Shallow Carbonate Seas

Shallow carbonate seas include several carbonate environments, all of which lay at or below fair-weather wave base. A high range of communities inhabited this zone, including level-bottom, reefal, and hardground communities. The latter two are scrutinized elsewhere (Pratt et al. and Rozhnov, both in this volume).

In terms of taxonomic composition and dominant feeding strategies, Early and early Middle Cambrian level-bottom communities were similar to coeval reefal settings but differed by absence of heavily calcified organisms. In both cases, filter and suspension feeders dominated in both number and diversity (Zhuravleva et al. 1982, 1986; Wood et al. 1993; Kruse et al. 1995) (figures 10.2.1 and 10.2.2).

The shallow level-bottom community underwent significant changes during the Cambrian (see tables 10.1 and 10.2). After the demise of the Tommotian Evolutionary Fauna by the end of the Early Cambrian, communities were dominated by trilobites and lingulate brachiopods until the Middle Ordovician in Laurentia and Siberia (Sep-koski and Sheehan 1983; Sukhov and Pegel' 1986; Varlamov and Pak 1993), as well as in Australia, China, and Kazakhstan. During the Steptoean-Early Ordovician, community reorganization proceeded through the addition of new elements, especially gastropods, rostroconchs, and, from the Datsonian, cephalopods (Chen and Teichert 1983). In the Marjuman, trilobites account for two-thirds of the species present, associated with inarticulate brachiopods and hyoliths (Westrop et al. 1995). By the Datsonian-Early Ordovician interval, paleocommunity compositions were split more or less evenly between trilobites and mollusks. Finally, during the Middle Ordovician, trilobites were reduced to about one-third of the species composing communities (Westrop et al. 1995).

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