Detailed geological mapping in the Dunmore–Halls Creek district as part of the Manilla 1:100 000 map sheet area mapping project has identified numerous complex fault slivers in what were previously mapped as Wisemans Arm Formation and undifferentiated Woolomin Group rocks. The fault slivers include schistose serpentinite masses and an association of limestone breccia and conglomerate, distinctively well-sorted sandstone and siltstone, and andesite and basalt. Previous research of the Wisemans Arm Formation in the area concluded that the dominant sedimentary component consists of deep-water marine argillite and sandstone with minor orthoconglomerate. The limestones, volcanic rocks and cherts were considered allochthonous within this package, representing exotic olistoliths. The limestones are of Late Ordovician to Early Silurian age, and the chert bodies are of possible Early Devonian or Early Carboniferous age. The otherwise undated strata are intruded by felsic dykes of Late Permian or Early Triassic age. Recent mapping, using high-resolution radiometric and magnetic imagery as an interpretative tool, has determined that the limestones (and associated distinctive sandstones), volcanic rocks and serpentinites are fault slivers developed along local to regional-scale, folded thrusts within the Wisemans Arm Formation. The serpentinites are commonly closely spatially associated with the limestone–sandstone–volcanic rock package. The bounding faults exhibit a general northerly strike, but curve abruptly to east–west along the flanks of the Moonbi Range. Those faults may represent early structures developed throughout an accretionary wedge which was produced adjacent to a subduction zone until the late Carboniferous. The recognition of the fault-bounded relationships of these limestones (previously interpreted as olistoliths) has resulted in their removal from the Wisemans Arm Formation, which is now regarded as a debris flow-rich package hosting allochthonous cherts. The interlayered, fault-bounded limestone–sandstone–volcanic rock package is now defined as the Glen Bell Formation.