Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part IA: The protobranchs (Nuculidae, Sareptidae, Pristiglomidae)
Hickman, C.S. (2025). Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part IA: The protobranchs (Nuculidae, Sareptidae, Pristiglomidae). Paleobios 42(4): 1-29. https://dx.doi.org/10.5070/p9.47113
In: Paleobios: Berkeley. ISSN 0031-0298, meer
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| Author keywords |
taxodont dentition, nacre, Eocene-Oligocene transition, Cascadia Margin, methane seep, peri-seep biotope |
| Abstract |
Systematic description and illustration of protobranch bivalves of the late Eocene–early Oligocene Keasey Formation in Oregon follows previous monographic treatments of the Keasey anomalodesmatans, heteroconchs and pteriomorphs. Of the three protobranch families documented here, this is the first recognition of Sareptidae and Pristiglomidae in the fossil record of the Northeastern Pacific and Cascadia Margin, as well as recognition of three undescribed species of Nuculidae. Small size and poor preservation contribute to previous failure to notice them in the field. New taxa include Nucula (Nucula) cascadensis, Ennucula keaseyesis, Sarepta oregonensis, Sarepta nascif, and Pristigloma mistensis. Nucula (Nucula) n. sp. is treated in open nomenclature pending discovery of additional material. Acila (Truncacila) nehalemensis is one of the most abundant and frequent bivalves in the formation. Because of the longstanding importance of the truncate acilas in Paleogene biostratigraphy, comparative accounts and illustrations are provided for three superposionally important species from the Eugene and Pittsburg Bluff formations in Oregon and the Twin River Formation in Washington. The Keasey Protobranch Association is an important component of the transitional peri-seep biotope at three distinctive Keasey methane seeps. The association also occurs throughout the formation at localities where protobranchs are preserved in fine-grained tuffaceous siltstones with gadilinid scaphopods and deposit-feeding taxa with living relatives adapted to dysoxia, diffuse methane seepage, and toxic geochemistry. Treatments include global biogeographic references and comparisons with similar taxa and molluscan assemblages, notably in the basins of southern New South Wales, South Australia, Western Australia, New Zealand, and Antarctica as well as active Western Pacific Margin settings in northern Japan and Far Eastern Russian Kuril Islands, Sakhalin Island, and Kamchatka Peninsula |
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