Siderophile elements from the Eyreville drill cores, of the Chesapeake Bay impact structure do not constrain the nature of the projectile

Fifteen impactites from various intervals within the Eyreville cores of the Chesapeake Bay impact structure were sampled to measure siderophile element concentrations. The sampled intervals comprise basement-derived rocks with veins, polymict impact breccias and associated rocks, and crater fill sediments. The platinum group element (PGE) concentrations obtained are generally low (iridium concentrations, seem to have fractionated and do not show a non-chondritic pattern. There is no clear distinction in terms of concentration between the different impactite units. Over the last few years, only the impact melt rocks from the 823 m deep Cape Charles test hole, drilled over the central uplift of the structure, have generated a bulk chondritic signature of 0.01 to 0.1 wt% meteoritic contribution based on a mixing model of 187Os/188Os isotopic ratios and Os concentrations (Lee et al., 2006). However, none of the samples studied shows PGE abundances that enable identification of the type of projectile responsible for the formation. Hence, it is at present not possible to link the Chesapeake Bay impact to the proposed ordinary chondrite falls recorded for other late Eocene craters, the 100-km diameter Popigai impact structure in Siberia and 7.5-km Wanapitei structure in Canada. The absence of a clear projectile signature hinders further possible discussions on the existence and the nature of the late Eocene shower event (asteroid versus comet) for now.