Short Lateral Distances Research Articles

Carbonate‐rich megabeds within a Triassic siliciclastic deep‐water system, West Qinling orogenic belt, Central China: Character, processes and implications

AbstractDeep‐water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep‐water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep‐marine systems. Less documented are carbonate‐rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep‐water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate‐rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow‐water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast‐supported conglomeratic division (Division I), an intermediate matrix‐supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep‐water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally‐supplied carbonate‐rich megaflows that eroded and incorporated the substrate during transport.

Lack of detectable chemosynthesis at a sponge dominated subarctic methane seep

We used high-resolution imagery within a Geographic Information System (GIS), free gas and porewater analyses and animal bulk stable isotope measurements to characterize the biotic and abiotic aspects of the newly discovered Vestbrona Carbonate Field (VCF) seep site on the Norwegian shelf (63°28′N, 6° 31′E, ∿270 m water depth). Free gas was mainly composed of microbial methane. Sediment porewater sulfide concentrations were in the millimolar range and thus high enough to sustain seep chemosymbiotrophic animals. Nonetheless, the VCF lacked chemosymbiotrophic animals despite an abundance of methane-derived carbonate crusts which are formed by the same anaerobic processes that sustain chemosymbiotrophic animals at seeps. Furthermore, none of the sampled taxa, across various trophic guilds exhibited a detectable contribution of chemosynthetically fixed carbon to their diets based on bulk stable isotope values, suggesting a predominantly photosynthetic source of carbon to the VCF seep food web. We link the absence of chemosymbiotrophic animals to highly localized methane flow pathways, which may act as a “shunt-bypass” of the anaerobic oxidation of methane (AOM) and by extension sulfide generation, thus leading to sediment sulfide concentrations that are highly heterogeneous over very short lateral distances, inhibiting the successful colonization of chemosymbiotrophic animals at the VCF seep. Instead, the seep hosted diverse biological communities, consisting of heterotrophic benthic fauna, including long lived taxa, such as soft corals (e.g., Paragorgia arborea) and stony corals (i.e., Desmophyllum pertusum, formerly known as Lophelia pertusa). Compared to the surrounding non-seep seafloor, we measured heightened megafaunal density at the seep, which we attribute to increased habitat heterogeneity and the presence of a variety of hard substrates (i.e., methane-derived authigenic carbonates, dropstones and coral rubble), particularly since the most abundant taxa all belonged to the phylum Porifera. Compared to the surrounding non-seep seafloor, marine litter was denser within the VCF seep, which we link to the more variable local topography due to authigenic carbonates, which can rip off parts of bottom trawling nets thereby making the seep act as catchment area for marine litter.

Safety Assessment of the Interaction Between an Automated Vehicle and a Cyclist: A Controlled Field Test

The operation of automated vehicles (AVs) on shared roads requires attention concerning their interactions with vulnerable road users (VRUs), such as cyclists. This study investigates the safety of cyclists when they interact with an AV and compares it with their interaction with a conventional vehicle. Overall, 29 cyclists participated in a controlled field experiment consisting of interaction scenarios in which a vehicle approached the cyclist from behind. Four interaction scenarios were included: manual and automated following and manual and automated overtaking of the cyclist. The vehicle operated in all scenarios in a manual mode for safety reasons. However, before each ride, participants received information about the vehicle’s operation mode (automated or manual). The following attributes were considered: overtaking speed, overtaking lateral distance, following distance, and roadside objects. The objective and the subjective risks were evaluated in each scenario. The objective risk was assessed using the probabilistic driving risk field, and the subjective risk was assessed based on the cyclists’ self-reported risk values, cycling behavior, and their trust in AVs. The results show that automated and manual following have similar objective and subjective risks, while automated overtaking has a higher level of objective and subjective risks than manual overtaking. The results also show that a longer interaction time leads to an increase in cycling speed and a decrease in the lateral distance of the cyclist to the curb. Thus, we conclude that automated following is a safer option for short traveling distances, while for longer traveling distances, manual overtaking is preferred. Additionally, a short lateral distance from the cyclist when overtaking increases the subjective and objective risks.

What Do P-Wave Velocities Tell Us About the Critical Zone?

Fractures in Earth's critical zone influence groundwater flow and storage and promote chemical weathering. Fractured materials are difficult to characterize on large spatial scales because they contain fractures that span a range of sizes, have complex spatial distributions, and are often inaccessible. Therefore, geophysical characterizations of the critical zone depend on the scale of measurements and on the response of the medium to impulses at that scale. Using P-wave velocities collected at two scales, we show that seismic velocities in the fractured bedrock layer of the critical zone are scale-dependent. The smaller-scale velocities, derived from sonic logs with a dominant wavelength of ~0.3 m, show substantial vertical and lateral heterogeneity in the fractured rock, with sonic velocities varying by 2,000 m/s over short lateral distances (~20 m), indicating strong spatial variations in fracture density. In contrast, the larger-scale velocities, derived from seismic refraction surveys with a dominant wavelength of ~50 m, are notably slower than the sonic velocities (a difference of ~3,000 m/s) and lack lateral heterogeneity. We show that this discrepancy is a consequence of contrasting measurement scales between the two methods; in other words, the contrast is not an artifact but rather information—the signature of a fractured medium (weathered/fractured bedrock) when probed at vastly different scales. We explore the sample volumes of each measurement and show that surface refraction velocities provide reliable estimates of critical zone thickness but are relatively insensitive to lateral changes in fracture density at scales of a few tens of meters. At depth, converging refraction and sonic velocities likely indicate the top of unweathered bedrock, indicative of material with similar fracture density across scales.

Stratigraphic architecture of a mixed clastic-carbonate succession and 87Sr/86Sr-based chronostratigraphy along the margin of a synorogenic extensional basin (Hochmoos Formation, upper Santonian, Northern Calcareous Alps)

Abstract The Gosau Group (Turonian to Ypresian) of the Eastern Alps is a synorogenic wedge-top succession that accumulated in active depocenters in an oblique-convergent plate tectonic setting. Due to high morphological differentiation of depocenters by tectonism, the Gosau Group displays a wide range of facies as well as marked facies heteropy and thickness variations over short lateral distances. In the area of the locations Gosau and Russbach, the Hochmoos Formation along the SE basin margin near Gosauschmied comprises coastal to shallow-marine deposits and small rudist bioconstructions and was investigated by way of field mapping, profile descriptions, microfacies analysis, isotope measurements and assessment of fossil content. Strontium isotope ratios (87Sr/86Sr) from 0.707485 (oldest) to 0.707549 (youngest) indicate a latest Santonian age, with the youngest parts of the Hochmoos Formation possibly extending into the Campanian. On the west side of the study area, the succession of lithologies and fossil content record transgression of a fan-delta to marginal-marine environment (lowstand to transgressive systems tract), followed by shallow neritic deposition (part of the transgressive systems tract) and, finally, by progradational stacking of limestone beds in the highstand systems tract, culminating in growth of rudist thickets in an inner shelf and partially protected ‘lagoonal’ milieu. Eventually, at the inception of the following falling stage systems tract, input of large clasts of Dachstein Limestone, quartz and chert record a recurrence of the subaqueous part of a fan-delta. On the east side of the study area, a preponderance of rudist-clastic limestones over a few rudist biostromes preserved in situ indicate a normal-marine environment punctuated by high-energy events, such as storms or tsunami. The scarcity of benthic foraminifera and the presence of only isolated specimens of colonial corals underscore a habitat with a calcarenitic substrate frequently shifted by currents. Several lines of evidence indicate that the western part of the study area was more proximal relative to the eastern one. With a maximum thickness of 68 m, the Hochmoos Formation at Gosauschmied is slightly thicker and more distal than outcrops located nearer to the basin margin and farther towards the SE (Schmiedsippl, Katzhofgraben), but significantly thinner than the nearly 300 m at Gosau Pass-Gschütt, or the thickness of 170 m observed in the area of Rigaus-Abtenau farther in the West. These thickness variations are interpreted as a result of extensional syndepositional tectonism. At Gosauschmied, the vertical arrangement of facies records a cycle of relative sea-level change that may have been tectonically enhanced.

Detection and modelling of strong topography of mid-mantle structures beneath the North Atlantic

SUMMARYThere is mounting evidence for the presence of seismic reflectors in the mantle at a depth of around 1000 km, however, the cause for these reflectors is not yet well established and published observations show a range of depth estimates for these structures. Discussion is also still ongoing whether it is one global or several different reflectors. Here, we investigate the presence of seismic reflectors beneath the North Atlantic using a large number of PP and SS underside reflections. We analyse over 2600 earthquakes with Mw ≥ 5.7 and use array seismic methods to improve the visibility of the small-amplitude reflected signals. The measured time lag between PP/SS arrivals and their corresponding precursors on robust stacks are used to estimate the depth of the reflector. Our results reveal the presence of mid-mantle structure beneath the North Atlantic in a depth range of ∼700–1300 km, consistent for both P- and S-wave observations. The reflector depth is shallower than 1000 km beneath the southern part of the investigation area and deepens seemingly abruptly towards the northern part of the North Atlantic. We find polarity variations in a region of strong depth change which we assume to be due to wave interference. Using 3-D waveform modelling, we implement models with strong topography as well as models with two overlapping reflectors and two separated reflectors and show that a large step in reflector depth over a short lateral distance, as imaged with our data set, can be resolved, while the discrimination between strong topography and two overlapping and separated reflectors, respectively, is also possible. The variations in precursor polarity can also be observed in our synthetic data in the region of strong topography confirming our assumption of wave interference for generating apparent precursor polarity and waveform changes. While the opposite polarity can be produced by the two overlapping reflectors as well, the strong topography model is preferred in this region, since we do detect only one reflected signal in our observations.

Cambrian reefs in the lower Poleta Formation: a new occurrence of a thick archaeocyathan reef near Gold Point, Nevada, USA

The lower member of the Poleta Formation is well known for its abundant archaeocyaths, including an exceptionally preserved reef at Stewart’s Mill in Nevada. Large archaeocyath-bearing reefs are relatively uncommon, with most occurring as small nearshore patch reefs. Here, we describe a new 70 m-thick archaeocyath reef from the lower Poleta Formation, herein referred to as the Gold Point Reef, located near the townsite of Gold Point, Nevada. In spite of broad similarities with the Stewart’s Mill exposure, the Gold Point Reef shows an interplay between shoal and reef development over the ~ 70 m exposure that differs from what is observed at Stewart’s Mill. This reef also preserves a small shelly fauna in its uppermost 10 m, dominated by Hyolithellus. Three successive ecological stages of reef development are observed here: the pioneer stage characterized by a single rare frame-building species; the diversification stage involving about nine species of both frame-building and mud-sticking archaeocyaths; and the final foundering stage represented by one to two species of archaeocyaths and facies indicating reef demise, including abundant grainstone/packstone shoals and a silicified upper bed with a settlement of hyolitheminthes. During the apex of reef development here, there are large modular archaeocyaths, which were able to produce thick secondary skeletal tissue for a firm attachment; these archaeocyaths were capable of building large reefs in a variety of settings. Additionally, the carbon isotope profile recorded in the Gold Point Reef shows similarities to nearby exposures of the equivalent lower Poleta Formation, with the exception of a small negative downturn at the top of the reef that is not found in other locations. Combined with the documentation of facies changes over short lateral distances, the isotope data suggest that archaeocyathan reefs may have been time-transgressive across the shelf during deposition of the lower Poleta. Additionally, our work suggests that both here and globally, the specific biotic assemblage reflected the local influences of the environment on reef development, creating highly variable coeval paleocommunities even within a restricted area.

Ultrasonic Total Focusing Imaging Method of Multilayer Composite Structures Using the Root‐Mean‐Square (RMS) Velocity

Multilayer composite structures have been widely used in industrial manufacturing, and nondestructive testing of these multilayer structures is to ensure their reliable quality and performance. Currently, ultrasonic total focusing method (TFM) imaging using full‐matrix capture (FMC) technology has been proven to sense small defects in a single homogeneous medium and improve the imaging signal‐to‐noise ratio. However, these algorithms cannot be accurately applied to imaging of multilayer composite structures, due to the acoustic impedance variation and because reflection and refraction occur at the interface between the layers, which makes it very difficult to calculate the ultrasonic propagation path and time. To solve this problem, a root‐mean‐square (RMS) velocity algorithm for total focusing imaging of multilayer structures is proposed in the article. Based on the theory of RMS velocity for processing of seismic data, the approximated delays can be easily and quickly calculated by a hyperbolic time‐distance relationship under circumstances of short lateral distance and horizontal layers. The performance of the proposed algorithm is evaluated by total focusing imaging of a two‐layer medium with drilled holes and conducted by the finite element simulation. To further improve imaging efficiency, the partial data in the full‐matrix data were used for imaging which is the simplified matrix focusing method (SFM). The results verify that the proposed methods are capable of total focusing imaging of two‐layered structures. However, the imaging performance and efficiency of these algorithms are different.

Upper Cretaceous volcaniclastic complexes and calcareous plankton biostratigraphy in the Western Pontides, NW Turkey

This study describes and interprets Upper Cretaceous volcaniclastics interbedded with hemipelagic to pelagic limestones, marls, and turbidites from the Western Pontides, northwestern Turkey. The Derekoy Formation, the Unaz Formation (red pelagic limestone unit), and the Cambu Formation can be distinguished, overlain by the turbiditic Akveren Formation. Biostratigraphic ages from the predominantly volcaniclastic Derekoy Formation indicate Turonian (Dicarinella concavata planktonic foraminifera zone, CC13/UC8-9 nannofossil zones) to middle/late Santonian ages up to CC17/UC13. The Unaz Formation, deposited during the late Santonian (UC13, Dicarinella asymetrica Zone), is overlain by the volcaniclastic Cambu Formation of latest Santonian (CC17b/UC13) to early/middle Campanian (CC20/UC15a) age. However, turbidite intercalations are already present diachronously from CC19/UC14d onwards, and the turbiditic Akveren Formation ranges up into the late Maastrichtian (Abathomphalus mayaroensis Zone). Geochemistry of the volcaniclastic units reveals information about the volcanic series and tectonic setting, although element mobility has to be considered. An overall trend of calc-alkaline to high-K calc-alkaline series and basaltic to basalt-andesitic rock types was identified. A negative Nb anomaly with respect to Th and Ce in all samples confirms the existence of a volcanic arc, also indicated by a negative Ti anomaly. Biostratigraphic age constraints give evidence for volcanic arc activity mainly between Turonian and early Campanian, ca. 91 - 79 Ma. Various geochemical data, especially element variations normalized to N-MORB, show two types of volcanic arc basalts (VAB): (1) Calc-alkaline to high-K calc-alkaline VAB have increased Nb and Zr values, (2) more tholeiitic VABs are depleted in Nb, Zr, Ti, V. The volcaniclastics successions were deposited in an arc setting triggered by different stages of subduction of the Neotethys Ocean to the south and contemporaneous spreading in the Western Black Sea Basin to the north. An extensional regime caused formation of small but deeper-water sedimentary basins along the southern shore of the Black Sea where volcaniclastic complexes interfingered within short lateral distances with pelagic and mass-flow deposits.

Receiver function images of the distorted Philippine Sea slab contact with the continental crust: Implications for generation of the 1891 Nobi earthquake (Mj 8.0)

The 28 October 1891 Nobi earthquake was one of the largest intraplate earthquakes in Japan, with an estimated magnitude of 8.0 determined by the Japan Meteorological Agency. It occurred in central Japan on the Eurasian Plate, beneath which the young Philippine Sea Plate is subducting. The geometry of this plate is not smooth; rather, beneath western Japan it appears distorted over a relatively short lateral distance. Beneath the Kinki region of central Japan, the subduction angle is approximately horizontal, and the Nobi earthquake occurred just above the horizontal section of the Philippine Sea slab. Temporary seismic stations were deployed in this area to investigate local seismic structure and its possible relationship to the cause of the earthquake. Crustal structure was investigated using receiver function analysis with a spatially dense temporary seismic network. A clear image of the subducted Philippine Sea slab was resolved, with ridge-like structures beneath the epicentral area of the Nobi earthquake. The ridge-like structure is in contact with the continental crust, and the fault plane of the Nobi earthquake is located at the edge of one such structure; i.e., in the contact area. The unique structure of the area is inferred to cause stress concentration and strain accumulation on local faults, which resulted in the large size of the Nobi earthquake.

Redox preconditioning deep cratonic lithosphere for kimberlite genesis \u2013 evidence from the central Slave Craton

We present the first oxygen fugacity (fO2) profile through the cratonic lithospheric mantle under the Panda kimberlite (Ekati Diamond Mine) in the Lac de Gras kimberlite field, central Slave Craton, northern Canada. Combining this data with new and existing data from garnet peridotite xenoliths from an almost coeval kimberlite (A154-N) at the nearby Diavik Diamond Mine demonstrates that the oxygen fugacity of the Slave cratonic mantle varies by several orders of magnitude as a function of depth and over short lateral distances. The lower part of the diamond-bearing Slave lithosphere (>120–130 km deep) has been oxidized by up to 4 log units in fO2, and this is clearly linked to metasomatic enrichment. Such coupled enrichment and oxidation was likely caused by infiltrating carbonate-bearing, hydrous, silicate melts in the presence of diamond, a process proposed to be critical for “pre-conditioning” deep lithospheric mantle and rendering it suitable for later generation of kimberlites and other SiO2-undersaturated magmas.

Seismic tomography of the Colorado Rocky Mountains upper mantle from CREST: Lithosphere–asthenosphere interactions and mantle support of topography

The CREST experiment (Colorado Rocky Mountains Experiment and Seismic Transects) integrated the EarthScope USArray Transportable Array with portable and permanent stations to provide detailed seismic imaging of crust and mantle properties beneath the highest topography region of the Rocky Mountains. Inverting approximately 14,600 P- and 3600 S-wave arrival times recorded at 160 stations for upper mantle Vp and Vs structure, we find that large Vp perturbations relative to AK135 of 7% and Vs variations of 8% take place over very short (approaching tens of kilometers) lateral distances. Highest heterogeneity is observed in the upper 300 km of the mantle, but well resolved low velocity features extend to the top of the transition zone in portions of these images. The previously noted low velocity upper mantle Aspen Anomaly is resolved into multiple features. The lowest Vp and Vs velocities in the region are found beneath the San Juan Mountains, which is clearly distinguished from other low velocity features of the northern Rio Grande Rift, Taos/Latir region, Aspen region, and below the Never Summer Mountains. We suggest that the San Juan anomaly, and a similar feature below the Taos/Latir region of northern New Mexico, are related to delamination and remnant heat (and melt) beneath these sites of extraordinarily voluminous middle-Cenozoic volcanism. We interpret a northeast–southwest grain in velocity structure that parallels the Colorado Mineral belt to depths near 150 km as being reflective of control by uppermost mantle Proterozoic accretionary lithospheric architecture. Further to the north and west, the Wyoming province and northern Colorado Plateau show high velocity features indicative of thick (∼150 km) preserved Archean and Proterozoic lithosphere, respectively. Overall, we interpret the highly heterogeneous uppermost mantle velocity structure beneath the southern Rocky Mountains as reflecting interfingered chemical Proterozoic lithosphere that has been, is currently being, replaced and modified by upwelling asthenosphere. Low velocity features resolved here indicate that this process may be sourced as deeply as the top of the mantle transition zone at 410 km. One driving mechanism for this is upper mantle interaction between upwelling hydration-induced partial melt and destabilized downwelling lithosphere in the deeper upper mantle. Tomographic imaging of mantle seismic velocity and crustal thickness results and modeling from the CREST experiment indicate that the highest elevations of the Colorado Rocky Mountains are substantially supported by the mantle, and strong correlations between low velocity mantle and thin crust/high topography are noted across the region. This, along with rich upper mantle seismic heterogeneity, suggests that mantle buoyancy and dynamics are central to present day topographic support and recent geomorphic evolution of the region.

Ultrasonic Synthetic Aperture Focusing Using the Root-Mean-Square Velocity

The synthetic aperture focusing technique (SAFT) can improve the image resolution of ultrasonic testing (UT) by applying a delay-and-sum (DAS) process to the received echoes. The drawback of using current SAFT to test a multi-layer medium is that the computation of delays is complicated and time-consuming. In this study, we propose a fast and simple method to calculate the approximated delays for using in SAFT to image flaws in multi-layer media without losing the resolution of the SAFT image. The approximated delays can be easily and quickly calculated by a hyperbolic time-distance relationship which is a function of the root-mean-square velocity (V rms ) of layers under circumstances of short lateral distance and horizontal layers. The error of approximated delays is very small when incorporating the amplitudes radiated from the transducer into the processing of SAFT. Two extreme experiments of immersion testing were carried out to test and evaluate the proposed method. The experimental results show that the proposed method is feasible. Thus, the approximated delays calculated by the V rms for using in SAFT to enhance the resolution of the scan image for testing the flaws in multi-layer medium are recommended.

Aeromagnetics assists Oil & Gas exploration in the Bedout Sub-basin, offshore Canning Basin

Finder Exploration and its joint venturer Carnarvon Petroleum commissioned Fugro Airborne Surveys to acquire and interpret 21,622 line kilometres of airborne magnetic data over Petroleum Exploration Permits WA-436-P and WA-438-P in the Bedout Sub-basin, offshore Canning Basin within the Northwest Shelf, Western Australia. These data were acquired to augment the existing sparse 2D seismic data in the study area. The newly acquired aeromagnetic data were integrated with selected seismic profiles, regional structural and geological data; tied to the well data to provide an interpretation of the tectono-structural evolution of the Bedout Sub-basin, a depth to magnetic basement and total sediment thickness estimation in the study area. The interpretation revealed a complex basin architecture reflecting multiple structural and depositional features which contributed to the development of the Bedout Sub-basin. The estimated depths to magnetic basement are consistent with previous assessments of sediment thickness derived from the interpretation of the existing 2D seismic dataset, with the exception of previously unrecognised thick sedimentary deposits interpreted in the eastern part of the study area. The interpretation of the aeromagnetic data shows variations in sediment thicknesses of up to 5kms over relatively short lateral distances in the vicinity of the Bedout High in the northern part of the study area. A significant shallowing of the basement towards the Lambert Shelf in the south is also identified. As part of the ongoing exploration effort, this new aeromagnetic data and interpretation has added to the understanding of the study area by identifying a possible additional hydrocarbon source kitchen and improving the tectono-structural understanding of the Bedout Sub-basin.

The initiation of subduction by crustal extension at a continental margin

SUMMARY We investigate how subduction may be triggered by continental crust extension at a continental margin. The large topography contrast between continental and oceanic domains drives the spreading of continental crust over oceanic basement. Subduction requires the oceanic plate to get submerged in mantle, so that negative buoyancy forces may take over and drive further descent. This is promoted by two mechanisms. Loading by continental crust bends the oceanic plate downwards. Extension in the continental domain induces crustal thinning, which acts to raise mantle above the oceanic plate. In this model, the width of the continental region undergoing extension is an important control parameter. The main physical controls are illustrated by laboratory experiments and simple theory for elastic flexure coupled to viscous crustal spreading. Three governing dimensionless parameters are identified. One involves the poorly constrained oceanic plate buoyancy. We find that the oceanic plate can be thrust to depths larger than 40 km even if it is buoyant, enabling metamorphic reactions and density increase in the oceanic crust. Another parameter is the ratio between the width of the continental extension region and the flexural parameter for the oceanic plate. Initiating subduction is easier if the continent thins over a short lateral distance or if the oceanic plate is strong. The third important parameter is the ratio of oceanic plate thickness to initial continental crust thickness, such that a weak plate and a thick crust do not favour subduction. Thus, the change from a passive to an active margin depends on the local characteristics of the continental crust and is not determined solely by the age and properties of the oceanic lithosphere. It is shown that the spreading of continental crust induces uplift of the margin as the adjacent seafloor subsides. Evidence for the emplacement of continental crust over oceanic basement at passive margins is reviewed.

Reservoir characterization of a CO 2 storage aquifer: The Upper Triassic Stuttgart Formation in the Northeast German Basin

Ketzin, in the Northeast German Basin (NEGB), is the site for pilot injection of CO 2 (CO 2SINK project) into a saline aquifer (the Upper Triassic Stuttgart Formation) situated at a depth of about 630–700 m. This paper reports the baseline characterization of the reservoir formation based on new core material and well-logs obtained from one injection well and two observations wells, drilled at a distance from 50 m to 100 m from each other. The reservoir is lithologically heterogeneous and made up by fluvial sandstones and siltstones interbedded with mudstones showing remarkable differences in porosity. The thickest sandstone units are associated with channel sandstone, whose thickness varies over short lateral distances. In-depth petrographic, mineralogical, mineral-chemical, and whole-rock geochemical analysis were performed focusing on the sandstone intervals, which display the best reservoir properties for CO 2 injection. The dominantly fine-grained and well to moderately-well sorted, immature sandstones classify as feldspathic litharenites and lithic arkoses. Quartz (22–43 wt.%), plagioclase (19–32 wt.%), and K-feldspar (5–13 wt.%) predominate mineralogically. Muscovite plus illite and mixed-layer minerals are omnipresent (4–13 wt.%). Quartz, feldspar, as well as meta-sedimentary and volcanic rock fragments comprise the most abundant detrital components, which often are rimmed by thin, early diagenetic coatings of ferric oxides, and locally of clay minerals. Feldspar grains may be unaltered and optically clear, partially to completely dissolved, partially altered to sheet silicates (mainly illite), or albitized. Analcime and anhydrite constitute the most widespread, often spatially associated pore-filling cement minerals. Authigenic dolomite, barite, and coelestine is minor. The percentage of cements ranges in total from about 5 vol.% to 32 vol.%. Except of samples intensely cemented by anhydrite and analcime, total porosities of the sandstones range from 13% to 26%. The fraction of intergranular porosity varies between 12% and 21%. About 1–5% porosity has been generated by dissolution of detrital plagioclase, K-feldspar, and volcanic rock fragments. The comparatively large modal abundance of feldspars, micas, chlorite, clay minerals, Fe–Ti-oxides, and analcime account for the richness in Ti, Al, Fe, Mg, Na, and K, and the paucity in Si, of the Stuttgart sandstones relative to mature sandstones. Altogether, these sandstones are comparatively rich in minerals that may potentially react with the injected CO 2.

Fast Integral Equation Solution Techniques for Planar-3D Structures in Multilayered Media

In this contribution, a hybrid space/spectral domain integral equation approach is presented for the characterization of quasi-3D structures in multilayered media. The verti- cal conductors for the quasi-3D components like vias, through holes, airbridges, flnite dielectric regions etc. can cross an arbitrary number of dielectric layers with arbitrary vertical discretiza- tion. The electrodynamic behavior of the vertical currents is incorporated by extended spectral domain Green's functions derived by analytical integrations over the vertical direction and by a summation over the Cartesian wavenumbers which must be computed only once and stored in a database. For short lateral distances, the couplings are computed with a subtraction tech- nique based on asymptotic representations of the extended Green's functions, whereas for larger distances and for group coupling computations in context with fast matrix vector product evalu- ations, adaptive integration path deformations with extended Laguerre quadrature methods are applied. For the solution of the linear systems of equations, a GMRES solver was implemented together with a diakoptic preconditioner based on the group decomposition of larger structures, combined with a reversed Cuthill McKee reordering applied to the submatrix pattern of the system matrix. With all these techniques, the analysis of complex quasi-3D structures can be carried out with the same performance than pure planar microstrip and/or slotline structures.

Numerical Simulation of Oil Recovery After Cross-Linked Polymer Flooding

Abstract Cross-linked polymer flooding can increase oil recovery 10 to 20% over conventional waterflooding, while using a lower concentration of polymer than conventional polymer flooding. Based on production data from a developed oil field, the average incremental oil recovery by polymer flooding is only 10%, indicating that much of the oil is bypassed. We need to know how this bypassed oil is distributed to design an optimal development strategy. Numerical simulations have been performed to study the mechanisms of polymer flooding. For the coarsening downward sedimentary cycle, the simulation model was divided into five layers with average geometric permeabilities of 100 mD, 300 mD, 500 mD, 980 mD and 2,190 mD, respectively. Five spot well patterns with 180 m distance between each injector and producer has been used. The injecting well was controlled by an injection rate of 100 m3/d and shut down as the water ratio reached 98%. Cross-linked polymer injection was introduced after the water cut was as high as 90% and stopped as the water cut reached 98%. It was found that most of the residual oil after polymer flooding existed in small areas far away from the diagonal line for heterogeneous reservoirs, and in layers with low or intermediate permeabilities for cycle reservoirs. Introduction The Xiaermen Oil Field lies in Biyang County, Henan Province. It is located in the middle of a large northeast fault edge, to the east of Biyang Sag, Nanxiang Basin (Figure 1). The structure of this field is a brachy-anticline in an east-west direction complicated by four major faults and many minor faults adjacent to the main oil-bearing area. Among these faults, a series of small faults to the east were originated from the big fault (Figure 1). The maximum height of the trap is 275 m. The Xiaermen sand was deposited by deltaic fans(1). Considerable variation in sand thickness occurring over short lateral distances is characteristic of this particular deposit and thick layers with high permeability are patchy and isolated. The sediment underlying the project area is finely grained and relatively clean quartz sand. The average porosity is about 24% and the mean geometric permeability is 2 µm2. The porosity and permeability is generally high, but fairly heterogeneous. The petroleum industry has recognized the problem of inefficient oil recovery by conventional waterflooding. Therefore, extensive research has been conducted using new techniques of enhanced oil recovery (EOR) of the reservoirs(2). Polymer flooding is a significant method used for this purpose, in which the mobility of the displacing phase can be reduced effectively by the addition of small amounts of water-soluble polymers. Polymer flooding will enhance oil recovery by increasing the water phase viscosity, improving the water/oil mobility ratio and improving sweep efficiency. Polymer flooding may have beneficial effects in relatively homogeneous oil reservoirs. However, the improvements might be more modest in a heterogeneous reservoir. By adding a cross-linking agent into the polymer and then forming a 3D reticulate texture through the intermolecular cross-linking, a cross-linked polymer can increase the viscosity of the injected fluid.

Spatial Variability of Soil‐Gas Concentrations near and beneath a Building Overlying Shallow Petroleum Hydrocarbon–Impacted Soils

AbstractData requirements for assessing the significance of the soil vapor intrusion pathway are evolving, and the collection and interpretation of subslab and near‐slab soil‐gas samples are under discussion. The potential for different assessment paradigms for aerobically biodegradable and recalcitrant chemicals is also frequently debated. In this work, the soil‐gas distribution beneath and around a slab‐on‐grade building overlying shallow (0.5 to >1.5 m below ground surface) petroleum hydrocarbon–impacted coarse alluvial soils was studied. The study spanned about 12 months, including the sampling of soil‐gas hydrocarbon and oxygen concentrations, subslab soil vs. building pressure differentials and included weather conditions. Three‐dimensional soil‐gas concentration “snapshots” using samples from 79 soil‐gas sampling points are presented here. Significant spatial variability was observed with hydrocarbon and oxygen concentrations ranging from about <0.01 to 200 mg/L and 0 to 21% v/v, respectively. The presence of oxygen and the depth to petroleum‐impacted soils appeared to be the dominant factors in controlling the soil‐gas distribution; the depletion of hydrocarbons over short lateral and vertical distances (<2 m) was observed in the well‐oxygenated regions. Composition data suggest preferential biodegradation of lighter compounds at some points, as reflected in the ratio of the masses of chemicals eluting on the gas chromatography between methane and pentane (C1 and C5) and all others after pentane (>C5).

Can Analysis of Historic Lagg Forms Be of Use in the Restoration of Highly Altered Raised Bogs? Examples from Burns Bog, British Columbia

Natural bogs are generally surrounded by a zone of hydrologic, hydrochemical, and ecological gradients called a lagg. In laggs, large changes over short lateral distances result in distinctive ecological gradients and vegetation patterns. Part of the restoration planning challenge for Burns Bog involves recreating such water and chemistry gradients to establish and maintain conditions for appropriate plant and animal communities that reflect natural transitions from nutrient-poor bog to adjacent mineral-soil-influenced wetlands. We present a conceptual model inferred from historic air photos and vegetation maps from the margins of Burns Bog and theorize how particular vegetation represents the hydrological and hydrochemical gradients of the past that existed in transition to surrounding landscapes. Understanding lagg ecosystems and how they function is important not only to restoring the ecological integrity of Burns Bog, but also to developing a conceptual model useful for predicting and interpreting these gradients in other peatlands.