391 A Silicified Late Triassic (Norian) Bivalve Molluscan Fauna

A taxonomically rich and ecologically diverse silicified bivalve-dominated fauna is critically examined from the upper Norian Hound Island Volcanics of Kuiu Island, southeast Alaska. More than 1000 silicified bivalve specimens isolated by acid digesion of carbonate blocks yield a wealth of taphonomic, paleoecologic, paleogeographic, and taxonomic information. Petrographic analyses and scanning electron microscopy reveal specimens are preserved with silicification fabrics of quartzine-lutecite bladed masses and spherulitic chalcedony conserving fine details of original skeleton by both selective and complete replacement. Taphonomic indices indicate the fauna represents a parautochthonous stormcondensed assemblage of a shallow subtidal and relatively soft-bottom carbonate setting. Bivalves, ammonoids, conodonts, and the hydrozoan Heterastridium largely suggest a late Norian (Gnomohalorites cordilleranus ammonoid zone) age for the fauna.