Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties   总被引：1，自引：0，他引：1  

Elena Piñero  Eulàlia Gràcia  Francisca Martínez-Ruiz  Juan Cruz Larrasoaña  Alexis Vizcaino  Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288

Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers. The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect to the other samples from the southern Hydrate Ridge.  相似文献   

The Equatorial Atlantic Mid-Ocean Channel: An Ultra High-Resolution Image of Its Burial History Based on TOPAS Profiles     

Baraza  J.  Ercilla  G.  Farrán  M.  Casamor  J. L.  Sorribas  J.  Flores  J. A.  Sierro  F.  Wersteeg  W. 《Marine Geophysical Researches》1997,19(2):115-135

Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC.  相似文献   

Hydrological characterization of dammed rivers in the NW Mediterranean region          下载免费PDF全文

Gemma Piqué  Ramon J. Batalla  Sergi Sabater 《水文研究》2016,30(11):1691-1707

Water scarcity and climatic variability in the Mediterranean region have traditionally required the construction of dams to guarantee water supply for irrigation, industrial and urban uses and hydropower production. Reservoirs affect the hydrology of the river downstream, but the magnitude and persistence of these effects are still poorly unknown. Understanding the magnitude of these effects is the objective of this paper, in which we analyse the flow regimes of twelve rivers located in the NW Mediterranean region. Different temporal scales (daily, monthly and annual) are used for the analysis and also to estimate flow variables associated with flow magnitude, frequency, duration and variability. It is shown that dams alter the hydrological regime of most of the studied rivers, with special influence on monthly flows and flood magnitude and frequency. The most altered rivers (Muga and Siurana, NE Iberian Peninsula) experience a complete overturn in their flow regime with, for instance, flood reduction reaching up to 76% for the 2‐year flood event. Other rivers showed lower changes in hydrology (e.g. Orb and Têt). Annual runoff showed a pattern of decrease in all the studied rivers (regulated and non‐regulated) indicating that besides dams (i.e. reservoir evaporation), other factors likely affect water yield. A general recovery downstream from dams is also observed at all temporal scales, mainly because of the inflow from tributaries. Although dams have a clear impact on the hydrology of Mediterranean rivers, water withdrawals and diversions for irrigation and other consumptive uses also affected the hydrological patterns. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Occurrence of pockmarks on the Ortegal Spur continental margin,Northwestern Iberian Peninsula     

G. Jané  A. Maestro  G. Ercilla  J. López-Martínez  J.R. De Andrés  D. Casas  D. González-Aller  M. Catalán-Morollón 《Marine and Petroleum Geology》2010

A total of 445 pockmarks were observed on the upper continental slope of the northwest corner of the Iberian Peninsula (the Ortegal Spur area) by swath bathymetric and ultrahigh resolution seismic data. The pockmarks are U-, V- and W-shaped and have terraces or indentations in cross-section, and are dish-shaped (circular to oval) in plan view. They occur on the surface of the seabed and buried within the Plio-Quaternary and Neogene sediments. Four types of pockmarks were identified and mapped on the basis of their plan-view and cross-section morphology: regular, irregular, asymmetric and composite. The concentration of pockmarks is attributed to seepage of fluids migrating up-dip from deeper parts of the sedimentary basin. A linear high-density concentration with a NNW to N, NE and ESE trend of pockmarks is observed above inferred basement faults that do not affect the Quaternary succession. These pockmarks are thus caused by seepage of thermogenic gas and/or other pore fluids from deeper Late Cretaceous units, and their distribution may help to improve our understanding of the fluid system and migration regime in this part of the Galicia continental margin.  相似文献   

Growth and feeding patterns of European anchovy (Engraulis encrasicolus) early life stages in the Aegean Sea (NE Mediterranean)     

Ignacio A. Catalán  Arild Folkvord  Isabel Palomera  Gemma Quílez-Badía  Fotini Kallianoti  Anastasios Tselepides  Argyris Kallianotis 《Estuarine, Coastal and Shelf Science》2010

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Reply to Discussion of “Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example”*     

Ida K. Westerberg  Giuliano Di Baldassarre  Keith J. Beven  Gemma Coxon  Tobias Krueger 《水文科学杂志》2020,65(Z2):2001-2003

ABSTRACT

Ertsen discusses the representation of reality and uncertainty in our paper, raising three critical points. In response to the first, we agree that discussion of different interpretations of the concept of uncertainty is important when developing perceptual models – making different uncertainty interpretations explicit was a key motivation behind our method. Secondly, we do not, as Ertsen suggests, deny anyone who is not a “certified” scientist to have relevant knowledge. The elicitation of diverse views by discussing perceptual models is a basis for open discussion and decision making. Thirdly, Ertsen suggests that it is not useful to treat socio-hydrological systems as if they exist. We argue that we act as “pragmatic realists” in most practical applications by treating socio-hydrological systems as an external reality that can be known. But the uncertainty that arises from our knowledge limitations needs to be recognized, as it may impact on practical decision making and associated costs.  相似文献   

Large-sample hydrology: recent progress,guidelines for new datasets and grand challenges     

Nans Addor  Hong X. Do  Camila Alvarez-Garreton  Gemma Coxon  Keirnan Fowler  Pablo A. Mendoza 《水文科学杂志》2020,65(5):712-725

ABSTRACT

Large-sample hydrology (LSH) relies on data from large sets (tens to thousands) of catchments to go beyond individual case studies and derive robust conclusions on hydrological processes and models. Numerous LSH datasets have recently been released, covering a wide range of regions and relying on increasingly diverse data sources to characterize catchment behaviour. These datasets offer novel opportunities, yet they are also limited by their lack of comparability, uncertainty estimates and characterization of human impacts. This article (i) underscores the key role of LSH datasets in hydrological studies, (ii) provides a review of currently available LSH datasets, (iii) highlights current limitations of LSH datasets and (iv) proposes guidelines and coordinated actions to overcome these limitations. These guidelines and actions aim to standardize and automatize the creation of LSH datasets worldwide, and to enhance the reproducibility and comparability of hydrological studies.  相似文献   

A predictive numerical model for potential mapping of the gas hydrate stability zone in the Gulf of Cadiz     

R. Len  L. Somoza  C.J. Gimnez-Moreno  C.J. Dabrio  G. Ercilla  D. Praeg  V. Díaz-del-Río  M. Gmez-Delgado 《Marine and Petroleum Geology》2009,26(8):1564-1579

This paper presents a computational model for mapping the regional 3D distribution in which seafloor gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment. The construction of the model is comprised of three primary steps, namely: (1) the construction of surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the thickness of the hydrate stability zone. The solution is based on a transcendental function, which is solved iteratively in a GIS environment.The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures, is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions, and explains the geometry and distribution of geological structures derived from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper continental slope.  相似文献   

Morphosedimentary features and recent depositional architectural model of the Cantabrian continental margin     

G. Ercilla  D. Casas  F. Estrada  J.T. Vázquez  J. Iglesias  M. García  M. Gómez  J. Acosta  J. Gallart  A. Maestro-González 《Marine Geology》2008,247(1-2):61-83

Multibeam bathymetry, high (sleeve airguns) and very high resolution (parametric system-TOPAS-) seismic records were used to define the morphosedimentary features and investigate the depositional architecture of the Cantabrian continental margin. The outer shelf (down to 180–245 m water depth) displays an intensively eroded seafloor surface that truncates consolidated ancient folded and fractured deposits. Recent deposits are only locally present as lowstand shelf-margin deposits and a transparent drape with bedforms. The continental slope is affected by sedimentary processes that have combined to create the morphosedimentary features seen today. The upper (down to 2000 m water depth) and lower (down to 3700–4600 m water depth) slopes are mostly subject to different types of slope failures, such as slides, mass-transport deposits (a mix of slumping and mass-flows), and turbidity currents. The upper slope is also subject to the action of bottom currents (the Mediterranean Water — MW) that interact with the Le Danois Bank favouring the reworking of the sediment and the sculpting of a contourite system. The continental rise is a bypass region of debris flows and turbidity currents where a complex channel-lobe transition zone (CLTZ) of the Cap Ferret Fan develops.The recent architecture depositional model is complex and results from the remaining structural template and the great variability of interconnected sedimentary systems and processes. This margin can be considered as starved due to the great sediment evacuation over a relatively steep entire depositional profile. Sediment is eroded mostly from the Cantabrian and also the Pyrenees mountains (source) and transported by small stream/river mountains to the sea. It bypasses the continental shelf and when sediment arrives at the slope it is transported through a major submarine drainage system (large submarine valleys and mass-movement processes) down to the continental rise and adjacent Biscay Abyssal Plain (sink). Factors controlling this architecture are tectonism and sediment source/dispersal, which are closely interrelated, whereas sea-level changes and oceanography have played a minor role (on a long-term scale).  相似文献   

Pedogenetic processes coeval with Neogene faults evolution in the Barcelona's Plain,NE Spain     

Irene Cantarero  Anna Travé  Gemma Alías 《Journal of Geochemical Exploration》2009

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