La Notion de Migration en Paléontologie     

Henri  Geneviève Termier 《International Journal of Earth Sciences》1956,45(1):26-42

Zusammenfassung Gemessen mit dem Maßstab der geologischen Zeiten, dauern die Wanderungen, wie sie die Biologen studieren, nur fast einen Augenblick; demgegenüber aber erstrecken sich die Verschiebungen der Fauna und Flora, wie sie die geologischen Studien festlegen, über Millionen von Jahren. Diese Verschiebungen sind statistische Erscheinungen aus dem Gebiet der Biogeographie und stellen das Ergebnis von zahlreichen biologischen Bewegungen dar. Die Verfasser untersuchen die Wanderungen der Säugetiere (stete Entwicklung durch erwachsene Typen), die Wanderungen der Pflanzen (unstete Entwicklung durch Keime), die Wanderungen der wirbellosen Seetiere, die man in die eine oder in die andere der vorhergehenden Abteilungen einreihen kann. Einige neue Ausdrücke werden vorgeschlagen.  相似文献   

⁸⁷Rb/⁸⁷Sr study of diogenites     

J.L. Birck  C.J. Allègre 《Earth and Planetary Science Letters》1981,55(1):116-122

The five diogenites, Johnstown, Roda, Ellemeet, Shalka and Tatahouine, give scattered data in the⁸⁷Rb/⁸⁶Sr,⁸⁷Sr/⁸⁶Sr diagram. This can result from a disturbance which occurred later than 4.45 Ga ago. However, it is shown that if samples of sufficient size were analyzed, there meteorites could plot on the eucrite isochron and are thereby in agreement with a genetic relation between eucrites, howardites and diogenites. The age of eucrite differentiation from diogenites has been computed using data from the two families yielding an age of 4.47±0.1Ga(2σ) (λ=1.42×10^?11a^?1), the initial⁸⁷Sr/⁸⁶Sr ratio being BABI.  相似文献   

⁸⁷Sr/⁸⁶Sr ratios in hydrothermal waters and deposits from the East Pacific Rise at 21°N     

F. Albarède  A. Michard  J.F. Minster  G. Michard 《Earth and Planetary Science Letters》1981,55(2):229-236

⁸⁷Sr/⁸⁶Sr ratios of three hydrothermal waters collected on the East Pacific Rise at 21°N define a mixing line between seawater and a hydrothermal end-member at 0.7030 which is derived by seawater-basalt interaction at ca. 350°C and water/rock ratio of about 1.5. Sr concentrations are not affected in the process while Mg uptake from seawater is almost complete. Up to2/3 of this hydrothermal component is involved in anhydrite precipitation while the Sr isotopic ratio in sulfides (chalcopyrite + sphalerite) cannot be distinguished from that of sulfate. It is estimated that ca. 1 × 10¹⁰ moles of strontium are yearly cycled in the hydrothermal systems of mid-oceanic ridges, thereby affecting the⁸⁷Sr/⁸⁶Sr budget of seawater. Mass balance between river runoff, limestone precipitation and ridge basalt alteration suggests that the⁸⁷Sr/⁸⁶Sr ratios of the river runoff are in the range 0.7097–0.7113, and are largely dominated by limestone alteration.  相似文献   

²³⁰Th-²³⁸U radioactive disequilibria in tholeiites from the FAMOUS zone (Mid-Atlantic Ridge, 36°50′N): Th and Sr isotopic geochemistry     

M. Condomines  P. Morand  C.J. Allègre 《Earth and Planetary Science Letters》1981,55(2):247-256

We analyzed, U, Th and²³⁰Th/²³²Th activity ratios for a few tholeiites from the Mid-Atlantic Ridge FAMOUS zone at 36°50′N. The results show a fairly wide scatter for both Th/U and (²³⁰Th/²³²Th) ratios. Seawater contamination appears to be responsible for this scatter and, for the uranium, produces an increase in content yielding a (²³⁴U/²³⁸U) ratio greater than 1 and, for the Th, an increase of the (²³⁰Th/²³²Th) ratio which is a very sensitive indicator for contamination. Also, the latter often is selective: U, Th and Sr are not affected in the same manner.When discarding all data for contaminated samples, the FAMOUS zone appears to be very homogeneous with aTh/U ratio value of 3.05 and a (²³⁰Th/²³²Th) ratio value of 1.24. Comparison with other active volcanic areas reveals a negative correlation between (²³⁰Th/²³²Th) and⁸⁷Sr/⁸⁶Sr ratios for present lavas which is indicative of a consistency in Th-U and Rb-Sr fractionation in the source regions of these magmas. The Th isotopic geochemistry can thus provide useful information for the study of present volcanism, information as valuable as that from Sr, Pb or Nd isotopes.  相似文献   

Flowage differentiation: Limitation of the “Bagnold effect” to the narrow intrusions     

Michel Barrière 《Contributions to Mineralogy and Petrology》1976,55(2):139-145

The Bagnold effect, the most important in the flowage differentiation, is practically inoperative in porphyritic rocks in the case of large dykes and pipes with a width or a diameter over 100 meters. For these large channels, the magmatic differentiation between the core and the walls is not related to the forced magmatic flow, but should be ascribed to other mechanisms: crystal settling, natural convection, synchronous injection of already differentiated materials.  相似文献   

Contrasting patterns of precipitation seasonality during the Holocene in the south‐ and north‐central Mediterranean     

Michel Magny  Odile Peyron  Laura Sadori  Elena Ortu  Giovanni Zanchetta  Boris Vannière  Willy Tinner 《第四纪科学杂志》2012,27(3):290-296

Pollen‐based quantitative estimates of seasonal precipitation from Lake Pergusa and lake‐level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid‐Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south‐central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north‐central Italy, where the mid‐Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non‐linear responses to orbitally driven insolation decrease in addition to seasonal and inter‐hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A synthesis of morphological evolutions and Holocene stratigraphy of a wave-dominated estuary: The Arcachon lagoon,SW France     

Jonathan Allard  Eric Chaumillon  Hugues Féniès 《Continental Shelf Research》2009,29(8):957-969

This work presents the first synthesis of secular to millenary morphological evolutions and stratigraphy of a wave-dominated estuary, the Arcachon lagoon, from a combination of unpublished bathymetric maps (1865 and 2001), core results and high-resolution seismic profiles recorded for the first time in this lagoon. The Arcachon lagoon is located on the Atlantic coast of France, facing the wave-dominated shelf of the Bay of Biscay. It is a mesotidal semi-enclosed environment of about 160 km².The sediment budget of the Arcachon lagoon was computed by subtracting the 1865 bathymetric map from that of 2001. The computed volume difference is low (?9.9±35×10⁶ m³ in 136 yrs) and is the result of the balance between erosion and accretion that occurs within tidal channels and tidal flats, respectively. This morphological evolution pattern is explained by low sediment supply and also by the tidal distortion resulting from the morphology of the lagoon. Deep channels connected to the inlet are dominated by ebb currents inducing erosion. Tidal flats and transverse channels display weak or flood-dominated tidal currents leading to the deposition of silts. The areas of tidal flat siltation locally correlate with the presence of oyster farms, suggesting the influence of Man on the lagoon sediment-fill. Transverse channel-infill is related to weak tidal currents resulting from the hydraulically inefficient orientation of these channels which served as an ancient drainage network.Evidence for tidal channel-infill and channel abandonment are also provided by seismic profiling and cores. The upper stratigraphic succession of the lagoon (about 10 m thick) includes four main stratigraphic units dominated by channel-fills. The two lower units (around 7500–2800 yrs BP) display tabular-shape sandy channels interpreted to be records of the open estuarine phase of the Arcachon lagoon. The two upper units (around 2800 yrs BP to present-day) display U-shaped mixed sand-and-mud channel-fills interpreted to be records of the closure of the lagoon. Given that the basal estuarine units are transgressive and the upper lagoonal units are regressive, the main stratigraphic change at around 2800 yrs BP is interpreted as being the maximum flooding surface (MFS). This late MFS is explained by the low sediment supply. It is proposed that the transition from the estuarine to the lagoonal phase is related to the development of the Cap-Ferret spit in response to an increase in the ratio between wave power to tide power. This change in wave-to-tide ratio may be triggered by wave power increase following the Subboreal/Subatlantic climate instability or a decrease in tide power following a decrease in tidal prism related to the lagoon sediment-fill.Thus, the evolution of the Arcachon lagoon over the last millenaries was mainly controlled by its spit development, leading to a wave-dominated estuary in terms of its geomorphology. Once it was partially closed, extensive mud flats developed in the lagoon which became ebb-dominated.  相似文献   

Effective permittivity of porous media: a critical analysis of the complex refractive index model     

Alessandro Brovelli  Giorgio Cassiani 《Geophysical Prospecting》2008,56(5):715-727

The availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi-empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker-Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker-Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker-Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore-scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker-Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data.  相似文献   

A structural and geophysical approach to the study of fractured aquifers in the Scansano-Magliano in Toscana Ridge, southern Tuscany, Italy   总被引：1，自引：0，他引：1  

Roberto Francese  Francesco Mazzarini  Andrea Bistacchi  Gianfranco Morelli  Giorgio Pasquarè  Nicola Praticelli  Henry Robain  Nigel Wardell  Annalisa Zaja 《Hydrogeology Journal》2009,17(5):1233-1246

Fresh water availability has recently become a serious concern in the Italian Apennines, as various activities rely on a predictable supply. Along the ridge between Scansano and Magliano in Toscana, in southern Tuscany, the situation is further complicated by contamination of the nearby alluvial aquifers. Aquifers locally consist of thin fractured reservoirs, generally within low-permeability formations, and it can be difficult to plan the exploitation of resources based on conventional techniques. An integrated study based on geological data investigated the link between tectonics and groundwater circulation, to better define the hydrological model. After the regional identification of fault and fracture patterns, a major structure was investigated in detail to accurately map its spatial position and to understand the geometry and properties of the associated aquifer and assess its exploitation potential. The subsurface around the fault zone was clearly imaged using ground probing radar, two-dimensional and three-dimensional resistivity tomography, and three-dimensional shallow seismic surveys. The vertical and horizontal contacts between the different geological units of the Ligurian and Tuscan series were resolved with a high degree of spatial accuracy. Three-dimensional high-resolution geophysical imaging proved to be a very effective means of characterising small-scale fractured reservoirs.  相似文献   

Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa          下载免费PDF全文

Niall F. Higgins  Solène Connan  Dagmar B. Stengel 《Marine Ecology》2015,36(4):1400-1414

Responses to abiotic and biotic stresses that potentially drive the vertical zonation of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra‐red gas analysis; results indicated a more hydration‐dependent nature of W. mucosa. Photosynthetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gradient from upper to lower shore levels. Pigment composition and concentration in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phenolic concentration and composition exhibited some seasonality across 13 different lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti‐herbivory function. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiological features of marine and maritime lichens that enable them to thrive in this extreme environment.  相似文献