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51.
The northern Wanganui Basin, New Zealand, is one of the key global sites for understanding marine cyclic sedimentation during the Quaternary. This paper presents the first evidence of marine cyclic sedimentation from its central-southern parts. Sedimentological, micropalaeontological and palynological analyses on a 280-m-deep borehole encountered units dating back to MIS 10. The sequence includes four marine cycles spanning MIS 9–5, which are overlain by terrestrial fluvial aggradation surfaces dating from MIS 4–2. Each marine unit represents a progressively shallowing depositional environment from the mid-shelf to coastal plain. This is overlain by a terrestrial sequence of lowstand fluvial terraces. Localized fault movements appear to have influenced the sedimentary character of the sequence during MIS 7a and 5e producing basement highs which provided protection to the shoreline. The cyclothems described in this paper now extend the already extensive, previously described record from MIS 17–10 to produce a combined eustatic record of Quaternary sea level change within the basin to MIS 5. They also provide an excellent example of the sedimentary response of a coastal basin to a progressive loss of sedimentation accommodation space. 相似文献
52.
Tyler G. Sproule Glenn A. Spinelli John L. Wilson Michael D. Fort Peter S. Mozley Jared Ciarico 《Ground water》2021,59(3):396-409
Fault zones are an important control on fluid flow, affecting groundwater supply, contaminant migration, and carbon storage. However, most models of fault seal do not consider fault zone cementation, despite the recognition that it is common and can dramatically reduce permeability. In order to study the field-scale hydrogeologic effects of fault zone cementation, we conducted a series of aquifer pumping tests in wells installed within tens of meters of the variably cemented Loma Blanca Fault, a normal fault in the Rio Grande Rift. In the southern half of the study area, the fault zone is cemented by calcite; the cemented zone is 2-8 m wide. In the center of the study area, the cemented fault zone is truncated at a buttress unconformity that laterally separates hydrostratigraphic units with a ∼40X difference in permeability. The fault zone north of the unconformity is not cemented. Constant rate pumping tests indicate that where the fault is cemented, it is a barrier to groundwater flow. This is an important demonstration that a fault with no clay in its core and similar sediment on both sides can be a barrier to groundwater flow by virtue of its cementation; most conceptual models for the hydrogeology of faults would predict that it would not be a barrier to groundwater flow. Additionally, the lateral permeability heterogeneity across the unconformity imposes another important control on the local flow field. This permeability discontinuity acts as either a no-flow boundary or a constant head boundary, depending on the location of pumping. 相似文献
53.
We present the first spectra of Neptune taken with the Spitzer Space Telescope, highlighting the high-sensitivity, moderate-resolution 10-20 μm (500-1000 cm−1) spectra. We report the discovery of methylacetylene (CH3C2H) and diacetylene (C4H2) with derived 0.1-mbar volume mixing ratios of (1.2±0.1)×10−10 and (3±1)×10−12 respectively. 相似文献
54.
55.
A number of archeological features, including in‐filled irrigation canals of uncertain prehistoric age, occur within the Holocene floodplain of the Salt River at Phoenix, Arizona. In the first attempt to date irrigation‐canal sediments using luminescence methods, we obtained age estimates of 1640 ± 190 yr B.P. (1σ) (multi‐aliquot or MA) and 1621 ± 95 yr B.P. (post‐IR single‐aliquot‐regenerative‐dose or SAR) for a single sample from the base of the oldest canal‐infilling deposits (all IR‐PSL ages reported in this article are in calendar years before A.D. 2001). For the remaining canal samples, weighted mean luminescence ages of 819 ± 45 yr (MA) and 826 ± 32 yr (post‐IR SAR) were obtained. Thus from photonic dating we can resolve the first and last phases of canal use at this Phoenix site: initiation at ca. 1600 years ago and final use at ca. 800 years ago. These results demonstrate the power of SAR luminescence sediment dating to enhance our understanding of prehistoric irrigation‐canal development and usage here and elsewhere in the world. © 2004 Wiley Periodicals, Inc. 相似文献
56.
Christopher K. Shuler Aly I. El-Kadi Henrietta Dulai Craig R. Glenn Joseph Fackrell 《Hydrogeology Journal》2017,25(8):2419-2434
This study presents a modeling framework for quantifying human impacts and for partitioning the sources of contamination related to water quality in the mixed-use landscape of a small tropical volcanic island. On Tutuila, the main island of American Samoa, production wells in the most populated region (the Tafuna-Leone Plain) produce most of the island’s drinking water. However, much of this water has been deemed unsafe to drink since 2009. Tutuila has three predominant anthropogenic non-point-groundwater-pollution sources of concern: on-site disposal systems (OSDS), agricultural chemicals, and pig manure. These sources are broadly distributed throughout the landscape and are located near many drinking-water wells. Water quality analyses show a link between elevated levels of total dissolved groundwater nitrogen (TN) and areas with high non-point-source pollution density, suggesting that TN can be used as a tracer of groundwater contamination from these sources. The modeling framework used in this study integrates land-use information, hydrological data, and water quality analyses with nitrogen loading and transport models. The approach utilizes a numerical groundwater flow model, a nitrogen-loading model, and a multi-species contaminant transport model. Nitrogen from each source is modeled as an independent component in order to trace the impact from individual land-use activities. Model results are calibrated and validated with dissolved groundwater TN concentrations and inorganic δ15N values, respectively. Results indicate that OSDS contribute significantly more TN to Tutuila’s aquifers than other sources, and thus should be prioritized in future water-quality management efforts. 相似文献
57.
The hydraulic gradient between aquifers and rivers is one of the most variable properties in a river/aquifer system. Detailed process understanding of bank storage under hydraulic gradients is obtained from a two‐dimensional numerical model of a variably saturated aquifer slice perpendicular to a river. Exchange between the river and the aquifer occurs first at the interface with the unsaturated zone. The proportion of total water exchanged through the river bank compared to the river bed is a function of aquifer hydraulic conductivity, partial penetration, and hydraulic gradient. Total exchange may be estimated to within 50% using existing analytical solutions provided that unsaturated zone processes do not strongly influence exchange. Model‐calculated bank storage is at a maximum when no hydraulic gradient is present and increases as the hydraulic conductivity increases. However, in the presence of a hydraulic gradient, the largest exchange flux or distance of penetration does not necessarily correspond to the highest hydraulic conductivity, as high hydraulic conductivity increases the components of exchange both into and out of an aquifer. Flood wave characteristics do not influence ambient groundwater discharge, and so in large floods, hydraulic gradients must be high to reduce the volume of bank storage. Practical measurement of bank storage metrics is problematic due to the limitations of available measurement technologies and the nested processes of exchange that occur at the river‐aquifer interface. Proxies, such as time series concentration data in rivers and groundwater, require further development to be representative and quantitative. 相似文献
58.
Leigh N. Fletcher Kevin H. Baines Adam P. Showman Glenn S. Orton C. Merlet 《Icarus》2011,214(2):510-533
The latitudinal variation of Saturn’s tropospheric composition (NH3, PH3 and AsH3) and aerosol properties (cloud altitudes and opacities) are derived from Cassini/VIMS 4.6-5.1 μm thermal emission spectroscopy on the planet’s nightside (April 22, 2006). The gaseous and aerosol distributions are used to trace atmospheric circulation and chemistry within and below Saturn’s cloud decks (in the 1- to 4-bar region). Extensive testing of VIMS spectral models is used to assess and minimise the effects of degeneracies between retrieved variables and sensitivity to the choice of aerosol properties. Best fits indicate cloud opacity in two regimes: (a) a compact cloud deck centred in the 2.5-2.8 bar region, symmetric between the northern and southern hemispheres, with small-scale opacity variations responsible for numerous narrow light/dark axisymmetric lanes; and (b) a hemispherically asymmetric population of aerosols at pressures less than 1.4 bar (whose exact altitude and vertical structure is not constrained by nightside spectra) which is 1.5-2.0× more opaque in the summer hemisphere than in the north and shows an equatorial maximum between ±10° (planetocentric).Saturn’s NH3 spatial variability shows significant enhancement by vertical advection within ±5° of the equator and in axisymmetric bands at 23-25°S and 42-47°N. The latter is consistent with extratropical upwelling in a dark band on the poleward side of the prograde jet at 41°N (planetocentric). PH3 dominates the morphology of the VIMS spectrum, and high-altitude PH3 at p < 1.3 bar has an equatorial maximum and a mid-latitude asymmetry (elevated in the summer hemisphere), whereas deep PH3 is latitudinally-uniform with off-equatorial maxima near ±10°. The spatial distribution of AsH3 shows similar off-equatorial maxima at ±7° with a global abundance of 2-3 ppb. VIMS appears to be sensitive to both (i) an upper tropospheric circulation (sensed by NH3 and upper-tropospheric PH3 and hazes) and (ii) a lower tropospheric circulation (sensed by deep PH3, AsH3 and the lower cloud deck). 相似文献
59.
Helen Glenn Diana TingleySonia Sánchez Maroño Dennis HolmGurpreet Padda Ingi Runar EdvardssonAlexis Conides Kostas KapirisMintewab Bezabih Premachandra WattageSakari Kuikka 《Marine Policy》2012,36(1):54-72
This paper explores the issue of “trust” in the fisheries science community, a key corollary of effective risk communication. It presents the findings of a survey undertaken in Iceland, Greece, Spain, United Kingdom and Faroe Islands during 2008. The findings reveal differing levels of trust and mistrust in the fisheries science community between countries and between stakeholder groups, demonstrating areas for future attention in the interests of improving fisheries science and management. As this paper explores, unfortunately the “trust” necessary for effective stakeholder cooperation and participation within current fisheries science is currently somewhat lacking. The cited reasons behind this lack of trust include: a lack of soundness, credibility, responsiveness, flexibility and stakeholder involvement, flawed data and weak science, poor communications and political and lobby group interference. Notable from the results is a lack of consensus on the existence of a common language and vision. It is evident, however, that certain aspects of fisheries science are strong contributors to trust and that there are opportunities for improvement. 相似文献
60.
We present the closed form of a general steady-state shape factor for a partially penetrating well in a uniform anisotropic aquifer. Our simple analytical expression for the shape factor has a uniform representation for full range of parameters and meets or exceeds the accuracy of previous results obtained through semiempirical methods (e.g., Bouwer and Rice [1976] equations). This general shape factor pertains to the flow of fluids (water or air) in subsurface formations when the upper formation boundary has constant potential and the lower boundary is impermeable. The results of our investigation are directly applicable to analyses of (1) slug tests with falling or rising head and (2) injection/extraction tests with constant head, essential techniques for the characterization of hydraulic conductivity of aquifers, streambeds, or lakebeds as well as the design of aquifer and soil remediation systems. 相似文献