Steffen Kiel

Cold-Seep Mollusks Are Older Than the General Marine Mollusk Fauna

The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. We used the fossil record of seep mollusks to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to those of deep-sea taxa, suggesting that seep faunas may be shaped by the factors that drive the evolution of life in the deep sea in general. Our data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events.

Molecular fossils reveal fluid composition and flow intensity at a Cretaceous seep

An isolated Hauterivian marine limestone from the Crimean Peninsula containing masses of articulated specimens of the dimerelloid brachiopod Peregrinella has previously been interpreted to represent a hydrocarbon-seep deposit. In order to constrain the intensity of seepage and the composition of fl uids, we investigated the lipid biomarker inventory of this seep limestone. The dominant biomarkers are (13)C-depleted isoprenoids including tail-to-tail linked pentamethylicosane (delta(13)C value: -108 parts per thousand), representing molecular fossils of methanotrophic archaea. This observation reveals that the seepage fl uids contained methane. Because the seep carbonates have been found to be only moderately (13)C-depleted (delta(13)C values as low as -14 parts per thousand), a signifi cant contribution from a less (13)C-depleted carbon source than methane, probably marine carbonate, is apparent. Such a degree of admixture of marine carbonate is typical for seep limestones resulting from low fl ow rates. The observed biomarker pattern with the prominent occurrence of biphytanes, but lacking crocetane, reveals that the methanotrophic archaea at the Hauterivian seep site were similar to archaea of the ANME-1 cluster. Archaea of this cluster are known to be able to cope with lower methane concentrations than ANME-2 archaea; therefore ANME-1 archaea are better adapted to low seepage rates and diffusive fl ow. The Peregrinella limestone contains only a small amount of early diagenetic cement. Based on a comparison with biomarker patterns of other ancient seep deposits, it is apparent that diffusive seepage typically results in limestones with little cement, whereas advective, more intense seepage appears to favor cement precipitation. If applied with caution, this supposed relationship can be used as a fi rst approximation of seepage intensity.

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.

Adaptive radiation of chemosymbiotic deep-sea mussels

Adaptive radiations present fascinating opportunities for studying the evolutionary process. Most cases come from isolated lakes or islands, where unoccupied ecological space is filled through novel adaptations. Here, we describe an unusual example of an adaptive radiation: symbiotic mussels that colonized island-like chemosynthetic environments such as hydrothermal vents, cold seeps and sunken organic substrates on the vast deep-sea floor. Our time-calibrated molecular phylogeny suggests that the group originated and acquired sulfur-oxidizing symbionts in the Late Cretaceous, possibly while inhabiting organic substrates and long before its major radiation in the Middle Eocene to Early Oligocene. The first appearance of intracellular and methanotrophic symbionts was detected only after this major radiation. Thus, contrary to expectations, the major radiation may have not been triggered by the evolution of novel types of symbioses. We hypothesize that environmental factors, such as increased habitat availability and/or increased dispersal capabilities, sparked the radiation. Intracellular and methanotrophic symbionts were acquired in several independent lineages and marked the onset of a second wave of diversification at vents and seeps. Changes in habitat type resulted in adaptive trends in shell lengths (related to the availability of space and energy, and physiological trade-offs) and in the successive colonization of greater water depths.

Bivalves from Cretaceous cold-seep deposits on Hokkaido, Japan

Cretaceous cold-seep deposits of the Yezo Group on Hokkaido, Japan, yield a rich and well-preserved mollusk fauna. The systematics of nine bivalve species previously reported from these deposits can now be reevaluated using newly collected fossils. The fossils include a Cenomanian specimen of Nucinella gigantea with a drill hole possibly made by a naticid, by far the oldest record of a drill hole from a cold seep site. In Japan, Cretaceous seep bivalve assemblages are characterized by (i) the unique occurrence of large specimens of Nucinella (Manzanellidae), (ii) the commonly present nuculid Acila (Truncacila), and (iii) a high diversity of lucinids, possibly as many as four distinct genera. Two new species described are the Albian Acharax mikasaensis (Solemyidae) and the Albian to Campanian Thyasira tanabei (Thyasiridae), of which the former had previously been misidentified as the oldest vesicomyid, the latter as the oldest Conchocele.

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.

Paleoecology and evolutionary significance of an Early Cretaceous Peregrinella-dominated hydrocarbon-seep deposit on the Crimean Peninsula

Abstract An isolated limestone deposit preserving thousands of specimens of the dimerelloid brachiopod Peregrinella multicarinata is exposed in fossil-poor Hauterivian strata northwest of the town of Planerskoje on the Crimean Peninsula in southern Ukraine. The limestone consists of micrite that encloses abundant detrital components, mostly brachiopod shell fragments, and also contains authigenic, framboidal pyrite. Cavities are rare; a few have been filled by a sequence of anhedral yellow calcite, seam micrite, banded and botryoidal cement, and equant calcite spar. The limestone preserves a diverse mollusk fauna of low abundance, including modiomorphid, lucinid, and buchiid bivalves and abyssochrysoid, ampullinid, and neritid gastropods. The negative δ13C values of the micrite (as low as −13.6‰) and the character of the associated mollusk fauna indicate that this limestone formed at an ancient hydrocarbon seep. This evidence supports the earlier interpretation of Peregrinella as a seep-restricted brachiopod. The new Ukrainian records of some of the mollusk taxa—notably Caspiconcha and Paskentana—significantly extend the geographic range of these apparently seep-restricted mollusks, suggesting that mollusks at Early Cretaceous seeps had a wider geographical distribution than previously appreciated.

Jurassic and Cretaceous Gastropods from Hydrocarbon Seeps in Forearc Basin and Accretionary Prism Settings, California

Fourteen gastropod species from 16 Mesozoic hydrocarbon seep carbonate deposits of the Great Valley Group and Franciscan Complex in California are described. Two genera are new: Bathypurpurinopsis has a fusiform shell with a siphonal fold, and variable Paskentana has turbiniform or littoriniform shells with spiral and/or scaly sculpture and convex or shouldered whorls. Due to the lack of data on shell microstructure and protoconch morphology, many of our taxonomic assignments have to remain tentative at present. Species that are described as new include: Hokkaidoconcha bilirata, H. morenoensis, H. tehamaensis (Hokkaidoconchidae), Abyssochrysos? giganteum (Abyssochrysidae?), Paskentana globosa, P. berryessaensis, and Bathypurpurinopsis stantoni (Abyssochrysoidea, family uncertain). The total fauna represents a mixed bag of taxa that were: (i) widely distributed during the late Mesozoic (Amberleya); (ii) restricted to late Mesozoic seep carbonates in California (Atresius, Bathypurpurinopsis, Paskentana); and (iii) members of seep/deep-sea groups with a long stratigraphic range (abyssochrysids, hokkaidoconchids).

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.

NEW RECORD OF ''BATHYMODIOLUS'' MAURITANICUS COSEL 2002 FROM THE GULF OF CADIZ (NE ATLANTIC) MUD VOLCANOES

Abstract The “Bathymodiolus” childressi group is the most geographically diverse assemblage of deep-sea mussel species. In this paper we consider several possible hypotheses to explain the present biogeographic distribution of the “B.” childressi species complex. Mussels were collected for the first time from mud volcanoes in the Gulf of Cadiz (NE Atlantic Ocean) during the training through research (TTR) 16 research expedition in 2006. Preliminary observations of the shell features indicate that they belong to the “B.” childressi species complex, which has been recognized as morphologically and genetically distinct from other Bathymodiolus species. Molecular analyses of two mitochondrial genes (COI-5 and ND4) were used to characterize the new mussel population from the Gulf of Cadiz (GOC) and to determine their phylogenetic relationships with other members of the “B.” childressi group. The results indicate that the GOC mussels are conspecific with “Bathymodiolus” mauritanicus Cosel (2002), described from West Africa margin, and support a previous hypothesis that “B.” mauritanicus is an amphi-Atlantic species