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Wilkes Land crater

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Wilkes Land crater is a hypothesized giant impact structure beneath the East Antarctic Ice Sheet in Wilkes Land, East Antarctica. The hypothesis is based on indirect geophysical observations, especially regional gravity anomalies and subglacial topography. It remains unconfirmed because the site is buried under ice and there are no direct bedrock samples to test for diagnostic impact evidence.

Contents

The name is used in connection with two candidate features discussed in published sources. The Wilkes Land anomaly refers to a general, large-scale gravity anomaly associated with a subglacial depression that has several proposed origins, including an impact structure. The Wilkes Land mascon refers to the specific positive gravity signal, a mascon, inferred from satellite gravimetry (including GRACE) and interpreted by some authors as consistent with a large impact basin.

Wilkes Land anomaly

A giant impact crater beneath the Wilkes Land ice sheet was first proposed by Richard A. Schmidt in 1962 on the basis of the seismic and gravity discovery of the feature made by the U.S. Victoria Land Traverse in 1959–60 (VLT), and the data provided to Schmidt by John G. Weihaupt, geophysicist of the VLT (Geophysical Studies in Victoria Land, Antarctica, Report No. 1, Geophysical and Polar Research Center, University of Wisconsin, 1–123). [1] Schmidt further considered the possibility that it might be the elusive source of the tektites of the Australasian strewnfield (which is only 790,000 years old).

EGM2008 gravity anomaly map EGM2008 gravity anomaly map.svg
EGM2008 gravity anomaly map

The hypothesis was detailed in a paper by Weihaupt in 1976. [2] Evidence cited included a large negative gravity anomaly coincident with a subglacial topographic depression 243 kilometres (151 mi) across and having a minimum depth of 848 metres (2,782 ft).

The claims were challenged by Charles R. Bentley in 1979. [3] On the basis of a 2010 paper by Weihaupt et al., [4] Bentley's challenge was proven to be incorrect, and the Earth Impact Database (Rajmon 2011) reclassified the Wilkes Land Anomaly from a "possible impact crater" to a "probable impact crater" on that basis. A potential impact crater site has been proposed by other investigators in the Ross Sea. [5] [6]

Mass concentration

Map of Antarctica showing Wilkes Land, with the crater conjectured by von Frese et al. marked in red Antarctica Map Wilkes L Crater.png
Map of Antarctica showing Wilkes Land, with the crater conjectured by von Frese et al. marked in red

The Wilkes Land mass concentration (or mascon) is centered at 70°S120°E / 70°S 120°E / -70; 120 and was first reported at a conference in May 2006 by a team of researchers led by Ralph von Frese and Laramie Potts of Ohio State University. [7] [8]

The team used gravity measurements by NASA's GRACE satellites to identify a 300-kilometre-wide (190 mi) mass concentration and noted that this mass anomaly is centered within a larger ring-like structure visible in radar images of the land surface beneath the Antarctic ice cap. That combination suggested to them that the feature may mark the site of a 480-kilometre-wide (300 mi) impact crater buried beneath the ice and more than 2.5 times larger than the 180-kilometre (110 mi) Chicxulub crater.

Due to the site's location beneath the Antarctic ice sheet, there are no direct samples to test for evidence of impact. There are alternative explanations for this mass concentration, such as formation by a mantle plume or other large-scale volcanic activity, but a variety of research methods lend support to the impact hypothesis. [9] If the impact crater hypothesis is correct, based on the size of the ring structure, it has been suggested by Frese's team that the impactor could have been four or five times wider than the Chicxulub impactor, which is believed to have caused the Cretaceous–Paleogene extinction event. [8]

Because mass concentrations on Earth are expected to dissipate over time, Frese and his collaborators believe the structure must be less than 500 million years old and also note that it appears to have been disturbed by the rift valley that formed 100 million years ago, during the separation of Australia from the Gondwana supercontinent. [8]

The researchers speculate that the putative impact and associated crater may have contributed to this separation by weakening the Earth's crust at this location. These bracketing dates also make it possible that the site could be associated with the Permian–Triassic extinction event. [8] The Permian–Triassic extinction occurred 250 million years ago and is believed to be the largest extinction event since the origin of complex multicellular life.

Plate reconstructions for the Permian–Triassic boundary place the putative crater directly antipodal to the Siberian Traps, and Frese et al. (2009) use the controversial theory that impacts can trigger massive volcanism at their antipodes to bolster their impact crater theory. [10] However, there are already other suggested candidates for giant impacts at the Permian–Triassic boundary, such as Bedout, off the northern coast of Western Australia, although all are equally contentious and it is currently under debate whether or not an impact played any role in this extinction.

The complete absence of a well-defined impact ejecta layer associated with the Permian–Triassic boundary at its outcrops within Victoria Land and the central Transantarctic Mountains argues against there having been any impact capable of creating a crater the size of the hypothesized Wilkes Land impact crater within Antarctica at the Permian–Triassic boundary. [11] [12] Nonetheless, according to Frese, recent studies in 2018 seem to sustain the impact origin of the crater, and the event may be linked to the separation of Eastern Antarctica from southern Australia. [13]

See also

References

  1. ↑ Schmidt, Richard A. (1962). "Australites and Antarctica". Science. 138 (3538): 443–444. Bibcode:1962Sci...138..443S. doi:10.1126/science.138.3538.443. PMID   17794921. S2CID   5626171. Abstract.
  2. ↑ Weihaupt, John G. (1976). "The Wilkes Land anomaly: Evidence for a possible hypervelocity impact crater". Journal of Geophysical Research. 81 (B32): 5651–5663. Bibcode:1976JGR....81.5651W. doi:10.1029/JB081i032p05651. Abstract.
  3. ↑ Bentley, Charles R. (September 10, 1979). "No giant meteorite crater in Wilkes Land, Antarctica". Journal of Geophysical Research. 84: 5681–5682. Bibcode:1979JGR....84.5681B. doi:10.1029/JB084iB10p05681. Abstract.
  4. ↑ Weihaupt, John G.; Rice, Alan; Van der Hoeven, Frans G. (2010). "Gravity anomalies of the Antarctic lithosphere". Lithosphere. 2 (6): 454–461. Bibcode:2010Lsphe...2..454W. doi: 10.1130/l116.1 . Abstract.
  5. ↑ Khryanina, L. P. (1985). "Possible meteorite impact structures in the Ross Sea, Antarctica" . International Geology Review. 27 (10): 1207–1211. Bibcode:1985IGRv...27.1207K. doi:10.1080/00206818509466495. ISSN   0020-6814.
  6. ↑ Gerard-Little, P.; Abbott, D.; Breger, D.; Burckle, L. (2006-03-01). "Evidence for a Possible Late Pliocene Impact in the Ross Sea, Antarctica". 37th Annual Lunar and Planetary Science Conference 1399. Bibcode: 2006LPI....37.1399G .
  7. ↑ Frese, Ralph R. B. von; Potts, Laramie V.; Wells, Stuart B.; Gaya-Piqué, Luis-Ricardo; Golynsky, Alexander V.; Hernandez, Orlando; Kim, Jeong Woo; Kim, Hyung Rae; Hwang, Jong Sun (2006). "Permian–Triassic mascon in Antarctica". American Geophysical Union, Fall Meeting 2007. 2007: Abstract T41A–08. Bibcode:2006AGUSM.T41A..08V.
  8. 1 2 3 4 Gorder, Pam Frost (June 1, 2006). "Big Bang in Antarctica – Killer Crater Found Under Ice". Ohio State University Research News. Archived from the original on March 6, 2016.
  9. ↑ Klokočník, Jaroslav; Kostelecký, Jan; Bezděk, Aleš (17 August 2018). "On the detection of the Wilkes Land impact crater". Earth, Planets and Space. 70 (1): 135. Bibcode:2018EP&S...70..135K. doi: 10.1186/s40623-018-0904-7 . hdl: 10084/131644 . ISSN   1880-5981.
  10. ↑ Frese, Ralph R. B. von; Potts, Laramie V.; Wells, Stuart B.; Leftwich, Timothy E.; Kim, Hyung Rae; Kim, Jeong Woo; Golynsky, Alexander V.; Hernandez, Orlando; Gaya-Piqué, Luis-Ricardo (25 February 2009). "GRACE gravity evidence for an impact basin in Wilkes Land, Antarctica". Geochemistry, Geophysics, Geosystems. 10 (2). Bibcode:2009GGG....10.2014V. doi: 10.1029/2008GC002149 . ISSN   1525-2027.
  11. ↑ Retallack, Gregory J.; Seyedolali, Abbas; Krull, Evelyn S.; Holser, William T.; Ambers, Clifford P.; Kyte, Frank T. (1998). "Search for evidence of impact at the Permian–Triassic boundary in Antarctica and Australia" . Geology. 26 (11): 979–982. Bibcode:1998Geo....26..979R. doi:10.1130/0091-7613(1998)026<0979:SFEOIA>2.3.CO;2.
  12. ↑ Retallack, Gregory J.; Greaver, Tara; Jahren, A. Hope (January 2007). "Return to Coalsack Bluff and the Permian–Triassic boundary in Antarctica" . Global and Planetary Change. 55 (1–3): 90–108. Bibcode:2007GPC....55...90R. doi:10.1016/j.gloplacha.2006.06.017.
  13. ↑ Klokočník, Jaroslav; Kostelecký, Jan; Bezděk, Aleš (2018). "On the detection of the Wilkes Land impact crater". Earth Planets Space. 70: 135. Bibcode:2018EP&S...70..135K. doi: 10.1186/s40623-018-0904-7 . hdl: 10084/131644 .

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