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Modelling facies heterogeneity in carbonate ramp systems. From petrophysical characteristics to forward modelling
Full text linkIn the last decades digital modelling applied to geological research is getting increasing attention (Alaei, 2012; Tomassetti et al., 2018; Trippetta et al., 2020; De Franco et al., 2019; Mascolo and Lecomte, 2021). Indeed, relevant implications both in scientific and economic terms could be inferred by using this technique. In particular, the application of digital models in complex geologic scenarios is critical for the understanding of potentially exploitable systems from multiple perspectives. Starting from the most classical model application for the exploitation of oil and gas fields passing through the implementation of extraction strategies - by reducing uncertainties (Macgregor & Moody, 1998; Racey 2001) - digital models find new place in latest applications such as natural gas storage. Recently, models are also applied for the study of geological bodies, potential reservoirs for the CO2 or hydrogen injection (Dockrill and Shipton, 2010; Trippetta et al., 2013; Aminu et al., 2017; Heinemann et al., 2018). Modelling contribute and facilitate to capture and store gases in the subsurface, balancing their release into the atmosphere. Digital modelling represents one of the major innovative strategies in the control of greenhouse gases concentration in atmosphere, a currently trending topic from media, public opinion, and political points of view. Another possible application of digital models for subsurface gas storage involves the monitoring of reservoirs in order to ascertain and quantify gas leakage through fault or fracture systems (Wang et al., 2018). Moreover, radioactive waste storage could be integrated as current and powerful employment of digital models (Malvić et al., 2020). In particular, the technological tools used for these purposes are called forward models since their outcomes gives predictive results on the processes happened in the past and protracted towards the future. They appear extremely suitable for the study of geological subsurface formations that can be also applied to an emerging field such as the development of geothermal energy power plants (De Franco et al., 2019). All these are topics of great actuality since world governments' plans are1
directed towards the total replacement of classic energy sources from hydrocarbons with green energies. However, digital modelling needs input data such as geometries and rock properties that should be well constrained. Seismic exploration is probably the most powerful tool for investigating subsurface rock formations (Avseth et al., 2010). Important progress has been made in recent years, but significant problems remain in the geologic interpretation of seismic data. The reflections that can be read in seismic data depend on the Acoustic Impedance (AI) contrast in the transit of the P-wave between layers in the subsurface. AI depends on the density (ϼ) and the P-wave velocity (Vp) of the medium through which wave propagates (AI= ϼ Vp). These petrophysical characteristics, in turn, are controlled by structure, texture, porosity, and boundary conditions of the rocks (Dvorkin et al., 2014; Tomassetti et al., 2018; Trippetta et al., 2020; Brandano et al., 2020). These two links, one between rock structure and its elasticity and the other between elasticity and signal propagation, form the physical basis of seismic interpretation (Anselmetti and Eberli, 1993; Eberli et al. 2003; Weger et al. 2009; Hairabian et al. 2014; Dvorkin et al., 2014). Dealing with these relationships, we are facing the so- called inverse problem. We see from seismic sections the resulting seismic images of rock formations where the same signal can be the result of a combination of different features. It should be, thus, very useful to well understand what are the features that lead to a certain seismic image. Synthetic seismic modelling (or forward modelling) is a fundamental prospecting method for understanding the features leading to the corresponding seismic images of subsurface structures and reservoir architectures (Alaei, 2012). Forward modelling methodology, as approach to the interpretation of seismic data, involves the detailed characterization of lithology, density, porosity, seismic velocity and fluid in the rock, as well as the reservoir geometry. As a result, the corresponding seismic properties are calculated, and then synthetic seismic traces are generated. These issues became essential for lithologies characterized by a complex seismic interpretation (Al-Salmi et al., 2019). In addition, synthetic seismic forward models allow accurate analysis of fault zones. The study of seismic response in fault zones is crucial since the2
fracturing or compaction that faults create strongly modifies the petrophysical characteristics of rocks by affecting their properties (Botter et al., 2017; Kolyukhin et al., 2017). Synthetic seismic forward models are, therefore, mandatory for the comprehension of faults behaviour through seismic imaging. Faults play a key role in reservoirs by increasing or limiting fluid flow. Even if interpretation of seismic data is a pivotal method for studying the subsurface, the internal structure and properties of fault zones are often below the limit imposed by seismic resolution (Botter et al., 2017). Despite the impact of faults on reservoir permeability, modelling tools and workflows still lack for realistic representation of fault zones in models (Tveranger et al., 2005; Braathen et al., 2009; Manzocchi et al., 2010). With facies analysis and petrophysical data it is possible to build field-based digital models fundamental in understanding architectures of carbonate sedimentary bodies which often constitute reservoir surface analogues of buried world-wide petroleum systems, CO2, hydrogen, radioactive waste storage sites and geothermal fields. Surface analogues are rocks with depositional, textural, and petrophysical characteristics similar to those constituting the petroleum system, but they outcrop on the surface. Starting from petrophysical characteristics of facies, forward models can be built. In this thesis, as a case study for the development of a forward model, rocks belonging to the carbonate realm, more specifically carbonate ramps, were analyzed. Carbonate ramps constitute important hydrocarbon deposits in North Africa (Macgregor & Moody, 1998), Venezuela, and many other regions of the World (Racey, 2001) due to their excellent porosity and permeability characteristics. However, the depositional model that is the basis for a proper interpretation produces many uncertainties arising from the difficulty in attributing different facies to a depositional environment and process due to the poor occurrence of sedimentary structures (Buxton and Pedley, 1989; Pomar and Kendall, 2008; Burchette, 2012; Bassi et al., 2013; Tomassetti et al., 2018; Tomassetti et al., 2022). In addition, strong lateral heterogeneity in terms of petrophysical characteristics, components, structure, and texture leads to complex distinction of facies belts (Tomassetti et al., 2018; Trippetta et al., 2020; Brandano et al., 2020). To overcome these issues, quantification of3
petrophysical characteristics can be crucial in understanding facies heterogeneity from a physical perspective to be incorporated in synthetic seismic forward models building. Carbonate rocks are often difficult to interpret seismically because the slight acoustic impedance contrast at the interface between carbonate facies in subsurface does not allow a clear resolution of major reflectors and reservoir formations. Strong constraints are often imposed by geophysical survey techniques characterized by low resolution especially in carbonates and interpretation capabilities that depend on the interpreter skill (Tomassetti et al., 2018; Trippetta and Geremia, 2019; Faleide et al., 2021). These constraints can be overtaken through the modelling of surface analogues allowing a detailed analysis on the facies association but also their petrophysical characteristics and seismic properties such as acoustic impedance (Tomassetti et al., 2018; Lipparini et al., 2018; Trippetta and Geremia, 2019; Brandano et al., 2020). In order to analyse the petrophysical characteristics and seismic response of the carbonate realm through modelling two carbonate ramps both belonging to the Adria plate were considered as case studies. The first is the Chattian carbonate ramp of the Porto Badisco calcarenite outcropping in the southern Salento peninsula, the southernmost portion of the Apulian carbonate platform. The Porto Badisco carbonate ramp is an excellent surface analogue of exploited oil and gas field in the offshore Venezuela, Philippine and South China Sea (Zampetti et al., 2005; Sattler et al.,2004; Fournier and Borgomano, 2007; Lallier et al., 2012; Marini and Spadafora, 2014; Pomar et al., 2015; Valencia and Laya, 2020) as well as fields in offshore Adriatic Sea such as Ombrina Mare field (Campagnoni et al., 2013). In this carbonate system firstly the analysis of outcropping facies was carried out observing over 100 thin sections produced. Consequently facies association modelling was performed through Petrel software (mark of Schlumberger) using TGSim stochastic approach algorithm adopting the depositional model based on field data. This model is useful for qualitatively understand the broad facies spacial distribution which reflects the abrupt heterogeneity from a sedimentary point of view. To physically quantify the lateral facies heterogeneity the petrophysical characteristics such as porosity, density and seismic velocity were measured and analyzed through a multi-analytical approach. Density4
measurements were carried out with the helium pycnometer. Porosity was firstly calculated from the density data and then was additionally measured through image analysis and point counting to cross-correlate the values. Seismic velocity was measured by using an ultrasonic generator connected to piezoelectic transducers and to an oscilloscope. The analysis performed on the carbonate ramp outcropping in Porto Badisco offers the opportunity to analyze facies heterogeneity, modeling its distribution and physically quantifying it through petrophysical characterization. From the petrophysical data, it was possible to construct 2D models of the distribution of porosity and P-wave seismic velocity along the depositional model. This study, which can be applied globally to carbonate platforms, emphasizes with the modelling exercise how facies heterogeneity is an intrinsic feature of these systems. The petrophysical characterization which provides quantitative values to the heterogeneity allow to build more complex models such as seismic forward models discussed in the second chapter. The other case study is represented by the Cenozoic carbonate ramp outcropping on the Majella Massif in Abruzzi, the northernmost portion of the Apulian carbonate platform which gives the opportunity to study a carbonate ramp surface analogue of a buried reservoir. Also in Majella the Oligo- Miocene stratigraphic interval represented by the Bolognano Formation which is the reservoir of the system is considered an excellent surface analogue of the productive fields in the Adriatic Sea, offshore Venezuela, Philippines and many others worldwide (Tomassetti et al., 2021). Specifically, this system offers the opportunity to integrate the facies heterogeneity in the synthetic seismic forward modelling and understand its seismic response without the introduction of artificial noise to obtain additional information. On the Majella Massif a model of the facies heterogeneity to understand their seismic response was performed. After analyzing the facies and measuring their petrophysical characteristics, the data obtained were used as input for build a 3D property modelling in Petrel software representing the entire carbonate ramp from the topographic surface to the Upper Cretaceous from the platform top going towards the basin located northward from the Majella Massif. From the 3D model was cut a section whose data were used as input in Matlab (mark of Mathworks) in order to perform the synthetic seismic forward model5
with the geophysical codes provided by the CREWES consortium. The resulting forward model represent the seismic response of the facies heterogeneity of carbonate rocks. In addition, from the obtained seismic images it is possible to evaluate the presence of hydrocarbons and to identify how the presence of important bituminous impregnations – that can be appreciated in the field in Majella – modify the seismic response. The workflow developed to quantify the signature of the facies heterogeneity of carbonate rocks and the presence of infilling hydrocarbons is applicable to other systems worldwide, which is a large issue that is still open and can help in the problems relative to seismic interpretation associated with these systems. Given the presence of a buried normal fault system in the study area, a forward modelling in the fault zones was performed as well. By measuring the petrophysical characteristics of the fault rocks characterized by both fracturing or compaction, fault zones were modeled. Two end member scenarios with two opposite behaviors of the rocks belonging to the damage zone were modeled in Matlab. A scenario in which the damage zone is characterized by fracturing and therefore rocks affected by greater porosity than the host rock. In the other scenario was modeled a damage zone with lower porosity than the host rock caused by the presence of compaction bands. Consequently, the seismic response of these end members was compared to understand how faults affect the seismic response of carbonate ramp systems. Notoriously, fault systems globally characterize carbonate ramps, and understanding their seismic response facilitates interpretation of the deformation behavior that a fault can assume under different boundary conditions. This can lead to an understanding of whether faults behave as barriers or conduits for fluids with the important implications for the study of fluid leakage from reservoirs
Reply to the comment on 'Sea-level control on facies architecture in the Cenomanian-Coniacian Apulian margin (Western Tethys): A record of glacio-eustatic fluctuations during the Cretaceous greenhouse?' by S. Galeotti, G. Rusciadelli, M. Sprovieri, L. Lanci, A. Gaudio and S. Pekar [Palaeogeography, Palaeoclimatology, Palaeoecology 276 (2009) 196-205]
No full textSea-level control on facies architecture in the Cenomanian–Coniacian Apulian margin (Western Tethys): A record of glacio-eustatic fluctuations during the Cretaceous greenhouse?
No full textThe integrated chemo-, bio- and sequence stratigraphy from the Cenomanian–Coniacian base-of-slope succession of Monte Turno (Abruzzo, central Italy) provides a fine scale calibration of the local sea-level curve inferred from the adjacent platform to records of global sea-level change. Our results indicate that regional marine regressions were coincident with episodes of global cooling and sea-level fall, providing evidences for a causal link between climate changes and sea-level changes. The presence of small polar ice- caps during the assumed ice-free Cretaceous is a likely explanation for the observed pattern
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
Coral sponge-microincruster-microbialite associations in the uppermost Jurassic reef complex of Eastern Sardinia (Italy)
No full textThe late Jurassic records one of the largest reefal expansions of the Phanerozoic, with a greater diffusion and differentiationin the Tethys realm. SEveral depositional models about Upper Jurassic reef types have been pubblished but little knowledge is available about the Eastern Sardinian reef. This study focuses on the detailed composition and sedimentological charcterization of the Upper Tithonian reef complex of Eastern Sardinia, which is presently exposed in the area of Calagonone (Orosei Gulf). This reef complex characterises the lower part of the Bardia Fm. which represents the upper lithostratigraphic unit of the tripartite Jurassic succession of eastern Sardinia. This formation developed after thr Early Tithonian regressive trend, locally marked by subaereal carbonate breccias. The Bardia Fm. reef complex represents an inferred off lap break\ramp margin succesison that was initially aggradational and then was followed by progradation of carbonate sigmidal clinoforms (3-15°).Compositional and sedimentological analysisi of the Bardia reef complex has been caried out though thr combination of "macroscopic (outcrop scale) and "microscopic" (microfacies-scale) observation on exceptional exposed saw-cut quarry facies, over a surface of a few hundred squared meters in three different locations. Reef components were grouped into three broad categories: 1) macroscopically detectable organisms, mainly represented by corals, sponges bivalves, gastropods, echinoderms, 2) microscopically detectable components corresponding to microencrusters and microbialites, 3) fine to coarse bioclastic debris and mud-supported facies. These components combine in various proportion forming peculiar facies associations. Their distribution and frequency vary among the quarries and highlight a mosaic of biocontructed structures throughout the reef complex.Hight biotic diversty, multivarious interaction among the main reef builders, such as corals, calcareous and siliceous sponges, microencrusters and microbialites, the great variety of coral forms, the strong coral zonation, and the adrupt lateral and vertical facies chnges, are some of the most prominent features of this reef complex. These structures illustrate the depositional, paleoecological and stratigraphic evolution of this reef complex, and provide a solid base for comparison with other Upper Jurassic Tethyan reef complexes
Coral-sponge-microencruster-microbialite associations in the Upper Jurassic reef: quantitative characterization of a case study from Eastern Sardinia (Italy)
No full textThe Late Jurassic records one of the largest reefal expansions of the Phanerozoic, with major diffusion and differentiation in the Tethys realm (WOOD, 1999; KIESSLING, 2002; CECCA et al., 2005). Several depositional and compositional models about Upper Jurassic reef types (see INSALACO et al.,1997; LEINFELDER et al., 2002, 2005; RUSCIADELLI et al., 2011 for a revision) have been published but little knowledge is available about the Eastern Sardinian reefs. This study focuses on the compositional and sedimentological characterization of the Upper Tithonian reef complex presently exposed in the area of Cala Gonone (Orosei Gulf) (Fig.1).
The Upper Jurassic carbonate succession of Eastern Sardinia consists of three Bathonian-Callovian to Berriasian (DIENI & MASSARI, 1985; JADOUL et al., 2010 and references therein) carbonate depositional systems developed on the southern Europe passive margin (Fig.1): 1) the first (Dorgali Fm.) is characterized by ooidal grainstone, accumulated above wave base on structural highs (Variscan basement), capped by an Upper Bathonian-Callovian condensed succession with a few Fe-phosphatic hardgrounds; 2) a low-angle Oxfordian-upper Tithonian depositional system: the shallow ramp deposition (Tului Fm.) is characterized by basal oolitic facies overlain by prograding coral-stromatoporoid reefs, interfingering with outer ramp-basinal peloidal packstone-wackestone (S’Adde and Baunei Fms.); 3) the third depositional carbonate system (Bardia Fm.) developed after an Early Tithonian regressive trend, locally marked by carbonate breccias indicative of subaerial exposure. The lower part of the Bardia Fm. (upper Tithonian) is locally characterized by gentle slopes (3-15°) with bioclastic-coral-sponge facies associations (LANFRANCHI et al., 2011). This progradational unit is followed by up to 400-500 m of back reef and inner platform shallow water carbonates.REEF COMPONENTS AND FACIES
Compositional and sedimentological analysis of the Bardia reef has been carried out through the combination of “macroscopic” (outcrop-scale) and “microscopic” (microfacies-scale) observations on exceptionally exposed saw-cut quarry walls, over a surface of a few hundreds square metres in three different locations. The external surface of each macroscopically detectable component has been emphasized on the quarry walls (Fig.2). The areal distribution of each portion has been stored as vector images, defining frequency, density and area occupied by the reef components. Microfacies and paleontological analyses have been performed on 280 thin sections.
Reef components were grouped into three broad categories: 1) macroscopically detectable organisms (mainly corals, sponges, bivalves, gastropods, echinoderms); 2) microscopically detectable components (microencrusters and microbialites); 3) fine- to coarse bioclastic debris and mud-supported facies. Corals show different degree of reworking, from in life-position skeletons more than 2.5 m2 in size to centimetre-sized rubble. The 49 recognized genera of corals have been classified according to external morphology and corallite type.
Calcified sponges (Stromatoporoids) are a few centimetres to tens of centimetres in size, occurring as isolated specimens and in densely-packed assemblages. Siliceous sponges and spiculae are replaced respectively by precipitated automicrite and calcite spar. Microbialite and microencruster organisms form domal, columnar or irregular accretionary crusts, few millimetres to several centimetres in thickness. Frequently, crusts bind neighbouring skeletons of large biota, developing metre-scale bioconstructions.
These components combine in various proportions within and among quarries, reflecting abrupt lateral and vertical changes of environmental conditions. Quarry 1 is characterized by large branched and massive coral colonies partially or totally encrusted by centimetre thick microencruster crusts and well-washed bioclastic facies, indicating sediment reworking in a high–energy environment. This facies abruptly passes laterally into a densely packed massive microsolenid coral and calcareous sponge assemblage and microbialite and microencruster (Tubiphytes. and other nubeculariids) boundstone. Microsolenid assemblages are commonly interpreted to have formed in deeper water (LATHULIÈRE & GILL, 1995; GILL et al., 2004) or alternatively related to poorly illuminated shallow-water cave environments, and adapted to low-sedimentation, low-energy and nutrient-rich conditions (INSALACO, 1996; DUPRAZ & STRASSER, 2002). Quarry 2 is characterized by progressive vertical variations from facies dominated by densely packed platy and flat coral colonies (microsolenids and others) to facies dominated by calcareous sponges and loosely packed phaceloid coral colonies. Microbialite and microencrusters (Tubiphytes and other nubeculariids) envelope and bind large biota. Platy growth forms are generally interpreted as a response to poor illumination (INSALACO, 1996). Consequently the whole association seems to be compatible with poorly illuminated water, low sedimentation rate in a low energy environment. Quarry 3 records large scale bedding (from 1 m to several metres) defined by six intervals dominated respectively by 1) bivalves; 2) dasycladacean algae; 3) reworked massive thamnasterioid coral colonies; 4) thin phaceloid corals and calcareous sponges in growth position; 5) branched ramose coral colonies and calcareous sponges; 6) reworked massive plocoid coral colonies and gastropods. Large biota within intervals 3, 4 and 5 are largely encrusted by different microencrusters such as Koskinobulina, Thaumatoporella, light-dependent Lithocodium-Bacinella, and microbial accrectionary crust. Coral assemblages and microencruster association reveal a progressive increasing of the energy regime and sediment reworking in well-lit waters (INSALCO, 1996; SCHIMD & LEINFELDER, 2002), while the presence of bivalve, algae and gastropod floatstone represents the temporary shifting to “peri-reefal” environments.
Despite variability of facies associations in the three quarries, a paleoecological evolution from quarry 1 to quarry 3 emerges, reflecting the change from moderate energy environment with more protected, poorly illuminated cave environment (quarry 1), through a low energy, poorly illuminated environment characterized by low sedimentation rate (quarry 2), to a high energy, well illuminated environment, characterized by high sedimentation rate and reworking (quarry 3). The relative position of the studied quarries along an ideal depositional profile remains speculative, although a medium-scale progradational trend, from distal to proximal setting, seems to be compatible with the long-scale stratigraphic trend of the Bardia Fm.
Spectacular outcrop conditions, amount of data collected, biota taxonomic classifications and the observed stratigraphic evolution provide the solid base for paleo-biogeographical comparisons with other Upper Jurassic Tethyan reef complexes.
REFERENCES
CECCA F., GARIN M., MARCHAND D., LATHUILIERE B. & BARTOLINI A. (2005). Paleoclimatic control of biogeographic and sedimentary events in Tethyan and peri-Tethyan areas during the Oxfordian (Late Jurassic). Pal.Pal.Pal., 222, 10–32.
DIENI I. & MASSARI F. (1985). Mesozoic of Eastern Sardinia. In: Cherchi A. (ed.), 19th European Micropaleontological Colloquium. Sardinia, October 1-10. Micropaleontological researches in Sardinia. Guidebook, 66-77.
DUPRAZ C. & STRASSER A. (2002) Nutritional modes in coral-microbialite reefs (Jurassic, Oxfordian, Switzerland): evolution of trophic structure as a response to environmental change. Palaios 17, 449-471.
GILL G., SANTANTONIO M. & LATHUILIÈRE B. (2004). The depth of pelagic deposits in the Tethyan Jurassic and the use of corals: an example from the Apennines. Sedimentary Geology, 166, (3-4), 311–334.
INSALACO E. (1996) Upper Jurassic microsolenids biostromes of northern and central Europe: facies and depositional environment. Pal. Pal. Pal., 121, 169–194.
INSALACO E., HALLAM A. & ROSEN B.R. (1997). Oxfordian (Upper Jurassic) coral reefs in western Europe: reef types and conceptual depositional model. Sedimentology 44, 707–734.
JADOUL F., LANFRANCHI A., CASELLATO C.E., BERRA F. & ERBA E. (2010). I sistemi carbonatici giurassici della Sardegna orientale (Golfo di Orosei). In Geol.F.Trips of ISPRA and Società Geologica Italiana Vol. 2, 122 pp.
KIESSLING,W. (2002). Secular variations in the Phanerozoic reef systems. In: Kiessling,W., Flügel, E., Golonka, J. (Eds.), Phanerozoic Reef Patterns: SEPM, Spec. Publ., 72, 625–690.
LATHULIÈRE B. & GILL G. (1995). Some new suggestions on functional morphology in pennular corals. In: B Lathuilière, J Geister (Eds.), Coral Reefs in Past, Present and Future. Proceeding of the 2nd European Meeting of the International Society for Reef Studies, Publications du Service Géologique du Luxembourg, 29, 259–264
LANFRANCHI A., BERRA F. & JADOUL F. (2011). Compositional changes in sigmoidal carbonate clinoforms (Late Tithonian, eastern Sardinia, Italy): insights from quantitative microfacies analyses. Sedimentology 58, 2039–2060
LEINFELDERR.R., SCHLAGINTWEIT F., WERNER W., EBLI O., NOSE,M., SCHMID D.U. & HUGHES G.W. (2005). Significance of stromatoporoids in Jurassic reefs and carbonate platforms—concepts and implications. Facies 51, 287–325.
LEINFELDER R.R., SCHMID D.U., NOSE M. & WERNER W. (2002). Jurassic reef patterns. The expression of a changing globe. In: Kiessling, W., Flügel, E., Golonka, J. (Eds.), Phanerozoic Reef Patterns: SEPM Spec Publ, 72,. 465–520.
RUSCIADELLI G., RICCI C., LATHUILIÈRE B. (2011) The Ellipsactinia Limestones of the Marsica area (Central Apennines): A reference zonation model for Upper Jurassic Intra-Tethys reef complexes. Sed. Geol., 233, 69–87
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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
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
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