1,721,026 research outputs found
Hybrid event bed character and distribution linked to turbidite system sub-environments: The North Apennine Gottero Sandstone (north-west Italy)
No full textThis study documents the character and occurrence of hybrid event beds (HEBs) deposited across a range of deep-water sub-environments in the Cretaceous-Palaeocene Gottero system, north-west Italy. Detailed fieldwork (>5200m of sedimentary logs) has shown that hybrid event beds are most abundant in the distal confined basin-plain domain (>31% of total thickness). In more proximal sectors, hybrid event beds occur within outer-fan and mid-fan lobes (up to 15% of total thickness), whereas they are not observed in the inner-fan channelized area. Six hybrid event bed types (HEB-1 to HEB-6) were differentiated mainly on basis of the texture of their muddier and chaotic central division (H3). The confined basin-plain sector is dominated by thick (maximum 957m; average 215m) and tabular hybrid event beds (HEB-1 to HEB-4). Their H3 division can include very large substrate slabs, evidence of extensive auto-injection and clast break-up, and abundant mudstone clasts set in a sandy matrix (dispersed clay ca 20%). These beds are thought to have been generated by highly energetic flows capable of delaminating the sea floor locally, and carrying large rip-up clasts for relatively short distances before arresting. The unconfined lobes of the mid-fan sector are dominated by thinner (average 038m) hybrid event beds (HEB-5 and HEB-6). Their H3 divisions are characterized by floating mudstone clasts and clay-enriched matrices (dispersed clay >25%) with hydraulically fractionated components (mica, organic matter and clay flocs). These hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport. Although there is a tendency to look to external factors to account for hybrid event bed development, systems like the Gottero imply that intrabasinal factors can also be important; specifically, the type of substrate available (muddy or sandy) and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts
HYBRID EVENT BEDS GENERATED BY LOCAL SUBSTRATE DELAMINATION ON A CONFINED-BASIN FLOOR
No full textThe outer parts of deep-water fans, and the basin plains into which they pass, are often described as areas where erosion is negligible and turbidite systems have net aggradation. Nevertheless, sedimentological and stratigraphic analysis of outer-fan-lobe and confined-basin-plain deposits in Cretaceous-Paleocene Gottero Sandstone (NW Italy) has revealed extensive but cryptic bedding-parallel substrate-delamination features at the base of many sheet-like event beds. These comprise a variety of shallow but wide scour structures showing evidence of lateral expansion by sand injection. The scours commonly occur at the base of beds made up of a basal clean sandstone overlain by argillaceous sandstone containing abundant mudstone clasts and locally large substrate rafts (up to 20 meters long). These strata are interpreted as a type of hybrid event bed. Field observations suggest that mud-clast entrainment occurred by delamination at the base of dense sandy flows. The large rafts, in some cases only partly detached, were incorporated in the flows locally and then carried for short distances (hundreds of meters to a few kilometers) before partly disaggregating and undergoing deformation due to internal shearing. The development of such features may be common in flat and/or confined basin settings where high-volume flows interact with a cohesive and well layered substrate (e.g., muddy outer fans or confined or ponded basins with thick mudstone caps). Delamination is therefore suggested as an alternative mechanism leading to the formation of hybrid event beds following local substrate entrainment on the basin floor as opposed to on more remote slopes and at channel-lobe transition zones
Neoichnology of a barrier-island system: The Mula di Muggia (Grado lagoon, Italy)
No full textBarrier-islands are common landforms and biodiverse habitats, yet they received scarce neoichnological attention. This gap is tackled by studying the Mula di Muggia barrier-island system (Grado lagoon, Italy), focusing on morphology, ecology and ethology of individual traces. The following incipient ichnotaxa are identified: Archaeonassa, Arenicolites, Bergaueria, 'diverging shafts', Helminthoidichnites, Lockeia, Macanopsis, Monocraterion, Nereites, Parmaichnus, Polykladichnus, Skolithos, Thalassinoides and 'squat burrows'. Vertebrate (Avipeda-/Ardeipeda-like, Canipeda) and invertebrate tracks ('parallel furrows') are also described.For each ichnotaxon, tracemaker and behavior are discussed, together with their position with respect to sediment barriers. Results suggest that sediment barriers impose a sharp contrast in terms of ichnological composition. Back-barrier is dominated by branched burrows (i.e. Thalassinoides, Parmaichnus), while the fore-barrier presents vertical and U-shaped burrows (Arenicolites, Skolithos). The environmental conditions of the back-barrier show that low-oxygen substrates favor intense bioturbation, provided that the water column is sufficiently oxygenated
A multidisciplinary study of ecosystem evolution through early Pleistocene climate change from the marine Arda River section, Italy
No full textThe Arda River marine succession (Italy) is an excellent site to apply an integrated approach to paleoenvironmental reconstructions, combining the results of sedimentology, body fossil paleontology, and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early Pleistocene climate change and tectonic activity. The succession represents a subaqueous extension of a fluvial system, originated during phases of advance of fan deltas affected by high-density flows triggered by river floods, and overlain by continental conglomerates, indicating a relative sea level fall and the establishment of a continental environment. An overall regressive trend is observed through the section, from prodelta to delta front and intertidal settings. The hydrodynamic energy and the sedimentation rate are not constant through the section, but they are influenced by hyperpycnal flows, whose sediments were mainly supplied by an increase in Apennine uplift and erosion, especially after 1.80 Ma. The Arda section documents the same evolutionary history of coeval successions in the Paleo-Adriatic region, as well as the climatic changes of the early Pleistocene. The different approaches used complement quite well one another, giving strength and robustness to the obtained results
Influence of flow containment and substrate entrainment upon sandy hybrid event beds containing a co-genetic mud-clast-rich division
No full textIndividual sandstone beds containing a co-genetic mud-clast-rich (MCR) division are being increasingly described from the distal reaches of many deep-water fan systems. These deposits, termed hybrid event beds, are considered to record a flow whose composition and rheology changed significantly to become increasingly more argillaceous (clay-rich), MCR and turbulence-suppressed during the deposition of a single event bed. Studies of confined systems, in which gravity flows were affected by confining sea-floor topography, have documented similar deposits recording turbulence suppression in proximity to confining sea-floor topography (e.g., basin margins). In new research from a confined, contained system from the Castagnola Basin of NW Italy, lateral transects of individual sandstone beds 5 km in extent show that individual sandstone beds contain a co-genetic MCR division which is often; 1) extensive across the basin rather than localised adjacent to confining topography; 2) exhibits rapid, significant and repeated variation in depositional character over short length scales (tens to hundreds of metres), specifically in terms of the thickness of co-genetic MCR divisions and the size and abundance of clasts contained within them; and 3) exhibits variation in depositional character over larger length scales (>1 km) which is non-systematic in relation to palaeoflow direction or increasing proximity towards the counter slope of the downstream confining northern basin margin. A suite of factors within the Castagnola Basin is thought to have resulted in the deposition of these co-genetic MCR divisions whose thickness and distribution are less predictable in relation to confining sea-floor topography than those described from other confined uncontained settings. Specific factors include; 1) recent and voluminous entrainment of muddy substrate at seemingly random locations across the basin floor and their support and transport within a high sediment concentration gravity flow; and 2) containment (ponding) of gravity flows within a confined basin, which is thought to have established exten\sive and complex three dimensional flow dynamics across the basin following flow interaction with multiple basin margins. This research highlights the role of entrainment of muddy substrate and subsequent transport processes of muddy substrate for developing co-genetic MCR divisions, as well as the importance of understanding the degree of containment depositional systems experienced when considering the spatial distribution of depositional facies, and thus reservoir quality, in topographically complex settings. (C) 2015 Elsevier B.V. All rights reserved
Evolution of Crustaceans at the edge of the end-Permian crisis: Ichnonetwork analysis of the fluvial succession of Nurra (Permian-Triassic, Sardinia, Italy)
No full textDecapod crustaceans are among the most efficient ecosystemengineers of the Phanerozoic, but the path that led to their engineering success is poorly known. The Permian-Triassic continental succession of Nurra (early Cisuralian-early Middle Triassic; Sardinia, Italy) sheds light on this obscure subject, because it preserves the oldest (Roadian) fluvial Ophiomorpha and Camborygma, ascribed to ghost shrimps (Decapoda: Axiidea, Gebiidea) and crayfishes (Decapoda: Astacidea, Parastacidea), respectively. These crustacean trace fossils are part of awellpreserved ichnofauna including Arenicolites, Diplocraterion, Helminthoidichnites, Palaeophycus, Planolites, rhizoliths, Skolithos, Spongeliomorpha, Taenidium, Treptichnus, alongside an undetermined tetrapod footprint, helical burrows and Sinusichnus-like traces. In light of the abundance of crustacean trace fossils, the Cala Viola section (Roadian-Anisian) was selected for ichnonetwork analysis. This novel approach, focusing on the topology of the association relationships of ichnotaxa, revealed six ichnoassociations, i.e., Rhizohaloes, Taenidium/Ophiomorpha, Helminthoidichnites, Palaeophycus, Skolithos and Arenicolites ichnoassociations. In addition, ichnonetwork analysis shown that Camborygma and Ophiomorpha colonised adjacent, partially overlapping fluvial subenvironments, ranging from active fluvial channels to periaquatic overbanks. As the Nurra occurrences are penecontemporaneous of the astacid/thalassinid diversification (Carboniferous-Early Permian) and coeval with the appearance of crayfishes (Middle Permian), fluvial environments played an important role in the evolution of both crayfishes and ghost shrimps. The most parsimonious explanation of the observed scenario is that astacid-thalassinid diversification happened in fluvial environments between the Carboniferous and Early Permian, while ghost shrimps invaded marine environments at the Permian-Triassic boundary. In addition, ichnonetwork analysis revealed that the ichnological system simplified across the Permian-Triassic boundary, accounting for a structured Permian ecosystem and fragmented, stressed habitats during the Early Triassic. This scenario is explained by a progressive drying trend that dramatically changed the hydrological features across the Permian-Triassic boundary. This supports the crucial role of global warming in driving the end-Permian crisis and its prolonged recovery
TETRAPOD FOOTPRINT PALEOECOLOGY: BEHAVIOR, TAPHONOMY AND ICHNOFAUNA DISENTANGLED. A CASE STUDY FROM THE LOWER PERMIAN OF THE SOUTHERN ALPS (ITALY)
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The IchnoGIS method : Network science and geostatistics in ichnology. Theory and application (Grado lagoon, Italy)
No full textA new method is proposed for capturing, managing, analyzing, and displaying geographically referenced ichnological data: IchnoGIS. This approach is based on the integration of spatial, geostatistical techniques with network theory, aiming to characterize the environmental significance of recent traces. The efficiency of the IchnoGIS method is tested against a case-study: the Grado lagoon (Italy). The studied site, located within the epeiric Northern Adriatic Sea, consists of a complex mosaic of peritidal environments in a barrier-island context. Here, a diverse ichnofauna includes the following incipient ichnotaxa: Arenicolites, Helminthoidichnites, Lockeia, Macanopsis, Monocraterion, Parmaichnus, Polykladichnus, Skolithos, Thalassinoides and 'squat burrows'. Ichnofaunal distribution is described by the spatial and geostatistical tools proper of the IchnoGIS approach. Additionally, the application of network theory documents the emergence of organized structures (ichnoassociations) from interactions driven by environmental factors. Our results elucidate the role that environmental processes play in producing the complex ichnological patterns of the Grado site. In particular, emersion time, hydrodynamics, substrate firmness and microbial binding are the major control factors determining the structure and distribution of trace associations. These structuring factors are used to define a predictive model of ichnoassociation composition, providing an immediate tool for future palaeoenvironmental reconstitutions
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
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