Gravity anomalies and crustal shortening in the eastern Mediterranean

Crustal shortening of the ocean floor in the eastern Mediterranean is recognized by a marked thickening of the sedimentary layer seaward of the Hellenic and Calabrian island arcs. Steep gradients and large negative free-air anomalies in the gravity field along with a highly uniform, low regional heat flow are manifestations of the thickened crust. Bodies of recently deformed sediment in and seaward of the Hellenic Trough reveal the style, polarity, and dynamics of the thickening mechanism.

A linear buried anticlinal structure, inferred from analysis of surface ship gravity profiles, may mark the site of contemporary intrabasinal underthrusting. The distribution of earthquakes beneath the Mediterranean Ridge supports the interpretation that the Anaximander, Ptolomy, and Strabo Mountains are features comparable to large basement nappes. Cyprus is one such structure, offset to the south, where the oceanic crust and part of the upper mantle have been involved in the décollement.     

La Géologie et la Tectonique de la Plateforme Amazonienne

Résumé Le travail met au point pour la première fois dans la Géologie brésilienne, une synthèse tectonique et géologique de la Plateforme amazonienne. Trois phases géologiques et tectoniques principales ont été considérées: le socle cristallin (d'âge précambrien); la couverture sédimentaire plissée ou phase géologique intermédiaire (developpée du Précambrien supérieur au Silurien) et la converture sédimentaire non-plissée (du Dévoniem inférieur au Tertiaire).Dans le socle cristallin, deux noyaux cratoniques ont été individualisés: le noyau cratonique Brésil-Central et le noyau cratonique guyannais.Dans le socle cristallin les zones tectoniques ou phases orogéniques suivantes ont été décrites: pour le noyau cratonique Brésil-Central: le Rondonide, et le Sud-Amazonide (ou phase orogénique Curua-Xingu); pour le noyau cratonique guyannais, du coté brésilien: l'Amapaïde, le Paruïde et le Negroïde (ou phase orogénique Rio Negro).La couverture sédimentaire plissée a été divisée en trois régions, chacune avec ses propres caractéristiques: Cachimbo-Cubencranquém (sur le noyau cratonique Brésil-Central), Uatumã-Trombetas (dans la partie moyenne et basse de la depression amazonique — la plus jeune) et Roraima (sur le noyau cratonique guyannais — la plus ancienne).La couverture sédimentaire non-plissée a été divisée dans deux sous-phases: péricratonique et intracratonique. Le Bassin amazonique a été divisé à son tour en 5 (cinq) petits bassins internes dénommés: Acre, Haut-Amazone, Moyen Amazone, Bas-Amazone et Marajó.

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In this article a synthesis of the geologic and tectonic history of the Amazonian Platform was made for the first time. Three principal geologic and tectonic phases were considered: the crystalline basement (of Precambrian age); the folded sedimentary cover (of late Precambrian to Silurian age), and the non-folded sedimentary cover (of Devonian to Tertiary age).In the crystalline basement, there are two cratonic nuclei separated by the Amazonian Depression: the Central-Brazil cratonic nucleus and the Guyannian cratonic nucleus.Also, in this crystalline basement the following tectonic zones or orogenic phases were described and separated: Rondonides and South-Amazonides in the cratonic nucleus of Central-Brazil; Amapaides, Paruides and Negroïdes, in the Guyannian cratonic nucleus.The folded sedimentary cover was characterized by different regions: Cachimbo-Cubencranquém (on the Central-Brazil nucleus); Uatumã-Trombetas (in the middle and low Amazonic Depression — the younger region considered) and Roraima, (on the Guyannian cratonic nucleus the older region).The non-folded sedimentary cover was divided into two (2) principal subphases: pericratonic and intracratonic. The Amazonian Basin was studied separately, and five (5) small tectonic basins were established: Acre, High-Amazonas, Middle Amazonas Low-Amazonas and Marajó basins.

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Zusammenfassung In dieser Arbeit wird zum ersten Mal eine Synthese der geologischen und tektonischen Geschichte der Amazonas-Plattform vorgelegt. Drei geologische und tektonische Hauptphasen werden untersucht: das kristalline Basement (Präkambrium), die gefaltete Sedimentdecke (jüngeres Präkambrium bis Silur) und die ungefaltete Sedimentdecke (Devon bis Tertiär).Im Basement werden zwei kratonische Kerne unterschieden, zwischen denen die Amazonas-Depression liegt: der zentralbrasilianische Kern und der guyannische Kern.Weiterhin werden im Basement die folgenden tektonischen Zonen oder orogenen Phasen beschrieben und unterschieden: Rondonides und Süd-Amazonides (im zentralbrasilianischen Kern); Amapaides, Paruides und Negroides (im guyannischen Kern).Die gefaltete Sedimentdecke ist in folgenden Gebieten anzutreffen: Cachimbo-Cubencranquém (auf dem zentralbrasilianischen Kratonkern); Uatumã-Trombetas (in der mittleren und unteren Amazonas-Depression: die jüngeren Schichten) und Roraima (auf dem guyannischen Kratonkern: die älteren Schichten).Die ungefaltete Sedimentdecke ist in zwei Phasen unterteilt: eine perikratonische und eine intrakratonische. Das Amazonasbecken wurde für sich untersucht; es ist in fünf kleinere tektonische Becken unterteilt: Acre-, Hochamazonas-, Mittelamazonas-, Unteramazonas- und Marajó-Becken.

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Resumo O presente artigo mostra pela primeira vez na geologia brasileira, uma síntese da tectônica e da geologia, do que se resolveu denominar Plataforma Amazônica. Três fases Geológicas e Tectônicas principais foram consideradas: a do Embasamento Cristalino (do Pré-Cambriano); a da cobertura Sedimentar Dobrada — ou Fase Geológica Intermediária — (do Pré-Cambriano Superior ao Siluriano) e a da Cobertura Sedimentar Não Dobrada (do Devoniano ao Terciário).No Embasamento Cristalino, dois Núcleos cratonicos foram individualizados, separados que estão, pela grande Depressão, Amazônica, de direção geral ENEOSO: o Núcleo cratónico Brasil-Central e o Núcleo cratônico Guianês. Neste Embasamento Cristalino as seguintes Zonas Tectônicas ou Fases orogênicas foram descritas e saparadas. Para o Núcleo Brasil-Central: o Rondonides e o Sul-Amazonides (ou Fase orogênica Curua-Xingu); para o Núcleo Guianês: o Amapaides, o Paruides e o Negroïdes (ou Fase orogênica Rio Negro).Quanto à cobertura Sedimentar Dobrada, às seguintes regiões foram caracterizadas: Cachimbo-Cubencranquém (sôbre o Núcleo Brasil-Central); Uatumã-Trombetas (no média e baixa Depressão Amazônica), a mais jovem, e o Roraima (sôbre o Núcleo Guianês), a mais antiga.A cobertura Sedimentar Não-Dobrada foi dividida em 2 (duas) Sub-Fases principais: a Pericratônica e a Intracratônica. A Bacia Amazônica, estudada também em separado, foi dividida em 5 (cinco) pequenas bacias internas: a do Acre, a do Alto-Amazônas a do Médio-Amazônas, a do Baixo-Amazônas e a. do Marajó.

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( , , ). , , - . - - , — , . Cachimbo-Cubencranquem, Uatuma-Trombetas Roraima . : perikratonische intrakratonische. : Acre, , , Marajó.

     

基于稳态碎岩方式的PDC钻头设计分析研究

自从20世纪80年代PDC复合片研发成功以来,PDC钻头由于其钻进性能强和耐磨性能好,在世界许多国家的石油钻井和地质勘探中得到了广泛应用,取得了很好的效果。但是,如何进一步提高其在钻探工程中的技术经济指标是一个很迫切的问题。俄罗斯博士Скоромных В. В.教授等对此进行多年研究,提出了稳态破碎岩石方式的思想,即在轴载和扭矩切力形成的合力R与切削面成垂直角度条件下,切入深度h不变时形成的一种碎岩方式。并在此基础上提出了一些设计PDC钻头方面的建议。     

Estimate of the evolution of the galactic gas component for the z interval from 0 to 3.6

The absorbers giving rise to features in the absorption spectra of quasars can be used to study the evolution of the dimensions of the galactic gas component and of gas clouds over substantial intervals of z. The evolution of the linear dimensions L of these objects is estimated for the z range from ～0 to 3.6. A total of 265 quasars with redshifts z from 0.288 to 3.803 and 809 absorbers with z from ～0 to 3.5575 were used for the analysis, which yields the relation L=L ₀(1+z)^1.73±0.07.     

Numerical and analytical observations on long and infinite slopes

Interest in the mechanics of landslides has led to renewed evaluation of the infinite slope equations, and the need for a more general framework for estimating the factor of safety of long and infinite slopes involving non‐homogeneous soil profiles. The paper describes finite element methods that demonstrate the potential for predicting failure in long slope profiles where the critical mechanism is not necessarily at the base of the soil layer. The influence of slope angle is also examined in long slopes, leading to some counter‐intuitive conclusions about the impact of slope steepness on the factor of safety. Copyright © 2010 John Wiley & Sons, Ltd.     

A Tsunami Generated by a Possible Submarine Slide: Evidence for Slope Failure Triggered by the North Anatolian Fault Movement

A tsunamigenic sediment layer has been discovered in fluvio-alluvial sequences on the northern coast of the Marmara Sea, northwestern Turkey. The layer consists of unsorted silty coarse sand including terrestrial molluscs and charcoal fragments. The AMS radiometric ages of the shells have been estimated at around BC 400, AD 300, AD 400, and AD 1000. We propose that a tsunami occurred in the Marmara Sea in the middle of 11th century and invaded the fluvial plains. The older fossils were derived from the underlying horizons, and it is probable that buoyant materials such as terrestrial molluscs and charcoals were isolated from liquefied sediments during submarine sliding. Slope failure of coastal blocks triggered by fault movement generated tsunamis, which might have transported floating materials to the backshore.     

Simplified approach for design of raft foundations against fault rupture. Part Ⅰ: free-field

Over the past few decades, earthquake engineering research mainly focused on the effects of strong seismicshaking. After the 1999 earthquakes in Turkey and Taiwan, and thanks to numerous cases where fault rupture causedsubstantial damage to structures, the importance of faulting-induced deformation has re-emerged. This paper, along withits companion (Part Ⅱ), exploits parametric results of finite element analyses and centrifuge model testing in developing afour-step semi-analytical approach for analysis of dip-slip (normal and thrust) fault rupture propagation through sand, itsemergence on the ground surface, and its interaction with raft foundations. The present paper (Part Ⅰ) focuses on the effectsof faulting in the absence of a structure (i.e., in the free-field). The semi-analytical approach comprises two-steps: the firstdeals with the rupture path and the estimation of the location of fault outcropping, and the second with the tectonically-induced displacement profile at the ground surface. In both cases, simple mechanical analogues are used to derive simplifiedsemi-analytical expressions. Centrifuge model test data, in combination with parametric results from nonlinear finite elementanalyses, are utilized for model calibration. The derived semi-analytical expressions are shown to compare reasonably wellwith more rigorous experimental and theoretical data, thus providing a useful tool for a first estimation of near-fault seismichazard.     

Embryo dune development drivers: beach morphology,growing season precipitation,and storms

For development of embryo dunes on the highly dynamic land–sea boundary, summer growth and the absence of winter erosion are essential. Other than that, however, we know little about the specific conditions that favour embryo dune development. This study explores the boundary conditions for early dune development to enable better predictions of natural dune expansion. Using a 30 year time series of aerial photographs of 33 sites along the Dutch coast, we assessed the influence of beach morphology (beach width and tidal range), meteorological conditions (storm characteristics, wind speed, growing season precipitation, and temperature), and sand nourishment on early dune development. We examined the presence and area of embryo dunes in relation to beach width and tidal range, and compared changes in embryo dune area to meteorological conditions and whether sand nourishment had been applied. We found that the presence and area of embryo dunes increased with increasing beach width. Over time, embryo dune area was negatively correlated with storm intensity and frequency. Embryo dune area was positively correlated with precipitation in the growing season and sand nourishment. Embryo dune area increased in periods of low storm frequency and in wet summers, and decreased in periods of high storm frequency or intensity. We conclude that beach morphology is highly influential in determining the potential for new dune development, and wide beaches enable development of larger embryo dune fields. Sand nourishment stimulates dune development by increasing beach width. Finally, weather conditions and non‐interrupted sequences of years without high‐intensity storms determine whether progressive dune development will take place. Copyright © 2017 John Wiley & Sons, Ltd.