Abstract

Emsian (upper Lower Devonian) limestones exposed on Kasaan Island in southeastern Alaska are preserved within the accretionary Alexander Terrane associated with Paleozoic deposits that formed within an island arc. These limestones yield nine benthic marine communities, including several new brachiopod associations, which are defined on the basis of field data correlated with a cluster analysis. Biologic and sedimentologic evidence is integrated with community group assignments in order to substantiate the paleoecology and evolutionary history of each community. These faunas were adapted to a spectrum of relatively quiet water habitats, including restricted, shallow subtidal areas nearshore, offshore biostromal banks, and open and restricted portions of a lagoon or shelf. A comparison of each community with coeval assemblages from the Cordillera and elsewhere reveals that these communities are unique to southeastern Alaska. Although patterns of community evolution are similar to those expressed in other areas of the world, these faunas originated in biogeographic isolation from other parts of the Cordillera, presumably a result of early Paleozoic island arc construction at a site offshore from the ancient continental margin.