Complex craters: Relationship of stratigraphy and rings to impact conditions

One of the key issues associated with the understanding of large scale impa cts is how the observable complex crater structural features (e.g., central peaks and pits, flat floors, ring shaped ridges and depressions, stratigra phic modifications, and faults) relate to the impactor's parameters (e.g., radius, velocity, and density) and the nonobservable transient crater measu res (e.g., depth of penetration and diameter at maximum penetration). We ha ve numerically modeled large-scale impacts on planets for a range of impact or parameters, gravity and planetary material strengths. From these we foun d that the collapse of the transient cavity results in the development of a tall, transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary str ength to produce a wide range of the observed surface features. In addition , we found that the underlying stratigraphy is inverted outside of the tran sient cavity diameter (overturned flap region), but not inside. This change in stratigraphy is observable by remote sensing, drilling, seismic imaging and gravity mapping techniques. We used the above results to develop scali ng laws and to make estimates of the impact parameters for the Chicxulub im pact and also compared the calculated stratigraphic profile with the intern al structure model developed by Hildebrand et. al. [1998], using gravity, s eismic and other field data. For a stratigraphy rotation diameter of 90 km, the maximum depth of penetration is similar to 43 km. The impactor diamete r was also calculated. from the scaling relationships we get for a 2.7 g/cm (3) asteroid impacting at 20 km/s, or a 1.0 g/cm(3) comet impacting at 40 k m/s, an impactor diameter of -13 km, and for a comet impacting at 60 km/s, an impactor diameter of -10 km.