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101.
R. Thompson T. D. J. Cameron C. Schwarz K. A. Jensen V. Van Maenhaut Lemberge L. P. Sha 《第四纪科学杂志》1992,7(4):319-334
Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex. 相似文献
102.
103.
Springs along the south rim of the Grand Canyon, Arizona, are important ecological and cultural resources in Grand Canyon National Park and are discharge points for regional and local aquifers of the Coconino Plateau. This study evaluated the applicability of electrical resistance (ER) sensors for measuring diffuse, low-stage (<1.0 cm) intermittent and ephemeral flow in the steep, rocky spring-fed tributaries of the south rim. ER sensors were used to conduct a baseline survey of spring flow timing at eight sites in three spring-fed tributaries in Grand Canyon. Sensors were attached to a nearly vertical rock wall at a spring outlet and were installed in alluvial and bedrock channels. Spring flow timing data inferred by the ER sensors were consistent with observations during site visits, with flow events recorded with collocated streamflow gauging stations and with local precipitation gauges. ER sensors were able to distinguish the presence of flow along nearly vertical rock surfaces with flow depths between 0.3 and 1.0 cm. Laboratory experiments confirmed the ability of the sensors to monitor the timing of diffuse flow on impervious surfaces. A comparison of flow patterns along the stream reaches and at springs identified the timing and location of perennial and intermittent flow, and periods of increased evapotranspiration. 相似文献
104.
A. M. S. Smith L. Hebb A. Collier Cameron D. R. Anderson T. A. Lister C. Hellier D. Pollacco D. Queloz I. Skillen R. G. West 《Monthly notices of the Royal Astronomical Society》2009,398(4):1827-1834
We present results from a search for additional transiting planets in 24 systems already known to contain a transiting planet. We model the transits due to the known planet in each system and subtract these models from light curves obtained with the SuperWASP (Wide Angle Search for Planets) survey instruments. These residual light curves are then searched for evidence of additional periodic transit events. Although we do not find any evidence for additional planets in any of the planetary systems studied, we are able to characterize our ability to find such planets by means of Monte Carlo simulations. Artificially generated transit signals corresponding to planets with a range of sizes and orbital periods were injected into the SuperWASP photometry and the resulting light curves searched for planets. As a result, the detection efficiency as a function of both the radius and orbital period of any second planet is calculated. We determine that there is a good (>50 per cent) chance of detecting additional, Saturn-sized planets in P ∼ 10 d orbits around planet-hosting stars that have several seasons of SuperWASP photometry. Additionally, we confirm previous evidence of the rotational stellar variability of WASP-10, and refine the period of rotation. We find that the period of the rotation is 11.91 ± 0.05 d, and the false alarm probability for this period is extremely low (∼10−13 ) . 相似文献
105.
Martin Reich Carlos Palacios Macarena Alvear Eion M. Cameron Matthew I. Leybourne Artur Deditius 《Mineralium Deposita》2009,44(6):719-722
Recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting Cu assemblages
to form atacamite during supergene oxidation of Cu deposits in the Atacama region. In this report, we document the occurrence
of (Ag–I) inclusions hosted by supergene chalcocite from Mantos de la Luna, an argentiferous Upper Jurassic stratabound Cu
deposit in the Coastal Range of northern Chile. The presence of this unusual mineral assemblage indicates that iodargyrite
precipitated from reducing iodine-rich waters, suggesting that the fluids involved in supergene enrichment of Cu deposits
in the Coastal Range were more complex than previously thought. This suggests the prevalence of hyperarid conditions during
the latest stages of supergene enrichment of the Mantos de la Luna Cu deposit in the Atacama region, supporting the notion
that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of
meteoric water. 相似文献
106.
Kenneth D. Adams Ted Goebel Kelly Graf Geoffrey M. Smith Anna J. Camp Richard W. Briggs David Rhode 《Geoarchaeology》2008,23(5):608-643
The Great Basin of the western U.S. contains a rich record of Late Pleistocene and Holocene lake‐level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial‐temporal relationships between these records in the Lahontan basin to consider whether lake‐level fluctuations across the Pleistocene‐Holocene transition controlled distribution of archaeological sites. We use the reasonably well‐dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230–1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief. Paleoindian and Early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (_1220–1225 m) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. © 2008 Wiley Periodicals, Inc. 相似文献
107.
Luis Andrés Guillén Mary Beth Adams Emily Elliot Jason Hubbart Charlene Kelly Brenden McNeil William Peterjohn Nicolas Zegre 《水文研究》2021,35(4):e14106
Long-term experimental watershed studies have significantly influenced our global understanding of hydrological processes. The discovery and characterization of how stream water quantity and quality respond to a changing environment (e.g. land-use change, acidic deposition) has only been possible due to the establishment of catchments devoted to long-term study. One such catchment is the Fernow Experimental Forest (FEF) located in the headwaters of the Appalachian Mountains in West Virginia, a region that provides essential freshwater ecosystem services to eastern and mid-western United States communities. Established in 1934, the FEF is among the earliest experimental watershed studies in the Eastern United States that continues to address emergent challenges to forest ecosystems, including climate change and other threats to forest health. This data note describes available data and presents some findings from more than 50 years of hydrologic research at the FEF. During the first few decades, research at the FEF focused on the relationship between forest management and hydrological processes—especially those related to the overall water balance. Later, research included the examination of interactions between hydrology and soil erosion, biogeochemistry, N-saturation, and acid deposition. Hydro-climatologic and water quality datasets from long-term measurements and data from short-duration studies are publicly available to provide new insights and foster collaborations that will continue to advance our understanding of hydrology in forested headwater catchments. As a result of its rich history of research and abundance of long-term data, the FEF is positioned to continue to advance understanding of forest ecosystems in a time of unprecedented change. 相似文献
108.
109.
The Al26 activity has been measured by gamma-ray coincidence spectrometry in a total of 30 stony meteorites (13 bronzite, 13 hypersthene, 1 carbonaceous and 1 enstatite chondrite, and 2 achondrites). The measured Al26 content has been compared with calculated values based on the method developed by Lavrukhina and Ustinova (1972a, 1972b), which takes account of the modulation of the galactic cosmic ray intensity along the meteorite orbit due to solar magnetic activity. The predictions have been modified empirically to allow for the difference in chemical composition between H- and L-chondrites. Comparison of the measured value with that predicted in the absence of solar modulation permits the estimation of the aphelion of the orbit of the meteorite. The great majority of the derived aphelia lie within the range 2.05–2.45 AU. While this result must be treated with considerable reserve owing to the uncertainties associated with the model, it is consistent with recent data from photometric observations of the asteroid belt. 相似文献
110.
Most meteoritic chondrules and inclusions appear to have been liquid droplets at one time, or at least to have been close to the melting point so that they are easily deformed. The simplest mode of formation of such objects would be to have the liquid phases of the chondrules in thermodynamic equilibrium with gas in the primitive solar nebula, as suggested some years ago by Wood, but unfortunately pressures in the primitive solar nebula are orders of magnitude too small at temperatures in the range of the liquid mineral phases. This difficulty has led to an abandonment of this basic idea, but we suggest that the idea should be reexamined in view of the presence of higher pressures at moderate temperatures, together with water vapor enrichments, in the protoplanetary atmosphere of Jupiter prior to the collapse stage, which was recently studied by Perri and Cameron. A number of advantages arise from the complexities of such a model, and we discuss these together with a number of constraints. 相似文献