Late Cambrian hard substrate communities from Montana/Wyoming: the oldest known hardground encrusters

摘要: Hardground surfaces from the Late Cambrian Snowy Range Formation in Montana/Wyoming are oldest known non-reefal hard substrates exhibiting encrusting fossils. These range age Early Franconian to early Trempealeauan. Hardgrounds were developed on slightly hummocky planar, truncated of glauconite-rich, carbonate, flat pebble conglomerates, which deposited during episodes storm scouring shallow subtidal environments shelf. hardgrounds encrusted by a low diversity assemblage fossils dominated simple discoidal holdfasts pelmatozoans, probably crinoids, and including small conical spongiomorph algae? probable stromatolites. Macroborings (e.g. Trypanites) notably absent all hardground surfaces, although sharp-walled, vertical, cylindrical holes (borings?) occur micrite clasts imbedded certain conglomerates. No evidence faunal succession or microecologic partitioning irregular was observed these hardgrounds.