Trace element and isotope geochemistry of Cretaceous-Tertiary boundary sediments: identification of extra-terrestrial and volcanic components

Trace element and stable isotope analyses were performed on a series of sediment samples crossing the Cretaceous-Tertiary (K-T) boundary from critical sections at Aumaya and Sopelano, Spain. The aim is to possibly distinguish extraterrestrial vs. volcanic or authigenic concentration of platinum group and other elements in K-T boundary transitional sediments. These sediments also have been shown to contain evidence for step-wise extinction of several groups of marine invertebrates, associated with negative oxygen and carbon isotope excursions occurring during the last million years of the Cretaceous. These isotope excursions have been interpreted to indicate major changes in ocean thermal regime, circulation, and ecosystems that may be related to multiple events during latest Cretaceous time. Results to date on the petrographic and geochemical analyses of the Late Cretaceous and Early Paleocene sediments indicate that diagenesis has obviously affected the trace element geochemistry and stable isotope compositions at Zumaya. Mineralogical and geochemical analysis of K-T boundary sediments at Zumaya suggest that a substantial fraction of anomalous trace elements in the boundary marl are present in specific mineral phases. Platinum and nickel grains perhaps represent the first direct evidence of siderophile-rich minerals at the boundary. The presence of spinels and Ni-rich particles as inclusions in aluminosilicate spherules from Zumaya suggests an original, non-diagenetic origin for the spherules. Similar spherules from southern Spain (Caravaca), show a strong marine authigenic overprint. This research represents a new approach in trying to directly identify the sedimentary mineral components that are responsible for the trace element concentrations associated with the K-T boundary

Applications of the Environmental Scanning Electron Microscope to Conservation Science

The environmental scanning electron microscope (E-SEM) provides electron imaging at relatively high sample pressure, with imaging and analysis capabilities comparable to those of traditional high vacuum SEM. Several case studies demonstrate the advantages and research potential of this new technology as applied to conservation science: 1) dynamic study of wetting and drying of consolidated and unconsolidated adobe samples; 2) semi-dynamic study of lead corrosion as a result of exposure to formaldehyde; 3) electron imaging of outgassing samples-parchment; 4) study of uncoated, non-conductive samples-swabs from Sistine Chapel cleaning; 5) X-ray analysis of uncoated insulators-gold and garnet jewelry. The environmental scanning electron microscope offers unique capabilities for dynamic experiments, imaging of outgassing samples and insulators, which may be applied to the study of deterioration mechanisms, material treatments, and ancient materials and technologies

La soldadura con aleaciones de oro en la América antigua: un análisis de dos pequeños adornos provenientes del Ecuador

La isla de La Tolita, localizada frente a la costa entre Colombia y Ecuador, es un sitio en el que se han realizado durante los últimos cien años espectaculares hallazgos de piezas de orfebrería muy delicadas. La mayor parte de este material proviene de guaquería y no tiene ningún contexto arqueológico; sin embargo, trabajos recientes sugieren que el inicio de la metalurgia en esta región data de antes de la era cristiana (Bray, 1988; Bouchard, 1979; Bergsoe, 1937). Además de indicar el uso de aleaciones con platino y otros desarrollos interesantes, el sitio ha producido un conjunto considerablemente rico de adornos pequeños como los descritos en este artículo. Aunque la evidencia arqueológica sugiere que la principal ocupación del sitio de La Tolita terminó alrededor del año 800 d.C., la utilización de diminutos ornamentos cuidadosamente elaborados continuó hasta la época de la conquista española en el siglo XV

Sales de sulfato magnésico y materiales de edificios históricos: simulación experimental de laminaciones en calizas mediante ciclos de humedad relativa y cristalización de sales

Magnesium sulfate salts often result from the combination of incompatible construction materials, such as stone or mortar with high magnesium content and sulfates from adjacent mortars or polluted air. When combined with a source of moisture, these materials react to form soluble salts, often leading to significant damage by flaking of the stone, as the magnesium sulfate responds to fluctuating environmental conditions. Several laboratory experiments were performed to reproduce surface flaking on different types of limestone from Spain and the UK to evaluate the effects of humidity cycling on the damage of stone by salt crystallization. The two salt solutions used for the experiments were a single salt of magnesium sulfate and a mixture of magnesium sulfate, calcium sulfate and sodium chloride, a typical salt mixture found in damaged stone at the site of Howden Minster (UK). A climate chamber with precise and programmable temperature and humidity control was used to test the hypothesis that salt damage in the stone can be readily caused by humidity fluctuations. Damage was monitored using Linear Variable Differential Transformer (LVDT), which measure transducers displacement by dimensional change on the order of microns. In addition, Ion Chromatography, Environmental Scanning Electron Microscopy with energy dispersive X-ray spectroscopy (ESEM-EDX) and X-ray Diffraction analyses (XRD) were also carried out to analyze salt behavior. Damage by flaking took place in two types of magnesian limestone cubes impregnated with the salt mixture, from Cadeby quarry and York Minster, apparently by deliquescent salts of low equilibrium relative humidity (RHeq), while the rest of the samples developed a salt crust over the surface, but no damage was observed in the stone. It is important to verify hypotheses developed from field observations with laboratory experiments. By combining both field and laboratory data, a clearer understanding the different mechanisms of decay and associated weathering types under different environmental conditions can be obtained.Las sales de sulfato magnésico a menudo se producen a partir de la combinación de materiales de construcción incompatibles, tales como piedra o mortero con un alto contenido en magnesio y sulfatos procedentes de morteros adyacentes o del aire contaminado. Cuando estos materiales se combinan con una fuente de humedad, reaccionan para formar sales solubles que con frecuencia dan lugar a un importante deterioro por laminaciones de la piedra, ya que el sulfato magnésico responde a las fluctuaciones de las condiciones ambientales. Varios experimentos de laboratorio se llevaron a cabo para reproducir laminaciones superficiales en diferentes tipos de calizas procedentes de España y Reino Unido, para evaluar los efectos de ciclos de humedad en el deterioro de la piedra por cristalización de sales. Una única sal de sulfato magnésico y una mezcla de sulfato magnésico, sulfato cálcico y cloruro sódico, típica mezcla de sales encontrada en la piedra deteriorada de Howden Minster (UK), fueron las dos soluciones salinas utilizadas para realizar los experimentos. Se utilizó una cámara climática con control preciso de programación de temperatura y humedad para probar la hipótesis de que el deterioro por sales en la piedra puede ser fácilmente causada por fluctuaciones de humedad. El deterioro se monitorizó utilizando un Transformador Diferencial de Variable Lineal (TDVL), que mide el desplazamiento de transductores por cambios dimensionales en el orden de micras. Además, también se realizaron análisis de Cromatografía de Iones, Microscopía Electrónica de Barrido Ambiental con energía dispersiva de rayos-X (MEBA-EDX) y Difracción de rayos-X (DRX) para analizar el comportamiento de las sales. El deterioro por laminaciones se produjo en dos tipos de calizas magnésicas impregnadas con la mezcla salina, procedentes de las canteras de Cadeby y de York Minster, aparentemente por sales delicuescentes de baja humedad relativa en el equilibrio (HReq), mientras que el resto de las muestras desarrollaron una costra salina sobre la superficie pero sin observarse deterioro de la piedra. Es importante verificar con experimentos de laboratorio hipótesis desarrolladas a partir de observaciones de campo. Mediante la combinación de datos de campo y de laboratorio se puede obtener una mejor comprensión de los diferentes mecanismos de deterioro y tipos de alteración asociados bajo diferentes condiciones ambientales

Stability of Actinolite on Venus

Venus currently has a hostile surface environment with temperatures of ~460 C, pres-sures near 92 bars, and an atmosphere composed of super critical CO2 hosting a myriad of other potentially reactive gases (e.g., SO2, HCl, HF). However, it has been proposed that its surface may not have always been so harsh. Models suggest there may have been billions of years of clement conditions allowing an Earth-like environment with liquid water oceans. If such conditions existed, it is possible Venus formed a similar array of hydrous or aqueous minerals as seen on other planets with liquid surface water (e.g., Mars, Earth). Based on thermodynamic modeling, many of these phases would not be stable under the current atmospheric conditions on Venus, dehydrating due to the high temperatures and low concentration of H2O in the atmosphere. However, the rate of decomposition of these phases may allow them to remain present on the surface over geologic time. For example, experiments on the reaction rate of tremolite (Ca2Mg5Si8O22(OH)2) show a 50% decomposition time of 2.7 Gyr for micrometer sized grains in unreactive atmospheres (i.e., without SO2) at 740 K, and a 50% decomposition time of 70 Gyr for crystals several millimeters to centimeters in size. If hydrous minerals can remain on the surface of Venus over geologic time, it has implications for our detection of evidence of these past environments, and also for the overall water budget of the planet. If after surficial dehydration the planet was able to still store water in its crust, possible processes such as subduction or metamorphism could still have operated using stored water long after liquid surface water evaporated. Several previous studies have focused on experimental investigations of mineral stability on Venus. In particular, the works of studied the decomposition rate of tremolite under conditions relevant to Venus. As their focus was on decomposition of the mineral due to lack of water in the atmosphere, their experiments were undertaken using only CO2 or N2 gas at atmospheric pressure. Re-cent experiments have examined reactivity of other minerals with the Venusian atmosphere using more complex gas compositions at similar pressures to those seen on Venus. These studies show reaction of silicate minerals with atmospheric components on relatively short timescales (i.e., on the order of days). The reported reactions of silicate materials in both studies produced iron oxides, Ca sulfates, and Na sulfates. These ions are present in many amphiboles, and Ca was proposed by Johnson and Fegley to potentially have an important role in the decomposition mechanism for tremolite, with the Ca-O bond being the first to break during decomposition. The potential involvement of Ca in both processes raises the question of whether or not the reaction to form a secondary mineral phase will influence the rate of amphibole break-down (e.g., discussion in for tremolite). Additionally, reaction of Ca with atmospheric gases may result in a different secondary mineral assemblage than simple amphibole decomposition, which will need to be recognized when searching for evidence of past hydrated minerals on the Venusian surface. In order to understand the effect of this reaction on the overall preservation potential of amphibole on the surface of Venus, we are conducting experiments in both reactive and nonreactive atmospheres using the mineral actinolite (Ca2(Mg,Fe)5Si8O22(OH)2), an amphibole with similar crystal structure to tremolite that contains both Ca and Fe

Next-Generation Ion Propulsion Being Developed

The NASA Glenn Research Center ion-propulsion program addresses the need for high specific-impulse systems and technology across a broad range of mission applications and power levels. One activity is the development of the next-generation ion-propulsion system as a follow-on to the successful Deep Space 1 system. The system is envisioned to incorporate a lightweight ion engine that can operate over 1 to 10 kW, with a 550-kg propellant throughput capacity. The engine concept under development has a 40-cm beam diameter, twice the effective area of the Deep Space 1 engine. It incorporates mechanical features and operating conditions to maximize the design heritage established by the Deep Space 1 engine, while incorporating new technology where warranted to extend the power and throughput capability. Prototype versions of the engine have been fabricated and are under test at NASA, with an engineering model version in manufacturing. Preliminary performance data for the prototype engine have been documented over 1.1- to 7.3-kW input power. At 7.3 kW, the engine efficiency is 0.68, at 3615-sec specific impulse. Critical component temperatures, including those of the discharge cathode assembly and magnets, have been documented and are within established limits, with significant margins relative to the Deep Space 1 engine. The 1- to 10-kW ion thruster approach described here was found to provide the needed power and performance improvement to enable important NASA missions. The Integrated In-Space Transportation Planning (IISTP) studies compared many potential technologies for various NASA, Government, and commercial missions. These studies indicated that a high-power ion propulsion system is the most important technology for development because of its outstanding performance versus perceived development and recurring costs for interplanetary solar electric propulsion missions. One of the best applications of a highpower electric propulsion system was as an integral part of a solar electric propulsion (SEP) stage to send a payload to outer planet targets. The IISTP studies showed that either trip time or launch vehicle class could be significantly reduced when compared with state-of-the-art systems