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11.
Maxime Virolle Benjamin Brigaud Raphaël Bourillot Hugues Fnis Eric Portier Thibault Duteil Julius Nouet Patricia Patrier Daniel Beaufort 《Sedimentology》2019,66(3):859-894
Porosity and permeability may be preserved in deep sandstone reservoirs by clay coating (mainly chlorite) which limits quartz overgrowths. Chloritization around quartz grains results mainly from mineralogical transformations of pre‐existing clays. It is fundamental to study those clay precursors to better understand and predict the location and distribution of clay coatings in subsurface sandstones for petroleum or geothermal prospecting. This paper reports a high‐resolution analysis of the composition, distribution and fabric of clays along a modern estuary, the Gironde (south‐west France). The scale of the study ranges from thin sections, through sand bar bodies, up to the entire estuary. Results show that clays are detrital and deposited at the same time as sand grains despite strong hydrodynamic conditions. Clays bind to medium‐grained sands forming detrital clay grain coats. On average, 26% of detrital sand grains are coated along the entire length of the estuary. Coat thickness varies from 1 μm to more than 200 μm, and coat coverage exceeds 30% in some samples. The turbidity maximum zone position (surface water turbidity from 1 to 10 g l?1) in the estuary, which is controlled by seasonal variations in hydrodynamic processes, significantly impacts the location of the maximum clay content and the abundance of coated grains in sandy facies along the estuary. Flocculation in the water column results in the accumulation of suspended matter and contributes to the high turbidity in the estuary. Exopolymeric substances produced by diatoms are observed both in the field and by cryo‐scanning electron microscopy, suggesting that they may play a major role in binding detrital clay around sand grains. Finally, tidal bars and heterolithic point bars in the estuary funnel and estuarine channels are prime sedimentological targets for finding clay coatings and potentially good reservoir quality in deeply buried sandstones. 相似文献
12.
Aurélien Beaufort Florentina Moatar Eric Sauquet Pierre Loicq David M. Hannah 《水文研究》2020,34(3):583-597
Identifying the main controlling factors of the stream temperature (Tw) variability is important to target streams sensitive to climate and other drivers of change. The thermal sensitivity (TS), based on relationship between air temperature (Ta) and Tw, of a given stream can be used for quantifying the streams sensitivity to future climate change. This study aims to compare TS for a wide range of temperate streams located within a large French catchment (110,000 km2) using 4 years of hourly data (2008–2012) and to cluster stations sharing similar thermal variabilities and thereby identify environmental key drivers that modify TS at the regional scale. Two successive classifications were carried out: (a) first based on Ta–Tw relationship metrics including TS and (b) second to establish a link between a selection of environmental variables and clusters of stations. Based on weekly Ta–Tw relationships, the first classification identified four thermal regimes with differing annual Tw in terms of magnitude and amplitudes in comparison with Ta. The second classification, based on classification and regression tree method, succeeded to link each thermal regime to different environmental controlling factors. Streams influenced by both groundwater inflows and shading are the most moderated with the lowest TS and an annual amplitude of Tw around half of the annual amplitude of Ta. Inversely, stations located on large streams with a high distance from source and not (or slightly) influenced by groundwater inflows nor shading showed the highest TS, and so, they are very climate sensitive. These findings have implications for guiding river basin managers and other stakeholders in implementing thermal moderation measures in the context of a warming climate and global change. 相似文献
13.
D. Beaufort P. Patrier A. Meunier M.M. Ottaviani 《Journal of Volcanology and Geothermal Research》1992,51(1-2)
Epidote and/or chlorite are common minerals in the roots of the fossil geothermal system of Saint Martin (Lesser Antilles). They appear in four distinct assemblages: (1) epidote+actinolite+quartz±magnetite near the contact between the tuffaceous host rocks (andesitic modal composition) and the quartz-diorite intrusion of Philipsburg; (2) epidote+chlorite+quartz in host rocks as far as a lateral distance of about 3 km from the intrusion; (3) epidote+chlorite+haematite+quartz locally in iron and manganese rich host rocks; (4) chlorite±phengite±magnetite appearing as late sealing of porosity in fracture-controlled quartz veins with strongly phengitized wall rocks. All these assemblages constitute a large alteration grading from propylitic alteration to thermal metamorphism (actinolite-bearing assemblage).Detailed microprobe studies of epidotes replacing plagioclases and of chlorites replacing glass and mafic minerals reveal notable compositional variations which have been studied with respect to temperature paleogradients (estimated from fluid inclusions study), distance from the thermal source and fo2 conditions. The mean Ps+Pm [100 × (Fe3+ + Mn3+)/(Al3+ + Fe3+ + Mn3+)] of epidotes vary from 21 in the presence of magnetite near the intrusion to 32 in haematite-bearing iron and/or manganese volcanic and sedimentary formations. The intra-grain chemical scattering of epidotes increases with increasing distance of the pluton and decreasing temperature of crystallization. All the chlorites coexisting with epidote are Mg-rich (XFe<0.50). Their main compositional variation consists in a significant enrichment in magnesium (toward the chlinochlore end member) in presence of haematite. The intra-grain chemical scattering of chlorite (expressed by the aluminium content in the structural formula) increases with increasing distance of the pluton and decreasing temperature of crystallization. Chlorites associated with phengite and magnetite in vein alteration are Fe- and Al-rich. The Mössbauer spectra indicate that the Fe3+ content of chlorite varies between 25 and 32% of total Fe in the presence of epidote; the higher content being attained in the presence of haematite. The Fe3+ content of chlorite associated with magnetite and phengite is 16% of total Fe. The compositional variations of epidote and/or chlorite of the four distinct assemblages observed at Saint Martin result from the combined effects of fO2, temperature, and time of heating. The effect of fO2 is particularly perceptible in the control of the epidote Ps content, of the chlorite XFe ratio of Fe3+ distribution between coexisting epidotes and chlorites. Despite the fact that it may be partially canceled out by the effect of fO2, the variation of compositional ranges of both epidotes and chlorites, which increases toward the outer part of the geothermal system in response to the combination of decreasing temperatures and decreasing time of heating of the rocks, suggests that chemical equilibrium has not been attained in the assemblages bearing epidotes and chlorites. 相似文献
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15.
Adriane Commin-Fischer Gilles Berger Mireille Polvé Michel Dubois Paul Sardini Daniel Beaufort Milton Formoso 《Journal of South American Earth Sciences》2010,29(3):751-760
The filling process of amethyst-bearing geodes from Serra Geral Formation basalts, Brazil, is investigated by different methods performed on the SiO2 filling phases. Image analysis of quartz–amethyst deposits suggests a single growing mechanism ruled by geometric selection of randomly oriented crystals. Microthermometry of fluid inclusions reveals formation temperature lower than 100 °C, probably lower than 50 °C, and fluid salinity as high as 3 mass% NaCl eq. Composition in REE and trace-elements measured by ICP-MS on acid-digested or laser-ablated samples indicates a common genesis for amethyst, quartz and chalcedony, as well as the absence of significant variations from one geode to another. 87Sr/86Sr data on chalcedony shows that both the host basalt or the Botucatu sandstone are possible silica sources. These data, combined with thermo-kinetic considerations, permit us to discuss the filling process. We argue in favor of the contribution of a mineralized fluid of hydrothermal origin producing a regional silica source which decreased with time. The observed mineral sequence is related to the depletion of silica in the solution. 相似文献
16.
This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic
illites related to unconformity-type uranium deposits of Canada and Australia were studied using electron paramagnetic resonance
(EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates
that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra
indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum
with apparent principal components as follows: g
∥ = 2.032 and g
⊥ = 1.993. The corresponding defect is named as Ai center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g
∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen
atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The Ai center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest
that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of
the Ai center requires additional work. 相似文献
17.
Kazuyo Tachikawa Olivier Cartapanis Laurence Vidal Luc Beaufort Tatiana Barlyaeva Edouard Bard 《Quaternary Science Reviews》2011,30(25-26):3716-3727
The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3°S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on 14C dates and benthic foraminiferal δ18O. Indicators of the coarse river particulate fraction (bulk and CaCO3-free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacial–interglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3°S, January) with time-dependent lag of 0 to 4 ka. They were generally in anti-phase for U–Th dated Chinese speleothem δ18O records. Based on an analogy to modern climate, we propose that precipitation over PNG was primarily determined by interhemispheric insolation contrast, and the contribution of austral fall/winter precipitation added second-order variability that formed the lags. For the last four climate cycles, the WPWP hydrological cycle was closely associated with the eastern Asian monsoon, and the influence of glacial conditions on the low-latitude hydrological cycle was estimated to be limited. 相似文献
18.
I. O. Murdmaa G. H. Kazarina L. Beaufort E. V. Ivanova E. M. Emelyanov V. A. Kravtsov G. N. Alekhina V. E. Vasileva 《Lithology and Mineral Resources》2010,45(2):154-171
Core MD02-2508 retrieved from the plateau of the continental slope off Baja California recovered a 40-m-thick section of sapropel
(up to 15% Corg), calcareous clay, and diatom ooze with the age of 120 ka at the core bottom. The section is subdivided into three units:
Unit I (Holocene) consists of the laminated sapropel; Unit II comprising oxygen isotope stages (MIS) 2, 3, and 4 is represented
by homogeneous calcareous clay with interbeds of slightly siliceous sapropelic mud; and Unit III (MIS-5) is composed of laminated
sapropelic diatom ooze. Laminated intervals are characterized by the intercalation of two lamina types: (1) dark-colored organic-rich
laminae containing multi-species “oceanic” diatom assemblages, as well as radiolarians, coccoliths, planktonic and benthic
foraminifera; (2) lighter-colored laminae consisting of diatom ooze with the neritic colonial diatom assemblages commonly
composed of one to three species of a single genera. The dark laminae are assumed to be generated within a high productivity
zone over the slope, whereas light ones likely represent diatom mats produced by short-term boisterous phytoplankton blooms,
possibly in the coastal upwelling. 相似文献