Английская Википедия:Corossol crater

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Шаблон:Infobox terrestrial impact site

The Corossol structure, which is also known as the Corossol crater, is a circular, Шаблон:Convert in diameter, underwater bedrock feature that is exposed on the gulf floor of the northwestern Gulf of Saint Lawrence Шаблон:Convert offshore of the city of Sept-Îles, Quebec, in eastern Canada. It is hypothesized to be a possible pre-Pleistocene, extraterrestrial impact structure. It lies underwater at a depth of Шаблон:Convert. This underwater feature was found during the study of high-resolution bathymetric and sub-bottom profiler data collected south of the city of Sept-Iles in the northwestern Gulf of Saint Lawrence.[1][2]

Geology

The Corossol structure has a maximum diameter of Шаблон:Convert and rises Шаблон:Convert above the surrounding sea floor. At its centre, there is central uplift is Шаблон:Convert in diameter and rises to the same elevation as the crater rim to a depth of about Шаблон:Convert below the surface of the Gulf of St Lawrence. This uplift lies within a Шаблон:Convert in diameter and Шаблон:Convert deep circular central cavity. The central cavity is surrounded by a Шаблон:Convert wide brim. In addition, three concentric rings form narrow (Шаблон:Convert wide), shallow, and discontinuous depressions around the central cavity.[1][2]

The central uplift, associated central cavity, brim, and rings likely represent both deformation and differential erosion of sedimentary rocks of the Ordovician Saint. Lawrence Platform. The sedimentary strata surrounding the Corossol structure show no deformation. However, seismic data reveal that they are highly fractured by a series of Шаблон:Convert deep faults. These faults also are associated with the concentric rings and form the irregular topography of the structure's brim.[1][2]

Less than Шаблон:Convert of Quaternary sediments partially fill the central cavity. These sediments consist of glaciomarine and postglacial sediments. The central cavity and its sediment fill are interrupted by two diagonal Шаблон:Convert high bedrock ridges that connect the brim to the central peak. Using high-resolution seismic, it was found that the bedrock is locally covered with a thin veneer of glacial till overlain by Шаблон:Convert of glaciomarine and postglacial sediments. The discontinuous nature of the rings results from either partial burial of the rings under these sediments or partial erosion of the rings.[1][2]

Geomorphology

The gulf bottom surrounding the Corossol structure is characterized by a relict cuesta landscape consisting of partially eroded, gently inclined sedimentary rock layers that decreases southwards into a flat topography. The cuestas consist of steep northward-facing scarps and gentle southward-dipping slopes. Along its north side, the crater is truncated by a steep scarp of one of these cuestas and a Шаблон:Convert wide and Шаблон:Convert deep basin. Distinct Шаблон:Convert long and Шаблон:Convert wide streamlined glacial lineations cut across the southern half of the Corossol structure.[2] The cuestas and associated paleovalleys likely were created by fluvial erosion during regional sea-level lowstand(s) that likely predates Quaternary glaciations.[3][4] The passage of the Laurentide Ice Sheet formed the streamlined glacial lineations that cut across the southern half of the Corossol structure. The orientation of these lineations indicate SE–SSE-directed ice flow that scoured the surface of the Corossol structure.[1][2]

Origin

It is proposed that the Corossol structure was created as a result of the impact of a meteorite of about 300 metres (980 ft) in diameter. The impact origin of the Corossol structure is indicated by its associated geology, faulting, fracturing, and a rock fragment recovered from the crater surface. This rock fragment exhibits, under the microscope, impact melt and shock-induced structures.[1][2][5]

Age

The precise, absolute age of the Corossol structure remains undetermined. It geological setting and cross-cutting relationships indicate that it was created long after the Middle Ordovician (470 million years ago) and before the accumulation of glacial till and creation of streamlined lineations, which are interpreted as subglacially produced mega-scale glacial lineations, on its surface. The relict cuestas and evidence of fluvial erosion observed on the outer walls of the structure, imply it was formed during one of the periods of regional lowstand of sea level prior to the Quaternary glaciations.[1][2][3]

In 2013, it was stated that the Corossol structure is related to a proposed impact event[6] that is hypothesized to have taken place at the start of the Younger Dryas Episode and it supports the hypothesis that a meteorite impact triggered this cooling episode.[7] A later paper[1] argues that their interpretation is based on the misreading of preliminary results, including a radiocarbon date, published in a conference abstract.[8] Later papers conclude on the basis of regional studies and the presence of till and glacial lineations cutting across the Corossol structure that the radiocarbon date only indicates that it was formed before deglaciation, which occurred approximately 12.7 and 12.4 cal. ka BP. Furthermore, the conference abstract did not take into account the fluvial erosion of the cuestas which support a Pre-Quaternary, possibly Paleogene or older, age for the Corossol structure. As a result, it was concluded that this structure has never been "provisionally dated to 12.9 cal. ka BP" as stated in 2013.[1][2] Moreover, the Younger Dryas impact hypothesis has now been refuted by earth scientists and planetary impact specialists.[9]

See also

References

Шаблон:Reflist

External links

Шаблон:Impact cratering on Earth Шаблон:Portal bar

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  1. ↑ 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 Lajeunesse, P., St‐Onge, G., Locat, J., Duchesne, M.J., Higgins, M.D., Sanfaçon, R. and Ortiz, J., 2013. The Corossol structure: A possible impact crater on the seafloor of the northwestern Gulf of St. Lawrence, Eastern Canada. Meteoritics & Planetary Science, 48(12), pp. 2542–2558.
  2. ↑ 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Lajeunesse, P., Duchesne, M.J., St-Onge, G., Locat, J., Higgins, M., Sanfaçon, R. and Ortiz, J., 2016. The Corossol Structure: a glaciated crater of possible impact origin in the northwestern Gulf of St Lawrence, eastern Canada. In Dowdeswell, J. A., Canals, M., Jakobsson, M., Todd, B. J., Dowdeswell, E. K. & Hogan, K. A. (eds) 2016. Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient. Geological Society, London, Memoirs, 46(1), pp.127–128.
  3. ↑ 3,0 3,1 Lajeunesse, P., 2014. Buried preglacial fluvial gorges and valleys preserved through Quaternary glaciations beneath the eastern Laurentide Ice Sheet. Geological Society of America Bulletin, 126(3–4), pp. 447–458.
  4. ↑ Loring, D.H. & Nota, D.J.G. 1973. Morphology and sediments of the Gulf of St. Lawrence. Bulletin of the Fisheries Research Board of Canada, 182, pp. 1–147.
  5. ↑ Higgins, M.D., P. Lajeunesse, G. St-Onge, R. Sanfacon, and M. Duchesne, 2013, Impact Breccia Clast from the Corossol Crater, Canada. 76th Annual Meteoritical Society Meeting. Meteoritics and Planetary Science Supplement. id.5190.
  6. ↑ Шаблон:Cite journal
  7. ↑ Wu, Y., Sharma, M., LeCompte, M.A., Demitroff, M.N. and Landis, J.D., 2013. Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary. Proceedings of the National Academy of Sciences, 110(38), pp.E3557-E3566.
  8. ↑ Higgins, M.D., Lajeunesse, P., St-Onge, G., Locat, J., Duchesne, M., Ortiz, J. and Sanfacon, R., 2011, Bathymetric and petrological evidence for a young (Pleistocene?) 4-km diameter impact crater in the Gulf of Saint Lawrence, Canada. In Lunar and Planetary Science Conference (Vol. 42, p. 1504).
  9. ↑ Шаблон:Cite journal
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