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101.
Juan Pablo Corella Achim Brauer Clara Mangili Valentí Rull Teresa Vegas‐Vilarrúbia Mario Morellón Blas L. Valero‐Garcés 《Quaternary Research》2012,78(2):323-332
The karstic Lake Montcortès sedimentary sequence spanning the last 1548 yr constitutes the first continuous, high-resolution, multi-proxy varved record in northern Spain. Sediments consist of biogenic varves composed of calcite, organic matter and detrital laminae and turbidite layers. Calcite layer thickness and internal sub-layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability. Higher temperatures occurred in Lake Montcortès in AD 555–738, 825–875, 1010–1322 and 1874–present. Lower temperatures and prolonged winter conditions were recorded in AD 1446–1598, 1663–1711 and 1759–1819. Extreme and multiple precipitation events dominated in AD 571–593, 848–922, 987–1086, 1168–1196, 1217–1249, 1444–1457, 1728–1741 and 1840–1875, indicating complex hydrological variability in NE Spain since AD 463. The sedimentary record of Lake Montcortès reveals a short-term relation between rainfall variability and the detrital influx, pronounced during extended periods of reduced anthropogenic influences. In pre-industrial times, during warm climate episodes, population and land use increased in the area. After the onset of the industrialization, the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio‐economic factors. 相似文献
102.
L.?C.?G?tzeEmail author R.?Abart R.?Milke S.?Schorr I.?Zizak R.?Dohmen R.?Wirth 《Physics and Chemistry of Minerals》2014,41(9):681-693
Polycrystalline spinel layers were grown experimentally at the contacts between single-crystal corundum substrates and initially amorphous, then polycrystalline MgO thin films. The growth behavior of the spinel layers was monitored in situ using synchrotron X-ray diffraction. The change in the integrated intensity of the 111 spinel Bragg peak was correlated with the thickness of the layer as determined from ex situ TEM characterization of the run products. At \(900\,^{\circ }\hbox {C},\) a transition from linear growth, corresponding to interface reaction control, to parabolic growth, corresponding to diffusion control, occurred at a layer thickness of less than 10 nm. At 1,000 \(^{\circ }\hbox {C},\) growth was largely linear up to a layer thickness in excess of 300 nm. A thermodynamic model was applied to extract the kinetic parameters characterizing interface motion and long-range diffusion from this growth behavior. 相似文献
103.
Ocean Dynamics - The input of mechanical power to the ocean due to the surface wind stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from... 相似文献
104.
Cr-Ca lamellae in a magnesian olivine grain (section 1611) from the Luna 24 regolith were investigated in detail by electron
microprobe analysis (EMPA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that
the lamellae are parallel to the (100) plane of oxygen closest packing in olivine and consist of regular vermicular intergrowths
of two phases, diopside (Di) and chromite (Chr), in the volume proportion Di: Chr ≈ 3: 1. The bulk chemical composition of the lamellae is approximated as Ca2Mg2Fe2+(Cr3+)2Si4O16. They are identical in phase composition to type A, F, and E symplectites from Apollo lunar samples [9]. Based on morphology
and phase composition, the lamellar aggregates in the olivine grain from the Luna 24 regolith were classified as pyroxene
(Px)-spinel (Spl) symplectites of a lamellar type, the formation of which was related to olivine oxidation at IW ≤ logfO2 ≤ QFM. The obtained data indicate a solid-phase mechanism of lamella formation and the existence of a lamellar precursor
phase, which transformed subsequently into the Px-Spl symplectite. It was supposed that uvarovite-knorringite garnet produced by the oxidation of olivine at high pressures and
t > 800°C could be the transitional phase during symplectite formation. The subsequent conversion of the garnet into the low-pressure
assemblage of Px-Spl symplectites could occur via cellular decomposition in accordance with the reaction Ca2MgCr2Si3O12 + (Mg,Fe)2SiO4 = 2CaMgSi2O6 + FeCr2O4. The reported results are the first data of a detailed nanomineralogical investigation of lamellar Px-Spl symplectites in lunar olivine. 相似文献
105.
Christoph Janssen Richard Wirth Andreas Reinicke Erik Rybacki Rudolf Naumann Hans-Rudolf Wenk Georg Dresen 《Earth and Planetary Science Letters》2011,301(1-2):179-189
With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured core samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1–5%) is comparable to the connected fault rock porosity (2.8–6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10? 21–10? 19 m2 and 10? 17 m2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radius > 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radius < 50 nm) are typically observed in the extremely fine-grained matrix (grain size < 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. 相似文献
106.
Waruntorn Kanitpanyacharoen Hans‐Rudolf Wenk Frans Kets Christian Lehr Richard Wirth 《Geophysical Prospecting》2011,59(3):536-556
Scanning and transmission electron microscopy, synchrotron X‐ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub’al‐Khali basin, Saudi Arabia. Kaolinite, illite‐smectite, illite‐mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4–6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P‐wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P‐wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P‐wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging. 相似文献
107.
Microstructural evolution during experimental albitization of K-rich alkali feldspar 总被引:1,自引:1,他引:0
Nicholas Norberg Gregor Neusser Richard Wirth Daniel Harlov 《Contributions to Mineralogy and Petrology》2011,162(3):531-546
Crystals of K-feldspar (C2/m), in contact with highly concentrated aqueous NaCl solutions at 500°C and 200 MPa, are pseudomorphically replaced by high
albite (C[`1]) (C\bar{1}) as a result of an interface-coupled dissolution/reprecipitation process. The reaction occurs at an extremely sharp reaction
front (<10 nm) and involves the complete breakdown of the initial framework structure. This results in the release of tetrahedrally
incorporated elements such as Fe3+ and Ti4+ and a significant increase in Si/Al disorder across the reaction interface. The evolving microstructure is controlled by
crystallographic relations between the phases. This leads to highly anisotropic, sawtooth-shaped intergrowths of albite and
initial K-feldspar, resulting in the least structural misfit between the two framework structures. As a result, the newly
formed interfaces appear to be semicoherent, and cracks across the reaction fronts even indicate elastic strain. The reaction
produces 2 distinctive albite types (albite-1 and albite-2). Both are polycrystalline, with albite-2 showing significantly larger subgrain sizes. This indicates a secondary coarsening step driven by the reduction in interfacial
energy within the polycrystalline replacement product. The reaction also produces a highly porous rim. However, the porosity
is not evenly distributed resulting in a porous albite-1 and a non-porous albite-2 that mostly surrounds large, euhedral pores. Despite the substantial volume fraction of porosity in albite-1, no significant 3D interconnectivity could be detected, making the presence of a pervasive porosity unlikely. However, the
result of coarsening is the continuous modification of the 3D porosity distribution. This could potentially provide a mechanism
for fluid transport through the replacement rim until textural and chemical equilibration is achieved. 相似文献
108.
Water and Iron effect on the P-T-x coordinates of the 410-km discontinuity in the Earth upper mantle
Fiorenza Deon Monika Koch-Müller Dieter Rhede Richard Wirth 《Contributions to Mineralogy and Petrology》2011,161(4):653-666
We performed multi-anvil experiments in the system MgO-SiO2 ± H2O at 13.0–13.7 GPa and 1,025–1,300°C and in the system MgO-FeO-SiO2 ± H2O, under reducing conditions, at 11.0–12.7 GPa and 1,200°C, to depict the effect of H2O on the P-T-x coordinates of the 410-km discontinuity, i.e. the olivine–wadsleyite phase boundary. The charges were investigated
with Electron Microprobe (EMP), Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Secondary Ion Mass Spectrometry
(SIMS) and Electron Energy Loss Spectroscopy (EELS). We observe in the MgO-SiO2-H2O system at 1,200°C a 0.6 GPa shift of the phase boundary to lower pressure compared to dry conditions, due to the stronger
water fractionation into wadsleyite (wad) rather than in olivine (ol). In the MgO-FeO-SiO2-H2O system, we reproduced the triple point, i.e. observed coexisting hydrous ol, wad and ringwoodite (ring). SIMS H quantifications
provided partitioning coefficients for water:
D\textwad/ol\textwater D_{\text{wad/ol}}^{\text{water}} ~ 3.7(5) and
D\textring/ol\textwater D_{\text{ring/ol}}^{\text{water}} ~ 1.5(2) and
D\textwad/ring\textwater D_{\text{wad/ring}}^{\text{water}} ~ 2.5(5). For a bulk composition of x
Fe = 0.1, our data indicate only a slight difference in the width of the loop of the two phase field ol–wad under hydrous conditions
compared to dry conditions, i.e. no broadening with respect to composition but a shift to lower pressures. For bulk compositions
of x
Fe > 0.2, i.e. in regions where wad–ring and ol–ring coexist, we observe, however, an unexpected broadening of the loops with
a shift to higher iron contents. In total, the stability field of hydrous wad expands in both directions, to lower and higher
pressures. Fe3+ concentrations as determined by EELS are very low and are expected to play no role in the broadening of the loops. 相似文献
109.
Grace Xingxin Gao Liang Heng Achim Hornbostel Holmer Denks Michael Meurer Todd Walter Per Enge 《GPS Solutions》2013,17(4):561-573
The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm. 相似文献
110.
The recent sediment record of Lake Belau (Schleswig–Holstein, Germany), deposited in the period 1945–2002, was compared with instrumental meteorological and limnological data. The sediments deposited during this period are annually laminated. A varve chronology was established and supported by 137Cs measurements. Micro-facies and diatom assemblage composition analyses were confirmed in thin sections and compared statistically with limnological and meteorological data. Comparison of phytoplankton data with diatom assemblage data from the sediment for the time interval from 1988 to 1999 proved that the sediments reflect limnological processes in the lake and record seasonal changes in the primary producer communities. Among the climatological data, the number of contiguous ice days (days with maximal temperatures ≤0 °C) and the state of the winter NAO are strong predictors for micro-facies development and diatom assemblage composition. Furthermore, solar and local (nutrient input) influences are visible in the diatom assemblage compositions. Our study illustrates the high potential for using analyses of micro-facies and diatom assemblages to reconstruct past weather conditions in varved sediments of Lake Belau. 相似文献