Guest “Missed It So Much” by David Middleton
Herein, Kjaer et al. (2018) reports the discovery of a large impact crater beneath the Hiawatha Glacier in northwest Greenland. From aerial radar surveys, they identified a circular depression, 31 kilometers wide, beneath ice up to a kilometer thick. They also suggest that the impact was more than 1 km wide and unlikely to have occurred before the Pleistocene, which is less than a few million years old (see Figure 11). This maximum age was confirmed one year later (Garde et al., 2020). Apparently, this crater is a YD-age impact structure candidate.
“Clearly, this crater is a candidate YD-age impact structure.”
Huge asteroid hit Greenland when it was a lush rainforest, craters under ice
By Stephanie Pappas published 3 days ago
Huge impact crater dating from 58 million years ago.
Scientists now know the age of a giant crater hidden under the ice of Greenland.
Hiawatha Crater, which lies under 0.6 miles (1 km) of ice in northwest Greenland, was formed 58 million years ago, according to a study published March 9 in the journal Nature. Scientific advance. While some early estimates measure the crater’s age as just 13,000 years, the new discovery means the impact occurred much earlier, at a time when Greenland was truly green and teeming with life.
Study co-author Michael Storey, a researcher at the Natural History Museum of Denmark who specializes in geological documents, said: “Greenland is actually covered with a temperate rainforest when the state is low in water. planet hit.
The new publication is very well dated to the impact of the Late Paleocene, about 58 million years ago (Ma), the same age as Marquez . impact crater. Many co-authors also participated in the first publication of the Hiawatha Crater (Kjaer et al., 2018). The full text is available and it is well worth reading.
Late Paleocene age for the Hiawatha impact structure of Greenland
The ~31 km wide Hiawatha Structure, located beneath the Hiawatha Glacier in northwest Greenland, has been suggested as an impact structure that may have formed after the Pleistocene formation of the Greenland Ice Sheet. To date structure, we have conducted 40Ar /39Ar analysis on glacial alluvial sand and U-Pb analysis on zircon separated from glacial alluvial gravel of impact melt rock, all sampled directly downstream of the Hiawatha Glacier. Unmarked zircon in impact-melted rocks dating to about 1915 million years (Ma), consistent with felsic intrusions found in local bedrock. The 40Ar /39The Ar data indicate that the Late Paleocene reset and the shocked zircon dated to 57.99 ± 0.54 Ma, which we interpret as the impact age. Thus, the Hiawatha impact structure predates the Pleistocene glaciation and is not related to the Paleocene-Eocene Thermal Maximum or the flood basalt volcanism of eastern Greenland. However, it is concurrent with the Paleocene Carboniferous Maximum, although the exact environmental and climatic significance of the impact awaits further investigation.
A new era for Hiawatha . structure
Two samples of impact melt rock, collected in 2019 from a riverbank less than 10 km downstream from the edge of the Hiawatha structure, contain unmarked zircon with age indistinguishable from intrusion the entrance of the massive local felsic adjacent to — and perhaps also under — the Hiawatha Glacier. Shock zircon in the same samples for a strong ~58-Ma U-Pb age, agreeing with two younger ages 40Ar /39The small Ar plateau dating from the 2016 sand sample has recovered even closer to the structure. In summary, these data point to the origin of the sample from a Late Paleocene impact event that occurred somewhere upstream but was close enough that the target geology was indistinguishable chronologically from the geologic one. exposed locally where the samples were recovered. Given the existing geomorphological evidence for a complex impact structure eroding beneath the Hiawatha Glacier, the belt is clearly broken by the glacial sub-channel that eventually becomes the sub-river channel from which the debris samples Ours is restored (first), the simplest explanation for our observations – which we accept unequivocally in the rest of the discussion – is that the Hiawatha structure is a relatively high-impact structure formed city in the Late Paleocene.
When the Hiawatha structure was first proposed as an impact structure, it was also suggested to date from the Late Pleistocene of the Greenland Ice Sheet at ~2.6 Ma (first). The ~58-Ma age for the structure suggests it formed long before ice formation and it is not related to the beginning of the Younger Dryas cold period ~12,900 years ago as has been speculated (19).
Pebble-sized coal particles (with a cellular structure indicative of larch) and impact-related organic carbon-rich sand particles were found in Hiawatha Glacier’s glacial discharge (2, 3). They are assumed to be derived from organic matter in early Pleistocene sediments and are therefore interpreted to support a young impact age (2). However, the new age of the Hiawatha structure indicates that – if these materials are involved in the impact – they should instead date to the Paleocene or earlier. The abundance of Late Paleocene plant fossils in the Arctic (eg, on Ellesmere Island, across the Nares Strait from Inglefield Land) indicates extensive high-altitude coniferous forests at this time (28), provides a reasonable source of organic material in the impact-associated sediments at Hiawatha Glacier.
The authors determined the date of the untested and shocking zircon using 40Ar /39Technical Ar. Unabraded zircon is dated to 1.9 Ga, which is consistent with the established date of the target rock formation. The shocking zircon is dated to 58 Ma. The U-Pb method also gives an age of 58 Ma for the shocked zircon. 40Ar / 39Ar (argon-argon) is a very versatile and relatively accurate method for geographical dating. It can date materials from a few thousand to billions of years old. U-Pb (uranium-lead) is one of the most widely used methods for radiometric dating, especially of ancient rocks.
Based primarily on the work of Garde et al., 2020, Christ et al., 2021 and Silber et al., 2021, I have previously defined the age of impact as between 1.4 to 0.9 Ma. Silber demonstrated that the collision could occur on an ice-free surface, and Garde set the maximum age to 2.4 to 3 Ma. Garde hypothesized that charred organic material was related to Late Pliocene to Early Pleistocene sediments containing fossil material from trees. They do not directly date the material or suggest that it may be related to much older periods when Greenland was actually green.
Hiawatha crater has now been dropped from the Younger Dryas impact structure candidate list.
Christ, AJ, Bierman, PR, Schaefer, JM, Dahl-Jensen, D., Steffensen, JP, Corbett, LB, Peteet, DM, Thomas, EK, Steig, EJ, Rittenour, TM, Tison, JL., Blard, PH., Perdrial, N., Dethier, D., Lini, A., Hidy, AJ, Caffee, M., Southon, J., 2021,”Million-year-old record of Greenland vegetation and glacial history preserved in sediments 1.4 km below ice at Camp Century“, Proceedings of the National Academy of Sciences of the United States of America.
Garde, Adam A., Anne Sofie Søndergaard, Carsten Guvad, Jette Dahl-Møller, Gernot Nehrke, Hamed Sanei, Christian Weikusat, Svend Funder, Kurt H. Kjær, Nicolaj Krog Larsen; Pleistocene organic matter modified by the Hiawatha impact, northwest Greenland. Geology Year 2020 ;; 48 (9): 867–871. doi: https://doi.org/10.1130/G47432.1
Kenny, Gavin G. et al. 2022.”Late Paleocene age for the Hiawatha impact structure of Greenland“. Scientific advance 8 (10); doi: 10.1126 / sciadv.abm2434
Kjær, Kurt, Larsen, Nicolaj, Binder, Tobias, Bjørk, Anders, Eisen, Olaf, Fahnestock, Mark & Funder, Svend & Garde, Adam & Haack, Henning & Helm, Veit, Houmark-Nielsen, Michael, Kjeldsen, Kristian, Khan, Shfaqat, Machguth, Horst, Mcdonald, Iain, Morlighem, Mathieu, Mouginot, Jeremie’ Paden, J., Waight, Tod & MacGregor, Joseph. (2018). “A large impact crater beneath the Hiawatha Glacier in northwest Greenland“. Scientific advance. 4. eaar8173. 10.1126 / sciadv.aar8173.
Silber, EA, BC Johnson, E. Bjones, et al. In 2021.”Effect of ice thickness on the formation of the Hiawatha crater. ” Earth and planetary science Letters, 566: 116972 [10.1016/j.epsl.2021.116972]
Sweatman, Martin B. Younger Dryas’ Impact Hypothesis: A Review of Impact Evidence, Earth Science ReviewsEpisode 218, 2021, 103677, ISSN 0012-8252, https://doi.org/10.1016/j.earscirev.2021.103677.