Fig. 2.

Sedimentary and diagenetic fabrics of BST mudstones. (A) SEM micrograph of mudstone fabric in the “Great Eldoniia Layer” (GEL) of the Burgess Shale, showing random orientations of clay mineral grains and absence of coarser grained particles. (B) Polished slab showing the GEL (arrow) with thinner beds over and underlying it. (C) SEM micrograph showing displasive growth of 5–15 μ rhombohedra of authigenic calcite (low-lying areas) within an extensively cemented bed in the Wheeler Formation. Individual clay mineral grains have been forced to the margins of the calcite crystals. The sample has been etched with HCl; clays stand out in relief. (D) Thin section micrograph of Burgess Shale (Greater Phyllopod Bed) showing concentration of authigenic calcite cements (bright) at bed tops (at both the top and bottom of image). (E) X-radiograph of polished slab of Burgess Shale containing the GEL (arrow), showing the distribution of bed-capping authigenic carbonate cements. Bright areas correspond to high wt. % CaCO₃. Extensive bed-capping cement is present at the top of the GEL as well as at the tops of the thin, millimeter-scale beds that overlie it. (F) Backscatter SEM micrograph of pyrite cluster from a Chengjiang event bed at 12.96-m depth in the Haikou core showing fine grain size (1–5 μ) and aggregative habit of octahedra and pyritohedra.