Tsikalas / Smelror The Mjølnir Impact Event and its Consequences

Geology and Geophysics of a Late Jurassic/Early Cretaceous Marine Impact Event
1. Auflage 2010
ISBN: 978-3-540-88260-2
Verlag: Springer-Verlag
Format: PDF
Kopierschutz: Wasserzeichen (»Systemvoraussetzungen)

E-Book, Englisch, 320 Seiten

The Mjølnir impact structure was recognized in 1993 and included in the Earth Impact Database in 1996, based on the discoveries of unequivocal meteorite impact indicators such as shocked quartz, Ir-enrichments, possible glass remnants, fragments of nickel-rich iron oxides, in addition to the convincing complex crater shape of the structure. This book presents the geological and geophysical history of the Barents Sea region along with the discovery of the Mjølnir impact crater. We place the Mjølnir event into the geological framework of the region and present elaborative numerical models of its formation and associated tsunami generation. The book represents an update and synthesis as well as the complete compilation of the Mjølnir crater studies.

Autoren/Hrsg.

Tsikalas, Filippos

Smelror, Morten

Inhaltsverzeichnis

1;Preface;5
2;Acknowledgements;7
3;Contents;8
4;Contributors;10
5;1 Introduction;12
5.1;1.1 Background;12
5.2;1.2 Barents Sea Geology;15
5.3;1.3 Mjlnir Impact at Volgian/Ryazanian Boundary;21
5.4;1.4 The Investigation History of Mjlnir;23
5.5;1.5 The Search for Oil and Gas in the Barents Sea;29
5.6;1.6 Future Mjlnir Studies;30
5.7;1.7 Etymology;33
6;2 Geological Framework;34
6.1;2.1 Plate Tectonic Evolution of the Arctic;34
6.2;2.2 Mesozoic Stratigraphy and Depositional Environments of the Arctic;35
6.2.1;2.2.1 Geological and Palaeogeographical Setting;37
6.2.1.1;2.2.1.1 Cretaceous Palaeogeographic Setting;37
6.2.1.2;2.2.1.2 The Barents Sea in Time and Space;38
6.2.2;2.2.2 Svalbard;39
6.2.3;2.2.3 Barents Sea;45
6.2.4;2.2.4 Greenland;47
6.2.5;2.2.5 Siberia;51
6.2.6;2.2.6 Late Jurassic and Early Cretaceous Depositional Configuration;53
7;3 Impact Structure and Morphology;57
7.1;3.1 Seismic Reflection Database;57
7.2;3.2 Shallow Structure;62
7.2.1;3.2.1 Main Features;62
7.2.2;3.2.2 Detailed Seismic Correlation to Nearby Shallow Boreholes;66
7.2.2.1;3.2.2.1 Borehole 7430/10-U-01;66
7.2.2.2;3.2.2.2 Borehole 7329/03-U-01;71
7.2.2.3;3.2.2.3 Impact Timing as Revealed from Seismic Correlation;73
7.2.3;3.2.3 Impact-Induced Deformation;74
7.2.4;3.2.4 Near-Field Erosional Features;76
7.2.4.1;3.2.4.1 Resurge Gullies;76
7.2.4.2;3.2.4.2 Crater Rim;78
7.3;3.3 Deep Structure;79
7.3.1;3.3.1 Impact-Induced Disturbance;79
7.3.1.1;3.3.1.1 Seismic Reflectivity Patterns;79
7.3.1.2;3.3.1.2 Shape and Dimensions;82
8;4 Impact Geophysics and Modelling;84
8.1;4.1 Features Related to the Cratering Process;84
8.1.1;4.1.1 Excavated Crater and Breccia;84
8.1.2;4.1.2 Impact Melts;90
8.1.3;4.1.3 Gravitational Collapse;91
8.1.4;4.1.4 Structural Uplift;92
8.2;4.2 Impact into a Marine Sedimentary Basin;94
8.3;4.3 Impact Crater Modelling;98
8.3.1;4.3.1 Potential Field Data;98
8.3.2;4.3.2 Marine Gravity Anomalies and Modelling;100
8.3.3;4.3.3 Marine Magnetic Anomalies and Modelling;106
8.3.4;4.3.4 Traveltime/Velocity Anomalies and Modelling;108
8.4;4.4 Modelled Porosity Anomalies;110
8.4.1;4.4.1 Density-Derived Porosity Anomaly;111
8.4.2;4.4.2 Velocity-Derived Porosity Anomaly;113
8.4.3;4.4.3 Postimpact Deformation-Derived Porosity Anomaly;113
8.4.4;4.4.4 Porosity Anomaly and Pore Space Volume;115
8.4.5;4.4.5 Porosity Anomaly and Hydrocarbon Potential;116
8.5;4.5 Potential Non-impact Origin;119
8.5.1;4.5.1 Clay Diapir;120
8.5.2;4.5.2 Salt Diapir;120
8.5.3;4.5.3 Igneous Feature;123
8.6;4.6 Alternative Interpretation of Mjlnir Crater Dimensions Based on Regional Gravity and Aero-magnetic Profiles and Modelling;123
8.6.1;4.6.1 The Mjølnir Aero-magnetic Anomaly;124
8.6.2;4.6.2 The Mjølnir Regional Free-Air Gravity Anomaly;126
8.6.3;4.6.3 Alternative Interpretation of Mjølnir Crater Dimensions;127
8.7;4.7 Impact-Induced Changes in Physical Properties;132
8.8;4.8 Mjlnir as an Oblique Impact Event;134
8.8.1;4.8.1 Elongated Crater Diameter;134
8.8.2;4.8.2 Seismic Disturbance Asymmetry;135
8.8.3;4.8.3 Peak-Ring Character;137
8.8.4;4.8.4 Offsets in Brecciation and Structural Uplift;138
8.8.5;4.8.5 Impact Direction and Angle;139
8.8.6;4.8.6 Mjølnir Impact Obliquity Constrains Models for Near-Field Perturbations;142
8.8.6.1;4.8.6.1 Nature and Distribution of Proximal Ejecta;143
8.8.6.2;4.8.6.2 Tsunami-Wave Distribution;144
9;5 Impact Cratering and Post-impact Sedimentation;147
9.1;5.1 Introduction;147
9.2;5.2 The Mjlnir Crater Core (7329/03-U-01);148
9.2.1;5.2.1 The Ragnarok Formation;148
9.2.2;5.2.2 Ragnarok Formation, Unit I;153
9.2.3;5.2.3 Ragnarok Formation, Unit II;155
9.2.4;5.2.4 Hekkingen Formation;164
9.2.5;5.2.5 Klippfisk Formation;165
9.2.6;5.2.6 Spectral Gamma Results;167
9.2.7;5.2.7 Paleontology of the Ragnarok Formation;167
9.2.8;5.2.8 Paleontology of the Hekkingen Formation;169
9.2.9;5.2.9 Magnetic Properties and Densities of the Mjølnir Crater Core (7329/03-U-01);170
9.3;5.3 The Mjlnir Impact Event in a Sequence Stratigraphical Framework;170
9.4;5.4 The Evidence for Impact Crater Formation;175
9.4.1;5.4.1 The Crater: Its Structure and Shape;175
9.4.2;5.4.2 Fracturing and Conglomerates;176
9.4.3;5.4.3 Mineralogical Evidence of Impact Cratering;176
9.4.4;5.4.4 Geochemistry;178
9.4.5;5.4.5 Paleontological Evidence of Impact Cratering;181
10;6 Ejecta Geology;183
10.1;6.1 The Identification of Ejecta Beds;183
10.1.1;6.1.1 Introduction;183
10.1.2;6.1.2 The Ragnarok Formation and Sindre Bed;184
10.1.3;6.1.3 The Discoveries of Large Amounts of Soot in Mjølnir Related Sediments;190
10.2;6.2 The Stratigraphical Distribution of the Ejecta Beds;198
10.2.1;6.2.1 Borehole 7430/10-U-01;199
10.2.2;6.2.2 Borehole 7018/05-U-01;201
10.2.3;6.2.3 Janusfjellet, Central Spitsbergen;201
10.2.4;6.2.4 Nordvik Peninsula, North-Western Siberia;202
10.2.5;6.2.5 The Mjølnir Ejecta as a Regional Stratigraphic Marker;202
11;7 The Impact Dynamics;203
11.1;7.1 Introduction;203
11.2;7.2 Numerical Model;204
11.3;7.3 Cratering Process;205
11.4;7.4 Ejecta Formation and Distribution;210
11.5;7.5 Resurge Flow and Tsunami Generation;215
11.6;7.6 Conclusions;217
12;8 Structural Analysis of Deformed Central Peak Sediments;218
12.1;8.1 Structural Position of the Mjlnir Impact Crater;218
12.2;8.2 Structural Geological Analysis;219
12.2.1;8.2.1 Type A Structures: Early Extensional Micro-faults and Fissures;220
12.2.2;8.2.2 Type B-Structures: Fragmentation of Semi-consolidated or Consolidated Beds;224
12.2.3;8.2.3 Type C-Structures: Liquefaction and Shearing;225
12.2.4;8.2.4 Type D-Structures: Folds, Rotated Strata and Shear Bands;227
12.2.5;8.2.5 Type E-Structures: Intensely Sheared Sequences;228
12.2.6;8.2.6 Type F-Structures: Late Brittle Fractures and Microfaults;229
12.3;8.3 Deformation History of the Ragnarok Formation;231
13;9 Postimpact Deformation Due to Sediment Loading: The Mjlnir Paradigm;236
13.1;9.1 Postimpact Burial;236
13.2;9.2 Mjlnir Crater;238
13.2.1;9.2.1 Postimpact Infilling;239
13.2.2;9.2.2 Faulting and Differential Vertical Movements;241
13.3;9.3 Other Craters: Chesapeake Bay, Chicxulub, Bosumtwi, and Montagnais;242
13.4;9.4 Original Crater Relief Reconstruction;246
13.4.1;9.4.1 Mjølnir;248
13.4.2;9.4.2 Chicxulub;252
13.4.3;9.4.3 Bosumtwi;256
13.4.4;9.4.4 Chesapeake Bay;257
13.5;9.5 Correction of Crater Morphological and Structural Parameters;259
13.5.1;9.5.1 Parameters Prone to Postimpact Burial Modification;259
13.5.2;9.5.2 Postimpact Modification Correction Factor;262
14;10 The Mjlnir Tsunami;264
14.1;10.1 Introduction;264
14.2;10.2 Tsunami Models;265
14.3;10.3 Tsunami Generation;267
14.3.1;10.3.1 Near Field Evolution;268
14.3.2;10.3.2 Far Field Propagation;273
14.3.2.1;10.3.2.1 Estimates of Far-Field Behaviour;273
14.3.2.2;10.3.2.2 Computations of Far-Field Behaviour;275
14.4;10.4 Discussion;277
15;References;280
16;Index;301