LARGE BURROWS IN FLUVIAL DEPOSITS OF THE EARLY PERMIAN (ASSELIAN) DUNKARD GROUP, SOUTHEAST OHIO, U.S.A

The Lower Marietta Sandstone of the early Permian (Asselian) Dunkard Group in southeastern Ohio contains large burrows exposed in cross section in laterally discontinuous sandstone beds. The Dunkard Group was deposited in a fluvial-lacustrine system in the continental interior at a paleolatitude between 15° N and S. This study examines the morphology of the burrows and their associated lithofacies to interpret the environmental conditions under which they were produced as well as the behavior and identity of the tracemaker. Stratigraphic sections were measured and described 1 m above and below the burrow-bearing sandstone. Sixty burrows were qualitatively and quantitatively described including general morphology, orientation, dimensions, and lateral distribution. Mudstone facies below and above the sandstone unit consist of reddish-brown to variegated paleosols containing rhizohaloes, argillans, and large-scale slickensides as well as thinly laminated, organic-rich shales containing plant fossils. The sandstone facies is 94-147 cm thick, thinly bedded to massive, and fine to medium grained. Exposed burrows consist of vertical, subvertical, J-shaped, Y-shaped, and complex branching shafts and tunnels. The burrow complexes range from 5.0–180.0 cm in length and 0.75–3.60 cm in width. The main shaft’s angles are ~90°, although some shafts can be 30–70°. Branch angles of subvertical and Y-shaped burrows vary from 0-90°. Many burrows have entrances at the top of the sandstone bed, but others turn into or out of the bed. Knowledge of the paleoenvironmental setting and extant animal behavior constrains potential tracemakers of the burrows to organisms that live in near-channel subenvironments of fluvial settings. The Dunkard burrows are similar to modern freshwater decapod burrows, particularly those of crayfish. Decapod body fossils are not known from the Dunkard Group, yet these burrows are highly suggestive of their presence. Decapod burrow morphologies are highly variable and dependent on burrow function and environment. The Dunkard burrows are indicative of secondary dwellings, with few open water attached architectures, multiple branches, and shafts likely going to the water table. The depths of the burrows suggest variance in water table level and that they were distal to the active channel.