Mjølnir structure: An impact crater in the Barents Sea

Dypvik, Henning; Guðlaugsson, Steinar Þór; Tsikalas, Filippos; Attrep, Moses; Ferrell, Ray E.; Krinsley, David H.; Mørk, Atle; Faleide, Jan Inge; Nagy, Jenő

doi:10.1130/0091-7613(1996)024<0779:mlsaic>2.3.co;2

Cited by 99 publications

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“…A welllog derived porosity-depth relationship for siliciclastic sediments (Ø o ∼55%; c 0.42 km− 1 ) developed for the southwestern Barents Sea (Tsikalas 1992) was used to decompact the post-impact sequences. In addition, a uniform Early Cretaceous paleowaterdepth of 500 m was incorporated, consistent with the shallow marine depositional environment (Dypvik et al 1996;Smelror et al 2001). The Mjølnir crater currently lies beneath ∼50-800 m of post-impact sediments (Fig.…”

Section: Reconstruction Of the Original Crater Reliefmentioning

confidence: 88%

Post‐impact structural crater modification due to sediment loading: An overlooked process

Tsikalas

Faleide

2007

Meteorit & Planetary Scien

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Abstract-Post-impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well-preserved impact craters: Mjølnir, Chesapeake Bay, Chicxulub, Montagnais, and Bosumtwi. The analysis demonstrates that the geometry and the structural and stratigraphic relations of post-impact strata provide information about the amplitude, the spatial distribution, and the mode of post-impact deformation. Reconstruction of the original morphology and structure for the Mjølnir, Chicxulub, and Bosumtwi craters demonstrates the long-term subsidence and differential compaction that takes place between the crater and the outside platform region, and laterally within the crater structure. At Mjølnir, the central high developed as a prominent feature during post-impact burial, the height of the peak ring was enhanced, and the cumulative throw on the rim faults was increased. The original Chicxulub crater exhibited considerably less prominent peakring and inner-ring/crater-rim features than the present crater. The original relief of the peak ring was on the order of 420-570 m (currently 535-575 m); the relief on the inner ring/crater rim was 300-450 m (currently ∼700 m). The original Bosumtwi crater exhibited a central uplift/high whose structural relief increased during burial (current height 101-110 m, in contrast to the original height of 85-110 m), whereas the surrounding western part of the annular trough was subdued more that the eastern part, exhibiting original depths of 43-68 m (currently 46 m) and 49-55 m (currently 50 m), respectively. Furthermore, a quantitative model for the porosity change caused by the Chesapeake Bay impact was developed utilizing the modeled density distribution. The model shows that, compared with the surrounding platform, the porosity increased immediately after impact up to 8.5% in the collapsed and brecciated crater center (currently +6% due to post-impact compaction). In contrast, porosity decreased by 2-3% (currently −3 to −4.5% due to post-impact compaction) in the peak-ring region. The lateral variations in porosity at Chesapeake Bay crater are compatible with similar porosity variations at Mjølnir crater, and are considered to be responsible for the moderate Chesapeake Bay gravity signature (annular low of −8 mGal instead of −15 mGal). The analysis shows that the reconstructions and the long-term alterations due to post-impact burial are closely related to the impact-disturbed target-rock volume and a brecciated region of laterally varying thickness and depthvarying physical properties. The study further shows that several crater morphological and structural parameters are prone to post-impact burial modification and are either exaggerated or subdued during post-impact burial. Preliminary correction factors are established based on the integrated reconstruction and post-impact deformation analysis. The crater morphological and structural parameters, corrected from post-impact loading and modification effects, can be used to better const...

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Section: Reconstruction Of the Original Crater Reliefmentioning

confidence: 88%

Post‐impact structural crater modification due to sediment loading: An overlooked process

Tsikalas

Faleide

2007

Meteorit & Planetary Scien

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“…Ejecta and fireball material were deposited and mixed with the common background (clays, silts, organic matter) of marine shelf sediments in the surrounding basin. Shock-metamorphosed grains of quartz and an Ir anomaly have been found in the sediments, which also display changes in the evolution of the sedimentological record (depositional facies) and clay mineralogical composition, for example, the smectite content (Dypvik et al, 1996;Dypvik and Ferrell, 1998). …”

Section: The Mjelnir Impactmentioning

confidence: 99%

“…The crater was formed in the Volgian stage by the impact of an extraterrestrial projectile in the paleoBarents Sea ( Fig. 2) (Gudlaugsson, 1993;Dypvik et al, 1996;Tsikalas et al, 1998 a,b,c). According to Tsikalas et al .…”

Section: The Mjelnir Impactmentioning

confidence: 99%

Geochemical signals of the late Jurassic, marine Mjølnir impact

Dypvik¹,

Attrep²

1999

Meteorit & Planetary Scien

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Abstract-Of the only seven submarine impact craters that have been found globally, the Mj0lnir crater is one of the best preserved and retains crater and ejecta. Geochemical studies (organic pyrolysis using the Rock Eva1 technique and XRF analysis for major, minor, and trace elements) of the Institute for Petroleum Research (IKU) core 7430/10-U-01 that was taken fiom a drillhole located -30 km north-northeast of the crater rim show gradual establishment of anoxic sea floor conditions through the late Jurassic. These poorly ventilated water conditions were overturned due to the Mjslnir impact event. Waves and currents transported impact glass (which is now partly weathered to smectite) into the depositional area where the drillhole is located. The succeeding crater collapse transported impact material (e.g., shocked quartz and Ir) from the crater rim and deeper levels to the core site. Normal marine depositional conditions were established a short time after the crater collapsed.

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“…The CL spectroscopic properties of shocked quartz, as well as its PDFs, have been described from various shock metamorphic environments such as terrestrial impact structures (e.g., Ramseyer et al 1992;Dypvik et al 1996;Seyedolali et al 1997;Boggs et al 2001;Trepmann et al 2005;Götte 2009; Hamers and Drury 2011 and references therein) and shock recovery experiments (Gucsik et al 2003). The question of whether shock metamorphic effects can modify the luminescent nature of quartz under high pressure was first addressed in a pioneering study by Boggs et al (2001).…”

Section: Introductionmentioning

confidence: 99%

“…The luminescence properties of shocked quartz and its shock-induced microstructures both in natural and experimental cases are poorly understood (e.g., Ramseyer et al 1992;Dypvik et al 1996;Seyedolali et al 1997;Boggs et al 2001;Gucsik et al 2003Gucsik et al , 2004Trepmann et al 2005;Götte 2009;Okumura et al 2009;Hamers and Drury 2011 and references therein). In this study our primary aim was to explain the CL behavior of shocked quartz, including the origin and characteristics of the CL signal in PDFs.…”

Section: Introductionmentioning

confidence: 99%

Non-luminescent nature of the planar deformation features in shocked quartz from the Ries impact structure, Germany: A new interpretation

Gucsik¹,

Okumura²,

Nishido³

et al. 2015

Central European Geology

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Quartz grains from the Ries impact structure containing shock-induced microstructures were investigated using Scanning Electron Microscopy in cathodoluminescence (SEM-CL), secondary electron (SEM-SE) and back-scattered electron (SEM-BSE) modes as well as Mott-Seitz analysis. The purpose of this study is to evaluate the mechanism by which CL detects Planar Deformation Features (PDFs) in quartz, which is one of the most important indicators of shock metamorphism in rock-forming minerals. PDFs are micron-scale features not easily identified using optical microscopy or scanning electron microscopy. The CL spectrum of PDFs in quartz that has suffered relatively high shock pressure shows no or a relatively weak emission band at around 385 nm, whereas an emission band with a maximum near 650 nm is observed independent of shock pressure. Thus, the ~385 nm intensity in shocked quartz demonstrates a tendency to decrease with increasing shock metamorphic stage, whereas the 650 nm band remains fairly constant. The result indicates that the emission band at 385 nm is related to the deformed structure of quartz as PDFs.

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Mjølnir structure: An impact crater in the Barents Sea

Cited by 99 publications

References 0 publications

Post‐impact structural crater modification due to sediment loading: An overlooked process

Post‐impact structural crater modification due to sediment loading: An overlooked process

Geochemical signals of the late Jurassic, marine Mjølnir impact

Non-luminescent nature of the planar deformation features in shocked quartz from the Ries impact structure, Germany: A new interpretation

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