The development of an Early Ordovician hard ground community in response to rapid sea-floor calcite precipitation

摘要: The Kanosh Shale (Upper Arenig, Lower Ordovician) of west-central Utah. USA. contains abundant carbonate hardgrounds and one the earliest diverse hardground communities. were formed through a combination processes including development early digenetic nodules in clay sediments which exhumed concentrated as lags by storms. These cobble deposits. together with plentiful biogenic metrical. cemented inorganically precipitated calcite on sea floor. forming intraformational conglomerate hardgrounds. Echinoderms may have -played critical role faunas since their disarticulated ossicles rapidly syntaxial overgrowths. additional cobbles echinoderms thus taphonomically facilitated some hard substrates they required. A significant portion cements been derived from dissolution aragonitic mollusk shells. species include bryozoans recorded large numbers stemmed echinoderms. primarily rhipidocystid cocrinoids. Bryozoans covered nearly equal areas surfaces. there was distinct polarization between preferred upper. exposed portions others most common undercut. overhang fossils combine elements Late Cambrian assemblages Middle Ordovician faunas, confirming predicted trends community evolution. especially replacement cocrinoids and. to lesser extent, other echinoderms, crinoids. marks transition Fauna Paleozoic ecosystem. *Carbonate hardgrounds, aragonite dissolution, cement, Echinodermara, Trepostomata, Nicholsonclla. Dianulites. Porifpra. taphonomic facilitation, Pogonip Group, Shale. Ordovician.