Revisiting the morphological method in two-dimensions to quantify bed-material transport in braided rivers     

Gilles Antoniazza  Maarten Bakker  Stuart N. Lane 《地球表面变化过程与地形》2019,44(11):2251-2267

Research in the 1990s showed that bed-material transport rates could be estimated at the reach scale in both one-dimension and, over small spatial scales (10s of m), in two-dimensions. The limit on the latter was the spatial scale over which it was possible to obtain distributed data on morphological change. Here, we revisit the morphological method given progress in both topographical data acquisition and hydraulic modelling. The bed-material transport needed to conserve mass is calculated in both one and two dimensions for a 1600 m × 300 m Alpine braided river “laboratory”. High-resolution topographical data were acquired by laser scanning to quantify Digital Elevation Models (DEMs), and morphological changes caused by the flushing of the water intake were derived from repeated surveys. Based on DEMs of differences, 1D bed-material transport rates were calculated using the morphological method. Then, a 2D hydraulic model was combined with a topographic correction to route sediment through the network of braided channels and to obtain a spatially variable estimate of transport in both downstream and cross-stream directions. Monte Carlo simulation was applied to the routing model parameters, allowing identification of the most probable parameter values needed to minimize negative transport. The results show that within-section spatial compensation of erosion and deposition using the 1D treatment leads to substantial local errors in transport rate estimates, to a degree related to braiding intensity. Even though the 2D application showed that a large proportion of the total transport was actually concentrated into one main channel during the studied low flow event, the proportion of transport in secondary anabranches is substantial when the river starts braiding. Investigations of the effects of DEM resolution, competent flow duration and survey frequency related to ‘travelling bedload’ and sequential erosion-deposition emphasized the critical importance of careful data collection in the application of the morphological method. © 2019 John Wiley & Sons, Ltd.  相似文献   

Mega-monsoon variability during the late Triassic: Re-assessing the role of orbital forcing in the deposition of playa sediments in the Germanic Basin   总被引：1，自引：0，他引：1  

André Bahr  Gilles Kolber  Stefanie Kaboth-Bahr  Lutz Reinhardt  Oliver Friedrich  Jörg Pross 《Sedimentology》2020,67(2):951-970

The formation of the supercontinent Pangaea during the Permo–Triassic gave rise to an extreme monsoonal climate (often termed ‘mega-monsoon’) that has been documented by numerous palaeo-records. However, considerable debate exists about the role of orbital forcing in causing humid intervals in an otherwise arid climate. To shed new light on the forcing of monsoonal variability in subtropical Pangaea, this study focuses on sediment facies and colour variability of playa and alluvial fan deposits in an outcrop from the late Carnian (ca 225 Ma) in the southern Germanic Basin, south-western Germany. The sediments were deposited against a background of increasingly arid conditions following the humid Carnian Pluvial Event (ca 234 to 232 Ma). The ca 2·4 Myr long sedimentary succession studied shows a tripartite long-term evolution, starting with a distal mud-flat facies deposited under arid conditions. This phase was followed by a highly variable playa-lake environment that documents more humid conditions and finally a regression of the playa-lake due to a return of arid conditions. The red–green (a*) and lightness (L*) records show that this long-term variability was overprinted by alternating wet/dry cycles driven by orbital precession and ca 405 kyr eccentricity, without significant influence of obliquity. The absence of obliquity in this record indicates that high-latitude forcing played only a minor role in the southern Germanic Basin during the late Carnian. This is different from the subsequent Norian when high-latitude signals became more pronounced, potentially related to the northward drift of the Germanic Basin. The recurring pattern of pluvial events during the late Triassic demonstrates that orbital forcing, in particular eccentricity, stimulated the occurrence and intensity of wet phases. It also highlights the possibility that the Carnian Pluvial Event, although most likely triggered by enhanced volcanic activity, may also have been modified by an orbital stimulus.  相似文献   

Advances and Practices on the Research,Prevention and Control of Land Subsidence in Coastal Cities     

YAN Xuexin  YANG Tianliang  XU Yan  Luigi TOSI  Esther STOUTHAMER  Heri ANDREAS  Philip MINDERHOUD  Anirut LADAWADEE  Ramon HANSSEN  Gilles ERKENS  Pietro TEATINI  LIN Jinxin  Roberta BONì  Jarinya CHIMPALEE  HUANG Xinlei  Cristina Da LIO  Claudia MEISINA  Francesco ZUCCA 《《地质学报》英文版》2020,94(1):162-175

Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea-level rise at regional scale. Although it is a well-known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International Geoscience Programme recently approved an international project (IGCP 663) aiming to bring together worldwide researchers to share expertise on subsidence processes typically occurring in coastal areas and cities, including basic research, monitoring and observation, modelling and management. In this paper, we provide the research communities and potential stakeholders with the basic information to join the participating teams in developing this project. Specifically, major advances on coastal subsidence studies and information on well-known and new case studies of land subsidence in China, Italy, The Netherlands, Indonesia, Vietnam and Thailand are highlighted and summarized. Meanwhile, the networking, dissemination, annual meeting and field trip are briefly introduced.  相似文献   

Sedimentary provenance in the central Ribeira belt based on laser-ablation ICPMSPb/Pb zircon ages     

Claudia Sayo Valladares  Nuno Machado  Monica Heilbron  Beatriz Paschoal Duarte  Gilles Gauthier 《Gondwana Research》2008,13(4):516-526

²⁰⁷Pb/²⁰⁶Pb ages from 420 zircons from 9 upper amphibolite and granulite facies quartzites of the post-1.8 Ga metasedimentary cover from the Occidental and Oriental terranes from the Neoproterozoic central Ribeira belt, in eastern Brazil, are discussed. Ages from the Occidental terrane show that Proterozoic ages predominate with a modal class at 2.1–2.2 Ga and that Archean ages are less common and lie within the 2.5–3.6 Ga range. A wider dispersion on Proterozoic ages down to 1.1 Ga and youngest Neoproterozoic ages (550–700 Ma) were also observed and could be related to the Brasiliano/PanAfrican metamorphic events. The data show that detrital sediments of the Occidental terrane were derived predominantly from erosion of a 1.8–2.2 Ga Paleoproterozoic terrane with a small proportion of a 2.6–3.6 Ga Archean crust. Ages from the Oriental terrane are greatly dispersed, but show a significant proportion of ages between 1.7 and 2.1 Ga, although the great majority are between 0.5 and 1.6 Ga. Only 3 out of 144 grains yield Archean ages, between 2.5 and 2.9 Ga. Based on the greatest errors observed on the data from the Oriental Terrane (100–300 Ma), and a continuum of obtained ages between 2072 Ma (Paleoproterozoic) and 517 Ma (Cambrian), the more plausible interpretation is that the dispersion of ages results from partial resetting of the U–Pb system by Brasiliano metamorphism in Proterozoic–Archean zircons, although a Mesoproterozoic source could not be discarded.  相似文献   

Tectono-metamorphic evolution of the Neyriz metamorphic complex, Quri-Kor-e-Sefid area (Sanandaj-Sirjan Zone, SW Iran)     

M.R. Sheikholeslami  A. Pique  P. Mobayen  M. Sabzehei  H. Bellon  M. Hashem Emami 《Journal of Asian Earth Sciences》2008,31(4-6):504-521

The Neyriz region includes outcrops of metamorphic rocks that are thrust over the Neotethyan ophiolites. These rocks are affected by a major deformational event, the result of which includes a shearing polyphase foliation present in gneissic core domes, overprinted by a crenulation cleavage. These fundamental structures developed contemporaneously with a medium-pressure metamorphism which is characterized by the syn-kinematic crystallization of kyanite and the beginning of anatexis, followed by the development of retrometamorphic mineral parageneses. The major deformation phase in the area occurred during the Early-Cimmerian orogeny in the Late Triassic. Following the orogeny, the gneiss domes started to rise into the upper levels of the crust. From the geodynamic point of view, after the Mid-Permian the studied area was situated at southern passive margin of the Iranian plate; the central Iranian microcontinent at that time was separated by the Neotethys ocean from the Gondwanian supercontinent. After the Late Triassic the region became an active margin associated with an accretionary prism. The margin was finally involved in an orogenic wedge after the closure of the Neotethyan oceanic basin in the Late Mesozoic. Closure of the basin resulted in a major thrusting of the metamorphic rocks of the southern Iranian margin over the Neotethyan ophiolites.  相似文献   

Evolution of volcanism in graben and horst structures along the Cenozoic Cameroon Line (Africa): implications for tectonic evolution and mantle source composition   总被引：2，自引：0，他引：2  

D. G. Nkouathio  A. Kagou Dongmo  J. M. Bardintzeff  P. Wandji  H. Bellon  A. Pouclet 《Mineralogy and Petrology》2008,94(3-4):287-303

Tombel graben and Mounts Bambouto are two volcanic fields of the typical system of alternating graben and horst structure of the Cameroon Volcanic Line. Tombel graben is a young volcanic field, whereas Mounts Bambouto horst is an old stratovolcano with calderas. Volcanic products in both settings have a signature close to that of Ocean Island Basalt implying a major role of FOZO (focal zone) component and varied contribution of depleted mantle (DMM) and enriched mantle (EM) components. The Cameroon Volcanic Line is a hot line essentially resulting from passive rifting. Eocene to Recent intraplate basaltic volcanism in the study area was probably a result of mantle upwelling coupled with lithospheric extension. The olivine basaltic magma of horst volcanoes evolved in a large-scale, steady-state magmatic reservoir via crystal fractionation and limited contamination to highly differentiated alkaline lavas (trachyte and phonolite). Conversely, rapid ascent of lavas along multiple fault lines of graben structures produced less evolved lavas (hawaiite) within small reservoirs. This model, evaluated for the study area, involves mantle upwelling inside zones of weakness in the lithosphere after intra-continental extension. It can be applied to other parts of the Cameroon Volcanic Line as well, and is similar to that described in other intra-continental rift-related areas in Africa.  相似文献   

Helping eco-labels to fulfil their promises     

Gilles Grolleau  Lisette Ibanez  Mario Teisl 《Climate Policy》2016,16(6):792-802

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Seismic expression of gas and gas hydrates across the western Black Sea     

Irina Popescu  Gilles Lericolais  Nicolae Panin  Marc De Batist  Hervé Gillet 《Geo-Marine Letters》2007,27(2-4):173-183

This study is a synthesis of gas-related features in recent sediments across the western Black Sea basin. The investigation is based on an extensive seismic dataset, and integrates published information from previous local studies. Our data reveal widespread occurrences of seismic facies indicating free gas in sediments and gas escape in the water column. The presence of gas hydrates is inferred from bottom-simulating reflections (BSRs). The distribution of the gas facies shows (1) major gas accumulations close to the seafloor in the coastal area and along the shelfbreak, (2) ubiquitous gas migration from the deeper subsurface on the shelf and (3) gas hydrate occurrences on the lower slope (below 750 m water depth). The coastal and shelfbreak shallow gas areas correspond to the highstand and lowstand depocentres, respectively. Gas in these areas most likely results from in situ degradation of biogenic methane, probably with a contribution of deep gas in the shelfbreak accumulation. On the western shelf, vertical gas migration appears to originate from a source of Eocene age or older and, in some cases, it is clearly related to known deep oil and gas fields. Gas release at the seafloor is abundant at water depths shallower than 725 m, which corresponds to the minimum theoretical depth for methane hydrate stability, but occurs only exceptionally at water depths where hydrates can form. As such, gas entering the hydrate stability field appears to form hydrates, acting as a buffer for gas migration towards the seafloor and subsequent escape.  相似文献   

Long-term fish and macro-crustacean community variation in a Mediterranean lagoon     

Gilles Poizat  Elizabeth Rosecchi  Philippe Chauvelon  Pascal Contournet  Alain J. Crivelli 《Estuarine, Coastal and Shelf Science》2004,59(4):615-624

The fish and macro-crustacean community of the Vaccarès lagoon (Rhône River delta, South France) was sampled monthly from 1993 to 2002. The lagoon salinity shifted from 15 in 1993 to 5 in 1994–1997 and went back to 15 in 1999–2002. Connections with the sea also varied during the study period with larger openings in 1996–1997. During the study period, the community changed to revert in 2002 to a state similar to 1993. These changes consisted of a sequence of increased and decreased patterns of freshwater species and some marine species. Typical lagoon species tended to resist to salinity changes. Freshwater species colonised the lagoon when the salinity was low. Marine species may have varied both in relation to connections with the sea and to indirect effects of freshwater outflow. This study shows that community changes following environmental variations can be delayed in time, and emphasises the need for long-term studies.  相似文献   

Modelling carbon cycling through phytoplankton and microbes in the Scotia—Weddell Sea area during sea ice retreat     

Christiane Lancelot  Gilles Billen  Cornelis Veth  Sylvie Becquevort  Sylvie Mathot 《Marine Chemistry》1991,35(1-4)

An ecological model to calculate phytoplankton development and microbial loop dynamics in the marginal ice zone of the antarctic ecosystem has been established on the basis of physical and biological (phyto- and bacterioplankton biomass and activity and counting of two classes of heterotrophic nanoplankton) measurements carried out in the marginal ice zone of the Scotia-Weddell Sea sector of the Southern Ocean during sea ice retreat 1988 (EPOS 1 and 2 expeditions). Application of this model at latitudes where sea ice retreat occurs and in adjacent open sea and permanently ice-covered areas demonstrated that the marginal ice zone is a region of enhanced primary and bacterioplankton production. Combining the results of the phyto- and bacterioplankton models allowed the quantitative estimate of the carbon fluxes through the lower level of the planktonic food web of the Weddell Sea marginal ice zone during the sea ice retreat period. The resulting carbon budget revealed the quantitative importance of microbial and micrograzing processes in the pathways of net primary production, 71% of this latter being assimilated in the microbial food web. However, total net microbial food web secondary production contributed 28% of‘marginal ice zone produced’ food resources available to krill and other Zooplankton.  相似文献