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Il Bacino Terziario Epimesoalpino e le sue implicazioni sui rapporti tra Alpi e Appennino
No full textThe Priabonian and Rupelian successions that crop out in the Tertiary Piedmont Basin (TPB, NW Italy) and in the epi-Ligurian Basin (Northern Apennines) are part of a large episutural basin formed along the inter nai margin of the Western Alps after the Ligurian or Mesoalpine collisional event. This basin, referred to herein as the Tertiary epi-Mesoalpine Basin (TEMB), is the counterpart of the classic "trilogie priabonienne" ofL. Moret (Cal caires Nummulitiques, Marnes Bleues, and Gres d'Annot) in the external margin of the Western Alps (Chaines sub alpines). The TPB is the marginai portion of the TEMB recording a very complex synsedimentary tectonic evolu tion which involved the reactivation of Mesoalpine thrusting along the Sestri-Voltaggio, the Villalvernia-Varzi-Ot tone and the Monferrato fronts. The TPB succession can be subdivided into five informai stratigraphic units (from base to top: Pizzo d'Oca, Rio Trebbio, Molare-Borbera, Valla-Persi and Monastero units) bounded below and above by regionally extensive upper Eocene (M. Piano Mari) and upper Oligocene (Rocchetta Formation and Rigoroso Mari) mudstone units. These mudstone units are thought to record periods of crustal inflection associateci with the Mesoalpine and the eariy Apenninic phases of thrusting respectively. The sedimentary and tectonic evolution of the TPB includes the following six main stages. (l) Bartonian and Priabonian transgression associateci with thrust-re lated subsidence and followed by the deposition of Priabonian turbidites (Pizzo d'Oca Unit); this stage is only re corded on top of internai Alpine units (Ligurides). The transgression is thought to be related to a regional or glo bal sea level rise that affected both the Alpine and the Pyrenean-Provençal domains. The turbidites of the Pizzo d'Oca Unit were probably fed by the Corsica and Sardinia massifs, suggesting that the Alpine system was stililarge ly submerged at the end of the Mesoalpine Phase of thrusting. (2) Thrusting of the Valtri Group onta internai Al pine units (Ligurides) and their eariy TEMB cover (Marne di M. Piano, Pizzo d'Oca and Rio Trebbio units). Dur ing this phase, the Sestri-Voltaggio line was apparently reactivated as a transpressive zone. From the end of this phase (Ligurian Phase II) onward, the Valtri Group acted as a relative "high" during sedimentation. (3) Extensional tec tonics related to the opening of the Balearic Basin concomitantly with (4) the depositian of thick successions of fiood dominated, alluvial and shallow-marine conglomerates and sandstones grading upward into bioturbated and fossi liferous mudstones. Contrary to previous interpretations, these transgressive strata (Molare-Borbera Unit) are char acterized by a depositional setting and palaeocurrent directions delineating a transgression from the south (Balear ic Basin) and Alpine source areas located in the north. These Alpine units undergoing subaerial erosion are related to thrusting of stage (2). (5) Tectonic inversion of the previous extensional setting resulting into the cannibalization of the transgressive deposits of stage (4) and their resedimentation into small, fault-bounded troughs through south eriy-derived gravity flows. This stage, recorded by the Valla-Persi Unit, leads to basin inversion and the ensuing for mation of rapidly subsiding basins in the north. (6) Thick accumulations of turbidites (Monastero Unit) followed by regional drowning and basin starvation (Rocchetta Formation and Rigoroso Mari). This final stage is thought to record the inflection of the Adria plate and the beginning of the Apenninic wedge. The external portion of the TEMB is the M. Piano-Ranzano Basin of the Northern Apennines, entirely lying on internai Alpine units (Ligurides). Part of an intermediate domain between the M. Piano-Ranzano Basin and the TPB is stili preserved in the eastern sec tor of the latter, indicating an area of substantial uplift ("Antola High") associateci with the reactivation of the Vil lalvernia-Varzi-Ottone front during the Ligurian Phase II. The originai relations between this intermediate sector and the M. Piano-Ranzano Basin were completely obliterated by subsequent thrusting and subaerial erosion along the Villalvernia-Varzi-Ottone front. Although deposited in a permanently deep-marine environment and therefore of more difficult interpretation, the turbidite deposits of the Ranzano Sandstone can be cleariy subdivided into un conformity-bounded units which are correlateci herein with the main evolutionary stages of the TPB. Spectacular chaotic units (Specchio Unit) record renewed thrusting associateci with the tectonic inversion of the TPB (stage 5; Ligurian Phase III). Detailed correlatian patterns of selected outcrop areas show facies and thickness changes of turbidite strata produced by virtually continuous structural deformation. The Priabonian and Rupelian strata of the TEMB pose a series of problems involving the boundary between the Alps and the Apennines. Since they predate the late Oligocene and Neogene foredeeps of the Apennines, these sediments are an epi-Mesoalpine succession and have no temporal and spatial relations with the epi-Ligurian Basin of the Northern Apennines, a younger basin de veloped on top of Ligurian thrust sheets already involved in an Apenninic wedge. The TEMB is actually a transi tional and stili pooriy understood feature between the Mesoalpine Phase of deformation and the beginning of the Apenninic wedge with its associateci foredeeps. Much of the story and significance of the TEMB is thus probablyhidden in the sub-Ligurian Canetolo Basin, i.e. an equally poorly understood palaeogeographic and tectonic domain, originally separating the Ligurian Basins from the Tuscan Realm
Deltaic, mixed and turbidite sedimentation of ancient foreland basins
No full textThe marine fill of ancient foreland basins is primarily recorded by depositional systems consisting of facies and facies associations
deposited by a variety of sediment gravity flows in shallow-marine, slope and basinal settings. Tectonism and climate were apparently the
main factors controlling the sediment supply, accommodation and depositional style of these systems. In marginal deltaic systems,
sedimentation is dominated by flood-generated hyperpycnal flows that build up impressive accumulations of graded sandstone beds in front
of relatively small high-gradient fan-deltas and river deltas. During periods of tectonically forced lowstands of sealevel, these systems may
commonly shift basinward to shelfal and slope regions. Instability along the edges of these lowstand deltas and sand-laden hyperpycnal flows
generate immature and coarse-grained turbidite systems commonly confined within structural depressions and generally encased in distal
delta-front and prodeltaic deposits. Because of the close vertical and lateral stratigraphic relations between deltaic and turbidite-like facies,
these marginal systems are herein termed ‘mixed depositional systems’. They are very common in the fill of foreland basins and represent the
natural link between deltaic and basinal turbidite sedimentation.
Basinal turbidite systems form in deeper water elongate highly subsiding troughs (foredeeps) that developed in front of advancing thrust
systems. The impressive volumes of sheet-sandstones that form the fill of these troughs suggest that basinal turbidite systems are likely to
form following periods of dramatic tectonic uplift of adjacent orogenic wedges and related high-amplitude tectonically-forced sealevel
lowstands. In such deep basinal settings, sediment flux to the sea is dramatically increased by newly formed sediment in fluvial drainage
basins and the subaerial and submarine erosion of falling-sealevel deltaic deposits generated during the uplift. Turbidity currents are very
likely to be mainly triggered by floods, via hyperpycnal flows and related sediment failures, but can fully develop only in large-scale
erosional conduits after a phase of catastrophic acceleration and ensuing bulking produced by bed erosion. This process leads to deepening
and widening of the conduits and the formation of large-volume highly efficient bipartite currents whose energy dissipation is substantially
reduced by the narrow and elongate basin geometry. These currents can thus carry their sediment load over considerable distances down the
basin axis
Delta-front associations of ancient flood-dominated fluvio-deltaic systems
No full textAncient flood-dominated fan-delta and river-delta systems of tectonically-active basins can be viewed as essentially small and immature fluvial systems (in the sense of Schumm, 1977) with relatively high-elevation catchment basins, short and high-gradient transfer zones, and marine depositional zones where transport and deposition are dominated by hyperpycnal flows. The delta-front deposits of these ancient systems are represented by facies and facies associations whose stratigraphic and sedimentological importance has been largely overlooked in previous literature. Both fan-delta and river-delta systems contain a common and very distinctive terminal depositional element consisting of sharp-based and parallel-sided, graded sandstone beds commonly containing HCS. These sediments, herein termed "flood-generated delta-front sandstone lobes", form impressive sedimentary accumulations in many basins worldwide. Commonly mistaken for storm-dominated nearshore and shelfal deposits, these sandstone lobes probably represent the most genuine expression of fluvial-dominated delta-front sedimentation.
In ancient river-delta systems, river-mouth deposits show a great variability in terms of geometry and facies types, essentially recording the locally prevailing conditions ranging from extensive erosion and sediment bypass to deposition of the entire sediment load carried by sediment-laden stream flows entering seawaters.
Flood-related processes are intrinsically catastrophic and, as such, under-represented in modern settings. It thus appears that ancient flood-dominated fluvio-deltaic systems cannot be described and interpreted following current sedimentological models for fluvial and deltaic sedimentation. Actually, these models are largely derived from modern depositional environments dominated by "normal" fluvial and marine processes. There are, on the other hand, impressive similarities between ancient flood-dominated fluvio-deltaic systems and turbidites - another category of catastrophic deposits which is under-represented in modern basins. Comparing facies and processes of these two groups of sediments deposited by density currents can provide significant insight into both types of sedimentation
THE TERTIARY PIEDMONT BASIN
No full textAs the reader will soon realize going
through the following pages, the TPB is a very
complex feature, which, despite its
importance, is still poorly known and
understood. The purpose of these preliminary
notes is simply that of introducing the
participants of the field trip to the general
stratigraphic and depositional setting of the
basin within which the visited exposures can
be easily framed in terms of time-equivalent
stratigraphic units of basinwide extent
Nuovi dati per l’interpertazione stratigrafico-deposizionale dell’Oligocene superiore e Miocene inferiore nel Bacino Terziario Piemontese
No full textAtti Riunione Annuale Gruppo Informale di Sedimentologi
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
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