Ash layers in deep-sea sediments as tracers of arc volcanic activity: Japan and Central America as case studies     

Herve  Cambray Jean-Paul  Cadet André  Pouclet 《Island Arc》1993,2(2):72-86

Abstract Arc volcanic activity on opposite sides of the Pacific Ocean (Japan and Central America) has been investigated by examining the number of volcanic ash layers recorded in Neogene and Quaternary deep-sea sediments. The data suggest that ash layers counted in deep-sea sediments may provide a reliable record of arc volcanism. The study is based on a quantitative analysis of arc volcanic activity using cores collected on DSDP (Deep-Sea Drilling Project) and ODP (Ocean Drilling Program) legs. Five distinct parameters which might affect ash distribution in marine sediments were reviewed: nature of the eruption, wind influence, settling conditions, diagenesis, and plate motion. Of these five, past atmospheric circulation was the most significant. The main constraint on the analysis is that temporal scattering of ash is not directly related to wind pattern variations. Results of this analysis are correlated with dating of terrestrial volcanic sequences. Although marine tephra records for individual regions reveal minor differences in the episodes of volcanic activity, a general correlation exists between activity of arc volcanism in Japan and in Central America. Two important pulses of arc volcanism occurred during Middle Miocene times (18–13 Ma) and Plio-Quaternary times (5–0 Ma). These episodes of intense volcanism are separated by a well recorded quiescent period during Late Miocene times. These correlating episodes of the volcanic record indicate a direct link between arc volcanism and the global tectonic evolution of the Pacific ocean margins.  相似文献   

Radiative surface temperature and convective flux calculation over crop canopies     

Jean-Paul Lhomme  Nader Katerji  Alain Perrier  Jean-Michel Bertolini 《Boundary-Layer Meteorology》1988,43(4):383-392

The analysis presented in this paper aims at a better understanding of the potential role of radiative temperature, as measured by a radiometer over crops, in sensible heat flux calculation. Defining radiative temperature as the mean temperature of the surfaces viewed by the radiometer (leaves and soil surface) and assuming that an Ohm's law type formula can be used to express sensible heat flux as a function of the difference between air temperature and radiative temperature, the aerodynamic resistance which divides this temperature difference has been analytically defined. The parameters which appear in the resistance expression depend essentially on wind velocity and canopy structure but also on the inclination angle of the radiometer. Finally an experimental verification is presented with data obtained over a potato crop.  相似文献   

Preface to the Proceedings of ENS''93 Conference     

Michael Elliott  Jean-Paul Ducrotoy 《Marine pollution bulletin》1994,29(6-12):253-254

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The 3100 BP eruption of the Soufrière of Guadeloupe     

Pascale Besson  Jean-Paul Poirier 《Bulletin of Volcanology》1994,56(3):184-192

Fragments of unaltered andesite found at all levels in the deposits of the catastrophic flank-failure, directed-blast eruption of the Soufrière of Guadeloupe in 3100 bp are thought to be remnants of the cryptodome. They were observed in analytical transmission electron microscopy for clues to the evolution of the intrusion prior to the eruption. Several features that could potentially be used as temperature markers were identified, among which the angle between microexsolutions of magnetite in augite phenocrysts was used to find an upper boundary of the temperature of the intrusion before the eruption: 600–700°C. Calculation of the time a dyke or sphere-shaped intrusion may have taken to cool from the emplacement temperature down to the temperature of exsolution of the magnetite leads to an estimate of the time between emplacement of the intrusion and the eruption, which could not have been less than a few tens of years. It therefore seems probable that the emplacement of the magmatic intrusion was not the immediate cause of the flank destabilization and catastrophic eruption of the Soufrière in 3100 bp.  相似文献   

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3     

Jean-Paul Cadet  Kazuo Kobayashi  Jean Aubouin  Jacques Boulgue  Christine Deplus  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kinichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km² and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary?  相似文献   

A model of the diagenetic evolution of coaly sedimentary organic matter     

Jean-Paul Boudou  Régis Pelet  René Letolle 《Geochimica et cosmochimica acta》1984,48(6):1357-1362

Elemental composition was used to calculate the amounts of compounds produced during the diagenetic evolution of a coal series from the Mahakam delta (Kalimantan, Indonesia). These calculations were based on the following hypotheses: organic nitrogen does not take part in reactions and remains unchanged in the residual organic matter, the only compounds produced are water, carbon dioxide and hydrocarbons.This approach shows that carbon loss during diagenesis is mainly as CO₂, and hydrogen loss is mainly as H₂O. Hydrocarbon production is negligible, in accordance with absence of bacterial methane accumulations in the Mahakam delta.The δ¹³C of coals in the sequence becomes about 2 per mil more positive over the diagenetic depth range of coal evolution. Accounting for the coal δ¹³C change in terms of CO₂ loss requires that the CO₂ given off have δ¹³C of about ?40%.. Such negative CO₂ has not been observed in natural systems, except when CH₄ is undergoing oxidation. Several plausible causes for this effect are discussed.  相似文献   

Diagenetic trends of a tertiary low-rank coal series     

Jean-Paul Boudou  Bernard Durand  Jean-Louis Oudin 《Geochimica et cosmochimica acta》1984,48(10):2005-2010

The Mahakam delta (Kalimantan, Indonesia) coals represent all the evolution stages between freshly-deposited plant/peat material, lignites and bituminous coals. The geochemical techniques used to study this coal series included elemental analysis, extraction of humic compounds, infrared spectroscopy and ¹³C nuclear magnetic resonance of the total coal.The main mechanisms of early maturation in this series are loss of oxygenated compounds, aromatisation and condensation of the organic matter. These changes, which have already been suggested for other coal series and partially reported for sedimentary organic matter, were confirmed and described in more detail for the Mahakam coal series.  相似文献   

Modelling the Mixing Function to Constrain Coseismic Hydrochemical Effects: An Example from the French Pyrénées     

Jean-Paul Toutain  Margot Munoz  Jean-Louis Pinaud  Stéphanie Levet  Matthieu Sylvander  Alexis Rigo  Jocelyne Escalier 《Pure and Applied Geophysics》2006,163(4):723-744

Groundwater coseismic transient anomalies are evidenced and characterized by modelling the mixing function F characteristic of the groundwater dynamics in the Ogeu (western French Pyrénées) seismic context. Investigations of water-rock interactions at Ogeu indicate that these mineral waters from sedimentary environments result from the mixing of deep waters with evaporitic signature with surficial karstic waters. A 3-year hydrochemical monitoring of Ogeu springwater evidences that using arbitrary thresholds constituted by the mean ± 1 or 2σ, as often performed in such studies, is not a suitable approach to characterize transient anomalies. Instead, we have used a mixing function F calculated with chemical elements, which display a conservative behavior not controlled by the precipitation of a mineral phase. F is processed with seismic energy release (E_s) and effective rainfalls (R). Linear impulse responses of F to E_s and R have been calculated. Rapid responses (10 days) to rainwater inputs are evidenced, consisting in the recharge of the shallow karstic reservoir by fresh water. Complex impulse response of F to microseismic activity is also evidenced. It consists in a 2-phase hydrologic signal, with an inflow of saline water in the shallow reservoir with a response delay of 10 days, followed by an inflow of karstic water with a response delay of 70 days, the amount being higher than the saline inflow. Such a process probably results from changes in volumetric strain with subsequent microfracturation transient episodes allowing short inflow of deep salted water in the aquifer. This study demonstrates that groundwater systems in such environments are unstable systems that are highly sensitive to both rainfall inputs and microseismic activity. Impulse responses calculation of F to E_s is shown to be a powerful tool to identify transient anomalies. Similar processing is suggested to be potentially efficient to detect precursors of earthquakes when long time-series (5 years at least) are available in areas with high seismicity.  相似文献   

利用MODIS和ASAR资料估算青藏高原念青唐古拉山脉地区冰雪范围及厚度   总被引：3，自引：1，他引：3  

文军  Dai Mo  王致君  张堂堂  Humbert Louis 《冰川冻土》2006,28(1):54-61

利用可见光和微波卫星遥感资料分析了青藏高原念青唐古拉山脉地区冰雪范围和厚度的季节变化.结果表明:青藏高原念青唐古拉山脉地区冰雪范围的季节变化非常明显,2003年4月上旬、5月中旬、7月下旬和9月下旬的冰雪范围分别占选定研究区域的28.9%、69.9%、11.6%和14.7%.在选定的西布冰川区域,由微波遥感得到的冰雪厚度季节变化也非常明显,5月份厚度的数值最大,7月份最小.由于主动微波观测受地面高程、地形和夏季冰雪融化等因素的影响比较大,主动微波遥感在大面积估算冰雪厚度还有一定困难,有待将来作进一步的深入研究.  相似文献   

Weathering, atmospheric deposition and vegetation uptake: role for ecosystem sensitivity to acid deposition and critical load     

David Moncoulon  Anne Probst  Jean-Paul Party 《Comptes Rendus Geoscience》2004,336(16):1417-1426

Critical loads of acidity represent the maximum acceptable atmospheric deposition for an ecosystem type. Two hundred and forty-one ecosystem types have been defined in France using pedologic, geologic and vegetation data. Weathering rate plays the most important part in soil buffering capacity, but for poor weatherable soils, non-marine atmospheric deposition represents up to 80% of base-cation inputs. Base-cation vegetation uptake decreases significantly the buffering capacity in case of high-productivity forests. Ecosystems combining low weathering rate and low non-marine base-cation deposition with high biomass productivity are the most sensitive to acidification. To cite this article: D. Moncoulon et al., C. R. Geoscience 336 (2004).

Résumé

Les charges critiques d'acidité représentent le dépôt atmosphérique maximal admissible pour un écosystème. Deux cent quarante et un types d'écosystèmes ont été définis en France à partir de données pédologiques, géologiques et de végétation. L'altération joue un rôle prépondérant contre l'acidification, mais pour les sols faiblement altérables, les dépôts atmosphériques non marins peuvent représenter jusqu'à 80 % des apports de cations basiques. Le prélèvement de cations par la végétation contribue significativement à diminuer le pouvoir tampon des sols pour les forêts à forte productivité. Les écosystèmes combinant faible altération et faibles dépôts de cations non marins ainsi qu'une forte productivité sont les plus sensibles à l'acidification. Pour citer cet article : D. Moncoulon et al., C. R. Geoscience 336 (2004).  相似文献