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Color: gravity over the Chicxulub impact structure (courtesy of Alan Hildebrand and Mark Pilkington, Geological Survey of Canada). In September-October 1996, 34 Ocean Bottom Seismograph (OBS) deployments were made along two of the three multi-channel seismic lines shot by the M/V GECO Sigma. Deployments were made by the R/V Longhorn (see cruise reports), operated by the University of Texas Marine Science Institute in Port Aransas, Texas. The data recorded by these instruments is being used to model the crustal structure beneath Chicx-A and Chicx-B. Below we show what these data reveal about the upper structure beneath Chicx-A (results are from Christeson, G.L., R.T. Buffler, Y. Nakamura, and the Chicxulub Working Group, Upper crustal structure of the Chicxulub impact crater from wide-angle ocean bottom seismograph data, GSA Special Paper #TBA, Proceedings of the 1997 Sudbury Conference on Large Meteorite Impacts and Planetary Evolution, in press, 1998).

Velocity model of the upper crustal structure along Chicx-A/A1 - velocities are only shown where constrained by the OBS data. The lowered velocities in the shallow crust between model offsets 85-225 km are interpreted as Tertiary sediments infilling the crater.