Importance of the oxidation/maturation pair in the evolution of humic coals     

Landais Patrick  Marc Monthioux  Jean-Dominique Meunier 《Organic Geochemistry》1984,7(3-4)

The natural thermal evolution of type III coals (Humic origin) is expressed during diagenesis by a loss of oxygen as CO₂ and H₂O. Other phenomena such as oxidation can cause extensive geochemical modifications and may complicate the effects of simple maturation.Humic coals from the Jurassic in southeastern Utah were studied by elemental analysis, Rock-Eval pyrolysis and infrared spectroscopy. In a van Krevelen diagram (atomic H/C vs atomic O/C), the samples fall within the envelope defined by 860 reference humic coals covering the entire range of diagenesis. Nevertheless, various criteria (geochemical, petrographic, geological and microscopic) cast doubt upon the interpretation that such a distribution of coal composition results from thermal maturation.The same criteria indicate the intervention of redox phenomena. Comparison of our results with those from artificial and natural oxidation shows that these coals were subjected to an oxidation process different from ordinary late alteration. This process was probably due to circulation of highly oxidizing saline water causing oxygen fixation and the transformation of carboxyls into carboxylate anions. The cations that were fixed are oxygenated and certainly contain calcium, but also uranium and perhaps several other cations (V, Mo, Fe...). Emphasis is placed on possible mechanisms that cause such phenomena.  相似文献   

Seasonal control of the Saint-Lawrence maximum turbidity zone by tidal-flat sedimentation     

Marc Lucotte  Bruno d’Anglejan 《Estuaries and Coasts》1986,9(2):84-94

The core of the turbidity maximum zone in the Saint-Lawrence Estuary is located in the North Channel and oscillates in front of the large (3×10⁶ m²) intertidal flats and marshes of Cap Tourmente. It is shown that seasonal fluctuations in the intensity and the position of this core are mainly determined by suspended sediment exchanges between the channel and the marshes. Fine sediments, most of them found 20 km downstream in the channel off Cap Maillard in late winter and early spring, are advected upstream over the flats during the summer months by the tide. The deposition, favored by marsh plant growth, reaches 5×10⁵ metric tons in three months. A period of intense erosion, at a mean rate of 4,500 metric tons per tide, coincides with the destruction of the plant cover by migratory geese. The material removed fills up the Chenal de l’Île d’Orléans upstream and is flushed back into the water column during the next spring freshette. This rotating seasonal sediment circulation, although very localized, exerts a major influence on the distribution and storage time of suspended particles in the upper estuary.  相似文献   

Local isotropy and anisotropy in the sheared and heated atmospheric surface layer     

Gabriel G. Katul  Marc B. Parlange  John D. Albertson  Chia R. Chu 《Boundary-Layer Meteorology》1995,72(1-2):123-148

Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal effects on the small-scale eddy motion. In order to explore these two anisotropy sources, we developed statistical measures that are sensitive to such interactions. It was found that the large-scale/small-scale interaction was significant in the inertial subrange up to 3 decades below the production scale, thus reducing the validity of the local isotropy assumption. The anisotropy generated by thermal effects was also significant and comparable in magnitude to the former anisotropy source. However, this thermal anisotropy was opposite in sign and tended to counteract the anisotropy generated by the large-scale/smallscale interaction. The thermal anisotropy was attributed to organized ramp-like patterns in the temperature measurements. The impact of this anisotropy cancellation on the dynamics of inertial subrange eddy motion was also considered. For that purpose, the Kolmogorov-Obukhov structure function equation, as derived from the Navier-Stokes equations for locally isotropic turbulence, was employed. The Kolmogorov-Obukhov structure function equation in conjunction with Obukhov's constant skewness closure hypothesis reproduced the measured second- and third-order structure functions. Obukhov's constant skewness closure scheme, which is also based on the local isotropy assumption, was verified and was found to be in good agreement with the measurements. The accepted 0.4 constant skewness value derived from grid turbulence experiments overestimated our measurements. A suggested 0.26 constant skewness value, which we derived from Kolmogorov's constant, was found to be adequate.  相似文献   

The study of molybdenites through the¹⁸⁷Re-¹⁸⁷Os chronometer     

Jean Marc Luck  Claude J. Allègre 《Earth and Planetary Science Letters》1982,61(2):291-296

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Verifying warnings for point precipitation     

Willi Schmid  Marc Wüest   《Atmospheric Research》2005,77(1-4):347

Short-term risk forecasts of point precipitation are obtained with COTREC/RainCast, a technique for extrapolation of radar images. The risk forecasts are updated every 5 min for the next 0–2 h. Risk levels are defined for moderate, heavy and extreme precipitation. Warning messages are generated if, at the locations of 23 rain gauges, these risk levels are reached or exceeded. The time-resolved gauge data are used to judge if the warning messages are in time, early or late.Data over a period of 4 months (summer 2002) are used for verification. The largest number of warnings (1790) was obtained for moderate precipitation. About 55% of these warnings were in time, 23% were early and 22% were late. This finding is in a good agreement with the defined risk level for warnings (50%), indicating that the model for calculating the risk factors is reliable. Less warnings in time, and more late warnings were found for heavy and extreme precipitation. Hence, the risk levels need to be lowered for heavy and extreme precipitation, in order to reduce the number of late warnings.  相似文献   

Slab dehydration and fluid migration at the base of the upper mantle: implications for deep earthquake mechanisms     

Guillaume Richard  Marc Monnereau  Michel Rabinowicz 《Geophysical Journal International》2007,168(3):1291-1304

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The radio frequency dielectric properties of the stratified UG1–UG2 geological unit in the Bushveld Complex     

Marc Rütschlin  Johannes H. Cloete  Iain M. Mason  Keith D. Palmer   《Journal of Applied Geophysics》2007,62(4):354-360

A new measurement technique enables the complex dielectric properties of the geological strata comprising the UG1–UG2 (Upper Group 1–Upper Group 2) unit of the Bushveld Complex in South Africa to be determined with unprecedented detail at radio frequencies (RF). Results of non-destructive laboratory measurements of representative diamond drill core samples from the UG1–UG2 unit are presented at 25 MHz. These data establish that the UG1 and UG2 chromitite layers are embedded in rock strata (norite, pyroxenite and anorthosite) which are translucent in the HF spectral band, whereas the chromitite layers themselves exhibit significant velocity contrast, making them good radar reflectors. The data presented here is useful for calibration of the radar system, and for predicting the range and resolution performance of borehole radars operating in both the hanging and footwalls of the economically important platiniferous UG2 reef.  相似文献   

Response to Discussion by Wolfe et al. on Bierman et al. (Geomorphology 25 (1999) 25–39)     

Paul R. Bierman  Kim A. Marsella  P. Thompson Davis  Marc W. Caffee 《Geomorphology》2001,39(3-4)

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The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks   总被引：1，自引：0，他引：1  

Rupert S. Adams  R. Marc Bustin   《International Journal of Coal Geology》2001,46(2-4)

Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound.Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (C_org/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The <25-μm fraction has TOC concentrations up to 2.0 wt.%, and a C_org/N ratio that ranges from 14 to 16. The 53–106-μm fraction has higher TOC concentrations and C_org/N ratios relative to the 25–53-μm fraction. The C_org/N ratio ranges from 9 to 18 in the 53–106-μm fraction and 5.5–10.5 in the 25–53-μm fraction. Surface area values for bulk sediments are low (0.5–3.0 m²/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration.The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks formed in other geological settings.  相似文献   

Considérations sur le volcanisme post-ophiolitique dans les Alpes occidentales     

Jacques Martini  Prof. Marc Vuagnat 《International Journal of Earth Sciences》1967,57(1):264-276

Résumé L'activité magmatique ophiolitique du géosynclinal alpin (diabases, gabbros, serpentines, etc.) a été suivie par une activité à caractère volcanique moins bien connue. En effet, les appareils correspondant à cette activité ont complètement disparu; nous devons nous contenter pour tous renseignements de l'étude des fragments de roches contenus dans des grauwackes tertiaires appartenant au Flysch (grès de Taveyanne, grès d'AItdorf pro parte, grès du Champsaur).La détermination de la nature originelle des laves est, en outre, rendue difficile par le fait, découvert récemment, que ces grauwackes ont subi un métamorphisme régional les plaçant dans le faciès à zéolites; on peut raisonnablement admettre qu'il s'agissait d'andésites basaltiques.L'áge des épanchements est encore indéterminé, il doit être compris entre le Crétacé supérieur et la fin de l'Eocène. L'hypothèse la plus plausible consiste à admettre que les volcans, aujourd'hui complètement érodés se trouvaient dans la partie la plus interne du domaine pennique. Toutefois au moment du dépôt des grès de Taveyanne, les coulées ne se trouvaient plus dans leur position initiale, elles avaient glissé vers l'avant-pays sous forme d'une nappe.Il est très probable que cette activité volcanique post-ophiolitique n'est pas restreinte au segment franco-suisse des Alpes occidentales mais que des formations analogues aux grès de Taveyanne se retrouvent ailleurs, notamment en Sicile et dans les Apennins.

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The magmatic activity which gave birth to the ophiolites (diabases, gabbros, serpentinites) of the alpine geosyncline was followed by subaerial volcanism. This volcanic activity is not well known as the volcanoes were completely destroyed by erosion. Our only source of information is to be found in fragments of volcanic rocks which are part of Tertiary Flysch graywackes (Taveyanne sandstones, part of the Altorf sandstones, Champsaur sandstones).The determination of the initial composition of the lavas is further complicated by metasomatic transformations; it has been recently shown that the Taveyanne graywackes were submitted to a light regional metamorphism corresponding to the zeolitic facies ofCoombs. However, it seems that these lavas were originally basaltic andesites.The age of this volcanism is not precisely known, it cannot be later than Upper Eocene as the time of deposition of the Taveyanne sandstones is Uppermost Eocene-Lower Oligocene; it is probably post-Cenomanian. It is likely that the volcanoes were located in the southern part of the Penninic zone; however at the time of deposition of the graywackes the volcanic flows had already left their initial location, gliding toward the Foreland as part of a Nappe.Very probably, remnants of this post-ophiolitic volcanism are not restricted to the French-Swiss segment of the Western Alps, but will be found elsewhere, particularly in the Apennine Mountains and in Sicily.

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Zusammenfassung Die magmatische Tätigkeit, die Ophiolithe (Diabase, Gabbros, Serpentinite) der alpinen Geosynklinale entstehen ließ, wurde von subärischem Vulkanismus abgelöst. Diese Vulkantätigkeit ist wenig bekannt, da die Vulkane durch Erosion völlig zerstört wurden. Unsere einzige Informationsquelle findet sich in vulkanischen Gesteinsfragmenten, die Bestandteile der Tertiär-Flysch-Grauwacken sind.Die Bestimmung der ursprünglichen Zusammensetzung der Laven wird weiter durch metasomatische Umwandlungen erschwert. Kürzlich wurde gezeigt, daß die Taveyanne-Grauwacken einem regionalen Metamorphismus ausgesetzt waren, welcher der zeolithischen Fazies von Coombs entspricht. Es scheint jedoch, daß diese Laven ursprünglich basaltische Andésite waren.Das Alter dieses Vulkanismus ist nicht genau bekannt; es kann aber nicht später sein als das Obere Eozän, da die Ablagerungszeit der Taveyanne-Sandsteine Oberstes Eozän—Unteres Oligozän ist. Wahrscheinlich lagen die Vulkane im südlichen Teil der penninischen Zone; zur Zeit der Ablagerung der Grauwacken waren die Vulkanite bereits in die Überschiebungsmassen mit einbezogen.Sehr wahrscheinlich sind die Überreste dieses nach-ophiolithischen Vulkanismus nicht auf den französisch-schweizerischen Abschnitt der Westalpen beschränkt, sondern werden sich auch andernorts speziell auf dem Apennin und in Sizilien finden lassen.

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