Bench development along the regulated,lower River Dee,UK     

Shi Changxing  Geoffrey Petts  Angela Gurnell 《地球表面变化过程与地形》1999,24(2):135-149

Channel change to regulated flows along large lowland rivers with cohesive bank materials has been investigated on the lower Welsh Dee, including the tidally influenced reach. Reduction of channel width has involved the formation of a 5–40m wide discontinuous bench, often linking ‘point’ and ‘concave’ locations. Map evidence shows that wide benches occur where historically the channel had migrated laterally; narrow benches were found at stable channel locations. Auger cores of the bench deposits clearly differentiated the two contrasting depositional environments within meandering rivers: ‘point bench’ and ‘concave bench’. Around an individual bend a morphologically continuous bench showed a gradient in sediment characteristics from coarser sediments (point locations) to finer organic deposits (concave locations); it also showed a topographic gradient, gaining 0.5m in elevation around the bend suggesting that bench accretion at concave locations is faster than at point locations in fluvially dominated reaches. Such patterns are suggested to have important implications for riparian ecosystems. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Evaluating Groundwater Interbasin Flow Using Multiple Models and Multiple Types of Data          下载免费PDF全文

Ming Ye  Liying Wang  Karl. F. Pohlmann  Jenny B. Chapman 《Ground water》2016,54(6):805-817

The groundwater interbasin flow, Q_y, from the north of Yucca Flat into Yucca Flat simulated using the Death Valley Regional Flow System (DVRFS) model greatly exceeds assessments obtained using other approaches. This study aimed to understand the reasons for the overestimation and to examine whether the Q_y estimate can be reduced. The two problems were tackled from the angle of model uncertainty by considering six models revised from the DVRFS model with different recharge components and hydrogeological frameworks. The two problems were also tackled from the angle of parametric uncertainty for each model by first conducting Morris sensitivity analysis to identify important parameters and then conducting Monte Carlo simulations for the important parameters. The uncertainty analysis is general and suitable for tackling similar problems; the Morris sensitivity analysis has been utilized to date in only a limited number of regional groundwater modeling. The simulated Q_y values were evaluated by using three kinds of calibration data (i.e., hydraulic head observations, discharge estimates, and constant‐head boundary flow estimates). The evaluation results indicate that, within the current DVRFS modeling framework, the Q_y estimate can only be reduced to about half of the original estimate without severely deteriorating the goodness‐of‐fit to the calibration data. The evaluation results also indicate that it is necessary to develop a new hydrogeological framework to produce new flow patterns in the DVRFS model. The issues of hydrogeology and boundary flow are being addressed in a new version of the DVRFS model planned for release by the U.S. Geological Survey.  相似文献   

Features of acid–saline systems of Southern Australia     

Bruce L. Dickson  Angela M. Giblin 《Applied Geochemistry》2009

The discovery of layered, SO₄-rich sediments on the Meridiani Planum on Mars has focused attention on understanding the formation of acid–saline lakes. Many salt lakes have formed in southern Australia where regional groundwaters are characterized by acidity and high salinity and show features that might be expected in the Meridiani sediments. Many (but not all) of the acid–saline Australian groundwaters are found where underlying Tertiary sediments are sulfide-rich. When waters from the formations come to the surface or interact with oxidised meteoric water, acid groundwaters result. In this paper examples of such waters around Lake Tyrrell, Victoria, and Lake Dey-Dey, South Australia, are reviewed. The acid–saline groundwaters typically have dissolved solids of 30–60 g/L and pH commonly <4.5. Many contain high concentrations of Fe and other metals, leached from local sediments. The combination of acidity and salinity also releases Ra. Around salt-lakes, these acidic waters often emerge at the surface in marginal spring zones where the low density (ρ ∼ 1.04) regional water flows out over the denser (ρ ∼ 1.16) lake brines. In the spring zones examined, large amounts of Fe are commonly precipitated. In a few places minerals of the alunite-jarosite family are formed which can trap many other metals, including Ra. The studied groundwater systems were discovered by U exploration programs following up radiometric anomalies related to this Ra. Evaporation concentrates the lesser soluble salts (gypsum and some halite) on the surface of the lakes. The lake brines contain most of the more soluble salts and form a column within the porous sediments which is held in place by hydrostatic forces around the salt-lake. These brines are near-neutral in pH.  相似文献   

Heterotrophic bacteria and their relationship with plankton in a New Zealand freshwater lake     

Angela J. Ramsay 《新西兰海洋与淡水研究杂志》2013,47(1):77-90

The viable heterotrophic bacteria of Lake Grasmere in inland Canterbury (43° 05 S, 171° 45 E) were studied. Numbers of bacteria in water above a spring were positively correlated with rainfall in the 7 days before sampling, but bacteria in open water and from over the macrophyte Elodea canadensis were not. There was some increase in the bacterial population in the water over E. canadensis in the autumn to winter months. Numbers of bacteria in the open water ranged from 55 to 1020 cells per millilitre, and were outnumbered by algae by a factor of between 4 and 34. The bacterial population tended to increase after blooms of zooplankton, but there was little or no response to changes in phytoplankton populations. Benthic bacteria rarely increased in numbers after the deposition of organic matter.  相似文献   

Book review     

Ronald C. Chaney  Marnie D. Chapman  William Miller III 《Marine Georesources & Geotechnology》2013,31(3):333-339

Geotechnical Aspects of Coastal and Offshore Structures. Edited by Yudhair and A. S. Balasubramaniam. Proceedings of the Symposium on Geotechnical Aspects of Coastal and Offshore Structures, Bangkok, December 14–18,1981. Rotterdam: A. A. Balkema, 1983. 280 pp. $40.00.

The Seaside Naturalist: A Guide to Nature Study at the Seashore. Written and illustrated by D. A. Coulombe. Englewood Cliffs, N.J.: Prentice‐Hall, Inc., 1984. 246 pp. $12.95.

Ichnology, Trace Fossils in Sedimentology and Stratigraphy. By A. A. Ekdale, R. G. Bromley, and S. G. Pemberton. Society of Economic Paleontologists and Mineralogists, Short Course No. 15. Tulsa, Okla.: S.E.P.M., 1984. 317 pp. S.E.P.M. members, $16.00; non‐members, $20.00.  相似文献   

New distribution records of macrothricid Cladocera in New Zealand     

M. A. Chapman 《新西兰海洋与淡水研究杂志》2013,47(1)

Neothrix armata is recorded for the first time from Lakes Rotorua and Rotokakahi, and Streblocerus serricaudatus from Lake Tikitapu.  相似文献   

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties     

Arne Schnack-Friedrichsen  Angela M. Davis  Jim D. Bennell  Dei G. Huws 《Marine Georesources & Geotechnology》2013,31(4):221-243

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.  相似文献   

Synoptic surveys of lakes Rotorua and Rotoiti     

G. R. Fish  M. A. Chapman 《新西兰海洋与淡水研究杂志》2013,47(4):571-584

Surface and bottom water samples were collected from 39 widely spaced stations in Lake Rotorua in February 1967 and from 12 stations in Lake Rotoiti in March 1967. In Lake Rotorua, data obtained from these samples showed that small horizontal differences existed between the southern and northern parts of the lake probably related to the higher inflow of plant nutrients at the southern end and to the prevailing southerly wind concentrating phytoplankton populations at the northern end. Lake Rotoiti, which differed from Lake Rotorua in being thermally stratified, showed no important horizontal differences, Vigorous mixing in the strata probably being accomplished by deep seiches except in the shallow western basin of the lake, where the inflow from Lake Rotorua occurs. Serial vertical hauls for a zooplankton survey of Lake Rotoiti were taken from three stations in March 1967. The distribution of zooplankton was complex because diurnal vertical migrations of the animals were combined with horizontal movement of the water layers.  相似文献   

Submerged vegetation of the Rotorua and Waikato lakes     

V. J. Chapman  J. M. A. Brown  F. I. Dromgoole  B. T. Coffey 《新西兰海洋与淡水研究杂志》2013,47(2):259-279

Five plant communities in Lake Rotoiti, North Island, New Zealand (38° 02’ S, 176° 24’ E) are described. In shallow water (0–2 m depth) partly protected from the prevailing westerly winds, some indigenous species form characteristic mounds. From 2 to 6 m depth the exotic macrophyte Lagarosiphon major (Ridley) Moss is the dominant and forms dense beds which appear to have completely replaced any native vegetation. Elodea canadensis Michx., a longer‐established exotic, may form a minor component of this zone, but may become the dominant species in water above and below the Lagarosiphon zone. Lagarosiphon appears to be primarily restricted to silty sand, but on pure silt areas it is replaced by Elodea and/or Nitella hookeri A. Braun. These zonations are probably static rather than successional. On underwater cliff faces and boulder shores a seasonal succession of algae was the major vegetation. Only filamentous cyanophytes grew within 1–2m of geothermal springs in the lake.  相似文献   

The Pelona–Orocopia–Rand and related schists of southern California: a review of the best-known archive of shallow subduction on the planet     

Alan D. Chapman 《International Geology Review》2017,59(5-6):664-701

ABSTRACT

The Pelona–Orocopia–Rand and related schists of southern California are an archetypal example of an exhumed shallow subduction complex. ‘The schist’ comprises mainly trench materials underthust beneath continental arc rocks during Late Cretaceous–early Cenozoic collision of one or more oceanic plateaux with southern California. The arc-on-trench relationship, without intervening mantle or lowermost crust, implies that significant subduction erosion accompanied shallow subduction. Upsection increases in metamorphic grade (~150 ± 100°C/km) and spatial variations in age and peak temperature provide an ~50 million year long record of tectonic underplating within a cooling system. Evidence for palaeoseismic events in earliest formed and hottest (locally transitional granulite grade) schists provides a possible field-based record of episodic tremor and slow slip events such as detected in several modern shallow subduction zones. Structural ascent of the schist was achieved in distinct Late Cretaceous–early Eocene and late Oligocene–early Miocene extensional pulses, the first during collapse of gravitationally unstable upper plate assemblages and accompanied by trench-directed (top-NE) lower plate extrusion and the second corresponding temporally, spatially, and in character with core complex formation in the SW United States. The line between schist and core complex belts is blurred by the recent discovery of schist within 40 km of the nearest core complex and containing synkinematic Miocene intrusions, a hallmark of SW U.S. core complexes. The history of schist assembly, metamorphism, and exhumation provides the most complete field-based record of thermo-mechanical processes, subduction erosion and tectonic underplating in particular, that operated during a shallow subduction event. Future cross-disciplinary investigations of, and comparisons between, the schist and other possible ancient (e.g. Swakane gneiss, Sanbagawa belt, Qiangtang terrane) and modern (e.g. Cascadia, SW Japan, central Mexico, Chile) shallow subduction zones will yield new insights into the tectonic and petrologic processes that operate within such systems.  相似文献