The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset I: The Nyong River Basin,Cameroon     

Stéphane Audry  Henriette Ateba Bessa  Jean-Pierre Bedimo Bedimo  Jean-Loup Boeglin  Laurie Boithias  Jean-Jacques Braun  Bernard Dupré  Mikael Faucheux  Christelle Lagane  Jean-Christophe Maréchal  Jules Remy Ndam-Ngoupayou  Bernadette Nka Nnomo  Justin Nlozoa  Jean-Claude Ntonga  Olivier Ribolzi  Jean Riotte  Emma Rochelle-Newall  Laurent Ruiz 《水文研究》2021,35(5):e14138

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.  相似文献   

Diachronic metamorphic and structural evolution of the Connecticut Valley–Gaspé trough,Northern Appalachians     

Morgann Perrot  Alain Tremblay  Gilles Ruffet  Loic Labrousse  Félix Gervais  Fabien Caroir 《Journal of Metamorphic Geology》2020,38(1):3-27

The Connecticut Valley–Gaspé (CVG) trough represents a major, orogen-scale Silurian–Devonian basin of the Northern Appalachians. From Gaspé Peninsula to southern New England, the CVG trough has experienced a contrasting metamorphic and structural evolution during the Acadian orogeny. Along its strike, the CVG trough is characterized by increasing strain and polyphase structures, and by variations in the intensity of regional metamorphism and contrasting abundance of c. 390–370 Ma granitic intrusions. In southern Quebec and northern Vermont, a series of NW–SE transects across the CVG trough have been studied in order to better understand these along-strike variations. Detailed structural analyses, combined with phase equilibria modelling, Raman spectrometry, and muscovite ⁴⁰Ar/³⁹Ar dating highlight a progressive and incremental deformation involving south–north variation in the timing of metamorphism. Deformation evolves from a D₁ crustal thickening event which originates in Vermont and progresses to southern Québec where it peaked at 0.6 GPa/380°C at c. 375 Ma. This was followed by a D₂ event associated with continuous burial in Vermont from 378 to 355 Ma, which produced peak metamorphic conditions of 0.85 GPa/380°C and exhumation in Quebec from 368 to 360 Ma. The D₃ compressional exhumation event also evolved from south to north from 345 to 335 Ma. D₁ to D₃ deformation events form part of a continuum with an along-strike propagation rate of ~50 km/Ma During D₁, the burial depth varied by more than 15 km between southern Quebec and Vermont, and this can be attributed to the occurrence of a major crustal indenter, the Bronson Hill Arc massif, in the New England segment of the Acadian collision zone.  相似文献   

A new late Pleistocene subfossil site (Tsaramody,Sambaina basin,central Madagascar) with implications for the chronology of habitat and megafaunal community change on Madagascar's Central Highlands     

Karen E. Samonds  Brooke E. Crowley  Tojoarilala Rinasoa Nadia Rasolofomanana  Miora Christelle Andriambelomanana  Harimalala Tsiory Andrianavalona  Tolotra Niaina Ramihangihajason  Ravoniaina Rakotozandry  Zafindratsaravelo Bototsemily Nomenjanahary  Mitchell T. Irwin  Neil A. Wells  Laurie R. Godfrey 《第四纪科学杂志》2019,34(6):379-392

Madagascar is a complex ‘biodiversity hotspot’ with a rapidly dwindling biota. The Late Quaternary subfossil record includes many extinct species whose loss is attributed to natural climate change and human impacts. Investigation of the chronology of these events is challenging because few localities document pre‐Holocene communities not impacted by humans. Caves with extinct lemurs of large body size comprise some of Madagascar's richest subfossil sites, but provide only a limited window into the island's past. Open highland sites may have fewer primates, but may better document other megafauna, and allow the analysis of the role of the Central Highlands as refugia and as corridors for the dispersal of vertebrates before and after human arrival. Here we present a new subfossil site, Tsaramody (Sambaina basin, Central Madagascar), a high‐altitude wetland area that preserves a diverse late glacial and postglacial vertebrate community. Tsaramody bears testimony to fluctuations in the highland flora during the transition from glacial to postglacial conditions, and the composition of a highland vertebrate community before humans arrived. We compare its biota to those of other sites to begin to document the decline and disappearance of megafauna from some of Madagascar's open ecosystems – wetlands dominated by hippopotamuses and crocodylians. © 2019 John Wiley & Sons, Ltd.  相似文献   

Isotopic heterogeneity in the Sudbury impact melt sheet     

J.R. Darling  C.J. Hawkesworth  P.C. Lightfoot  C.D. Storey  E. Tremblay 《Earth and Planetary Science Letters》2010,289(3-4):347-356

A unique terrestrial large impact melt sheet is preserved in the 1850 Ma Sudbury Structure, Ontario. We have undertaken a Pb isotope investigation of the southern limb of the melt sheet, termed the South Range Main Mass. The model initial Pb isotope ratios (²⁰⁷Pb/²⁰⁴Pb_m) vary stratigraphically through the predominantly quartz monzogabbroic Lower Unit, varying from 15.40 to 15.45 at the base to ca. 15.35 at the top of the sequence. Lateral variations of similar range occur in basal Lower Unit samples over scales of less than 5 km. The range of these variations is similar to those of locally exposed upper crustal target rocks, and it is evident that the melt sheet has efficiently preserved inherited variability. During the violent phases of crater formation superheated impact melts are expected to be well-mixed mechanically, therefore significant post-impact melting of target rocks, fallback material and entrained clasts is required to explain such heterogeneity.The Sudbury Structure hosts world class Ni-Cu-PGE sulphide ore deposits. Systematic variation in ²⁰⁷Pb/²⁰⁴Pb_m occurs throughout sulphide ores within the Creighton Embayment, from massive (15.42–15.45) to interstitial (ca. 15.40–15.41) and disseminated (ca. 15.39) sulphide. Linking the Pb isotope composition of these ores to the immediately overlying Lower Unit stratigraphy, a protracted sulphide segregation history is apparent. Massive sulphides segregated early, prior to or during initial silicate crystallisation, although the total time involved in sulphide accumulation spanned much of the crystallisation of the Lower Unit. It is also shown that lateral variations in Ni depletion throughout the Main Mass correlate with Pb isotopes. Those segments with the strongest chalcophile element depletion signatures, reflecting the accumulation of significant basal sulphides, have high initial Pb isotope values, consistent with early sulphide segregation. The characterisation of Pb isotopic heterogeneity has therefore provided insights into the evolution and scales of mixing of the melt sheet, with the identified chemical variability between melt cells having a significant influence on ore forming processes.  相似文献   

Trap‐based indicators of egg production following increases in minimum legal size in Homarus americanus fisheries     

M. John Tremblay  Marc Lanteigne 《新西兰海洋与淡水研究杂志》2013,47(3):775-783

Minimum legal size (MLS) is an important conservation measure in trap fisheries for Homarus americanus. MLS has increased in several management areas in the Canadian Maritimes since 1987. A key conservation objective has been to increase egg production, with predictions of the effects of MLS increase based on egg‐per‐recruit models. We evaluated whether expectations of increases in ovigerous females (OF) were realised when MLS was increased. Data were examined from at‐sea samples of the commercial trap catch from 11 ports from 1986 to 2003. OF indicators were developed based on the OF catch‐per‐unit‐effort (CPUE) of different sizes, and on the percentage (PCT) of females that were ovigerous. Because there were within‐season increases in CPUE and PCT, annual indicators were based on regressions of CPUE on day in the season. There was considerable variability in all the time series of OF annual indicators and any effects of smaller MLS increases could not be detected. Increases in OF indicators were evident in areas that undertook the largest MLS increases (6–6.5 mm CL).  相似文献   

基于全局低分辨率CT扫描的合成层析成像技术     

曾凯  赵世英  王革 《CT理论与应用研究》2005,14(2):63-69

合成层析成像可由有限几个投影数据重建三维物体,与传统CT相比,该方法所需的射线剂量少得多.由于投影数据不完备,导致的重建图像伪影是合成层析成像的一个主要问题.本文提出一种对感兴趣区域进行合成层析成像方法,和其他方法相比可以得到更好的重建图像质量.该方法首先对目标进行低分辨率全局扫描,然后对感兴趣区域进行高分辨率局部扫描,最后,利用两次扫描的投影数据集合重建感兴趣区域的图像.数值仿真结果表明,用本方法重建感兴趣区域图像,要明显好于没有使用全局扫描信息的方法.  相似文献   

From outcrop and petrographic studies to basin-scale fluid flow modelling: The use of the Albanian natural laboratory for carbonate reservoir characterisation   总被引：1，自引：0，他引：1  

Nadge Vilasi  Julien Malandain  Laurie Barrier  Jean-Paul Callot  Khalid Amrouch  Nicole Guilhaumou  Olivier Lacombe  Kristaq Muska  Franois Roure  Rudy Swennen 《Tectonophysics》2009,474(1-2):367

The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by means of seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary records help to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios.Since the mid-90s, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools as well as the application of new analytical methods for the study petroleum systems in tectonically complex areas.The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The fracturing of the reservoir intervals has a pre-folding origin in the Albanides and relates to the regional flexuring in the foreland. The first recorded cement has a meteoric origin, implying downward migration and the development of an earlier forebulge in the Ionian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium, attesting for important fluid–rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal vein. The tectonic burial increased due to the overthrusting, that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, up- or downward migration of SO₄²⁻, Ba²⁺ and Mg²⁺-rich fluids, which migrated probably along the décollement level, allows a precipitation in thermal disequilibrium. This period corresponds to the onset of the thrusting in the Ionian Zone. The last stage characterised the uplift of the Berati belt, developing a selective karstification due likely to the circulation of meteoric fluid.The main results of the fluid flow modelling show that the Upper Cretaceous–Paleocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flow barriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur.  相似文献   

More than a checkbox: engaging youth in disaster risk reduction and resilience in Canada     

Cox  Robin S.  Hill  Tiffany T.  Plush  Tamara  Heykoop  Cheryl  Tremblay  Crystal 《Natural Hazards》2019,96(1):213-224

Fire has become one of the main disturbances in terrestrial ecosystems worldwide. It is known that elevation influences the occurrence of fire events; however, this variable has been poorly studied, although it is of particularly relevance to the Mexican topography. The objective of this research was to analyze the altitudinal distribution of forest fires in Mexico over a period of 11 years. Elevation gradients were defined based on a Digital Elevation Model and the main ecoregions of the country: (1) shrubland and tropical forests (0–1000 masl), (2) grasslands (1001–2000 masl) and (3) temperate forests (>?2000 masl). Each ecoregion was divided into Climate Research Units and the number of fires per unit was quantified. The G Getis–Ord statistic was applied in order to define the spatial patterns presented by the fire events. A relationship between the occurrence of fires and the El Niño Southern Oscillation phenomenon was also determined through a Pearson correlation. The results showed that the occurrence of fire events presented variability along elevation gradients, with elevation a determining factor in their occurrence. Gradient 3, with the highest elevation, had the greatest number of fires and also presented the largest area of fire event clustering. These results contribute to the knowledge of the spatial distribution of forest fires in Mexico and are of value to appropriate decision-making for effective fire management.

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Consistency of dynamic site response at Port Island     

Laurie G. Baise  Steven D. Glaser  Takahiro Sugano 《地震工程与结构动力学》2001,30(6):803-818

System identification (SI) methods are used to determine empirical Green's functions (EGF) for soil intervals at the Port Island Site in Kobe, Japan and in shake table model tests performed by the Port and Harbor Research Institute (PHRI) to emulate the site during the 17 January 1995 Hyogo‐ken Nanbu earthquake. The model form for the EGFs is a parametric auto‐regressive moving average (ARMA) model mapping the ground motions recorded at the base of a soil interval to the top of that interval, hence capturing the effect of the soil on the through‐passing wave. The consistency of site response at Port Island before, during, and after the mainshock is examined by application of small motion foreshock EGFs to incoming ground motions over these time intervals. The prediction errors (or misfits) for the foreshocks, the mainshock, and the aftershocks, are assessed to determine the extent of altered soil response as a result of liquefaction of the ground during the mainshock. In addition, the consistency of soil response between field and model test is verified by application of EGFs calculated from the shake table test to the 17 January input data. The prediction error is then used to assess the consistency of behaviour between the two cases. By using EGFs developed for small‐amplitude foreshock ground motions, ground motions were predicted for all intervals of the vertical array except those that liquefied with small error. Analysis of the post‐liquefied ground conditions implies that the site response gradually returns to a pre‐earthquake state. Site behaviour is found to be consistent between foreshocks and the mainshock for the native ground (below 16 m in the field) with a normalized mean square error (NMSE) of 0.080 and a peak ground acceleration (PGA) of 0.5g. When the soil actually liquefies (change of state), recursive models are needed to track the variable soil behaviour for the remainder of the shaking. The recursive models are shown to demonstrate consistency between the shake table tests and the field with a NMSE of 0.102 for the 16 m to surface interval that liquefied. The aftershock ground response was not modelled well with the foreshock EGF immediately after the mainshock (NMSE ranging from 0.37 to 0.92). One month after the mainshock, the prediction error from the foreshock modeled was back to the foreshock error level. Copyright © 2001 John Wiley Sons, Ltd.  相似文献   

The ReOs systematics of the Ronda Ultramafic Complex of southern Spain     

Laurie C. Reisberg  Claude J. Allgre  Jean-Marc Luck 《Earth and Planetary Science Letters》1991,105(1-3)

The Os isotopic compositions of twelve ultramafic and six mafic layer samples from the Ronda Ultramafic Complex of southern Spain have been determined. Among the ultramafic rocks, ¹⁸⁷Os/¹⁸⁶Os varies from 0.98 to 1.12. A weak correlation is observed between ¹⁸⁷Os/¹⁸⁶Os and Re/Os. A much stronger correlation exists between Os isotopic ratio and Mg#, suggesting that the Re/Os ratios have been perturbed to some extent. Two alternatives are proposed to explain the relationship between Os composition and Mg#: (1) Continuous processes in the convecting mantle; (2) Radiogenic ingrowth since an ancient melt depletion event. No relationship is observed between ¹⁸⁷Os/¹⁸⁶Os and ¹⁴³Nd/¹⁴⁴Nd. This is probably because the Nd systematics were strongly affected by a recent metasomatic event, which apparently had little effect on the Os isotopic compositions.The Os isotopic ratios of the mafic layers range from 1.7 to 47.9. Within a single thick layer, the ratios vary from 16.5 to 47.9. These high ratios demonstrate that the layers are ancient features. Among the mafic samples, Os isotopic ratio is found to decrease strongly with increasing Os concentration, which ranges from 0.009 ppb to 1.16 ppb. One layer, which had a SmNd model age of less than 200 Ma, yielded a ReOs model age of about 2 Ga. This implies that neither system can be trusted to give accurate information about the time of mafic layer formation.  相似文献