Age measurement of the submarine montagnais impact crater

Bottomley, R. J.; York, Derek

doi:10.1029/gl015i012p01409

Cited by 24 publications

(9 citation statements)

References 8 publications

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“…Such a location is also supported by the findings of Wu (1992a, 1993). This would have made the Montagnais crater, 200 km southeast of Nova Scotia, the first underwater crater ever discovered (Jansa and Pe-Piper, 1987), an attractive candidate, but unfortunately neither its age (51.5 Ma;Bottomley and York, 1988) nor the isotopic systematics (Stecher et al, 1989) agree with those of the North American tektites.…”

Section: North American Strewn Fieldmentioning

confidence: 99%

Tektite origin by hypervelocity asteroidal or cometary impact: Target rocks, source craters, and mechanisms

Koeberl¹

1992

Geological Society of America Special Papers

123

164

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Tektites are natural glasses that occur on earth in four distinct strewn fields (North American, Central European, Ivory Coast, and Australasian). Geochemical arguments have shown that tektites have been derived by hypervelocity impact melting from terrestrial upper crustal rocks, most likely sediments. The contents of Be-10 in tektites are evidence for a derivation of tektites from surface rocks, thus precluding an origin from greater depth in the crater. For two of the four tektite strewn fields (Ivory Coast, Central European), a possible connection to impact craters (Bosumtwi, and Ries, respectively) has been suggested on the basis of chemical, isotopic, and age data. No clear crater identifications have been made for the North American or Australasian strewn fields, although there are good candidates for both. Even though the geochemistry of tektites is in unequivocal favor of an origin by impact melting of terrestrial rocks, the unambiguous demonstration of the presence of an extraterrestrial contribution to the chemistry of tektites remains a problem. However, recent osmium isotope studies have shown that there is a clear meteoritic signature in at least some tektites. The exact mechanism of tektite formation is still not obvious, although some facts become increasingly clear. Tektite production requires specific impact conditions-otherwise there would be many more tektite strewn fields connected to the 150 or so known impact craters. Tektites are produced by nonequilibrium shock melting of surficial rocks, and the superheated melt may be subjected to a plasma phase during which they are subjected to partial reduction. They are then lofted through the atmosphere (probably in the wake of the expanding vapor cloud), quenched, and distributed over a geographically extended area-the strewn field. Some tektites solidify in a near-vacuum and re-enter the atmosphere. During the re-entry they melt again and form ablation-shaped tektites. Larger tektites, from a lower part of the target stratigraphy, are only distributed closer to the source crater. Many of them are more inhomogeneous melts and show a layered structure; they are called Muong Nong-type tektites. The study of tektites and the identification of possible new strewn fields provide important contributions toward the understanding of impact cratering.

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Section: North American Strewn Fieldmentioning

confidence: 99%

Tektite origin by hypervelocity asteroidal or cometary impact: Target rocks, source craters, and mechanisms

Koeberl¹

1992

Geological Society of America Special Papers

123

164

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“…Four craters have been mentioned as possible source craters for the North American tektites: Lake Wanapitei, Lake Mistastin, Popigai, and Montagnais (Dietz, 1977;Bottomley et al, 1979;Glass, 1988). It now appears that all of these craters are too small (or too far away), too old, and/or on too old crust to be the source crater for the Site 612 ejecta layer and/or the North American tektites (Shaw and Wasserburg, 1982;Ngo et al, 1985;Jansa and Pe-Piper, 1987;Stecher et al, 1989;Bottomley and York, 1988).…”

Section: Source Crater For the North American Tektitesmentioning

confidence: 99%

North American tektite debris and impact ejecta from DSDP Site 612

Glass

1989

Meteoritics

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A layer of tektite glass and shock-metamorphosed grains found in an upper Eocene section of core 21 from DSDP Site 612 taken on the continental slope off New Jersey may belong to the North American tektite strewn field. However, the Site 612 glasses generally have higher K,O and lower Na,O contents for a given SiO, content and different Sr and Nd isotopic compositions. In order to better define the layer, a series of samples was taken continuously through the layer at I ern intervals. Tektite fragments are in an 8 em thick layer; microtektites are concentrated in the upper 4 em, while spherules with "crystalline" textures (microkrystites) are concentrated in the lower half of the layer. Millimeter-size splash forms are mostly in the lower part of the tektite-bearing layer. Rock and mineral grains showing evidence of shock metamorphism are abundant in the upper half of the tektite-bearing layer. Coesite is abundant, and stishovite was found in one rock fragment. The size and abundance of the tektite glass and the abundance of shocked debris indicate that Site 612 is relatively close to the source crater, which may be to the north of Site 612 on the coastal plain or adjacent continental shelf.

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“…A recently discovered underwater impact crater, the Montagnais structure, 200 km southeast of Nova Scotia (Jansa and Pe-Piper, 1987), has been suggested as the source of NAT and 612-tektites (Glass, 1988).4°Arf3 9 Arage determinations on samples from the Montagnais crater give an age of 51.5 ± 0.8 Ma (Bottomley and York, 1988), that is different from the age of NAT. Rb-Sr and Sm-Nd determinations on samples from the Montagnais crater give isotopic compositions and model ages that exclude a genetic relationship between the Montagnais impact crater and NAT or 612-tektites (Stecher et al, 1989).…”

Section: Possible Source Cratersmentioning

confidence: 99%

Nd and Sr isotopic evidence for the origin of tektite material from DSDP site 612 off the New Jersey coast

et al. 1989

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Abstract-Late Eocene tektite material from DSDP site 612 is composed of angular to spherical tektites and microtektites containing abundant vesicles and a few unmelted to partially melted mineral inclusions. The major element compositions of the 6l2-tektites are generally comparable to those of North American tektites, but the physical features suggest that the DSDP-6l2 tektites were formed by less severe shock melting. The 8'Sr/ 8·Sr and 143Nd/ 144Nd compositions of 6l2-tektites: a) show much wider ranges than the tightly constrained group of North American tektites and microtektites, and b) are significantly different from those of other groups of tektites. The existence of large isotopic variations in tektites from DSDP site 612 requires that they were formed from a chemically and isotopically heterogeneous material in a regime that is distinctive from that of other groups of tektites. T~~uR and T~R model ages of the 6l2-tektites indicate that they were formed from a crustal source of late Precambrian mean age (800-1000 Ma) which in middle Palaeozoic time (""400 Ma) was further enriched in Rb/Sr during sedimentary processes. These source characteristics suggest that the impact which produced the 6l2-tektites occurred in rocks of the Appalachian orogeny or sediments derived from this orogenic belt. Potential source materials for both 6l2-tektites and North American tektites are present on the eastern and southeastern part of the North American continent and its adjacent shelf. The distinct isotopic differences between 6l2-tektites and North American tektites indicate that the two groups of tektites were either formed by the impact of more than one bolide in the same general area, or by a single impact event that sampled different layers.

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Age measurement of the submarine montagnais impact crater

Cited by 24 publications

References 8 publications

Tektite origin by hypervelocity asteroidal or cometary impact: Target rocks, source craters, and mechanisms

Tektite origin by hypervelocity asteroidal or cometary impact: Target rocks, source craters, and mechanisms

North American tektite debris and impact ejecta from DSDP Site 612

Nd and Sr isotopic evidence for the origin of tektite material from DSDP site 612 off the New Jersey coast

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