The Brangane Asteroid Family Disruption: Source of the Late Eocene 2.5 Million Years of Dust Deposition, Impacts, and H Chondrite Meteoroids

Extraterrestrial material fell on the Earth at an enhanced rate during the Late Eocene (~35 Ma): anomalous 3He abundances in marine sediments indicate that the flux of <50 μm dust was enhanced by up to ~8 times for ~2.5 My; during this interval at least two multi-km bodies impacted to form the Popigai and Chesapeake Bay craters.

Siderophile element ratios from impactites of the Popigai crater and the associated, globally-distributed, spinel-bearing spherules have been interpreted as indicating an L or LL chondrite impactor. Cr isotope data from the spinel-bearing spherules unequivocally indicate that this impactor was an ordinary chondrite, but don't distinguish between H, L and LL. However, disruption of an H chondrite parent is indicated by a peak in H chondrite cosmic ray exposure ages of 33 - 36 My matching the interval of enhanced dust production. The meteorites of this peak have types of 3 to 6 indicating that a sizeable body was disrupted.

Increasing numbers of asteroid orbits allow identification of additional asteroid families whose cogenesis may be further tested with SDSS spectral data. Only one young S-type family named after asteroid 606 Brangäne has an age (50±40 My) encompassing the indicated Late Eocene disruption. Analysis of proper orbital elements in conjunction with SDSS colours now yields ~40 members of the Brangäne family. The amount of spectral reddening of the family members is reasonable for this age. SDSS family colours are unusual compared to those of other S-type families, but this could be consistent with an H chondrite lithology as some of the other S-type families are indicated as of L chondrite affinity. The Brangäne family is relatively well positioned in the inner part of the Middle Belt near the 3:1 resonance to allow large bodies to be perturbed into Earth-crossing orbits within the necessary <1 My.