Late Devonian-Early Mississippian ichnofossils from western Montana and northern Utah

Shell borings, burrows, and other trace fossils occur within the Sappington Member (Famennian-Tournaisian) of the Three Forks Formation and overlying Lodgepole Limestone (Tournaisian-late Kinderhookian) sequence of western Montana, and the Leatham (= Sappington) Formation of northern Utah. Four distinct types of well-preserved borings have been recognized on silicified invertebrate skeletons which are present within calcareous oncolites common to Sappington and Leatham strata. Two linear types are ascribed to the work of polychaete annelids and are interpreted as pre-depositional. The third boring type is slit-like and is attributed to the activity of acrothoracican barnacles. A fourth type, which is cylindrical, is thought to represent a postdepositional living burrow, probably of annelid worms. Middle Sappington shales and siltstones contain the striking double arrow-shaped Bifungites burrow. Scalaritubа burrows are present in the middle Leatham and in both the upper Sappington and lower Lodgepole beds. Zoophycos occurs at the top of the Sappington, is characteristic of the Cottonwood Canyon Member (basal Lodgepole) and common in the upper Lodgepole Limestone. Double ribbon herring-bone trails, cylindrical burrow-fills, and fine, vermicular, meandering grazing trails are also present.

The succession of ichnofacies ranges from shallow littoral Cruziana? facies (Sappington and Leatham) to Zoophycos facies (upper Sappington and Lodgepole) with some alternation in the lower Lodgepole Limestone. Palaeoichnology supplements the modern carbonate analog model for interpretation of the environments of deposition.