Marine faunal assemblages in the Silurian‐Devonian Keyser Limestone of the central Appalachians

Abstract

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).

Tempestites recorded as variable Pentamerus layers in the Lower Silurian of southern Norway

“…The model of Silurian communities regulated by factors as sociated with water depth and accordingly restricted to zones running parallel to the shore face (Ziegler, 1965;Ziegler et al, 1968) has been criticized by other Silurian researchers, partic ularly those favoring a more detailed sedimentological approach (Makurath, 1977;Watkins, 1979;Pickerill and Hurst, 1983). Baarli (1987Baarli ( , 1988 has provided detailed analyses of the Clorinda and Stricklandia communities from the Solvik Formation of southern Norway, including appraisal of water depth linked to proximality trends after the method of Aigner (1985).…”

Benthic faunal associations in the Lower Silurian Solvik Formation of the Oslo‐Asker Districts, Norway

“…The eurytopic species stood the best chance of enduring and responding to deterioration of the environment in order to ultimately take over vacant niches (Bretsky & Lorentz 1970). In Wenlock or Ludlow time this close relationship with depth seems not to have persisted (Hurst 1975;Watkins 1979;and Makurath 1977). Bretsky & Lorentz (1970) suggested that long stability leads to the development of complex biotic systems composed of stenotypic species.…”

Ordovician trimerellacean brachiopod shell beds

“…~ The Eodinobolus (trimerellacean) shell beds in the Ordovician of central New South Wales exhibit some resemblances to the pentameride shell beds described from Silurian and Devonian strata of Europe and North America (Ziegler et ul. 1966;Makurath 1977;Johnson 1977), but there are also some important differences. Both community types are characterized by large biconvex to globose brachiopods frequently 6&70 mm in length, orientated vertically, umbo downwards with the anterior commissure raised well above the level of the sediment.…”