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Models of nearshore marine communities from the Paleozoic described by Bretsky, Ziegler, Boucot, Walker, Laporte, Anderson, and Goodwin overlap in species content, space, and time. These models show that (1) recurrent lateral patterns of communities exist; (2) communities persist in time; (3) communities and community patterns are linked closely to environment sequence; and (4) the same lateral community sequences may be present in terrigenous and carbonate rocks. Not well understood is (1) the relation of lateral community pattern to the onshore-offshore sequence of environments; (2) variability in the number of laterally coexisting communities; and (3) the coexistence of independently defined communities based on organisms from different phyla in a single environment. >
Two environmental patterns recur in epeiric seas. The first--low energy offshore, high energy shoal or barrier, low energy restricted, tidal flat--is a sequence associated with stable and transgressing seas. The other sequence--low energy offshore, high energy shoreline or tidal flat without restricted onshore environments--is associated with prograding shorelines (regressive seas). In Appalachian Helderbergian deposits the transgressive pattern produces a sequence of brachiopod communities which have been correlated by Boucot with Ziegler's Early Silurian brachiopod community
patterns. Tidal flat and lagoonal communities (Walker and Laporte) and an offshore cystoid-ectoproct community (Anderson and Goodwin), which are both recognized in Ordovician rocks, persist into the Devonian and coexist with the Devonian brachiopod communities. Restricted subtidal and barrier communities are absent from progradational Helderbergian rocks. This pattern is analogous to Bretsky's three-community sequence of the Late Ordovician.
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