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Meteoritic event recorded in Antarctic ice

¹ Department of Geological Sciences, Case Western Reserve University, Cleveland, Ohio 44106
² Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801
³ Space Sciences Laboratory, University of California, Berkeley, California 94720
⁴ Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755-1290
⁵ Lawrence Livermore National Laboratory, Livermore, California 94550

During systematic sampling of volcanic ash (tephra) layers at a well-known Antarctic meteorite collection site (the Allan Hills main ice field), a band of unusually dark and rounded (many spheroidal) particles was discovered. This debris layer (BIT-58) extends parallel to the stratigraphy of the ice established from the tephra bands, apparently marking a single depositional event. The shapes, internal texture, major element composition, and levels of cosmogenic nuclides of particles from within BIT-58 all strongly suggest that this material represents ablation debris from the passage of a large H-group ordinary chondrite. Preliminary cosmogenic isotope dating suggests an age of 2.8 Ma, implying that the East Antarctic ice sheet has been stable since that time. The relationship of the Bit-58 layer to known impact events is not clear.

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