1,721,032 research outputs found
Erosion of Tortonian phosphatic intervals in upwelling zones. The role of internal waves
No full textDuring the Miocene, the upwelling is assumed to be important in the formation of many Mediterranean phosphate deposits in carbonate platform successions. There are different types of upwelling mechanisms such as equatorial upwellings, ice-edge upwellings and coastal upwellings. The carbonate platforms are mainly affected by wind-driven coastal upwelling systems. During upwelling season, the seawater in coastal areas is strongly density stratified and the permanent pycnocline rises inshore forming an inclined frontal layer. The liaison between upwellings and internal waves is widely documented in the literature. Internal waves result from perturbations of the hydrostatic equilibrium, where balance is sustained between the force of gravity and buoyant restoring force. Many perturbations of the pycnocline can propagate as an internal wave. In a coastal upwelling, a key role for wave propagation is played by permanent pycnocline. The run-up swash currents develop during the break of internal waves and produce erosional processes. In particular, the backwash return flow may induce the erosion of seafloor sediments and transport these sediments downslope as bedload. Erosion of phosphate-rich intervals has been extensively documented. The deposition of gravity-flow sediments is followed by intervals of non-deposition, incipient lithification, phosphogenesis and erosion. In this work, we evaluate the role of internal waves in the formation of the resedimented phosphate-rich intervals characterising the basal portion of the hemipelagic Orbulina marls. These marls are deposited on the low-angle Latium-Abruzzi carbonate ramp and represent deposition in a foreland basin during the initial stages of evolution of the Central Apennine Belt during the early Tortonian age
Black Coral Distribution in the Italian Seas: A Review
Full text linkAntipatharian corals are important structural and complex members of benthic communities inhabiting the Italian seafloor. In this study, the distribution of black corals in Italy is reported and mapped for the first time. This review has permitted the identification of occurrences of such vulnerable marine ecosystems along the Italian coasts in a bathymetric range of 42 m to 790 m. Black corals appear to be most conspicuous and widely distributed in the mesophotic zone (from around 60 to 300 m depth), with a major occurrence on the rocky bottom and shoals. This review also highlights that these communities suffer direct damage from anthropogenic impacts (fishing activity and lost garbage). Finally, this study provides evidence that the reported Italian submarine sites associated with the occurrence of black corals probably represent only a small portion of their real distribution. This finding urges the need to increase monitoring efforts to support the protection and the conservation of these pristine species assemblages
On the role of hemodynamics in predicting rupture of the abdominal aortic aneurysm
No full textHemodynamics plays a crucial role in the growth of an abdominal aortic aneurysm (AAA) and its possible rupture. Due to the serious consequences that arise from the aneurysm rupture, the ability to predict its evolution and the need for surgery are of primary importance in the medical field. Furthermore, the presence of intraluminal thrombus (ILT) strongly affects the evolution of the pathology. In this study, we analyzed the influence of hemodynamics on the growth and possible rupture of AAAs. Numerical investigations of pulsatile non-Newtonian blood flow were performed in six patient-specific AAAs reconstructed from diagnostic images, having different sizes and shapes, and with or without ILT. Wall shear stress and vorticity distribution in the bulge and their evolution during the cardiac cycle were analyzed. The results indicate that blood flow dynamics acts synergistically with atherosclerotic degeneration in the development of the disease. The high surface complexity and tortuosity of the aneurysms significantly affect the blood motion, and the presence of inflection in the aneurysm centerline has a noticeable effect on the vortex dynamics. Links between regions of slow recirculating flows, low values of time-averaged wall shear stress, high values of oscillatory shear index, and zones of ILT deposition were found. In the absence of ILT, possible thrombus accumulation areas and consequent aneurysm growth were identified. The findings of this study highlight the importance of hemodynamics in assessing the vulnerability of the aortic wall and underline the crucial role of patient-specific investigations in predicting the rupture of individual aneurysms
The Bolognano Fm in the south-eastern sectors of Majella and correlation with the north-western domain
No full textThis work investigated the evolution of the Bolognano Fm in the southern
portion of the Majella Mountain and correlated it with the northwestern sector.
Here the Bolognano Fm overlies unconformably the Eocene deposits of the S.
Spirito Fm. The first unit is the Burdigalian Bryozoan Calcarenite, overlain by the
Hemipelagic limestone to calcareous marls Burdigalian to Langhian in age. Lastly,
the Tortonian to early Messinian interval is represented by different units. The
first unit, which unconformably overlies the hemipelagic limestone to calcareous
marls, is the Bioclastic calcarenites unit, which is fed by sediments produced
within a euphotic inner ramp and accumulated in a deep environment. Upwards,
the Marly limestones and laminated calcareous marls unit shows a mixing of
deep water and shallow skeletal components deposited in an outer ramp. Moving
southward, the Coralline algal limestone crops out, identifying a productive
middle ramp environment. Lastly, a coral limestone unit was identified, where
coral bioconstructions interfinger with seagrass meadows and ooidal shoals, in
the euphotic zone. The Marly limestone and laminated calcareous marls testify
for a deterioration of environmental conditions due to both global climate change
as well as the approaching of the Apennines accretionary wedge, which triggered
an increase of terrigenous runoff
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
Study of mass-wasting processes offshore NE Vulcano (Aeolian islands): A multidisciplinary approach
No full textVulcano is the southernmost island of the Aeolian Archipelago in the Southern Tyrrhenian Sea and represents the tip of a large stratovolcano that rises from ≈ 1000 mbsl. Its northern sector is dominated by La Fossa Caldera, whose
northeastern part lies underwater and has been deeply eroded and breached. The dismantling of the caldera rim and
infill has fed a large volcaniclastic fan in the offshore through repeated mass-wasting events. A multi-disciplinary
approach was used to infer the main sedimentary processes acting in this submarine sector through the integration of a
large dataset of marine geophysical data (multibeam, side scan sonar and seismics) and the results of sedimentological
and micropaleontological analyses of seafloor samples. Overall, the northeastern submarine flank of Vulcano is mostly covered by relatively coarse-grained volcaniclastic sediments, resulting from sediment-laden gravity flows; this high-energy sedimentary system is able to transport fine and medium sand over 1100 mbsl down to the Stromboli Canyon.
In detail, three morpho-sedimentary zones were recognized from the coastal sector to the offshore, each of them
characterized by one (or more) prevalent reworking and transport processes: the first one corresponds to the highly incised submerged prosecution of La Fossa and is characterized by rock falls/avalanches and granular inertial flows. The second zone is represented by the wide Baia di Levante Fan system, where turbiditic sedimentation prevails, whereas the third zone encompasses most part of the lower submarine flank of Vulcano and the sedimentary highs located both inside and outside the BLF system, being dominated by hemipelagic deposition
New insights on the fossil arc of the Tyrrhenian Back-Arc Basin (Mediterranean Sea)
No full textGeology, geophysics and geodynamics of the Tyrrhenian Back-Arc Basin (BAB; central Mediterranean Sea) have been studied extensively during the last 50 years. However, some topics are still open: for example, the possible migration of the volcanic arc during the Ionian subduction of the past few Ma. We improved our knowledge of the geodynamics of the Tyrrhenian BAB in the area South of the Vavilov Volcano by analyzing multibeam ba- thymetry and unpublished single-channel re ection seismic and magnetic data. Furthermore, we studied the petrology of igneous rocks as well as facies and microfaunas of carbonates dredged from the Aurelia and Augusto seamounts. The Aurelia basement is made of basalts with calc-alkaline af nity. Carbonates from the Aurelia and Augusto seamounts consist of cemented Mg-calcite biomicrite crusts rich in planktonic foraminifera not older than Early Pleistocene. Based on our results, we interpret the Augusto and Aurelia seamounts as part of the active volcanic arc seaward of the Tyrrhenian BAB in Late Pliocene–Early Pleistocene
Inizio della sedimentazione di avanfossa nella Maiella meridionale: la sezione di Fonte dei Pulcini (Taranta Peligna)
No full textI foraminiferi bentonici di due laghi costieri del Lazio meridionale. Valutazione preliminare della qualità ambientale
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