1,720,954 research outputs found
Tectonic controls on sequence stacking pattern and along-strike architecture in the Pleistocene Mejillones Formation, northern Chile: implications for sequence stratigraphic models.
No full textIn the Mejillones Formation, a shallow-marine Pleistocene succession of northern Chile, the cyclic stratigraphic record is the result of the complex interaction of regional uplift, glacio-eustasy, local tectonics, sediment supply, and sedimentary processes. Stratal geometries, characteristics of sedimentary facies, and nature of sequence-bounding unconformities have been investigated to evaluate the influence of: (i) intrabasinal, short-term normal faulting on both along-strike variations in sequence architecture and genetic complexity of key stratal surfaces; and (ii) long-term regional uplift on sequence stacking pattern. The stratigraphic succession, dissected by small-displacement (few meters) normal faults striking obliquely with respect to the palaeo-shoreline trends, displays systematic variations in sequence architecture and the nature of bounding surfaces across them. Indeed, depending on position with respect to the fault plane, two basic types of internal organisation can be recognised in the examined shallow-marine, almost clastic-starved sequence. Within grabens it consists of a siliciclastic-rich transgressive systems tract (TST), which is bounded beneath by a transgressively modified, Glossifungites-demarcated sequence boundary (SB/RS), overlain by a mollusc-bearing falling-stage systems tract (FSST). The erosional downlap surface that separates the TST from the FSST is the regressive surface of marine erosion (RSME). On the footwall crests the combination of marine regressive erosion, during falls in relative sea-level, and uplift has resulted in complete removal of the sediments of the TST from these sites, leading to the formation of a tectonically enhanced basal unconformity composed of the RSME superimposed onto the previous SB/RS (SB/RS/RSME). The prominent lateral change in component units (systems tracts) and nature of bounding surfaces within the studied sequence is directly related to the presence of normal faults and indicates that fault activity had a major impact on the sequence stratigraphic evolution of the Mejillones Formation, enhancing subsidence within the grabens and promoting unconformities in the horsts. Overall, the Mejillones Formation records a long-term sea-level fall driven by the contemporaneous regional uplift, punctuated by repeated, high-frequency eustatic sea-level changes. The effect of this superimposition was that glacio-eustatic sequences were displaced progressively downward and basinward and stacked in a distinct downstepping, tectonically enhanced falling-stage sequence set, which reflects basin-wide loss in accommodation space. The sequence set is underlain by a composite RSME that becomes progressively younger basinward and is made up by the lateral and down-dip connection of a series of lower-rank sequence boundaries including hanging-wall SB/RSs and footwall SB/RS/RSMEs of successive sequences
Sequence stratigraphy of the Punta Ballena Member of the Jama Formation (Early Pleistocene, Ecuador): insights from integrated sedimentologic, taphonomic and paleoecologic analysis of molluscan shell concentrations.
No full textEarly Pleistocene strata are well exposed along the uplifted eastern margin of the Esmeraldas–Caraquez Basin, particularly on the coastal cliff west of the city of Jama (a type locality for shallow marine Quaternary sedimentary exposures on northcentral Ecuador). Here, at least 180 m of sediments accumulated in inner-shelf to subaerial settings are present (Jama Formation). This paper is concerned with the middle stratigraphic unit of the Jama Formation (the Punta Ballena Member, PBM). Integrated sedimentologic, paleontologic, and stratigraphic observations reveal that the PBM is composed of eight, disconformity-bounded depositional sequences. Hiatal shell concentrations, which formed as a consequence of landward and seaward stratal attenuation, are associated with sequence bounding and intrasequence surfaces. Together with sedimentologic characteristics, these fossiliferous levels are important indicators of facies architecture and, therefore, are useful tools for interpreting sequence stratigraphy. According to their taphonomic features and taxonomic composition, the hiatal shell concentrations occurring within the PBM may be grouped into two main types, each of which occupies a predictable stratigraphic position within the sequences: current/wave-winnowed beds at the cycle base and community shell concentrations in a roughly mid-cycle position. Current/wave-winnowed beds, commonly underlain by Thalassinoides burrows that penetrate to depths of as much as 1.5 m below ravinement surfaces, are transported skeletal concentrations and formed through physical processes in shallow, highenergy environments. They comprise a time-averaged mixture of specimens having different ecologies and states of preservation and accumulated mainly under conditions of total passing of siliciclastic sediment (i.e. terrigenous sediments are delivered to the site as suspended load but, owing to the high environmental energy, failed to accumulate). Community shell concentrations occur in sparsely fossiliferous intervals and result from reduced net sedimentation within low-energy, relatively deeper settings. They are composed of matrix-supported, loosely clustered, life-oriented and little-disturbed fossil assemblages, but are packed in excess of likely living densities and are visually dominated by successive generations of the infaunal bivalve Raeta undulata, which colonized a slowly aggrading muddy seafloor. The sedimentological and paleontological evidence presented here not only supports the results of previous studies, which demonstrate the value of condensed shell concentrations in the identification of stratigraphically significant surfaces, but also provides adds to the distinctive features of these shell beds
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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