1,720,974 research outputs found
Hybrid event bed distribution in a mixed siliciclastic-calcareous turbidite succession: a cross-current perspective from the Bordighera Sandstone, Ligurian Alps, NW Italy
No full textTransitional flow deposits (TFDs) and hybrid event beds (HEBs) form part of the high-density sediment gravity flow spectrum. They record flow characteristics intermediate between fully turbulent and laminar flow states. The transformation from initially frictional into transitional or quasi-laminar cohesive flow behaviour results from enhanced detrital clay concentrations that dampen flow turbulence, triggering the development of an argillaceous sandstone interval that displays characteristics of a cohesive debris flow deposit. Since excess detrital clay proportions reduce primary porosity and permeability, the presence of TFDs and HEBs hinders turbidite sandstone reservoir properties. In applied scenarios, understanding their spatial distribution is crucial for avoiding well misplacement. Spatial distribution models for TFDs and HEBs largely document them as a characteristic feature of distal and lateral outer fan environments. These models are compared with results from facies analysis conducted on a dataset derived from the detailed investigation of three stratigraphic sections, acquired along a cross-current transect of the distal depositional domain of the Bordighera Sandstone (BGS). In its distal domain, the sand-rich Bordighera turbidite system is characterized by direct interbedding with calcareous fine-grained turbidites of the San Remo Helminthoid Flysch, and features high proportions of HEBs and TFDs. Analysis of spatial trends in facies distribution allows the detailed allocation of intra- bed- to sandbody-scale heterogeneity to different axial and off-axis lobe sub-environments which are determined through quantitative sedimentological parameters. Results reveal that in the Bordighera turbidite system argillaceous sandstone bed types are not limited to lobe-fringe environments, but instead are primarily occurring in more proximal high net-to-gross zones of the largely unconfined terminal lobe domain. They account for more than 70% of stratigraphic thickness in axial zones (net-to-gross ratio = 0.87), whereas their proportions decrease towards off-axis lobe (36%; net-to-gross = 0.58) and marginal lobe to lobe fringe domains (23%; net-to-gross = 0.49)
Quantitative bed-type classification for a global comparison of deep-water sedimentary systems
Full text linkCharacterisation of deep-water successions is often undertaken at the scale of sedimentary beds. However, different studies often apply alternative bed-type classification schemes, rendering the quantitative comparison of bed properties of different deep-water systems difficult. In this study a quantitative approach to the development of a universal deep-water bed-type classification scheme is proposed based on the synthesis of a large sedimentological dataset, containing >32,000 deep-water facies and >10,000 beds accumulated in 27 turbidite-dominated systems. The classification scheme is applicable to discriminate and categorise lithological (sand, gravel) layers and is based on: (i) the proportion of, gravel, sand, sandy-mud and muddy-sand in the bed, (ii) the presence and nature of vertical sharp grain-size changes, and (iii) the presence and thickness ratio of laminated sedimentary facies. Comparing the bedding properties of channel-fills, terminal deposits (e.g. lobes or sheets) and levees showed that the three architectural-element types are characterised by differences in bed frequency and thickness, overlying mudstone proportions, vertical bed thickness trends, mud thickness and sand-gravel fraction values. Building on these recognised statistical differences an algorithm was developed that is capable of generating, in a stochastic manner, geologically realistic synthetic sedimentary logs depicting deep-water terminal-deposit, channel-fill and levee elements. The one-dimensional facies modelling is governed by a series of input parameters, including total number of beds, sand-gravel thickness, and sand-gravel fraction. The approach can be tailored to produce synthetic logs for specified types of depositional systems (e.g., categorised according to dominant grain size of deposits, age of deposition and global climate (icehouse vs. greenhouse conditions)). A large number of synthetic sedimentary logs can be generated, which can be utilised as training datasets in machine learning algorithms developed to aid subsurface interpretations of clastic sedimentary successions
Tectonic control on trench-type basin stratigraphic succession in Apenninic-Maghrebian Orogen. An example from the Tufiti di Tusa Formation (Calabria - Lucania border, Southern Italy)
No full textTectonic Influence on the Geomorphology of Submarine Canyons: Implications for Deep-Water Sedimentary Systems
No full textA database-informed metastudy of 294 globally distributed submarine canyons has been conducted with the aim of elucidating the role of tectonic setting on submarine-canyon geomorphology. To achieve this, data from seafloor and subsurface studies derived from 136 peer-reviewed publications and from open-source worldwide bathymetry datasets have been statistically analyzed. In particular, relationships between margin type (active vs. passive) or plate-boundary type (convergent vs. transform vs. complex) have been assessed for key morphometric parameters of submarine canyons, including: streamwise length, maximum and average width and depth, canyon sinuosity, average canyon thalweg gradient, and maximum canyon sidewall steepness. In addition, possible scaling relationships between canyon morphometric parameters and characteristics of the associated terrestrial catchment, continental shelf and slope, and of the broader physiographic setting for canyons along both active and passive margins have been evaluated. The following principal findings arise: 1) overall canyon geomorphology is not markedly different across tectonic settings; 2) slope failure might be more important in passive-margin canyons compared to active ones, possibly due to seismic strengthening in the latter; 3) some aspects of canyon geomorphology scale with attributes of the sourceto-sink system and environmental setting, but the strength and sign in scaling might differ between active and passive margins, suggesting that the extent to which canyon geomorphology can be predicted depends on the tectonic setting. Insights from our analysis augment and improve conceptual, experimental and numerical models of slope systems at the scale of individual canyons and source-to-sink systems, and increase our understanding of the complex role played by tectonic setting in shaping deep-water systems
Depositional architectures and facies distribution in turbiditic sandstone channel-fills. A case-study from the Gorgoglione Flysch Formation (Basilicata, Southern Italy)
No full textTurbidite channels are among the most important deep-water hydrocarbon reservoirs currently being explored. Recent advances in the understanding of these depositional systems result from significant improvements in modern 3-D seismic imaging, showing their three-dimensional stratal complexity and architectures at multiple scales. However, lateral and vertical variability of reservoir properties are associated with differences in the nature of channel fill and their stacking patterns, which commonly are at scales below the resolution of even high resolution 3-D seismic datasets. For this reason, outcrop studies are powerful tools to investigate the properties of channel-fill deposits and improve the characterization of channel systems.
A field-based study is presented from a key stratigraphic interval of the Gorgoglione Flysch Fm, a Miocene turbiditic succession exposed within a piggy-back basin in the Southern Apenninic Chain of Italy. This formation includes 10-to-60-m-thick amalgamated sandbodies, systematically offset-stacked to form channel complexes that are laterally associated with heterolithic overbank deposits. There is an upward evolution from these laterally-migrating amalgamated channelized sedimentary bodies into isolated sand-filled channels, 4-to-35 m thick, displaying considerable lateral thickness variability. Systematic bed-scale stratigraphic measurements on the sandbodies reveal a recurring motif of three main coarse-grained facies forming a distinctive channel-fill facies association. The basal LC1 lithofacies consists of pebble- to cobble-sized conglomerate within a poorly-sorted, very coarse-grained sandstone matrix, interpreted as a channel-base lag resulting from the bypassing of high-density turbidity currents, characterizing the earlier phases of the channel formation. LC1 lithofacies is commonly overlain by LC2 lithofacies, composed of normally-graded, coarse-to medium-grained sandstones, predominantly structureless or plane-parallel laminated. This lithofacies has been interpreted as the sedimentary product of collapsing, sand-rich high-density turbidity currents during the backfilling stage. LC3 lithofacies is dominant towards the top of the sandbodies; it is characterized by multiple sets of 3D dune-scale cross stratification in medium- to coarse-grained sandstones, whose deposition is related to the influence of persistent energetic traction currents at the end of turbiditic events that reworked the topmost part of the channel-fills. Geometry, continuity, and distribution of sandstone facies at the scale of channel-fills, combined with palaeoflow analysis, provide insights for the identification of the different parts of the channels (axis / off-axis / margin) and locally the characterization of the degree of sinuosity. The detailed description and interpretation of these deposits can help to better understand the processes involved in the evolution of turbiditic channels for an accurate characterization of deep-water reservoirs
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
The stratigraphic evolution of a submarine channel system in a tectonically-confined basin: the Miocene Gorgoglione flysch formation, southern Italy
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