.3 Janusfjellet, Central Spitsbergen 200
6.2.4 Nordvik Peninsula, North-Western Siberia 201
6.2.5 The Mj酶lnir Ejecta as a Regional Stratigraphic Marker 201
7 The Impact Dynamics 202
7.1 Introduction 202
7.2 Numerical Model 203
7.3 Cratering Process 204
7.4 Ejecta Formation and Distribution 209
7.5 Resurge Flow and Tsunami Generation 214
7.6 Conclusions 216
8 Structural Analysis of Deformed Central Peak Sediments 217
8.1 Structural Position of the Mjlnir Impact Crater 217
8.2 Structural Geological Analysis 218
8.2.1 Type A Structures: Early Extensional Micro-faults and Fissures 219
8.2.2 Type B-Structures: Fragmentation of Semi-consolidated or Consolidated Beds 223
8.2.3 Type C-Structures: Liquefaction and Shearing 224
8.2.4 Type D-Structures: Folds, Rotated Strata and Shear Bands 226
8.2.5 Type E-Structures: Intensely Sheared Sequences 227
8.2.6 Type F-Structures: Late Brittle Fractures and Microfaults 228
8.3 Deformation History of the Ragnarok Formation 230
9 Postimpact Deformation Due to Sediment Loading: The Mjlnir Paradigm 235
9.1 Postimpact Burial 235
9.2 Mjlnir Crater 237
9.2.1 Postimpact Infilling 238
9.2.2 Faulting and Differential Vertical Movements 240
9.3 Other Craters: Chesapeake Bay, Chicxulub, Bosumtwi, and Montagnais 241
9.4 Original Crater Relief Reconstruction 245
9.4.1 Mj酶lnir 247
9.4.2 Chicxulub 251
9.4.3 Bosumtwi 255
9.4.4 Chesapeake Bay 256
9.5 Correction of Crater Morphological and Structural Parameters 258
9.5.1 Parameters Prone to Postimpact Burial Modification 258
9.5.2 Postimpact Modification Correction Factor 261
10 The Mjlnir Tsunami 263
10.1 Introduction 263
10.2 Tsunami Models 264
10.3 Tsunami Generation 266
10.3.1 Near Field Evolution 267
10.3.2 Far Field Propagation 272
10.3.2.1 Estimates of Far-Field Behaviour 272
10.3.2.2 Computations of Far-Field Behaviour 274
10.4 Discussion 276
References 279
Index 1
Index 300