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Spatial variations in grain-size parameters (i.e. grain-size trends) contain information on sediment transport patterns. Analytical procedures have been proposed using the grain-size trend to determine net sediment transport pathways. In the first part of this study, the fundamentals of the theory are presented through methods for analysing 1D and 2D variations. The methods used are critically discussed, while pointing out some severe problems. So far, these methods suffer from limitations leading to serious interpretational errors, making it necessary to take account of two kinds of uncertainties. Inputs uncertainties are linked to the physical sediment properties as well as procedures of sampling and analysis. Model uncertainties are then discussed for each step of the grain-size trend analysis. The validity of Sediment Trend Analysis under natural conditions is tested against published field studies to determine the most appropriate variation trend to use in a specific environment. Proposals are given for each step of the procedure for optimal use of the method using a Quality Assurance (QA) approach. Further developments are proposed, such as integration into a Geographic Information System. 相似文献
3.
The Barra Nova inlet, in south Portugal, is known to migrate progressively southeastwards under wave action. The morphodynamics
of this system during a representative year suggests that this long-term evolution is dependent on a seasonal behavior of
the tidal inlet which can be described through a three-stage model of post-storm, transition and extended fair-weather conditions.
Processes involved in this evolution indicate that the historical migration of the Barra Nova is not dependent on the longshore
drift forcing constricting the channel on the updrift coast, but rather on the adjustment of the system to a major erosion
of the downdrift coast during short storm events. 相似文献
4.
Yann Hautevelle Raymond Michels Fabrice Malartre Marcel Elie Alain Trouiller 《Applied Geochemistry》2007
The Callovo-Oxfordian claystones located at 500 m depth at Bure (Meuse, France) are currently being investigated by Andra (the French National Radioactive Waste Management Agency) for testing the feasibility of long-term and deep geological nuclear waste disposal. In order to evaluate its potential as a geological barrier, it is very important to study, assess and describe its physico-chemical variability. The molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter, the chemistry of the depositional environment, the preservation and diagenesis conditions. It also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series. The abundance of unsaturated biomarkers, the distribution of steroids and hopanoids and CPI values >2 prove the thermal immaturity of the organic matter. The co-occurrence of plankton, bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions. The data also reveal that the organic matter was deposited under oxic and open-sea conditions except for a brief event of photic zone anoxia at the beginning of the Middle Callovian. In the claystones, the geosynthesis of diasterenes is favored to the detriment of the formation of steranes, especially in smectite-rich levels, and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays. On the scale investigated, the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view. Yet, detailed investigation of specific molecular families indicates changes related to major claystone–limestone transitions. The homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub-horizontal paleotopography on which they were deposited. This study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers. 相似文献
5.
Yann Marcon Heiko Sahling Anne‐Gaëlle Allais Gerhard Bohrmann Karine Olu 《Marine Ecology》2014,35(1):77-95
The Regab pockmark is a large cold seep area located 10 km north of the Congo deep sea channel at about 3160 m water depth. The associated ecosystem hosts abundant fauna, dominated by chemosynthetic species such as the mussel Bathymodiolus aff. boomerang, vestimentiferan tubeworm Escarpia southwardae, and vesicomyid clams Laubiericoncha chuni and Christineconcha regab. The pockmark was visited during the West African Cold Seeps (WACS) cruise with RV Pourquoi Pas? in February 2011, and a 14,000‐m2 high‐resolution videomosaic was constructed to map the most populated area and to describe the distribution of the dominant megafauna (mussels, tubeworms and clams). The results are compared with previous published works, which also included a videomosaic in the same area of the pockmark, based on images of the BIOZAIRE cruise in 2001. The 10‐year variation of the faunal distribution is described and reveals that the visible abundance and distribution of the dominant megafaunal populations at Regab have not changed significantly, suggesting that the overall methane and sulfide fluxes that reach the faunal communities have been stable. Nevertheless, small and localized distribution changes in the clam community indicate that it is exposed to more transient fluxes than the other communities. Observations suggest that the main megafaunal aggregations at Regab are distributed around focused zones of high flux of methane‐enriched fluids likely related to distinct smaller pockmark structures that compose the larger Regab pockmark. Although most results are consistent with the existing successional models for seep communities, some observations in the distribution of the Regab mussel population do not entirely fit into these models. This is likely due to the high heterogeneity of this site formed by the coalescence of several pockmarks. We hypothesize that the mussel distribution at Regab could also be controlled by the occurrence of zones of both intense methane fluxes and reduced efficiency of the anaerobic oxidation of methane possibly limiting tubeworm colonization. 相似文献
6.
The North Qinling Orogenic Belt(NQOB) is a composite orogenic belt in central China. It started evolving during the Meso–Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic. The Meso–Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt, with the tectonic evolution of the middle part of the belt being particularly controversial. The granites... 相似文献
7.
Molcard Anne Gramoullé Anthony Mazoyer Camille Bourg Natacha Ourmières Yann 《Ocean Dynamics》2021,71(10):993-1009
Ocean Dynamics - Coastal regions are vulnerable areas with often high population density, as well as tourism and maritime activities that may have negative impact on the environment. From a... 相似文献
8.
Tectonometamorphic evolution of the Atbashi high‐P units (Kyrgyz CAOB,Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction–exhumation of the South Kazakh continental margin 下载免费PDF全文
Chloé Loury Yann Rolland Stéphane Guillot Pierre Lanari Clément Ganino Raphael Melis Anthony Jourdon Carole Petit Olivier Beyssac Sylvain Gallet Patrick Monié 《Journal of Metamorphic Geology》2018,36(8):959-985
The South Tien Shan (STS) belt results from the last collision event in the western Central Asian Orogenic Belt (CAOB). Understanding its formation is of prime importance in the general framework of the CAOB. The Atbashi Range preserves high‐P (HP) rocks along the STS suture, but still, its global metamorphic evolution remains poorly constrained. Several HP units have been identified: (a) a HP tectonic mélange including boudins of mafic eclogites in a sedimentary matrix, (b) a large (>100 km long) high‐P metasedimentary unit (HPMU) and (c) a lower blueschist facies accretionary prism. Raman Spectroscopy on carbonaceous material combined with phengite and chlorite multiequilibria and isochemical phase diagram modelling indicates that the HPMU recorded homogeneous P–T conditions of 23–25 kbar and 560–570°C along the whole unit. 40Ar/39Ar dating on phengite from the HPMU ranges between 328 and 319 Ma at regional scale. These ages are interpreted as (re‐) crystallization ages of phengite during Tmax conditions at a pressure range of 20–25 kbar. Thermobarometry on samples from the HP tectonic mélange provides similar metamorphic peak conditions. Thermobarometry on the blueschist to lower greenschist facies accretionary prism indicates that it underwent P–T conditions of 5–6 kbar and 290–340°C, highlighting a 17–20 kbar pressure gap between the HPMU‐tectonic mélange units and the accretionary prism. Comparison with available geochronological data suggests a very short time span between the prograde path (340 Ma), HP metamorphic peak (330 Ma), the Tmax (328–319 Ma) and the final exhumation of the HPMU (303–295 Ma). Extrusion of the HPMU, accommodated by a basal thrust and an upper detachment, was driven by buoyant forces from 70–75 km up to 60 km depth, which directly followed continental subduction and detachment of the HPMU. At crustal depths, extrusion was controlled by collisional tectonics up to shallow levels. Lithological homogeneity of the HPMU and its continental‐derived character from the North Tien Shan suggest this unit corresponds to the hyper‐extended continental margin of the Kazakh continent, subducted southward below the north continental active margin of the Tarim craton. Integration of the available geological data allows us to propose a general geodynamic scenario for Tien Shan during the Carboniferous with a combination of (a) N‐dipping subduction below the Kazakh margin of Middle Tien Shan until 390–340 Ma and (b) S‐dipping subduction of remaining Turkestan marginal basins between 340 and 320 Ma. 相似文献
9.
Pierre Lanari Yann Rolland Stéphane Schwartz Olivier Vidal Stéphane Guillot Pierre Tricart Thierry Dumont 《地学学报》2014,26(2):130-138
Pressure–Temperature–time (P–T–t) estimates of the syn‐kinematic strain at the peak‐pressure conditions reached during shallow underthrusting of the Briançonnais Zone in the Alpine subduction zone was made by thermodynamic modelling and 40Ar/39Ar dating in the Plan‐de‐Phasy unit (SE of the Pelvoux Massif, Western Alps). The dated phengite minerals crystallized syn‐kinematically in a shear zone indicating top‐to‐the‐N motion. By combining X‐ray mapping with multi‐equilibrium calculations, we estimate the phengite crystallization conditions at 270 ± 50 °C and 8.1 ± 2 kbar at an age of 45.9 ± 1.1 Ma. Combining this P–T–t estimate with data from the literature allows us to constrain the timing and geometry of Alpine continental subduction. We propose that the Briançonnais units were scalped on top of the slab during ongoing continental subduction and exhumed continuously until collision. 相似文献
10.
Yann Rolland Romain Darnault Régis Braucher Didier Bourlès Carole Petit Stéphane Bouissou ASTER Team 《地球表面变化过程与地形》2020,45(2):393-410
Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif is located at the transition between the Alps and the Mediterranean Sea, therefore, its deglaciation chronology can be compared to the sediment budget of the Var River basin. Based on 13 new cosmic-ray exposure (CRE) beryllium-10 (10Be) datings performed on moraines and polished crystalline bedrocks and 22 reassessed 10Be CRE ages from similar altitude nearby steep basement surfaces, and from a lake sediment core, we can constrain the deglaciation chronology of the Argentera-Mercantour massif. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif in agreement with a major glacier recession at c. 15 ka, at the onset of Bølling transition between the Oldest and Older Dryas. Main deglaciation of the upper slopes [2700–2800 m above sea level (a.s.l.)] occurred after the Last Glacial Maximum (LGM) at 20.8–18.6 ka, followed by the main deglaciation of the lower slopes (2300 m a.s.l.) at 15.3–14.2 ka. Finally, the flat polished surfaces above 2600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8–9 ka. At lower elevations, the Vens Lake located at 2300 m a.s.l., allows evidence of the onset of lake sedimentation at c. 14 ka and a transition towards a vegetated environment that mainly occurred before 8 ka. Moraine final stabilization at 5 ka might reflect denudation acceleration during the Holocene humid phase. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after c. 15 ka. This major deglaciation is correlated with a 2.5-fold decrease of sediment discharge of rivers into the Mediterranean Sea. © 2019 John Wiley & Sons, Ltd. 相似文献