Wednesday, January 23, 2008

Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater

Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater

Sean P. S. Gulick1, Penny J. Barton2, Gail L. Christeson1, Joanna V. Morgan3, Matthew McDonald1,6, Keren Mendoza-Cervantes4, Zulmacristina F. Pearson5,7, Anusha Surendra2, Jaime Urrutia-Fucugauchi4, Peggy M. Vermeesch3,7 & Mike R. Warner3
Top of page

Impact craters are observed on the surfaces of all rocky planets and satellites in our Solar System1; some impacts on Earth, such as the Cretaceous/Tertiary one that formed the Chicxulub impact crater2, 3, have been implicated in mass extinctions4, 5, 6, 7, 8, 9, 10, 11, 12. The direction and angle of the impact—or its trajectory—is an important determinant of the severity of the consequent environmental damage, both in the downrange direction (direction bolide travels) and in the amount of material that enters the plume of material vaporized on impact2, 13, 14, 15. The trajectory of the Chicxulub impact has previously been inferred largely from asymmetries in the gravity anomalies over the crater2, 3. Here, we use seismic data to image the Chicxulub crater in three dimensions and demonstrate that the strong asymmetry of its subsurface correlates with significant pre-existing undulations on the end-Cretaceous continental shelf that was the site of this impact. These results suggest that for rocky planets, geological and geomorphological heterogeneities at the target site may play an important role in determining impact crater structure, in addition to impact trajectories. In those cases where heterogeneous targets are inferred, deciphering impact trajectories from final crater geometries alone may be difficult and require further data such as the distribution of ejecta.

Acid rain is something that I do believe has largely been discredited as a killing mechanism by and large: far too many of the critters that ought to have been vulernable to acid rain came through just fine (ie the freshwater critters such as amphibians and fish).

No comments: