Extended Data Fig. 1. Vermiform microstructure of microfacies i.

Elaboration of Fig. 2d. a, Vermiform microstructure is intercalated with detrital sediment (lower 1/3 of image) that includes calcimicrobialite clasts. b, Three-dimensional meshwork of vermiform microstructure transected by the plane of the 30-μm-thick thin section shows anastomosing tubule system; enlarged from a. c, Anastomosing tubules occluded by clear blocky calcite enclosed by cloudy calcite groundmass of slightly smaller crystals; enlarged from b. The tubules have no constructional walls and are defined by the dark enclosing groundmass. Oriented sample MV63 in plane-polarized transmitted light.