The Extraterrestrial Origin of Canadian Craters

Dence, M. R.

doi:10.1111/j.1749-6632.1965.tb20411.x

Cited by 103 publications

(77 citation statements)

References 20 publications

(17 reference statements)

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“…The range of impactor sizes investigated also included impacts that form both simple and complex craters. Simple craters are bowlshaped depressions, with a raised rim and a depth-to-diameter ratio of about 0.2, that form on Earth with diameters smaller than ∼2-4 km (Dence 1965). Complex craters are larger.…”

Section: Methodsmentioning

confidence: 99%

The effect of the oceans on the terrestrial crater size‐frequency distribution: Insight from numerical modeling

Davison

Collins

2007

Meteorit & Planetary Scien

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available online at http://meteoritics.orgThe effect of the oceans on the terrestrial crater size-frequency distribution:Insight from numerical modeling Abstract-On Earth, oceanic impacts are twice as likely to occur as continental impacts, yet the effect of the oceans has not been previously considered when estimating the terrestrial crater size-frequency distribution. Despite recent progress in understanding the qualitative and quantitative effect of a water layer on the impact process through novel laboratory experiments, detailed numerical modeling, and interpretation of geological and geophysical data, no definitive relationship between impactor properties, water depth, and final crater diameter exists. In this paper, we determine the relationship between final (and transient) crater diameter and the ratio of water depth to impactor diameter using the results of numerical impact models. This relationship applies for normal incidence impacts of stoney asteroids into water-covered, crystalline oceanic crust at a velocity of 15 km s −1 . We use these relationships to construct the first estimates of terrestrial crater size-frequency distributions (over the last 100 million years) that take into account the depth-area distribution of oceans on Earth. We find that the oceans reduce the number of craters smaller than 1 km in diameter by about two-thirds, the number of craters ~30 km in diameter by about one-third, and that for craters larger than ~100 km in diameter, the oceans have little effect. Above a diameter of ~12 km, more craters occur on the ocean floor than on land; below this diameter more craters form on land than in the oceans. We also estimate that there have been in the region of 150 impact events in the last 100 million years that formed an impact-related resurge feature, or disturbance on the seafloor, instead of a crater.

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Section: Methodsmentioning

confidence: 99%

The effect of the oceans on the terrestrial crater size‐frequency distribution: Insight from numerical modeling

Davison

Collins

2007

Meteorit & Planetary Scien

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“…At older structures (e.g., Dence, 1965Dence, , 1968, distinctively shocked rocks tend to be preserved in only two areas: in the target rocks immediately beneath the crater floor, and in the breccia and melt deposits that fill the crater itself. natures, ant unusual glassy objects.…”

Section: MMmentioning

confidence: 99%

“…However, in many of these structures, erosion has largely removed the ejecta deposits outside the crater, and the suevites occur only as crater-fill units, where they are associated with, and often interbedded with, lithic breccias and impact-melt rocks. Examples include Brent (Canada) (Dence, 1965(Dence, , 1968Grieve, 1978); Rochechouart (France) (Kraut and French, 1971); Popigai (Russia) (Masaitis et al, 1980;Masaitis, 1994); Manson (Iowa) (KoeberlandAnderson, 1996a;Koeberletal., 1996b); Gardnos (Norway) (French et al, 1997); Slate Islands (Canada) (Dressier and Sharpton, 1997); and Roter Kamm (Namibia) (Reimoldet al, 1997a).…”

Section: Pseudotachylitementioning

confidence: 99%

“…In earlier discussions ofimpactites and the cratering process (Dence, 1965(Dence, , 1968Grieve, 1991), a fundamental and useful distinction has been made between the parautochthonous rocks beneath the crater floor and the allogenie (or allochthonous) units (breccias and melt rocks) that fill the crater (crater-fill units) and form the units of ejecta outside it (Figs. 3.7 and 3.13).…”

Section: Classification Of Impactitesmentioning

confidence: 99%

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Traces of catastrophe: a handbook of shock-metamorphic effects in terrestrial meteorite impact structures

French

1999

Choice Reviews Online

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“…From a geomorphic point of view, impact structures are classifi ed as simple or complex (Dence, 1965). Simple impact structures are generally circular depressions with diameters between 3 and 6 km, depending on the host rock, with approximately parabolic cross--profi les and raised margins (ex: Barringer Meteor Crater, Arizona -USA).…”

Section: São Miguel Do Tapuio Circular Structurementioning

confidence: 99%

Análise Morfológica Da Estrutura Circular De São Miguel Do Tapuio, Piauí - Brasil

Martins

Branco

Castro

et al. 2016

Rev. Bras. Geomorfol.

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Abstract:The São Miguel do Tapuio Circular Structure (SMTCS) is one of the largest recognized in the Phanerozoic sedimentary rocks of the Parnaiba Basin, in Piauí (PI), Brazil. Research works on the genesis of the SMTCS consider either an endogenetic origin or meteoritic impact formation. The present study is based on bibliographic survey, fi eldwork and laboratory analyses (remote sensing). The SMTCS superfi cial morphological features, their organization, total diameter, multi-directional pattern and high density of lineaments inside the structure were characterized by remote sensing. Also, the morphostructural units such as the outer margin, intermediate ring, annular depression and a central topographic high were defi ned. The fi eldwork allowed identifying a variable thermal metamorphism in the Keywords:Bacia do Parnaíba; Astroblemas; Sensoriamento Remoto. 764Martins J. A. et al. Rev. Bras. Geomorfol. (Online), São Paulo, v.17, n.4, (Out-Dez) p.763-781, 2016 sandstones that formed the SMTCS. The metamorphism grade increased clearly from the margin to the center, with the presence of highly recrystallized and consolidated metasandstones around the center of the structure. Finally, the geomorphic characterization and the geometric signature obtained for the SMTCS seem to correspond to those of complex impact structures (presence of a central uplift). Moreover, the identifi cation of macro and microscopic deformation structures in the sandstones (while not typical of shock origin) may be more conclusive of a meteoritic origin, and the lack of evidence of igneous activity might explain the observed thermal metamorphism. Resumo:A estrutura circular de São Miguel do Tapuio (ECSMT) corresponde a uma das maiores do gênero registrada em rochas sedimentares fanerozoicas da Bacia do Parnaíba, Estado do Piauí, Brasil. As pesquisas considerando a gênese da ECSMT dividem-se entre uma origem endógena e uma através de impacto meteorítico. No presente estudo foram realizados trabalhos envolvendo o estágio do conhecimento atual, campo e laboratoriais (sensoriamento remoto). Os trabalhos de sensoriamento serviram para delinear a confi guração morfológica superfi cial, o diâmetro total e compartimentos, bem como o padrão multidirecional e alta densidade dos lineamentos no interior da estrutura. Puderam ser defi nidas unidades morfoestruturais como a borda externa, o anel intermediário, a depressão anelar e um alto topográfi co central. Os trabalhos de campo evidenciaram uma intensidade de metamorfi smo termal variável observado nos arenitos interiores à ECSMT. Da borda para o centro observa-se nítido aumento no grau de metamorfi smo nos arenitos, caracterizando metarenitos intensamente recristalizados e consolidados no entorno do centro da estrutura. Finalizando, a caracterização morfológica superfi cial e a assinatura geométrica obtida para a ECSMT são semelhantes e condizentes com várias estruturas de impacto do tipo complexa (presença de um núcleo soerguido). Somado a estes fatos temos a presença de estruturas deformaci...

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The Extraterrestrial Origin of Canadian Craters

Cited by 103 publications

References 20 publications

The effect of the oceans on the terrestrial crater size‐frequency distribution: Insight from numerical modeling

The effect of the oceans on the terrestrial crater size‐frequency distribution: Insight from numerical modeling

Traces of catastrophe: a handbook of shock-metamorphic effects in terrestrial meteorite impact structures

Análise Morfológica Da Estrutura Circular De São Miguel Do Tapuio, Piauí - Brasil

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