Continuous Depth Profiles Research Articles

Episodic marine anoxia, primary production, and weathering controls on carbon‑sulfur cycling in the Early Cambrian Yangtze Block

The Early Cambrian Period has received significant attention for decades owing to its geological records of unprecedented skeletal fossils, suggesting a major bio-event known as “the Cambrian Explosion.” Notwithstanding, related primary production and marine redox variation with respect to evolution of biota remain elusive. These factors are intimately linked to marine carbon‑sulfur cycling, promoting an extensive use of related isotopes (e.g., δ13C and δ34S) as paleoenvironmental proxies. Nevertheless, bulk-rock δ34S and δ13C may reflect multigenerational 34S/32S and 13C/12C isotopic fractionations. Herein, we analyzed drill cores from continuous depth profiles in the recently discovered Qingchuan-Ziyang-Yibin intrashelf basin for δ34S of sedimentary sulfate (δ34Ssulf), δ13C of carbonates (δ13Ccarb), and bulk-rock elements. We find that highly positive (+23.60 ‰ to +29.90 ‰) and negative (as low as −12 ‰) δ34Ssulf V-CDT are associated with samples exhibiting low and high detrital inputs, respectively. In contrast, total sulfur and δ13Ccarb V-PDB show no relationship with terrigenous materials. Enrichment factors of molybdenum (MoEF) and uranium (UEF), biogenic contents of nickel (Nibio) and copper (Cubio), as well as total organic carbon (TOC), are all widely distributed among the samples. Integration of these findings with existing data from shallow to deep marine environments in the Yangtze Block, supports the following conclusions: (1) Five episodes of widespread marine anoxia coincide with extensive primary production. (2) Inputs of terrigenous materials promote 32S-enriched sulfate, which adds to subsequent biochemical fractionations, resulting in generally complex pathways for δ34S of pyrite. (3) Terrigenous nutrients were critical to extensive marine primary production.

Indirect analysis of unconventional shale hydrocarbon resources in the Recôncavo Basin, Brazil. A case study

The Recôncavo basin is a mature basin with great potential for extracting hydrocarbons from conventional and unconventional reserves. It is inserted in an extensive taphrogenic basin, that is the Recôncavo-Tucano-Jatobá aborted rift in the Brazilian northeast region, where the beginning occurred with the rupture of the western Gondwana paleocontinent. Stratigraphically, it presents six sedimentary sequences related to the pre-rift and rift stages. The study area is located in the structural low named Camaçari Low, in the Southern compartment of the basin, what it is the deepest depocenter, with a preserved sedimentary section of 6900 m, it is in addition to being main oil and gas generation kitchen. So to evaluate the potential abundance of a rock formation, in the case of both conventional and unconventional reserves, it is of key importance to quantify the total organic content (TOC), hydrogen index (HI), vitrinite reflectance (Ro), maximum hydrocarbon generation temperature (Tmax) and level of organic maturation (LOM). These parameters can be estimated by direct methods (in the laboratory) using geochemical analysis or by indirect methods using well log data. Direct analysis provides point estimates, while indirect analysis provides a continuous depth profile of them. For this study, data from geochemical analysis and logging of well 1 CGL 1D BA from the Recôncavo basin, in the Camaçari Low, to estimate the TOC profiles by means of simple linear regression, LOM by the Passey method utilizing the ΔDT, Ro, HI and Tmax, for depths greater than 1000 m. The linear regression resulted in a moderately positive correlation of the TOC estimate. Replacing the ΔLogR method of Passey for ΔDT method of Bowman proved to be a rapid and easily determined technique. The estimates of the vitrinite reflectance and hydrogen index based on the estimated LOM values were compatible with the measured values, as was the estimate of maximum hydrocarbon generation temperature based on the vitrinite reflectance. The organic matter was characterized as type I and II kerogen.

Gravity inversion for heterogeneous sedimentary basin with b-spline polynomial approximation using differential evolution algorithm

We have developed a MATLAB-based inversion program, b-spline polynomial approximation using the differential evolution algorithm (SPODEA), to recover the concealed basement geometry under heterogeneous sedimentary basins. Earlier inversion techniques used the discretized subsurface interface topography into a grid of juxtaposed elementary prisms to estimate the basement depth of a basin. Such discretization leads to the failure of the depth profile continuity and requires a higher number of inversion parameters for achieving the desired accuracy. The novel approach of SPODEA overcomes such limitations of earlier inversion techniques. SPODEA is based on the segment-wise b-spline optimization technique to estimate the basement depth by using high-order polynomials. Moreover, it can achieve an optimal misfit with minimal parametric information, which reduces the computational expense. Our inversion approach uses the differential evolution algorithm, which provides real parametric optimization and uses b-splines for accurate estimation of continuous depth profiles. The efficiency of our algorithm was determined with two complex synthetic sedimentary basin models comprised of constant and depth-varying density distributions. Furthermore, the uncertainty analysis of our inversion technique is evaluated by incorporating white Gaussian noise into the synthetic models. Finally, the utility of SPODEA is evaluated by inverting gravity anomalies for two different real sedimentary basins. It produces geologically reasonable outcomes that are in close agreement with basement structures from previously reported results.

Continuous borehole optical televiewing reveals variable englacial debris concentrations at Khumbu Glacier, Nepal

Surface melting of High Mountain Asian debris-covered glaciers shapes the seasonal water supply to millions of people. This melt is strongly influenced by the spatially variable thickness of the supraglacial debris layer, which is itself partially controlled by englacial debris concentration and melt-out. Here, we present measurements of deep englacial debris concentrations from debris-covered Khumbu Glacier, Nepal, based on four borehole optical televiewer logs, each up to 150 m long. The mean borehole englacial debris content is ≤ 0.7% by volume in the glacier’s mid-to-upper ablation area, and increases to 6.4% by volume near the terminus. These concentrations are higher than those reported for other valley glaciers, although those measurements relate to discrete samples while our approach yields a continuous depth profile. The vertical distribution of englacial debris increases with depth, but is also highly variable, which will complicate predictions of future rates of surface melt and debris exhumation at such glaciers.

Strength Profile of the Inner Nankai Accretionary Prism at IODP Site C0002

AbstractThe strength of accretionary prisms is important for understanding their formation and the generation of earthquakes along the underlying plate boundary faults. We establish a continuous depth profile of rock strength and possible ranges of the minimum and maximum horizontal stresses (Shmin and SHmax) based on indentation tests on cuttings samples at the Integrated Ocean Drilling Program (IODP) Site C0002 in the Nankai accretionary prism. The rock strength (i.e., differential stress) increases with depth from 5.1 and 11.0 MPa at 975 meters below the seafloor (mbsf) to 22.8 and 59.6 MPa at 3005 mbsf in normal and reverse faulting regimes, respectively. The minimum value of Shmin and the maximum value of SHmax range from 33.2 and 49.4 MPa at 975 mbsf to 57.1 and 139.6 MPa at 3005 mbsf, respectively. Our estimated strength, in combination with Coulomb wedge model, may improve understanding of the evolution of accretionary prisms.

Joint analysis of P-wave velocity and resistivity for morphology identification and quantification of gas hydrate

Abstract A knowledge of hydrate morphology is essential for assessing its resource potential, understanding its formation, and determining optimum strategies for exploitation. Previous studies have suggested two general morphologies of gas hydrates distributions in sediment settings: pore- and fracture-filling. However, because of a lack of effective morphology identification methods, it is currently difficult to quantitatively model gas hydrates. Here we propose a joint analysis of P-wave velocity and resistivity to identify hydrate morphology and estimate hydrate saturation in a continuous depth profile. First, we perform numerical modeling to investigate the effects of hydrate morphology on the P-wave velocity and resistivity properties of gas hydrate-bearing sediments (GHBS). The results demonstrate that, in the case of identical hydrate concentration, fracture-filling GHBS typically exhibit higher resistivity but lower P-wave velocity than those of pore-filling GHBS. Consequently, the cross plot between these two properties are strikingly different for the two types of GHBS. By comparing the cross plot of field measurements to the theoretical cross plot, we hypothesize that hydrate morphology can be identified and hydrate saturations estimated. We test and verify the hypothesis using the velocity and resistivity log data at different sites in China's second gas hydrate expedition in 2013 in the South China Sea, where the two morphologies were confirmed via core samples. Cross plots of field measurements agree closely with the theoretical results, and gas hydrate morphologies are successfully identified. The estimated hydrate saturations are comparable to measurements of pore-water freshening in the majority of cases.

Marine Tests of a Digital Holographic Module Using a Measuring Technological Platform

The paper presents the results of marine testing of a digital holographic module for recording and measuring zooplankton. The tests based on the use of measuring-technological platform earlier developed at IO RAS were performed in summer 2016 in the Kara Sea during cruise 66 of the R/V Akademik Mstislav Keldysh. The upper water layer was sensed down to the 240 m horizon, which resulted in successful recording of about 100 Gb of digital holographic frames with reference to continuous depth profiles of electric conductivity in situ. Tests conducted under summer Arctic sea conditions confirmed the validity of the technical solutions. Based on the results, a list of upgrades to the holographic module was compiled for successful implementation of the latter in ocean research.

Simple and fast calculation algorithm for computer-generated hologram based on integral imaging using look-up table.

We proposed a simple and fast algorithm for computer-generated hologram (CGH) based on pinhole-type II using a look-up table. The method consists of two steps: in the first step, the unity amplitude diffraction pattern of the center pinhole on hologram plane is pre-calculated and stored as many sub-regions. Secondly, diffraction patterns for other pinholes are obtained by simply shifting and tiling the pre-calculated sub-regions, and the final CGH is obtained by adding them all together. The calculation time is short because only addition and multiplication of the stored diffraction pattern are required. In addition, the required memory space is small since only one diffraction pattern is stored. Numerical simulation and reconstruction are performed on both plane object and object with continuous depth profile to verify the proposed method. Result shows that the proposed method can easily achieve real-time hologram generation with several CPU threads running simultaneously.

Continuous depth profile of the rock strength in the Nankai accretionary prism based on drilling performance parameters

A new method for evaluating the in situ rock strength beneath the seafloor is proposed and applied to the Nankai Trough accretionary prism. The depth-continuous in situ rock strength is a critical parameter for numerous studies in earth science, particularly for seismology and tectonics at plate convergence zones; yet, measurements are limited owing to a lack of drilled cores. Here, we propose a new indicator of strength, the equivalent strength (EST), which is determined only by drilling performance parameters such as drill string rotational torque, bit depth, and string rotational speed. A continuous depth profile of EST was drawn from 0 to 3000 m below the seafloor (mbsf) across the forearc basin and accretionary prism in the Nankai Trough. The EST did not show a significant increase around the forearc basin–accretionary prism boundary, but it did show a clear increase within the prism, ca. below 1500 mbsf. This result may indicate that even the shallow accretionary prism has been strengthened by horizontal compression derived from plate subduction. The EST is a potential parameter to continuously evaluate the in situ rock strength during drilling, and its accuracy of the absolute value can be improved by combining with laboratory drilling experiments.

Thermophysical continuous profiles and their discretization

Most of the time the surface of materials presents profiles of physical properties that are variable along the depth. The heat diffusion equation of current thermophysical profiles rarely accepts analytical solutions that can be introduced in a rapid minimization scheme. A thermal Riccati equation is defined in case of any continuous profiles, the solutions of which are shown to be the limit of the exact solutions for simple staircase multilayer modellings when the layers are taken thinner and thinner. Thanks to the use of iterative methods based on the thermal wave or the quadrupole descriptions, it is shown that the choice of the multilayer approach to describe continuous depth profiles of materials leads to exact solutions of the problem.

Mapping the thickness of sediments in the Ljubljana Moor basin (Slovenia) using microtremors

The Ljubljana Moor basin is characterized by moderate bedrock topography and thicknesses of Quaternary lacustrine and fluvial sediments ranging from 0 to 200 m. More than 65 boreholes which reached the bedrock were drilled in the area, but their distribution in the basin is very uneven and some data from the boreholes uncertain. There are also no data on S-velocity distribution within the basin, but seismic refraction measurements pointed out a rather uniform increase of P-velocity with depth, great impedance contrast with the bedrock and relatively small lateral velocity variations. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied as a complementary tool to seismic refraction survey to map the thickness of sediments. First, microtremors were measured at the locations of boreholes which reached the bedrock and the resonance frequencies determined. The inverse power relationship between the resonance frequency and the thickness of sediments was then determined from 53 data pairs. The quality of the correlation is moderate due to possible heterogeneities in sediments and possible 3D effects in some minor areas, but the obtained parameters correspond well to the values obtained in six other European basins. Secondly, a 16 km-long discontinuous seismic refraction profile was measured across the whole basin, leaving uncovered some larger segments where active seismic measurements were not possible. Microtremors were then measured at 64 locations along the same profile, using 250 m point spacing, without leaving any gaps. The frequency–thickness relationship was used to invert resonance frequencies to depths. These were first validated using the results of the seismic refraction survey, which showed good agreement, and finally used for interpolation in the segments of missing refraction data to obtain a continuous depth profile of the bedrock. The study has shown that the microtremor method can be used as a complementary tool for mapping the thickness of unconsolidated sediments also in areas characterized by moderate bedrock topography. As the input data are always to some extent uncertain, it is important to have a sufficiently large number of borehole data to establish a frequency–thickness relationship, as well as some additional independent geophysical information for its validation.

Efficient calculation method for glancing angle x‐ray techniques

AbstractGeneral depth profiling involves all kind of concentration profiles. The most complex samples present a wide variation of elemental composition with depth. In those cases, calculations of x‐ray propagation at grazing angles are done by representing the sample as a stratified structure in order to obtain an analytical solution of the problem. The density of each layer is an average of the real density inside the layer, and a large number of surface layers may be necessary for a correct representation of the sample. This involves a large number of mathematical operations and therefore an efficient calculation method of x‐ray propagation at glancing angles is required. In this paper, a mathematical algorithm for the calculation of x‐ray propagation at grazing angles is presented. It applies a new formalism introduced recently in the field. This formalism uses a matrix approach to take advantage of well‐known mathematical results, such as Hessenberg's matrix properties. The model allows one to reduce the number of mathematical operations for glancing angle x‐ray techniques. The method was used to study surface oxidation of copper and roughness of a glass surface by the grazing exit XRF technique. Data analysis in these samples shows the advantage of the present mathematical algorithm since both samples present a continuous depth profile. Copyright © 2002 John Wiley & Sons, Ltd.

Micro-scale geotechnical variability in continental slope and abyssal sediments influenced by the oxygen minimum zone in the Arabian Sea

We describe a new micro-scale method of measuring the penetration resistance of the surficial layers of slope and abyssal plain sediments within and below the OMZ on the Oman continental slope. The micro-scale load resistance penetrometer (MLRP) continuously measures the penetration resistance ( q) of a cylindrical probe driven at constant velocity into cores of sediment recovered by sub-coring box core samples. Measurements are recorded at 0.8 mm depth intervals into the sediment by an automated data acquisition system. These provide continuous depth profiles of penetration resistance ( q) and its variability ( qr) in surficial sediments (0–100 mm). The results represent the first published application of this technique to slope and abyssal plain sediments. The q data divide the stations into shallow OMZ (SOMZ) stations (391–854 m), deep OMZ (DOMZ) stations (987–1285 m), and abyssal non-OMZ (ANOMZ) stations (3392–3396 m). One station (688 m) was anomalous. Penetration resistance ( q) was positively related to shear strength and inversely related to water content, but not to bioturbation measured as burrow numbers. Relaxation and pull-out data were obtained from three stations. Three patterns of qr were observed, consisting of well-confined data, data containing large negative and positive spikes, and data showing a progressive down-core increase in spikes. Four additional measures of q variability were defined, which show statistically significant relationships with burrow numbers. An increase in bioturbation, estimated by burrow numbers, is associated with a decrease in micro-scale variability in q. This is related to the activity of burrowing macrofauna. Our results are discussed in the context of biogeotechnical modifications of sedimentary environments.

Depth profiling of inhomogeneous layers by ellipsometry

The inverse problem of ellipsometry for inhomogeneous layers is formulated in terms of a nonlinear operator equation. The Newton-Gauss method is implemented to develop an iterative numerical procedure for its solution. The algorithm is capable to retrieve continuous depth profiles of optical and some structural parameters of the layer from experimental ellipsometric data without prior knowledge about the concrete mathematical function describing their depth variation. The linear inverse theory is employed to provide an estimation of the error variance and the reliability of the calculated results. A particular case of damage depth profile determination of 40 keV Ge + implanted silicon is considered. The effectiveness and the reliability of the method calculations are demonstrated using both simulated and experimental spectroellipsometric data.

Effects of intravenous acetazolamide on retinal pH in the cat

Double-barreled H +-selective microelectrodes were used to study the effect of intravenous acetazolamide on intraretinal pH in the cat. Acetazolamide (11·4–27·8 mg kg −1 intravenously) caused a rapid acidification of the subretinal space. This change in pH originated in the most distal portion of the subretinal space and could not be attributed to a change in pH or PCO 2 of the arterial blood. Slow light-evoked alkalinizations in distal retina, attributable to a decrease in rod photoreceptor energy metabolism, were relatively unaltered by acetazolamide. This result indicated that acetazolamide had not crossed the blood-retinal barrier in sufficient amounts to change this response. In time, following intravenous perfusion of acetazolamide, continuous depth profiles of intraretinal pH showed an acidification of the entire retina and the vitreous also became more acidic. These results indicate that the rapid or primary effect of acetazolamide is an acidification of the distal portion of the subretinal space, which is thought to originate in a change in the transport of H + or HCO 3 − by the retinal pigment epithelium. This is followed by an acidification of the entire retina and vitreous, presumably due to diffusion of acid from the distal retina, although there could be additional causes.

Performance and analysis of cone pressuremeter tests in sands

This Paper presents the results of tests performed in sand with a prototype cone pressuremeter. Values of shear modulus and friction angle of the sand are derived from the data using cavity expansion/contraction theory. These values are compared with those obtained from seismic cone penetration tests and self boring pressuremeter tests. The Paper aimsto stimulate the development of methods to evaluate and apply data obtained from testsin sands with this operationally convenient in situ test. The values of shear modulus obtained with the cone pressuremeter are compatible with those obtained from the other tests. The availability of a cone resistance profile provided by the cone pressuremeter, at the same location as the pressuremeter derived shear moduli, facilitates the production of a continuous depth profile of shear modulus based on a reliable site specific correla- tion. Available cavity expansion theory produces unrealistic values of peak friction and dilation angle from cone pressuremeter data. Available cavity contraction theory produces unrealistic values of friction and dilation angle from both cone pressuremeter and self boringpressuremeter data. Creep deformations contribute to the difficulties associated with theapplications of cavity expansion and contraction theories. However, with appropriate tes procedures the creep deformation can be identified. A standard test procedure is proposedto facilitate comparisons of data obtained from further tests in different sands. Such comparisons are needed to advance understanding of cone pressuremeter test data. L'article présente les résultats d'essais effectués dans du sable à l'aide d'un pressiométre à c^ane prototype. Des valeurs du module de cisaillement et de I'angle de frottement du sable sont déduites de ces données par l'emploi de la tMorie de l'expansion–contraction des cavités. Ces valeurs sont comparées avec celles obtenues à partir d6essais sismiques de péneration au cône et d'essais au pressiométre à autoforeur. Le but est de stimuler le développement de méthodes pour Evaluation et I'application des données obtenues à partir d'essais effectués dans le sable à I'aide de cet essai in-situ trés pratique. On en tire les conclusions suivantes: les valeurs du module de cisaillement obtenues par moyen du pressiométre à cône sontcompatibles avec celles obtenues à partir des autres essais; la production d'un profile continu de profondeur du module de cisaillement basée sur une corrélation spécifique et fiable est facilitée par la disponibiliti d'unprofil de réisstance au cône fourni par le pressiométre à cône au meme emplacement que les modules de cisaillement dérivés du pressiométre; la théorie actuelle de I'expansion des cavités donne des valeurs peu rélles du frottement et de l'angle de dilatation 1 partier desdonées du pressiométre à cône; la théorie actuelle de là contraction des cavités donne des valeurs peu réelleses du frottement et de I'angle de dilatation à partir des données du pressiométre à cône et du pressiométre à autoforeur; les défor-mations par fluage augmentent les difflcultés lorsque les théories de l'expansion et de la contraction des cavités sont employées, bien qu'il soit possible de définir la déformation par fluage à I'aide de procédures d'essais appropriées. L'article propose une procédure normale d'essai pour faciliter la comparaison des données obtenues à partir d'autres essais effectués dans des sables différents. De telles comparaisons sont n&essaires pour améiorer la comprithension des données des essais de pressiométre à cône.

The optical properties of SiOxformed by high-dose Si ion implantation into fused silica

Abstract SiOx layers with continuous depth profiles of the oxygen concentration are formed about 2 μ below the surface by 2 MeV Si ion implantation into fused silica. The depth distribution of the changed optical properties is revealed by high-resolution reflection and transmission profiles measured across the beveled surface of the irradiated samples. The underlying depth profiles of the refractive index and of the extinction coefficient are evaluated from reflection and transmission measurements by a method which is based on exact formulas for the light propagation within continuous depth profiles of the complex refractive index. The resulting n and k profiles are correlated with depth profiles of the oxygen concentration which are theoretically calculated for the investigated dose range (1 × 1016 to 6 × 1017 cm−2). The optical data of SiOx for x between 2 and 1.1 are presented in the wavelength range from 365 to 1000 nm. Comparison with the effective medium model proposed by Zuther for evaporated SiOx and with experimental data of evaporated layers shows the influence of bonding defects on the optical properties of ion implanted SiOx.

Double Kelvin waves with continuous depth profiles

The possibility of long waves in a rotating ocean being trapped along a straight discontinuity in depth was demonstrated in a recent paper (Longuet-Higgins 1968). The analysis is now extended to the situation where the depth varies continuously, in a zone separating two regions of different depths. The trapping of waves in the transition zone is investigated, taking full account of the horizontal divergence of the motion.If the profile of the depth is assumed to be monotonic, then it is shown that the trapped waves always travel along the transition zone with the shallower water to their right in the northern hemisphere and to their left in the southern hemisphere. The wave period must always exceed a pendulum-day. The period is also bounded below by a quantity depending inversely on the maximum bottom gradient.By allowing the width W of the transition zone to vary, asymptotic forms for the trapped modes are obtained, both as W → 0 and as W → ∞. In the limit as W → 0 the depth becomes discontinuous, and it is shown that the lowest mode then becomes a double Kelvin wave (Longuet-Higgins 1968) propagated along the discontinuity. The periods of the higher modes, on the other hand, all tend to infinity; these modes become steady currents.Numerical calculations of the trapped modes are presented for two different laws of depth in the transition zone. It is found that as W → 0 the lowest mode is insensitive to the form of the depth profile. Higher modes depend on the details of the profile. Hence the lowest mode is the most likely to be observed in the real ocean.The dispersion relation is also investigated. It is shown that the group-velocity of all modes must change sign at some point in the range of wave-numbers, if the divergence is taken into account. When the divergence was neglected the lowest mode appeared to be exceptional, in that the group-velocity was always in the same direction. This anomaly is now removed.