Oxytropidoceras Posted August 2, 2014 Share Posted August 2, 2014 (edited) Some articles: Ancient Asteroid Destroyer Finally Found, And It's a New Kind of Meteorite. by Becky Oskin, Live Science, June 27, 2014 http://www.livescience.com/46563-new-meteorite-type-fossil-ordovician.html Tiny Traces of a Big Asteroid Breakup, March 9, 2004 http://www.psrd.hawaii.edu/Mar04/fossilMeteorites.html The Great Ordovician meteor shower. Metageologist http://all-geo.org/metageologist/2013/09/the-great-ordovician-meteor-shower/ The people on this list, who regularly collect fossils from mid- Ordovician age strata, specially limestones that accumulated as condensed intervals, should also be looking for such fossil meteorites. Over 100 ordinary chondrites have been recovered from a southern Sweden limestone quarry and more certainly should be preserved elsewhere in mid-Ordovician (Darriwilian) carbonate beds of the same age. The Swedish fossil meteorites are associated with the lower Microzarkodina hagetiana, entire Yangtzeplacognathus crassus, and upper Lenodus variabilis conodont zones. It certainly would worth while for people to look for fossil meteorites in carbonate strata associated with these conodont zones while collecting fossils from them. The latest paper (open access, freely downloadable): Schmitz, B., G. R. Huss, M. M.M. Meiera, B. Peucker- Ehrenbrink, R. P. Church, A. Cronholm, M. B. Davies, P. R. Heck, A. Johansen, K. Keil, P. Kristiansson, G. Ravizza, M. Tassinari, and F. Terfelt, 2014, A fossil winonaite-like meteorite in Ordovician limestone: A piece of the impactor that broke up the L-chondrite parent body? Earth and Planetary Science Letters. vol. 400, pp. 145-152. http://www.sciencedirect.com/science/article/pii/S0012821X14003367 another paper is: Schmitz, B., D. A. T. Harper, B. Peucker-Ehrenbrink, S. Stouge, C. Alwmark, A. Cronholm, S. M. Bergstrom, M. Tassinari, and W. Xiaofeng, 2008, Asteroid breakup linked to the Great Ordovician Biodiversification Event. Nature Geoscience. vol. 1, pp. 49-53, http://www.nature.com/ngeo/journal/v1/n1/full/ngeo.2007.37.html http://www.nature.com/ngeo/journal/v1/n1/pdf/ngeo.2007.37.pdf https://darchive.mblwhoilibrary.org/handle/1912/2272 Pictures of Yangtzeplacognathus crassus can be found in: Zhen, Y. Y. I., Z. Wang; Y. Zhang; S. M. Bergstrom, I. G. Percival, and J. Cheng, 2011, Middle to Late Ordovician (Darriwilian-Sandbian) Conodonts from the Dawangou Section, Kalpin Area of the Tarim Basin, Northwestern China. Records of the Australian Museum. vol. 63, pp. 203–266. http://www.ozcam.org/Uploads/Journals/23694/1586_complete.pdf Yours, Paul H. Edited August 2, 2014 by Oxytropidoceras Link to comment Share on other sites More sharing options...
Tethys Posted August 2, 2014 Share Posted August 2, 2014 It certainly would worth while for people to look for fossil meteorites in carbonate strata associated with these conodont zones while collecting fossils from them. I live within 100 miles of two impact sites. Rock Elm, Wisconsin and Decorah, Iowa. What would I be looking for? I have no idea what a fossil meteorite or winonaite would look like, but I would be thrilled to find either. The infill of Rock Elm is dated at 455 mya. Which Ordovician strata does that correspond to? Link to comment Share on other sites More sharing options...
Missourian Posted August 2, 2014 Share Posted August 2, 2014 (edited) I live within 100 miles of two impact sites. Rock Elm, Wisconsin and Decorah, Iowa. What would I be looking for? I have no idea what a fossil meteorite or winonaite would look like, but I would be thrilled to find either. The infill of Rock Elm is dated at 455 mya. Which Ordovician strata does that correspond to? Any meteorites will have deteriorated into clay and oxides. All that'd remain in the rock would be an excess of chromium spinel and iridium. The image in one of the articles implies that the meteorite remnants appear as inclusion in the limestone. If such meteoritic events occur on a global scale, and if each event can be isolated, they have the potential to serve as reliable and precise stratigraphic markers. Edited August 2, 2014 by Missourian Context is critical. Link to comment Share on other sites More sharing options...
Stocksdale Posted August 5, 2014 Share Posted August 5, 2014 (edited) I was also trying to correlate the timing with local stratigraphy. I understand that the impact in space is dated pretty precisely to around 470 ma. And then the meteorite impacts occurred abundantly around 469 and onward. (Correct me where i'm in error). So locally, in Illinois, I'm thinking St Peter Sandstone and the layers immediately under St. Peter Sandstone. Somewhere i saw the base of St. Peter being 459 ma. Anyone have better idea? Edited August 5, 2014 by Stocksdale Somewhere, something incredible is waiting to be known.–Carl Sagan Link to comment Share on other sites More sharing options...
Stocksdale Posted August 6, 2014 Share Posted August 6, 2014 http://m.bulletin.geoscienceworld.org/content/116/1-2/200.abstract Here's a paper on the Rock Elm Wisconsin impact from around 469 ma. Somewhere, something incredible is waiting to be known.–Carl Sagan Link to comment Share on other sites More sharing options...
Tethys Posted August 6, 2014 Share Posted August 6, 2014 The Decorah impact contains the Winneshiek Shale. I have tracked down this paper which states; The Middle Ordovician (Whiterockian) Winneshiek Lagerstätte is found within the provisionally named “Winneshiek Shale” which lies disconformably beneath the Tonti Member of the St. Peter Sandstone at Decorah, Iowa. The 60 to 120 ft. thick Lagerstätte-bearing shale is the uppermost facies of a 600+ ft. sedimentary succession that fills a 3.6 mile diameter circular basin of suspected meteorite impact origin. This thick sedimentary sequence differs substantially from pre-St. Peter incised-valley and paleokarst fills as typified by subsurface sections assigned to the Readstown or Kress members of the St. Peter. The St. Peter is highly eroded at Rock Elm. Exposures remain where it is protected by overlying Platteville, or it fills in low areas and sinkholes in the underlying Prairie du Chien formation. Link to comment Share on other sites More sharing options...
Tethys Posted March 24, 2015 Share Posted March 24, 2015 Ever since this thread I have been looking for an odd, dark, pitted rock my son brought me over 20 years ago, that he collected from a stream bed in Martell. (appx 13 miles from the rock elm uplift) He also brought me several other very glacially smoothed pebbles of shiny quartz and feldspar from the stream, but this rock does not appear to be glacially smoothed so I think it weathered out of the local sandstone. It is made of semi translucent green chert (?) matrix, filled with particles that look somewhat like ooids or pyrite ooids. The oddest thing about it though is a subtle silver, iridescent shimmer that it has in bright light. It is most likely something that came out of one of the metal mining strata from the area, but I want to eliminate possible fossil meteorite as an ID and make sure that it is not a health hazard to wet grind on galena ores before I cut this up into lapidary rough. It really is as green as it looks in the close ups. Field of view in the dry photo is 1 cm, and 1.5 cm in the wet closeup photo. The pits are about 2mm across. It leaves no scratch, and is not magnetic. It polishes up very easily in comparison to the usual oolitic cherts from the Prairie du Chein. Link to comment Share on other sites More sharing options...
Tethys Posted March 24, 2015 Share Posted March 24, 2015 (edited) I tried to use cut off discs to slice off a corner. The rock breaks when I hit a particle of soft sediment, or the disc explodes when I hit tiny dark pink/ red very hard crystals. I really dislike being sprayed in the face with high speed debris. I used a mizzy stone and a series of three rubber wheels to polish a little window. The harder rubber wheels rip the crystals right out of the matrix. I had to lighten it up quite a bit to make them visible, but you can see the dark red crystals in the center of this pic and a few silver metal looking flakes in the lower edge between 5 and 7 o'clock. The close-up FOV is 1 cm. and the second photo just shows the polished window. Grinding sediment is a chocolate milk brown color It worked and polished up very nicely when I stopped trying to slice it. Edited March 24, 2015 by Tethys Link to comment Share on other sites More sharing options...
Tethys Posted March 25, 2015 Share Posted March 25, 2015 U of W has a nice page devoted to Rock Elm, with several informative graphics, links, and a map. http://wgnhs.uwex.edu/wisconsin-geology/meteorites/ The Field Museum had several of these meteorites on display until Feb. They will be put on permanent display later this year. http://meteorites.fieldmuseum.org/node/216 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now