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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Current status of the impact theory for the terminal Cretaceous extinction

An iridium abundance anomaly at the Cretaceous/Tertiary (C/T) boundary has been disclosed at 36 sites throughout the globe. The impact of a large extraterrestrial object is now widely accepted as the best explanation of this anomaly. Au/Ir and Pt/Ir ratios from two C/T boundary clays indicate a type I carbonaceous chondrite composition for the impacting object, for which a sea floor impact with subsequent subduction has been calculated to have a 20 percent probability. The extinction's 'killing mechanism' has not yet been established, but both temperature changes and darkness due to atmospheric dust are probable contributors. In view of the rapid dispersal of dust in ballistic trajectories, the rapid settling of heavy, coagulated dust particles, the effects of darkness on phytoplankton, and plant records, it is suggested that darkness would have lasted a few months, rather than the originally hypothesized few years.

Alvarez, W.↗
NASA NTRS1984

Fault friction, regional stress, and crust-mantle coupling in southern California from finite element models

To determine the correct fault rheology of the Transverse Ranges area of California, a new finite element to represent faults and a mangle drag element are introduced into a set of 63 simulation models of anelastic crustal strain. It is shown that a slip rate weakening rheology for faults is not valid in California. Assuming that mantle drag effects on the crust's base are minimal, the optimal coefficient of friction in the seismogenic portion of the fault zones is 0.4-0.6 (less than Byerly's law assumed to apply elsewhere). Depending on how the southern California upper mantle seismic velocity anomaly is interpreted, model results are improved or degraded. It is found that the location of the mantle plate boundary is the most important secondary parameter, and that the best model is either a low-stress model (fault friction = 0.3) or a high-stress model (fault friction = 0.85), each of which has strong mantel drag. It is concluded that at least the fastest moving faults in southern California have a low friction coefficient (approximtely 0.3) because they contain low strength hydrated clay gouges throughout the low-temperature seismogenic zone.

Bird, P.↗
NASA NTRS1983

Luminescence induced by dehydration of kaolin - Association with electron-spin-active centers and with surface activity for dehydration-polymerization of glycine

Experimental data concerning emission of light upon dehydration as a function of preheating and pre-gamma-irradiation are correlated with reported studies of electron-spin resonance (ESR) activity after similar pretreatments. The effect of these pretreatments on the kaolin-promoted incorporation of glycine into peptide oligomers in a wet/cold, hot/dry fluctuating environment is compared to their effect on the ESR and luminescent signals. The existence of spectroscopically active centers appears to be loosely anticorrelated with reaction yield; these yields are increased by increasing the overall energy content of the material. It is concluded that some part of the chemical yield is produced by a mechanism involving intrinsic, excited electronic states of the clay crystal lattice. These states may be derived from thermally, interfacially, and/or mechanically induced charge reorganization within interspersed energy levels in the band structure of the material.

Coyne, L.↗
NASA NTRS1984

The prebiotic chemistry of nucleotides

Diminosuccinonitrile (DISN), formed by the oxidation of diaminomaleonitrile, has been investigated as a potential prebiotic phosphorylating agent. DISN affects the cyclization of 3'-adenosine monophosphate to adenosine 2',3'-cyclic phosphate in up to 39 percent yield. The mechanism of this reaction was investigated. The DISN-mediated phosphorylation of uridine to uridine monophosphate does not proceed efficiencly in aqueous solution. The reaction of DISN with uridine-5'-phosphate and uridine results in the formation of 2,2'-anhydronucleotides and 2,2'-anhydronucleosides respectively, and other reaction products resulting from an initial reaction at the 2'- and 3'-hydroxyl groups. The clay mineral catalysis of the cyclization of adenosine-3'-phosphate was investigated using homoionic montmorillonites.

Ferris, J. P.↗
NASA NTRS1984

Magnetic cristobalite (?) - A possible new magnetic phase produced by the thermal decomposition of nontronite

The effect of heat treatment for 1 h or more at 900-1000 C on the magnetic properties of nontronite, an iron-rich smectite clay thought to be an important component of Martian regolith, is investigated experimentally, extending the findings of Moskowitz and Hargraves (1982). The results are presented in graphs and tables and discussed. A phase with Curie temperature 200-220 C, remanent coercivity greater than 800 mT, and a type-2 room-temperature-coercivity response to thermomagnetic cycling is observed and attributed to an iron-substituted cristobalite which may form by topotactic growth from a smectite precursor.

Moskowitz, B. M.↗
NASA NTRS1984

Laboratory Investigations

The primary objectives were to examine the site-specific physical, chemical, and biological factors that impact construction, durability and performance of the proposed 5-MW (sub e) solar pond system at the Salton Sea. The interactions of the water, salt, and soil of the site and on material compatibility were examined. Potential interactions of the water/brine and soil are particularly important because the pond will utilize the naturally occurring clays as a bottom seal. Although there is a considerable and growing solar pond literature, little written information deals with the important site-specific investigations of water, salt, and soil. Therefore, technical effort was directed toward identifying the factors that should be investigated and determining methods of investigation. As a result, a by-product was the development of an approach for site-specific investigations and some specific methodologies. This development should continue in order to establish a generic approach for evaluating the suitability of any site for the construction of large-scale solar ponds.

Source record↗
NASA NTRS1985

Permafrost and Subsurface Ice in the Solar System

The properties and behavior of planetary permafrost are discussed with reference to the ability of such surfaces to sustain loads characteristics of spacecraft landing and planetary bases. In most occurrences, water ice is in close proximity to, or in contact with, finely divided silicate mineral matter. When ice contacts silicate mineral surfaces, a liquid-like, transition zone is created. Its thickness ranges from several hundred Angstron units at temperatures near 0 degrees C to about three Angstrom units at -150 degrees C. When soluble substances are present, the resulting brine enlarges the interfacial zone. When clays are involved, although the interfacial zone may be small, its extent is large. The unfrozen, interfacial water may amount to 100% or more weight at a temperature of -5 degrees C. The presence of this interfacial unfrozen water acts to confer plasticity to permafrost, enabling it to exhibit creep at all imposed levels of stress. Nucleation processes and load-bearing capacity are examined.

Anderson, D. M.↗
NASA NTRS1985

Analysis of SMIRR Data for Volcanic and Sedimentary Terrains of the Trans-pecos Region, Texas

The Shuttle Multispectral Infrared Radiometer (SMIRR) carried on the second mission of the Space Shuttle produced spectral data for portions of Presidio and Jeff Davis Counties, Texas during the eighteenth orbit of the spacecraft in November of 1981. The data covers an area approximately 100 m in width and 100 km in length extending from the Rio Grande just north of Candelaria in the southwest to Fort Stockton in the northeast. The area is part of the Chihuahua Desert ecosystem. The purpose of the project is to provide groundtruth for the spectral data produced by the SMIRR scanner. The ten filters on the SMIRR scanner extend from 0.50 to 2.35 microns. It has been found that the bands from 2.0 to 2.35 microns are particularly useful for discriminating carbonate and clay minerals.

Blount, H. G.↗
NASA NTRS1985

Chemical Weathering of Soils from the Dry Valleys of Antarctica: a Terrestrial Analog of Martian Weathering Processes

Martian soil subjected to chemical weathering processes could contain the following likely constituents: (1) fresh primary silicate material; (2) partially altered primary silicates; (3) secondary minerals, possibly including clay minerals, evaporites, carbonates, sulfates, hydrates, and zeolites; and (4) altered volcanic glass or impact glass. The soil may also include palogonite and other alteration products and secondary minerals. It is unlikely therefore that an equilibrium assemblage of minerals would be present. From the detailed study of the soils from the Dry Valleys of Antarctica, it is obvious that the complex processes in operation produce major changes in the parent materials, depending upon where the constituents reside and the degree to which weathering and diagenesis operates. It is clear that natural near surface environments, even in very cold and dry regions, may produce extremely complex soils. Extreme caution must be taken when interpreting the results and drawing conclusions, especially about possible processes operating in regoliths in cold, arid environments similar to those of the Dry Valleys or Mars.

Gibson, E. K., Jr.↗
NASA NTRS1983

Spectral reflectance of surface soils - A statistical analysis

The relationship of the physical and chemical properties of soils to their spectral reflectance as measured at six wavebands of Thematic Mapper (TM) aboard NASA's Landsat-4 satellite was examined. The results of performing regressions of over 20 soil properties on the six TM bands indicated that organic matter, water, clay, cation exchange capacity, and calcium were the properties most readily predicted from TM data. The middle infrared bands, bands 5 and 7, were the best bands for predicting soil properties, and the near infrared band, band 4, was nearly as good. Clustering 234 soil samples on the TM bands and characterizing the clusters on the basis of soil properties revealed several clear relationships between properties and reflectance. Discriminant analysis found organic matter, fine sand, base saturation, sand, extractable acidity, and water to be significant in discriminating among clusters.

Crouse, K. R.↗
NASA NTRS1983

Fungi and bacteria involved in desert varnish formation

Desert varnish is a coating of ferromanganese oxides and clays that develops on rock surfaces in arid to semi-arid regions. Active respiration but not photosynthesis was detected on varnished rock surfaces from the Sonoran Desert. Light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, and cultivation experiments indicate that both fungi, primarily dematiaceous hyphomycetes, and bacteria are found on and within desert varnish coatings from the arid regions studied. Some fungi grow as microcolonial fungi (MCF) on rocks, and microscopic observations suggest MCF become incorporated in the varnish coating. SEM-EDAX (energy dispersive X-ray systems) analyses indicate the MCF contain 3 of the characteristic elements of varnish: iron, aluminum, and silicon. In some locations, MCF are also enriched in manganese relative to the rock substratum. Furthermore, some of the dematiaceous hyphomycetes that have been cultivated are able to oxidize manganese under laboratory conditions. It is possible that manganese-oxidizing bacteria, which are found in varnish, also play an important role in varnish formation.

Taylor-George, S.↗
NASA NTRS1985

Spectroscopic observation of Mars

A review is given of what is known about the surface of Mars from reflectance spectroscopy, including some new results and providing an overview of the principles involved. While some form of bound water and/or OH has been known on Mars for many years, a new result presented is the identification of structural OH in a dilute or poorly crystalline magnesian clay. The detection of water ice in the residual north polar cap is noted. Also considered is the role that reflectance spectroscopy will play in the future, from earth and as an important part of the NASA Mars Geosciences/Climatology Orbiter mission.

Singer, R. B.↗
NASA NTRS1985

Experiments with solid particle seeding

Kaoline, a hydrated aluminum silicate clay, is investigated as a seeding material for laser velocimetry. It is inexpensive but is polydispersed with some of the fineparticles being too large to follow wind tunnel flow and is in the form of nonspherical platelets having an aspect ratio of approximately 4/1. Gravity sedimentation experiments as a means of narrowing the fineparticle sizes distribution are being conducted. The fineparticle size distribution of Engelhard ASP 200 kaolin suspended in ethanol (0.00792 grams kaolin/ml ethanol) as received, after 24 hours gravity sedimentation and after 48 hours sedimentation, respectively is shown. A shearing atomizer is used to inject the fineparticles. Gravity sedimentation is carried out in an 800 ml pyrex beaker. Following gravity sedimentation, the top 3.5 inches are siphoned from the liquid, which has a column height of 4.5 inches. In a like manner, longer settling times will serve to further narrow the fineparticle distribution range. As successive sedimentations are effected, the number of fineparticles per unit volume of ethanol decreased markedly.

Nichols, C. E., Jr.↗
NASA NTRS1983

Spectral reflectance of surface soils: Relationships with some soil properties

Using a published atlas of reflectance curves and physicochemical properties of soils, a statistical analysis was carried out. Reflectance bands which correspond to five of the wavebands used by NASA's Thematic Mapper were examined for relationships to specific soil properties. The properties considered in this study include: Sand Content, Silt Content, Clay Content, Organic Matter Content, Cation Exchange Capacity, Iron Oxide Content and Moisture Content. Regression of these seven properties on the mean values of five TM bands produced results that indicate that the predictability of the properties can be increased by stratifying the data. The data was stratified by parent material, taxonomic order, temperature zone, moisture zone and climate (combined temperature and moisture). The best results were obtained when the sample was examined by climatic classes. The middle Infra-red bands, 5 and 7, as well as the visible bands, 2 and 3, are significant in the model. The near Infra-red band, band 4, is almost as useful and should be included in any studies. General linear modeling procedures examined relationships of the seven properties with certain wavebands in the stratified samples.

Kiesewetter, C. H.↗
NASA NTRS1985

Performance evaluation and geologic utility of LANDSAT-4 thematic mapper data

The overall objective of the project was to evaluate LANDSAT-4 Thematic Mapper (TM) data in the context of geologic applications. This involved a quantitative assessment of the data quality including the spatial and spectral characteristics realized by the instrument. Three test sites were selected for the study: (1) Silver Bell, Arizona; (2) Death Valley, California; and (3) Wind River/Bighorn Basin area, Wyoming. Conclusions include: (1) Artificial and natural targets can be used to atmospherically calibrate TM data and investigate scanner radiometry, atmospheric parameters, and construction of atmospheric Modulation Transfer Functions (MTF's), (2) No significant radiometric degradation occurs in TM data as a result of SCROUNGE processing; however, the data exhibit narrow digital number (DN) distributiosn suggesting that the configuration of the instrument is not optimal for each science applications, (30 Increased spatial resolution, 1:24,000 enlargement capability, and good geometric fidelity of TM data allow accurate photogeologic/geomorphic mapping, including relative age dating of alluvial fans, measurement of structural and bedding attitudes, and construction of such things as structural cross sections and stratigraphic columns. (4) TM bands 5 and 7 are particularly useful for geologic applications because they span a region of the spectrum not previously sampled by multispectral scanner data and are important for characterizing clay and carbonate materials.

Paylor, E. D.↗
NASA NTRS1986

Use of laboratory simulated pyrolysis in tracing the history of sedimentary organic matter

Results from laboratory simulated pyrolyses experiments show that in addition to depth of burial, preservation of kerogen, and hence any morphologic structure in it, is also dependent on the mineral matrix with which it is associated. In the presence of clay minerals, and especially under dry conditions, extractable lipids released during kerogen decomposition are more rapidly destroyed than in the presence of calcite or chert matrices. The result is production of gas, polar bitumen and pyrobitumen and destruction of biomarkers. During such an early reorganization of the kerogen, the biomarker constituents can be destroyed, or unrecognizably altered. The above process of organic residues maturation appears to be inhibited in the presence of water and is significantly reduced where kerogen is hosted in limestones, dolomites or cherts. These minerals have been characteristically found to be the most reliable in yielding morphological fossils and small quantities of extractable bitumen in Archean and Proterozoic rocks. To understand the validity of chemical and morphological fossils, in the early geologic record, it will be necessary to understand the process of kerogen in sedimentary rocks. To test the role of various minerals on the preservation process, kerogen extracted from a variety of rocks has been heated together with montmorillonite, illite and calcite. The kinetics of the process has been monitored and the products quantitatively identified.

Kaplan, I. R.↗
NASA NTRS1985

The microbial community at Laguna Figueroa, Baja California Mexico - From miles to microns

The changes in the composition of the stratified microbial community in the sediments at Laguna Figeroa following floods are studied. The laguna which is located on the Pacific coast of the Baja California peninsula 200 km south of the Mexican-U.S. border is comprised of an evaporite flat and a salt marsh. Data collected from 1979-1983 using Landsat imagery, Skylab photographs, and light and transmission electron microscopy are presented. The flood conditions, which included 1-3 m of meteoric water covering the area and a remanent of 5-10 cm of siliciclastic and clay sediment, are described. The composition of the community prior to the flooding consisted of Microcoleus, Phormidium sp., a coccoid cynanobacteria, Phloroflexus, Ectothiorhodospira, Chloroflexus, Thiocapsa sp., and Chromatium. Following the floods Thiocapsa, Chromatium, Oscillatora sp., Spirulina sp., and Microcoleus are observed in the sediments.

Stolz, J. F.↗
NASA NTRS1986

Relation between L-band soil emittance and soil water content

An experimental relation between soil emittance (E) at L-band and soil surface moisture content (M) is compared with a theoretical one. The latter depends on the soil dielectric constant, which is a function of both soil moisture content and of soil texture. It appears that a difference of 10 percent in the surface clay content causes a change in the estimate of M on the order of 0.02 cu m/cu m. This is based on calculations with a model that simulates the flow of water and energy, in combination with a radiative transfer model. It is concluded that an experimental determination of the E-M relation for each soil type is not required, and that a rough estimate of the soil texture will lead to a sufficiently accurate estimate of soil moisture from a general, theoretical relationship obtained by numerical simulation.

Stroosnijder, L.↗