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Lake Murray (Carter County, Oklahoma, USA) IIB (iron) Found 1933

A Piece of the Smoking Gun? A single 254kg mass of Lake Murray with an iron-shale coating up to 6 inches thick was found in a gully in 1933 and recognised as a meteorite in 1952. At 110 million years, this is the oldest meteorite yet discovered. Lake Murray was found in undisturbed Antler Sandstone dating from the Lower Cretaceous, suggesting that Lake Murray landed in a near-shore shallow sea while these beds were being deposited about 110 million years ago.

With such a long Earth-age, the exterior was heavily corroded and about 450kg of rusty shale surrounded the iron. However, the 254kg inner nickel-iron core was relatively unweathered, unaltered and wonderfully preserved, probably due to the thick oxide layer giving a high degree of protection to the inner core.

While acquiring the giant 3.9kg slice of Lake Murray in Tucson recently, I met with meteorite guru O. Richard Norton who explained the history and special interests of this wonderful iron to me. His following thought provoking article appeared in the centre pages of the November '99 issue of Meteorite! magazine, and has been reproduced here with the kind permission of the editor:

"Is Lake Murray a Piece of the Smoking Gun?" - by O. Richard Norton

Lake Murray dates from the early Cretaceous Period. The Cretaceous Period ended 65 million years ago with the extinction of the dinosaurs along with more than 65% of the then living species. The Antler Sandstone dates from 110 million years. Thus, the two impact events differ in time by 35 million years. Is it possible that Lake Murray is a fragment of the 10km diameter iron asteroid that impacted Earth in the Yucatan Peninsula? It is not unreasonable to imagine a main mass breaking along a pre-existing fracture zone as it neared Earth 35 million years before the great event. Lake Murray may have been an early warning signal of things to come.

Only one other known meteorite strives for the title of oldest terrestrially aged meteorite - the Brunflow, Sweden "fossil" chondrite found in Ordovician limestone dated at 450 million years. All of the meteoric material has been completely terrestrialised and replaced by barite & calcite, so it can no longer be considered a meteorite or anything more than a fossil replica.

Lake Murray is a coarsest octahedrite and the etched faces reveal large kamacite & taenite bands measuring up to 115mm across....several of these large bands contain central "rosettes" of swirling schreibersite inclusions that are so typical for Lake Murray, and some troilite nodules.


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