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Potential seasonal calibration for palaeoenvironmental reconstruction using skeletal microstructures and strontium measurements from the cold‐water coral Lophelia pertusa 
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By ALBERTO CARRASSI STEPHANE VANNITSEM DUSANKA ZUPANSKI MILIJA ZUPANSKI 《地球，A辑:动力气象学与海洋学》2009,61(5):587-600
The performance of the maximum likelihood ensemble filter (MLEF), is investigated in the context of generic systems featuring the essential ingredients of unstable dynamics and on a spatially extended system displaying chaos. The main objective is to clarify the response of the filter to different regimes of motion and highlighting features which may help its optimization in more realistic applications. It is found that, in view of the minimization procedure involved in the filter analysis update, the algorithm provides accurate estimates even in the presence of prominent non-linearities. Most importantly, the filter ensemble size can be designed in connection to the properties of the system attractor (Kaplan–Yorke dimension), thus facilitating the filter setup and limiting the computational cost by using an optimal ensemble. As a corollary, this latter finding indicates that the ensemble perturbations in the MLEF reflect the intrinsic system error dynamics rather than a sampling of realizations of an unknown error covariance. 相似文献
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Disequilibrium Induced by Fast Decompression in St-Bt-Grt-Ky-Sil-And Metapelites from the Betic Belt (Southern Spain) 总被引：1，自引：0，他引：1
Medium-grade metapelites from the Torrox unit (Western Alpujarrides,Betic Cordilleras) provide an example of the phase relationshipsto be expected from extensional collapse of thickened crust.The rocks contain assemblages formed by combinations of St–Bt–GrtKySil–And,and are characterized by a marked state of textural and compositionaldisequilibrium that originated during post-peak, near-isothermaldecompression at moderately high temperatures (from >10 to2–3 kbar, at 550–650C). Major disequilibrium featuresinclude abundant reaction textures, metastable coexistence ofthe three aluminium silicate (Als) polymorphs, wide heterogeneitiesin the composition of phases within single samples and unsystematicor abnormal Mg-Fe partitioning among biolite, garnet and staurolite.Reaction relations and compositional trends of phases can beshown to be consistent with expectations from model systems,however, indicating that disequilibrium was a consequence ofreaction overstepping along the isothermal decompression path.Ensuing fast, near-isobaric cooling abruptly terminated metamorphism,and allowed for the preservation of disequilibrium featuresafter decompression. Given that the rocks decompressed at relativelyhigh temperature, the occurrence of reaction overstepping suggeststhat decompression proceeded at a very fast rate, consistentwith a bulk exhumation velocity in the range of 5–10 km/Ma,as estimated from available radio-metric data for this stage. KEY WORDS: decompression; disequilibrium; extensional collapse; medium-grade metapelites; reaction overstepping
*Corresponding author. Telephone: + 34 58 243355. Fax: + 34 58 243368. e-mail: agcasco{at}goliat.ugr.es 相似文献
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Experimental Melting of Cordierite Gneiss and the Petrogenesis of Syntranscurrent Peraluminous Granites in Southern Brazil 总被引：8，自引：1，他引：8
KOESTER EDINEI; PAWLEY ALISON R.; FERNANDES LUIS A. D.; PORCHER CARLA C.; SOLIANI ENIO JR 《Journal of Petrology》2002,43(8):1595-1616
To understand the petrogenesis of peraluminous granites syntectonicto the Dorsal de Canguçu Transcurrent Shear Zone in theSul-rio-grandense Shield, Brazil, melting experiments were performedon one of the potential protoliths, a cordierite-bearing semi-peliticmetasedimentary gneiss (PE-1). Experiments were conducted atpressures of 5, 10 and 15 kbar, at temperatures of 700–900°C,and under fluid-absent and 5% H2O-present conditions. The experimentsshow that fluid-absent melting begins at near-solidus conditions,around 700°C, promoted by participation of retrogressivephengitic muscovite in the reaction Mus + Kf ± Qz = melt± Fe–Ti oxide ± Als, producing a very smallamount of melt (<9%) with widely ranging composition. Allhypersolidus experiments (>800°C) produced S-type graniticmelts promoted by participation of biotite or cordierite inthe reactions Bio + Pl + Crd + Qz = Px + Fe–Ti oxide +melt at 5 kbar, and Bio + Pl + Crd ± Qz = Grt + Als ±Kf + melt at 10 and 15 kbar, both producing a high amount ofmelt (10–63% by volume). The melt compositions obtainedat 900°C and 15 kbar under fluid-absent conditions, promotedby biotite or cordierite breakdown, are similar to the syntectonicgranites. However, it is unlikely that the granites were formedat this pressure (corresponding to a depth of melting of 相似文献
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Metasomatism and Melting in Carbonated Peridotite Xenoliths from the Mantle Wedge: The Gobernador Gregores Case (Southern Patagonia) 总被引：8，自引：5，他引：8
LAURORA ANGELA; MAZZUCCHELLI MAURIZIO; RIVALENTI GIORGIO; VANNUCCI RICCARDO; ZANETTI ALBERTO; BARBIERI MARIA ADELAIDE; CINGOLANI CARLOS A. 《Journal of Petrology》2001,42(1):69-87
Spinel-facies mantle xenoliths occur in a diatreme cutting throughthe Neogene Southern Patagonia Plateau at Gobernador Gregores(Santa Cruz Province, Argentina). This plateau is in a back-arcposition with respect to the Chile trench. Xenoliths differin their whole-rock composition from other South America occurrences,having higher CaO/Al2O3 ratios and, in some samples, TiO2 enrichment,whereas the Na2O/Al2O3 variation range is similar. Three assemblagescan be distinguished. Assemblage 1, in anhydrous protogranularlherzolites and harzburgites, contains clinopyroxene with adepleted major and trace element composition, indicating pre-metasomaticdepletion processes. This assemblage fully recrystallized toAssemblage 2 (amphibole ± phlogopite ± Cl-apatite-bearing)during a metasomatic episode. This causes clinopyroxene to acquiregeochemical characteristics often attributed to carbonate-meltmetasomatism. Noticeably, amphibole is markedly enriched inNb (up to 298 ppm), especially when depleted in Ti. A furtherevent, related to decompression during xenolith uplift to thesurface, induces closed-system (perhaps with the exception ofCO2 addition) disequilibrium melting of Assemblage 2, dominantlyof amphibole. It is found in pockets (where amphibole is a residualphase) consisting of Na–Si-rich glass and carbonate (Mg-richcalcite) drops, and in veins originating from the pockets (Assemblage3). Euhedral olivine, clinopyroxene and spinel crystallize onlyin the silicate glass. So do new, euhedral apatite crystalswhen glass is in contact with previous Assemblage 2 apatite.Textural evidence and comparison with experimental work suggestthat silicate glass and carbonates are the result of unmixingof a former homogeneous melt. Because of the different flowrates of carbonate and silicate melt, the xenoliths become enrichedin carbonate, which is found in the veins during their migration.Thus, the high CaO/Al2O3 ratio of whole rocks provides inconclusiveevidence of carbonatite metasomatism. This factor, and otherminor deviations from the expected results of carbonatite metasomatism,lead us to hypothesize an aqueous, Cl-rich fluid, possibly slabderived, as an alternative agent. Amphibole, resulting fromreactive porous flow of this agent in the mantle, could fullyexplain the observed geochemical features, as indicated by estimatesof its partition coefficients. KEY WORDS: carbonated xenoliths; Gobernador Gregores; LAM–ICP-MS; mantle metasomatism; silicate glass 相似文献
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Sedimentary dynamics and evolutionary history of a Late Carboniferous Gondwanic lake in north-western Argentina 总被引：1，自引：0，他引：1
Lacustrine deposits are well represented in the lower part of the Late Carboniferous Agua Colorada Formation in the north-west Sierra de Narváez, Catamarca Province, Argentina. Lake Narváez was one of the several water bodies formed in the region immediately after the Gondwana glaciation. The lacustrine transport system has been divided into three distinct zones: delta, shallow lake and deep lake. Delta progradation proceeded from the ESE. Coarse-grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters (‘short-headed stream delta’type). During periods of high discharge, river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents. The clastic material supplied by the deltaic system was partially reworked by wave action. Sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation. As a result of the addition of clastics in the steep delta front, turbidity currents were formed, spreading their load along the lower delta slope. Deep lacustrine deposits are typically stacked, forming two different kinds of progradational turbidite lobe sequences. Type I lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment-bypassing in a shallow lake during periods of low lake level. These turbidite lobes are replaced upwards by type II lobes, which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation. The presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting, whereas the occurrence of hummocky cross-stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents. Therefore, the inner part of type II lobes was formed above storm wave base. The depositional history of Lake Narváez can be traced through four evolutionary stages: lake transgression, formation of type I lobes, formation of type II lobes and delta progradation. Tectonic activity was probably important at the early stage of lake evolution, but the subsequent depositional history was mainly controlled by fluctuations of lake level. 相似文献
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LUIS A. BUATOIS NUBIA SANTIAGO MEYLIN HERRERA PIRET PLINK‐BJÖRKLUND RON STEEL MARÍA ESPIN KAOLU PARRA 《Sedimentology》2012,59(5):1568-1612
Analysis of Neogene cores from the Eastern Venezuela Basin along 65 km of a west–east trending shoreline allows characterization of the sedimentological and ichnological signatures of wave, river and tidal processes. The area displays deltas prograding northward from the Guyana Shield. Twenty‐three facies are defined and grouped into four categories (wave‐influenced, river‐influenced, tide‐influenced and basinal). Wave‐dominated deltaic deposits occur mostly in the Tácata Field. The delta plain was characterized by tide‐influenced distributary channels separated by interdistributary bays. Fluvial discharge in the delta front and prodelta was repeatedly interrupted by storm‐wave reworking and suspended sediment fallout. Delta‐front and prodelta deposits contain some ichnotaxa that typically do not occur in brackish water (for example, Chondrites and Phycosiphon). Amalgamated storm deposits are unburrowed or contain vertical Ophiomorpha. Lateral (especially on the updrift side) to the river mouths, waves caused nearly continuous accretion of the associated strandplains. These deposits are the most intensely bioturbated, and are dominated by the estenohaline echinoid‐generated ichnogenus Scolicia. River‐dominated deltaic deposits are present in the Santa Bárbara, Mulata, Carito and El Furrial Fields. Low‐sinuosity rivers characterized the alluvial plain, whereas the subaerial delta plain was occupied by higher‐sinuosity rivers. The subaqueous delta plain includes distributary channels and tide‐influenced interdistributary bays. Further seaward, successions are characterized by terminal distributary‐channel and distributary mouth‐bar deposits, as well as by delta‐front and prodelta deposits showing evidence of sediment gravity‐flow and fluid‐mud emplacement. Delta‐front and prodelta deposits are unbioturbated to sparsely bioturbated, suggesting extreme stress, mostly as a result of high fluvial discharge and generation of sediment gravity flows. Tidal influence is restricted to interdistributary bays, lagoons and some distributary channels. From an ichnological perspective, and in order of decreasing stress levels, four main depositional settings are identified: river‐dominated deltas, tide‐influenced delta plains, wave‐dominated deltas and wave‐dominated strandplain–offshore complexes. 相似文献
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ALBERTO CONSONNI PAOLA RONCHI CLAUDIO GELONI† ALFREDO BATTISTELLI† DOMENICO GRIGO SIMONA BIAGI‡ FABRIZIO GHERARDI‡ GIOVANNI GIANELLI‡ Associate Editor: Dave Cantrell 《Sedimentology》2010,57(1):209-231
Dolomitization of a carbonate platform can occur at different times and in different diagenetic environments, from synsedimentary to deep burial settings. Numerical simulations are valuable tools to test and select the model that, among different hypotheses compatible with field and geochemical data, best honour mass balance, kinetic and thermodynamic constraints. Moreover, the simulation can predict the distribution of the dolomitized bodies in the subsurface and evaluate porosity changes; valuable information for the oil industry. This study is the first attempt to reproduce and investigate the compaction dolomitization model. The diagenetic study of the Jurassic carbonate basin and palaeohigh system of the Po Plain indicates that the carbonates of the palaeohighs were dolomitized by basin compaction fluids. The main goal of the simulations is to evaluate the origin and evolution of the dolomitizing fluids and to provide insights regarding the distribution of the potential reservoir‐dolomitized bodies in the Po Plain. The modelling process is subdivided into two steps: basin modelling and reactive transport modelling. The SEBE3 basin simulator (Eni proprietary) was used to create a three‐dimensional model of the compacting system. The results include compaction fluid flow rate from the basin to the palaeohigh, compaction duration and a determination of the total amount of fluid introduced into the palaeohigh. These data are then used to perform reactive transport modelling with the TOUGHREACT code. Sensitivities on dolomite kinetic parameters suggest that dolomitization was an efficient process even at low temperatures, with differences mainly related to the dynamics of the process. Fluid composition is one of the main constraints, the sea water derived compaction fluid is proven to be efficient for dolomitization due to its relatively high Mg content. Simulations also confirmed that permeability is the most important factor influencing fluid flow and, consequently, the dolomite distribution in the formation. Permeable fractured zones have a strong influence, diverting the dolomitizing fluids from their normal path towards overlying or lateral zones. Moreover, the simulations showed that, after dolomite replacement is complete, the dolomitizing fluids can precipitate dolomite cement, causing over‐dolomitization, with related localized plugging effects in the zone of influx. Mass balance calculations indicate that in the dolomitization compaction model, the amount of compaction water fluxed from the basin to the carbonate is the main constraint on dolomitization efficiency. This observation implies that the ratio between the volume of the basin undergoing compaction and the volume of the palaeohigh is a limiting factor on the final size of the dolomitized bodies. An isolated palaeohigh could be an ideal site for pervasive replacement dolomitization due to the large volume of compaction fluids available compared with the carbonate rock volume. In the case of large platforms, the more permeable margin lithofacies are the most likely sites for compaction model dolomitization. The combined use of a basin simulator and reactive transport modelling has proved to be a successful method to verify model reliability and it provides insights into the volumetric distribution of diagenetic products. 相似文献
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A multi‐proxy study of Holocene environmental change recorded in alluvial deposits along the southern coast of the Pampa region,Argentina 下载免费PDF全文
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