Five sequences are defined in the Oligocene succession of the Danish North Sea sector. Two of the sequences, 4.1a and 4.3, have been identified onshore Denmark.Two types of prograding lowstand deposits are recognized. Sand-dominated deposits occur proximally, comprising sharp-based forced regressive deposits covered with prograding low-stand deposits. Clay-dominated prograding lowstand deposits occur distally in the sequences. The highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals.The main sediment input direction was from the north and the northeast. A succession oif lithofacies, from shallow marine facies dominated by sand to outer shelf facies dominated by clay, is mapped in each of the sequences. An overall southward progradation of the shoreline took place during the Oligocene, interrupted only by minor shoreline retreats. 相似文献
Hydraulic flow and transport (heat and solute) within crystalline rocks is dominated by the fracture systems found within
them. In situ stress conditions have a significant impact on the hydraulic, mechanical and thermal coupled processes, and
quantification of these processes provides a key to understanding the often transient time-dependent behaviour of crystalline
rocks. In this paper, a geomechanical model is presented which describes fracture closure as a function of effective stress
and the changes in parameters such as storage, permeability, porosity and aperture. Allowing the fracture closure to be defined
by the change in normal effective stress provides a link to the numerical consideration of parametrical changes due to rock
stress alterations caused for example by changes in fracture fluid pressure, stress release, tectonic stress, thermal stress,
orientation of the natural fracture in the pervasive stress system and local changes in a rock mass due to stress alteration.
The model uses geometrical considerations based on a fractal distribution of apertures on the fracture surface, and applies
well-established analytical elastic deformation solutions to calculate the deformation response to changes in effective stress.
Analysis of the fractal generation method allows a standard normal distribution of fracture apertures to be predicted for
all common fractal dimensions relating to a 2D surface. Changes in the fracture aperture are related to hydraulic functions
such as permeability, storage and porosity of the fracture. The geomechanical model is experimentally validated against laboratory
scale experimental data gained from the closure of a fractured sample recovered at a depth of 3,800 m from the KTB pilot borehole.
Parameters for matching the experimental data were established externally, the only fitting parameters applied were the minimum
and maximum contact area between the surfaces and the number of allowable contacts. The model provides an insight into the
key processes determining the closure of a fracture, and can act as a material input function for numerical models linking
the effects of changes in the stress field, hydraulic or thermal conditions, to the flow and transport parameters of a fractured
system.
Résumé L’écoulement et le transport (chaleur et soluté) dans les roches cristallines sont dominés par les systèmes de fracture. Les
conditions de stress in-situ ont un impact significatif sur l’hydraulique, les processus couplés de mécanique et thermique
et la quantification de ces processus apportent une clé pour comprendre le comportement transitoire des roches cristallines.
Dans cet article un modèle géomécanique est présenté, modèle qui décrit la fermeture des fractures comme une fonction de la
contrainte effective et des changements de paramètres tels le coefficient d’emmagasinement, la perméabilité, la porosité et
l’ouverture. En s’accordant que la fermeture des fractures est définit par les changements de la contrainte effective normale,
on apporte le lien avec la considération numérique des changements paramétriques dus aux altérations de la contrainte des
roches, causés par exemple par des variations de la pression des fluides dans les fractures, du dégagement de la contrainte,
des contraintes tectoniques et thermiques, des orientations des fractures naturelles dans le système de contraintes pénétrantes,
et des changements locaux dans un massif de roches dus à l’altération des contraintes. Le modèle utilise des considérations
géométriques basées sur une distribution fractale des ouvertures à la surface des fractures, et permet d’établir des solutions
analytiques de la déformation élastique pour calculer la réponse de la déformation à la contrainte effective. L’analyse de
la méthode par génération fractale permet de prédire une distribution normale standard de l’ouverture des fractures, pour
toutes les dimensions fractales en relation avec les surfaces 2D. Les changements dans l’ouverture des fractures sont mis
en relation avec les fonctions hydrauliques tels la perméabilité, l’emmagasinement et la porosité de la fracture. Le modèle
géoméchanique est expérimentalement validé à l’échelle du laboratoire sur un échantillon fracturé récupéré à une profondeur
de 3,800 mètres sur le puits du site pilote KTB. Les paramètres du calibrage des données expérimentales ont été établies extérieurement,
les seuls paramètres utilisés étant les surfaces de contact minimum et maximum, et le nombre de contacts permis. Le modèle
apporte une connaissance perspicace sur le processus clé déterminant la fermeture des fractures, et peut servir de fonction
input dans les modèles numériques reliant les effets des variations de la contrainte du terrain, les conditions hydrauliques
ou thermales, les paramètres de l’écoulement et du transport et les systèmes de fracture.
Resumen El flujo hidráulico y transporte (de calor y solutos) dentro de rocas cristalinas está dominado por los sistemas de fracturas
que se encuentran en ellas. Las condiciones de esfuerzos in-situ tienen un impacto significativo en los procesos aparejados
termales, mecánicos e hidráulicos y la cuantificación de estos procesos aporta una clave para entender el frecuente comportamiento
transitorio dependiente de las rocas cristalinas. En este artículo se presenta un modelo geomecánico que describe el cierre
de fracturas en función del esfuerzo efectivo y los cambios en parámetros tal como almacenamiento, permeabilidad, porosidad
y apertura. El definir el cierre de fractura mediante el cambio en esfuerzo normal efectivo aporta un vínculo con la consideración
numérica de cambios paramétricos ocasionados por alteraciones de esfuerzos en la roca causadas, por ejemplo, por cambios en
presión de fluidos en fractura, liberación de esfuerzo, esfuerzo tectónico, esfuerzo termal, orientación de fracturas naturales
en el sistema de esfuerzos penetrante, y cambios locales en una masa rocosa ocasionados por alteración de esfuerzos. El modelo
utiliza consideraciones geométricas basadas en la distribución fractal de aperturas en la superficie de fractura y aplica
soluciones analíticas bien establecidas de deformación elástica para calcular la respuesta de deformación a cambios en el
esfuerzo efectivo. Los análisis del método de generación fractal permiten predecir una distribución normal standard para la
distribución de aperturas de fracturas para todas las dimensiones fractales comunes que se relacionan con una superficie 2D.
Los cambios en la apertura de fractura se relacionan con funciones hidráulicas tal como permeabilidad, almacenamiento y porosidad
de la fractura. El modelo geomecánico se ha validado experimentalmente en contra de datos experimentales a escala de laboratorio
obtenidos a partir del cierre de una muestra fracturada recuperada a una profundidad de 3,800 m en el pozo piloto KTB. Se
establecieron externamente parámetros que se ajustan a los datos experimentales, con los parámetros de ajuste aplicados que
fueron el área máxima y mínima de contacto entre las superficies y el número de contactos permisibles. El modelo arroja luz
sobre los procesos clave que determinan el cierre de una fractura y puede actuar como un material de función de entrada para
modelos numéricos que vinculan los efectos de cambios en el campo de esfuerzos, condiciones termales o hidráulicas, con los
parámetros de flujo y transporte de un sistema fracturado.
The spatial distribution of hydraulic properties in the subsurface controls groundwater flow and solute transport. However, many approaches to modeling these distributions do not produce geologically realistic results and/or do not model the anisotropy of hydraulic conductivity caused by bedding structures in sedimentary deposits. We have developed a flexible object-based package for simulating hydraulic properties in the subsurface—the Hydrogeological Virtual Realities (HyVR) simulation package. This implements a hierarchical modeling framework that takes into account geological rules about stratigraphic bounding surfaces and the geometry of specific sedimentary structures to generate realistic aquifer models, including full hydraulic-conductivity tensors. The HyVR simulation package can create outputs suitable for standard groundwater modeling tools (e.g., MODFLOW), is written in Python, an open-source programming language, and is openly available at an online repository. This paper presents an overview of the underlying modeling principles and computational methods, as well as an example simulation based on the Macrodispersion Experiment site in Columbus, Mississippi. Our simulation package can currently simulate porous media that mimic geological conceptual models in fluvial depositional environments, and that include fine-scale heterogeneity in distributed hydraulic parameter fields. The simulation results allow qualitative geological conceptual models to be converted into digital subsurface models that can be used in quantitative numerical flow-and-transport simulations, with the aim of improving our understanding of the influence of geological realism on groundwater flow and solute transport. 相似文献
Access to information about past states of the environment and social systems is fundamental to understand, and cope with, the challenges of climate change and over-exploitation of natural resources at the onset of the 21st century. The loss of (old) data is a major threat to understanding better and mitigating long-term effects of human activities and anthropogenic changes to the environment. Although this is intuitively evident for old and local literature of any kind, even present-day international publishing of papers without the underlying raw data makes access to basic information a crucial issue. Here, we summarise experience resulting from a EU-funded International Science & Technology Cooperation (INCO) project (CENSOR) addressing Coastal Ecosystem Research and Management in the El Niño Southern Oscillation (ENSO) context. We show that indeed “Grey Literature” is still one of the most important sources of knowledge about natural science research and management of natural resource systems in Latin American countries. We argue that public archiving of original data of present-day research and old (Grey) Literature and easy public access are important for appreciating today's global environmental challenges caused by human activities, both past and present. 相似文献
Concentrations of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in 14 sediment samples collected from four sites in the Mai Po Marshes Nature Reserve (within a RAMSAR Site) and from another six sites in Victoria Harbour and along the Hong Kong coastline. Elevated levels of PCDDs, and particularly OCDD, were detectable in all samples collected from the Mai Po Marshes and five of the six sites. In contrast to PCDDs, PCDFs were mainly found in sediment samples collected from industrial areas (Kwun Tong and To Kwa Wan) in Victoria Harbour. PCDD/F levels and congener profiles in the samples from the Mai Po Marshes Nature Reserve in particular show strong similarities to those reported in studies which have attributed similar elevated PCDD concentrations to nonanthropogenic PCDD sources. 相似文献
In the German State Brandenburg, water clarity and the concentrations of the water quality components chlorophyll a, seston and gelbstoff were measured in 27 lakes. Correlation analysis showed, that spectral beam attenuation at 662 and 514 nm was mainly dependent on changes in chlorophyll a concentrations. In the UV-channel at 360 nm, beam attenuation depended mostly on gelbstoff.
Multiple linear regression provided a direct model of beam attenuation at 514 nm with the inputs of inorganic seston, chlorophyll a and gelbstoff. The specific beam attenuation coefficients were comparable to other natural waters around the world. An inverse model is presented, from which gelbstoff and chlorophyll a could be predicted with some accuracy from the inputs of beam attenuation coefficients at 514 and 360 nm. However, it became obvious that biological variability put major constraints on the predictive capacity of both the direct and the inverse model.
Furthermore, we observed a good correspondence of Secchi depth and the inverse of beam attenuation at 514 nm. The predictions of Secchi depth and chlorophyll a concentration from the inverse model were assessed in perspective of using this instrument instead of laborious chemical analysis for future trophic status classification according to LAWA (Länderarbeitsgemeinschaft Wasser). Predictions of trophic status were principally good when using calibrated models, however, quality of classification critically depended on predictions of chlorophyll a. 相似文献
This paper presents the hydrological coupling of the software framework OpenGeoSys (OGS) with the EPA Storm Water Management
Model (SWMM). Conceptual models include the Saint Venant equation for river flow, the 2D Darcy equations for confined and
unconfined groundwater flow, a two-way hydrological coupling flux in a compartment coupling approach (conductance concept),
and Lagrangian particles for solute transport in the river course. A SWMM river–OGS aquifer inter-compartment coupling flux
is examined for discharging groundwater in a systematic parameter sensitivity analysis. The parameter study involves a small
perturbation (first-order) sensitivity analysis and is performed for a synthetic test example base-by-base through a comprehensive
range of aquifer parametrizations. Through parametrization, the test cases enables to determine the leakance parameter for
simulating streambed clogging and non-ocillatory river-aquifer water exchange rates with the sequential (partitioned) coupling
scheme. The implementation is further tested with a hypothetical but realistic 1D river–2D aquifer model of the Poltva catchment,
where discharging groundwater in the upland area affects the river–aquifer coupling fluxes downstream in the river course
(propagating feedbacks). Groundwater contribution in the moving river water is numerically determined with Lagrangian particles.
A numerical experiment demonstrates that the integrated river–aquifer model is a serviceable and realistic constituent in
a complete compartment model of the Poltva catchment. 相似文献