SHOCK-INDUCED EFFECTS OF CALCITE CRYSTALS WITHIN THE KAIBAB LIMESTONE AT METEOR CRATER, ARIZONA

Samples of the Permian Kaibab Limestone in Meteor Crater, Arizona are being studied to determine the crystal defects (e.g. twinning, dislocations) within the calcite crystals in conjunction with indicators for the level of shock in which the samples were subjected to (e.g. XRD peak half-width intensities) as a result of a meteorite impact. Samples were taken along transects within the crater wall and from the crater rim outward within the debris sheet. The Kaibab within the crater is predominantly dolomudstone with layers that contain coarse secondary calcite crystals, resulting from replacement of evaporites before the impact. The debris sheet is composed of a fine dolomudstone in a fine sandstone dolomudstone matrix. The samples collected within the crater can be compared to the Kaibab exposed outside the impact crater. The samples outside of the impact crater are considered a baseline for understanding the deformation that occurred during the impact event. Interestingly, Meteor Crater does not contain any shatter cones, yet the pressures were high enough to convert quartz into coesite and stishovite. Meteor Crater is a prime environment to study calcite deformation because of its relatively recent formation (49,000 ± 3000 ybp) and the absence of post impact tectonic events. Since the hand samples contain no obvious signs of deformation, microscopic techniques are used for the determination of structural deformation (e.g. plane light petrography, scanning electron microscopy, and XRD). Examining the calcite deformation at various locations within and surrounding the crater provide information about the levels of shock the samples were subjected to. This information should provide insight into how calcite deforms during an impacting event. Criteria developed in this study may be used at other proposed impact sites hosted by carbonates (i.e. Haughton, Chicxulub, Kentland) that lack shocked quartz or shatter cones in order to decipher the record of impacting events where an impact event is proposed but not certain.