A fossil winonaite-like meteorite in Ordovician limestone : a piece of the impactor that broke up the L-chondrite parent body?

Abstract

About a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body ∼470 Ma∼470 Ma ago, the largest documented breakup in the asteroid belt in the past ∼3 Ga∼3 Ga. A window into the flux of meteorites to Earth shortly after this event comes from the recovery of about 100 fossil L chondrites (1–21 cm in diameter) in a quarry of mid-Ordovician limestone in southern Sweden. Here we report on the first non-L-chondritic meteorite from the quarry, an 8 cm large winonaite-related meteorite of a type not known among present-day meteorite falls and finds. The noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the L-chondrite parent body, creating one of the major asteroid families in the asteroid belt. After two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone, it appears that the meteorite flux to Earth in the mid-Ordovician was very different from that of today.