Depositional Textures Research Articles

Foraminiferal distribution and palaeoecological interpretation of the Eocene–Miocene carbonates at Al Jabal al Akhdar (northeast Libya)

Abstract. In the coastal area of northeastern Cyrenaica (Libya), the excellent exposures of Cenozoic limestone sequences of Al Jabal al Akhdar average around 1000 m in thickness and allow detailed stratigraphic investigations to be undertaken. This study of the biostratigraphy and depositional environments has been augmented by an analysis of the microfacies and of matrix-free foraminiferal assemblages. The biotic contents of the microfacies provide a good tool for correlation with the Letter classification developed from the Indo-Pacific region. The palaeoecological significance of the biota has been evaluated by comparison with the ecological requirements of their present day counterparts. Limitations for the palaeoecological interpretations are mainly due to the inadequate relationships with existing ecological data sets and to some local bias in fossil recovery because of some unfavourable lithologies. In the investigated Eocene to Miocene shallow marine carbonate succession nine different microfacies and sub-microfacies were distinguished through depositional texture and biotic components. Wilson’s standard carbonate facies belts, integrated with present day foraminiferal distribution models, have been used for reference in microfacies analysis and description. Most of the microfossils present are foraminifera and a total of 150 taxa, including larger, small and planktonic foraminifera, have been recognized and their stratigraphic and palaeaeocological distribution reported. Physiographically, the rock sequences investigated are referred to a shelf–carbonate platform complex, in which the depositional environments range from open shelf to restricted platform conditions. The nature and distribution of the foraminiferal assemblages and related biota, in association with sedimentological evidence, indicate a generalized shallowing upward trend in which several bathymetric oscillations, especially in the Oligocene, are reported. These reflect the interplay between local tectonics and large-scale eustatic changes.

The Influences of Organic Additives on Zinc Electrocrystallization from KCl Solutions

The effects of some conventional additives such as triton X‐10 (TX‐10), sodium methylene bis(naphthalene sulfonate) (NNO), phenylbenzylketone (PBK), and a CH‐1 brightener on the electrodeposition of zinc onto the glassy carbon electrode were examined using chronoamperometry. The surface morphology, grain size, and texture of the deposits were characterized by scanning electron microscope, transmission electron microscope, and X‐ray diffraction. It was found that the electrocrystallization mechanisms of zinc and microstructure of deposits are sensitive to the identity of organic additives. On one hand, in the absence of additive or in the presence of NNO or PBK, zinc deposition proceeds by three‐dimensional instantaneous nucleation and growth, while in the presence of TX‐10 or a CH‐1 brightener, zinc deposition follows the three‐dimensional progressive nucleation and growth. On the other hand, in the absence of additive, the deposit forms a loose and porous structure with no texture. In the presence of PBK and TX‐10, the deposits are (101) and (110) texture, respectively. And in the presence of a CH‐1 brightener, deposit is smooth and bright and forms a (101) and (110) texture, where a homogeneous distribution of small 8 nm grains appears. These facts show that the effects of a CH‐1 brightener on the zinc electrodeposition mainly result from the combinational action of TX‐10 and PBK. In addition, we also found that surface morphology of deposits is strongly correlated to deposit texture. © 1999 The Electrochemical Society. All rights reserved.

Microporosity in Arab Formation Carbonates, Saudi Arabia

ABSTRACT Microporosity occurs throughout Arab Formation carbonates of Saudi Arabia, and affects the log response, fluid flow properties and ultimate recovery of hydrocarbons in these reservoirs. Qualitative examination of Arab samples indicates that microporosity occurs as four major types: (1) microporous grains, (2) microporous matrix, (3) microporous fibrous to bladed cements, and (4) microporous equant cements. Quantitative estimation of microporosity abundance was measured in two ways: (1) thin section point counts, and (2) pore throat size distributions derived from capillary pressure data. Point count data shows that microporosity can vary widely from sample to sample, ranging from 0% to 100% of the total measured porosity of a sample. Capillary pressure data confirms the volumetric significance of pore throats that are 10 microns or less in size. Variations in microporosity abundance and type appear to be controlled by depositional texture, grain mineralogy and grain microstructure. We suggest that microporosity in Arab Formation carbonates formed diagenetically, via three mechanisms: (1) leaching and incomplete reprecipitation of metastable carbonate, (2) crystal growth contact inhibition, and (3) (locally) endolithic borings of grains.

Textures and structures of vapor deposits

The texture of vapor deposits (PVD and CVD) changes from the orientation that places the lowest energy lattice plane parallel to the substrate under the condition of low atom or ion concentration adjacent to the deposit, to the orientation that places the higher energy crystal planes parallel to the substrate as the atom or ion concentration adjacent to the deposit increases. However, in the early stage of deposition, the deposit-substrate interface energy and the surface energy constitute the most important energies of the system. Therefore, if the lattice match is established between the substrate and the deposit without generating much strain energy, the epitaxial growth takes place to reduce the interfacial energy. When the epitaxial growth does not take place, the surface energy is dominant in the early stage of deposition and the lowest energy crystal plane tends to be placed parallel to the substrate up to a critical thickness. The critical thickness depends on the deposition conditions. If the deposition condition does not favor placing the lowest energy crystal plane parallel to the substrate, the initial texture will change to that compatible with the deposition condition as the film thickness increases, and the texture turnover thickness will be short. The microstructure and surface topography of deposits are related to their textures.

Microtaphofacies of a Warm-Temperate Carbonate Ramp (Uppermost Tortonian/Lowermost Messinian, Southern Spain)

The combined analysis of the sedimentary structures, internal depositional geometries, and microfacies of uppermost Tortonian/lowermost Messinian shallow-marine carbonates (Agua Amarga Basin, southern Spain) has aided in unraveling the geological record of a highly dynamic ramp environment. The biogenic BRYOMOL association with large benthic foraminifers inhabited a warm, temperate climate (17-20 degrees C). Sediment distribution was governed by physical parameters, and redistribution and mixing of particles blurred original biogenic zonations. Thus, although the carbonate factory can be localized on the mid ramp based upon sedimentary structures and depositional textures, sediment composition is quite uniform over the depositional profile, and only qualitative paleontological evidence exists for the original presence of seagrass patches (benthic foraminifers, biomuration fabrics in bryozoans). Originally aragonitic biota (i.e., molluscs), quantitatively important in all Cenozoic shallow-marine environments, were dissolved during or soon after deposition and left no significant trace in the fossil record. Consequently, the diagenetic potential of the sediments was low, and the deposits remained essentially unlithified for a long period. During lowstands and transgressions, particles were partly reworked from previously deposited material. Sediment compositions within these units are increasingly biased toward concentrations of mechanically more resistant carbonate grains as a function of many deposition and exhumation cycles. In line with taphonomic experiments, nodular (celle-poriform) bryozoans disappear before robust and delicate branching bryozoans. Resistant grains include echinoderm ossicles, bivalve shell materials (calcitic), foraminifers, balanids, and non-carbonate particles. The quantitative proportions of these grains have been used to define microta-phofacies (new term). Particle and, therefore, sequence dynamics of temperate carbonate-ramp systems resemble these in siliciclastic environments, and challenge the classic concept of (tropical) carbonate sequence stratigraphy. Careful microfacies analysis of temperate skeletal carbonate depositional systems and depositional sequences provides an important additional tool in further understanding the architecture of bioclastic carbonate bodies in the subsurface.

Reservoir development, sequence stratigraphy and geological modelling of Westphalian fluvial reservoirs of the Caister C Field, UK southern North Sea

The earliest Westphalian B reservoir of the Caister C Field (informally named the Caister Sandstone Unit consists of erosive conglomeratic sandstones deposited in stacked low sinuosity fluvial channels. Channel types and architectural elements demonstrate an upward change to more sinuous forms. The Caister Sandstone Unit is believed to contain incised valley-fill sediments deposited as late lowstand and transgressive systems tracts when rising base level generated accommodation space. The dominant control on reservoir quality is primary depositional texture with the best permeability found in higher energy coarse sandstone and pebbly intervals associated with basal channel-fill units; crevasse channel and splay sandstones offer poor reservoir properties. The robust correlation framework, which is based upon laterally extensive coal seams, enables a sequence stratigraphic model of the field to be developed, thereby allowing a better understanding of reservoir extent and sandbody continuity. A 3D geocellular geological model is built with reservoir architecture elements controlled by the sedimentological model. This is used for volumetrics calculations, input to a reservoir simulator and in the locating and planning of in-fill wells.

Petrofacies analysis and depositional environment of the Jahrum Formation (Eocene), south-southwest of Burujen, Iran

A progressive carbonate environment from supratidal to near-shore, retricted to intertidal and restricted shallow marine environment existed during deposition of the Jahrum Formation. The main facies characteristics of the Jahrum Formation in the study area are: (1) a laminated, unfossiliferous dolomite and pelleted dolomitic mudstone with solution collapse breccias; (2) a pelleted laminated fossiliferous dolomitic mudstone; (3) reworked skeletal wackestone to packstone; (4) highly reworked biointraclastic grainstone; (5) fossiliferous wackestone to packstone. As a result, two major depositional systems tracts can be defined: (1) the lower portion, are transgressive systems tract; and (2) the upper portion, as highstand systems tract. Diagenetic processes involved in supratidal rocks of the Jahrum Formation reflect dolomitization of initial sediments, leaching of calcium sulfate and carbonate grains, replacement of dolomite and stylolitziation. Voids are the most common pore type, and porosity was controlled by diagenesis that was influenced by primary depositional texture.

Quantitative texture analysis in pulse reverse current electroforming of nickel

The crystallographic texture of nickel deposits is known to be related to its magnetic and mechanical properties. However, up to now, most of the texture analyses of electrodeposited nickels have been semi-quantitative and still use a nickel sulphate bath, which is mainly for decorative industrial applications. In this paper, a quantitative texture analysis using ODF (orientation distribution function) has been carried out to study the effect of a pulse reverse current on the crystallographic texture of electroformed nickels, with the use of a nickel sulphamate bath, which is now commonly used for functional industrial applications and micro- or precise components. It was found that the [100] fibre texture with different orientation densities was formed at different on-times and off-times. With a constant off-time of 0.5 ms, an increase in on-time led to a gradual decrease in the orientation density of the [100] texture, whereas with a constant on-time of 5 ms, an increase in off-time has affected the change of the orientation density of the [100] texture in a more complicated manner. All of these phenomena are considered to be related to the change of the amount of inhibiting chemical species such as nickel hydroxide adsorbed on the cathode surface and the nickel deposition rate.

Regionalized Loads of Sediment and Phosphorus to Lakes Michigan and Superior—High Flow and Long-term Average

Daily loads of suspended sediment and total phosphorus for the 10-year, 1-day design high flow and average of the 16-year period (1975 to 1990) were computed for 18 well-monitored tributaries to Lake Michigan and Lake Superior by use of constituent-transport models. The loads from these 18 reference tributaries were used to estimate the loads from all the United States tributaries (with drainage basins greater than 325 km2) to Lake Michigan and Lake Superior by selection of a reference tributary with the most similar physical characteristics and use of a unit-area yield. Statistical comparisons between computed yields and environmental factors were used to determine the physical characteristics that were most influential in selecting a reference tributary. Suspended sediment yields were affected primarily by river gradient and secondarily by the texture of surficial deposits, whereas total phosphorus yields were affected primarily by the texture of surficial deposits and secondarily by river gradient. Average total phosphorus loads were greatest in rivers entering the middle to southern part of Lake Michigan, especially those draining clayey surficial deposits in agricultural areas. During high flow, loads of phosphorus and suspended sediment from tributaries entering the southwestern part of Lake Superior dominate the total input of these constituents because of the steep gradients of the rivers and the clayey surficial deposits that they drain. These loads were used to compute regional loads and to rank the tributaries on the basis of their respective loads during a specified high flow and over extended periods.

Textural evolution in electrodeposits under the influence of adsorbed foreign species. Part II A simulation study on effects of potassium chloride on textural evolution in copper electrodeposits

The texture of copper deposits produced in the bath containing potassium chloride changes with the content of the potassium chloride. This change in texture was usually explained to be caused by chloride adsorption on the cathode. This paper reports simulation studies on textural evolution in copper electrodeposits under the influence of potassium chloride, using a Monte Carlo simulation approach. The study was conducted based on the assumption that the textural development results from the minimization of the system free energy in which the surface-energy anisotropy plays the most important role. The simulation demonstrates that adsorbed potassium ions may change the surface-energy anisotropy of copper, and therefore, they also affect texture variation in copper deposits in addition to the chloride effect. It was observed the potassium effect on textural variation in copper deposits is even stronger than that of the Cl- adsorption.

Development of minor outwash fans at kötlujökull, Iceland

Throughout the 1980s, the development of minor outwash fans was studied at and beyond a northeastern section of the steep, advancing ice front of Kötlujökull, the largest outlet-glacier on the east side of the ice-cap Myrdalsjökull in central south Iceland. In contrast to the extensive outwash fans of gravelly and stony material deposited by high energy streams from underneath the glacier, the minor fans consist of fine-grained material, mainly of sand size, deposited by low energy streams draining the debris-covered glacier surface. The vertical alteration in texture of the minor fan deposits results from changing influx of sediments, which in turn is coupled to varying activity in the processes working in the supraglacial sediment source area. These processes are ablation, sudden drainage of pockets of water, influx of rainwater, and resedimentation of debris by fall, slide, and flow. Along with the glacier advance during the 1980s, slabs of fan sediments were incorporated in the push-moraine ridge being formed. The subsequent glacier retreat during the 1990s has largely curtailed the production of minor outwash fans. It is concluded that this type of outwash fan is likely to be produced along advancing, or stationary, glaciers where the frontal slope is steep and covered by debris. Similar minor outwash fans, termed hochsander fans, have been identified beyond ice-marginal moraine ridges bounding dead-ice morainic terrain in Pleistocene landscapes.

Textural evolution in electrodeposits under the influence of adsorbed foreign species: Part I Textural evolution in iron electrodeposits affected by hydrogen co-deposition

Textural evolution in electrodeposits is strongly affected by foreign species in the electrolyte and also by the co-deposition of hydrogen. The effects of foreign species on textural development in electrodeposits were studied by employing a Monte Carlo model. This model is based on physical principles and incorporates parameters which are used to control electrodeposition processes. An attempt was made in the simulation to reflect the basic process of the deposit growth, and to identify the factors responsible for the texture formation and its variation with the deposition condition. It is assumed that the texture of the deposit results from the minimization of the free energy of the system. Based on this assumption, it was demonstrated that the surface-energy anisotropy played an important role in the formation of fibre texture. In particular, the model can be used to simulate textural evolution under the influence of adsorbed foreign species, because the surface-energy anisotropy is modified by the adsorbed foreign species. Part I of the paper presents results of our studies on iron electrodeposition with the emphasis on the effect of hydrogen adsorption on iron deposit texture. Relevant experimental results have also been presented to corroborate the simulation study. Part II of the paper presents simulation studies of textural evolution in copper deposits under the influence of adsorbed potassium and chloride ions.

Environmental Controls on Groundwater Chemistry in an Offshore Island Aquifer: Fiesta Key, Florida

A field study was undertaken on the Florida Bay side of Fiesta Key, Florida, to identify the chemical characteristics of a previously unexplored offshore groundwater system and to define the critical parameters affecting groundwater movement and interaction with sediment pore fluids and bedrock. Emphasis was placed on the upper 2 meters of bedrock, where groundwater recharge and discharge potentials are maximized, along a 100 meter transect extending from the island margin. Bedrock cores were used to describe Pleistocene depositional textures, and were sampled at discrete depths to determine the extent of water-rock interaction. Piezometers installed into each core hole were used to monitor surface and ground water tide levels, and for the systematic collection of water samples for a large suite of chemical determinations. Aqueous chemical data indicate that these groundwaters are marine in origin, anoxic, and moderately hypersaline (S = 36–40). Exchange of bedrock pore fluids with overlying Bay waters is restricted by a layer of Holocene sediment and a discontinuous soilstone crust formed at the modern bedrock surface. Groundwater chemistry near the sediment/bedrock interface is marked by elevated concentrations of total alkalinity and Ca2+, and by significant Mg2+ depletion. These waters likely acquired their unusual chemistry by mixing between deeper groundwaters and overlying, early diagenetically altered, sediment porewaters. High alkalinity and calcium concentrations presumably result from the combination of the effects of aerobic metabolism, carbonate dissolution, and sulfate reduction. Mg-depletion most likely resulted from the precipitation of Mg-calcite. These unusual chemistries disappear by 2 m depth in the groundwater system, where Ca2+ and Mg2+ concentrations are similar to those expected for seawater under slightly hypersaline conditions. The Pleistocene bedrock contains low Mg, Sr, F, and P concentrations relative to the overlying unconsolidated Holocene carbonate sediments. This is consistent with the diagenetic recrystallization processes that the bedrock has undergone. Hydraulic conditions favor the net recharge of Florida Bay seawater to the groundwater system, but there are insufficient tide data to identify cyclical water exchange rates or groundwater flow patterns.

Analysis of carbonate microfacies in the Chachao Formation (cretaceous), Barda Blanca-malargüe, Mendoza province-Argentina: A cluster analytic approach

The Chachao Formation (Valanginian), which occupies a middle position in the Mendoza Group, is a carbonate unit consisting of packstones and grainstones, with subordinate wackestones and rare mudstones. Its average thickness is 35 meters. Pelecypods, echinoderms, gastropods, crinoids, ostracods, worm tubes, sponge spicules, and foraminifera dominate the fauna in the studied sequence. Rare remains of bryozoans, ammonoids, brachiopod shells, coral fragments, and algae are present too. Phosphatic debris occurs in minor quantities. Pyrite, glauconite and phosphate minerals commonly occlude foraminiferal chambers, ostracods shells, as well as borings in skeletal particles. Taphonomic features enable this association to be considered as parautochthonous in response to compositeevent concentrations. The Barda Blanca sequence was divided into six microfacies in order of relative increasing energy level. Each one is characterized by the dominance of depositional textures, bioclasts and sorting. In order to determine the degree of interrelationships among bioclasts, data were subject to cluster analysis. Two isolated nuclei (calcispheres & sponge spicules/fish scales & coprolites), and a big group integrated by three subgroups were recognized. Each one was distinguished by the existence of pelecypods, echinoderms, gastropods, annelids, ostracods, and foraminifers. Changes in microfacies types and in fauna content reveal considerable variation in the frequency-distribution curves of bioclasts. These variations point out discontinuities, which may indicate that water depth increased with time. These discontinuities suggest the presence of different parasequence boundaries and they could be used as time lines in the reconstruction of the depositional events. The fossil assemblage and deposit suggest an open marine condition below the influence of fairweather waves, and reworking by action of smaller storms (gradient currents) eventually.

Geochemistry of Precambrian carbonates: VII. Belt supergroup, Montana and Idaho, USA

Carbonates from the ~1100–1450 Ma old Proterozoic Belt Supergroup were collected from stratigraphic sections throughout Montana and Idaho, USA. The sampled sequences, in ascending stratigraphic order, include the Newland, Altyn, Spokane/Greyson transition, Empire, Wallace, Helena, Siyeh, Snowslip, Shepard, and Libby formations. An increase in the degree of postdepositional alteration of Belt limestones is reflected in a diminution of Sr and Mg contents, an increase in Mn, and depletion in 13C and 18O. Two diagenetic trends can be resolved for the limestones. One, affecting the presumed originally aragonite-rich sediments, includes carbonates from the Lower Belt Newland Formation. In contrast, the Middle Belt Carbonate (Wallace, Helena, Siyeh formations) may have been originally of high-Mg calcitic mineralogy. Projection of the alteration trends for the Lower and Middle Belt limestones suggest ~21‰ SMOW and ~ +2.5‰ to +1.0‰ PDB as the best preserved values for the δ 18O and δ 13C of seawater, respectively; both comparable to results from other Mesoproterozoic carbonate sequences. The oxygen isotope data for limestones show a regional westward depletion of ~8‰ in 18O, possibly reflecting a higher temperature of postdepositional alteration in the western Belt basin. This depletion in 18O is accompanied by a comparable decrease in δ 13C values, most likely because a higher proportion of carbon was incorporated from CO 2 generated by thermal cracking of hydrocarbons at depth. Dolostones in the Belt basin are dominantly micritic, with good preservation of depositional textures. Chemically and isotopically, their alteration trends mimic those of limestones, leading to comparable projected “best” values for δ 13C. 87Sr/ 86Sr values of Belt carbonates range between 0.70484 and 0.74991. Progressive diagenesis, as indexed by decreasing concentrations of Sr and depletions in 18O and 13C, results in an increase in 87Sr/ 86Sr values. The least radiogenic measurement, from a Lower Belt Newland limestone sample, appears to fit reasonably well into the general trend for Proterozoic seawater, as discussed in Mirota and Veizer (1994). This and the consistency of δ 18O and δ 13C in limestones with other coeval sequences suggests that the (Lower and Middle) Belt carbonate sections are marine, deposited in an environment that was not continuously separated from the open ocean.

Texture and Related Phenomena of Copper Electrodeposits

AbstractThe texture of copper electrodeposits changes from the orientation that places the lowest energy crystal facets parallel to the substrate under a condition of low ion concentration adjacent to the deposit, to the orientation that places the higher energy crystal facets parallel to the substrate as the ion concentration adjacent to the deposit increases. The copper electrodeposits have peculiar surface morphologies and microstructures depending on their textures, which in turn may affect their mechanical properties even when they are obtained in similar electrolysis conditions. The electrodeposits undergo recrystallization, when annealed. The recrystallization texture may be different from the original deposit texture. These phenomena have been discussed.

Seismic Estimation of Porosity in the Permian San Andres Carbonate Reservoir, Welch Field, Dawson, County, Texas: ABSTRACT

OXY and the DOE Are partners in a advanced technology demonstration project at OXY`s West Welch Unit. Production is from a low permeability San Andres reservoir of Permian age similar to many shallow shelf carbonate reservoirs in the Permian Basin. The project involves the construction of a detailed geological model for numerical simulation to design and then conduct a CO{sub 2} flood of the reservoir. Depositional textures of the reservoir rock are highly variable from diagenesis, mostly anhydritic cementing, creating a highly complex pore system. Identification of the interwell reservoir continuity and flow units present the greatest challenge to the reservoir description. A 1993 vintage 3-D seismic survey with a bin spacing of 110{prime} by 165{prime} has been used to assist with the interwell reservoir description. The structure definition at the top and base of the reservoir have been accurately mapped with respect to the well data. Core and well log measurements of porosity, permeability and water saturation were computed and summed across the seismic reservoir interval. Measurements of amplitude, frequency and phase within the 3-D volume were summed across the reservoir interval. All seismic attributes were sampled to the wells and compared through scatterplots to the well log andmore » core measurements. Excellent correlation between three seismic attributes and porosity has been documented. A deterministic method has been used to estimate porosity values at each seismic bin location. The method uses the seismic measurements to shape the geology between the wells while maintaining agreement with the well data at the well locations.« less

Diagenetic Exaggeration of Primary Texural Variations in Incised Valley Fills, Cusiana Field, Colombia: ABSTRACT

Incised Valley Fills in the late Eocene Mirador Formation of the Cusiana Field are dominated by quartz arenite sandstones that vary in grain size from fine sandstones to sandy conglomerates. The average porosity of the valley sandstones is [approx]8% which reflects significant compaction during deep burial ([approximately]20,000feet) and abundant quartz cement ([approximately]14%) precipitated over a wide temperature range (85-140[degrees]C). Surprisingly, the present permeability structure of the valley fill sandstones still reflects grain size variations. Indeed, the effect of the large amounts of quartz cement has been to exaggerate the primary textural variation in permeability. Very coarse, well sorted sandstones at the valley bases possess two orders of magnitude higher permeability than fine-grained equivalents of the same porosity. This permeability contrast is more than original depositional textures in sandstones would predict and is consistent with predictions from simple sphere pack models which show that at low porosity (<12%), the contrast in permeability due to grain size is greatly enhanced. As a result the reservoir characterization has been based on the primary sedimentary fabric, not on diagenesis. Production logging results show that the coarse grained bases of the valley fills are indeed the major contributors to flow. Thus the impact of diagenesismore » on the flow structure of these valley fills has been to selectively reduce the permeability of finer-grained sandstones, while maintaining high permeability in the coarsest grained bases of the valley fills.« less

Effect of Deposition Conditions on the Texture of Zinc Deposits

Effect of Deposition Conditions on the Texture of Zinc Deposits

Simulating Epitaxial Textures

The way of calculating the texture of a polycrystalline deposit over a polycrystalline substrate is considered in this paper. The proposed procedure consists in taking into account the epitaxial relationships and in defining some kind of selection rules according to the assumed crystallographic surface state of the substrate. To illustrate the interest of such a procedure, textures are calculated under various conditions and compared with ‘experimental’ textures for electrodeposited zinc deposits over steel sheets.