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121.
122.
Chlorophyll a, zeaxanthin, and pheophytin a were measured from sediment core samples from three lakes (Dewey, Island, and Two Mile Lakes) in the Nebraska Sand Hills.
Pigments were extracted and identified by high performance liquid chromatography (HPLC) and used to estimate changes in the
relative proportion of cyanobacteria to the algal community. The cyanobacterial toxins microcystin-LR and LA were extracted
and measured using electrospray ionization liquid chromatography tandem mass spectrometry (LC/MS/MS). Microcystin-LR was found
in core sections estimated to be as early as 1832, and was present in all three lake cores. Pigment and toxin data were used
to determine if there were changes that occurred in the algal community structure with the onset of modernized agriculture
in the region. No significant changes were found in the relative percent of cyanobacteria or chlorophyll a accumulation, indicating the frequency and intensity of cyanobacterial blooms has not changed over the last century. Despite
this trend, there was a dramatic increase in microcystin-LR accumulation during the 1980s in Dewey Lake, which may be human
induced. 相似文献
123.
124.
Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land,South Africa
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Jörg Fritz Roald Tagle Luisa Ashworth Ralf Thomas Schmitt Axel Hofmann Béatrice Luais Phillip D. Harris Desirée Hoehnel Seda Özdemir Tanja Mohr‐Westheide Christian Koeberl 《Meteoritics & planetary science》2016,51(12):2441-2458
A Paleoarchean impact spherule‐bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro‐X‐ray fluorescence (μXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer‐scale, assisted in the localization and characterization of eight spherule‐bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The μXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni‐Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3‐rich and can be distinguished from the Al2O3‐poor marine sediments by distinct Al‐OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al‐OH‐rich spherule layers in Al2O3‐poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism. 相似文献
125.
Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation. 相似文献
126.
Microcrystals (1–15 μm) of unusual monazite (La) with 41–47 mol% cheralite [ThCa(PO4)2] component and a strong negative Ce anomaly are described from a metadiorite from the SW Slavonian Mountains, Psunj, Croatia. The dioritic host rock still shows a relictic igneous fabric on macroscopic scale. However, metamorphic reaction textures can be recognized in thin section. These include partial recrystallization of igneous plagioclase to albite coupled with the formation of epidote. Furthermore, partial replacement of igneous hornblende by a fine-grained orthoamphibole-chamosite-epidote paragenesis can be observed and replacement of ilmenite by titanite. The compositions of the metamorphic minerals indicate upper greenschist facies conditions (460–500 °C according to two-feldspar geothermometry) under a high oxygen fugacity. Microstructures show that the monazite crystals belong to the metamorphic paragenesis and formed at the expense of magmatic allanite. Their negative Ce anomalies reflect the oxidizing conditions of metamorphism. Application of the xenotime in monazite solvus geothermometer provides unrealistically high temperatures of ~500–660 °C which disagree with the greenschist facies metamorphic paragenesis. We interpret that the presence of cheralite has a profound effect on the nature of the monazite-xenotime solvus curve and hence the existing calibrations of this geothermometer may be generally unsuitable for cheralite-rich monazite. An important geological result is that the Th-U-total Pb ages of the monazite grains are uniformingly Upper Cretaceous. Our data thus suggest that the imprint of the Alpine orogeny on the Slavonian Mountains was stronger than presumed until now. 相似文献
127.
V. A. Fernandes J. Fritz B. P. Weiss I. Garrick‐Bethell D. L. Shuster 《Meteoritics & planetary science》2013,48(2):241-269
New petrography and 40Ar‐39Ar ages have been obtained for 1–3 mm sized rock fragments from Apollo 16 Station 13 soil 63503 (North Ray crater ejecta) and chips from three rocks collected by Apollo 16 and Apollo 17 missions. Selection of these samples was aimed at the old 40Ar‐39Ar ages to understand the early history of the lunar magnetic field and impact flux. Fifteen samples were studied including crustal material, polymict feldspathic fragmental breccias, and impact melts. The impact ages obtained range between approximately 3.3 and 4.3 billion years (Ga). Polymict fragmental breccia 63503,1 exhibits the lowest signs of recrystallization observed and a probable old relic age of 4.547 ± 0.027. The plateau age of 4.293 ± 0.044 Ga obtained for impact melt rock 63503,13 represents the oldest known age for such a lithology. Possibly, this age represents the minimum age for the South Pole‐Aitken (SPA) Basin. In agreement with literature data, these results show that impact ages >3.9 Ga are found in lunar rocks, especially within soil 63503. Impact exhumation of deep‐seated warm crustal material onto the lunar surface is considered to explain the common 4.2 Ga ages obtained for weakly shocked samples from soil 63503 and Apollo 17. This would directly imply that one or more basin‐forming events occurred at that time. Some rock fragments showing none to limited petrologic features indicate thermal annealing. These rocks may have lost Ar while resident within the hot‐ejecta of a large basin. Concurrent with previous studies, these results lead us to advocate for a complex impact flux in the inner solar system during the initial approximately 1.3 Ga. 相似文献
128.
Harald Fritz 《Geodinamica Acta》2013,26(2):53-62
AbstractThe multiply deformed Upper Austro-Alpine nappe pile of the Graz area is built up of low-grade metamorphosed Paleozoic rocks which are discordantly overlain by sediments of Santonian (Late Cretaceous) age (“Gosau” formation). Slices of Permo-Mesozoic rocks are absent. Analyses of structures, microfabrics, strain and shear directions were used to decipher the kinematic history; geochronological investigations to date the age of thrusting. K/Ar and Rb/Sr ages of synkinematically grown mica suggest an eo-Alpine (Early Cretaceous) age for the major deformation D1. D1 is characterized by non-coaxial rock flow which caused SW- to W directed nappe imbrication. Incremental strain measurements indicate the progressive superposition of D2 over Dl. In the higher nappe (Rannach Nappe) nappe imbrication continued during D2 changing the direction of nappe transport from SW to NW. Enhanced flattening strain in the deeper nappe (Schöckel Nappe) led to recumbent folds in all scales during D2. This study emphasized two interpretations : (1) The Alpine deformation in the Upper Austro-Alpine nappe pile of the Paleozoic of Graz started in the Earliest Cretaceous (about 125 Ma.). (2) The emplacement of nappes followed a curved translation path in the studied area. 相似文献
129.
Sherilyn C. Fritz 《Journal of Paleolimnology》2008,39(1):5-16
Reconstructing climate from lake sediments can be challenging, because the response of lakes and various components of lake
systems are mediated by non-climatic factors, such as geomorphic and hydrologic stetting. As a result, the magnitude of lake
response to climatic forcing may be non-linear. In addition, changes in the lake system associated with the aging process
or non-climatic influences may alter the response to a given climate perturbation. These non-linear and non-stationary characteristics
can produce spatial heterogeneity in the pattern and timing of inferred change. One approach for generating regionally robust
climatic interpretations from lakes is to increase coordinated efforts to generate and synthesize large data sets, so that
localized influences can be more clearly distinguished from broad-scale regional patterns. This approach will be most successful
for evaluating climate variation at multi-decadal or longer temporal scales; the climatic interpretation of higher frequency
limnological variation can be more complicated, because of dating uncertainties and differential response times of individual
proxies and systems.
This paper is based on a plenary talk at the 10th International Paleolimnology Conference in Duluth, Minnesota in July 2006. 相似文献
130.
Vince R. Vermeul Jim E. Szecsody Brad G. Fritz Mark D. Williams Robert C. Moore Jonathan S. Fruchter 《Ground Water Monitoring & Remediation》2014,34(2):28-41
An injectable permeable reactive barrier (PRB) technology was developed to sequester 90Sr in groundwater through the in situ formation of calcium‐phosphate mineral phases, specifically apatite that incorporates 90Sr into the chemical structure. This injectable barrier technology extends the PRB concept to sites where groundwater contaminants are too deep or where site conditions otherwise preclude the application of more traditional trench‐emplaced barriers. An integrated, multiscale development and testing approach was used that included laboratory bench‐scale experiments, an initial pilot‐scale field test, and the emplacement and evaluation of a 300‐feet‐long treatability‐test‐scale PRB. The apatite amendment formulation uses two separate precursor solutions, one containing a Ca‐citrate complex and the other a Na‐phosphate solution, to form apatite precipitate in situ. Citrate is needed to keep calcium in solution long enough to achieve a more uniform and areally extensive distribution of precipitate formation. In the summer of 2008, the apatite PRB technology was applied as a 91‐m‐long (300 feet) PRB on the downgradient edge of a 90Sr plume beneath the Hanford Site in Washington State. The technology was deployed to reduce 90Sr flux discharging to the Columbia River. Performance assessment monitoring data collected to date indicate that the barrier is meeting treatment objectives (i.e., 90% reduction in 90Sr concentration). The average reduction in 90Sr concentrations at four downgradient compliance monitoring locations was 95% relative to the high end of the baseline range approximately 1 year after treatment, and continues to meet remedial objectives more than 4 years after treatment. 相似文献