A hindered settling model for the prediction of settling and consolidation of cohesive sediment

The prediction of the settling and consolidation behavior of mixtures of cohesive and non-cohesive sediment is possible using a numerical model that solves the solids mass balance for each fraction. Consistency with the hindered settling theory as well as classical soil mechanics is preserved. Semi-empirical relationships for settling rate and effective stress as a function of density are required as constitutive equations. A simple procedure, using settling column experiment data, for calibration is proposed. The possibility of distinguishing different kinds of particles allows prediction of layered deposits.     

Spatio-temporal changes in totally and enzymatically hydrolyzable amino acids of superficial sediments from three contrasted areas

Spatio-temporal changes in totally and enzymatically hydrolyzable amino acids (THAA and EHHA) and EHAA/THAA ratios of superficial sediments were assessed during 1997-1999 in three areas (i.e., the Gulf of Lions, the Bay of Biscay, and Central Chile) differing in their primary productivity. In all three areas, and even off Central Chile where a strong El Niño event took place during 1997-1998, spatial changes were always much greater than temporal ones. The factors affecting the spatial distributions of amino acid concentrations differed among areas. In the Gulf of Lions, sediment granulometry was apparently the most important driving force of THAA, EHAA, and EHAA/THAA, and there was no marked difference between stations located on the open slope and those in submarine canyons. Conversely, in the Bay of Biscay, there were clear differences between the stations located off Cap-Breton, on the open slope, and those in the Cap-Ferret canyon; the latter two featuring lower EHAA and THAA but higher EHAA/THAA. This pattern is likely to result from the predominance of different sources of organic matter and especially from the importance of continental inputs to the Cap-Breton canyon. Off Central Chile, amino acid concentrations and ratios were both maximal around 100 m depth, probably reflecting the interaction between the primary productivity gradient and the presence of an oxygen minimum zone (OMZ) reducing the degradation of sedimentary organics. When comparing the average values collected in the three areas studied, THAA and EHAA were highest in Central Chile, intermediate in the Bay of Biscay and lowest in the Gulf of Lions. EHAA/THAA ratios were also highest in Central Chile but were lowest in the Bay of Biscay. Differences between the Gulf of Lions and the Bay of Biscay could have been affected by sampling design. In Central Chile, the use of labile organic carbon to total organic carbon (C-LOM/TOC) and EHAA/THAA as indices of organic matter lability led to very similar results. This was not the case in the Bay of Biscay. It is therefore argued that the use of C-LOM/TOC should be restricted to highly productive areas.     

Limiting similarity, niche filtering and functional diversity in coastal lagoon fish communities

The fundamental idea behind the study of biodiversity patterns is the presumed connection between the shape of species assemblages and the functional ways in which they are organized, this functional organization referring to how species are related to one another, as competitors or members of a web of interactions and to how species are facing similar environmental constraints. Amongst the different facets of biodiversity, functional diversity is certainly a key for ecosystem processes in coastal areas. However, surprisingly, patterns of functional diversity have received little attention until now. After presenting a common framework linking functional diversity patterns to species coexistence theories, the aim of our study was twofold: (1) to seek assembly rules in brackish lagoon fish communities drove by functional traits. To this aim we used null models to examine the influence of two opposing forces acting on community structure: interspecific competition that might prevent the coexistence of the most similar species, and environmental filters that might result in the most similar species to coexist. (2) To seek relationships between fish functional diversity and environmental gradients, if any. Fish sampling was carried out in two coastal lagoons where stations differ considerably in terms of physicochemical parameters. Using morphological functional traits, functional diversity of fish communities was estimated using two recently published indices as well as a new proposed index. Firstly our study was not able to demonstrate a limitation of similarity in coexisting lagoon fishes due to interspecific competition. Conversely our results support the niche filtering hypothesis preventing species too dissimilar from one another to co-occur at the same station. Secondly, salinity was positively related to the functional diversity of fishes in both lagoons suggesting that within species assemblages near the channel species are less redundant than at stations far from the channel where species tend to be functionally similar (benthic and eating zooplankton).     

Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific)

The Easter microplate-Crough Seamount region located between 25° S–116° W and 25° S–122° W consists of a chain of seamounts forming isolated volcanoes and elongated (100–200 km in length) en echelon volcanic ridges oriented obliquely NE (N 065°), to the present day general spreading direction (N 100°) of the Pacific-Nazca plates. The extension of this seamount chain into the southwestern edge of the Easter microplate near 26°30 S–115° W was surveyed and sampled. The southern boundary including the Orongo fracture zone and other shallow ridges (< 2000 m high) bounding the Southwest Rift of the microplate consists of fault scarps where pillow lava, dolerite, and metabasalts are exposed. The degree of rock alternation inferred from palagonitization of glassy margins suggests that the volcanic ridges are as old as the shallow ridges bounding the Southwest Rift of the microplate. The volcanics found on the various structures west of the microplate consist of depleted (K/Ti < 0.1), transitional (K/Ti = 0.11–0.25) and enriched (K/Ti > 0.25) MORBs which are similar in composition to other more recent basalts from the Southwest and East Rifts spreading axes of the Easter microplate. Incompatible element ratios normalized to chondrite values [(Ce/Yb)_N = 1–2.5}, {(La/Sm)_N = 0.4–1.2} and {(Zr/Y)_N = 0.7–2.5} of the basalts are also similar to present day volcanism found in the Easter microplate. The volcanics from the Easter microplate-Crough region are unrelated to other known South Pacific intraplate magmatism (i.e. Society, Pitcairn, and Salas y Gomez Islands). Instead their range in incompatible element ratios is comparable to the submarine basalts from the recently investigated Ahu and Umu volcanic field (Easter hotspot) (Scientific Party SO80, 1993) and centered at about 80 km west of Easter Island. The oblique ridges and their associated seamounts are likely to represent ancient leaky transform faults created during the initial stage of the Easter microplate formation ( 5 Ma). It appears that volcanic activity on seamounts overlying the oblique volcanic ridges has continued during their westward drift from the microplate as shown by the presence of relatively fresh lava observed on one of these structures, namely the first Oblique Volcanic Ridge near 25° S–118° W at about 160 km west of the Easter microplate West Rift. Based on a reconstruction of the Easter microplate, it is suggested that the Crough seamount (< 800 m depth) was formed by earlier (7–10 Ma) hotspot magmatic activity which also created Easter Island.     

Sedimentary record of redox-sensitive elements (U, Mn, Mo) in a transitory anoxic basin (the Thau lagoon, France)

In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H₂S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H₂S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.     

法国Beauvoir和Montebras花岗岩中富铌钽锡石的拉曼光谱特征

法国Beauvoir花岗岩和Montebras花岗岩中的锡石都含有较丰富的微量元素,如Nb、Ta,并含有铌钽矿包裹体。将锡石晶体制成光薄片,运用拉曼探针,对不同部位进行的研究表明,锡石的A_(1g)峰的振动频率与其所含的Nb、Ta、Fe、Mn含量成反比。值得指出的是,在富含铌钽包裹体的部分,发现了一个新的拉曼光谱峰(定为An峰),其振动频率为827—830cm~(-1),对其进行的研究表明,该峰的出现与锡石晶格中(Nb,Ta)的过量和铌钽矿包裹体的出溶所造成的晶体结构的变化有关。     

Clay mineral assemblages of Mesozoic pelagic and flysch sediments of the Lombardian Basin (Southern Alps): implications for palaeotectonics,palaeoclimate and diagenesis

Clay mineral assemblages determined by X-ray diffraction, in the Jurassic to Lower Cretaceous hemipelagic/pelagic sediments and in the Upper Cretaceous flysch sequences of the Lombardian Basin (Southern Alps) record tectonic and possibly climatic changes in the source areas and to a lesser extent, alterations during burial diagenesis.In the hemipelagic/pelagic sediments exposed in the Breggia valley in southern Switzerland, the clay fraction is dominated by illite and smectite and seems not to be altered much by burial diagenesis. The varied clay mineral assemblages of the Liassic sediments result from intense erosion of emergent source areas exposed during early rifting phases. A distinction between smectite-rich limestones and illite-rich marls in these syn-rift to early post-rift sediments could reflect short-term climatic fluctuations or, alternatively, a preferential replacement of smectite by illite during incipient burial diagenesis in the marls. The predominantly smectitic composition of the clay fraction in the upper Middle Jurassic to Lower Cretaceous sediments documents gentle erosion of smectite-rich soils developing under a warm and seasonally humid climate on a relatively stable distant source area.In the Aptian, an increase in illite in the clay fraction of the hemipelagic Scaglia Lombarda Group points to an increased detrital influx from emergent source areas. This influx is related to the onset of orogenic movements along the Austroalpine/South Pennine active margin, resulting in Middle Cretaceous flysch sedimentation in the Austroalpine realm.Increasing influx from emergent continental crust is reflected by the high amounts of illite and chlorite in the Upper Cretaceous flysch sequences of the eastern Brianza area. However, the high amounts of chlorite in limestone turbidites in the lower part of the flysch sequence (Pontida Formation, Turonian) suggest transformation of smectite to chlorite under conditions of burial diagenesis. In the younger flysch deposits (Bergamo Flysch, Upper Santonian-Campanian) detrital clay minerals are preserved. The occurrence of kaolinite and smectite beside illite and minor chlorite suggests intense weathering and less relief during deposition of the Bergamo Flysch.

---

Zusammenfassung Röntgendiffraktometrisch bestimmte Tonmineral-Assoziationen in den jurassisch-unterkretazischen hemipelagischen und pelagischen Sedimenten sowie in den Oberkreide-Flyschen des Lombardischen Beckens der Südalpen erlauben wichtige Rückschlüsse über tektonische und eventuell klimatische Änderungen in den Liefergebieten sowie, in etwas geringerem Maße, über Veränderungen während der Uberlagerungs-Diagenese.Die vorwiegend illitisch-smektitische Tonfraktion der hemipelagisch/pelagischen Sedimente der Breggia-Schlucht (Tessin, Süd-Schweiz) scheint wenig verändert durch die Überlagerungs-Diagenese. Die stark variable Zusammensetzung der Tonfraktion der liassischen Sedimente deutet auf eine intensive Erosion der während des frühen Riftings herausgehobenen Liefergebiete. Eine Differenzierung zwischen Smektit-reichen Kalken und Illitreichen Mergeln in den syn- und frühen post-rift-Sedimenten des Lias deutet auf kurzfristige klimatische Fluktuationen (Milankovitch-Zyklen) oder auf einen Ersatz von Smektit durch Illit während der beginnenden Überlagerungs-Diagenese in den Mergeln. Die hauptsächlich smektitische Zusammensetzung der Tonfraktion in den mittel-jurassischen bis unter-kretazischen Sedimenten weist auf eine weniger intensive Erosion Smektit-reicher Böden in relativ stabilen, weit entfernten Liefergebieten mit einem warmen und saisonal humiden Klima.Eine deutliche Zunahme der Sedimentationsraten und des Illits in der Tonfraktion der hemipelagischen Scaglia Lombarda belegt einen zunehmenden detritischen Einfluß vom Aptian an. Dieser detritische Einfluß läßt sich mit dem Einsetzen orogener Heraushebung längs des aktiven Kontinentalrandes an der Süd-Penninikum/Ostalpin-Grenze in Verbindung bringen, da er mit Flysch-Ablagerungen in Süd-Penninikum und Ostalpin zeitlich zusammenfällt.Eine zunehmend detritische Schüttung aus kontinentalen kristallinen Liefergebieten läßt sich in den Illit- und Chlorit-reichen Tonmineral-Assoziationen der Oberkreide-Flysche der östlichen Brianza (Provinz Como, Nord-Italien) erkennen. Die hohen Chlorit-Konzentrationen in Kalk-Turbiditen im unteren Teil der Flysch-Abfolge (Pontida-Formation, Turonian) lassen hingegen eher eine diagenetische Umwandlung von Smektit in Chlorit vermuten. In den jüngeren Flysch-Ablagerungen (Bergamo-Flysch, Oberes Santonian bis Campanian) läßt sich die ursprüngliche detritische Tonmineral-Vergesellschaftung noch erkennen. In dieser Formation deutet das Vorkommen von Kaolinit und Smektit neben Illit und wenig Chlorit auf eine intensive Verwitterung und ein kleineres Relief im Hinterland.

---

Résumé Les minéraux argileux des formations jurassiques et crétacées du Bassin Lombard (Alpes méridionales) sont étudiés par diffraction des rayons X. Les variations des cortèges argileux des sédiments pélagiques et des flyschs du Crétacé supérieur résultent de modifications tectoniques, climatiques et dans une moindre mesure d'évolutions diagénétiques liées à l'enfouissement.L'illite et la smectite dominent très largement les assemblages minéralogiques dans les sédiments pélagiques et hémipélagiques étudiés dans les gorges de la Breggia (Tessin, Suisse méridionale). L'influence de la diagenèse d'enfouissement paraît modérée et les assemblages argileux très diversifiés des formations liasiques reflètent une érosion active des zones continentales au début du rifting. Dans les formations syn-rift alternantes calcaire-marne, la fraction argileuse des marnes est systématiquement enrichie en illite par rapport à celle des calcaires. Ces relations entre minéralogie des argiles et lithologie résultent soit de fluctuations climatiques, soit d'une illitisation préférentielle des smectites dans les intervalles marneux.A partir du Jurassique moyen et supérieur et jusqu'au Barrémien inclus, la fraction argileuse des sédiments est très smectitique. Elle reflète l'érosion superficielle de sols riches en smectites développés sous climat chaud à humidité saisonnière contrastée sur des domaines continentaux aplanis et probablement très éloignés. A l'Aptien, les apports illitiques importants traduisent, le long de la marge active Austroalpine/Sud Pennique, le début de mouvements orogéniques responsables du dépôt des flyschs dans le domaine Austro-alpin.Dans les faciès flysch du Crétacé supérieur de la Brianza orientale, les apports d'illites et de chlorites s'accordent avec l'augmentation de l'érosion sur les domaines continentaux. Cependant, l'influence d'une diagenèse d'enfouissement est attestée en particulier par les très fortes proportions de chlorites présentes dans les turbidites calcaires (Pontida formation, Turonien). Dans les dépôts de flysch plus récents (Bergamo flysch, Santonien-Campanien), les minéraux argileux détritiques sont mieux préservés. La présence systématique de kaolinite et de smectite suggère le développement d'une altération continentale importante sur des reliefs moins marqués par rapport aux périodes plus anciennes du Crétacé supérieur.

---

- . , , . Breggia (Tec, ), . . /, , , . , , . , , , , , , , ( ), . , , . Scaglia Lombarda . / , . , , Brianza ( , ). ( , ) . ( , ) . , , , .

     

The clinopyroxene/plagioclase symplectite in retrograde eclogites: A potential geothermobarometer

The retrograde P-T-t path of intermediate and high-temperature eclogites (T 500 ± 50°C) is characterized by the transformation of omphacite into a symplectitic intergrowth of clinopyroxene and plagioclase lamellae. Often, this symplectite shows a two stage microstructural evolution, i.e. a coarse lamellar width symplectite, »S1«, followed by a thinner lamellar width symplectite, »S2«. Each symplectite may also evolve independently into a final globular microstructure, »SG«.According to metallurgical concepts, the phase transition »omphacite clinopyroxene + plagioclase« is classified as a discontinuous precipitation reaction. In discontinuous precipitation reactions, the lamellar spacing (L) depends on temperature (T) according to the growth law log (L) = A-B/T, in which A and B are constants. Therefore thin symplectites characterize low temperatures, where-as coarse symplectites characterize higher temperatures.In order of specify the thermal evolution of continental collision zones, the reliability of the discontinuous precipitation growth law has been tested on eclogites showing contrasted retrograde P-T-t histories in different geological environments, i.e. Alpine, Caledonian and Variscan Belts. Indeed, our investigations reveal that the clinopyroxene/plagioclase symplectite can be used as a potential geothermobarometer in eclogites recording temperatures above 500 ± 50°C. The temperature is obtained by the lamellar spacing and pressure by the Jadeite content of the symplectite clinopyroxene in the presence of plagioclase and quartz.

---

Zusammenfassung Der retrograde P-T-t Pfad von intermediären und hochtemperierten Eklogiten (T 500 ±50°C) ist charakterisiert durch die Umformung von Omphazit in symplektitische Verwachsungen von Klinopyroxen und Plagioklas-Lamellen. Häufig zeigt dieser Symplektit eine zweiphasige mikrostrukturelle Entwicklung, das heißt, ein Symplektit mit breiten Lamellen »S1« wird gefolgt von einem Symplektit mit dünneren Lamellen »2«. Jeder Symplektittyp kann sich schließlich selbständig zu einer kugelförmigen MikroStruktur »SG« entwikkeln.Auf Grund von metallurgischen Vorstellungen wir die Phasenumwandlung Omphazit zu Klinopyroxen + Plagioklas als diskontinuierliche Ausfällungsreaktion klassifiziert. In diskontinuierlichen Ausfällungsreaktionen hängt der Lamellenabstand (L) von der Temperatur (T) nach dem Wachstumsgesetz log (L) = A-B/T ab, in dem A und B Konstanten sind. Daher zeigen dünne Symplektite niedrige Temperaturen an, während breite Symplektite höhere Temperaturen anzeigen.Um die thermische Entwicklung von kontinentalen Kollisionszonen zu spezifizieren mußte die Zuververlässigkeit des diskontinuierlichen Ausfällungswachstumsgesetz an Eklogiten getestet werden, die unterschiedlich retrograde P-T-t Geschichten aus verschieden Umgebungen zeigen; das heißt aus alpinen, kaledonischen und variszischen Gebirgszügen. Tatsächlich offenbaren unsere Bemühungen, daß der Klinopyroxen/Plagioklas Symplektit als potentielles Geothermobarometer in Eklogiten benutzt werden kann, die Temperaturen über 500°C ± 50°C erfahren haben. Die Temperatur kann man aus dem Lamellenabstand erhalten; den Druck durch den Jadeitgehalt des symplektitischen Pyroxens, in Anwesenheit von Plagioklas und Quarz.

---

Résumé La déstabilisation de l'omphacite, en une symplectite à alternance de lamelles de clinopyroxène et de plagioclase, caractérise l'initiation du trajet rétrograde P-T-t pour les éclogites de température 500 ± 50°C. Cette symplectite présente parfois une évolution microstructurale depuis une symplectite grossière à alternance de lamelles larges, »S1«, relayée par une symplectite à alternance de lamelles fines, »S2«. Chaque symplectite peut aussi évoluer indépendemment en une microstructure globulaire tardive, »Sg«.En accord avec les concepts établis par les métallurgistes, la transformation »omphacite clinopyroxène + plagioclase« est une précipitation discontinue. Pour ce type de transformation, l'espace interlamellaire (L) dépend de la température (T) selon la loi de croissance Log (L) =A-B/T (*), où A et B sont des constantes. Ainsi, une symplectite fine (de type S2) caractérise des températures relativement plus basses qu'une symplectite grossière (de type S1).Afin de préciser l'évolution thermique des zones de collision continentale, nous avons testé la loi de croissance (*) sur des éclogites échantillonnées dans divers contextes géologiques (chaînes alpine, calédonide et varisque), présentant des trajets rétrogrades P-T-t contrastés. Les résultats montrent que la symplectite à clinopyroxène/plagioclase représente un géothermobaromètre potentiel de la rétromorphose des éclogites: la taille de l'espace interlamellaire dépend de la température et la teneur en jadéite des lamelles de clinopyroxène, en présence de quartz et à l'équilibre avec le plagioclase, dépend de la pression.

---

. , .. , «S 1», «S 2». «SG». , . (L) () — — log (L) = - /, . , . , , , .: , . , , / , , 500° + 50°. , — , .

     

Integration of a continuum damage model for shale with the cutting plane algorithm

The stability of integration is essential to numerical simulations especially when solving nonlinear problems. In this work, a continuum damage mechanics model proposed by the first author is implemented with an integration method named cutting plane algorithm (CPA) to improve the robustness of the simulation. This integration method is one type of return mapping algorithm that bypasses the need for computing the gradients. We compare the current integration method with the previous direct method, and the result shows that the cutting plane algorithm exhibits excellent performance under large loading rate conditions. To enhance accuracy of the new method, a control procedure is utilized in the implementation of the algorithm based on error analysis. Thereafter, the theory of poromechanics is utilized with the damage model to account for the effects of fluid diffusion. Laboratory tests simulated with finite element method illustrate distinct behaviors of shale with different loading rates and indicate the development of microcrack propagation under triaxial compression. Copyright © 2016 John Wiley & Sons, Ltd.