Showing papers in "Veliger in 1996"

A new species of Abyssochrys (Gastropoda : Loxonematoidea) from a middle Eocene cold-seep carbonate in the Humptulips Formation, western Washington

Abstract: A very small, localized, authigenic carbonate deposit within the lower part of the middle and early late Eocene Humptulips Formation in Grays Harbor County, Washington, preserves a molluscan fauna that is unique among recognized ancient chemosynthetic assemblages because the dominant faunal member is a large loxonematoidean gastropod, Abyssochrysos raui, sp. nov. The associated megafauna includes an unidentified neritiform gastropod, modiolid, thyasirid, and lucinid bivalves, numerous specimens of the bivalve Vesicomya sp., worm tubes, and crustacean fragments. This is the first record of the genus Abyssochrysos from the northeastern Pacific Ocean, the oldest record for the genus, and the first report of Abyssochrysos from a chemosynthetic environment. I N T R O D U C T I O N The gastropod superfamily Loxonematoidea Koken, 1889, has a diverse pre-Cretaceous fossil record worldwide (Hoare & Sturgeon, 1985), but is almost unknown in Tertiary rocks. The Loxonematoidea contains only two surviving families; the Provannidae Waren & Ponder, 1991, and the Abyssochrysidae Tomlin, 1927. The Provannidae presently includes four genera (Waren & Bouchet, 1993), and almost all are exclusively from hydrothermal vents or cold seeps. The only fossil record for the Provannidae is Provanna antiqua Squires, 1995, from late Eocene and Oligocene cold-seep deposits in Washington State (Goedert & Campbell, 1995; Squires, 1995). The Abyssochrysidae includes five living species, and all are rare: Abyssochrysos bicinctum Bouchet, 1991, from the Makassar Strait, Indonesia; A. brasilianum Bouchet, 1991, from the continental slope, southeastern Brazil; A. eburneum (Locard, 1897), from off of northwestern Africa; A. melanioides Tomlin, 1927, from bathyal depths off South Africa (Houbrick, 1979) and southeast Asia (Bouchet, 1991); and A. melvilli (Schepman, 1909) from bathyal depths in the Indo-West-Pacific (Figure 1). The only previous fossil record for the genus Abyssochrysos was from early Miocene strata at Suva, Fiji, where fossils of A. melvilli have been found (Ladd, 1977; Houbrick, 1979). Little is known about the ecology of Abyssochrysos, and Abyssochrysos has not been reported previously from chemosynthetic environments. A fossil molluscan assemblage preserved in an authigenic carbonate deposit within the Humptulips Formation in western Washington was first described by Goedert & Squires (1990). We have discovered another previously unrecognized paleocommunity within a cold-seep carbonate (CSUN loc. 1583) in the lower part of the Humptulips Formation (Figure 2), and the purpose of this paper is to Page 66 The Veliger, Vol. 39, No. 1 . bicinctum V , A. melvilli _ Abyssochrysos melanioides ^ ^ ^