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Jet-efflux deposits of a subaqueous ice-contact fan, glacial Lake Rinteln, northwestern Germany
No full textThe coarse-grained, ice-contact, Porta Subaqueous Fan/Delta Complex was deposited in glacial Lake Rinteln at the margin of the Saalian ice sheet that advanced south of the Weser Chains, NW Germany. The ice-proximal depositional system was up to 15 km long and 10 km wide. The present study deals with ice-proximal subaqueous fan deposits, which are interpreted as products of a subcritical plane-wall outflow jet that periodically passed into a supercritical jet with hydraulic jump. The proximal facies assemblage consists of the coarse, clast-supported gravelly deposits of a hyperconcentrated (high-density) effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment. The intermediate facies assemblage, attributed to the outflow jet proximal zone of flow transition, is dominated by normally graded and cross-stratified gravels with scour structures at their bases; these gravels were deposited by a high-density effluent capable of forming mouthbar-like features. These deposits pass downcurrent into an assemblage of planar parallel-stratified and planar and trough cross-stratified sands and pebbly sands (partially interpreted as antidunes), with abundant scour structures and intercalated layers of fine sand/silt and silty mud, attributed to the jet distal zone of flow transition. The distal facies assemblage consists of trough cross-stratified sands and pebbly sands, and is attributed to the outflow jet proximal zone of established flow. The sedimentary succession as a whole has wedge-shape geometry, with a gentle fan-shaped inclination of the bedding from the southeast to the southwest. Repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow, whereas the overall upward fining of the succession indicates a net decline of meltwater discharges. (c) 2006 Elsevier B.V All rights reserved
Recent intraplate earthquakes in Northwest Germany : glacial isostatic adjustment and/or a consequence of hydrocarbon production?
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Tiefwasser-Sedimentationsprozesse und -produkte in den Forearc-Becken des mittelamerikanischen Inselbogensystems eine sequenzstratigraphische Analyse
No full textHistoria del Antearco Mesoamericano Austral y sus implicaciones para la evolución de la placa del Caribe
No full textThe cornplex, pre-Campanian history of northem Costa Rica results from allochthonous slabs, which are the remains of an old accretionary prism, which can be traced back to the subduction of proto-Caribbean crust during late Jurassic to Cretaceous times before the southerly Chortis block. The deactivation of this subduction system place in Cenomanian times. It was only when the subduction process taking place there was completed that an inter-American subduction zone was formed, from which the Central American island arc systems later emerged. A left lateral strike-slip-system later developed in the area of the former northern Caribbean subduction zone, represented today by the Hess Escarpment. Thrusts in a southerly direction took place along this transform margin during the Campanian. The remains of the former subduction complex were thus transported southwards, and thrusted to the primitive island arc rocks of northern Costa Rica. Owing to this structural evolution of the Central American are the origin of the thickened Caribbean crust ("Horizon B”) cannot be explained by the passive insertion of an pacific oceanic plateau. The Caribbean sill event is therefore interpreted to be a parautochthonous fomation in the western Caribbean and eastern part of the Phoenix plate. The basin systems of Central America demonstrate a similar, if not identical development, starting at the late Campanian. Five 2nd order depositional sequences can be identified within the foreaar basins, which can be correlated with the cycles ZC-4, TA l, TA 2, TA 3, and TA 4 (HAQ et al., 1988). Although thick submarine systems have been documented in the forearc basins of south-western Nicaragua and northem Costa Rica as far as the Eocene, the south-lying island are segments (southern Costa Rica, Panama) are mainly charcterized by hemipelagic sedimentation systems which, as a result of basaltic lava, breccias and chaotic mass flow deposits, are indicative of a fault-controlled enviroment in the area of a transform fault. This transform fault may have been the link to island arc segments lying further south which collided with the Central Cordillera of South America during late Cretaceous to early Tertiary times. The northely and southerly island are segments of Costa Rica and Panama only demonstrate a similar sedimentary development from the middle Eoceno, thereby signifying the formation of a continuous inter-American subduction zone. The internal architecture of the depositional sequences is mainly charcterized by the fomation of repetitive lowstand systems tracts. Either sandrich tabular lobe systems (Type I, cf. MUTTI & NORMARK, 1987) or channellobe systems of smaller dimensions (Type II, cf., MUTTI & NORMARK, 1987) developed, depending on the supply of sediment and tectonics. These in tum were overlain by thick channel-overbank complexes or prograding wedges (Type III, cf. MUTTI & NORMARK, 1987). The plant material and resediment neritic fossil content is generally high in lowstand systems tract deposits. The composition of these varies in accordance with the position of the relative se level. The depositional systems of the transgressive and highstand systems tracts can only be segregated in areas of low sedimentation rates. In these areas, il typically consists of fine-grained calcareous deposits. The fast rise and highstand of the sea level is therefore documented through the progressive increase in the carbonate content.La compleja historia precampaniana del norte de Costa Rica, resulta del emplazamiento de secciones de corteza alóctonas que representan los restos de una antigua cuña de acreción. La misma habría sido generada por la subducción de corteza frente al margen sur del bloque Chortís, durante el Jurásico Superior y el Cretácico Inferior. La desactivación de este sistema de subducción del Caribe Norte ocurrió en el Cenomaniano. Posteriormente al terminar éste, se estableció una nueva zona de subducción, la interamericana, a partir de la cual se originó el sistema de arco de islas de América Central. Subsecuenœmenle se creó en la antigua zona de subducción norcaribeña un sistema de falla transformante sinestraln el cual está actualmente representado por el Escarpe de Hess. En el Campaniano fueron originados a lo largo de este margen transformable, sobrecorrimientos vergentes hacia el sur. Las restos del antiguo complejo de subducción así expelidos sobrecorrieron al conjunto rocoso del amo insular primitivo. El “sill event" del Caribe y el consiguiente aumento de espesor conical no pueden ser explicados mediante la penetración pasiva de un plateau de origen pacífico, sino que ha de ser interpretado como una formación parautóctona en el área Occidental del Caribe y oriental de la placa de Phoenix. A partir del Campaniano Superior los sistemas de cuencas de América Central muestran un desarollo comparable aunque no idéntico. En las cuencas de antearco se pueden reconocer 5 secuencias deposicionales de segundo orden, las cuales pueden ser correlacionadas con los ciclos ZC-4, TA l, TA 2, TA 3 y TA 4 de HAQ et al. (1988). Mientras en las cuencas de antearco del suroeste de Nicaragua y norte de Costa Rica está documentada la sedimentación de espesos sistemas de depósitos de abanicos submarinos aún hasta el Eoeno, en los segmentos sur del arco de isla (Costa Rica meridional y Panamá) prevalece un sistema de sedimentación hemipelágico. La intercalación dentro de la misma de lavas basálticas brechas y depósitos de flujos de masas exóticos, evidencian un medio deposicional limitado por fallas, dentro del contexto de un sistema de fallas transformantes. Este sistema transformante probablemente estableció el enlace con los segmentos de arco insular situados más al sur, los cuales colisionaron en el transcurso del Cretácico Superior y del Terciario Inferior con la Cordillera Central de Sudamérica. Es primeramente a partir del Eoceno Medio que los segmentos norte y sur del arco de isla de Costa Rica y Panamá muestran un desarollo común indicando así el carácter continuo de la zona de subducción interamericana. La constitucíon interna de las secuencias deposicionales se caracteriza fundamentalmente por la superposición de cortejos sedimentarios de nivel bajo (“Lowstand systems tracts"). En función del aporte de sedimento y de la tectónica se pueden desarrollar sistemas de lóbulos tabulares arenosos (Tlpo I, cf. MUTT'I & NORMARK, 1987) o sistemas de lóbulos y canales (Tipo II, cf.. MUTTI & NORMARK, 1987), los cuales son sobreyacidos por espesos complejos de canales y de depósitos de desbordamiento(Tipo III, cf. MUTTI & NORMARK, 1987). En general, los depósitos de los cortejos sedimentarios de nivel bajo presentan altlos contenidos de material vegetal y fósiles neríticos resedimentados, cuya composición varía dependiendo de la posición del nivel del mar. Los sistemas deposicionales delos cortejos sedímentarios de nivel alto ("Highstand systems tracts") y transgresivos ("Transgressiv systems tract") sólo pudieren ser clasificados en ámbitos de escasa sedimentación, donde típicamente consisten en sedimentos carbonatados de grano. El rápido ascenso y estado alto del nivel del mar queda documentado en este caso por un progresivo incremento del contenido de carbonato de los sedimentos
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Response of deep-water fore-arc systems to sea-level changes, tectonic activity and volcaniclastic input in Central America
Get PDFThe incipient island-arc system of southern Central America (Cretaceous - early Oligocene) is characterized by thick turbidite systems, which mainly filled inner fore-arc troughs. Outcrop data show four second-order depositional sequences in the deep-water sediments. The formation of these depositional sequences is strongly related to the morphotectonic evolution of the island-arc system. Each depositional sequence reflects the complex interaction between global sea-level fluctuations, sediment supply and tectonic activity. Strong marginal uplift and high volcaniclastic sediment supply during early to late Paleocene and late Eocene times caused the formation of coarse-grained channel-lobe systems. During late Paleocene and mid-Eocene times, fine-grained, thin-bedded turbidite systems were deposited, owing to regional subsidence and a decrease in volcanic supply. Uplift and subsidence of sediment-source areas acted as major controls on deposition of basinal cycles
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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