Supporting Online Material Captions
Table S-1 The chemical compositions of a few key minerals and glasses of impact origin in the heterolithic Bedout suevite and melt breccia, obtained by electron microprobe analysis. Uncertainties are +/- 3% when there is more than 1 wt% of an element and +/- 5% at 0.2 wt%. (data collected on a JEOL Superprobe at Cornell University, under the supervision of J. Hunt). Analyses 21 and 22 do not add up to 100% and are attributed to water in the chlorite. Oxide sums do not add to 100% because all iron is assumed to be FeO. Natural and synthetic glass and mineral standards are used for the calibration.

Table S-2 S-7a,b (1-3) - Lagrange-3255 m. Electron microprobe analysis of the lighter (K-spar) and darker (albite) parts of the feldspar lath in Fig. 7a,b including the glassy matrix.

S-1, Large shocked quartz grains with planar deformation features (PDFs) identified in the Fraser Park, Sydney Basin Permian-Triassic boundary layer. Quartz grains are mounted in oil and photographed in plane polarized light.

S-2. Stratigraphic columns of key wells in the Canning Basin region (after Smith et al, 1999, ref 15).

S-3. The Bedout-1 core (A) displays numerous large and sub-rounded and angular inclusions set in a dense glassy matrix. The term ‘melt breccia’ is used to describe impact breccias that contain discrete fragments of rock and minerals together with bodies of melt in a glassy matrix of fine-grained material. The Bedout melt breccia is similar in appearance to impact breccias in the Chicxulub Yax-1 core (B) (Yax-1 figure provided by B. Dressler).

S-4. Top photomicrograph of Bedout 3044 m (9986 ft.) in plane light shows a transparent plagioclase lath set in a matrix of plagioclase microlites, opaques and altered glass. Lower photomicrograph shows the same view in crossed nicols with a maskelynite core (as isotropic glass) of plagioclase lath. Field of view is 330 µm.

S-5. Top photo of Bedout 3044 m (9986 ft.) in plane light shows a transparent plagioclase lath. Lower photo shows the same view under crossed nicols with a maskelynite core (as isotropic glass) of the plagioclase lath. Note that the orientation of the plagioclase lath is at 45 degrees to the polarizer. Field of view is 660 microns.

S-6. Back Scattered Electron Image of Bedout-1 3044 m (9986 ft.) that shows rounded clasts of chlorite surrounded by a reaction rim of Fe-Ti oxides (bright specks). Matrix is a heterogeneous mixture of albitic feldspar, altered glass and Fe-Ti oxides. Scale bar is 50 microns (in top photo).

Enlargement of Fe-Ti oxide grain that displays complex chemical heterogeneity (lower photo). Darker regions are Ti-rich and lighter regions are Fe-rich. Volcanic phenocrysts would typically show concentric zonation rather than discontinuous linear regions, each with a distinct chemical composition. Scale bar is 10 microns (in lower photo).

S-7. Lagrange-1 (LG-3255 m) cuttings sample (S-7a top photo) displays feldspar crystallites in 'swallowtail' terminations, indicative of rapid crystallization from the glassy matrix. The laths display heterogeneous compositions (Table S-2) derived from the impact process and are chemically unique in comparison to ordinary volcanic feldspars. Fig. 7b. (lower photo) #1 denotes the chemistry of albite, #2, feldspar and #3, the glass matrix.

S-8. A single plagioclase lath with multiple sets of fractures from 3041 m (B-9977 ft.). Lamellae structures are approximately perpendicular to the length of the crystal. Upper photo is in plane polarized light; lower photo is under crossed nicols. Long dimension of slide is 3 mm.

S-9. Altered plagioclase lath under crossed nicols from the Bedout-1 core at 3041 m (B-9977 ft.). Note the shattered lamellae perpendicular to the length of the plagioclase crystals. Fractured/altered plagioclases in B-9977 ft. have suffered argon loss and perhaps K addition resulting in anomalously young Ar/Ar ages. Long dimension of slide is 3 mm.

S-10. A glassy fragment from Bedout-1 at 3036 m (B-9960 ft.). Upper photo is in plane light; lower photo is under crossed nicols. Several clasts contain mostly dark colored glass with microlites of plagioclase feldspar, rimmed by brownish glass with a flow pattern. This glass is partially chloritized. Notice the black fragment (likely coal) lower center. To the far upper/lower right are microcyrstalline feldspars (whitish) of a distinctly different composition that contrast to the darker glassy fragments. Long dimension of slide is 3 mm.

S-11. Multiple, glassy, microcrystalline clasts at 3036 m (B-9960 ft.). Variable glass compositions are indicated by different colors in plane polarized light (upper photo). Notice the brownish, glassy, patches, partially chloritized within larger, darker, glassy fragments. Alternatively, these glassy patches could be later pore/vug fillings/alteration phases now chloritized. The thin vein in the center is calcite. Long dimension is 3 mm.

S-12. Heterolithic glassy, microcrystalline fragments from 3036 m (9960 ft). Notice the different shapes and sizes of clasts with varying degrees of microcrystallinity of the plagioclase microlites. Brighter, white areas are carbonate. Upper photo is in plane polarized light; lower photo is taken under crossed nicols. Long dimension is 3mm.

S-13. A calcite glassy vein between two dark glassy feldspar microcrystalline fragments at 3037 m (9964 ft). Colors are enhanced in the lower photo under crossed nicols by insertion of a gypsum plate. Long dimension is 0.6 mm.

S-14. Heterolithic, glassy, microcrystalline fragments with interstitial altered glass at 3037 m (9964 ft). Upper photo is in plane polarized light. Lower photo (crossed nicols) has interference colors enhanced by insertion of a gypsum plate. Long dimension of slide is 0.6 mm.

S-15. 1994 AGSO multichannel seismic line S120-04 showing both wells, a more pronounced annular depression, central uplift and end-Permian (blue line) and older sequences (orange, Pre-Permian; red, Precambrian). The reflectors for the older sediments are not well resolved as the lines are carried toward the central uplift and in the deeper Precambrian basement and appear dashed on the interpretation.

S-16. High-resolution single channel seismic profiles and interpretations crossing the Mjolnir crater structure. The central uplift extends well above the pre-impact surface (horizon UB) and is attributed to differential subsidence in the annular trough around the peak due to loading of post-impact sediments. A similar process may have altered the elevation of the Bedout High. Figure provided by Filippos Tsikalas.

S-17. Fraction of Ar release with respect to K/Cl during step heating of the Lagrange-1 plagioclase separate.

S-18. Fraction of Ar release with respect to K/Ca during step heating of the Lagrange-1 plagioclase separate.

S-19. Ar step release (36Ar/40Ar versus 39Ar/40Ar) for the Lagrange-1 plagioclase separate.