Intensely-bioturbated mudshale in the Pennsylvanian of Ohio, USA.

The Pottsville Group is a Pennsylvanian-aged cyclothemic succession in eastern Ohio that contains nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Member (?).

The rock shown above is mudshale from the Pottsville Group. It was found loose, scattered among numerous pieces of Lower Mercer Shale in a minor landslide pile along a railroad cut. The Lower Mercer Shale is a marine unit that caps the Lower Mercer Limestone in the Pottsville Group. The non-indurated shale matrix makes up significantly less than 50% of the specimen - the rest consists of closely-packed, weathering-resistant burrow fillings. The slight orangish brown-colored areas are from iron oxide staining.

Trace fossils are any indirect evidence of ancient life. They refer to features in rocks that do not represent parts of the body of a once-living organism. Traces include footprints, tracks, trails, burrows, borings, and bitemarks. Body fossils provide information about the morphology of ancient organisms, while trace fossils provide information about the behavior of ancient life forms. Interpreting trace fossils and determination of the identity of a trace maker can be straightforward (for example, a dinosaur footprint represents walking behavior) or not. Sediments that have trace fossils are said to be bioturbated. Burrowed textures in sedimentary rocks are referred to as bioturbation. Trace fossils have scientific names assigned to them, in the same style & manner as living organisms or body fossils.

Stratigraphy: possibly (probably?) derived from the Lower Mercer Shale (just above the Lower Mercer Limestone), Pottsville Group, lower Atokan Stage, lower Middle Pennsylvanian