Response to Comment on "Bedout: A Possible End-Permian Impact Crater Offshore of Northwestern Australia"

Glikson suggests that any "true" extraterrestrial impact structure should include shocked minerals (for example, quartz with planar deformation features, or PDFs), high-pressure polymorphs (for example, coesite or diamond), shatter cones, and chondritic chemical signatures of platinum group elements (PGEs). He ignores the criteria we present (shocked glass or maskelynite) and later dismisses the data as being indicative of a volcanic breccia. Moreover, his suggestion that the identification of maskelynite in an impact breccia necessitates the presence of PDFs is incorrect. As stated in, the shock pressures for the formation of maskelynite (35 to 45 GPa) and silica glass (>45 to 65 GPa) that characterize the Bedout core are well above the shock pressures for preserved PDFs. In addition, some researchers now distinguish between "plagioclase diaplectic glass" and "maskelynite," with the latter forming without being initiated in PDFs as suggested by Glikson. Chen and El Goresy recently described maskelynite grains in several SNC martian meteorites as smooth with no cleavage, no contraction cracks, and no shock-induced fractures, which is what we see in the Bedout core [see, for example, figure 6 in ]. Thus, the notion that the presence of preserved PDFs is required to interpret maskelynite in a melt breccia core: especially one that is 250 million years old and highly altered: is overstated. The petrology and geochemistry of this "volcanic breccia," as interpreted by Glikson, are unlike those of any volcanic rock in the world. It is not surprising that, as Glikson notes, some of the clasts resemble altered basalts; as we stated in, the target rocks likely contained basalts, and unmelted basalt clasts are among the more noticeable features of the Bedout-1 core.