Dome-shaped Features Research Articles

Subsurface Structural Mapping over Koton Karifi and Adjoining Areas, Southern Bida Basin, Nigeria, using High-Resolution Aeromagnetic Data

In this current work, we aim to delineate the subsurface structural trends, determine the depth to basement surface, and provide an illustrative 3D model for its subsurface structure. Four digitized aeromagnetic maps were acquired from the Nigerian Geological Survey Agency, Abuja. The total field aeromagnetic anomalies over Koton Karifi and adjoining areas have been evaluated. In order to map the subsurface structures and estimate the depth to basement surface the spectral analysis method was applied. To achieve such goals, a detailed analysis of the aeromagnetic data for the study area was performed. 2D interpretation was carried out for the aeromagnetic data. The processes used include contouring of the Total Magnetic Intensity (TMI) data, separation of regional and residual anomalies, structural detection methods such as analytic signal, vertical derivatives, and magnetic lineament mapping were used to map the contacts and faults within the study area. The first vertical derivative and the magnetic lineament maps show major geologic lineaments trending in East-West with minor ones trending Northeast-Southwest. In the south-eastern part of the study area, there is a dome-shaped linear feature. The result obtained using the spectral analysis method reveals two source depth models. The depths to deeper magnetic sources range from 2.81 km to 3.24 km with an average depth of 2.90 km. The deeper magnetic source bodies are identified with the magnetic basement. The shallower magnetic sources which range from 0.45 km to 1.81 km with an average depth of 1.13 km could be attributed to near surface magnetic sources which are magnetic rocks that intruded into the sedimentary formations or magnetised bodies within the sedimentary cover. Based on the sedimentary thickness range of 0.45 to 3.24 km, there is an indication that the possibility of hydrocarbon generation in the study area is feasible.

New insights into the Cretaceous-Cenozoic tectono-stratigraphic evolution of the southern Lofoten margin, offshore Norway

Abstract The tectono-stratigraphic evolution of the southern Lofoten margin and its immediate transition towards the northern Voring margin has been studied in detail utilizing 2D multi-channel seismic reflection profiles, available wells, in addition to gravity and magnetic data. New and better refined structural elements have been mapped within the study area, including (informally named) the West Rost High Fault Complex, Rost Syncline, and Sandflesa High. Furthermore, four main rift phases have been recognised and refined. Late Jurassic-earliest Cretaceous rifting controlled the initial structuring of the main structural elements. Mid-Cretaceous rifting was responsible for initiation of faulting in the West Rost High Fault Complex, while a composite Late Cretaceous rift phase took place and led to westward propagation of fault activity. Paleocene rifting generated new faults and reactivated several earlier faults, prior to continental breakup and seafloor spreading initiation at the Paleocene-Eocene transition. The Bivrost Lineament, separating the southern Lofoten and northern Voring margins, has exhibited a distinct morphological expression during Cretaceous-Cenozoic and is recognised as a structural “corridor” which segments highs and basins/sub-basins. Furthermore, two dome-shaped features have been observed on the southern Lofoten margin and have probably experienced several phases of growth from Late Cretaceous to Miocene times. The domes are located in close proximity to the outer Voring margin and Bivrost Lineament that are believed to have facilitated the transfer of imposed compressional deformation on the NE Atlantic margins. Finally, a comparison of the study area to the conjugate Northeast Greenland margin provides valuable insights on the margin evolution in a regional and conjugate setting.

Modulation of adhesion microenvironment using mesh substrates triggers self-organization and primordial germ cell-like differentiation in mouse ES cells.

The cell adhesion microenvironment plays contributory roles in the induction of self-organized tissue formation and differentiation of pluripotent stem cells (PSCs). However, physical factors emanating from the adhesion microenvironment have been less investigated largely in part due to overreliance on biochemical approaches utilizing cytokines to drive in vitro developmental processes. Here, we report that a mesh culture technique can potentially induce mouse embryonic stem cells (mESCs) to self-organize and differentiate into cells expressing key signatures of primordial germ cells (PGCs) even with pluripotency maintained in the culture medium. Intriguingly, mESCs cultured on mesh substrates consisting of thin (5 μm-wide) strands and considerably large (200 μm-wide) openings which were set suspended in order to minimize the cell-substrate adhesion area, self-organized into cell sheets relying solely on cell-cell interactions to fill the large mesh openings by Day 2, and further into dome-shaped features around Day 6. Characterization using microarray analysis and immunofluorescence microscopy revealed that sheet-forming cells exhibited differential gene expressions related to PGCs as early as Day 2, but not other lineages such as epiblast, primitive endoderm, and trophectoderm, implying that the initial interaction with the mesh microenvironment and subsequent self-organization into cells sheets might have triggered PGC-like differentiation to occur differently from the previously reported pathway via epiblast-like differentiation. Overall, considering that the observed differentiation occurred without addition of known biochemical inducers, this study highlights that bioengineering techniques for modulating the adhesion microenvironment alone can be harnessed to coax PSCs to self-organize and differentiate, in this case, to a PGC-like state.

Estratigrafia e estrutura do Cerro do Jarau: nova proposta

The Cerro do Jarau structure is located near the town of Quarai, in the Rio Grande do Sul state, close to the international boundary with Uruguay. This circular feature has a diameter with approximately 8 km, presents some evidence of an origin by a meteoritic impact. It is located in the Parana Basin and characterized by a central area with occurrence of sandstone surrounded by basalts of Serra Geral Formation. Previous works considered the structure as a dome-shaped feature. The objective of this paper is to present new data on the stratigraphy and structure of the Cerro Jarau, showing that the sandstones are structurally and stratigraphically overlying the basalts and both units exhibit centripetal dips. The structure of Cerro Jarau is therefore a basin-like feature and not a dome as admitted in previous studies.

Interpretation of the coronal magnetic field configuration of the Sun

The origin of the heliospheric magnetic flux on the Sun, and hence the origin of the solar wind, is a topic of hot debate. While the prevailing view is that the solar wind originates from outside the coronal streamer helmets, there also exists the suggestion that the open magnetic field spans a far wider region. Without the definitive measurement of the coronal magnetic field, it is difficult to unambiguously resolve the conflict between the two scenarios. We present two 2-dimensional, Alfvénic-turbulence-based models of the solar corona and solar wind, one with and the other without a closed magnetic field region in the inner corona. The purpose of the latter model is to test whether it is possible to realize a picture suggested by polarimetric measurements of the corona using the Fe XIII 10747 Å line, where open magnetic field lines seem to penetrate the streamer base. The boundary conditions at the coronal base are able to account for important observational constraints, especially those on the magnetic flux distribution. Interestingly, the two models provide similar polarized brightness (pB) distributions in the field of view (FOV) of SOHO/LASCO C2 and C3 coronagraphs. In particular, a dome-shaped feature is present in the C2 FOV even for the model without a closed magnetic field. Moreover, both models fit the Ulysses data scaled to 1 AU equally well. We suggest that: 1) The pB observations cannot be safely taken as a proxy for the magnetic field topology, as is often implicitly assumed. 2) The Ulysses measurements, especially the one showing a nearly uniform distribution with heliocentric latitude of the radial magnetic field, do not rule out the ubiquity of open magnetic fields on the Sun.

Spectral evidence of volcanic cryptodomes on the northern plains of Mars

The composition and detailed morphology of dome-shaped features located in western Arcadia Planitia and just west of Utopia Planitia were examined in this study utilizing data from Mars Reconnaissance Orbiter and Mars Odyssey sensors. The domes have diameters averaging 1.5 km and heights averaging 160 m, and are generally dark-toned, although some are lighter toned or have split dark and light-toned surfaces. The domes are surrounded by annular deposits comprising, with increasing distance from the domes, dark-toned aprons, light-toned aureoles, and dark-toned aureoles. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data over several areas in the western Arcadia region show that spectra from the flanks of several domes have 1 and 2 μm absorption features consistent with the presence of olivine and a high-Ca pyroxene, nominally augite. Modified Gaussian Model (MGM) analysis of these spectra indicates Fe-rich olivine compositions. The tops of domes and the aprons surrounding many domes have negative sloping flat spectra in the near infrared, which is consistent with tachylite-rich, glassy compositions. High Resolution Imaging Science Experiment (HiRISE) images over several domes indicate that relatively high thermal inertia values associated with the tops of domes can be attributed to boulder strewn surfaces. HiRISE images also reveal that light-toned aureoles around domes consist of crenulated ground resembling “brain terrain” textures previously described for ice-rich concentric crater fill elsewhere on the northern plains. The plains surrounding the domes also display lineations that are interpreted to be lava channels or tubes. The combination of volcanic and ice-related features are consistent with the domes having formed as cryptodomes in the near sub-surface. We suggest that the domes could be basaltic in composition if the magmas were degassed and/or highly crystallized, and thus more viscous than typical basaltic magmas. The intrusion of these magmas into an ice-rich horizon would have produced a pervasively jointed chilled margin on the domes, which, once the domes were exposed, would have mechanically weathered to form the dark aprons. The domes could have served as local centers for ice accumulation during periods of high orbital obliquity, which ultimately would have led to the formation of the “brain terrain” surrounding the features. The domes represent late stage volcanic products on the northern plains of Mars and associated features provide more evidence for the role that ice accumulation and modification has played in recent martian history.

Thematic Set: Full-azimuth modelling and field trial at Heidrun

Over recent decades, the Heidrun Field in the Norwegian Sea has been imaged several times with conventional narrow-azimuth seismic surveys. The extensively faulted structure and the presence of a dome-shaped feature cause imaging challenges in some areas. A modelling study shows that a survey design with increased crossline offset and fold, such as a four-vessel wide-azimuth or coil shooting design, can produce improved subsurface images with fewer artefacts, sharper fault edges, and more consistent amplitudes along horizons compared to images from conventional acquisition. Based on the modelling results, a field trial with coil shooting acquisition was carried out at Heidrun. The survey design with 18 intersecting coils provided full-azimuth, high fold data over a 2.5 × 2.5 km2 target area with sufficient surrounding aperture for comparing the migrated data with previously acquired conventional seismic data. Preliminary processing of the coil shooting data show fewer dip conflicts and an improved fault definition at the reservoir level compared to conventional survey data. However, due to a smaller migration aperture, the images from the field trial have lower spatial frequency content, so some details of the structure are lost.

Superconducting properties of the oxygen-deficient iron oxyarsenideTbFeAsO1−δfrom underdoped to overdoped compositions

A wide-range doping was achieved by a high-pressure method for ${\text{TbFeAsO}}_{1\ensuremath{-}\ensuremath{\delta}}$ from ``underdoped'' to ``overdoped'' superconducting compositions throughout the optimized superconductivity (${T}_{\text{c}}$ of 44 K). ${T}_{\text{c}}$ vs $\ensuremath{\delta}$ shows a dome-shaped feature, while ${T}_{\text{c}}$ vs the lattice constant likely follows a unique empirical curve over the doping range. The relatively large amount of oxygen vacancies up to $\ensuremath{\sim}0.3$ per the formula unit was introduced possibly because of the smaller replacement Tb than the other Ln (rare-earth element) in the ${\text{LnFeAsO}}_{1\ensuremath{-}\ensuremath{\delta}}$ system.

Thermal structure of lithosphere in Central Asian and Pacific belts and their adjacent cratons, from data of geoscience transects

We investigate the 2D thermal structure of lithosphere in the Central Asian and Pacific tectonic belts and adjacent cratonic areas of Siberia and North China using a synthesis of geothermal data from six geoscience transects covered by seismic, resistivity, and gravity surveys. The patterns of rock density, radiogenic heat production derived from U and Th abundances, thermal conductivity, temperatures, and respective heat flows reveal a layered structure. The model with layers distinguished according to density and thermal parameters includes well pronounced dome-shaped features in the crust which correlate with upwarps of the asthenospheric top. The domes are marked by high heat flows of 60–90 mW/m 2 with a mantle component higher than the crustal one (30–60 mW/m 2 against 20–30 mW/m 2) and temperatures as high as 800–1100 °C at the Moho. Many of these features correspond to known and potential petroleum basins.

Protein-conjugated, glucose-sensitive surface using fluorescent dendrimer porphyrin

A multi-functional dendrimer-coated surface has been prepared for the effective protein immobilization and detection of protein activity. The silicon surface was first modified with positively-charged amino groups using 3-aminopropyltriethoxysilane (APTES), and subsequently coated with ionic dendrimer porphyrin (DP) by electrostatic interaction. Fluorescence and atomic force microscopy (AFM) studies showed that the dendrimer was homogeneously coated on the APTES-modified silicon surface as dome-shaped features that protruded 1.0–2.5 nm above the surface and had diameters ranging from 50 nm to 100 nm. The dendrimer-modified surface showed a higher capacity to covalently bind proteins, compared to the control surfaces, and the protein activity was higher by a factor of two. Using the fluorescent property of the porphyrin core, the relative amounts of dendrimer and the enzyme-catalyzed reactions on the dendrimer-coated surface were examined by fluorescence microscopy. Glucose oxidase (GOX)-mediated glucose oxidation quenched fluorescence emission from the focal porphyrin core through a peroxidase-coupled system and from the quantitative relationship between quenching and glucose concentration, the GOX-catalyzed reaction could be characterized.

Atomic Force Microscopy Studies of Mesoscopic Membranous Bubbles on Monolayers Derived from SiCl3-Terminated Carbosilane Dendrons on Mica

Monolayers of dendrimers were prepared on mica by spin-coating of the second generation carbosilane dendrons with 9 SiCl(3) periphery groups. AFM images of the films showed the presence of soft yet robust, dome-shaped features with a base diameter of 100-2000 nm. The apparent height of the features, ranging from 10 to 200 nm, rapidly reduced under increasing compression force, eventually to the same value ( approximately 2.5 nm) corresponding to a bilayer of the flattened dendrons. The change in shape of the features in response to the compression force from the AFM tip was fully reversible, indicating that the features were robust. The contrast of the features in the tapping mode AFM (TMAFM) phase images flipped at a setpoint ratio of approximately 0.55. In contrast to the reported amplitude vs displacement (A/z) curves for compliant materials, A/z curves of the features showed that the reduction of amplitude was larger than the tip displacement as if the cantilever tip were repelled by the soft features. This result cautions the use of amplitude/phase vs displacement (APD) curves for interpreting TMAFM images and for optimizing conditions for TMAFM imaging of very soft and "sticky" surfaces. On the basis of the AFM studies, we believe that the dome-shaped features are membranous air bubbles. The membranes of the bubbles were probably composed of a bilayer of the dendron molecules bound through the peripheral silanol groups. The bilayer could be formed by self-assembly of the molecules on top of the air bubbles entrapped at the monolayer/solution interface during spin-coating.

An exceptional case of endogenous lava dome growth spawning pyroclastic avalanches: the 1999 Bocca Nuova eruption of Mt. Etna (Italy)

During an eruption at the Bocca Nuova, one of the summit craters of Mt. Etna, in October–November 1999 a part of the crater floor near its WNW rim was uplifted to form a dome-shaped feature that consisted of older lava and pyroclastics filling the crater. This endogenous dome grew rapidly over the crater rim, thus being perched precariously over the steep outer slope of the Bocca Nuova, and near-continuous collapse of its steep flanks generated swiftly moving pyroclastic avalanches over a period of several hours. These avalanches advanced at speeds of 10–20 m/s and extended up to 0.7 km from their source on top of lavas emplaced immediately before. Their deposits were subsequently covered by lava flows that issued from vents below the front of the dome and from the Bocca Nuova itself. Growth of the dome was caused by the vertical intrusion of magma in the marginal western part of the crater, which deformed and uplifted previously emplaced, still hot and plastically deformable eruptive products filling the crater. The resulting avalanches had all the characteristics of pyroclastic flows spawned by collapse of unstable flanks of lava domes, but in this case the magma involved was of mafic (hawaiitic) composition and would, under normal circumstances, have produced fluid lava flows. The formation of the dome and the generation of the pyroclastic avalanches owe their occurrence to the rheological properties of the eruptive products filling the crater, which were transformed into the dome, and to the morphological configuration of the Bocca Nuova and its surroundings. The density contrast between successive erupted products may also have played a role. Although events of this type are to be considered exceptional at Etna, their recurrence might represent a serious hazard to visitors to the summit area.

Permian–Triassic boundary interval in the Abadeh section of Iran with implications for mass extinction: Part 1 – Sedimentology

The uppermost Permian strata of the Abadeh section in Iran consist of 56 m of skeletal limestone (Abadehian), that grades upward into 18 m of grey, bioturbated lime mudstone (Djulfian), which in turn grades upward to 18 m of red, nodular wackestone (Dorashamian) containing an abundant pelagic fauna. The overlying lowermost Triassic includes two enigmatic layers at its base. Immediately above the boundary is a 1-m-thick layer of inorganically precipitated synsedimentary carbonate cement. The cement is composed of 10–20-cm-long crystals oriented either perpendicular to the bedding or as dome-shaped features resembling botryoids. About 0.5 m of wackestone overlies the cement layer. The second layer is a 1.5-m-thick grainstone overlying the cement horizon and consists of recrystallised spherical grains (ooids or peloids). The remainder of unit ‘A’ is composed of 100+ m of grey, bioturbated to nodular lime mudstone. The lithofacies succession of the uppermost Permian is interpreted to represent deposition under increasing water depth, related to rising of relative sea level, which led to drowning of the carbonate platform to below storm wave base. Sedimentologic characteristics, lithology, wide distribution, and slow sedimentation rates indicate that strata immediately below the Permian–Triassic (P–T) boundary (Dorashamian interval) were deposited in deep, oxygenated waters. The enigmatic lowermost Triassic synsedimentary carbonate cement and grainstone layers are interpreted to have been deposited in shallow waters, indicating a rapid and major drop in relative sea level at the end of Permian time in this area, followed by a relative sea-level rise during the earliest Triassic. Precipitation of synsedimentary cement immediately above the P–T boundary in Iran and elsewhere (South China) suggests a global change in ocean chemistry. One possible explanation is that dissolved calcium and bicarbonate concentrations in seawater increased sufficiently to promote spontaneous carbonate precipitation, a rare event in the Phanerozoic but common during Precambrian time. Alternatively, a massive heating event could have resulted in CO 2 degassing and decreases in oceanic carbonate solubility, both leading to inorganic, synsedimentary carbonate precipitation. Inorganic precipitation of synsedimentary carbonate cement may indicate that biochemical production of carbonate was halted due to the P–T boundary events. Our study indicates that shallow and moderately deep waters during the latest Permian were well oxygenated in the open ocean setting of the central Tethys Sea in Iran. Therefore, P–T mass extinction scenarios that invoke upon widespread marine anoxia should be viewed with caution.

Characterisation of oxygen plasma-modified mica surfaces using XPS and AFM

Atomic force microscopy (AFM), together with X-ray photoelectron spectroscopy (XPS), has been used to investigate the microstructure of air-cleaved mica surfaces modified by an oxygen RF plasma discharge run under a range of different conditions. The dramatic changes in the topography and the chemical composition in the mica surfaces processed are found to depend strongly on the plasma etching parameters used. At relatively low power levels (≤150 W), the main oxygen plasma interaction with the mica surface is energy-dependent physical etching enhanced by structure-dependent chemical processes. The formation of the regular topographical features observed is attributed mainly to lattice anisotropy of and the defects in the mica surface. When the oxygen plasma power level is above 150 W, the dome-shaped features formed on the treated mica surfaces are determined mainly by the power-enhanced non-selective sputter etching by energetic plasma species, coupled with the local re-deposition of involatile sputter products and reorganisation of such residues on the surfaces concerned. The effects of oxygen pressure and etching time on the morphology of the processed mica surface have also been investigated. XPS analysis revealed that the oxygen plasma etching can cause a build-up of oxygen species on the treated mica surface while the aluminium and silicon present are decreased significantly. Moreover, the changes observed in atomic abundances in the processed mica surface depend strongly on the etching parameters involved.

Organic carbon provenance and maturity in the mud breccia from the Napoli mud volcano: Indicators of origin and burial depth

Mud volcanism on the Mediterranean Ridge is caused by extrusion of overpressured sediments, with consequent formation of spectacular dome-shaped features composed of mud breccias at the seafloor. The organic material in the mud breccia of the Napoli mud volcano is a mixture of different facies, stratigraphic origin and thermal maturities. One portion is synsedimentary organic material with only minor diagenetic alterations and represents sedimenting material that was embedded into the mud volcano during its extrusion. The mud breccia also contains thermally mature organic material of mainly terrestrial provenance with algae of fresh- and brackish-water origin. Vitrinite reflectance data of this maturity generation range from 0.65 to 0.90% R oil and thus characterize thermally mature source rocks, a rank which is corroborated by fluorescence and molecular characteristics. The predominance of vitrinite in the maceral assemblages and the occurrence of biomarkers of terrigenous origin suggest that the major part of the mud matrix derives from a lacustrine or riverine sedimentary unit in the subsurface, possibly from the Messinian stage. A third generation of organic material includes inertinites and vitrinites of high reflectance, which represent recycled organic matter present in any marine sediment. By use of the Lopatin method for modelling the thermal maturation of hydrocarbon source rocks from the vitrinite reflectance data, we calculated that the depth of mobilization ranges from 4900 m to 7500 m, depending upon the temperature gradient used.

Neutrally buoyant diapirs: A model for Venus coronae

Coronae are typically circular features, 100–600 km in diameter, characterized by a deformed annular ring that is often topographically high. The central region may be raised or depressed relative to the ambient elevation. Previous studies have proposed an evolutionary progression beginning with dome‐shaped features which have radiating extensional rifts, followed by plateau‐shaped features which have both concentric deformation and radial extension, ending with the classic corona as described above. Previous dynamical calculations of a rising and spreading diapir simulated the evolution from dome to plateau‐shaped topography, but could not account for the raised rim or depressed central topography of some coronae. We demonstrate that these features can be modeled by a diapir that spreads laterally at a depth of neutral buoyancy.

Enhancement of adhesive property of epithelial cell line Mm2T by culture in the presence of methylated vitamin B12.

A thymic epithelial cell line Mm2T was cultured in a medium containing a high concentration (100 micrograms/ml) of methylated vitamin B12 (CH3-B12). After 19 days, cells were found to have a flat phenotype, to have lost the floating cells which were observed in the control cells at the confluent stage, and to have acquired a resistance to trypsin. However, treatment of the CH3-B12-treated cells with EDTA resulted in a dissociation of cell-to-cell contact and reaggregation was achieved by addition of Ca2+, indicating the involvement of Ca2+ ion in cell-to-cell contact. Electron microscopic analyses revealed that the CH3-B12-treated cells were nearly square in their vertical section, which was in contrast to the dome-shaped feature of the control cells, and their cell-to-cell contact area was significantly widespread, as compared to those of the control, indicating that Mm2T cells acquires an adhesive property by treatment with CH3-B12. Biochemical analyses of both cells indicated that the concentration of glucosylceramide in the CH3-B12-treated cells was higher than that of the control. Free glucose characteristically inhibited the reattachment of cells dissociated with EDTA, suggesting the involvement of glucose in the cell-to-cell adhesion of CH3-B12-treated cells. In addition, WGA-binding glycoconjugates were intensely observed in the boundary region of CH3-B12-treated cells by immunohistochemical staining, but not in that of the control cells. It is suggested that CH3-B12 may affect the morphological alteration of Mm2T by enhancing cell adhesion through elevated expression of the C-type lectin.

Preliminary study of the erosion mechanisms in a biancana badland (Tuscany, Italy)

Italian badlands are present along the Appennini mountains, with an annual precipitation which ranges from 400 to 1200 mm. The genesis of these badlands has often been studied, whereas current processes and erosion rates have only rarely been examined and measured. This paper describes a preliminary study on a badland developed in temperate mediterranean climate and located in SW Tuscany (Italy). The selected site is characterized by biancane, dome-shaped features a few meters in height, generally having a vegetated NNE aspect and severely eroded SSW slope, with a sub-horizontal basal pediment. Field rainfall and runoff experiments were carried out. Field results were substantiated by data collected in specially devised laboratory tests. It was concluded that near-surface pipes — which develop at the point of contact between a surficial layer of weathered and severely fractured regolith and the less fractured and weathered regolith underneath — are the main drainage channels, while rills play a secondary role. Soil detachment is largely due to mechanical and chemical slaking of the regolith during infiltration. The role of runoff is almost solely transport. In particular, it was found that the runoff detachment rate is limited by the rate at which the water front penetrates into the regolith.

Environmental effects of submarine seeping natural gas

It is suspected that most shallow reservoirs of natural gas vent to the surface to some degree. This seeping may be through diffusion of dissolved gas or by a flow of gas bubbles which entrain interstitial water during the rise through the sediments to the surface. Methane bubbles dissolved other gases, notably hydrogen sulphide and carbon dioxide, during their ascent. Under suitable temperature-pressure conditions gas hydrates may be formed close to or at the seabed Black suphide-rich sediments and mats of sulphur oxidizing bacteria are frequently observed close to the sediments surface at seep sites, including a sharp oxic/anoxic boundary. Animal species associated with these gas seeps include both species which obtain nutrition from symbiotic methane-oxidizing bacteria and species with symbolic sulphur-oxidizing bacteria. It is suspected that at some microseepage an enhanced biomass of meiofauna and macrofauna is supported by a food chain based on free-living and symbiotic sulphur-oxidizing and methane-oxidizing bacteria. The most common seep-related features of sea floor topography are local depressions including pockmark craters. Winnowing of the sediment during their creation leads to an accumulation of larger detritis in the depressions. Where the deprssions overlies salt diapirs they may be filled with hypersaline solutions. In some areas dome-shaped features are associated with seepage and these may be colonized by coral reefs. Other reefs, “hard-grounds”, columnar and disc-shaped protrusions, all formed of carbonate-cemented sediments, are common on the sea floor in seep areas. Much of the carbonate appears to be derived from carbon dioxide formed as a result of methane oxidation. The resulting hard-bottoms on the sea floor are often colonized by species not found on the neighboring soft-bottoms. As a result seep areas may be characterized by the presence of a rich epifauna.

Suspected gas-associated clay diapirism on the seabed off Mid Norway

On the continental shelf off Mid Norway at water depths ranging from 150 to 350 m, large areas of the seabed consist of plastic clays with a rugged surface topography and an amorphous (opaque) subsurface acoustic appearance. Five topographic (side-scan sonar) and shallow seismic examples are presented and discussed. Many of the mounds and ridges are suspected to be of a clay diapiric nature. Numerous gas seepages originating from opaque clays have also been found off Mid Norway. A tentative formation model for the ridges and dome-shaped features is proposed. The model is based on suspected differential gas charging of subsurface sediments and clay diapirism caused by differential clay buoyancy.