Emergent geomorphic–vegetation interactions on a subalpine alluvial fan          下载免费PDF全文

Stuart N. Lane  Laure Borgeaud  Pascal Vittoz 《地球表面变化过程与地形》2016,41(1):72-86

Following perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co‐development of geomorphic processes with ecosystems over very short through to very long (evolutionary) timescales. Alpine environments have been a particular focus of this co‐development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co‐develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across‐fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil–vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Influence of lithostratigraphy on the retreat of an unconsolidated sedimentary coastal cliff (St. Lawrence estuary,eastern Canada)          下载免费PDF全文

Gabriel Joyal  Patrick Lajeunesse  Antoine Morissette  Pascal Bernatchez 《地球表面变化过程与地形》2016,41(8):1055-1072

This paper investigates the processes involved in unconsolidated cliff recession using LiDAR surveys (2005, 2010 and 2013) and aerial photographs (1964–2012) at Pointe‐au‐Bouleau, on the north shore of the St. Lawrence estuary, in eastern Canada. The high lithostratigraphic variability of the sediments allowed for the identification of stratigraphic and lithological variables that explain the evolution of coastal cliffs. Space‐for‐time substitution was also used to assess how lithostratigraphy controls the evolution of emerged glaciomarine coastal cliffs over decadal to centennial timescales. This case study presents new quantitative data that contributes to a better understanding of the role of sediment architecture, stratigraphy and geomorphology on coastal evolution. The methodological approach includes the development of a new conceptual model suitable for identifying erosion on cliff coastlines. The high spatial resolution methodology (<5 cm) used herein demonstrates the need for further research using LiDAR data in order to quantify the processes involved in the evolution of coastal cliffs. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Modelling the impact of a La Niña event on a South West Pacific Lagoon     

Fuchs R  Dupouy C  Douillet P  Caillaud M  Mangin A  Pinazo C 《Marine pollution bulletin》2012,64(8):1596-1613

In view of increasing environmental awareness and biodiversity conservation, understanding the main forcing mechanism driving biogeochemical cycles in coral reefs and lagoon coastal areas is a priority. La Ni?a events cause unbalanced situations in the Equatorial Pacific and result in enhanced precipitation in South West Pacific coastal areas. We investigated the impact of heavy rainfalls during the 2008 La Ni?a event on the New Caledonia lagoon using a 3D coupled on-line hydrodynamic-biogeochemical model. Simulations and data showed that the whole lagoon was impacted by river inputs and stronger hydrodynamics, enhancing chlorophyll-a concentration by a factor between 1.7 and 1.9. The coupled model provided new insights into plume transport, highlighting that eastern plumes can be advected northwards or can reach the South West Lagoon, depending on the balance between regional, tide-induced, and wind-induced surface currents. It also provided a synoptic view of lagoon biogeochemical-hydrodynamic response, when remote sensing data are not available due to cloud coverage.  相似文献   

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)     

Guilhem Amin Douillet  Benjamin Bernard  Mlanie Bouysson  Quentin Chaffaut  Donald Bruce Dingwell  Lukas Gegg  Inga Hoelscher  Ulrich Kueppers  Clia Mato  Vanille Ariane Ritz  Fritz Schlunegger  Patrick Witting 《Sedimentology》2019,66(5):1531-1559

Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s^?1 (equivalent to pure wind velocity of 6 to 8 m.s^?1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s^?1.  相似文献   

Provenance analysis of the Voirons Flysch (Gurnigel nappe,Haute-Savoie,France): stratigraphic and palaeogeographic implications     

Ragusa  Jérémy  Kindler  Pascal  Segvic  Branimir  Ospina-Ostios  Lina Maria 《International Journal of Earth Sciences》2017,106(8):2619-2651

International Journal of Earth Sciences - The Chablais Prealps (Haute-Savoie, France) represent a well-preserved accretionary wedge of the Western Alpine Tethys. They comprise a stack of...  相似文献   

SORTAN: An Analytical Method to Determine Fault Slip as Induced by Stress     

Christophe Pascal  Jacques Angelier 《Mathematical Geology》2003,35(5):627-642

We propose an analytical method, namely the SORTAN method, to determine the sense of slip on faults as induced by stresses. This method is useful to infer the sense of motion along faults whose surface cannot be directly accessed, such as faults imaged in the subsurface. Because the SORTAN method is based on the Wallace–Bott hypothesis, we assume that the shear stress vector applied to a given fault is parallel to the slip vector on this fault. The assumptions allow for simplification of the method that in turn implies very short calculation times. A concise formalism is adopted. We introduce the stress ratio ' that accounts for (1) the type of stress regime (i.e., strike-slip, reverse or normal) and (2) the degree of anisotropy of the stress state. The formalism of the SORTAN method permits an easy exploration and imaging of the complete collection of slip motions that may theoretically occur on fault planes. The input parameters are the fault plane orientation, the type and anisotropy of the stress regime, and the azimuth of the horizontal stress axes.  相似文献   

Observation of sections of oceanic crust and mantle cropping out on the southern wall of Kane FZ (N. Atlantic)     

Jean-Marie Auzende  Mathilde Cannat  Pascal Gente  Jean-Pierre Henriet  Thierry Juteau  Jeffrey Karson  Yves Lagabrielle  Catherine Mével  Maurice Tivey 《地学学报》1994,6(2):143-148

The objective of the 20 Nautile dives of the recent Kanaut cruise was to study the southern wall of the Kane Fracture Zone from its eastern intersection with the Mid-Atlantic Ridge (MAR) to 5 Myr in age. The geological mapping shows four successive massifs, wrench faulted and slightly tilted. The transform-facing walls of these massifs exhibit outcrops of fresh and serpentinized peridotites, gabbros and basalts. The entire crustal exposure is cataclased and metamorphosed to greenschist facies.  相似文献   

Orbit of an Astrometric Binary System     

Pascal?DescampsEmail author 《Celestial Mechanics and Dynamical Astronomy》2005,92(4):381-402

We present a new method to solve the problem of initial orbit determination of any binary system. This method is mainly based on the material available for an observer, for example relative positions at a given time of the couple in the “plane of sky”, namely the tangent plane to the celestial sphere at the position of the primary component. The problem of orbit determination is solved by splitting in successive stages in order to decorrelate the parameters of each other as much as possible. On one hand, the geometric problem is solved using the first Kepler’s law from a single observing run and, on the other hand, dynamical parameters are then inferred from the fit of the Kepler’s equation. At last, the final stage consists in determining the main physical parameters involved in the secular evolution of the system, that is the spin axis and the J₂ parameter of the primary if we assume that it is a quasi-spherical body. As a matter of fact there is no need to make too restrictive initial assumptions (such as circular orbit or zero eccentricity) and initial guesses of parameters required by a non-linear least-squares Levenberg–Marquardt algorithm are finally obtained after each stage. Such a protocol is very useful to study systems like binary asteroids for which all of the parameters should be considered a priori as unknowns. As an example of application, we used our method to estimate the set of the Pluto–Charon system parameters from observations collected in the literature since 1980.  相似文献   

Use of two inverse techniques. Application to a local structure in the New Hebrides island arc     

J. R. Grasso  M. Cuer  G. Pascal 《Geophysical Journal International》1983,75(2):437-472

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Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia     

Sylvain Ouillon  Pascal Douillet  Renaud Fichez  Jean-Yves Panch 《Comptes Rendus Geoscience》2005,337(16):231

The variability in salinity and temperature in the southwest lagoon of New Caledonia (2100 km²) under non-storm conditions is analysed using a 4-year dataset (1997–2001). Seasonal and interannual variations in salinity are amplified nearshore. Temperature is larger in bays than in the open lagoon during summer, the reverse is true in winter. El Niño Southern Oscillation (ENSO) related nearshore temperature variations parallel those at regional scale, but with seasonal variations amplified. Haline stratification, if any, is enhanced in coastal areas. To cite this article: S. Ouillon et al., C. R. Geoscience 337 (2005).  相似文献