Individual Laminae Research Articles

Microfabric analysis of laminated diatom ooze (Holocene) from the eastern Bransfield Strait, Antarctic Peninsula

Selected intervals of laminated diatom ooze (Holocene) from the eastern Bransfield Strait, Antarctic Peninsula were analyzed using high-resolution section images of impregnated samples to reveal potential annual-to-seasonal scale signatures of the lamination. The results show a probable seasonality within individual diatom ooze laminae which mainly reflects spring blooms ofChaetoceros followed by summer production ofCorethron orRhizosolenia. Alternating monospecific diatom ooze and terrigenous laminae are suggestive of annual cyclicities, representing alternation of diatom mass flux during the spring or autumn with terrigenous flux during the rest of year.

Petrologic analysis and geochemistry of the Late Neogene-Early Quaternary hardpan calcretes of Western Rajasthan, India

Calcretes formed over bedrock such as Precambrian hornblende-chlorite schist, rhyolite and carbonaceous phyllites in Western Rajasthan, India, were studied for their mineralogical composition and geochemistry. They form a distinct element of the Quaternary landscape of Western Rajasthan, India. The study area is located within the Nagaur–Churu–Jaipur tract of Western Rajasthan. The purpose of this study was to determine the processes governing the development of hardpan calcretes, and to evaluate the local and regional controls on their formation. Micromorphology included pedogenetic and groundwater features within the hardpan calcretes. Thickening of calcite laminae downward and tapering at the sideward edges around the unweathered minerals of quartz and feldspars indicated cumulative and compound pedogenesis, which probably occurred locally, and downward movement of carbonate solution and pore water. Carbonate solutions were probably derived from the upper horizons or surfaces bringing about the process of dissolution and recementation of individual laminae. Occurrence of fibrous palygorskite as coatings around the detrital grains and siderite (oolitic and pisolitic in shape) points to a subalkaline–subacidic process of pedogenesis in a semi-arid to arid climate. Stable δ 13C and δ 18O isotope data of the hardpan calcrete laminae vary between 0.3‰ to 1.5‰ and −5.9‰ and −1.5‰, respectively indicating their formation at or near surface (capillary fringe), probably supporting a thin column of soil. The source of most of the calcite is groundwater; however, calcite nodule formation was largely dependent on pedogenic processes associated with evaporation, evapotranspiration and /or microenvironmental changes in pH and CO 2 partial pressure. Dust is also a major source for carbonate precipitation. Although it is commonly assumed that the powdery calcretes are younger in age compared to the more complex forms, the occurrence of Middle Palaeolithic tools below the hardpan calcrete at Roopangarh and Dayalpura, and above the hardpan calcretes at Mitri, Genana and Rol, indicates that the morphology of calcretes is not a reliable indicator of age.

C-fos induction in rat superficial dorsal horn following cutaneous application of noxious chemical or mechanical stimuli

The method of c-fos immunodetection was used to map the distributions of neurons in the lumbar spinal dorsal horn that were activated following intracutaneous (i.c.) microinjection, or iontophoretic application, of different irritant chemicals to the lateral hindpaw of rats. Microinjections (1 microl) of histamine, serotonin (5-HT), nicotine, capsaicin, or formalin each elicited similar distributions of Fos-like immunoreactivity (FLI) in laminae I-II of the ipsilateral superficial dorsal horn, with little or no FLI in deeper laminae or contralaterally. In laminae I and II, FLI cell counts were significantly higher following i.c. histamine, 5-HT, capsaicin, formalin, and noxious pinch, compared to i.c. saline controls. Capsaicin-evoked FLI was dose-dependent. Multivariate analysis of variance revealed no significant difference in spatial distributions of FLI induced by any of the chemical or pinch stimuli. Iontophoretic application of histamine, 5-HT, or nicotine also elicited similar distributions of FLI in the superficial dorsal horn, and cell counts of FLI were significantly higher compared to controls receiving iontophoretic vehicle (methyl cellulose). These results indicate either that individual laminae I-II neurons are activated by each of the irritant chemicals, or that neurons selectively responsive to a given irritant are comingled without any apparent laminar segregation.

Microfabric study of diatomaceous and lithogenic deposition in laminated sediments from the Gotland Deep, Baltic Sea

The deep basins of the Baltic Sea are commonly anoxic, and finely laminated diatomaceous sediments have been deposited at intervals throughout the last 8000 yr. The origin and composition of individual laminae in Gotland Deep sediments have often proved difficult to characterise using traditional micropalaeontological and sedimentological studies. Here, we present a scanning electron microscope study in which lamina down to 30 μm in thickness with distinct mineralogical or micropalaeontological composition have been identified and described. Depositional laminae sequences in the form of couplets, triplets and quadruplets of diatomaceous and lithogenic laminae are observed with an average thickness of approximately 700 μm. Diagenetic Ca-rhodochrosite laminae also occur within these depositional sequences. Examination of the diatom assemblages suggests that these bundles of laminae represent annual deposits, or varves. Varves are relatively uncommon, and typically occur in small intervals of two to five varves, which are interrupted by more diffusely laminated and homogenous sediments. The origin of these more massive sediments probably relates to periodic re-oxygenation of the basin on inter-annual time scales and destruction of varves by bioturbation.

Temporal distribution of diastems in deposits of an open-coast tidal flat with high suspended sediment concentrations

Based on field observations of the preservation potential and genesis of couplets and small sequences, diastems occur within tidal flat deposits at scales of semi-tidal, daily, monthly, and yearly intervals. Thus, tidal flat deposition is riddled with more diastems of different scales than previous assumptions. Units that are apparently complete when examined at longer time scales actually contain many diastems when examined at a shorter time scale. Diastems within tidal flat deposits are generated not only by high-magnitude storm waves, which occur during typhoon seasons, but also by daily erosion produced by tides and weak waves during calm-weather seasons. The missing intervals in diastems generated by storm waves can be several days to several years. Preservation potential of storm-generated small sequences is of the order of one-third. Diastems generated by erosion, by tides, and weak waves can have spans from a semidiurnal cycle to several days. They are easily overlooked because of the low-magnitude destruction and lack of distinctive sedimentary features. Net erosion by tides and weak waves is unexpectedly increased by day-to-day processes. Alternations of sandy and muddy laminae are related to tidal rhythm, but individual laminae can be separated by a significant diastem. Documentation of erosion by tides and weak waves under normal (non-typhoon) conditions is the principal focus of this report.

Opal and organic carbon in laminated diatomaceous sediments: Saanich Inlet, Santa Barbara Basin and the Miocene Monterey Formation

Laminated biosiliceous sediments from Saanich Inlet, British Columbia (SI), the Monterey Formation, California (MF), and Santa Barbara Basin, California (SBB) are organic-rich and were studied to assess the suitability of SI and SBB as modern analogs of the Miocene MF and to explore the controls on distributions of opal and organic carbon. To this end, individual laminae and groups of laminae extracted from ODP cores and outcrop samples were analyzed using a multi-tracer geochemical approach.

Open‐coast intertidal deposits and the preservation potential of individual laminae: a case study from east‐central China

Monitoring of sedimentation and erosion was conducted on an open coastal tidal flat on the southern flank of the Yangtze delta. Various elevation references were established in the intertidal zone and monitored intensively for 4 months in order to examine fortnightly and seasonal (calm weather and storm season) sedimentation and erosion. Longer term (100 years) sedimentation and preservation were investigated through examination of cores and trenches. Two different vertical grouping patterns of tidal bedding were distinguished with thinner and thicker sandy laminae. The number of sand‐dominated layers and individual muddy and sandy lamina in the cores were compared with theoretically derived sedimentation rates in order to assess long‐term preservation potential. Waves, especially high storm waves, have a significant influence on sedimentation and the preservation of intertidal deposits along the open‐coast tidal flat. Monitoring during one season indicated that the sand‐dominated layer was directly related to storm deposits, while the mud‐dominated layer was deposited during calm weather conditions. The variation in sandy lamina thickness was not related to spring–neap tidal cycles during the monitoring period. The assumption of 100% preservation of sandy laminae deposited during every tidal cycle, which has been assumed in previous time‐series analyses for the identification of palaeotidal periodicity, was found to be unrealistic along this open‐coast tidal flat. Preservation potential decreases as temporal scale increases. During one neap–spring tidal cycle, the preservation potential of individual sandy and muddy laminae was of the order of 10%. Over a period of 100 years, the estimated preservation potential of individual laminae, including both calm weather and storm deposits, decreased to 0·2%. The 100‐year preservation potential of storm‐induced, sand‐dominated layers was estimated to be of the order of 10%.

Formation of lamina-specific synaptic connections

In many parts of the vertebrate central nervous system, inputs of distinct types confine their synapses to individual laminae. Such laminar specificity is a major determinant of synaptic specificity. Recent studies of several laminated structures have begun to identify some of the cells (such as guidepost neurons in hippocampus), molecules (such as N-cadherin in optic tectum, semaphorin/collapsin in spinal cord, and ephrins in cerebral cortex), and mechanisms (such as activity-dependent refinement in lateral geniculate) that combine to generate laminar specificity.

Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves

Conventional high resolution studies of varved sediments are able to identify clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provides us with the highest potential resolution from the sedimentary record and can be resolved using scanning electron microscopy (SEM). Six case studies from lacustrine and marine settings are presented to illustrate the combination of clastic and biogenic fabric types typically found in laminated sediments. Clastic laminae fabrics include those which originate through grain settling and those which are ‘event deposits’. The correct identification of event deposits is essential if varves are to be used chronologically. SEM-based biogenic laminae fabric studies have identified seasonal faunal successions where individual laminae may be less than 100 μ thick and most recently, deep chlorophyll maxima (DCM) summer diatom floras, providing an insight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual variability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation.

Analytical Solutions for Partitioned Diffusion in Laminates: II. Harmonic Forcing Conditions

The migration of organic compounds in stratified media is of fundamental concern in environmental and chemical engineering research. The diffusive transport of volatile organic compounds through laminate systems is characterized by partitioning, i.e., the development of concentration discontinuities at the interfaces between the individual laminae. If the transport is governed by cyclic transients, the relevant equations can be written in terms of coupled systems of diffusion equations subject to sinusoidal boundary conditions. This paper solves these systems of equations to present new algebraic solutions for propagation of the sinusoidal modes through arbitrary (finite) numbers of contiguous one-dimensional laminae. Both Cartesian and radial coordinate systems are considered. Two independent formulations of the lamina interface matching conditions are considered, corresponding to (1) an instantaneous partitioning model and to (2) a mass-limited partitioning model. It is shown that sinusoidal components of the concentration solutions propagate dispersively throughout the laminates. This is manifested, for example, in changes in shape of concentration pulses as measured at different points in the laminate system. Algorithms for generating exact dispersion relations for partitioning laminates are given, and an experimental technique for studying interfacial dynamics via frequency domain measurements is proposed.

Organic geochemistry in Pennsylvanian tidally influenced sediments from SW Indiana

Tidal rhythmites are vertically stacked small-scale sedimentary structures that record daily variations in tidal current energy and are known to overlie some low-sulfur coals in the Illinois Basin. Tidal rhythmites from the Pennsylvanian Brazil Formation in Indiana have been analyzed sedimentologically, petrographically, and geochemically in order to understand the character and distribution of organic matter (OM) preserved in an environment of daily interactions between marine and fresh waters. The concentration of organic matter (TOC) ranges from traces to 6.9% and sulfur rarely exceeds 0.1% in individual laminae. Angular vitrinite is the major organic matter type, accounting for 50–90% of total OM. The C/S ratio decreases as the vertical distance from the underlying coal increases. A decreasing C/S ratio coupled with decreases in Pr/Ph, Pr/ n-C17, Ph/ n-C18 ratios and a shift of carbon isotopic composition towards less negative values suggest an increase in salinity from freshwater in the mudflat tidal rhythmite facies close to the coal to brackish/marine in the sandflat tidal rhythmite facies further above from the coal. Within an interval spanning one year of deposition, TOC and S values show monthly variability. On a daily scale, TOC and S oscillations are still detectable but they are of lower magnitude than on a monthly scale. These small-scale variations are believed to reflect oscillations in water salinity related to tidal cycles.

Preliminary studies in the processing and characterization of Al2O3/SnO2 laminated composites

All oxide composites (reinforcement and matrix both being oxides) exhibit high temperature oxidation resistance in addition to high strength and hardness. A major drawback of these materials is that the oxide fiber and oxide matrix tend to react, which strengthens the interface and therefore drastically reduces the damage tolerance. To overcome this problem, a mechanically weak interphase material, which also serves as a diffusion barrier, is generally used. One such materials system is tin dioxide (SnO2) in alumina-based composites. Previous attempts to fabricate such alumina matrix composites have been unsuccessful due to the higher temperatures needed to densify Al2O3 coupled with the fact that SnO2 decomposes to SnO in reducing environments. SnO has a relatively low melting point (1125 °C). In this paper we report the successful fabrication of Al2O3/SnO2, laminated composites and some observations on microstructural and mechanical characterization of the laminates. As expected from the phase diagram, no chemical compound formation was observed between Al2O3 and SnO2 which means that no primary chemical bonding developed between individual laminae. TEM observations showed, however, a strong mechanical interlocking at the SnO2/Al2O3 interfaces. In spite of the relatively strong interfacial bond, cracks did deflect. Our microstructural studies showed that SnO2 served as a weak interphase material.

Mn- and Fe-rich black travertine shrubs; bacterially (and nanobacterially) induced precipitates

ABSTRACT Black shrubs (i.e., arborescent forms) are present within hot-water travertine deposits from Morocco. The shrubs are commonly a few centimeters high and laterally grouped along individual laminae. Other than in mineral composition, the black shrubs closely resemble the calcite shrubs from other hot-water travertine deposits (e.g., Bagni di Tivoli, Italy, and Mammoth Hot Springs, Yellowstone National Park). They are composed of a variety of minerals that are Mn-rich and also have a significant Fe-oxide component. Similar Mn- and Fe-rich shrub-like forms have been described from desert varnish, deep-sea Mn nodules, and marine carbonates (Frutexites). SEM analyses show that bacterial bodies are densely packed within the Mn-rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae. The bacterial bodies range in shape and size from rods (commonly 0.8 m long by 0.1 m in diameter), to spherical forms (commonly 0.3 m in diameter) that form chains up to 1 m long, to nanobacterial spheres (150 to 200 nm in diameter) that make up densely packed chains commonly 15 m in length. It is well documented within the microbiological literature that, not only do bacteria have the ability to induce the precipitation of Mn and Fe, they can concentrate Mn in mineral precipitates from waters with very low to essentially undetectable concentrations of Mn. The black Mn-rich shrubs within the Moroccan travertines, other hot-water travertines, and related features such as desert varnish, deep-sea Mn nodules, and Frutexites are postulated to also be the result of bacterially induced precipitation.

Expression of brain-derived neurotrophic factor and apoptosis in the rat fetal brain following maternal stress

In many parts of the vertebrate central nervous system, inputs of distinct types confine their synapses to individual laminae. Such laminar specificity is a major determinant of synaptic specificity. Recent studies of several laminated structures have begun to identify some of the cells (such as guidepost neurons in hippocampus), molecules (such as N-cadherin in optic tectum, semaphorin/collapsin in spinal cord, and ephrins in cerebral cortex), and mechanisms (such as activity-dependent refinement in lateral geniculate) that combine to generate laminar specificity.

Material Characterization of Pultruded Laminates and Shapes

This paper discusses the material characterization of wide flange pultruded structural shapes (E-glass, Vinylester). The material was subjected to three loading conditions: tension, shear, and bending. Coupon samples were obtained from web and flanges of the I-section for tension and shear tests. Tensile properties were obtained from rectangular coupons with end tabs loaded in tension to failure. Shear properties were obtained from two different test methods: Iosipescu shear test method and torsion of rectangular samples. Experimentally determined material properties were compared to analytical predictions based on micro and macromechanics. Micromechanical models are used for the prediction of individual laminae (roving layers, continuous strand mat, nexus veils) properties. Classical lamination theory (CLT) is then used to predict the laminate properties. In addition, I-beams were tested in bending to evaluate their response and the experimental results were compared to predictions using Mechanics of Laminated Beams (MLB) approach. Results indicate a good correlation between experimental data and theoretical predictions, showing that the properties of pultruded composites can be predicted with sufficient accuracy. The superiority of the torsion test for determination of in-plane shear stiffness is demonstrated.

70 Million Years of Coastal Upwelling in California; Source Rocks and Paleoceanography: ABSTRACT

The Late Mesozoic-Cenozoic marine sequence of California displays a unique record of coastal upwelling and productivity in the form of distinctive diatomaceous and organic-rich deposits including the upper Cretaceous-lower Paleocene Moreno Formation, the Eocene Kreyenhagen Formation and the Miocene Monterey Formation. Unique sedimentological characteristics of these ancient upwelling systems include (a) Finely laminated biosiliceous-rich shales (>30% biogenic silica content), (b) Distinctive laminae composed by monospecific diatom resting spores, (c) Good source rock quality (>300 mg HC/mg org C), and (d) High accumulation rates in mid water anoxic conditions. Detailed study of individual laminae in sediments of these formations revealed concentration of monospecific diatom resting spores and an abundance of Stephanopyxis sp. and Coscinodiscus sp. Like Recent upwelling systems, preserved laminations of monospecific resting spores reflect strong seasonal upwelling that lead to high organic matter production and enhancement of anoxia. The presence of spores in the ancient and modern upwelling systems is evidence that diatoms have adapted and successfully competed in the highly productive California Margin since the Late Cretaceous. The Moreno, the Kreyenhagen and the Monterey Formation account for a significant portion of major petroleum source beds in California and contain an important record of coastal upwelling and paleoceanographic changemore » in the northeastern Pacific Ocean over the past 70 million years. It is suggested that potential Late Maestrichtian source rocks could have been deposited along other favorable upwelling areas of the Eastern Pacific Rim.« less

An assessment of failure criteria for fibrereinforced composite laminates

Abstract Failure criteria are often used to assess the structural integrity of laminated composite plates subjected to multiaxial loading conditions, and to determine which laminae within a laminate may fail. Although many such criteria are successful from the point of view of the numerical results obtained, the way in which they are formulated often leads to results that are physically incorrect. Two factors that may lead to difficulty are, first, criteria are often adapted from those used for isotropic materials and, second, individual laminae are usually taken to be homogeneous. The purpose of the present paper is to discuss these two problems and to suggest the form that a physically acceptable failure criterion should adopt. Results are compared with experimental failure loads in uniaxial tension on carbonfibre-reinforced epoxy laminates having different ply lay-up configurations.

LOCAL PHASE VELOCITY MEASUREMENTS IN PLATES

A method for measuring local phase velocities in panels, in the range 5–50 kHz, in the presence of a strongly reverberant field, and within 10 cm of structural discontinuities such as ribs, is described. The method gives a resolution of 1–2% and a 2–3% reproduceability. Measurements of the phase velocity as a function of direction for a three-ply and a 12-ply carbon-fibre composite plate are presented. Local values of the elastic properties of individual laminae in the plates, as a function of direction, are calculated from the phase velocities. Small variations in the lay-up angles of some of the laminae are also detected.

A Self-Sensing Piezolaminated Actuator Model for Shells Using a First Order Shear Deformation Theory

A composite piezolaminated shallow thin shell theory has been developed in which the individual laminae are capable of electromechanical transduction. Utilizing a first order shear deformation approximation and assuming that an electrical field may be applied only across the thickness of a given lamina, the resulting shell theory shows that piezolaminae are capable of exciting and sensing bending, torsion, inplane shearing, and inplane stretching. Piezolaminae are shown to be incapable of exciting and sensing transverse shear unless a three-dimensional electrical field is applied. Inplane shearing and torsion transduction only becomes possible when the dominant rolling axis of a given piezolamina is skewed such as not to coincide with a principal geometric axis. Constitutive relationships are derived which describe how each piezolamina may function simultaneously as both a sensor and an actuator. Two-dimensional piezoelectric field functions are introduced which describe how nonuniformly distributed electromechanical transduction will affect the nature of the applied excitation and acquired measurement. The equations of motion are also given for a shell in which transverse shear deformation is neglected according to Love's first approximation.

Geochemical and sedimentologic variations in inter-annually laminated sediments from Santa Monica Basin

Laminated sediments were recently discovered in the center of Santa Monica Basin, California Continental Borderland and extend from the present day to at least the Little Ice Age (ca. 1600 A.D.). Unlike the annual varves observed in Santa Barbara Basin, the light-dark lamination couplets observed in 210Pb-dated cores from the center of Santa Monica Basin occur at 3 to 6 year intervals, very similar in length to the El Niño Southern Oscillation (ENSO) phenomena. The mechanisms that control the temporal patterns of laminations in this basin are unknown. Potential causal mechanisms of lamination formation in Santa Monica Basin include: (1) changes in the flux of terrigenous vs. marine organic carbon and detritus; (2) surface water processes which affect marine productivity and organic carbon flux to the sediments; and (3) deep water processes which affect oxygen renewal and preservation of organic matter within the basin. A box core from the central portion of Santa Monica Basin was analyzed using a suite of geochemical, sedimentary, and micropaleontologic techniques in order to: (a) investigate which, if any, of these mechanisms has contributed to the occurrence of laminations; and (b) reconstruct proxy records of climate change. Samples were extracted from this core at 1 mm increments and provide a temporal resolution of 1–3 years per sample, a resolution which is comparable in length to the thickness of individual laminae within the core. Geochemical and micropaleontologic analyses of core samples provide paleoclimatic and paleoceanographic records which are comparable to, and extend beyond, historical regional and global climate records. In addition to direct comparisons between these records, spectral analysis was used to investigate whether there were similar patterns of variability that would implicate dominant forcing functions in the historic and proxy records. Herein we present preliminary results of records from ca. 1860 to the present. Our results suggest that organic carbon fluxes are the dominant factors that affect lamination variability. Input of organic carbon is primarily a function of primary productivity, and, to a lesser extent, a function of percentage of terrestrial input. Thus, (1) and (2) are both mechanisms of lamination formation. Stability of (3) only allows preservation of the record of these variations. Variations in Southern California rainfall appear to be linked to decadal-scale variations in downcore density profiles, and thus cause variations in the thickness and character of the laminations in the deepest portions of this basin. Thus, filtered density records can be used to reconstruct general paleo-rainfall trends which compare well with historic rainfall records. Variations in the isotopic composition of total organic carbon (TOC) are compared to historic ENSO and climate records and primarily reflect changes in the relative contribution of marine organic carbon to the basin. Variations in the carbon isotopic composition of N. pachyderma mirror changes in the sedimentary δ 13C TOC record from Santa Monica Basin, and suggest that primary productivity is the primary control on the flux of organic carbon to the sediments and exerts a strong influence on the interannual variability in lamination composition. Variations in paleo-sea surface temperatures generated from the oxygen isotopic composition of N. pachyderma correlate well with historical SST records and suggest potential usage as a proxy for general paleoSST patterns. Oxygen-sensitive assemblages of benthic foraminifera ( Bolivina argentea and B. spissa) have been used to identify potential large-scale flushing events and construct a historical record of variations in deep water oxygen levels. Spectral analysis of regional historic records indicate dominance of short-term (ENSO-length) and long-term (decadal) patterns of climate variability. The short-term ENSO signal is not dominant in the Santa Monica proxy records. However, strong decadal-length signals are identified in all of the proxy records and suggest that the dominant forcing mechanisms in Santa Monica Basin may be decadal in length.