A silicified Late Triassic (Norian) bivalve molluscan fauna from the Alexander terrane, southeastern Alaska by C. A. McRoberts. Bulletins of American Paleontology, 391: 1-108. 2017
This 108-page volume presents a a taxonomic description and taphonomic and paleoecologic analyses of a well-preserved silicified Late Triassic bivalve fauna from the Alexander terrane of southeastern Alaska. If you are interested in ordering Bulletin 391, it costs $40 and and may be purchaed through the Publicatoins Office of the Paleontological Research Institution at publications@museumoftheearth.org. 
Abstract—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 storm condensed 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.
The assemblage is taxonomically rich, containing 31 recognizable bivalve species (or equivalent taxa in open nomenclature) distributed amongst 11 orders, 17 superfamilies, 24 families, and 30 genera. Of the 31 taxa, 12 are incompletely known and left in open nomenclature and the following 11 are new: Palaeonucula muffleri n. sp., Pinna keexkwaanensis n. sp., Plagiostoma scallanae n. sp., Entolium alaskanum n. sp., Filamussium walleri n. sp., Harpax articulatum n. sp., Erugonia boydi n. sp., Minetrigonia newtonae n. sp., Myophorigonia parva n. sp., Palaeopharus orchardi n. sp., and Tancredia norica n. sp. The Erugoniidae n. fam. is proposed for smooth shelled trigonoideans with trigoniid grade dentition but lacking marginal carina. The fine-scale preservation and large sample size revealed previsoulsy unrecognized morphologic details permitting revision of two bivalve families (Palaeopharidae Marwick, 1953 and Palaeocarditidae Chavan, 1969) and one genus (Septocardia Hall & Whitfield, 1877). The most diverse group is the Pteriomorphia with 16 species (51.6% of species and 69% of individuals), followed by the Heteroconchia with 12 species (38.7% of species and 28% of individuals) and Protobranchia with three species (9.7% of species and 2.8% of individuals). The assemblage is dominated by the pterioid Cassianella cordillerana McRoberts in McRoberts & Blodgett, 2002, which, taken with other reclining suspension-feeding species, accounts for 43.9% of individuals. Shallow infaunal burrowers comprise the second most common
trophic group (27.6% of individuals), followed by epifaunal cementing forms (15.5% of individuals). The assemblage is dominated by endemic taxa, yet several species are known from other Norian faunas of the South American Cordillera and, to a lesser extent, North American terranes (Wrangell, Nixon Fork, and Wallowa). The biogeographic relationship with the Norian molluscan faunas of South America supports a southerly paleolatitude for the Alexander terrane with some biogeographic connection with other tropical terranes of eastern Panthalassa.