scholarly journals REMAINS OF PALEOFLORA IN THE BRECCIAS OF THE ONAPING FORMATION, SUDBURY IMPACT STRUCTURE, ONTARIO, CANADA

2021 ◽  
pp. 17-31
Author(s):  
E.P. Gurov ◽  
V.V. Permiakov ◽  
B.M. French
Keyword(s):  
Plant Residues ◽  
Algal Flora ◽  
Impact Structure ◽  
Electron Microscopic ◽  
Fine Grained ◽  
Plant Detritus ◽  
Sudbury Structure ◽  
Plant Remains ◽  
The Matrix ◽  
The Impact

Electron microscopic investigations of four breccia samples of the Onaping Formation, Sudbury impact structure, Canada, have been carried out for the search of possible remains of paleoflora and identification of the nature of organic matter and their composition. Two forms of plant remains were discovered in the breccias. The first form is represented by single plant particles scattered in the matrix of breccias and included in gas vesicles in devitrified glasses. These particles are leaf-shaped, stem-shaped, tubular, and spherical objects, ranging from 5-10 to 200-300 µm in size. It is supposed that algal flora inhabiting the sea basin before the Sudbury impact was the source of this form of plant residues in breccias. The second form of plant remains in breccias is represented by plant detritus in carbon-bearing fragments of mudstones included in the breccia matrix. These fragments, reaching a size to 1000-1200 µm, have irregular shapes and complicated rugged contacts with the host breccia. Plant residues in mudstones are mainly ribbon-like scraps from 3-5 to 200-300 µm long, some while rare particles have a more complex shape. The matrix of the mudstones is a heterogeneous fine-grained clay-like substance with a network of micron-wide open joint fissures. The carbon content in mudstone matrix ranges from 7-10 to 20-25 wt%. Muddy bottom sediments of the pre-impact sea basin are supposed to be a source of mudstone fragments in breccias, while the algal flora inhabited the sea during their sedimentation served as a source of plant detritus in mudstones.  Fragments of mudstones and floral residues are an important source of organic carbon in breccias of the Onaping Formation. The discovery of paleofloral remains in the breccias indicates the existence of a previously unknown complex algal flora that inhabited the pre-impact sea before the impact event 1.85 billion years ago at the very end of the Paleoproterozoic. The Sudbury impact structure is comparable in size to the Chicxulub impact structure, the formation of which caused the Cretaceous-Paleogene mass extinction.  We assume that the formation of the Sudbury structure had a catastrophic impact on the paleoflora of the late Paleoproterozoic, the remnants of which were preserved in the breccias of the Onaping Formation.

Distinguishing shock-related microstructures in gneisses from the Vredefort impact structure, South Africa

2021 ◽  
Author(s):  
Fabian Dellefant ◽  
Claudia Trepmann ◽  
Stuart Gilder ◽  
Iuliia Sleptsova ◽  
Melanie Kaliwoda ◽  
...  
Keyword(s):  
South Africa ◽  
Magnetic Properties ◽  
Frictional Heating ◽  
Rapid Quenching ◽  
Impact Structure ◽  
Impact Event ◽  
Lightning Strikes ◽  
Fine Grained ◽  
The Impact ◽  
Drill Cores

<p>Shocked gneiss (~8 GPa) from the Vredefort impact structure (South Africa) contain planar fractures in quartz decorated by magnetite and ilmenite, which are commonly attributed to the impact event. However, the surface at Vredefort is riddled by lightning strikes, which also produce rapid pressure-temperature pulses that can modify the microstructure and the magnetic properties of the rocks. To understand the differences between lightning and impact-related shock effects, we investigated samples from two, 10 m-deep drill cores by Raman spectroscopy, polarized light microscopy/U-stage and electron microscopy/electron backscatter diffraction techniques. Magnetite and ilmenite within planar fractures in quartz occur at all depths, and are therefore intrinsic to the impact event, independent of lightning. Primary iron-bearing minerals were locally heated by the generation of shear fractures in neighboring quartz, leading to small volumes (micrometer scales) of melt intruding into nearby fractures. Frictional heating and rapid quenching of feldspar and quartz is indicated by localized, fine-grained aggregates along intragranular planar fractures as well as transgranular pseudotachylytic veins. On the other hand, altered ilmenite grains with exsolved magnetite occur only in gneisses from the uppermost 80 cm of both drill cores. When in contact with biotite, the ilmenite-magnetite boundaries are altered to chlorite, and the ilmenite is partly transformed to anatase. These alteration products contain fine-grained magnetite. It appears that lightning strikes altered the existing ilmenite-magnetite in the Vredefort samples to produce smaller, more single-domain like magnetite grains, consistent with the observed magnetic properties of the samples</p>

Twinned calcite within polymict impact breccias from the Nördlinger Ries impact structure, Germany – shock effects and post-shock annealing

2021 ◽  
Author(s):  
Lina Seybold ◽  
Claudia A. Trepmann ◽  
Stefan Hölzl ◽  
Melanie Kaliwoda
Keyword(s):  
Grain Boundaries ◽  
Second Generation ◽  
High Stress ◽  
High Density ◽  
Impact Structure ◽  
Electron Microscopic ◽  
Fine Grained ◽  
Calcite Veins ◽  
Post Shock ◽  
Scanning Electron

<p>Approximately one third of the worlds known impact structures are formed in carbonate-bearing target rocks. However, the response of their main constituent mineral, calcite, upon shock loading and unloading is still not well understood. Mechanical twins in calcite are described from natural impactites and shock experiments, yet, reliable indicators to distinguish these shock effects from the very common calcite twins generated in tectonites are missing. Here, we present scanning electron microscopic investigations of twinned calcite within calcite cemented brecciated gneisses from the Ries impact structure.</p><p>Calcite cemented brecciated gneisses occur at several outcrops of the Ries impact structure as well as in samples recovered from depth as low as 977 m in the research drilling 1973. At Maihingen, the polymict impact breccias contain shocked gneiss fragments and various generations of calcite in veins. The occurrence of rhombohedral PDFs in quartz from the gneiss fragments indicates shock conditions of >10 GPa. Coarse calcite grains, representing an early generation of calcite in the veins, show exceptionally fine-lamellar twins, indicating high stress and strain rates. The calcite twins show widths of < 0.5 µm, a high density of up to a few hundred lamellae per mm, and appear to crosscut each other, which has been suggested as a criterion for shock-induced twinning. Furthermore, a high density of sets of planar features occur associated and parallel to these twins, but along which no twin domains were resolved in the scanning electron microscope. Twin systems detected by EBSD measurements include e-twins, common also in calcite from tectonites, and another more rarely occurring twin system, characterized by a rotation axes parallel to <-2110> and a rotation angle of ca. 35°. A second generation of calcite without twins is represented by elongate palisade calcite, fine-grained aggregates and rims forming sutured grain boundaries surrounding twinned coarse calcite grains. EDS measurements show that these calcite grains contain up to 2.5 % Fe as well as traces of Mn, Mg, Si, Na and Al. In contrast, the coarse twinned calcite is almost pure CaCO<sub>3</sub>. Whereas the fine-grained aggregates and sutured grain boundaries indicate recrystallization, the palisade grains indicate precipitation from the pore fluid.</p><p>The twinned coarse calcite grains within the polymict impact breccias are interpreted to be shock induced. As coarse calcitic sedimentary target rocks are not known from the Ries area, they can either represent pre-shock calcite veins within the gneisses or possibly marbles that were brecciated together with shocked gneisses during impact cratering. The second generation of calcite represents post-shock recrystallization and precipitation from a fluid.</p>

Meteorite traces on a shatter cone surface from the Agoudal impact site, Morocco

2015 ◽  
Vol 152 (4) ◽  
pp. 751-757 ◽  
Author(s):  
M. SCHMIEDER ◽  
H. CHENNAOUI AOUDJEHANE ◽  
E. BUCHNER ◽  
E. TOHVER
Keyword(s):  
Iron Meteorite ◽  
Impact Structure ◽  
Iron Meteorites ◽  
Electron Microscopic ◽  
Impact Site ◽  
Scanning Electron Microscopic Study ◽  
Scanning Electron Microscopic ◽  
Cone Surface ◽  
Shatter Cones ◽  
The Impact

AbstractThe recently discovered Agoudal impact site in Morocco is a small, eroded impact structure with well-developed shatter cones. A scanning electron microscopic study of a shatter cone surface has revealed the presence of schreibersite – a phosphide very rare on Earth but common in iron meteorites – and Fe–Ni oxides. This is the first reported evidence for primary meteoritic matter adherent to shatter cones and suggests that the Agoudal crater was formed by the impact of an iron meteorite, probably the Agoudal IIAB iron. Shatter cones from other terrestrial impact structures might also hold valuable information about the nature of the impacting projectiles.

Effect of Carbon Fibre Ratio to the Impact Properties of Hybrid Kenaf/Carbon Fibre Reinforced Epoxy Composites

2013 ◽  
Vol 393 ◽  
pp. 136-139 ◽  
Author(s):  
Mimi Azlina Abu Bakar ◽  
Sahrim Ahmad ◽  
Wahyu Kuntjoro ◽  
Salmiah Kasolang
Keyword(s):  
Carbon Fibre ◽  
Hybrid Composites ◽  
Epoxy Composites ◽  
Resin Matrix ◽  
Fibre Reinforcement ◽  
Carbon Fibres ◽  
Electron Microscopic ◽  
Impact Properties ◽  
The Matrix ◽  
The Impact

Effects of the incorporation of untreated and treated hybrid kenaf/carbon fibre reinforced epoxy composites on the impact properties were studied. Hybrid kenaf/carbon fibres and thermoset matrices were hand-laid up and characterized in terms of its mechanical properties. The kenaf fibres were alkali treated whilst the carbon fibres were gamma radiation treated before use as reinforcement in the epoxy resin matrix. The reinforcing effects of kenaf hybridized with carbon fibre in epoxy composites were evaluated at various fibre loadings with overall fibre contents 20 wt%. Hybrid composites with different ratios of kenaf fibre : carbon fibre ; 0.9:0.1, 0.8:0.2, 0.7:0.3 and 0.6:0.4 were prepared. Impact tests of untreated and treated hybrid kenaf/carbon fibres were performed. The fractured surfaces of these composites were investigated by using scanning electron microscopic technique (SEM) to determine the interfacial bonding between the matrix and the fibre reinforcement. It was found that the treated hybrid composites increased the impact strength by 26% compared to the untreated ones.

Determination of the phase structure of polymerblends by electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 492-493
Author(s):  
Dr. G. Kaemof
Keyword(s):  
Screw Extruder ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Single Screw Extruder ◽  
Transmission Electron ◽  
The Matrix ◽  
Twin Screw ◽  
Special Case ◽  
Microscopic Investigations

A mixture of polycarbonate (PC) and styrene-acrylonitrile-copolymer (SAN) represents a very good example for the efficiency of electron microscopic investigations concerning the determination of optimum production procedures for high grade product properties.The following parameters have been varied:components of charge (PC : SAN 50 : 50, 60 : 40, 70 : 30), kind of compounding machine (single screw extruder, twin screw extruder, discontinuous kneader), mass-temperature (lowest and highest possible temperature).The transmission electron microscopic investigations (TEM) were carried out on ultra thin sections, the PC-phase of which was selectively etched by triethylamine.The phase transition (matrix to disperse phase) does not occur - as might be expected - at a PC to SAN ratio of 50 : 50, but at a ratio of 65 : 35. Our results show that the matrix is preferably formed by the components with the lower melting viscosity (in this special case SAN), even at concentrations of less than 50 %.

TEM comparison of osmium vs osmium with potassium ferricyanide secondary fixatives and the impact of secondary fixative temperature on tissue preservation/contrast quality

1996 ◽  
Vol 54 ◽  
pp. 910-911
Author(s):  
J. W. Horn ◽  
B. J. Dovey-Hartman ◽  
V. P. Meador
Keyword(s):  
Osmium Tetroxide ◽  
Potassium Ferricyanide ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Microscopic Evaluation ◽  
Cacodylate Buffer ◽  
Transmission Electron Microscopic ◽  
Glutaraldehyde Solution ◽  
Temperature Impact ◽  
The Impact

Osmium tetroxide (OsO4) is a universally used secondary fixative for routine transmission electron microscopic evaluation of biological specimens. Use of OsO4 results in good ultrastructural preservation and electron density but several factors, such as concentration, length of exposure, and temperature, impact overall results. Potassium ferricyanide, an additive used primarily in combination with OsO4, has mainly been used to enhance the contrast of lipids, glycogen, cell membranes, and membranous organelles. The purpose of this project was to compare the secondary fixative solutions, OsO4 vs. OsO4 with potassium ferricyanide, and secondary fixative temperature for determining which combination gives optimal ultrastructural fixation and enhanced organelle staining/contrast.Fresh rat liver samples were diced to ∼1 mm3 blocks, placed into porous processing capsules/baskets, preserved in buffered 2% formaldehyde/2.5% glutaraldehyde solution, and rinsed with 0.12 M cacodylate buffer (pH 7.2). Tissue processing capsules were separated (3 capsules/secondary fixative.solution) and secondarily fixed (table) for 90 minutes. Tissues were buffer rinsed, dehydrated with ascending concentrations of ethanol solutions, infiltrated, and embedded in epoxy resin.

Impact Strength, Flexural Modulus and Wear Rate of PMMA Composites Reinforced by Eggshell Powders

2020 ◽  
Vol 38 (7A) ◽  
pp. 960-966
Author(s):  
Aseel M. Abdullah ◽  
Hussein Jaber ◽  
Hanaa A. Al-Kaisy
Keyword(s):  
Impact Strength ◽  
Wear Rate ◽  
Flexural Modulus ◽  
Matrix Material ◽  
Weight Fraction ◽  
Pure Pmma ◽  
Calcination Process ◽  
The Matrix ◽  
The Impact ◽  
Interface Bond

In the present study, the impact strength, flexural modulus, and wear rate of poly methyl methacrylate (PMMA) with eggshell powder (ESP) composites have been investigated. The PMMA used as a matrix material reinforced with ESP at two different states (including untreated eggshell powder (UTESP) and treated eggshell powder (TESP)). Both UTESP and TESP were mixed with PMMA at different weight fractions ranged from (1-5) wt.%. The results revealed that the mechanical properties of the PMMA/ESP composites were enhanced steadily with increasing eggshell contents. The samples with 5 wt.% of UTESP and TESP additions give the maximum values of impact strength, about twice the value of the pure PMMA sample. The calcination process of eggshells powders gives better properties of the PMMA samples compared with the UTESP at the same weight fraction due to improvements in the interface bond between the matrix and particles. The wear characteristics of the PMMA composites decrease by about 57% with increases the weight fraction of TESP up to 5 wt.%. The flexural modulus values are slightly enhanced by increasing of the ESP contents in the PMMA composites.

scholarly journals The Interactions between Polyphenols and Microorganisms, Especially Gut Microbiota

Antioxidants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 188
Author(s):  
Małgorzata Makarewicz ◽  
Iwona Drożdż ◽  
Tomasz Tarko ◽  
Aleksandra Duda-Chodak
Keyword(s):  
Intestinal Bacteria ◽  
Research Data ◽  
Bioactive Metabolites ◽  
Human Organism ◽  
Comprehensive Knowledge ◽  
Bidirectional Relationship ◽  
The Matrix ◽  
Intestinal Pathogens ◽  
The Impact

This review presents the comprehensive knowledge about the bidirectional relationship between polyphenols and the gut microbiome. The first part is related to polyphenols’ impacts on various microorganisms, especially bacteria, and their influence on intestinal pathogens. The research data on the mechanisms of polyphenol action were collected together and organized. The impact of various polyphenols groups on intestinal bacteria both on the whole “microbiota” and on particular species, including probiotics, are presented. Moreover, the impact of polyphenols present in food (bound to the matrix) was compared with the purified polyphenols (such as in dietary supplements) as well as polyphenols in the form of derivatives (such as glycosides) with those in the form of aglycones. The second part of the paper discusses in detail the mechanisms (pathways) and the role of bacterial biotransformation of the most important groups of polyphenols, including the production of bioactive metabolites with a significant impact on the human organism (both positive and negative).

scholarly journals Reliability Assessment of a Multi-State HVDC System by Combining Markov and Matrix-Based Methods

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3097
Author(s):  
Roberto Benato ◽  
Antonio Chiarelli ◽  
Sebastian Dambone Sessa
Keyword(s):  
Current System ◽  
Estimation Method ◽  
Reliability Estimation ◽  
Voltage Source ◽  
Voltage Source Converter ◽  
Hvdc System ◽  
Critical Elements ◽  
The Matrix ◽  
The Impact

The purpose of this paper is to highlight that, in order to assess the availability of different HVDC cable transmission systems, a more detailed characterization of the cable management significantly affects the availability estimation since the cable represents one of the most critical elements of such systems. The analyzed case study consists of a multi-terminal direct current system based on both line commutated converter and voltage source converter technologies in different configurations, whose availability is computed for different transmitted power capacities. For these analyses, the matrix-based reliability estimation method is exploited together with the Monte Carlo approach and the Markov state space one. This paper shows how reliability analysis requires a deep knowledge of the real installation conditions. The impact of these conditions on the reliability evaluation and the involved benefits are also presented.

scholarly journals Potential Impacts of Future Climate Change Scenarios on Ground Subsidence

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 219 ◽  
Author(s):  
Antonio-Juan Collados-Lara ◽  
David Pulido-Velazquez ◽  
Rosa María Mateos ◽  
Pablo Ezquerro
Keyword(s):  
Climate Change ◽  
Land Subsidence ◽  
Ground Subsidence ◽  
Lower Percentage ◽  
Future Climate Change ◽  
Climate Change Scenarios ◽  
Fine Grained ◽  
Fine Grained Material ◽  
The Impact

In this work, we developed a new method to assess the impact of climate change (CC) scenarios on land subsidence related to groundwater level depletion in detrital aquifers. The main goal of this work was to propose a parsimonious approach that could be applied for any case study. We also evaluated the methodology in a case study, the Vega de Granada aquifer (southern Spain). Historical subsidence rates were estimated using remote sensing techniques (differential interferometric synthetic aperture radar, DInSAR). Local CC scenarios were generated by applying a bias correction approach. An equifeasible ensemble of the generated projections from different climatic models was also proposed. A simple water balance approach was applied to assess CC impacts on lumped global drawdowns due to future potential rainfall recharge and pumping. CC impacts were propagated to drawdowns within piezometers by applying the global delta change observed with the lumped assessment. Regression models were employed to estimate the impacts of these drawdowns in terms of land subsidence, as well as to analyze the influence of the fine-grained material in the aquifer. The results showed that a more linear behavior was observed for the cases with lower percentage of fine-grained material. The mean increase of the maximum subsidence rates in the considered wells for the future horizon (2016–2045) and the Representative Concentration Pathway (RCP) scenario 8.5 was 54%. The main advantage of the proposed method is its applicability in cases with limited information. It is also appropriate for the study of wide areas to identify potential hot spots where more exhaustive analyses should be performed. The method will allow sustainable adaptation strategies in vulnerable areas during drought-critical periods to be assessed.

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