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Impact cratering is one of the fundamental processes in our planetary system and an important factor in forming the lithosphere of the Earth and the planets. The active surface processes on Earth, e.g. weathering, erosion, plate tectonics, and volcanism change the Earth’s surface continuously. Therefore only a modest number of crater structures have been preserved and discovered on the surface of...
The Arctic Ocean comprises two main deep subocean basins, the Amerasia and Eurasia basins, separated by the elongate Lomonosov Ridge (Fig. 2.1). In a plate tectonic framework the Eurasia Basin is linked to the Norwegian-Greenland Sea and the Atlantic through the northernmost part of the Eurasia-North America plate boundary (Fig. 2.2). The plate boundary comprises two mid-ocean ridges, the Knipovich...
The Mjølnir crater (Fig. 3.1) was first interpreted as an impact structure by Gudlaugsson (1993) based on its geophysical signature and overall geological setting. This inference was derived from a limited amount of multichannel seismic profiles, and regional gravity and magnetic profiles. The impact hypothesis prompted the acquisition of high-resolution seismic, gravity and magnetic profiles by the...
During impact, the passage of the shock wave results in extensive in situ fracturing and autochthonous target rock brecciation. Target material is excavated and ejected in ballistic trajectories upward and outward from the impact site. As excavation of the brecciated volume advances, the excavated crater is formed. It delimits the provenance of material expelled from the crater and provides the void...
The impact origin of the Mjølnir structure has been confirmed by detailed studies of lithologies from two shallow boreholes; one close to the crater center (7329/03-U-01) and one 30 km NE from the crater periphery (7430/10-U-01) (Fig. 1.7). The boreholes revealed brecciated sediments containing shocked quartz grains. In 7430/10-U-01 a prominent ejecta layer with strong iridium enrichment has been...
Ejecta recognition is an important factor in impact research and has been a key element in the Mjølnir impact studies. The characterization of ejecta covers several different geological and geophysical topics as summarized in French (1998) and Montanari and Koeberl (2000). In particular in studies of marine impact events (submarine craters) or in cases where the impact site has not been recognized,...
Together with geological/geophysical studies and laboratory-scale experiments numerical simulations of impacts contribute a great deal to our knowledge of the cratering process. Whereas field studies give information about target conditions and final crater configuration, numerical modeling allow us to follow the evolving process in time and to reconstruct several important features not surviving...
The buried Mjølnir crater in the Barents Sea (Figs. 1.8 and 1.10) classifies as a complex impact structure with a central peak and an initially subtle peak ring (Gudlaugsson 1993; Dypvik et al. 1996, 2004b; Tsikalas et al. 1999). The Mjølnir bolide hit the paleo-Barents Sea (˜400–500 m water-depth at the time of impact) at an impact angle of 45° from a SW-SSW direction (Tsikalas ). The crater later...
Although protective at initial stages, extensive burial and associated processes, such as mechanical- and chemical-compaction, and diagenesis, may eventually lead to considerable changes in the original crater structure and morphology. Extensive postimpact modifications may obscure many marine impact craters formed in sedimentary, water-covered targets. The same postimpact processes may result in...
Propagation characteristics of impact-generated tsunamis are different from most tsunami originating from other sources in that both nonlinearity and dispersion remain important for a long time after generation. This is particularly true for bolides with diameters that are comparable to, or larger than, the ocean depth. Submarine earthquakes and mass gravity flows on the other hand generally produce...
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