Figure 5
Location of FIB-SEM trenches and tomographic volumes. (a) Exposed grain from targeted XRM slice and surface material removal. Blue boxes highlight the milled trenches (1 and 2) (b) Schematic explaining the orientations associated with trench milling and sample surface. (c-h) Trench 1 (crust). Sample surface view (c), accompanying chemical map (key the same as for Fig. 4) (d), and view of the trench face after Atlas 5(3D) sample preparation and fine polish (e–h); yellow arrow indicates filamentous structure on crust. (f, h) Trench face highlighting false colour segmented components; yellow = crust, pink = filamentous portion of crust, blue = interior tunnel, green = (probable organic) filament within tunnel. (g) Final post-mill trench face highlighting subsurface tunnel containing a filament, with segmented version (h). (i-o) Trench 2 (tunnels/holes). (i) Sample surface view showing the milled area over hole types 1a,b from Fig. 4. (j, k) Trench face highlighting subsurface tunnels that are unobservable from XRM imaging (green circles) and surface holes (red arrow). Segmented subsurface tunnels shown in (k). (l, m) Close up view of surface holes (red arrows) from two different slices through the volume highlighting segmented Fe nodules (yellow arrows). (n, o) Two examples of slices of subsurface tunnels, both exhibiting inhabiting potential organic filamentous (white arrow) and coccoid structures (red circle).
