1,721,034 research outputs found
40Ar/39Ar detrital thermochronology on Eocene-Oligocene sediments of the Alps-Apennines junction area provides insights on the early stages of the Alpine orogenesis.
No full textThe early stages of the Alpine collision: An image derived from the upper Eocene-lower Oligocene record in the Alps-Apennines junction area
No full textThe upper Eocene-lower Oligocene sediments deposited in the eastern part of the Tertiary Piedmont Basin in northern Italy provide a complete record of the unroofing of the Alpine orogenic prism during the early stages of exhumation in the Ligurian sector. From late Priabonian till late Rupelian time, the sediments in the study area were derived from two different sources, one characterised by white micas with Si7 pfu and Eocene-Oligocene 40 Ar/ 39 Ar ages (32-50 Ma). The first source is considered to be indicative of low-pressure metamorphic rocks that covered the HP rocks of the Ligurian Alps, and were completely eroded by Chattian time. From this time on, the study area started to record the first input from western Alpine sources characterised by a larger span of ages with a more frequent Eoalpine signal. Thus, sediments deposited in the eastern part of the Tertiary Piedmont Basin contain the only available evidence of rocks belonging to high crustal levels in the Alpine orogenic prism that were not affected by the Alpine overprint. These data also provide time constraints to the poorly dated first conglomerates deposited in this area. 40 Ar/ 39 Ar geochronology reveals a minimum age of 33±1.4 Ma for the Pianfolco Conglomerates in the type locality, and of 31.4±3.5 Ma for the Borbera Conglomerates
Faulting and erosion in the Argentine Precordillera during changes in subduction regime: Reconciling bedrock cooling and detrital records
Full text linkThe Argentine Precordillera is an archetypal retroarc fold-and-thrust belt that records tectonics associated with changing subduction regimes. The interactions between exhumation and faulting in the Precordillera were investigated using apatite and zircon (U–Th–Sm)/He and apatite fission track thermochronometry from the Precordillera and adjacent geologic domains. Inverse modeling of thermal histories constrains eastward in-sequence rock cooling associated with deformation and erosion from 18 to 2 Ma across the Central Precordillera tracking thrusting during this time. The youngest AHe ages (5–2 Ma) and highest erosion rates are located in the eastern and western extremities of the Precordillera and indicate that recent denudation is concentrated at its structural boundaries. Moreover, synchronous rapid Pliocene cooling of the Frontal Cordillera, Eastern Precordillera, and Sierra del Valle Fértil was coeval with initiation of basement-involved faulting in the foreland. Detrital zircon U–Pb geochronology from the ca. 16–8.1 Ma Bermejo foreland basin strata suggests fluvial connectivity westward beyond the Frontal Cordillera to the Main Cordillera and Coast Range followed by an important shift in sediment provenance at ca. 10 Ma. At this time, we suggest that a substantial decrease in Permo-Triassic igneous sources in the Frontal Cordillera and concurrent increase in recycled zircons signatures of Paleozoic strata are best explained by uplift and erosion of the Precordillera during widening of the thrust-belt. Bedrock thermochronology and modeling indicate a 2–6 Myr lag time between faulting-related cooling in the hinterland and the detrital record of deformation in the foreland basin, suggesting that for tectonically active semi-arid settings, bedrock cooling may be more sensitive to onset of faulting. We suggest that high erosion rates in the Frontal Cordillera and Eastern Precordillera are associated with increased interplate coupling during shallowing of the subducting Nazca plate that may concentrate stress along weak structural boundaries of the Precordillera.Fil: Fosdick, Julie. Indiana University; Estados UnidosFil: Carrapa, Barbara. University of Arizona; Estados UnidosFil: Ortiz, Gustavo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentin
Recognizing drainage reorganization in the stratigraphic record of the Neogene foreland basin of the Central Andes
No full textChanges in drainage basin reorganization as preserved in the stratigraphic record have direct implications for the composition, organization, and scaling relationships of sedimentary systems. However, isolating the stratigraphic signature of drainage basin reorganization in response to tectonic and/or climatic drivers can be challenging. In the Neogene foreland basin of the southern Central Andes between 28°–31°S, the tectonically-controlled reorganization of basin catchment area has been cited as an important control on the basin stratigraphy. To resolve the signature of drainage basin reorganization in the Central Andean foreland, we conducted a basin-scale study integrating detailed sedimentology from four measured sections with multi-method provenance analysis to reconstruct foreland sediment routing pathways between 28°–31°S. Our regional synthesis suggests that the foreland basin has been connected by an axial sediment routing system since the early Miocene. Statistical analysis and graphical comparison using multidimensional scaling of new and published detrital zircon data from 45 samples resolves tectonically controlled changes in the catchment area in the late Miocene, including an eastward shift of the Andean drainage divide. This study provides the first evidence for expansion of the catchment area east of the basin draining the emerging basement-cored highlands of the Sierras Pampeanas. This study demonstrates that, when combined, provenance and detailed sedimentologic data sets provide a powerful tool to recognize and interpret drainage basin reorganization in the stratigraphic record and thus reconstruct the tectono-climatic and paleogeographic evolution of sedimentary systems.Fil: Stevens Goddard, Andrea. Indiana University; Estados Unidos. Rowan University; Estados UnidosFil: Carrapa, Barbara. University of Arizona; Estados UnidosFil: Aciar, Rafael Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Recommended from our members
U-Pb Geochronology Of Igneous Rocks In Southeastern Arizona To Constrain A Minimum Age Of Deposition For The Fort Crittenden Formation With Implications For Laramide Tectonics
No full textThe Fort Crittenden Formation comprises a ~2.5 km thick sequence of fluvial-alluvial upper-Cretaceous sedimentary units of interest due to rich fossil record, and implications for Laramide tectonics in southeastern Arizona. Dating of the Fort Crittenden Formation is important for understanding geological evolution of Arizona and western North America. Previous studies (Dickinson and Hayes, 1986) provided an age of ca. 75 Ma based on K-Ar geochronology for the age of deposition for the Fort Crittenden Formation. The Salero Formation, which is stratigraphically on top of the Fort Crittenden Formation was dated to ca. 74 Ma (Inman, 1982) using K-Ar geochronology. Based on paleontological content, the Fort Crittenden Formation has been interpreted to be Campanian-Maastrichtian in age (84-67 Ma). This research aims at more precisely constraining the depositional age of this formation using zircon Uranium-Lead geochronology (LA-ICPMS) from four samples (Figure 1): a hypabyssal intrusion within the Fort Crittenden Formation, an andesite unit of the Salero Formation overlying the Fort Crittenden Formation near Mount Fagan, a dacite unit of the Salero Formation above the andesite unit, and a rhyolite unit of the Salero Formation. New zircon U-Pb data ages from the intrusion (75.8 Ma), dacite (75.4 Ma), and rhyolite (73.4 Ma) reveal an abundance of late-Cretaceous ages for these samples whereas U-Pb ages of the andesite sample reveal no late-Cretaceous ages. Our results indicate the top of the Fort Crittenden Formation is 75 Ma (older than Maastrichtian), and the base is older than 75 Ma. This has implications for the timing and mechanism of Laramide tectonics and magmatism in southeastern Arizona. Deposition of the upper Fort Crittenden Formation marks changes in volcanism from andesitic-dacitic (75.4 Ma) to rhyolitic (73.4 Ma) over 2 million years, which may reflect changes in subduction dynamics
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
