Fig. 6
Microscopic characteristics of type 4 oncoids. a A type 4 oncoid from the Sandaogou section, characterized by a concentric laminar structure and two nuclei (made up of trilobite debris and dark micrite); b A type 4 oncoid from the Diaoquan section, characterized by a concentric rough-laminar structure, unsmooth edges and two nuclei; c Local magnification of a, showing typical Girvanella fossils inside the dark micritic laminae with an intertwined arrangement; d Local magnification of b, showing typical Girvanella fossils inside the dark micritic laminae