Fault seal prediction of seismic-scale normal faults in porous sandstone: A case study from the eastern Gulf of Suez rift,Egypt

A study of normal faults in the Nubian Sandstone Sequence, from the eastern Gulf of Suez rift, has been conducted to investigate the relationship between the microstructure and petrophysical properties of cataclasites developed along seismic-scale faults (slip-surface cataclasites) and smaller displacement faults (deformation bands) found in their damage zones. The results help to quantify the uncertainty associated with predicting the fluid flow behaviour of seismic-scale faults by analysing small faults recovered from core, a common procedure in the petroleum industry. The microstructure of the cataclasites was analysed as well as their single-phase permeability and threshold pressure. Faulting occurred at a maximum burial depth of ∼1.2 km. The permeability of deformation band and slip-surface cataclasites varies over ∼1.5 orders of magnitude for a given fault. Our results suggest that the lowest measured deformation band permeabilities provide a good estimate for the arithmetic-mean permeability of the major slip-surface cataclasites. This is because the cataclastic permeability reduction is mostly established early in the deformation history. Stress at the time of faulting rather than final strain appears to be the critical factor determining fault rock permeability. For viable predictions it is important that the slip-surface cataclasites and deformation bands originate from the same host. On the other hand, a higher uncertainty is associated with threshold pressure predictions, as the arithmetic-mean slip-surface cataclasite threshold pressure exceeds the highest measured deformation band threshold pressure by at least a factor of 4.     

Discovery of Messinian canyons and new seismic stratigraphic model,offshore Provence (SE France): Implications for the hydrographic network reconstruction

The interpretation of high-resolution 2D marine seismic profiles together with the analysis of sea-bottom cores allowed a stratigraphic and structural framework of the Provence continental shelf to be proposed. The integration of onshore and offshore stratigraphy, structure and geomorphology provided new insights into Messinian paleotopography and paleohydrography. A geological map of the offshore Provence continental shelf, isobath map of the base Plio-Quaternary surface are presented for the first time in this area. The base Plio-Quaternary surface is a polyphased unconformity that is composed of deep canyons developed by fluvial erosion during the Messinian event, and wave-cut surfaces formed during post-Messinian transgressions. The study evidenced a deep, E–W-trending canyon (Bandol canyon) connected to the head of the Cassidaigne canyon, and filled with up to 600 m-thick Plio-Quaternary deposits. The development of canyons on the Provence margin during the Messinian event was dominantly controlled by the lithology and structure of pre-Messinian formations. A map of the Messinian paleo-drainage network is proposed to explain the presence of deep canyons in the Eastern area and the lack of incision in the Western area. An underground karst drainage scheme is proposed, linked with the current submarine Port-Miou spring.     

Impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir. The case of the Oolithe Blanche Formation (Bathonian,Paris Basin,France)

The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CT-scans and petrophysical measurements.The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity.Early cementation vs. early compaction processes (mainly grain interpenetration) may have considerable influence on fluid-flow properties and parameters such as permeability, acoustic velocities and tortuosity. Better reservoir properties are found when compaction processes begin before cementation.From statistical analyses, e.g. Principal Component Analysis and Linear Discriminant Analysis, a sedimentological/diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work.     

Diagenetic alterations and reservoir heterogeneity within the depositional facies: A case study from distributary-channel belt sandstone of Upper Triassic Yanchang Formation reservoirs (Ordos Basin,China)

Diagenesis is of decisive significance for the reservoir heterogeneity of most clastic reservoirs. Linking the distribution of diagenetic processes to the depositional facies and sequence stratigraphy has in recent years been discipline for predicting the distribution of diagenetic alterations and reservoir heterogeneity of clastic reservoirs. This study constructs a model of distribution of diagenetic alterations and reservoir heterogeneity within the depositional facies by linking diagenesis to lithofacies, sandstone architecture and porewater chemistry during burial. This would help to promote better understanding of the distribution of reservoir quality evolution and the intense heterogeneity of reservoirs. Based on an analogue of deltaic distributary channel belt sandstone in Upper Triassic Yanchang Formation, 83 sandstone plug samples were taken from 13 wells located along this channel belt. An integration of scanning electron microscopy, thin sections, electron microprobe analyses, rate-controlled porosimetry (RCP), gas-flow measurements of porosity and permeability, and nuclear magnetic resonance (NMR) experiments, together with published data, were analysed for the distribution, mineralogical and geochemical characteristics of detrital and diagenetic components and the distribution of reservoir quality within the distributary channel belt.Distribution of diagenetic alterations and reservoir heterogeneity within the distributary channel belt sandstones include (i) formation of high quality chlorite rims in the middle part of thick sandstones with coarser grain sizes and a lower content of ductile components resulted from the greater compaction resistance of these sandstones (providing larger pore spaces for chlorite growth), leading to formation of the intergranular pore – wide sheet-like throat and intergranular pore - intragranular pore – wide sheet-like throat (Φ>15%, k>1mD) in the middle part of thick sandstones; (ii) formation of thinner chlorite rims in the middle part of thinner sandstones is associated with the intergranular pore - intragranular pore – narrow sheet-like throat (9%<Φ<14%, 0.2mD<k<0.8mD); (iii) strong cementation by kaolinite in the more proximal sandstones of distributary channel owing to the strong feldspar dissolution by meteoric water, resulting in the intragranular pore - group of interstitial cement pores – narrow sheet-like throat/extremely narrow sheet-like throat (8%<Φ<11%, 0.1mD<k<0.3mD) due to the pore-filling kaolinite occluding porosity; (iv) formation of dense ferrocalcite zones (δ¹⁸O_VPDB = −23.4‰ to −16.6‰; δ¹³ C_VPDB = −4.0‰ to −2.3‰) favoured in the top and bottom of the channel sandstone which near the sandstone-mudstone bouding-surface, destroying pore space (Φ<8%, k<0.1mD); (v) strong compaction in sandstone of distributary channel edge laterally as a result of fine grain size and high content of ductile components in those sandstones, forming the group of interstitial cement pores – extremely narrow sheet-like throat with porosity values less than 8%.     

Budgets of Mn,Cd and Cu in the macrotidal Gironde estuary (SW France)

The behavior and budget of Mn, Cd and Cu in the Gironde estuary were investigated through data from both the water column (WC) and sediment depth profiles. In the estuarine freshwater reaches, Mn and Cd removal from and Cu addition to the dissolved phase occurs with a magnitude equivalent to 10%, 30% and 25% of their respective annual fluvial gross dissolved input, respectively. In the saline estuary, diffusive benthic outflow is the main source of dissolved Mn (74% of the total gross dissolved input within the estuary) to the WC. In contrast, Cd (96%) and Cu (89%) are mainly released into the dissolved phase of the WC from fluvial, estuarine and dredging-related particles through complexation (Cd) and organic carbon mineralization (Cu). Anthropogenic activities (sediment dredging) induce pore water inputs, particulate sulfide oxidation and sediment resuspension, significantly contributing to the metal budget of the WC. The related amounts of metals released could be equivalent to 20–50% (Cd) and up to 70% (Cu) of their respective net dissolved addition. Mass balances suggest that a large part of the metals previously released into the dissolved phase from processes within the estuary are removed by suspended particles due to (co-)precipitation of Fe/Mn (oxy)hydroxides and scavenging on autochthonous organic matter. On an annual basis, the Gironde estuary acts as a net sink of dissolved Mn, removing 60% of the dissolved fluvial inputs, and as a net source of dissolved Cd and Cu, contributing ∼ 85% and 20–45% to the dissolved Cd and Cu fluxes to the ocean.     

Diversity and large-scale biogeography of Paramesochridae (Copepoda, Harpacticoida) in South Atlantic Abyssal Plains and the deep Southern Ocean

Multicorer samples for meiofaunal study were obtained within the framework of the international project CeDAMar, at 21 stations occupied during the DIVA and ANDEEP campaigns (2000, 2002 and 2005) to the southern Atlantic Ocean (Guinea, Angola and Cape Basins) and the Southern Ocean (Weddell and Scotia Seas), respectively. A total of 311 adult Paramesochridae Lang, 1944 (Copepoda, Harpacticoida) was extracted from 437 cores obtained during 83 deployments of the corer at depths between 1107 and 5655 m. All specimens were determined to species based on morphological characteristics. They belonged to 19 species and four genera (Kliopsyllus Kunz, 1962, Leptopsyllus T. Scott, 1894, Paramesochra T. Scott, 1892 and Scottopsyllus Kunz, 1962). Eleven species were restricted to single regions, whereas the others showed a much wider distribution. For example, Kliopsyllus andeep Veit-Köhler, 2004 and Kliopsyllus diva Veit-Köhler, 2005, were both collected from Guinea, Angola and Weddell Abyssal Plains, and Kliopsyllus schminkei Veit-Köhler & Drewes, 2009 occurred in the three West-African basins. This study provides a first insight into the large-scale biogeography of deep-sea harpacticoids, represented by the Paramesochridae, and indicates that distribution ranges, at least in this family, may extend across South Atlantic and Southern Ocean Abyssal Plains.     

Effects of simulated benthic fluxes on phytoplankton dynamic and photosynthetic parameters in a mesocosm experiment (Bay of Brest,France)

Benthic faunal activity and density play an important role in determining the rates of benthic nutrient fluxes, which enrich the water column and contribute to phytoplankton growth. The intensity of nutrient fluxes in the Bay of Brest depends on the density of the invasive gastropod, Crepidula fornicata. In order to study the impact of benthic fluxes on phytoplankton dynamics, realistic daily nutrient inputs simulating various densities of C. fornicata were added to six enclosures during three weeks. The increase in fertilization intensity influenced the phytoplankton biomass. A succession from Chaetoceros spp. to Pseudo-nitzschia spp. and Leptocylindrus danicus was observed in all enclosures, but the dynamics of successions were different. Pseudo-nitzschia spp. was favored in the three more fertilized enclosures, while Chaetoceros spp. persisted longer in less enriched enclosures. Despite an apparent nitrogen limitation, the quantum efficiency of PSII (F_v/F_m) was high (>0.5) and stable in all enclosures. The maximal photosynthetic capacity (P^Bmax) was also invariable and oscillated around an average value of 2.23 mg C (mg Chl a)⁻¹ h⁻¹. The stability of F_v/F_m and P^Bmax observed at different nutrient input intensities demonstrates that the daily inputs maintained the physiological balance of the microalgae. The maximal light utilization efficiency (α) and the light saturation parameter (E_k) were also quite stable after day 8, which reveals that photosynthetic parameters were driven by growth constraints due to nutrient availability and not by incident light or species successions. We suggest that our results correspond to an “E_k independent variation” regulation. We propose that such regulation of photosynthetic parameters appears when there are frequent nutrient additions which do not allow replete nutrient conditions to be reached but lead to physiological equilibrium.     

Composition and distribution of meiobenthos in amursky bay (peter the great bay, the east sea)

Qualitative and quantitative composition of meiobenthos was studied in Amursky Bay (Peter the Great Bay, the East Sea). Ten taxonomic groups were found, where nematodes were dominant. Density of meiobenthos in ground sediments of the Bay were not uniform, and the average density was measured at 126.4±62.3 ind. m^-2. 56 species of nematodes were detected, and dominant species wereSabatieria palmaris, Paracanthonchus macrodon, Sphaerolaimus limosus, S. gracilis andOncholaimium ramosum. Five taxocenes of nematodes were allocated based on the results of cluster analysis and species domination according to density. Low diversity in species composition of nematodes was noted in the northwestern part of the Bay, which is a zone of desalination, and in the eastern part, which is exposed to household drains.     

Growth and demise of the Jurassic carbonate platform in the intracratonic Paris Basin (France): Interplay of climate change,eustasy and tectonics

It is usually very difficult to identify and quantify the relative influence of tectonics, eustasy and climate on carbonate system evolution from sedimentary records. In order to improve our understanding of these mechanisms, we have traced for the first time, the evolution of the eastern Paris Basin platform throughout the entire Jurassic period. This carbonate platform underwent eight successive growth and demise phases, with different depositional profiles ranging from ramps to flat-topped geometries. The eight carbonate growth periods are compared with the standard sea-level curves, local tectonic regimes and recently published oxygen-isotope and/or clay mineralogy databases. Prograding heterozoan facies along ramp profiles mark periods dominated by second-order eustatic sea-level rise, relatively cool sea surface temperatures, and mesotrophic and humid conditions (Hettangian, Pliensbachian, late Oxfordian, Tithonian). During these periods, variable detrital contents in the sedimentary succession hampered the efficiency of shallow-marine carbonate factories. Higher sea surface temperatures, oligotrophic and humid conditions associated with either eustatic sea-level rise or very high local subsidence occurred during the early Bajocian and the mid-Oxfordian. These seawater properties seem to have favoured the aggradation of scleractinian corals forming dome-shaped bioherm buildups. An oolitic and lime-mud carbonate system, deposited during the Bathonian second-order eustatic sea-level fall, is characterised by miliolid-rich micritic facies on a rimmed-ramp under stable, cooler and drier conditions. The second-order maximum flooding associated with a sea surface temperature decline and/or a seawater eutrophication caused at least five carbonate demise periods (i.e. Toarcian, earliest late Bajocian, Callovian/Oxfordian transition, earliest late Oxfordian and Kimmeridgian).     

Differential response of benthic macrofauna to the formation of novel oyster reefs (Crassostrea gigas,Thunberg) on soft and rocky substrate in the intertidal of the Bay of Brest,France

When the Pacific oyster (Crassostrea gigas, Thunberg) was introduced into France for aquaculture in the mid-sixties, it was initially confined to the sites where it was farmed. Subsequent global warming most likely facilitated the establishment of wild populations throughout the French coastline. This phenomenon of spread has become so great that oyster reefs have recently appeared in sheltered estuaries, on both soft and hard substrate. The present study examined two such sites in the Bay of Brest, Brittany. It is the first to investigate the impacts of this new substrate on the biocoenosis of uncolonised intertidal habitats in France. Increased species richness and abundance of intertidal macrofauna were observed in the presence of oyster reefs on both, mud (4 and 20 fold respectively) and rock (5 fold for both). The dominance of suspension feeders in mud changed to carnivores in reefs and their underlying sediment. Calculation of biotic coefficients (BC) of the soft-bottom fauna revealed only a slight organic enrichment, and the organic and silt composition in the sediment beneath oyster reefs were not significantly different from that on bare sites. On rock, the dominance of grazers remained unchanged between bare rock and oyster reef, while reef on rock was also characterised by deposit and detritic feeders. C. gigas is suspected to cause a homogenisation of coastal habitats with an impoverishment of overall quality but we detected only 11 common species between reefs on mud (60 species) and those on rock (55 species).     

Influence of Naineris laevigata (Polychaeta: Orbiniidae) on vertical grain size distribution,and dinoflagellate resting stages in the sediment

Short-term experiments were performed with the polychaete Naineris laevigata Grube, a conveyor-belt deposit feeder, to evaluate: the daily sediment reworking rate, the influence of the activity of this burrowing worm on the vertical redistribution of the sediment and dinoflagellate cysts. We also tested the germination success of cysts after their passage through the gut of the polychaete. Vertical particle distribution was studied in small aquaria with and without worms and with an initially layered sediment. After 30 days, sediment cores were collected in controls and treatments at 3 different depths (upper, intermediate and deep) and the diameter of 100 particles from each depth was measured to obtain the size-frequency distribution. The burrowing activity of 3 worms may completely mix a pre-existent layering within 30 days. The translocation of a mud layer from 4 cm depth towards the surface was observed. The mud layer deposited on the surface by the end of the experiment was at least 1 cm thick.Daily average production of faecal pellets was 0.443±0.032 g per worm. From the first day of the experiment, the particle size distribution of the faecal pellets released at the surface revealed the presence of sediment and cysts originating from underlying layers. Tests showed that the germination percentage of the cysts significantly diminished after passage through the guts of the worms.Our results indicate that N. laevigata is an effective vertical mixer of sediment and plays a role in the vertical transport and germination success of resting stages.     

Abundance,distribution, and feeding patterns of juvenile coho salmon (Oncorhynchus kisutch) in the Juan de Fuca Eddy

The Juan de Fuca Eddy is a seasonal, counter-clockwise gyre off the mouth of the Strait of Juan de Fuca between Washington, USA and British Columbia, Canada that may provide favorable feeding habitat for juvenile coho salmon (Oncorhynchus kisutch) during their early marine existence. In late September 2002, physical and biological sampling was conducted along two transects of the eddy region. Surface rope trawling was conducted to capture juvenile salmon and other nekton, along with bongo and neuston net tows to examine potential mesozooplanktonic salmon prey. Presence of the Juan de Fuca Eddy was confirmed with vertical water profiles. In addition, nutrient and chlorophyll a concentrations collected from 3-m depth were within the range observed in previous studies within the eddy region. In the mesozooplankton community, euphausiids, chaetognaths, and decapod megalopae were common. In the diet of juvenile coho salmon, euphausiids and decapod megalopae were dominant by percent number, and larval and juvenile fish were dominant by percent weight. Feeding intensity (percent body weight) based on stomach contents was variable, but not significantly different among stations. To compare the Juan de Fuca Eddy region with an upwelling area, we sampled along a transect off La Push (LP), Washington, USA which is south of the eddy. The eddy region was found to be less productive than the LP transect. Nutrients were lower, chlorophyll a concentrations were higher, and zooplankton abundance was generally higher along the LP transect than in the eddy region. In addition, more juvenile coho salmon were captured from the LP transect than the eddy region. Prey items in stomachs of salmon from the LP transect were heterogeneous compared to those from the eddy region. Feeding intensity along the LP transect was slightly lower and more variable than in the eddy region, and differences in feeding intensity among LP stations were significant. In addition, feeding intensities among stations nested within regions were significantly different.     

Factors affecting the distribution and abundance of Macrobrachium petersi (Hilgendorf) in the Keiskamma River and estuary,South Africa

A dry (1979–1980) and a wet (1980–1981) season had a marked effect on the freshwater inflow into the Keiskamma estuary. Under low inflow conditions, which results in elevated salinities in the upper reaches, an upstream migration of adult Macrobrachium petersi (Hilgendorf) to freshwater takes place. During periods of increased river inflow adult M. petersi move downstream to the more saline reaches of the estuary. These two migratory responses have been interpreted as (a) a breeding migration under high inflow conditions which ensures that larvae are in close proximity to salinities that favour growth and development, and (b) an adult upstream migration back to freshwater to escape elevated estuarine salinities as a result of the low freshwater inflow.     

Differential distribution of the two cryptic species, Pomatoschistus microps and P. marmoratus, in the lagoons of southern France, with an emphasis on the genetic organisation of P. microps

The presence and the distribution of two cryptic sedentary gobies, Pomatoschistus microps and Pomatoschistus marmoratus, were investigated in several lagoons stretching along the Golfe du Lion, southern France Mediterranean coast, and Corsica. Pomatoschistus microps is the only sedentary Pomatoschistus species in two shallow lagoons with large variations of salinity and temperature. In contrast, P. marmoratus, another sedentary species, can be found preferentially in a deep salty lagoon with small salinity variations. Both species occur sympatrically in the Rhone Delta and hybridise, producing fertile offspring. Using allozymes, competition, linked to fitness, is invoked to explain the distribution pattern of these sibling species.     

Geometry and architectural associations of co-genetic debrite–turbidite beds in basin-margin strata, Carboniferous Ross Sandstone (Ireland): Applications to reservoirs located on the margins of structurally confined submarine fans

Co-genetic debrite–turbidite beds are most commonly found in distal basin-plain settings and basin margins. This study documents the geometry, architectural association and paleogeographic occurrence of co-genetic debrite–turbidite beds in the Carboniferous Ross Sandstone with the goal of reducing uncertainty in the interpretation of subsurface data in similarly shaped basins where oil and gas is produced.The Ross Sandstone of western Ireland was deposited in a structurally confined submarine basin. Two outcrops contain co-genetic debrite–turbidite beds: Ballybunnion and Inishcorker. Both of the exposures contain strata deposited on the margin of the basin. An integrated dataset was used to characterize the stratigraphy of the Ballybunnion exposure. The exposure is divided into lower, middle, and upper units. The lower unit contains laminated shale with phosphate nodules, structureless siltstone, convolute bedding/slumps, locally contorted shale, and siltstone turbidites. The middle unit contains co-genetic debrite–turbidite beds, siltstone turbidites, and structureless siltstone. Each co-genetic debrite–turbidite bed contains evidence that fluid turbulence and matrix strength operated alternately and possibly simultaneously during deposition by a single sediment-gravity-flow event. The upper unit contains thin-bedded sandy turbidites, amalgamated sandy turbidites, siltstone turbidites, structureless siltstone, and laminated shale. A similar vertical facies pattern is found at Inishcorker.Co-genetic debrite–turbidite beds are only found at the basin-margin. We interpret these distinct beds to have originated as sand-rich, fully turbulent flows that eroded muddy strata on the slope as well as interbedded sandstone and mudstone in axial positions of the basin floor forming channels and associated megaflute erosional surfaces. This erosion caused the axially dispersing flows to laterally evolve to silt- and clay-rich flows suspended by both fluid turbulence and matrix strength due to a relative increase in clay proportions and associated turbulence suppression. The flows were efficient enough to bypass the basin center/floor, physically disconnecting their deposits from coeval lobes, resulting in deposition of co-genetic debrite–turbidite beds on the basin margin. The record of these bypassing flows in axial positions of the basin is erosional surfaces draped by thin siltstone beds with organic debris.A detailed cross-section through the Ross Sandstone reveals a wedge of low net-to-gross, poor reservoir-quality strata that physically separates sandy, basin-floor strata from the basin margin. The wedge of strata is referred to as the transition zone. The transition zone is composed of co-genetic debrite–turbidite beds, structureless siltstone, slumps, locally contorted shale, and laminated shale. Using data from the Ross Sandstone, two equations are defined that predict the size and shape of the transition zone. The equations use three variables (thickness of basin-margin strata, thickness of coeval strata on the basin floor, and angle of the basin margin) to solve for width (w) and trajectory of the basinward side of the low net-to-gross wedge (β). Beta is not a time line, but a facies boundary that separates sandy basin floor strata from silty basin-margin strata. The transition zone is interpreted to exist on lateral and distal margins of the structurally confined basin.Seismic examples from Gulf of Mexico minibasins reveal a wedge of low continuity, low amplitude seismic facies adjacent to the basin margin. Strata in this wedge are interpreted as transition-zone sediments, similar to those in the Ross Sandstone. Besides defining the size and shape of the transition zone, the variables “w” and “β” define two important drilling parameters. The variable “w” corresponds to the minimum distance a well bore should be positioned from the lateral basin margin to intersect sandy strata, and “β” corresponds to the deviation (from horizontal) of the well bore to follow the interface between sandy and low net-to-gross strata. Calculations reveal that “w” and “β” are related to the relative amount of draping, condensed strata on the margin and the angle of the basin margin. Basins with shallowly dipping margins and relatively high proportions of draping, clay-rich strata have wider transition zones compared to basins with steeply dipping margins with little draping strata. These concepts can reduce uncertainty when interpreting subsurface data in other structurally confined basins including those in Gulf of Mexico, offshore West Africa, and Brunei.     

Influence of environmental variability on distribution and relative abundance of baleen whales (suborder Mysticeti) in the Gulf of California

The Gulf of California (GC) is one of the most productive seas in the Pacific Ocean because of several oceanographic phenomena that support many marine mammal species, particularly of the cetacean order. The environmental variability of the GC was analysed during the cold and warm periods of 2005 and 2006 and its effects on the distribution and relative abundance of baleen whales using sea surface temperature (SST) and chlorophyll a (Chl a) concentration. Satellite image analysis allowed us to detect important differences in both Chl a concentration and SST including cold to warm periods, even between the two cold periods and between the two warm periods. The cold periods had the highest number of whales: 99 individuals in 2005 and 183 in 2006, which were distributed along the entire gulf. Fewer animals were recorded in the warm period: 46 individuals in 2005 and 30 in 2006, which were mainly distributed in the northern part of the gulf. We concluded that SST influenced the relative abundance of baleen whales while Chl a concentration influenced their distribution.