Abstract

A low-diversity brachiopod assemblage from the upper member of the Zorritas Formation in the Sierra de Almeida, northern Chile, further confirms the presence of Lower Carboniferous (Tournaisian) strata in that region. Key taxa include Schuchertella? sp., Chilenochonetes anna new genus and species, Paurorhyncha chavelensis (Amos), and Septosyringothyris covacevichi new species. Other elements of the assemblage, including Paraconularia sp., Posidoniella sp., Bellerophon (Bellerophon) sp., Eocanites sernageominus, and Imitoceras? sp. support this Early Carboniferous age assignment. Local distribution of taxa suggests small-scale environmental control. Rhynchonelloid and syringothyroid shells, many articulated, occur in lenticular sandstone bodies that were deposited in deltaic distributary channels; chonetids, schuchertellids and mollusc-bearing, iron-rich concretions are found in siltstones and mudstones that reflect interdistributary quiet-water settings and possibly a delta-front setting. Certain elements of this fauna are also present in north-western Argentina and Peru, indicating a regional nearshore clastic regime. The closest correlation elsewhere is with the Tournaisian faunas of southeastern Australia, although analogous big-shell assemblages are found in lower Mississippian clastic strata of the central Appalachians, Ohio, and Indiana.

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