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Lake Murray   contributed by Steve Brittenham, IMCA 2184   MetBul Link


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View all entries for   Meteorite (3)   Steve Brittenham (112)


Copyright (c) Steve Brittenham.
281.6 grams, 123 x 71 x 6 mm.   Iron, IIAB

TKW 270 kg. Fall not observed. Found 1933 in Oklahoma, USA.



Steve writes:
Sometime before 1930 in a gully on the Carter County, Oklahoma farm of J. C. Dodson Sr., a weathered 270 kg mass was found exposed among another 2 kg of oxidized iron and shale. The mass was embedded in the 110 million year old lower Cretaceous Antlers Sandstone, likely near the shore of what was a shallow sea at that time. But it was only in 1952, after several years of Dodson’s begging for it to be studied, that Allen A. Graffham – the Tucker Tower museum curator at the newly created Lake Murray State Park1 – finally recognized it to be a meteorite.

Graffham wrote a letter to the University of New Mexico’s Dr. Lincoln La Paz describing the meteorite and the presence of its extremely thick rusted crust that to Graffham supported Lake Murray’s extreme age. La Paz had the meteorite excavated and shipped to Albuquerque. After its thick oxide and shale coating was removed, the remaining 60 x 40 x 23 cm unaltered mass – the oldest meteorite found to date2 – was subsequently cut in half for further study3. La Paz initially classified Lake Murray as an octahedrite, but noted it could also be an example of a transitionary hexaoctahedrite. Today it is known to be a type IIAB iron, chemically related to such other irons as the more famous Sikhote-Alin.

While debris found around the main mass was initially assumed to be smaller pieces from the same fall, it’s more likely that Lake Murray’s single mass partially disintegrated from its long terrestrial exposure, and millions of years of water, snow, and wind subsequently scattered pieces of the oxidized material around it. Its weight before weathering is thought to have been at least 500 kg and might possibly have exceeded 900 kg, making Lake Murray the largest meteorite from Oklahoma.

Etched sections of Lake Murray display both granular areas and Widmanstӓtten structures whose orientations suggest the original mass was a single austenite crystal at one time; there are also indications of significant reheating before impact – likely from some extraterrestrial shock event. While the meteorite’s kamacite previously had numerous Neumann bands, they have now largely disappeared. Its troilite is shock-melted and composed of fine-grained iron-sulfide eutectics. Schreibersite inclusions take on distinctive shapes that have been described by some as "hieroglyphic".

This 281.6 gram slice exhibits some of the aforementioned characteristics. Photo 1 shows it framed with a smaller piece that I acquired a year or so earlier. Photos 2 and 3 provide better pictures of its front and rear sides. I’ve personally found irons difficult to photograph, so Photo 4 is an animated gif taken with light reflecting at different angles to better show some of the characteristics of its crystalline structure. Photo 5 provides a front and back side close-up of the “hieroglyphic” inclusion characteristic of Lake Murray. Finally, Photo 6 depicts a cut edge to help visualize how this inclusion permeates the meteorite.


FOOTNOTES:
1 Lake Murray is a man-made earthen dam reservoir on a 10,000 acre park created in April of 1933 when Oklahoma purchased the land for $90,000. Dodson’s farm was part of that purchase.

2 Some might argue that the Brunflow, Sweden chondrite is the oldest known meteorite (it was found in Ordovician limestone dated at 450 million years old), but unlike Lake Murray, Brunflow has been completely replaced by barite and calcite with no extant extra-terrestrial material remaining.

3 One half was returned to the Tucker Museum where it has been on display ever since.
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Steve Brittenham
 3/7/2017 1:26:20 AM
Hi MexicoDoug. Thanks for the compliment - I'm glad you enjoy my submissions! I researched Lake Murray some time ago and recall the Antler Sandstone formation is dated as lower Cretaceous and the meteorite's undisturbed overlaying formation suggests Lake Murray hit at the same time the sand was being deposited. I lost a lot of my bookmarks a while back, but I believe that information came from a University of Hawaii document. Sorry I couldn't be of more help.
MexicoDoug
 3/6/2017 9:26:03 AM
Great write-up Steve, I always enjoy all you put together here! There is some nice circumstantial evidence for the age of this iron, but hopefully such a remarkable claim regarding the terrestrial age can be backed also by scientific analysis .. did you run across anything quantitative? It seems much an extrapolaton to me if the precise origin of the shale is not certain, that the main mass can be dated with certainty, ...old as it surely is!
Steve Brittenham
 3/5/2017 11:26:58 PM
Thanks all for your kind comments. I'm happy you enjoyed the pictures and write up. As an aside, I have been collecting fossils even longer than I have meteorites - more than 30 years now - and given its age, Lake Murray is for me a nice connection between the two (similarly, I also like the "paleo" meteorite NWA 2965 and its pairings, which being "fossilized" by terrestrial mineral replacement is something I often show when giving fossil talks at schools). Again, thanks for all your feedback, and also thanks to Paul for his work maintaining this site for the rest of us to enjoy!
Jansen Lyons
 3/5/2017 2:36:24 PM
Awesome story, and such a bizarre yet impressive symbol-like inclusion!
Paul Kurimsky
 3/5/2017 10:54:29 AM
Interesting history, awesome specimen!
Graham
 3/5/2017 4:37:58 AM
One of my favourites...great specimen and write up Steve.
paul gessler
 3/5/2017 1:18:52 AM
Beautiful glyphs love the slumpy nature of Lake Murray
 

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