Initial Assessment of the Excavation and Deposition of Impact Lithologies Exposed by the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico

Introduction: The Chicxulub Scientific Drilling Project (www.icdp-online.de) recovered a continuous core from a depth of 404 m (in Tertiary cover) to 1511 m (in a megablock of Cretaceous target sediments), penetrating ~100 m of melt-bearing impactites between 794 and 895 m. The Yaxcopoil-1 (YAX-1) borehole is ~60-65 km from the center of the Chicxulub structure, which is ~15 km beyond the limit of the estimated ~50 km radius transient crater (excavation cavity), but within the rim of the estimated ~90 km radius final crater. In general, the impactite sequence is incredibly rich in impact melts of unusual textural variety and complexity, quite unlike melt-bearing impact formations from other terrestrial craters. Impact Lithologies: A coherent 24-m thick green impact melt lies near the base of the impactite sequence above one or more megablocks of target sediments. Thus far we have examined four samples from the top to the bottom of this green melt zone: YAX-1_861.4, YAX-1_863.51, YAX-1_876.46, and YAX-1_883.13, where the numbers following YAX-1 indicate the depth of the samples in meters. The green melt is generally massive in appearance, but contains flow lines on both macroscopic and microscopic scales that are suggestive of glass; nevertheless, all the melt is aphanitic and no glasses were observed. The melt is dominated by microcrystalline (2 to 50 mm) Ca-rich pyroxene (Wo 46