Variability Of Depositional Processes Research Articles

Sedimentology and stratigraphy of the earliest deltaic shorelines of the Paleocene Lower Wilcox Group in the Gulf of Mexico

ABSTRACT Large-scale growth of shelf-to-slope margins is well documented in regional 2-D seismic data, but it is only rarely linked to sedimentological processes and detailed stratigraphic architecture at smaller scales. This study documents the building of a shelf-to-slope margin topset through successive shoreline regressions and transgressions by using data from 824 wells, 80 m of core from 4 wells, and 3750 km3 of seismic data with a focus on the complexities of shoreline behavior during repeated cross-shelf transits. Our combined data set allows understanding of the variability of depositional processes on the shelf at the scale of individual regressive–transgressive cycles (less than 105 years), and shows that the paleogeography of the Wilcox Group in the northern Gulf of Mexico is more diverse than commonly depicted. At a fourth-order scale dominant processes (river, wave, and tide) control shoreline morphology and as a result are critical to understanding sandstone body distribution on the shelf and sediment delivery to the shelf margin and deep water. The earliest deltas of the Lower Wilcox prograded southward under conditions of rising relative sea level across a 50-km-wide shelf, but the sandstone rich deltas remained 10–20 km updip from the shelf edge, and the shelf margin grew through accretion of mud-rich clinothems. The plan-view morphology and internal architecture reflect depositional systems with wave-influenced and tide-modified deltas on the inner and mid shelf, and river flood and wave-reworked hyperpycnite deposits on the outer shelf. An abundance of normal and inverse graded beds, alternation of massive to flat to undulating lamination, and low intensities of bioturbation observed in cores indicate that the shelf sandstone bodies were deposited from hyperpycnal flows. Overall the study shows that the deltaic depositional systems of the Lower Wilcox Group in Texas have a greater architectural complexity and process variability than previously interpreted. Wave-modified hyperpycnites were identified for the first time in the Wilcox and are considered to form a significant component of the muddy shelf succession. The hyperpycnite lobes are located laterally from the deltaic supply fairway in more distal positions than previous studies identified on the shelf. This along-shore redistribution of sediment suggests that it takes more time for deltas to reach the shelf edge than is inferred for many shelf-to-slope margins, and there is likely to be correspondingly less delivery of sediment to deep water.

Stratigraphic hierarchy and three‐dimensional evolution of an exhumed submarine slope channel system

AbstractSubmarine slope channel systems have complicated three‐dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub‐seismic‐scale detail, although most exhumed systems only afford two‐dimensional constraints on the depositional architecture. A rare example of an accessible fine‐grained slope channel complex set situated in a tectonically quiescent basin that offers seismic‐scale, down‐dip and across‐strike exposures is the Klein Hangklip area, Tanqua‐Karoo Basin, South Africa. This study investigates the three‐dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel‐fill and the implications this has for both sediment transport to the deep‐oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km2 area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect‐ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect‐ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic‐scale both down‐dip and across‐strike in three‐dimensions; (iv) channel‐base‐deposits exhibit spatial heterogeneity on one to hundreds of metres length‐scales, which can inhibit accurate recognition and interpretations drawn from one‐dimensional or limited two‐dimensional datasets; and (v) channel‐base‐deposit character is linked to sediment bypass magnitude and longevity, which suggests that time‐partitioning is biased towards conduit excavation and maintenance rather than the fill‐phase. The data provide insights into the stratigraphic evolution and architecture of slope channel‐fills on fine‐grained continental margins and can be utilised to improve predictions derived from lower resolution and one‐dimensional well data.

Down‐slope facies variability within deep‐water channel systems: Insights from the Upper Cretaceous Cerro Toro Formation, southern Patagonia

AbstractIn southern Patagonia, outcrops of the Upper Cretaceous Cerro Toro Formation preserve a >150 km long deep‐water axial channel belt in the Magallanes–Austral Basin, providing a unique opportunity to investigate longitudinal variations in the depositional characteristics of a deep‐water channel system. This study documents sedimentological, stratigraphical and geochronological data from the Cerro Toro Formation in the Argentine sector of the basin. New results are integrated with previous work from the Chilean basin sector to conduct a basin‐scale comparison of the timing of deposition, provenance and lithofacies proportions. The Cerro Toro channel belt includes a nearly 1000 m thick section characterized by high‐density turbidites and mass‐wasting deposits. Two ash beds from the base of the section yield U–Pb zircon ages of 90·4 ± 2 Ma and 88·0 ± 3 Ma, indicating similar initiation ages as documented in the Chilean sector. The U–Pb detrital zircon age spectra from samples in the study area reveal similar provenance trends to samples from the Chilean basin sector, with peak age populations at 310 to 260 Ma, 160 to 135 Ma and 110 to 82 Ma. The maximum depositional age of the channel belt in the Argentine sector is 87·8 ± 1·5 Ma and all new geochronology data corroborate an 86 to 80 Ma depositional age for the main Cerro Toro channel belt. Statistical analyses of 7370 beds from nearly 8000 m of new and previously published stratigraphic sections along the entire outcrop belt suggest progressive variations in the down‐system proportion of lithofacies. In the up‐slope region, lithofacies representing mass wasting processes (for example, debris‐flow and mass‐transport deposits) account for ca 29% of the stratigraphic thickness, as opposed to 5% in the down‐slope region of the channel belt, where turbidity current deposits are more prevalent. The proportion of beds >1 m thick also decreases systematically down slope, particularly for conglomeratic turbidite deposits. This work highlights that: (i) the proportion of thick beds and distribution of lithofacies are key down‐system changes in the stratigraphic fill of this deep‐water channel belt; (ii) detrital zircon trends suggest a relatively well‐mixed longitudinal depositional system; and (iii) geochronology of the main Cerro Toro outcrop belt supports but does not necessitate the model of a single, roughly age‐equivalent, channel system. This study has implications for understanding the downslope variability in depositional processes, stratigraphic architecture and reservoir quality of submarine channel systems.

Effect of electron-beam deposition process variables on the film characteristics of the CrOx films

The film characteristics and optical properties of the chromium oxide films on the glass substrates prepared by electron-beam deposition with different process variables were investigated. The process variables included are the various oxygen flow rates, the different applied substrate temperatures, and the preparation process in Ar or O2 surrounding environment with and without ion-assisted deposition. The optical constants of the deposited films are determined from the reflectance and transmittance measurements obtained using a spectrophotometer with wavelengths ranging from 350 nm to 2000 nm. The microstructures of the films were examined by the XRD, SEM, and XPS. The electrical conductivity was measured by a four-point probe instrument. The resulting microstructures of all the prepared films are amorphous and the features of the films are dense, uniform and no pillar structure is observed. The refractive index of deposited films decrease with oxygen flow rate increase within studied wavelengths and the extinction coefficients have the same trend in wavelengths of UV/Vis ranges. Increasing substrate temperature to 200 oC results in increase of both refractive index and extinction coefficient, but substrate temperatures below 150 oC show negligible effect on optical constants. The optical and electrical properties in the prepared CrOx films are illustrated by the analyzed XPS results, which decompose the enveloped curve of chromium electron energy status into the constituents of metal Cr, oxides CrO2 and Cr2O3. The relative occupied area contributed from metal Cr and area contributed from the other oxides can express the concentration ratio of free electron to covalent bonds in deposited films and the ratio is applied to explain the film characteristics, including the optical constants and sheet resistance.

Depositional processes within the frontal ice-cored moraine system, Ragnar glacier, Svalbard

Depositional processes within the frontal ice-cored moraine system, Ragnar glacier, Svalbard The marginal zone of the Ragnar glacier has been divided into four zones: ice surface, proglacial lake, lateral moraine and frontal moraine complex. Detailed researches were carried out in the last one - frontal moraine complex consisting of three subzones: (1) outer moraine ridge, (2) culmination moraine ridge and (3) inner moraine plateau. The frontal moraine complex of the Ragnar glacier shows large variability of lithofacies and depositional processes. The aim of this study was to reconstruct the intensity and variability of depositional processes from early stage of the frontal ice-cored moraines creation till present situation. Debris flow processes, glaciofluvial and glaciolacustrine sedimentation as well as aeolian activity and down- and backwasting are identified as most important processes. Intensity of these processes has varied through the time. Presently the frontal ice-cored moraine complex of the Ragnar glacier is relatively stable, except few areas affected by the river or streams.

무전해 도금법을 이용한 전자소재용 은-구리 복합분말의 제조

【Silver coated copper composite powders were prepared by electroless plating method by controlling the activation and deposition process variables such as feeding rate of silver ions solution, concentration of reductant and molar ratio of activation solution $(NH_4OH/(NH_4)_2SO_4)$ at room temperature. The characteristics of the product were verified by using a scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic absorption (A.A.). It is noted that completely cleansing the copper oxide layers and protecting the copper particles surface from hydrolysis were important to obtain high quality Ag-Cu composite powders. The optimum conditions of Ag-Cu composite powder synthesis were $NH_4OH/(NH_4)_2SO_4$ molar ratio 4, concentration of reductant 15g/l and feeding rate of silver ions solution 2 ml/min.】

Changes in deposition on a colluvial fan during the upper holocene in the tindastóll mountain, skagafjörður district, north iceland: preliminary results

.This study investigates variability in depositional processes and landforms on the Innstaland colluvial fan, northern Iceland, over the late Holocene. This is completed using geomorphological mapping, historical records and relative‐age dating tools (vegetation survey, rock hardness and tephrochronology). Debris flows are the main contributors to fan development. Six main phases of deposition are distinguished, varying in deposit magnitude along a general trend of decreasing magnitude over time. With the help of dated tephra layers, the aggradation rates of the fan are calculated for the upper Holocene and in particular over the historical period (post‐ AD 1104). An episodic sediment transfer system is reconstructed, with several phases of low activity between more rapid aggradational episodes. The interpretation of the colluvial deposits suggests that the main phase of aggradation on the fan ended during the historical period after which incision started (between AD 1300 and 1766). Incision tracks act as the main pathways for debris distribution at the present time. These variations are related to the changing response of the catchment system over time.

Thermal process maps for predicting solidification microstructure in laser fabrication of thin-wall structures

The ability to predict and control microstructure in laser-deposited materials requires an understanding of the thermal conditions at the onset of solidification. To this end, the focus of this work is the development of thermal process maps relating solidification cooling rate and thermal gradient (the key parameters controlling microstructure) to laser deposition process variables (laser power and velocity). Attention is restricted to thin-wall deposits, which are commonly manufactured using Laser Engineered Net Shaping (LENS ™ ) and other small-scale laser deposition techniques. The approach employs the 2D Rosenthal solution for a moving point heat source traversing a semi-infinite substrate, which has been previously used in the literature to guide the development of process maps for controlling melt pool size and residual stress. In the current study, cooling rates and thermal gradients at the onset of solidification are numerically extracted from the 2D Rosenthal solution throughout the depth of the melt pool, and results are plotted on dimensionless process maps for predicting solidification microstructure. Results suggest that changes in laser power and velocity can have a substantial effect on solidification cooling rate and thermal gradient, which depending on the material system could have a significant effect on the resulting microstructure. Results are further plotted on solidification maps for predicting grain morphology specifically in Ti–6Al–4V, and the effects of laser power and velocity on trends in grain morphology are discussed. Although the Rosenthal predictions neglect the nonlinear effects of temperature-dependent properties and latent heat of transformation, a comparison with 2D nonlinear thermal finite element (FEM) results suggests that they can provide reasonable estimates of trends in grain morphology. In particular, both the Rosenthal and FEM results indicate a trend from columnar toward mixed/equiaxed microstructure with increasing laser incident energy, which is in keeping with recent experimental observations of thin-wall Ti–6Al–4V deposits.

Developing process for coating copper particles with silver by electroless plating method

Silver–copper composite powders were prepared by electroless plating method in aqueous system at room temperature. The dense and uniform silver coating layer was obtained by strictly controlling the activation and deposition process variables such as: NH4OH/(NH4)2SO4 molar ratio, activation time and feeding rate of silver ion solution. The mechanism of composite powders formation and their characteristics were discussed in detail. It is noted that completely cleansing the oxide layers and protecting the copper particles surface from hydrolysis were key factors to obtain high quality Ag–Cu composite powders.

Carbon and oxygen isotope compositions of the carbonate facies in the Vindhyan Supergroup, central India

The Vindhyan sedimentary succession in central India spans a wide time bracket from the Paleoproterozoic to the Neoproterozoic period. Chronostratigraphic significance of stable carbon and oxygen isotope ratios of the carbonate phase in Vindhyan sediments has been discussed in some recent studies. However, the subtle controls of facies variation, depositional setting and post-depositional diagenesis on stable isotope compositions are not yet clearly understood. The Vindhyan Supergroup hosts four carbonate units, exhibiting a wide variability in depositional processes and paleogeography. A detailed facies-specific carbon and oxygen isotope study of the carbonate units was undertaken by us to investigate the effect of these processes and to identify the least altered isotope values. It is seen that both carbon and oxygen isotope compositions have been affected by early meteoric water diagenesis. The effect of diagenetic alteration is, however, more pronounced in case of oxygen isotopes than carbon isotopes. Stable isotope compositions remained insensitive to facies only when sediments accumulated in a shallow shelf setting without being exposed. Major alteration of original isotope ratios was observed in case of shallow marine carbonates, which became exposed to meteoric fluids during early diagenetic stage. Duration of exposure possibly determined the magnitude of alteration and shift from the original values. Moreover, dolomitization is found to be accompanied by appreciable alteration of isotope compositions in some of the carbonates. The present study suggests that variations in sediment depositional settings, in particular the possibility of subaerial exposure, need to be considered while extracting chronostratigraphic significance from δ13C data.

Alluvial Fans as Records of Holocene Sediment Yield in the Central Great Plains of Southwest Nebraska

Soils buried by alluvial fan deposits in southwest Nebraska record several intervals of increased sediment yield from small watersheds during the Holocene. These intervals, which began at ca. 9000, 5800, 4000, 3000, and 1000 14C yrs. B.P., were probably caused by some sort of change in regional climatic conditions. Existing evidence of Holocene climate change suggests that increased sediment yields were caused by periodic shifts toward drier climatic conditions, except for the intervals that began at 5800 and 4000 14C yrs. B.P. The cause of increased sediment yields at those times is unclear, although an increased frequency of large intense storms may have been a contributing factor. The record of soil burial exhibits considerable spatial variability both within individual fans and between fans. This is partly due to practical limitations on the number of buried soils that could be sampled on each fan. But it is also due to the inherent spatial variability of depositional processes and to differences in the geomorphic development of the four fans. Thus, researchers who use data from fans to reconstruct sediment-yield histories need to investigate several sites on several fans in order to obtain as complete a record as possible of changing sediment yields.

Flow and Sediment Transport on a Tidal Salt Marsh Surface

The physical processes that control mineral sediment deposition on a mesotidal salt marsh surface on the Atlantic Coast of Virginia were characterized through a series of measurements of sediment concentration, flow velocity, turbulence, water surface elevation, marsh topography and particle size distributions of sediment deposited on the marsh surface. The comprehensive nature of the data set allowed assessment of the temporal and spatial variability in marsh surface deposition, the variability in depositional processes among tides of different amplitudes, as well as the specific processes that control deposition on this tidal marsh. Through three different types of measurements, it was found that sediment deposition occurred on the marsh surface during rising tides at tidal elevations ranging from those barely flooding the creek bank to high spring tides, and that sediment was not remobilized by tidal flows after initial deposition. Sediment deposition occurred on this marsh surface largely because fine sediment in suspension formed flocs. Analysis of inorganic grain size distributions of sediment deposited within 8m of the tidal creek indicated that 70–80% of this sediment was deposited in a flocculated form. The rest (particles larger than 20μm) were deposited as individual particles. In the marsh interior, 25m from the tidal creek, single grain settling predominated. Reduction of turbulence levels within the vegetation canopy on the marsh also promoted particle settling. The processes controlling sediment deposition did not vary among tides. However, suspended sediment concentrations near the creek bank increased with increasing tidal amplitude, consequently promoting higher rates of deposition on higher tides.

3D architecture of lowstand and transgressive Quaternary sand bodies on the outer shelf of the Gulf of Lion, France

A restricted area (700 km 2 ) of the outer continental shelf in the Gulf of Lions (Western Mediterranean Sea) has been surveyed in detail, in order to reconstruct the 3D architecture of large Quaternary sand bodies that are exceptionally well preserved in the western part of the Rho ne delta. Data sources include digital {very high resolution| seismic, swath bathymetry and some shallow cores. In two dimensions, the seismic data display a complex superposition of alternating seismic units, consisting of high and low angle prograding clinoforms, corresponding to 'high’ and ‘low’ energy environments. The combination of faunal and grain size analysis from shallow cores, geometry of sedimentary bodies, showed that these two types of seismic facies can be attributed, respectively, to upper shoreface and prodelta( c settings. Despite a similar geometry in 2D, it appears that the prograding sand units have very different 3D geometries (lateral extent, direction of progradation with respect to the paleoshorelines . ), implying different sedimentary processes. At least two major sand units have shore parallel orientations and can be mapped along the entire study area. The mechanism responsible for the formation of these sand bodies seems similar to that described for many ‘sharp-based’ sand bodies from the stratigraphic record, especially in the Western Interior Seaway ; their isolated position on the shelf being related to (forced) regressions. In contrast, some other sand units have lobate shapes, with divergent directions of progradation and limited lateral extent. They are often overlying (fluvial) incisions and they pinch out landward ; it is still not clear whether they are related to some allocyclic or autocyclic processes, like shifting of delta( c lobes as observed on the Texas coast. The very high resolution, and high quality of the seismic data have enabled us to characterise the three-dimensional architecture of small-scale sedimentary bodies. The study has pointed out the variability of depositional processes and has given an insight on reservoir characteristics. ©1998 Elsevier Science Ltd. All rights reserved.

Ophthalmic lens coatings

This paper reviews modern coatings on plastic ophthalmic lenses whereby particular attention is given to multilayer dielectric antireflection (AR) coatings. The optimisation of coating performance, coating processes and coating characterisation methods continues to be a considerable technical challenge for the manufacturer of coated ophthalmic lenses. Coatings are needed on polymer ophthalmic lenses to enhance both the mechanical durability of the relatively soft plastic surface and the optical performance of the lens. High value ophthalmic lenses are coated with a multilayer system consisting of a primer coating, abrasion resistant hard coating and a multilayer AR coating stack. The physical properties of the AR coating need to be carefully balanced and controlled. Optimising the adhesion of the coating stack to the relatively soft substrate may entail some compromises in the achievable coating hardness. During a deposition process, plastic substrates cannot be elevated to nearly the same temperatures that are permissible for glass substrates. This can restrict the achievable level of durability and adhesion of a film deposited on a plastic lens. Raising the substrate temperature to near the limit plastic lenses can withstand often results in crazed coatings. The main factor is the large differences in the temperature expansion coefficient between the plastic substrate and the dielectric coating which leads to large stress differentials. One other major factor affecting the coatability of plastic substrate is the desorption of water vapour from the substrate during the deposition process. Some of the traditional restrictions on coating plastic substrates have been overcome by modern ion beam assisted deposition processes. Hard films are usually under compressive stress and there are indications that stress free coating stacks perform better in service even if the hardness of the film has been greatly compromised. Data from a limited study suggest a correlation between film brittle failure during hardness measurement induced indenter penetration and in-service performance. The brittle failure may indicate large stress differentials between layers in the film stack. The difficulty in the optimisation of multilayer coatings on plastic lenses is in the measurement and correlation of the film parameters to the deposition process variables and in-service performance criteria.

Structural properties of vapor deposited silicon nitride

Some of the chemical and physical properties of silicon nitride films have been studied to determine the effects of deposition process variables and wafer preparation prior to deposition. The boat temperature and the reaction gas mixture were changed to optimize the quality of the silicon nitride films. This resulted in amorphous films free of pinholes, cracks, and impurities, together with good electrical properties such as an effective barrier against sodium ions and a low fast and fixed surface state density. Most of the work has been done on silicon nitride deposited over silicon dioxide films or silicon dioxide steps on a siliconsubstrate. The silane-ammonia and the silicon tetrachloride-ammonia reactions resulted in silicon nitride of comparable physical and chemical properties. Cleaning procedures are most effective if they include an etching step to take off 50 to 100A of the oxide prior to nitride deposition. The influence of subsequent heat treatments (up to 1200°C) on cracking and etch rates of the silicon nitride films has been studied. Films thicker than 2000A deposited over oxide steps were found to crack after heat treatments above 1000°C. Films in the lower thickness range of 500 to 1000A are most suitable because they have good resistance against cracking after heat treatments up to 1200°C, do not need excessively long etch times, and are still an excellent barrier against a heavy sodium contamination applied at 535°C.

A Continuous Process for the Production of Whisker Reinforced Composites

Various techniques have been proposed and developed for aligning the whisker reinforcing phase of metal matrix composites. Most of these techniques involve multi-step alignment processes, and are not suitable for economical, continuous production of metal-whisker com posites. A laboratory scale, prototype system for the continuous dielectro phoretic deposition and alignment of micron sized, ultra high strength whiskers has been designed, developed and tested. This process consists of the deposition of whiskers onto one of two electrodes placed in a suspension of the whiskers, when a voltage is applied between the electrodes. By employing a metal matrix foil as the deposition elec trode, this technique has demonstrated that the continuous production of metal-whisker combinations suitable for fabrication into advanced whisker reinforced composites is feasible. The volumetric loading of the reinforcing whiskers on the metal foil can be controlled by varying such process parameters as voltage, foil speed, electrode separation and geometry, and the concentration of whiskers in the supporting media. A discussion of these alignment and deposition process variables is presented. The metal foils containing the deposited, aligned whiskers are then sandwiched into a preform structure consisting of successive layers of metal foil and fibers. Consolidation of the stacked layers into a com posite is accomplished by hot pressing and diffusion bonding. Photo micrographs of the consolidated composite, showing alignment of the whiskers and the microscopic composite structure are shown and discussed for a range of whisker compositions. Preliminary mechanical properties data for selected composite compositions are presented and discussed.