Alamo impact

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The arrow shows the location of the Alamo breccias near Hancock Summit, Pahranagat Range , Nevada.

The Alamo impact occurred about 375 million years ago near what is now the Worthington Mountains and Schell Creek Range in southeastern Nevada , USA. This event was named after the city of Alamo , Nevada, after breccias ("Alamo Breccia") were found in the area .

geology

In the geochronological period of the Devonian , a meteorite impact occurred , which, according to current knowledge, was one of the largest impact disasters of the Phanerozoic . This was associated with a significantly increased occurrence of the noble metal iridium in this time horizon . This element is extremely rare on Earth, but is often found in elevated concentrations in the vicinity of impact structures (see also Iridium Anomaly ). The size of the impact crater was previously difficult to determine. At that time this area was covered by a primeval sea. It was therefore a submarine impact. Recent studies published in 2015 showed a diameter of around 150 km. Previously, the diameter was estimated at 65 km. This means that the diameter is twice as large as previously assumed.

The detonation of the celestial body hurled large blocks of stone into the surrounding area in addition to extensive soot and dust masses and most likely triggered a far-reaching megatsunami . In geological terms, connections can be found with species extinction . On the threshold of carbon that found Hangberg event instead. This event marks a drastic and permanent cooling phase of the climate on earth. Over a period of around 100,000 years, the sea level fell by 100 meters. Due to the changed conditions in the oceans, prehistoric life forms such as ammonites , brachiopods , trilobites , conodonts , stromatopores , ostracods (mussel crabs), placodermi (armored fish) died out on a mass scale. It is conceivable that several impact events were responsible for the mass extinction. The Australian Woodleigh impact and the Swedish Siljan impact also took place during this period .

After initial opposition from the Geological Society of America , the first publication on Alamo breccias was written by John Warme, Brian Ackman, Yarmanto, and Alan Chamberlain in the 1993 Nevada Petroleum Society Field Conference Guidebook.

  • Faulty limestone formation as a result of the Alamo impact near the Irish Range, Nevada

  • Close up of an Alamo breccia near Hancock Summit, Pahranagat Range, Nevada

  • Alamo breccia near Hancock Summit, Pahranagat Range, Nevada

  • Top of the Alamo breccia near Hancock Summit, Pahranagat Range, Nevada

  • Calcite globules ("spherical lapilli ") from the Alamo impact deposits near the Irish Range, Nevada. Scale bar is 5.0 mm.

See also

Web links

Commons : Alamo Impact  - Collection of images, videos, and audio files

swell

  1. Jump up ↑ Andrew J. Retzler, Leif Tapanila, Julia R. Steenberg, Carrie J. Johnson, Reed A. Myers: Post-impact depositional environments as a proxy for crater morphology, Late Devonian Alamo impact, Nevada. February 1, 2015, accessed June 15, 2018 .
  2. ^ Discussion of this topic in Terra Nova: High-precision U – Pb age and duration of the Latest Devonian (Famennian) Hangenberg Event, and its implications. Reachgate Net, April 30, 2014, accessed June 15, 2018 .
  3. ↑ Mitchell Mccormack: All About Devonian Period and Events . University Publications, New York 2016, ISBN 978-1-283-49843-2 (English, archive.org [PDF; 6,9 MB ; accessed on August 23, 2020]).
  4. ^ Charles W. Gillespie: Structural and stratigraphic relationships of Devonian reservoir rocks, east central Nevada: Nevada Petroleum Society 1993 Field Conference guidebook. In: ebook. Reno, Nev. : The Society, 1993, accessed June 17, 2018 .