1,721,072 research outputs found
The impact of high discharge variability on sedimentology and architecture of bar deposits in the meandering Powder River (Montana, USA)
Full text linkPoint bars are emblematic deposits of meandering rivers. Classical facies models that define their architecture and sedimentology are essentially based on rivers with low to moderate peak discharge variability. However, many global rivers experience high peak discharge variability, which may significantly impact point-bar sedimentological features. This study investigates how high peak discharge variability affects the sedimentology and architecture of point-bar deposits along the meandering Powder River in south-eastern Montana, USA. The analysis integrates detailed sedimentological data from trenches and natural exposures at four point bars where century-long discharge records and more than four decades of geomorphic surveys are available. Sedimentological data reveals substantial deviations from classical facies models. Coarsening-upward and blocky vertical grain-size trends are common, in contrast with the classic fining-upward model. Upper-flow regime structures are abundant features that record rapid waning of high-magnitude floods, whereas lateral accretion surfaces matching the original extent of bar slopes are rare due to frequent bar slope reworking. Chute channels are large, occupying significant portions of the bar area, with complex internal architectures of coarse-grained upper-flow regime deposits that further obscure lateral accretion geometries of the hosting bar. Oxidized mud layers suggest prolonged sub-aerial exposure of most of the bar slope between floods. Results from this study challenge assumptions of classical point-bar models and provide new criteria for recognizing ancient deposits of meandering rivers with high peak discharge variability, with implications for palaeohydrological reconstructions, understanding pre-vegetation fluvial dynamics and interpreting deposits on other planetary bodies. This new evidence accounts for hydrological modulation effects on fluvial deposits, enabling more robust facies analysis of alluvial successions across a spectrum of discharge variability regimes
Discharge variability drives point-bar macroform degradation in the meandering Powder River (Montana, USA)
No full textMost extant facies models depict the internal architecture of fluvial point bars as large-scale, inclined beds formed by the lateral migration of channel bends. However, recent studies have revealed that discharge variability can significantly influence these architectures, highlighting that the genetic processes governing their formation remain poorly understood. This study examines point-bar deposits along the meandering Powder River in Montana, USA, to understand how a highly variable hydrological regime impacts bar depositional architecture. Sedimentological data reveal that the bars consist of amalgamated beds and lack well-preserved, large-scale, inclined (macroform) bedding. By integrating architectural data with 27 years of hydrological and geomorphological records, we linked distinct beds to specific water discharge conditions, highlighting that major floods play a crucial role in constructing and reshaping point-bar architecture, whereas minor floods have marginal impacts. Bar-scale sedimentation occurs briefly during early flood-waning stages, forming limited bar-scale, inclined beds, which are later disrupted by localized scouring from subsidiary flood pulses. The preservation of these deposits is primarily controlled by the frequency of subsidiary peaks during the waning phase, rather than by intermittency or total duration of the waning stage. Consequently, the complex bedding in the Powder River point bars reflects autogenic intraflood reworking rather than interflood reworking. Major floods produce both slope-scale and localized deposits, with subsidiary peaks during waning stages driving macroform-bedding disruption. These results provide valuable insights for interpreting hydroclimatic environments and refining interpretations of past depositional processes from the rock record, and they emphasize the need to explicitly account for discharge variability in fluvial facies models
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
Carbonate isotope data of sediment core CRP-1 (Table 3)
No full textCarbonate isotope data of sediment core CRP-1 (Table 3
Modal analsyis of sediment core CRP-1 (Table 1)
No full textModal analsyis of sediment core CRP-1 (Table 1
Carbonate microprobe data of sediment core CRP-1 (Table 2)
No full textCarbonate microprobe data of sediment core CRP-1 (Table 2
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