Figure F4. Firmground in light olive gray bioclastic wackestone overlain by light gray bioclastic packstone at 29 cm. The top of the firmground marks the boundary between Subunits IIIB and IIIC. The boundary is diffuse due to burrow mottling. Note how the lighter packstone is piped down into the upper 23 cm of the darker wackestone. The vertical 1-cm-wide burrow that extends downward from 46 to 51.5 cm probably belongs to a new ichnogenus (interval 182-1132B-21X-5, 15-55 cm).