On the distinction of tectonic and nontectonic faulting in palaeoseismological research: a case study from the southern Marmara region of Turkey

International Journal of Earth Sciences - This study reports on spectacular deformation structures, including arrays of striated thrusts, discovered by excavation work in Holocene deposits in...     

Sedimentological and ichnological signatures of changes in wave,river and tidal influence along a Neogene tropical deltaic shoreline

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.     

Neogene basin development around Söke-Kuşadası (western Anatolia) and its bearing on tectonic development of the Aegean region

The AMS study has been performed on various types of the basement – Variscan granitic and surrounding – Mesozoic sedimentary rocks in the Velká Fatra Mountains, Tatric Superunit of the Central Western Carpathians. The Velká Fatra Mts. provides good opportunity for AMS study because of composite S-type and I-type granite character of pluton and clear relations to Mesozoic sedimentary rocks in the cover and nappe positions. The granitic massif consists of the three types of weakly magnetic peraluminous granites (350 – 340 Ma in age), ranging from two-mica granites to biotite granodiorites in composition and carrying accessory monazite and ilmenite; whereby they resemble common S-type and/or Ilmenite Series granite. This pre-existing granitic body was intruded by relatively young (304 Ma old) metaluminous to subaluminous, strongly magnetic (due to magnetite) tonalitic intrusion of the I-type and/or Magnetite Series granite. In all S-types investigated as well as in the I-type tonalite body, the magnetic fabrics are not uniform, but slightly variable within a body and differing from body to body. The magnetic fabrics in all granitic rocks can be classified as mostly magmatic in origin, only subordinately affected by ductile deformation. The Alpine overprint of the magnetic fabric of the Variscan granite frequent in the central areas of the Central Western Carpathians was only weak in the Velká Fatra Mts. and the magnetic fabrics of these granites thus mostly comprise the original Variscan magmatic fabrics. On the other hand, in the marginal parts of the Velká Fatra Mts. the magnetic fabrics in granites are locally conformable to the deformational magnetic fabrics in surrounding sedimentary rocks (Mesozoic in age) thus indicating at least local effects of the Alpine deformation. The magnetic fabrics in Mesozoic sedimentary rocks covering the crystalline basement are partially (Cover Formation) to entirely (Nappe Units) deformational in origin.     

Geochemistry and Petrogenesis of Intracontinental Basaltic Volcanism on the Northwest Arabian Plate,Gaziantep Basin,Southeast Anatolia,Turkey

Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.     

Various filtering algorithms used to eliminate outliers in velocity time series obtained by ADVs (acoustic Doppler velocimeter)

The correct measurement of velocities in rivers is important for the true determination of discharge, erosion, scouring, and sediment transport processes. With the goal of increased accuracy, the use of acoustic Doppler velocimeters (ADVs) is increasing in hydrological measurements in rivers, lakes, and laboratories. ADVs are extensively used in the USA. ADVs have advantages when compared with classical measurement devices; however, one must be careful while using an ADV because their sampling approach creates a large number of extreme values by sending signals into the flow, measuring the velocities of particles moving with the water and assuming that these particles move with same velocity as the water. To calculate unbiased statistical properties, outliers must be removed from the time series. This study explains the methods used to filter velocity time series collected with ADVs and investigates the effects of these filters on the statistical characteristics of the filtered time series.     

Back-analysis of a seismically induced highway embankment failure during the 1999 Düzce earthquake

An earthquake of magnitude 7.2 on the Richter scale occurred on 12 November 1999 in the Düzce-Bolu region of Turkey. The region was also hit approximately 3 months before during the devastating Kocaeli earthquake of 17 August 1999. Besides high casualties and damage to various engineering structures and buildings, slope and embankment failures on the highway and the country roads occurred. In this study, the authors are concerned with the back-analysis of an embankment failure that occurred on the four lanes E-5 highway connecting Ankara to Gstanbul at Bakacak in the Bolu Province during the 1999 Düzce earthquake. Both pseudo-dynamic and dynamic limiting equilibrium methods are used to back analyse the conditions for the initiation of failure and also displacement responses of the embankment during the earthquake shaking. After having given a brief summary of the investigations on the post-failure state, the geology and geotechnical characteristics of the site, and the dynamic limiting equilibrium method developed and used for analyses are described. The results of the back-analysis based on a pseudo-dynamic approach, revealed that the maximum ground acceleration to initiate the failure of the embankment was probably about 0.125 g. On the other hand, the application of a method for computing the displacement and velocity responses of the failed embankment showed that the failure was possible when the embankment was subjected to ground accelerations similar to that recorded at the Düzce station. In addition, the computations also revealed that the time history of accelerations could be very important for the failure of slopes and embankments.     

Geophysical and geochemical evidence of Proterozoic collision in the western marginal zone of the Baltic Shield

New continental crust was formed in the Svecofennian domain of the Baltic Shield c. 1.9 Ga ago. Approximately 0.1–0.15 Ga later, new crust accreted to the SW part of the Shield. In this paper an attempt is made, on the basis of gravity measurements and lithogeochemistry, to describe the tectonic processes responsible for the continental growth c. 1.75–1.8 Ga ago. The Transscandinavian Granite Porphyry Belt (TGPB) separates the Svecofennian domain from the polymetamorphic terrain of the SW Swedish gneiss region. Red orthogneisses occurring immediately west of the TGPB are the deformed equivalents of the TGPB type granitoids, while grey orthogneisses, displaying a tonalitic-granodioritic trend and situated further west, were generated in a »volcanic arc« environment. The TGPB granitoids and the red SW Swedish gneisses represent a transition from this volcanic arc type rock to contemporaneous »within-plate« type granites intruded in the Svecofennian crust. The volcanic arc was forced against the Svecofennian crust in which large tensional fracture zones ensued with strike directions normal to the collision front. In such tensional environments the »withinplate« type granites were generated. In the collision zone the crust was down-warped, and huge amounts of granitic melts were generated at the base of the crust. This TGPB Magma rose upwards utilizing the fracture zone between the arc rocks, generated slightly earlier, and the Svecofennian crust. A relatively thin upper part of the TGPB that spread laterally westwards became strongly deformed during the collision (i.e. the red SW Swedish gneisses), while the major deep-reaching TGPB root zone that was not completely solidified yet, acted as a buffer against the foliation front.

---

Zusammenfassung Vor 1,9 Milliarden Jahren kam es zur Neubildung von kontinentaler Kruste im svecofennischen Bereich des Baltischen Schildes. Ungefähr 100–150 Millionen Jahre später wurde im Südwesten des Schildes neue Kruste hinzugefügt. In diesem Artikel wird auf der Basis von Gravimetriemessungen und Lithogeochemie der Versuch unternommen die tektomschen Vorgänge, die zu diesem 1,75–1,8 Milliarden Jahre alten Krustenzuwachs führten, zu beschreiben.Der Transskandinavische-Granit-Porphyr-Gürtel (Transscandinavian-Granite-Porphyry-Belt/TGPB) trennt das Svecofennium von der polymetamorphen, im Südwesten Schwedens gelegenen Gneis-Region. Ein direkt westlich des TGPB gelegenes Vorkommen roter Orthogneise entspricht den deformierten TGPB Granitoiden. Graue Orthogneise, die weiter im Westen aufgeschlossen sind, zeigen eine mehr tonalitische bis granodioritische Zusammensetzung und werden auf einen vulkanischen Inselbogen zurückgeführt. Die TGPB Granitoide und die roten südwest-schwedischen Gneise stellen einen Übergang von den Inselbogen-Vulkaniten zu den zeitgleichen »Intra-Platten-Graniten« der svecofennischen Kruste dar. Der Inselbogen kollidierte mit der svecofennischen Kruste, es entstanden großräumige Bruchzonen mit Streichrichtungen senkrecht zur Kollisionsebene. Während des Zustands der hohen Druckspannung des Gebietes intrudierten die »Intra-Platten-Granite«. Innerhalb des Kollisionsbereiches wurde die Kruste nach unten gebogen, und so entstanden an der Basis der Kruste große Mengen granitischen Magmas. Dieses TGPB Magma stieg entlang der Störungszone innerhalb der Inselbogengesteine, die nur wenig älter sind, und der svecofennischen Kruste, auf. Nur ein, von relativ geringer Mächtigkeit, weiter westlich gelegener Teil des TGPB, die roten südwest-schwedischen Gneise, wurde während der Kollision intensiv deformiert. Dagegen war der Hauptanteil der tiefreichenden TGPB Wurzelzone noch nicht vollständig erstarrt und wirkte deshalb wie eine Pufferzone gegen die Schieferungsfront.

---

Résumé De la croûte continentale nouvelle s'est formée il y a 1,9 Ga dans le domaine des Svecofennides (Bouclier baltique). Environ 100 à 150 Ma plus tard, de la croûte nouvelle s'est accrétionnée à la bordure sud-ouest du bouclier. Cette note basée sur des mesures de gravité et la lithogéochimie, présente un essai d'analyse des processus tectoniques responsables de cette croissance continentale d'âge 1,75 à 1,8 Ga. Le «Transcandinavian Granite Porphygry Belt» (TGPB) sépare le domaine svécofennien des gneiss polymétamorphiques du sud-ouest de la Suède. Immédiatement à l'ouest de TGPB affleurent des orthogneiss rouges qui représentent l'équivalent déformé de granitoïdes du TGPB, tandis que des orthogneiss gris de tendance tonalitique-granodioritique, situés plus à l'ouest, ont été engendrées dans un environnement d'arc volcanique. Les granitoïdes du TGPB et les gneiss rouges du sud-ouest de la Suède représentent une transition entre ces produits d'arc volcanique et les granites intra-plaque de même âge intrudés dans la croûte svécofennienne. L'arc volcanique a été accrétionné à la croûte svécofennienne avec production dans celleci de grandes fractures d'extension perpendiculaires au front de collision. C'est dans ce domaine en extension que les granites intra-plaque se sont mis en place. Dans la zone de collision, la croûte s'est incurvée vers le bas et de grandes quantités de liquides granitiques ont été engendrées à la base de la croûte. Ces magmas TGPB sont montés à la faveur de la zone fracturée entre les roches de l'arc engendrée un peu plus tôt, et la croûte svécofennienne. Seule une fraction supérieure relativement mince du TGPB, développée vers l'ouest, a subi une déformation importante au cours de la collision, pour former les gneiss rouges du sud-ouest de la Suède; par contre, la partie principale de la racine profonde du TGPB, qui n'était pas encore entièrement solidifiée, a joné le role tampon en avant du front de foliation.

---

, 1,9 100–150 - . - (Transscandinavian Granite-Porphyry-Belt - TGPB) , - . TGPB , , , - , . TGPB - . , , . («within plate» type granites) , . . TGPB , , . TGPB, , - , . TGPB, , .

     

Main sequence for rotating stars of intermediate mass

We have investigated the evolutionary behaviour of intermediate mass (2, 3, 4, 5, and 7M ) Population I stars, assuming two different rates of rotation at the threshold of stability.In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age Main Sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars.In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age Main Sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the Main Sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age Main-Sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age Main Sequence are in good agreement with observed values.