The Upper Silurian Keyser Limestone is a relatively thin ( < 8 5 m) unit of lagoonal, barrier, and shallow offshore sediments that crops out in the central Appalachians. Lithologies include massive micritic limestones to calcarenites, calcisiltites, and calcareous quartz arenites. The barrier lithofacies is preserved p r e dominantly as tidal inlet channel-fill. Its presence is supported by two lines of evidence: (1) the sequence of sedimentary textures and structures resembles that observed in modern inlets, and (2) the sequence occupies a position immediately above a disconformity, and is accompanied by an abrupt vertical change in faunal

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Sedimentological analysis of the Keyser Limestone (Upper Silurian ‐ Lower Devonian of the central Appalachians) indicates that its sediments were deposited in a range of marginal and shallow marine environments. Major depositional environments include: tidal flat, lagoon, barrier bar and island, and open marine shelf. Each major environment is represented by a lithofacies which is lithologically and faunally distinct. Tidal flat lithofacies are characterized by eurytopic organisms, including ostracodes, gastropods, stromatoporoids and blue‐green algae. Lagoon lithofacies are dominated by bryozoans, brachiopods, ostracodes and stromatoporoids. Barrier lithofacies are characterized by rooted crinoids, encrusting bryozoans and robust brachiopods. Open shelf lithofacies contain a diverse fauna of cystoids, crinoids, bryozoans and brachiopods. The distributions of faunal assemblages in the Keyser show no simple relationship to either water depth or distance from shore. They are, in general, related to the distributions of depositional environments. Recurring associations of brachiopod genera were not found in the Keyser. With few exceptions, any genus may be found in any subtidal environment. Abundance of brachiopods is related to the abundance of local hard substrates (usually bryozoans).