The impact of the last European deglaciation on the deep-sea turbidite systems of the Celtic-Armorican margin (Bay of Biscay)

The compilation of results obtained on three giant piston cores from the Whittard, Shamrock and Guilcher turbidite levees reveals a high-resolution stratigraphic record for the Bay of Biscay. Due to the abundance of reworked sediments in these sedimentary environments, a specific methodological approach, based on an X-ray-assisted subsampling phase associated with sedimentological, geochemical and micropalaeontological analyses, was implemented. With an accurate chronological framework, this multi-proxy investigation provides observations on the ‘Fleuve Manche’ palaeoriver and the British-Irish Ice Sheet (BIS) histories over the last 20,000 years. The results obtained highlight the direct influence of the decay of the BIS on the Bay of Biscay deep-sea clastic sedimentation during the last European deglacial phase. During this period, the annual BIS cycle of meltwater seems enough to generate seasonal turbidity currents associated with exceptional sedimentation rates in all the Celtic and Armorican turbidite systems. With very high sedimentation rates, the turbidite levees represent the main deep-sea clastic depositional area. Long coring combined with a very careful subsampling method can provide continuous high-resolution palaeoenvironmental signals.     

Deep and shallow structures of large pockmarks in the Turkish shelf, Eastern Black Sea

Circular and elongated pockmarks are present between 180- and 300-m water depths in the Eastern Black Sea shelf. The circular pockmarks have diameters of 50–120 m and the elongated pockmarks are 150–200 m wide with crater depths of 10–25 m. In deeper sediments, buried pockmarks were vertically stacked, indicating that the pockmarks developed under periodically varying overpressure conditions driven by the seismologically active North Anatolian Fault. Linear elongated pockmarks were formed by downslope tensional stretching, which caused linear weak zones together with strong seafloor currents acting as a connector of circular pockmarks.     

Liquefaction analysis and soil improvement in Beydag dam

Beydag dam is under construction on Kucukmenderes River for irrigation purposes. Due to the scarcity of core material and liquefaction of alluvium at the dam site, the original design was changed to Roller Compacted Concete (RCC) from rockfill dam with claycore. Although the new design was safer, it nearly doubled the cost of the dam, so the owner, State Hydraulic Works of Turkey, (DSI) set out to find more economical but equally safe alternative. Since jet-grouting is a cheap ground improvement tool in Turkey, such an alternative was developed for the ground improvement against liquefaction together with concrete face rockfill dam sitting on top of improved ground. This paper presents a detailed discussion of how the new alternative was developed and evaluated: it discusses the determination of jet grouting pattern, the placement of jet grouted blocks, and the assesment of liquefaction. On one hand the soil cement strength of jetgrout columns, internal friction angle of alluvium and rockfill were important in determining the dimensions of the blocks, on the other hand the location of the blocks were highly affected by the areas where liquefaction occurred. One of the most important parameter that has a considerable influence in delineating the boundary betweeen liquefaction and non-liquefaction was the value of stress reduction coefficient (r _d), being primarily sensitive to the weight of overburden, which is calculated by the height from the face of dam to the depth where the calculation was made. This approach is justified by two-dimensional ground response analysis. Most importantly, this paper shows that there exists an alternative solution for building dams on the liquefaction prone sites without removing alluvium by using a well known jet grouting technique for improving ground at only selected places.     

Ordering-based nonlinear solver for fully-implicit simulation of three-phase flow

The Fully Implicit Method (FIM) is often the method of choice for the temporal discretization of the partial differential equations governing multiphase flow in porous media. The FIM involves solving large coupled systems of nonlinear algebraic equations. Newton-based methods, which are employed to solve the nonlinear systems, can suffer from convergence problems—this is especially true for large time steps in the presence of highly nonlinear flow physics. To overcome such convergence problems, the time step is usually reduced, and the Newton steps are restarted from the solution of the previous (converged) time step. Recently, potential ordering and the reduced-Newton method were used to solve immiscible three-phase flow in the presence of buoyancy and capillary effects (e.g., Kwok and Tchelepi, J. Comput. Phys. 227(1), 706–727 9). Here, we improve the robustness of the potential-based ordering method in the presence of gravity. Furthermore, we also extend this nonlinear approach to interphase mass transfer. Our algorithm deals effectively with mass transfer between the liquid and gas phases, including phase disappearance (e.g., gas going back in solution) and reappearance (e.g., gas coming out of solution and forming a separate phase), as a function of pressure and composition. Detailed comparisons of the robustness and efficiency of the potential-based solver with state-of-the-art nonlinear/linear solvers are presented for immiscible two-phase (Dead-Oil), Black-Oil, and compositional problems using heterogeneous models. The results show that for large time steps, our nonlinear ordering-based solver reduces the number of nonlinear iterations significantly, which leads to gains in the overall computational cost.     

A revised stratigraphic framework for later Cenozoic sequences in the northeastern Mediterranean region

This study describes the lithostratigraphic character of mid-Cenozoic (Oligocene-Pliocene) sequences in different parts of the northeastern Mediterranean area and offers a detailed stratigraphic correlation for this region. The sequences concerned are drawn from the Camardi area (south-central Anatolia), the Adana Basin, the Misis Mountains and the Kyrenia Range (northern Cyprus) and the submerged Florence Rise (west of Cyprus). The stratigraphic relationships identified here indicate the following: (a) Following the middle Eocene (Lutetian) regression there was uplift throughout the entire region; (b) Episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late Eocene/early Miocene interval; (c) Following a regionally extensive phase of tectonic compression, major marine transgression commenced in the late Oligocene in northern Cyprus and in the early Miocene in adjacent southern Turkey, with the exception of the Ecemi§ Fault Zone where continental deposition continued; (d) These Oligo-Miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies, including reefal carbonates, littoral clastics, basinal shales and fan-turbidites; (e) Deeper marine Miocene facies persisted longer in the Misis area and in northern Cyprus; (f) A regional regression occurred throughout most of the area during the late Serravallian to Tortonian interval and is marked by the abrupt, locally discordant appearance of extensive shallow marine, deltaic and fluvial deposits; (g) Continued regression in the Messinian led to the formation of significant evaporite deposits in the western and southern parts of the region, but localized uplift of the Misis area is attested by the initial deformation of the Neogene rocks there and the absence of Messinian sediments from this area; (h) In the Pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions. The present-day drainage pattern was established at this time; (i) Marine conditions persisted longer in northern Cyprus, where emergence occurred only in the latest Pliocene.     

The phoshate mineral associations of the Tsaobismund pegmatite,Namibia

A detailed mineralogical investigation using the classical methods of identification by X-ray diffraction and by optical properties in thin sections, has revealed thirty one phosphate minerals occurring in the Tsaobismund pegmatite. This investigation is complemented by wet chemical and, mainly, electron microprobe analyses performed on the phosphates known to be typomorphic or considered to be relevant to the hydrothermal alteration. Additionally, microprobe analyses are also given for garnet, gahnite, and ferrocolumbite associated with the phosphates. On the basis of their chemical composition, particularly in terms of their Fe, Mn, and Mg contents, three types of triphylites are distinguished. Triphylite 1 only occurs as a primary phase, triphylite 2 shows exsolution lamellae of sarcopside, and triphylite 3 is partly replaced by a fluorophosphate of the triplite-zwieselite series. These minerals constitute three generations of the parent phases, which were progressively transformed by metasomatic processes, hydrothermal alteration, and by weathering, to give finally three types of complex associations. The Li(Fe,Mn)PO₄ minerals appear to be more sensitive to such transformations than those of the (Fe,Mn)₂PO₄F series. Four main stages of hydrothermal alteration processes have been recognized in the Tsaobismund pegmatite: (i) the Mason-Quensel sequence results from a progressive oxidation of Fe and Mn, and a concomitant Li-leaching of triphylite yielding ferrisicklerite and heterosite, successively; (ii) the metasomatic exchange of Na for Li produces alluaudite; in the present case, the formation of hagendorfite from triphylite 2 is considered to be earlier than the generation of alluaudite-Na occurring in the three associations; (iii) the hydration phase mainly transforms the parent Li(Fe,Mn)PO₄ phase into grey hureaulite, associated with barbosalite and tavorite; (iv) the formation of fluorapatite, not particularly widespread, replaces alluaudite-Na, as well as zwieselite s.l. The following crystallization sequence of the initially formed phosphate minerals is proposed: triphylite 1 triphylite 2 + sarcopside (associated with garnet) triphylite 3 + zwieselite s.l. The most prominent feature of this succession is the increase in the Mg and Zn contents in the composition of the phosphates, as well as the decrease in their Li contents. The variations of the Fe/Mn ratios in this sequence are discussed. The succession triphylite-zwieselite within weakly differentiated and Li-poor pegmatites is of general significance.     

Oligocene deposits of the Zara-Hafik region (Sivas,Central Turkey): evolution from storm-influenced shelf to evaporitic basin

New stratigraphical and micropalaeontological data, supplemented by detailed sedimentological and petrographical observations, have been obtained from an almost completely exposed Oligocene-Miocene succession near Celalli in the Zara-Hafik basin, which forms part of a long-lived zone of subsidence associated with the North Anatolian Fault system. Four laterally extensive lithostratigraphical units have been distinguished and ostracod microfaunas indicate that the lower two units are of Middle Oligocene age, while bivalve/brachiopod faunas from the third unit are also Oligocene. The status of the uppermost unit of redbeds remains equivocal, but microfaunas from the capping marls are of lowermost Miocene age.The basal brown sandstone unit was formed in a shallow marine environment dominated by southwards transport of sand by offshore-directed storm-surges, with associated east-west longshore movement also important. The discordantly succeeding limestone unit records a phase of carbonate bar migration across the basin while the third formation (in which medium-scale facies cyclicity is prominent) was formed in a southwards-prograding coastal plain complex, following a renewal of terrigenous supply to this region. The late Oligocene-Miocene redbed unit resulted from continued terrestrial progradation and is characterised by alluvial deposits formed by small, southwards-flowing streams of high sinuosity, ultimately succeeded by carbonate and evaporitic deposits marking the early Miocene marine transgression.Stratigraphical analysis of sandstone petrography reveals a gradual change in provenance through the Oligocene, from sources of »oceanic« character (rich in ophiolitic rocks) to those of »continental« nature (with silicic metamorphics and sedimentary cover-rocks prominent), and the compositional data thus accord with models suggesting closure of a small oceanic or arc-related basin in this region during the late Palaeogene.

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Zusammenfassung Aus einer nahezu vollständig aufgeschlossenen Schichtenfolge des Oligozän und Miozän im Gebiet von Celalli im Zara-Hafik-Becken/Türkei werden neue Daten zur Stratigraphie und Mikropaläontologie vorgestellt. Diese werden ergänzt durch sedimentologische und petrographische Beobachtungen. Das Becken ist Teil einer Zone mit lange anhaltender Subsidenz, die mit dem System des Nordanatolischen Lineaments in Verbindung steht. Es lassen sich vier lateral aushaltende lithostratigraphische Einheiten unterscheiden, von denen die beiden unteren mit Ostracoden-Mikrofaunen in das Mittel-Oligozän eingestuft werden. Nach Muschel- und Brachiopoden-Faunen ist die dritte Einheit ebenfalls oligozänen Alters. Das Alter der obersten Einheit von Rotsedimenten ist nicht genau bekannt, doch besitzen die Mikrofaunen der hangenden Mergel ein tiefstmiozänes Alter.Der basale braune Sandstein wurde in einem flachmarinem Milieu gebildet, das von einem südwärts gerichteten Sandtransport durch ablandige Sturmwellen beherrscht wird. Zusätzlich ist eine ost-west-gerichtete Küsten-Längsdrift von Bedeutung. Die diskordant darüber lagernde Kalkfolge wurd durch eine Phase von durch das Becken wandernden karbonatischen Bänken aufgebaut. Die dritte Einheit (in der eine Fazies-Zyklizität mittlerer Größe vorherrscht) baute sich in dem südwärts vorschreitenden Komplex einer Küstenebene auf, die einer neuerlichen terrigenen Schüttung in diesem Gebiet folgt. Die spätoligozän-miozäne Einheit von Rotsedimenten ist das Ergebnis weiter voranschreitender terrestrischer Sedimente. Sie besteht aus alluvialen Ablagerungen von kleinen nach Süden fließenden Flüssen mit hoher Sinuosität, gefolgt von karbonatischen und evaporitischen Bildungen, die die frühmiozäne Transgression anzeigen.Die stratigraphische Analyse der Sandstein-Petrographie offenbart einen allmählichen Wandel der Provenienz im Oligozän, der von »ozeanischem« Liefergebiet (reich an ophiolithischen Gesteinen) zu »kontinentalem« (mit vorherrschend kieseligen Metamorphiten und sedimentärer Bedeckung) überwechselt. Die Zusammensetzung stimmt mit Modellen überein, die die Schließung eines kleinen ozeanischen oder inselbogen-artigen Beckens während des späten Paläogens nahelegen.

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Résumé De nouvelles données stratigraphiques et micropaléontologiques, associées à des observations sédimentologiques et pétrographiques détaillées ont été recueillies dans une série oligocène-miocène exposée de manière presque complète près de Celalli dans le bassin de Zara-Hafik, lequel fait partie d'une zone de subsidence de longue durée associée au système de failles de l'Anatolie du Nord. Quatre unités lithostratigraphiques d'extension latérale notable ont été distinguées. Les deux unités inférieures sont datées de l'Oligocène moyen par une microfaune à Ostracodes, et la troisième de l'Oligocène par une faune à brachiopodes et autres bivalves; l'âge de l'unité supérieure reste incertain, mais les marnes terminales renferment une microfaune éo-miocène.L'unité inférieure, constituée de grès bruns, s'est formée dans un milieu marin peu profond dans lequel le sable était transporté à la fois vers le large (vers le Sud), par des vagues de tempête, et vers l'Ouest parallèlement au rivage. La deuxième unité, discordante et de nature calcaire, témoigne de la migration d'une barre carbonatée à travers le bassin. La troisième unité, caractérisée par une disposition cyclique des faciès à moyenne échelle, a été élaborée dans un complexe de plaine côtière progressant vers le Sud, comme suite à de nouveaux apports terrigènes. La quatrième unité (Oligocène tardif-Miocène), formée de couches rouges, résulte d'une sédimentation continentale continue et consiste en alluvions déposées par de petits cours d'eau très sinueux coulant vers le Sud; ces couches sont surmontées finalement de dépôts carbonates et évaporitiques marquant la transgression éo-miocène.L'analyse pétrographique du grès, opérée en fonction de la stratigraphie, révèle au cours de l'Oligocène un changement graduel de provenance, depuis un domaine nourricier de type »océanique« (riche en ophiolites) jusqu'à un domaine de type »continental« (à dominance de roches métamorphiques et sédimentaires siliceuses). Ces données sont en accord avec un modèle suggérant la fermeture d'un petit bassin océanique ou d'arc insulaire pendant le Paléogène tardif.

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