排序方式： 共有35条查询结果，搜索用时 109 毫秒
21.
Jean Benkhelil Mazhar Bayerly Stéphane Branchoux Thierry Courp Eliane Gonthier Christian Hübscher Agnès Maillard Elias Tahchi 《Comptes Rendus Geoscience》2005,337(12):1075-1083
The eastern bend of the Cyprus Arc, at the transition between the submerged Mediterranean subduction and the onshore fault zones that underline the Eurasian, African and Arabic plates boundaries is a submarine feature undergoing a complex tectonic deformation. The BLAC marine geophysical survey helps to better assess the type of the deformation that affects the Messinian to Quaternary sediments along this plate boundary. The deformation, focussed between two tectonic corridors, displays compressive and transpressive features in the central part, becoming thrusting when moving westward in connection with the Cyprus accretionnary wedge. The northeastern end of this submarine range connects with the Latakia Ridge, which is, together with its continental extension, under a tensional tectonic regime. To cite this article: J. Benkhelil et al., C. R. Geoscience 337 (2005). 相似文献
22.
23.
Fadl Raad Ronja Ebner Hanneke Heida Paul Meijer Johanna Lofi Agnès Maillard Daniel Garcia-Castellanos 《Basin Research》2023,35(1):1-27
The Central Mallorca Depression (CMD) located in the Balearic Promontory (Western Mediterranean) contains a well-preserved evaporitic sequence belonging to the Messinian Salinity Crisis (MSC) salt giant, densely covered by high- and low-resolution seismic reflection data. It has been proposed recently that the MSC evaporitic sequence in the CMD could be a non-deformed analogue of the key MSC area represented by the Caltanissetta Basin in Sicily. This presumed similarity makes the CMD an interesting system to better understand the MSC events. Physics-based box models of the water mixing between sub-basins, built on conservation of mass of water and salt, help constrain the hydrological conditions under which evaporites formed during the MSC. Those models have been widely used in the literature of the MSC in the past two decades. They have been mostly applied to the Mediterranean Sea as a whole focusing on the Mediterranean–Atlantic connection, or focusing on the influence of the Sicily Sill connecting the Western and Eastern Mediterranean Sea. In this study, we apply a downscaled version of such modelling technique to the CMD. First, we quantify the present-day volumes of the MSC units. We then use a reconstructed pre-MSC paleo-bathymetry to model salinity changes as a function of flux exchanges between the CMD and the Mediterranean. We show that a persistent connection between the CMD and the Mediterranean brine near gypsum saturation can explain volume of Primary Lower Gypsum under a sea level similar to the present. For the halite, on the contrary, we show that the observed halite volume cannot be deposited from a connected CMD-Mediterranean scenario, suggesting a drawdown of at least 850 m (sill depth) is necessary. Comparison between the deep basin halite volume and that of the CMD shows that it is possible to obtain the observed halite volume in both basins from a disconnected Mediterranean basin undergoing drawdown, although determining the average salinity of the Western Mediterranean basin at the onset of drawdown requires further investigation. 相似文献
24.
Françoise Andrieux-Loyer Afi Azandegbé Florian Caradec Xavier Philippon Roger Kérouel Agnès Youenou Jean-Louis Nicolas 《Aquatic Geochemistry》2014,20(6):573-611
This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l?1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS2). In the Aber Benoît, dissolved Fe/PO4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO4 ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m?2 h?1). At other periods, Fe/PO4 ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO4 ratios more difficult in terms of indicators of phosphate release. 相似文献
25.
Although the main events of the Messinian Salinity Crisis (MSC) are today mostly known, the exact succession of the different episodes remains unclear. This, in particular, is because (i) no drilling has reached the base of the Salt, and thus the onset of the MSC in the basins is unknown, and (ii) lateral correlations between the margins and the deep basins are missing. The Valencia Basin, which is intermediate in depth between the marginal basins and the deep basins, is an ideal location for studying the transitional domain. It displays the relationships between the polygenic erosion on the margins, the deposition of the thin Upper Evaporites bracketed by basal and top erosion surfaces in the central part of the basin, and the thick MSC sequence in the deep oceanic Provençal Basin. Early detrital deposits located below the MSC sequence of the deep basin suggest an early lowering of the sea level prior to the MSC desiccation. 相似文献
26.
Guilhem Hoareau Francis Odonne Elie-Jean Debroas Agnès Maillard Christophe Monnin Pierre Callot 《Marine and Petroleum Geology》2009,26(5):724-737
Numerous dolomite concretions have been discovered in marls of the Eocene Sobrarbe deltaic complex as part of the Ainsa Basin (Spain). This paper presents the first analyses of the shapes, the spatial relationships, the mineralogical, chemical and isotopic compositions of these concretions.The concretions are located above a major fossil submarine slide scar. They are mainly perpendicular to the sedimentary layers. Four distinct shapes of concretions have been distinguished: horizontal flat, sub-vertical cylindrical or cylindrical-complex and stocky. Three main mineral phases are associated with most of the concretions: calcite, celestite and barite. Concretion shapes and mineral occurrences are organized vertically in the marls from bottom to top: (i) at the bottom, flat shapes with septarian cracks filled by calcite and celestite, (ii) in the middle and at the top, cylindrical and cylindrical-complex concretions associated with prismatic barite, calcite and celestite filling conduits related to bioturbations, and (iii) at the top, cylindrical and cylindrical-complex concretions associated with calcite and celestite filling conduits related to bioturbations, and stocky shape concretions.We postulate that concretions have formed by dolomite cementation of the surrounding marls during early diagenesis in the zone of methanogenesis. The high sedimentation rate of the infilling seems to be a factor controlling the mineralogical composition of the concretions. Brown calcite precipitated in voids and fractures of the concretions. Celestite precipitated during burial, completing the filling of voids and fractures. Barite precipitated before celestite, but its time of precipitation relative to brown calcite remains unknown. 相似文献
27.
Jean Vallance Lluís Fontboté Massimo Chiaradia Agnès Markowski Susanne Schmidt Torsten Vennemann 《Mineralium Deposita》2009,44(4):389-413
The Jurassic (approximately 145 Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit
in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad20–98) with subordinate pyroxene (Di46–92Hd17–42Jo0–19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed
at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone
in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn
and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data
for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up
to 65 wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures
around 100–120 MPa, corresponding to about 4-km depth. Lower-temperature (510–300°C) and moderate- to low-salinity (23–2 wt.%
eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th
from 513°C to 318°C and salinity from 1.0 to 23 wt.% eq. NaCl) and δ18O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid
was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50–100 MPa, in line with the evidence
for CO2 effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during
the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external
fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde
alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated
at this stage as a result of cooling and pH increase related to CO2 effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external
fluids took place after gold deposition only, as recorded by δ18O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C)
meteoric fluids (δ18Owater between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and
indicate mixing with cooler fluids of higher salinities (about 100°C and 25 wt.% eq. NaCl). The latter are similar to low-temperature
fluids (202–74.5°C) with δ18O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3 wt.% eq. CaCl2, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized
gold skarn class, the presence of CO2 in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn
deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic
origin. 相似文献
28.
Georgia Poursoulis Agnès Levret Nathalie Lambert Alain Rideaud Bruno Helly 《Journal of Seismology》2006,10(4):511-526
Archaeological techniques and methodology are used to identify seismic traces and disorders in ancient buildings. Clear evidence could be identified as direct seismic consequences or as communities’ technical answers for repair or reinforcement of buildings in order to reduce their vulnerability. This methodology is called “archaeological reading of buildings.” It is based on the identification of different construction phases, modifications and past events (human actions or natural phenomena) suffered by buildings during their life. The data read from the buildings are successively observed, identified, described, and recorded, following the principal of archaeological stratigraphy, in order to explain the buildings history. The seismic pathologies are identified according to detailed engineering knowledge of the behaviour of buildings during seismic motion. In this case study, our approach is applied to the historical city of Manosque, located in a seismic area along the “Moyenne–Durance” active fault. As a result of historical researches (Quenet G, Baumont D, Scotti O, Levret A, Ann Geophys, 47(2/3):583–595, 2004), many historical documents gave evidence about this earthquake’s effects. Among these documents, was an exceptional one: the record of a survey made in Manosque by bricklayers a few days after the 14th August 1708 shock. This gave us specific information concerning the seismic damage caused in the town of Manosque and was the starting point to validate the method. In the present paper, the archaeological reading of buildings method is illustrated by two specific cases: the Charité building in Manosque and the Sainte-Agathe chapel in Saint-Maime village. The buildings suffered various modifications during many centuries. This complicates the application of the method, however the observations made from the buildings correlate well with the indications deduced from written sources, validating our approach. The study highlights the necessity to cross correlate different field data in the frame of a multidisciplinary approach in order to obtain valuable results concerning details of seismic damage, its approximate dating by architectural chronology and the communities’ reaction in terms of repairs and reinforcement techniques. 相似文献
29.
Agnė Venckutė-Aleksienė Andrej Spiridonov Andrius Garbaras Sigitas Radzevičius 《Swiss Journal of Geoscience》2018,111(1-2):341-352
The Cenomanian–Turonian transition marks one of the most important extinction episodes of the Mesozoic era. This extinction event was associated with the development of widespread oceanic anoxia and pronounced stable carbon isotopic excursion. Despite its importance, the effects of the perturbation on higher latitude biotas, and from the Baltic region in particular, are currently underexplored. Therefore, in this contribution we present the fossil record of a foraminifera succession integrated with δ13C trends from two deep cores: Bliūdsukiai-19 from western Lithuania and Balta?i?k?-267 from southern Lithuania. Two foraminiferal zones were distinguished: Rotalipora cushmani from the upper Cenomanian and Whiteinella archaeocretacea from the boundary strata between the Cenomanian and Turonian in the Balta?i?k?-267 core section, and a W. archaeocretacea Zone in the Bliūdsukiai-19 core section. A chemostratigraphical analysis of the stable carbon isotopes revealed a positive Cenomanian–Turonian δ13C anomaly, with maximum values reaching 3.57‰ in the upper part of the Bliūdsukiai-19 core section. A non-metric multidimensional scaling analysis of the foraminifera communities revealed that the major changes in their assemblages were strongly temporally organized and associated with the changes in the stable carbon isotopic ratios. This fact points to the significant effects of the C–T extinction event on the northern Neotethys paleocommunities. 相似文献
30.
Sébastien Nomade Agnès Gauthier Hervé Guillou Jean-François Pastre 《Quaternary Geochronology》2010,5(1):20-27
The Alleret maar (Massif Central, France) is part of the few Western European early middle Pleistocene lacustrine sequences. In the AL3 core several new ash layers were recovered in the 10 first meters of the sedimentary filling. We obtained three 40Ar/39Ar ages, which range from 683 ± 5 ka (MSWD: 1.2, n = 17) to 722 ± 6 ka (MSWD: 3.2, n = 18). All the studied ash layers belong to the Super-Besse eruptive cycle of the Sancy volcano. Based on the chronostratigraphy that we have derived we estimate that the age of the main eruption could correspond to the Sancy volcano caldera formation at 725 ka close to the end of MIS 18 and that the Super-Besse explosive episode duration lasted only about 40 ka. The time framework we build evidences that the Alleret lacustrine sequence represents a time interval of probably 180 ka spanning from MIS 18 to MIS 14. This sequence offers the first well constrained comparison between terrestrial environmental history and that preserved in marine sediments during the Mid-Pleistocene Revolution. 相似文献