Fossil Meteorites From Ordovician Asteroid Breakup

[Oxytropidoceras]

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

[Tethys]

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?

[Missourian]

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

[Stocksdale]

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

[Stocksdale]

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.

[Tethys]

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.

[Tethys]

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.

[Tethys]

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

[Tethys]

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