Effect of macrofaunal bioturbation on bacterial distribution in marine sandy sediments, with special reference to sulphur-oxidising bacteria

We have studied the impact of the bioturbating macrofauna, in particular the lugworm Arenicola marina and the bivalve Cerastoderma edule, on abundances and distribution patterns of total bacteria and of bacteria of selected functional groups in sandy intertidal sediments. The selected groups comprised the colourless sulphur-oxidising bacteria and the anoxygenic phototrophic bacteria, which are expected to occupy small zones at the oxygen–sulphide interface in stable (non-bioturbated) sediments. The presence of a wooden wreck buried in the sediment at 10 cm depth within a large area of intertidal sand flat colonised by lugworms provided a unique opportunity to confront field observations with laboratory simulations. The site with the wooden wreck, which was used as control site, was devoid of both A. marina and C. edule, while the composition of the rest of the zoobenthic community was rather similar to that of the surrounding area. In the field, the density of total bacteria was approximately one order of magnitude higher in the control site than in the natural (bioturbated) site. This can be explained by the higher contents of silt and clay particles (higher surface-area/volume ratio) and higher total organic-carbon contents found at the control site. It appears that the presence of macrofauna affects sedimentation processes, which indirectly influence bacterial dynamics. Samples from the control site have been incubated in the laboratory with A. marina and C. edule added (bioturbated core), while an unamended core served as a control. The laboratory experiments contrasted with the field observations, because it was found that total bacteria were actually higher in the deeper layers of the bioturbated core. Moreover, the populations were more homogeneous (less stratified) and colourless sulphur bacteria were on average less numerous in the bioturbated core. In general, laboratory incubations resulted in a decrease of total bacteria with a concomitant increase of colourless and phototrophic sulphur-oxidising bacteria and thus in modifications of the bacterial community structure. Hence, our results demonstrate that care must be taken in extrapolating results from laboratory experiments (e.g. mesocosm research) to field situations.     

Evolution of an ancient coastal plain: palaeosols, interfluves and alluvial architecture in a sequence stratigraphic framework, Cenomanian Dunvegan Formation, NE British Columbia, Canada

To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of non-marine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single-storey, very fine- to fine-grained sandstone ribbons with W/T ratios <30, encased in fine-grained floodplain sediments are interpreted as anastomosed channels. Fine- to medium-grained, laterally accreted point-bar deposits forming multistorey sand bodies with individual W/T ratios >30 are interpreted as the deposits of meandering rivers filling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, floodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol profiles and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Interfluve, sequence-bounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identified using a combination of (1) stratigraphic position; (2) field observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Interfluve palaeosols are similar to modern Alfisols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high-frequency base level cycles (eustatic?) that are expressed as transgressive–regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage. In contrast, well-developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate. The detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under-used technique for the recognition of key surfaces in the geological record. This has broad implications for non-marine sequence stratigraphy.     

粘弹介质本构理论讨论

阐述了建立物质本构关系时应满足的基本公理,较详细地推导了各种类型粘弹性物质的本构关系,论述了变率理论与泛函数论之间的关系,推导了对于粘弹性问题求解具有实用意义的对应定理,并以简单的例子说明对应定理的应用。     

Numerical studies of hyperplasticity with single,multiple and a continuous field of yield surfaces

The development of a new constitutive model would normally require a new procedure to be established for derivation of the incremental response. However, for models generated within the framework of hyperplasticity (using single, multiple or continuous yield surfaces), this derivation can be carried out using standard procedures. In this paper we present first the unified incremental response for a model using a single internal variable for general loading conditions. Next, we develop and explore three different numerical techniques for implementation of this procedure. One of the approaches, which seems superior, is extended to the multi‐surface hyperplastic formulation. Finally, to allow integration of continuous hyperplastic models within the same multi‐surface hyperplastic setting, the issue of discretization of the continuous field of yield surfaces is addressed. Copyright © 2003 John Wiley & Sons, Ltd.     

Deep-sea submersible survey in the Suruga, Sagami and Japan Trenches: preliminary results of the 1985 Kaiko cruise, Leg 2

Nine submersible dives were made in three trenches off central Japan, between 2990 and 5900 m of water depth. Our observations confirm the interpretation that Daiichi-Kashima Seamount is a Cretaceous guyot formed on the Pacific plate that has traveled into the Japan Trench. We also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves, the lower one being now subducting beneath the Japan margin. Compressional deformation was identified within the lower part of the inner slope in front of the seamount. The pattern of deformation that affects Quaternary sediments is in agreement with the present kinematics of the convergence between the Pacific plate and Japan. Deep-water (5700 m) clam colonies are associated with advection of fluids, driven by the subduction-related overpressures. In the northern slope of the Boso Canyon, along the Sagami Trough system (Philippine Sea plate-Japan boundary), the deformation affecting a thick upper Miocene to lower Pliocene sequence indicates two directions of shortening: a N175°E direction which is consistent with the present relative motion along the Sagami Trough (N285–N300°E) and a N30°E direction which could be related to a more northerly direction of convergence that occured during the early Quaternary and earlier.     

Carbon in olivine single crystals analyzed by the 12C(d,p)13C method and by photoelectron spectroscopy

Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60–180 wt.-ppm, were analyzed by means of the ¹²C(d. p)¹³C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar⁺ ion sputtering respectively, between 200–930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1–2 μm or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0–0.6, 0.6–1.2, and 1.2–1.8 μm. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D= 10^?13 exp(?7.8/RT) [m²· sec^?1; KJ · mole^?1] and from XPS data between 450–925 K: D = 10^?14 exp(-6/RT) [m² · sec^?1; KJ · mole^?1] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole^?1 respectively.     

Tepee structures and associated diagenetic features in intertidal carbonate sands (lower Jurassic,Morocco)

In southeastern Morocco, Early Jurassic inter- to supratidal carbonates can be followed for 200–300 km along the southern slopes of the High Atlas mountains. These beds form intervals of several tens to more than one hundred metres.Tepee structures, which are common in these beds, are confined to coarse-grained, early lithified beaches. Comparison with similar features in the Recent, and analysis of the diagenetic history of the sheetcrack-fills suggests that the formation of the tepees is an early, almost synsedimentary event.     

Analcimic zones in the tertiary of anatolia and their geological positions

The Anatolian Tertiary and especially the Neogene have some geological series with analcime as the principal rock-forming mineral. Sedimentation basins receiving material in suspension and in solution permit the authigenesis of analcime dolomite, calcite and opal(C-T). Analcimes formed by hydrothermal alteration on the ocean floor, after the pillow lava and diabasic dyke complexes of ophiolites, can form a source of detrital analcime when they are on the continental medium. Continental alteration of the pillow lavas and diabasic dykes permits the formation of solutions suitable in composition for analcime authigenesis. Analcimes formed in these environments are particularly related to the silica content of these media.Principal clay minerals formed with analcimic formations are smectites and (14_s—14_c) mixed layers. Illite, chlorite and corrensite are also present in smaller quantities.     

On the velocity of jets powering hot spots similar to those in Cygnus A

Hot spots similar to those in the radio galaxy Cygnus A can be explained by the strong shock produced by a supersonic but classical jet \(\left( {u_{jet}< c/\sqrt 3 } \right)\) . The high integrated radio luminosity (L?2×10⁴⁴ erg s^?1) and the strength of mean magnetic field (B?2×10^?4 G) suggest the hot spots are the downstream flow of a very strong shock which generates the ultrarelativistic electrons of energy ?≥20 MeV. The fully-developed subsonic turbulence amplifies the magnetic field of the jet up to 1.6×10^?4 G by the dynamo effect. If we assume that the post-shock pressure is dominated by relativistic particles, the ratio between the magnetic energy density to the energy density in relativistic particles is found to be ?2×10^?2, showing that the generally accepted hypothesis of equipartition is not valid for hot spots. The current analysis allows the determination of physical parameters inside hot spots. It is found that:

1. The velocity of the upstream flow in the frame of reference of the shock isu ₁?0.2c. Radio observations indicate that the velocity of separation of hot spots isu _sep?0.05c, so that the velocity of the jet isu _jet=u ₁+u _sep?0.25c.
2. The density of the thermal electrons inside the hot spot isn ₂?5×10^?3 e ^? cm^?3 and the mass ejected per year to power the hot spot is ?4M ₀yr^?1.
3. The relativistic electron density is less than 20% of the thermal electron density inside the hot spot and the spectrum is a power law which continues to energies as low as 30 MeV.
4. The energy density of relativistic protons is lower than the energy density of relativistic electrons unlike the situation for cosmic rays in the Galaxy.

     

Détection de carrières souterraines par sismique haute résolution à Annet-sur-Marne (France)Underground cavities detection by using high resolution seismics at Annet-sur-Marne (France)

Seismic methods were tested to detect underground cavities in the surroundings of Annet-sur-Marne (Seine-et-Marne, France). Cavities are located in three Ludian gypsum layers, between 30 and 80 m in depth. A high resolution seismic profile 450 m long was carried out so that the first third and the other part are respectively above non-exploited and exploited areas. Data processing highlights a series of reflections related to the marl–gypsum interfaces in the non-exploited area, while these reflections disappear in the exploited area. With the help of numerical simulations, this feature is interpreted as a disorganisation of wave fronts reflected on interfaces because of the presence of cavities. To cite this article: G. Grandjean et al., C. R. Geoscience 334 (2002) 441–447.