New Late Eocene Mollusks From Localized Limestone Deposits Formed By Subduction-Related Methane Seeps, Southwestern Washington

The trochid archaeogastropod Margarites (Pupillaria) columbiana n. sp., the mytilid bivalve Modiolus (Modiolus) willapaensis n. sp., and the vesicomyid bivalve Calyptogena chinookensis n. sp. are described from the earliest known fossil communities associated with subduction-related methane seeps. The communities are in very localized limestones of late middle to late Eocene age along the southwestern margin of Washington. These limestones contain large numbers of chemosynthetic bivalves and worm tubes, as well as other macrobenthos, that colonized around cool-temperature methane seeps along the landward slopes of an ancient subduction-zone complex.