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Facies and architecture of a sand-rich turbidite system in an evolving collisional-trench basin: a case history from the upper Cretaceous-Palaeocene Gottero system (Nw apennines)
Full text linkThis study documents the main depositional elements of a dynamically-controlled sand-rich deep-water turbidite system (Upper Cretaceous–Palaeocene Gottero system, north-west Italy). The large exposures and the wide range of facies and deep-water sub-environments recognised, ranging from proximal channels, unconfined proximal and distal lobes and confined basin plain deposits make this an instructive case study to investigate the spatial-temporal relationships between fan features (channels and lobes) and confined to ponded basin-plain deposits developed in a trench-fill basin. The study focus on stratigraphic and palaeo-environmental reconstruction of the Gottero system in the western sector of the basin. Bed types, facies associations and depositional sub-environments are described in main outcrop locations and used to feed a comprehensive bed-scale database. A coherent stratigraphic framework of the system is proposed for the first time, linking its stratigraphic evolution with the collisional-trench context of the Ligurian units during the Upper Cretaceous-Palaeocene. It includes a first stage in which the Gottero was a prograding extensive basin-floor fan developed in a relatively unconfined setting (Gottero 1 and 2), and a second stage in which the system deepens and got progressively confined and segmented in multiple distal depocentres, dominated by sheet-like high magnitude events, meanwhile the proximal area forms a series of fan elements which display an overall retrograding trend (Gottero 3). The basin fill terminates with the deposition of the Giaiette mass-transport complex interepreted to represent the final collapse of the growing Ligurian accrectionary wedge
Cryptic delamination beneath distal hybrid event beds: evidence for local substrate entrainment
No full textHybrid event beds (HEBS) are increasingly recognised as an important component of the stratigraphy of many deepsea fan and sheet systems. Previous models have attributed their origin to vertical and/or longitudinal segregation of co-genetic turbidite and debritic flows in a downcurrent direction, triggered by mud acquisition in up-dip channels or channel-lobe transition zones.
Sedimentological analysis of the deep-water Cretaceous-Paleocene Gottero Sandstone (NW Apennines, Italy) has revealed large substrate delamination features at the bases of mudclast-rich HEBs in the distal sector of the basin. The delamination features are generally bedding-parallel and can be shallow (15–20 cm deep and few 10s of meters wide) or deep (c. 1–2 m deep and several hundred meters wide). Such features can remain completely undetected without a careful sedimentological analysis and bed by bed correlations, and the minimum amount of stratigraphy removed can be estimated only in a few cases where at least part of the original stratigraphic succession is preserved laterally. The deepest features are overlain by thick hybrid event beds containing large rafts derived from the underlying substrate and composed of mudstone and intervening thin sandstone beds, passing rapidly along both downstream and lateral facies tracts into chaotic or mud-clast-rich HEB debrites. Similar bed types are present in other deep-water systems (Castagnola, Marnoso Arenacea, Ventimiglia flysch, Ross Formation), usually associated with more conventional HEB types. However, their significance and association with substrate delamination has not been demonstrated before. The field observations suggest that in the Gottero system incorporation of muddy substrate occurred when dense sandy flows were able to extend sand injections into the shallow substrate and detach large slabs, carrying them for short distances before they broke up due to sand injection and internal shearing. The substrate entrainment was therefore not due to turbulent processes that could not have picked up and carried such large rafts. Remnants of undetached sea floor ‘flaps’ are only occasionally preserved. Similar process at smaller scale may have accompanied the widening of tiered down-cutting surfaces seen elsewhere in the Gottero and these may have contributed smaller mudclasts to down-dip HEBs. An angular gradient change between the proximal fan-lobe area and the distal basin plain sectors, possibly accentuated by distal basin confinement, could have promoted substrate delamination and the development of raft-bearing and mudclast-rich hybrid event beds in this and other basins
Bed by bed correlations and lateral variability in hybrid event beds in the Ramaceto area (Gottero Sandstone, northern Apennines, Italy)
No full textTowards a classification of hybrid event beds
No full textHybrid event beds (HEBs) are a type of deep-water sediment gravity flow deposit comprising a basal clean (H1) and/or banded (H2) sandstone overlain by a muddier sandy facies (H3) emplaced during the same transport event. They generally have a tabular geometry but an internal complexity in terms of relative thickness and texture of the component divisions. HEBs are increasingly recognised in outcrop and in hydrocarbon reservoirs, requiring an improved understanding of their textural make-up, association, context and impact on reservoir properties.
Although HEBs share the described common characters that allow them to be differentiated from ‘classic’ turbidites, observations from a range of sedimentary basins show great variability in their sedimentological character. The texture of the relatively mud-rich H3 division and the size and shape of substrate clasts within it are key feature for classification and process interpretation. Two important and recurring bed associations are identified: (1) a range of commonly thick beds in which the H3 division can include very large substrate slabs and blocks, evidence of extensive autoinjection and clast break-up, and dense mudclast concentrations, all set in a sandstone with elevated interstitial clay. This association typically is found in outer fan and confined sheet systems in a downdip position. (2) beds in which H3 divisions are characterised by high levels of dispersed clay, floating mudstone clasts and matrices that are enriched in hydraulically-fractionated components (mica, organic matter, clay flocs). Beds with thin H3 divisions typically pass down-dip to those in which H3 is expanded. This association is found in fan lobe successions where it can alternate with turbidites. The two associations are interpreted to reflect different modes of flow transformation. In the first case, the rafts and chaotic textures are related to local substrate delamination processes that culminated in the formation of a linked cohesive debris flow because of intense internal shearing and clast disaggregation. The second association formed by mud entrainment at channel mouths, proximal lobe locations or flow expansion points and developed through progressive longitudinal flow transformation and rapid deceleration and may include deposition from transitional flows
Hybrid event beds in the Miocene Cilento flysch and Cretaceous-Palaeocene Gottero fan : insights into short-length lateral facies variability in event bed make up
No full textCoalesced 3D scours on the base of a hybrid event bed from the Gottero Sandstone, NW Italy
No full textErosion beneath sediment gravity flows can determine patterns of bed amalgamation and hence sand connectivity. Where significant clay is incorporated in the flow, this may impact on subsequent flow dynamics down-dip. Evidence for scouring beneath turbidites is commonly seen in outcrops, mainly in vertical profile or on limited bedding plane exposures where small-scale (cm to m-scale) sole structures are well documented. The presence of broader scour features is also often inferred on the basis of erosive steps although the 3D geometry of such features is generally unclear as it is rare to be able to inspect large-scale (10-100s m scale) bedding plane exposures. The Cretaceous-Palaeocene Gottero Sandstone on Mount Ramaceto, NW Italy provides one such example. Here an overturned syncline provides a spectacular inverted bed base on which a shallow (up to 15 cm) but extensive (100s m2) scour field is preserved. This was formed beneath a flow that emplaced a 2.3 m thick sheet-like hybrid event bed that can be correlated laterally for up to four kilometres in what was a relatively distal setting.
The scour field comprises a composite erosional feature up to 150 m wide and at least 40 m long. It is made up of a terraced surface reflecting three levels of substrate erosion. The shallowest level is covered by small-scale grooves and flutes and is cut by larger elongate scours that coalesced to excavate the sea floor in patches down to a mid-level bed-parallel surface. The latter is then further incised by the deepest scours. Individual scours (40-150 cm across and 1-5m long) have distinctive asymmetric cross-sections with both inclined and undercut lateral margins. The undercut margins are associated with mudclast detachment.
The extent of erosion given the distal setting is curious and implies hybrid flow development could be triggered or enhanced by clay entrainment in relatively distal settings. Distal erosion may be promoted by enhanced turbulence during the early stages of flow transformation, as suggested by some experimental work (see Baas et al. 2011, Sedimentology 58 1953-1987). As scour coalescence results in mainly bedding parallel terraces, it can easily be overlooked in vertical sections
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
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