Cold Seep Carbonates Research Articles

NEW RECORDS AND SPECIES OF MOLLUSCS FROM TERTIARY COLD-SEEP CARBONATES IN WASHINGTON STATE, USA

Eighteen gastropod and seven bivalve species are reported from Eocene to Oligocene cold-seep carbonates in Washington State, USA. Four species are new (Niso littlei, Turrinosyrinx hickmanae, Xanthodaphne? campbellae, and Lurifax goederti), and 16 are described in open nomenclature. Previously unknown features of protoconch or prodissoconch morphology and/or shell microstructure are provided for Retiskenea statura (Goedert and Benham), Provanna antiqua Squires, Nuculana? aff. N. grasslei Allen, and Bathymodiolus willapaensis (Squires and Goedert). Modiolus (M.) willapaensis is placed within Bathymodiolus based on the elliptical-triangular shape of its juvenile shell, indicating that the divergence between vent/seep and whale/wood-fall inhabiting bathymodiolines took place at least 40 Ma. The first fossil species of the vent/seep genera Pyropelta (Pyropeltidae), Lurifax (family uncertain), and Catillopecten? (Propeamussidae) are reported. Niso (Eulimidae), Xanthodaphne, Turrinosyrinx, Benthomangelia (Turridae), Ledella (Nuculanidae), Tindaria? (Tindariidae), and Delectopecten (Pectinidae) are reported for the first time from fossil cold-seep assemblages. Larval developmental strategies are inferred from protoconch and prodissoconch morphologies in 14 species, which largely reflect the species' phylogenetic groups, as in modern vent and seep molluscs. The data presented here indicate that the radiation of toxoglossate turrids (Gastropoda) into deep water took place already in the Oligocene, and not in the Miocene as previously thought. Healed shell injuries and presumed naticid drill holes represent the oldest known fossil evidence of predation at cold-seeps.

Palaeozoic cold seep carbonates from Europe and North Africa—an integrated isotopic and geochemical approach

In this paper, we report the highest and lowest carbon isotope values known from Palaeozoic carbonate rocks. These unusual δ13C values (−50 to +23.5‰) are due to microbial methanogenesis and methanotrophy in Silurian to Carboniferous carbonates. Trace elements were used to decipher the primary mineralogy of the carbonate cements. Very high Sr values and low amounts of Mg, Fe and Mn point toward aragonite precursors, whereas high Fe and Mn values are indicative of primary calcites and allow reconstruction of the redox conditions. Four carbonate deposits are described from the Meseta and the Antiatlas of Morocco, the Pyrenees (France) and the Harz mountains (Germany). The highest δ13C values in concretion below the uppermost Silurian Spinatrypa Mound (Moroccan Meseta) give evidence, that CO2 was produced during methanogenesis. δ13C values between −10 and −32‰indicate that the formation of microbial carbonates and cements in the Middle Devonian Hollard Mound (Antiatlas) and in the Lower Carboniferous sediments of the Iberg (Harz) formed at thermogenetic methane or petroleum seeps. The Late Bashkirian carbonate mound of the High Pyrenees (Tantes Mound) is the first Palaeozoic carbonate with seepage fluids being dominated by biogenic methane. Matrix carbonates exhibit δ13C values as low as −34‰. In some parts, voids make up more than 50 vol% of the mound. They are filled with several generations of cement. The earliest void filling is isopachous fibrous cement, which represents former aragonite. Most negative δ13C values of −50‰were measured in these isopachous fibrous cements. The difference of 55‰in δ13C values between normal sediments and early aragonite cements can only be explained by the contribution of CO2 from anaerobic oxidation of biogenic methane in a cold seep setting.

Microbial fabrics from Neogene cold seep carbonates, Northern Apennine, Italy

A number of hydrocarbon seep-carbonate masses are hosted within Miocene and Pliocene siliciclastic units along the Apennine Range and Sicily, and are mainly composed of micritic and microsparitic textures. Geomicrobiological analysis of some of these deposits shows that preserved microbial processes are few and the contribution of microbe-derived textures to their construction is volumetrically very limited. In the carbonate groundmass of two northern Apennine Miocene and Pliocene seep-carbonate deposits uncommon and well-preserved features suggest direct and indirect evidence of microbial activity. Some of these features are interpreted as the mineralization products of microbial textures, and include complex alveolar textures and fossilized biofilms that line and fill microconduits, pores and other voids, similar to living bacterial aggregations recovered in modern seep-carbonates. Other mineral structures, such as spheroids and rhombs, with concentric fabrics composed of calcite–dolomite alternations, abound as cement components and suggest a nucleation via bacterial sulfate reduction processes. A similar origin is also assumed for the acicular aragonite bundles that in the Miocene seep-carbonate mass enclose dense clusters of millimeter-size, filamentous morphologies of biological origin.

Lithomphalus enderlini gen. et sp. nov. from cold-seep carbonates in California—a Cretaceous neomphalid gastropod?

The new genus and species Lithomphalus enderlini is described from two Early Cretaceous (Valanginian) suspected cold-seep carbonates in western California, USA. These carbonates were found within turbidites of the Great Valley Group, and were deposited at slope depth. Considering its shell shape and its crossed-lamellar shell structure, this species might belong to the enigmatic vent and seep endemic gastropod group Neomphaloidea. It cannot be assigned with certainty to any of the extant neomphaloidean families, and thus may represent an independent Mesozoic radiation of the Neomphalina. However, until additional and better-preserved specimens are discovered (e.g., those with protoconchs), caution is advised with regard to verifying the earliest occurrence of the Neomphalidea in the fossil record.

Organic geochemical investigation of cold-seep carbonates accompanied with chemosynthetic community

Organic geochemical investigation of cold-seep carbonates accompanied with chemosynthetic community

The evolution of chemosynthetic biological community at the site of cold-seep carbonate precipitation

The evolution of chemosynthetic biological community at the site of cold-seep carbonate precipitation

Chemical, biological and hydrological controls on the 14C content of cold seep carbonate crusts: numerical modeling and implications for convection at cold seeps

Understanding the hydrology of cold seep environments is crucial to perform accurate estimates of fluid and chemical fluxes at sedimentary wedges. Shallow convection processes may affect fluid flux estimates and could favor the destabilization of gas hydrate accumulations, increasing the sediment-ocean methane flux. Evidence for the occurrence of convection at cold seeps, however, is still limited. We use the concentration of 14C (D 14C) in carbonate crusts formed at cold seeps of the eastern Mediterranean Sea as a tracer for convective recirculation of seawater-derived fluids. A numerical model is applied to investigate the controls on 14C incorporation in cold seep carbonates. Our simulations show that increased amounts of CH 4 in the expelled fluids result in elevated crust D 14C, while high Ca 2+ and HCO 3 − concentrations produce the opposite effect. Convection is the only transport process that can significantly increase crust D 14C. Advection, bioirrigation, eddy diffusion and bioturbation instead, have little effect on, or produce a decrease of, crust D 14C. In addition, the presence of old or modern carbon (MC) in host sediments prior to cementation and the 14C-decay associated to the time needed to form the crust contribute in defining the D 14C of carbonate crusts. We then use the model to reproduce the 14C content of the eastern Mediterranean Sea crusts to constrain the chemical and hydrological conditions that led to their formation. Some crusts contain relatively low amounts of 14C (−945.0<D 14C ‰<−930.2) which, assuming no ageing after crust formation, can be reproduced without considering convection. Other crusts from two sites (the Amsterdam and Napoli mud volcanoes), instead, have a very high 14C-content (−899.0<D 14C ‰<−838.4) which can only be reproduced by the model if convection mixes deep fluids with seawater. Order-of-magnitude calculations using the Rayleigh criterion for convection suggest that the slow seepage (about 10 cm year −1) of low salinity (20‰) fluids at the Amsterdam sites could trigger haline convection there. On the Napoli mud volcano, where high-density brines are expelled, density-driven convection cannot take place and other processes, possibly involving the rapid movement of free gas in the sediment, could be important.

Biomarker compositions for anaerobic methane oxidation in cold-seep carbonates

Biomarker compositions for anaerobic methane oxidation in cold-seep carbonates

Cold seep carbonate mounds with Vesicomya (Calyptogena) kawamurai (Bivalvia: Vesicomyidae) in slope-mud fades of the Pliocene forearc basin of the Sagara-Kakegawa area, central Japan

Abstract Cold-seep carbonate mounds containing Vesicomya (Calyptogena) kawamurai paleocommunity occur in massive siltstones of the Pliocene Tamari and Hijikata Formations, both deposited on the upper to middle slope of a forearc basin in the Sagara-Kakegawa area, central Japan. The shell-rich carbonate mounds vary from lenticular (2 m in diameter and 0.5 m in maximum thickness) to barrel-shaped (0.8 m in diameter and 1.5 m in length). One lenticular shelly concretion consisted of densely crowded vesicomyid shells lying parallel to bedding, and overlies a brecciated siltstone with dolomicritic cement. A barrel-shaped concretion contained abundant articulated valves of V. (C.) kawamurai in life orientation, and preserves a three-dimensional view of a chemosymbiotic habitat maintained over several generations of these large clams. In addition, the carbonate mounds contain various void spaces (open burrows and dissolved-shell molds) which are fringed by authigenic carbonates (splayed fibrous aragonites and do...

Geophysical constraints on the surface distribution of authigenic carbonates across the Hydrate Ridge region, Cascadia margin

On active tectonic margins methane-rich pore fluids are expelled during the sediment compaction and dewatering that accompany accretionary wedge development. Once these fluids reach the shallow subsurface they become oxidized and precipitate cold seep authigenic carbonates. Faults or high-porosity stratigraphic horizons can serve as conduits for fluid flow, which can be derived from deep within the wedge and/or, if at seafloor depths greater than ∼300 m, from the shallow source of methane and water contained in subsurface and surface gas hydrates. The distribution of fluid expulsion sites can be mapped regionally using sidescan sonar systems, which record the locations of surface and slightly buried authigenic carbonates due to their impedence contrast with the surrounding hemipelagic sediment. Hydrate Ridge lies within the gas hydrate stability field offshore central Oregon and during the last 15 years several studies have documented gas hydrate and cold seep carbonate occurrence in the region. In 1999, we collected deep-towed SeaMARC 30 sidescan sonar imagery across the Hydrate Ridge region to determine the spatial distribution of cold seep carbonates and their relationship to subsurface structure and the underlying gas hydrate system. High backscatter on the imagery is divided into three categories, (I) circular to blotchy with apparent surface roughness, (II) circular to blotchy with no apparent surface roughness, and (III) streaky to continuous with variable surface roughness. We interpret the distribution of high backscatter, as well as the locations of mud volcanoes and pockmarks, to indicate variations in the intensity and activity of fluid flow across the Hydrate Ridge region. Seafloor observations and sampling verify the acoustic signals across the survey area and aid in this interpretation. Subsurface structural mapping and swath bathymetry suggest the fluid venting is focused at the crests of anticlinal structures like Hydrate Ridge and the uplifts along the Daisy Bank fault zone. Geochemical parameters link authigenic carbonates on Hydrate Ridge to the underlying gas hydrate system and suggest that some of the carbonates have formed in equilibrium with fluids derived directly from the destabilization of gas hydrate. This suggests carbonates are formed not only from the methane in ascending fluids from depth, but also from the shallow source of methane released during the dissociation of gas hydrate. The decreased occurrence of high-backscatter patches and the dramatic reduction in pockmark fields, imaged on the eastern part of the survey, suggest gas hydrate near its upper stability limit may be easily destabilized and thus, responsible for these seafloor features. High backscatter along the left-lateral Daisy Bank fault suggests a long history of deep-seated fluid venting, probably unrelated to destabilized gas hydrate in the subsurface.

Methane-related carbonates formed at submarine hydrothermal springs: a new setting for microbially-derived carbonates?

Numerous small calcite mounds, up to 2.5 m in diameter and 0.75 m in height, accompanied by Ba, Hg and Tl mineralisation, occur in shallow submarine hydrothermal vents on the sea bottom, at 10 m depth, near Punta Mita, on the western coast of Mexico. The hydrothermal activity consists in water and gas (mainly nitrogen and methane) venting at 85°C, through a 100-m-long fissure hosted in basaltic rocks and partially covered by a thin layer of unconsolidated detrital sediments. The mounds consist of travertine-like calcite aggregates that develop around the main submarine hot springs amidst a hydrothermally altered basaltic host rock. Two main calcite generations are texturally recognisable: the first generation shows a radial-fibrous texture; the second is fine-grained calcite, which cements detrital grains and fills the pore spaces. The δ 13C analyses of calcite reveal a strong depletion in 13C, with values as low as −39.2‰ (Vienna PeeDee Belemnite), which suggest that microbial communities may have induced calcite precipitation through microbial methane oxidation. Barite, sulphides (mainly pyrite and cinnabar) and phosphates (carbonate–hydroxylapatite) are also present in the mounds in lower concentrations and form by direct precipitation from the hydrothermal fluid. The Punta Mita hydrothermal carbonate mounds represent a potentially novel environment for microbially induced carbonate mineralisation, which is characterised by high temperatures not encountered in areas of cold seep carbonate formation. Stable isotope results suggest that microorganisms responsible for the oxidation of methane may be present and active at temperatures near 85°C at the Punta Mita vents.

CH4-consuming microorganisms and the formation of carbonate crusts at cold seeps

To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy.

Three series of non-isoprenoidal dialkyl glycerol diethers in cold-seep carbonate crusts

Three novel series of non-isoprenoidal dialkyl glycerol diethers with an inferred sn-1,2 stereochemistry were tentatively identified in carbonate crusts precipitated from methane-rich bottom-waters and pore-waters associated with Mediterranean mud volcanoes. In the first series of diethers, an 11,12-methylenehexadecyl moiety is ether-bound at the sn-2 position of the glycerol group, and in diethers from the second series, an anteiso pentadecyl group is ether-bound at the sn-2 position. In the third and minor series a pentadecyl moiety is ether-bound at the sn-2 position. In all series, ether-bound C 14–C 17 alkyl units (either n-alkyl, branched alkyl, alkylcyclohexyl or methylenealkyl) occur at the sn-1 position. The two major series are also distinguished by their δ 13C values, which differ by 15–30‰ at the sites studied. Only the minor series has been previously reported in sediments. Members of the second and third series are similar to diethers containing C 16–C 18 iso, anteiso, and n-alkyl units present in the thermophilic bacteria Thermodesulfobacterium commune, Ammonifex degensii and Aquifex pyrophilus. The first series is unique, in that diethers possessing alkyl chains that contain a cyclopropane ring have never been reported.

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

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.

Worm tubes in an allochthonous cold-seep carbonate from lower Oligocene rocks of western Washington

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.

The role of bacteria in the formation of cold seep carbonates: geological evidence from Monferrato (Tertiary, NW Italy)

Abstract Methane-derived carbonate rocks (Lucina limestone and Marmorito limestone) crop out in Monferrato (NW Italy) and represent one of the first described examples of rocks produced at fossil cold seeps. These rocks, of Miocene age, consist of strongly carbonate-cemented siliciclastic sediments ranging in grain size from mud to coarse sand. The methane-related origin of Monferrato carbonates is based on: (a) outcrop-scale evidence: patchiness of cementation, chemosymbiotic fossil communities, presence of a network of polyphase carbonate-filled veins not related to tectonics; (b) isotope geochemistry: very depleted δ13C values, as low as −50‰ PDB; (c) peculiar petrographic features. Diverse microbial communities have been observed in present-day cold seeps. These communities include sulphate-reducing, sulphur-oxidizing and methane-oxidizing bacteria. The present work is focused on the identification and description of fossil evidence of such microbial activity in the Monferrato carbonates. Examples of fossilization of microbial structures are probably represented by pyritic rods and dolomite tubes referable to sulphur-oxidizing and to unspecified bacteria, respectively. Less direct but more abundant evidence has been found through petrographic and SEM studies of seep carbonates. Many features point to the presence of organic clumps or mats capable of trapping sediment and promoting carbonate precipitation: microcrystalline calcite peloids; dolomite crystals with irregular hollow cores; dolomite spheroids with dumbbell-shaped cores; laminated internal sediments lining cavities completely. All these features are interpreted to result from bacterially mediated, sedimentary and diagenetic processes and can therefore be considered as an additional evidence of ancient methane seeps.

Abstract: Fingerprints of Methanotrophic Bacteria in a Miocene Cold Seep Carbonate

Abstract: Fingerprints of Methanotrophic Bacteria in a Miocene Cold Seep Carbonate

Cold Seep Carbonates of the Northern Gulf of Mexico Continental Slope: A Synthesis of Submersible Investigations

Cold Seep Carbonates of the Northern Gulf of Mexico Continental Slope: A Synthesis of Submersible Investigations