Abstract
From mid-Ordovician ∼470 Myr-old limestone >100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body. Recently one anomalous meteorite, Österplana 065 (Öst 65), was found in the same beds that yield L chondrites. The cosmic-ray exposure age of Öst 65 shows that it may be a fragment of the impactor that broke up the L-chondrite parent body. Here we show that in a chromium versus oxygen-isotope plot Öst 65 falls outside all fields encompassing the known meteorite types. This may be the first documented example of an ‘extinct' meteorite, that is, a meteorite type that does not fall on Earth today because its parent body has been consumed by collisions. The meteorites found on Earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ∼500 Myr ago.
Highlights
From mid-Ordovician B470 Myr-old limestone 4100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body
The samples of the fossil L chondrites yield e54Cr results in agreement with an ordinary chondrite origin, that is, in the range À 0.34 to À 0.24. This indicates that whole-rock analyses of fossil meteorites provide reliable Cr-isotopic results. This is in line with previous elemental analyses of whole-rock fossil L chondrites showing that they have retained most of their original chromium[11]
The two whole-rock samples of Osterplana 065 (Ost 65) yield e54Cr values of À 0.26 to À 0.23, which are within the uncertainties of previously measured ordinary chondrites[12]
Summary
From mid-Ordovician B470 Myr-old limestone 4100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body. On the basis of 21Ne cosmic-ray exposure ages of its spinel grains this meteorite, Osterplana 065, previously referred to as the ‘mysterious object’, appears to have been liberated as a meteoroid at the same time as the other fossil meteorites[6,7,8]. It may represent a piece of the impactor that broke up the L-chondrite parent body[6]. The 54Cr values of Ost 65 are similar to those of ordinary chondrites, whereas oxygen isotopes show its affinity with some rare primitive achondrites
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