scholarly journals Transport and modification of glaciovolcanic glass from source to sink on Mars

2015 ◽  
Vol 95 (2) ◽  
pp. 171-182 ◽  
Author(s):  
S.J. de Vet
Keyword(s):  
Volcanic Glass ◽  
High Energy ◽  
Microbial Interactions ◽  
Geologic History ◽  
Physical Weathering ◽  
Spectral Signatures ◽  
Source To Sink ◽  
Aeolian Sediments ◽  
Transport Cycle ◽  
Alteration Processes

AbstractSpectral observations show that volcanic glass is the dominant ingredient of the aeolian landforms which cover the northern lowlands on Mars. Surface winds subject these sands to physical alteration processes in the present-day surface environment. This work highlights the role of glaciovolcanism throughout Mars’ geologic history and the parallels with landforms and materials found in Iceland. As the physical properties of Martian volcanic glass particles are difficult to constrain from orbit, Icelandic materials can provide valuable insights in their transport and modification characteristics. The processing of glass grains by environmental processes by means of the dune transport cycle is discussed. Experiments targeted the grain-size alteration effects experienced during the dune transport cycle, including the effect of ‘low-energy’ avalanching and ‘high-energy’ aeolian regimes (i.e. particle rolling and saltation). Saltation transport was found to rapidly alter grains and particle size distributions, which contributes to a positive feedback loop where the new smaller grains are mobilised more easily after fracturing and surficial abrasion. Post-depositional physical alteration therefore needs to be reconciled with the present-day silicic spectral signatures of these glasses in order to infer the relevant landform genetic. This effort is especially relevant in respect to the loss of possible signatures of biochemical alteration from microbial interactions, as glaciovolcanic environments are favourable habitats for life. As chemical and physical weathering is limited to the grain exterior, the grain interior may still retain a geochemical record of the subglacial eruption environment in which these grains were formed. Quantification of the volatiles sequestered in the glass can therefore be used to identify the formative conditions of the amorphous component in aeolian sediments.

scholarly journals Local structures of Zr in impact-related natural glass probed by XAFS

2014 ◽  
Vol 70 (a1) ◽  
pp. C1531-C1531
Author(s):  
Tsubasa Tobase ◽  
Akira Yoshiasa ◽  
Ling Wang ◽  
Hidetomo Hongu ◽  
Tatsuya Hiratoko ◽  
...  
Keyword(s):  
Local Structure ◽  
High Energy Physics ◽  
National Laboratory ◽  
Glass Structure ◽  
Volcanic Glass ◽  
High Energy ◽  
Local Structures ◽  
Geological Processes ◽  
The Earth ◽  
Volcanic Glasses

The local structures of tektites and natural glasses were studied by Zr K-edge XANES and EXAFS in order to provide quantitative data on bonding distances and coordination numbers. The XAFS measurements were performed at the beam line BL-NW10A of the PF-AR in National Laboratory for High Energy Physics (KEK), Tsukuba, Japan. Zr4+ ion in tektite has different kinds of coordination environment. Various natural glasses are formed under different physical conditions. Impact-related glass, fulgurite and volcanic glasses are typical natural glasses. Upon a devastating impact of a giant meteoroid on the Earth, particles of the Earth's surface were melted and catapulted into outer space, where they finally solidified and fell back to the Earth. Tektites should be formed by this series of processes [1]. Tektite has special local structure of Ca[2]. Glass structure is affected by the pressure and temperature conditions during the glass formation and quenching process. This study indicated that different formation process of natural glasses gives different local structure of zirconium ions. The Zr K-edge XANES spectra of tektite have the double post-edge peaks with different heights. The volcanic glasses and other impact-related glasses such as impactite possessed more simple XANES patterns. The average coordination number of Zr4+ in darwin glass, LDG, volcanic glass and tektite are between 6 and 7. The eight-coordinated Zr4+ shows different XAFS pattern in suevite and köfelsite. All tektites are classified in same type. According to EXAFS measurements, Zr-O distances in tektites are 2.198 – 2.215Å and XANES spectra of tektites have similar shape. It indicates that tektites have similar Zr local structure with 7-fold coordination Zr ions. Impact-related glasses are classified to different types. Volcanic glasses are classified to same types. Impact glasses are formed under different geological processes at impact event and are experienced different physical environments.

Spectrally Resolved Cathodoluminescence (SRCL) of Hydrothermal ZnO crystals

2005 ◽  
Vol 878 ◽  
Author(s):  
J. Mass ◽  
M. Avella ◽  
J. Jiménez ◽  
M. Callahan ◽  
E. Grant ◽  
...  
Keyword(s):  
High Energy ◽  
Luminescence Spectra ◽  
Growth Sector ◽  
High Energy Part ◽  
Spectral Signatures ◽  
Energy Part ◽  
Good Crystalline Quality ◽  
Recombination Centers ◽  
Band Tailing ◽  
Spectrally Resolved

AbstractLarge hydrothermal ZnO crystals were grown using 3N NaOH, 1N KOH and 0.5N Li2CO3mineralizer. The crystals were studied by cathodoluminescence (CL), showing a good crystalline quality. Different growth regions were identified by CL imaging. These regions were characterized by their corresponding luminescence spectra, showing that the incorporation of impurities and non radiative recombination centers depend on the growth sector. The surface is shown to introduce band tailing modifying the high energy part of the spectrum. The main spectral signatures of each sector are discussed.

scholarly journals GAMMA-RAY BURSTS — OBSERVATIONS

2010 ◽  
Vol 19 (06) ◽  
pp. 977-984
Author(s):  
N. GEHRELS ◽  
J. K. CANNIZZO
Keyword(s):  
Gamma Ray ◽  
Optical Emission ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Medium Energy ◽  
Host Galaxies ◽  
Data Set ◽  
Spectral Signatures ◽  
High Energy Emission ◽  
Combined Data

We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. The Fermi observatory is observing 250 bursts per year with its medium-energy GRB instrument and about 10 bursts per year with its high-energy LAT instrument. In addition, rapid-response telescopes on the ground are providing new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and high-energy emission.

A Study of Paleosols in the Saskatoon Area of Saskatchewan

1974 ◽  
Vol 11 (7) ◽  
pp. 905-915 ◽  
Author(s):  
L. W. Turchenek ◽  
R. J. St. Arnaud ◽  
E. A. Christiansen
Keyword(s):  
Classification Criteria ◽  
Soil Profiles ◽  
Climatic Fluctuations ◽  
Radiocarbon Dates ◽  
Dune Sands ◽  
Aeolian Sediments ◽  
Alteration Processes ◽  
Buried Soil ◽  
Aeolian Sands

Postglacial paleosols developed in lacustrine and aeolian sediments occur on terraces and in banks of the South Saskatchewan River near Saskatoon. At each of three sites a sequence of two paleosols was studied: a lower soil of immediate postglacial age as indicated by radiocarbon dates, that is buried by aeolian sands, and an upper one, located within the dune sands, that marks a period of stability of the dunes. Climatic fluctuations are inferred to be the cause of aeolian activity.One paleosol met the classification criteria for an Orthic Black Chernozemic soil. The other soils, particularly those developed in the dune sands, were weakly developed, Regosolic types of soils.Pedogenic interpretations were based on macro- and micromorphological observations as well as chemical characteristics. Micromorphology and the determination of calcite and dolomite distribution were particularly useful in differentiating sedimentary, pedogenic, and postburial alteration processes in the buried soil profiles. Studies of the organic matter suggest that it had changed markedly after burial.

The Role of Case Hardening in the Preservation of the Cavates and Petroglyphs of Bandelier

MRS Advances ◽  
2017 ◽  
Vol 2 (37-38) ◽  
pp. 1969-2005
Author(s):  
Douglas Porter ◽  
David Broxton ◽  
Angelyn Bass ◽  
Deborah A. Neher ◽  
Thomas R. Weicht ◽  
...  
Keyword(s):  
Pore Space ◽  
Volcanic Glass ◽  
Case Hardening ◽  
Textile Production ◽  
Near Surface ◽  
Secondary Minerals ◽  
National Monument ◽  
Alteration Processes ◽  
Bandelier National Monument ◽  
Unconsolidated Rock

ABSTRACTBandelier National Monument (BNM) was created to protect an extraordinary inventory of archaeological resources carved in the Tshirege Member of the Bandelier Tuff. These include more than one thousand excavated chambers, called cavates, used for dwelling, storage, and textile production. The glass-rich tuffs at the base of the Tshirege Member are poorly consolidated and susceptible to erosion by wind, rain, and mechanical abrasion, with resultant loss of cultural material. However, rock surfaces develop protective weathering rinds that are resistant to erosion. Using optical microscopy, SEM-EDS, XRD, and electron microprobe analysis, we determined that this rind consists of clay and silt sediments colonized by lichens and other surface biota, accompanied by the precipitation of secondary minerals in the near-surface pore space. Scoping experiments focused on glass-organic acid interactions indicate that oxalic acid excreted by microbial crust constituents catalyzes biogeochemical reactions that lead to the preferential dissolution of Si, Al, and Fe components of the volcanic glass; these cations become available for precipitation of opal, and smectite and sepiolite clays. Enzyme assays that quantify biological activity at outcrop surfaces indicate that microbial populations initially thrive as they derive nutrients from the dissolution reactions of the glass, but activity starts to decline as precipitation of secondary minerals limits access to new sources of nutrients, so that alteration processes are self-limiting. As case hardening progresses, imbibition rates at the surface decrease, and the erosion resistance of the altered surfaces is substantially improved. This article presents summary results of research conducted over a period of five years to characterize the roles of lichens and other microflora in rind formation, and the resulting contributions to tuff stability. The interaction of lichens and other microflora with rock surfaces in archaeological sites and monuments is usually explored in terms of biodeterioration and consequent damage. However, this study shows that, under some circumstances, lichens and microflora provide a level of erosion protection to relatively porous and unconsolidated rock strata that outweighs their biodeteriorative effects.

scholarly journals Vitamin and Amino Acid Auxotrophy in Anaerobic Consortia Operating under Methanogenic Conditions

mSystems ◽  
2017 ◽  
Vol 2 (5) ◽  
Author(s):  
Valerie Hubalek ◽  
Moritz Buck ◽  
BoonFei Tan ◽  
Julia Foght ◽  
Annelie Wendeberg ◽  
...  
Keyword(s):  
Energy Conservation ◽  
Public Good ◽  
Microbial Communities ◽  
Energy Demand ◽  
High Energy ◽  
Microbial Interactions ◽  
Chemical Transformations ◽  
Pollutant Degradation ◽  
Toxic Compounds ◽  
And Function

ABSTRACT Microbial interactions between Archaea and Bacteria mediate many important chemical transformations in the biosphere from degrading abundant polymers to synthesis of toxic compounds. Two of the most pressing issues in microbial interactions are how consortia are established and how we can modulate these microbial communities to express desirable functions. Here, we propose that public goods (i.e., metabolites of high energy demand in biosynthesis) facilitate energy conservation for life under energy-limited conditions and determine the assembly and function of the consortia. Our report suggests that an understanding of public good dynamics could result in new ways to improve microbial pollutant degradation in anaerobic systems. Syntrophy among Archaea and Bacteria facilitates the anaerobic degradation of organic compounds to CH4 and CO2. Particularly during aliphatic and aromatic hydrocarbon mineralization, as in the case of crude oil reservoirs and petroleum-contaminated sediments, metabolic interactions between obligate mutualistic microbial partners are of central importance. Using micromanipulation combined with shotgun metagenomic approaches, we describe the genomes of complex consortia within short-chain alkane-degrading cultures operating under methanogenic conditions. Metabolic reconstruction revealed that only a small fraction of genes in the metagenome-assembled genomes encode the capacity for fermentation of alkanes facilitated by energy conservation linked to H2 metabolism. Instead, the presence of inferred lifestyles based on scavenging anabolic products and intermediate fermentation products derived from detrital biomass was a common feature. Additionally, inferred auxotrophy for vitamins and amino acids suggests that the hydrocarbon-degrading microbial assemblages are structured and maintained by multiple interactions beyond the canonical H2-producing and syntrophic alkane degrader-methanogen partnership. Compared to previous work, our report points to a higher order of complexity in microbial consortia engaged in anaerobic hydrocarbon transformation. IMPORTANCE Microbial interactions between Archaea and Bacteria mediate many important chemical transformations in the biosphere from degrading abundant polymers to synthesis of toxic compounds. Two of the most pressing issues in microbial interactions are how consortia are established and how we can modulate these microbial communities to express desirable functions. Here, we propose that public goods (i.e., metabolites of high energy demand in biosynthesis) facilitate energy conservation for life under energy-limited conditions and determine the assembly and function of the consortia. Our report suggests that an understanding of public good dynamics could result in new ways to improve microbial pollutant degradation in anaerobic systems.

scholarly journals Sedimentary Petrographic Study of Tephra, Glacial and Aeolian Grains in a Quaternary Paleosol Sequence on Mount Kenya, East Africa William

2007 ◽  
Vol 42 (2) ◽  
pp. 137-146
Author(s):  
William C. Mahaney ◽  
Walter Vortisch ◽  
Klaus Fecher
Keyword(s):  
East Africa ◽  
Volcanic Glass ◽  
Aeolian Sediments ◽  
Petrographic Study

ABSTRACT Tephra, aeolian and glacial grains in a lithostratigraphic-paleosol sequence on Mount Kenya were studied to determine if their pétrographie properties would provide evidence for different paleoenvironments over the period of - 100,000 to - 500,000 yr BP. Till containing high quantities of ferromagnetic minerals alternate in the sequence with aeolian sediments and tephras containing an abundance of volcanic glass, quartz, and feldspars with variable degrees of etching. Quartz, an allochthonous mineral on Mount Kenya, appears to have an aeolian origin followed by ice transport which produced glacially-crushed surfaces. A comparison of weathering products in the two paleosols leads to the conclusion that precipitation-drainage conditions were quite different during the formation of these inter-glacial paleosols.

Impact during the proterozoic era possibly inundated the earth with phosphorus

2009 ◽  
Vol 8 (3) ◽  
pp. 187-191 ◽  
Author(s):  
M.S. Sisodia
Keyword(s):  
High Energy ◽  
Chemical Energy ◽  
Post Mortem ◽  
Mass Extinctions ◽  
Geologic History ◽  
The Earth ◽  
Aravalli Supergroup ◽  
Phosphate Deposit ◽  
Event Triggered

AbstractThe stromatolites of the Precambrian Aravalli Supergroup outcropping around Udaipur, Rajasthan, India are classified into two distinct lithofacies: the older carbonate stromatolites facies and the younger phosphate-bearing stromatolite facies. Phosphate-bearing stromatolites of the same age have been reported from China, Russia and Australia. The phosphate-bearing stromatolites of Udaipur show fossil cyanobacteria. These cyanobacteria grew luxuriantly in the absence of any competitors and accumulated abnormal amounts of phosphorus from the novo phosphorus-rich environment, eventually forming a workable phosphate deposit owing to their post-mortem alteration. There is a sharp and abrupt contact between the two facies. This sharp contact or diastem underlying the phosphate-bearing stromatolites is of extreme importance as it denotes a stratigraphic hiatus characterizing a period of overall change in the environment. This change could be due to some catastrophic episode. The Earth during its geologic history has been subjected to several such episodes caused by certain high-energy events, such as impacts by extraterrestrial bodies. These impacts caused mass extinctions as occurred at the Permian–Triassic or Cretaceous–Tertiary boundary or the emergence of new flora and fauna as occurred at the Precambrian–Cambrian boundary. It is therefore argued that the diastem noted between carbonate and phosphate-bearing stromatolites is possibly due to an impact that inundated the Earth with phosphorus. Phosphorus is a key constituent of proteins, which are the major repository of chemical energy for metabolism. Its abundance after this event triggered the emergence of new advanced species.

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