Fig. 4.

Thin sections perpendicular to bedding plane (upper bedding surface on top; G is a scanning electron photomicrograph, and all others (A–F, H, and I) are transmitted light photomicrographs). (A and B) Serial thin sections corresponding to labeled lines in Fig. 3C. Tri-layered vertical side walls consist of a poorly defined carbonaceous/clay layer flanked by calcispar layers (light color). Stylolites partially truncate floor walls (arrows). (C and D) Partially preserved roof (arrows) and arching vertical side walls (arrowheads) indicative of prior existence of roof. (E and F) Tri-layered pendent vertical walls with poorly preserved crystal termini (serrate interface between carbonaceous/clay and calcispar layers). Stylolites (arrows) completely truncate roof walls. (G) Backscattered electron (BSE) image of a vertical wall consisting of carbonaceous/clay layer (CC) flanked by calcispar layers (CS). (H) Lensoidal pockets of calcispar (arrows) crosscut calcispar layer of vertical wall. (I) Lensoidal pockets of calcispar (arrow) in the same thin section, with surrounding microbial laminae. (Scale bar in C applies to C–F and H–I.)