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1.
Alan E. RUBIN Paul BENOIT Blaine REED Otto EUGSTER Ernst POLNAU 《Meteoritics & planetary science》1996,31(6):925-927
Abstract— Richfield is a moderately shocked (shock stage S4) LL3.7 genomict breccia find consisting mainly of light-colored recrystallized clasts and dark clasts exhibiting significant silicate darkening; a few impact-melt-rock clasts and LL5 chondrite clasts also occur. The cosmic-ray exposure age of 14.5 Ma is indistinguishable from the main exposure peak for LL chondrites (15 Ma). Although the exposure ages indicate little He loss, the gas-retention ages indicate high gas losses that must have occurred prior to or during ejection from the LL parent body. 相似文献
2.
JAAP J. M. VAN DER MEER REED WICANDER 《Boreas: An International Journal of Quaternary Research》1992,21(2):153-158
Micropaleontological analysis of a silt intraclast in till exposed near Steenwijk in the northern Netherlands revealed an acritarch flora of Late Silurian–Early Devonian age, of southeastern Baltic Basin origin. The age of this assemblage contrasts with what is known about the palynomorph content of Dutch tills. Petrologic analysis of the silt intraclast provides further insight in the direction and mode of Saalian glacier transport. 相似文献
3.
In natural waters,exopolymers or extracellular polymeric substances(EPS) exuded by microorganisms interact with clay particles,resulting in the flocculation of clays and hence alteration to the properties of suspended cohesive sediments.To investigate and further understand how neutral EPS affect cohesive sediment transport and the final sediment yield,an experimental study was conducted on laboratory-prepared clay and guar gum(used as an analog for neutral EPS) suspensions to characterize EPS-induced flocculation and the settling velocity of resultant floes.Four different clays consisting of kaolinite,illite,Ca-montmorillonite,and Na-montmorillonite were studied to examine the influence of different layer charges on clay flocculation induced by neutral EPS.Floc size was determined by a laser particle size analyzer,and settling velocity estimated by analyzing the time-series floc settling images captured by an optical microscope.Results indicate that neutral EPS promote clay-EPS flocculation for all four clays with the particle/floc size significantly increased from～0.1-60μm to as large as～600μm.Clays’ layer charge has a profound influence on the clay-EPS flocculation.With the same floc size,the settling velocity of clay-EPS flocs is typically smaller than that of pure clay flocs,which is attributed to the reduced density of flocs caused by the EPS. However,for flocs of the same composition(e.g.pure clay or hybrid clay-EPS mixture),the settling velocity increases with size.The fractal dimension of these clay-EPS flocs estimated from settling velocity ranges from 1.39 to 1.47,which are smaller than that of pure clay flocs,indicating that these flocs are less compacted than the pure clay flocs. 相似文献
4.
VEERLE VANDEGINSTE RUDY SWENNEN MARK H. REED ROB M. ELLAM KIRK OSADETZ FRANÇOIS ROURE 《Sedimentology》2009,56(7):2044-2060
The Upper Devonian carbonate reefs in West‐central Alberta are important petroleum reservoirs that are well‐known for their extensive secondary porosity. An outcrop analogue study indicates that an early matrix‐selective dolomitization event occurred which is characterized by a major Late Devonian sea water component with increased salinity because of evaporation. It is interpreted that the matrix (replacive) dolomite formed during the Famennian as the result of a combination of both seepage and latent reflux dolomitization, although an additional type or overprinting of later intermediate burial dolomitization cannot be excluded. Formation of the moulds is attributed mainly to the dissolution of undolomitized fossil cores, most typically stromatoporoids. Geochemical modelling indicates that carboxylic acid fluids have the highest potential for dissolving residual calcite in this case. Geochemical models consistent with this analysis and interpretations can reproduce the secondary porosity and suggest a viable dolomitization process for the localities studied. 相似文献
5.
GAO StephenShangxing LIU KellyHong FU Xiaofei Haider DAHM KONG Fansheng LIU Lin Cory REED SUN Muchen YU Youqiang 《《地质学报》英文版》2019,93(Z2):3-4
The North Qaidam is an Early Paleozoic UHP metamorphic belt located at the north margin of the Tibet plateau. Eclogites in this belt contain both continental‐and oceanic‐type ones. In which, the continental‐type eclogites have protolith ages of 750–850 Ma and WPB or CFB geochemical signatures and are believed to have formed in a continental rift or an incipient oceanic basin setting related to the breakup of the Rodinia supercontinent, their metamorphic ages (421–458 Ma) and P–T paths are comparable to their host gneisses; oceanic‐type eclogites have cumulate gabbro or E‐MORB geochemical signatures, their protolith and metamorphic ages are 510–516 Ma and 425–450 Ma, respectively(Zhang et al., 2008). Therefore, the North Qaidam UHP belt was thought to record the whole Neoprotoerozoic–Paleozoic Wilson cycle (Song et al., 2014). In this study, we reported three new kinds of eclogites: kyanite‐bearing eclogite, lawsonite pseudomorph‐bearing eclogite and double mineral eclogite. They occur as big lentoid blocks in regional granitic gneiss in the western part of the belt. Phase equilibrium modelling and zircon LA‐ICPMS U‐Pb dating show that all these three eclogites experienced a clockwise P–T path with peak metamorphic conditions close to or fall in the coesite stability field, and their peak metamorphic age were around 436‐439 Ma, similar to those continental‐type eclogites in this belt. But their protolith ages are between 1273 and 1070 Ma, and some of them recorded an amphibolite facies metamorphic age of 927 Ma, and geochemical data and zircon Lu‐Hf and O isotope analysis indicate these eclogites have features of present day N‐MORB. Combined with the existing results, we propose that the North Qaidam is a polycyclic composite orogenwhich recorded tectonic evolution of Mesoproterozoic ocean floor spreading, assembly and breakup of Rodinia supercontinent, Early Paleozoic oceanic deep subduction and subsequently continental deep subduction. 相似文献
6.
JAAP J. M. VAN DER MEER RUUD T. SLOTBOOM IRENE M. E. DE VIRES-BRUYNSTEEN 《Boreas: An International Journal of Quaternary Research》1984,13(4):393-402
In a sandpit in an alluvial fan in the central Netherlands, four interstadials could be recognized. The upper two are 14 C-dated and assigned to Hengelo and Moershoofd, while the lower two belong to either Odderade or Brorup. Lithological evidence suggested the existence of two zones indicative of permafrost separated by a zone in which running water was more important. The lower permafrost zone was found to be situated between the Moershoofd and Odderade interstadials, the younger zone to belong to the Upper Pleniglacial. 相似文献
7.
The advantages of using a lithium-drifted silicon X-ray detectorinstead of conventional Bragg spectrometers in microprobe analysisinclude simplicity and speed of operation. Also electron beamdamage to minerals can be almost eliminated, owing to the lowprobe current required. A procedure for quantitative analysisis outlined here, and its scope and limitations are discussed,with special reference to silicate analysis. Analyses of 34silicates independently analysed by chemical methods and conventionalprobe analysis are given. Above about 0.2 wt. per cent (element)systematic differences between energy-dispersive and conventionalprobe results are hardly significant. There are some discrepanciesbetween probe and chemical data, probably mostly due to errorsin the latter (e.g. high A12O3 and low FeO). Concentrationsbelow 0.2 per cent but above the theoretical limit of detectionare sometimes not recorded. This is presumed to be due to slightover-correction for background, which could be rectified bya more complicated background correction procedure. 相似文献
8.
The advantages of using a lithium-drifted silicon X-ray detectorinstead of conventional Bragg spectrometers in microprobe analysisinclude simplicity and speed of operation. Also electron beamdamage to minerals can be almost eliminated, owing to the lowprobe current required. A procedure for quantitative analysisis outlined here, and its scope and limitations are discussed,with special reference to silicate analysis. Analyses of 34silicates independently analysed by chemical methods and conventionalprobe analysis are given. Above about 0?2 wt. per cent (element)systematic differences between energy-dispersive and conventionalprobe results are hardly significant. There are some discrepanciesbetween probe and chemical data, probably mostly due to errorsin the latter (e.g. high Al2O3 and low FeO). Concentrationsbelow 0?2 per cent but above the theoretical limit of detectionare sometimes not recorded. This is presumed to be due to slightover-correction for background, which could be rectified bya more complicated background correction procedure. 相似文献
9.
REED KNOX 《Meteoritics & planetary science》1967,3(4):235-238
Abstract. Some very small particles of metal, revealed by polishing a chunk of Wolf Creek meteoritic iron oxide, appear to consist entirely of moderately shocked kamacite. The apparent lack of surviving taenite tentatively suggests that the Wolf Creek crater was formed by a hexahedrite, although medium octahedrites have recently been found within 4000 meters of the crater. Macrosegregation of nickel within the Wolf Creek meteoroid could account for the discrepancy. Further research on surviving metal is indicated. 相似文献
10.
MARK GRASMUECK GREGOR P. EBERLI JOHN K. REED KLAAS VERWER SAM PURKIS 《Sedimentology》2012,59(4):1278-1304
Cold‐water coral mound morphology and development are thought to be controlled primarily by current regime. This study, however, reveals a general lack of correlation between prevailing bottom current direction and mound morphology (i.e. footprint shape and orientation), as well as current strength and mound size (i.e. footprint area and height). These findings are based on quantitative analyses of a high‐resolution geophysical dataset collected with an Autonomous Underwater Vehicle from three cold‐water coral mound sites at the toe of slope of Great Bahama Bank. The three sites (80 km2 total) have an average of 14 mounds km?2, indicating that the Great Bahama Bank slope is a major coral mound region. At all three sites living coral colonies are observed on the surface of the mounds, documenting active mound growth. Morphometric analysis shows that mounds at these sites vary significantly in height (1 to 83 m), area (81 to 6 00 000 m2), shape (mound aspect ratio 0·1 to 1) and orientation (mound longest axis 0 to 180°). The Autonomous Underwater Vehicle measured bottom current data depict a north–south flowing current that reverses approximately every six hours. The tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity. An additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites. At most locations sedimentation rate lags slightly behind mound growth rate, causing mounds to develop into large structures. Where sedimentation rates are higher than mound growth rates, sediment partially or completely buries mounds. The spatial distribution and alignment of mounds can also be related to gravity mass deposits, as indicated by geomorphological features (for example, slope failure and linear topographic highs) in the three‐dimensional bathymetry. In summary, variability in sedimentation rates, current regime and underlying topography produce extraordinarily high variability in the distribution, development and morphology of coral mounds on the Great Bahama Bank slope. 相似文献