James L. Goedert

Eocene deep-sea communities in localized limestones formed by subduction-related methane seeps, southwestern Washington

Densely populated communities of soft-bottom-dwelling taxa similar to those found today along subduction zones off the coasts of Japan and Oregon have been discovered in very localized deep-water limestones of late middle to late Eocene age along the southwestern margin of Washington. Subduction was prevalent in this area during this time, and compressive forces squeezed subsurface methanerich waters onto the ocean floor, where opportunistic bivalves (especially Modiolus , Calyptogena , and Thyasira ), vestimentiferan? tube worms, serpufid tube worms, siliceous sponges, very small limpets, trochid and turbinid archaeogastropods, and other macrobenthos colonized. These assemblages are the earliest recorded biologic communities formed in response to methane seeps in subduction zones.

Deep-sea food bonanzas: early Cenozoic whale-fall communities resemble wood-fall rather than seep communities

The evolutionary history of invertebrate communities utilizing whale carcasses and sunken wood in the deep-sea is explored using fossil evidence. Compared to modern whale-fall communities, the Eo-Oligocene examples lack those vent-type taxa that most heavily rely on sulphide produced by anaerobic breakdown of bone lipids, but are very similar in their trophic structure to contemporaneous wood-falls. This sheds doubt on the hypothesis that whale-falls were evolutionary stepping stones for taxa that now inhabit hydrothermal vents and seeps. We suggest that the whale-fall communities reported here represent a new ecologic stage among whale-falls, which we have coined the ‘chemosymbiotic opportunist stage’ and that the ‘sulphophilic stage’ of modern whale-falls developed during the Early Miocene, resulting from a significant increase in both body size and/or oil content of bones among cetaceans during this time.

A WOOD-FALL ASSOCIATION FROM LATE EOCENE DEEP-WATER SEDIMENTS OF WASHINGTON STATE, USA

Abstract Fossil wood fragments and an associated species-rich invertebrate assemblage, analogous to those found on wood falls in the deep sea today, were found in late Eocene deep-water sediments of the Lincoln Creek Formation in Washington State, United States. This assemblage is the earliest known complex deep-sea biologic community based on decaying wood as its primary source of nutrients. The 495 recovered fossils (exclusive of foraminiferans) belong to 21 species; 7 species relied directly on the wood, either by ingesting it or by feeding on xylophagous microbes; these species are also the most abundant. Seven species were predators or scavengers that were most likely attracted by the wood-dependent species. The remaining seven species represent predators, detritus feeders, and suspension feeders that may or may not have had a relation to the wood fall or its fauna. All species had a benthic mode of life, and pseudoplanktonic taxa are absent, indicating that the colonization of the wood began only once it had arrived on the deep-sea floor. The wood-dependent species belong to taxa that fill the same ecologic niche in the deep sea today, indicating that the modern wood-fall ecosystem had evolved at least by late Eocene time. There is no uniformity or specialization of dispersal strategies among the recovered taxa; they rather reflect those of the phylogenetic group to which they belong. The wood-fall assemblage described here shares several families with fossil whale falls and cold seeps but very few species, a condition that can also be observed at modern examples of these ecosystems.

Paleoecology of whale-fall habitats from deep-water Oligocene rocks, Olympic Peninsula, Washington state

Fossil mollusks associated with eight Oligocene whales from the Makah and Pysht Formations on the northwestern part of the Olympic Peninsula, Washington, suggest that whale carcass sulfide production supported small numbers of some chemosymbiotic invertebrates as early as 30 million years ago. Thyasirid and modiolid bivalves usually dominate these very localized molluscan assemblages; lucinid and nuculanid bivalves, scaphandrid, naticid, and buccinid gastropods are rarely present; brachiopods were found once. These fossils include, tentatively, the first fossil record for the bivalve genus Idasola, and the first record of the bivalve Thyasira peruviana Olsson, outside of probable cold-seep deposits in South America. n nStrata surrounding the fossil whales contain low diversity megafaunas that include rare deep-water gastropods and bivalves, large isopods, and localized cold-seep communities. The whale-fall assemblages differ significantly because of the presence of Idasola? sp. and Thyasira peruviana? and the absence of vesicomyid bivalves. Vertebrate carcasses have probably not contributed significantly to the dispersal of cold-seep and hydrothermal vent invertebrates. Seep/vent communities were well established much earlier than the evolution of cetaceans, and seep/vent invertebrates have not been found with carcasses of other large vertebrates.

The Late Eocene 'Whiskey Creek' methane-seep deposit (western Washington State) - Part II: Petrology, stable isotopes, and biogeochemistry

SummaryThe Late Eocene ‘Whiskey Creek’ deposit (Pysht Formation, Olympic Penisula, Washington State) formed at a methane-seep. Early diagenetic micrites and aragonite cement have δ13C values as low as −36‰ indicating that the seepage fluids contained methane. With respect to micrite samples, low δ13C values correlate with relatively high δ13O values andvice versa. Ongoing micrite formation after the cessation of the seepage during increased burial might have altered the isotopic composition of the microcrystalline carbonates toward lower δ13O values and higher δ13C values. Alternatively, the trend in isotope values may reflect a change in the composition of seepage fluids. The principal difference between these scenarios is the duration of seepage with respect to micrite formation. Two petrographically similar varieties of blocky calcite spar are related to different carbonate sources. The δ13C values range from −32 to −29‰ for one type of blocky spar and are either the result of methane oxidation or indicate thermal decarboxylation of organic matter. Low δ18O values are in favour of the latter. For the other type of spar, δ13C values as high as +6‰ indicate carbonate formation within the zone of methanogensis.The ‘Whiskey Creek’ limestone exhibits a chaotic fabric produced by a variety of processes, including bioturbation, concretionary carbonate formation, earlyin situ brecciation, carbonate corrosion, and late fracturing of the rock. Two varieties of micrite aggregates are responsible for the nodular fabric of the limestone. Smoothly-shaped pyritiferous micrite nodules are of diagenetic origin and formed in a manner similar to that which produces carbonate concretions. Apart from being induced by anaerobic oxidation of methane, their formation is proposed to be linked to iron reduction and sulphide formation. The second, dominant variety is represented by irregularly-shaped, nodular to angular micrite aggregates surrounded by massive rims of pyrite, resulting from carbonate corrosion. A pure, fluorescent seam-micrite, constructive in origin, lines cavities or surrounds micritic aggregates.Among authigenic non-carbonate minerals, large quartz crystals and quartz replacing aragonite cement are common constituents of the limestone. Gypsum and an unidentified prismatic calcium sulphate mineral formed in the limestone matrix. The prismatic mineral is tentatively identified as bassanite, the Ca-sulphate hemihydrate. Gypsum is the potential precursor of bassanite, the formation of which could have been induced by elevated temperatures, highly saline solutions, or both.The wide range of δ34S values obtained from ‘Whiskey Creek’ pyrite and the strong depletion in34S (S values as low as −15‰) reveal that bacterial sulphate reduction was the sulphide generating process. Comparative analyses of pyrite from other seep deposits yielded even lower values (as low as −28‰) possibly indicating the involvement of microbial disproportionation of sulphur.

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. Calyptogena chinookensis n. sp.is the earliest known species of this genus, which was previously known from Miocene to Recent.

Fossil traces of the bone-eating worm Osedax in early Oligocene whale bones

Osedax is a recently discovered group of siboglinid annelids that consume bones on the seafloor and whose evolutionary origins have been linked with Cretaceous marine reptiles or to the post-Cretaceous rise of whales. Here we present whale bones from early Oligocene bathyal sediments exposed in Washington State, which show traces similar to those made by Osedax today. The geologic age of these trace fossils (∼30 million years) coincides with the first major radiation of whales, consistent with the hypothesis of an evolutionary link between Osedax and its main food source, although older fossils should certainly be studied. Osedax has been destroying bones for most of the evolutionary history of whales and the possible significance of this “Osedax effect” in relation to the quality and quantity of their fossils is only now recognized.

Mass Occurrences of the Brachiopod Halorella in Late Triassic Methane-Seep Deposits, Eastern Oregon

The temporally and geographically scattered Phanerozoic record of methane-seep deposits hampers reconstruction of the evolution of life in chemosynthesis-based ecosystems. Unlike modern, Cenozoic, and late Mesozoic seeps, many of the known older seep deposits are typified by assemblages with profuse rhynchonellide brachiopods. Late Triassic (Norian) limestone bodies in eastern Oregon are enclosed in deep-water strata, extend laterally for up to a few hundred meters, and contain the dimerelloid rhynchonellide Halorella in rock-forming quantities. The analysis of two large limestone bodies in the Rail Cabin Member of the Vester Formation exposed near Graylock Butte, Grant County, Oregon, fosters the reconstruction of the paleoenvironmental setting of these unusual Halorella deposits, resulting in the first recognition of Triassic methane-seep deposits. The faunal assemblage includes few fossils other than Halorella. Although occasionally found at seeps, the recognized nuculanids are not seep-endemic bivalves. A Nucinella-like bivalve and a possible permophorid bivalve were likely endemic to this chemosynthesis-based environment; related bivalves lived at Jurassic and Cretaceous seeps. The superabundant, mostly articulated brachiopod shells are enclosed in a variety of micrites, including peloidal to clotted micrite. Early fibrous cement, forming banded and botryoidal crystal aggregates, preferentially occurs at the margin of the large limestone bodies but is scarce overall. Peloidal to clotted micrite and banded and botryoidal cement are common constituents of methane-seep limestones. Their negative δ13C values as low as −36‰ reveal that carbonate formation was induced by the oxidation of methane. The presence of pyrobitumen (i.e., metamorphosed crude oil) in the limestones may indicate that the seepage fluids contained oil in addition to methane. Apart from the diagnostic 13C-depleted carbonate phases, mud injections recognized in one of the two limestone bodies also bear testament to former seepage activity.

WORM TUBES IN AN ALLOCHTHONOUS COLD-SEEP CARBONATE FROM LOWER OLIGOCENE ROCKS OF WESTERN WASHINGTON

Abstract Tubes suspected to be those of vestimentiferan worms are abundant in carbonate boulders at one locality in the lower Oligocene part of the Lincoln Creek Formation along the Canyon River, Grays Harbor County, Washington. The largest tubes exhibit the same general orientation and are arranged in clusters. The tube walls are preserved as aragonite that is, in some cases, replaced by silica. The original tube walls either had a high carbonate content or were indurated very early by aragonite mineralization of the organic wall. The carbonate cements around, on, and inside of the tubes were precipitated due to the microbial oxidation of hydrocarbons at a cold-seep. After lithification, the carbonate fragmented as it slid or slumped, along with other sedimentary debris, downslope into deeper waters. This is one of the few reports of an ancient cold-seep chemosynthetic community dominated by tube worms, and the third report of an allochthonous cold-seep carbonate within a deep-water depositional setting.

Fossil Sponges from a Localized Cold-Seep Limestone in Oligocene Rocks of the Olympic Peninsula, Washington

ABsTRACr-A limited fauna of relatively simple, thin-walled, hexactinellid sponges, including moderately coarse-textured, funnellike Hexactinella(?) conica new species, fine-textured, tubular to branched Hexactinella(?) tubula new species, fragments of delicate Eurete goederti(?) Rigby and Jenkins, 1983, and Farrea(?) species, has been found in the Oligocene Lincoln Creek Formation on Canyon River, in the southcentral part of the Olympic Peninsula, Washington. These sponges dominate a chemosynthetic invertebrate assemblage that included the gastropod Provanna antigua Squires, 1995; the polyplacophoran Leptochiton alveolus (Lov6n, 1846), and radiolarians. Most of the sponges are preserved as silica in a localized cherty and botryoidal, calcareous cement-filled limestone formed at bathyal depths by bacterial oxidation of methane at a cold seep. This is the third known report of sponges from ancient chemosynthetic deposits.