1,721,065 research outputs found
Slope fans and aprons dominated by supercritical bedforms: topographic and feeding system controls (Southeastern Tyrrhenian Sea)
No full textIn the marine environment, turbidite supercritical bedforms have been widely reported from channel-axis and overbank wedges. On the contrary, their dominance in the make-up of fans and apron, apart from local areas such as channel mouths, is at present not recognized. However, since it has been postulated that turbidity currents reach the supercritical conditions for slope > 0.5°, submarine slopes should contain abundant supercritical flow deposits. Here, we provide a review of different types of slope fans and aprons dominated by supercritical bedforms, based on examples from the modern seafloor. We compare depositional elements located in different intraslope basins of the Tyrrhenian Sea, through high-resolution bathymetry, chirp subbottom section and, where available cores. The variable geological context results in axial and transvers slope fans with highly variable sizes (few to tens of kilometres) and geometries, dependent upon the erosive and/or depositional processes involved, as well as the seafloor topography of the area. In particular, we have recognized two types of lobe-shaped deposits characterized by supercritical bedforms: channel-attached fans and detached aprons. The first ones are connected to a canyon-channel system and develop on slope gradients of 0.5° to 1.2°, display small-scale bedforms (wavelength of about 150 m and height < 10 m), with upslope asymmetric or symmetric cross-sections, interpreted as cyclic steps and antidunes. According to the amplitude of the reflections, cores, and to the bedform aspect ratio, the channel-attached fans are interpreted to be composed of coarse-grained sediments. Our examples highlight that cyclic steps and antidunes dominate the channel-attached fans both in axial and lateral portion while scours mark topographic changes such as breaks in slope or laterally confined areas. Detached aprons develop from the un-incised shelf edge on steep slopes of about 1.2° to 3° and are composed by large-scale bedforms (wavelength of about 500 m and height of about 5 m) mainly upslope asymmetric, associated with cyclic steps. The low amplitude of the seismic reflections suggests the fine-grained nature of the aprons. This study shows that there are significant differences in the distribution and character of supercritical bedforms in slope settings according to the type of feeding system, the degree of flow confinement and the seafloor topography. The analysis of the downslope evolution of turbidity currents, and of the character of associated bedforms in deep-water systems can contribute new perspectives to refine our models of deep-sea depositions
Downslope evolution of supercritical bedforms in a confined deep-sea fan lobe, Amantea Fan, Paola Basin (Southeastern Tyrrhenian Sea)
No full textThe sedimentology of upper flow regime bedforms represents an important research topic at the present. Deposits interpreted as those of supercritical flows are widely recognized in modern fan systems, but their recovery is challenging. Most of the sedimentological information has come from channel thalwegs but supercritical bedforms are also frequently downslope from the channel mouths. Such an environment has been identified in the Paola basin, where erosive and depositional cyclic steps have been imaged and identified in a sandy submarine lobe of the Amantea Fan. High-resolution sub-bottom profiles provide insight into the bedform internal architecture and their relationships with a frontally-confining ridge. For the first time, supercritical bedforms in a submarine lobe have been interpreted in two distinct positions: in the scour of an erosional cyclic step and in the stoss side of a depositional cyclic step. Coarse to medium-grained massive sand with flame structures, indicating rapid sediment fall-out and frequently associated with the occurrence of hydraulic jumps, has been identified in the scour and at the toe of the ridge. The latter represents an example of topographically induced hydraulic jumps driven by a frontal confinement. Top-cut-out medium to fine sands with tractive structures have been interpreted as the deposits related to the stoss side of a cyclic step or small-scale antidune superimposed on the cyclic step surface. The presented data broaden the understanding of the range of processes that are driven by the interaction between turbidity currents and seafloor topography and the dip of the slope. The recognition that topography influences the density structure and the degree of criticality of the flow and, consequently, the morphodynamics and facies of the relative deposits may help to explain sediment distribution and improve depositional models of fan lobes in confined settings
Downslope evolution of supercritical bedforms in a confined deep-sea fan lobe, Amantea Fan, Paola Basin (Southeastern Tyrrhenian Sea)
Full text linkThe sedimentology of upper flow regime bedforms represents an important research topic at the present. Deposits interpreted as those of supercritical flows are widely recognized in modern fan systems, but their recovery is challenging. Most of the sedimentological information has come from channel thalwegs but supercritical bedforms are also frequently downslope from the channel mouths. Such an environment has been identified in the Paola basin, where erosive and depositional cyclic steps have been imaged and identified in a sandy submarine lobe of the Amantea Fan. High-resolution sub-bottom profiles provide insight into the bedform internal architecture and their relationships with a frontally-confining ridge. For the first time, supercritical bedforms in a submarine lobe have been interpreted in two distinct positions: in the scour of an erosional cyclic step and in the stoss side of a depositional cyclic step. Coarse to medium-grained massive sand with flame structures, indicating rapid sediment fall-out and frequently associated with the occurrence of hydraulic jumps, has been identified in the scour and at the toe of the ridge. The latter represents an example of topographically induced hydraulic jumps driven by a frontal confinement. Top-cut-out medium to fine sands with tractive structures have been interpreted as the deposits related to the stoss side of a cyclic step or small-scale antidune superimposed on the cyclic step surface. The presented data broaden the understanding of the range of processes that are driven by the interaction between turbidity currents and seafloor topography and the dip of the slope. The recognition that topography influences the density structure and the degree of criticality of the flow and, consequently, the morphodynamics and facies of the relative deposits may help to explain sediment distribution and improve depositional models of fan lobes in confined settings
Benthic foraminifera from a recent, shallow-water hydrothermal environment in the Aeolian Arc (Tyrrhenian Sea)
No full textBenthic foraminiferal assemblages from sediments around active or recently active hydrothermal vents in the Aeolian Arc
have been investigated in four areas with different hydrothermal mineralization and seafloor exhalative activity at depths
between ~60 and ~300 m. Active hydrothermal spots were distinguished from the surrounding sediments by direct observations
by a Remotely Operated Vehicle (ROV) and subsequent seafloor sampling. Samples were taken at different water depths and are
characterized by a number of mineralogies reflecting the changing temperature of the hydrothermal fluids.
Overall, benthic foraminifera are absent from sites with high-temperature hydrothermal emissions, and their distribution at
sites of low-temperature emissions is very patchy, depending on the physical and/or chemical conditions reflecting differences
in temperature and composition of the emitted fluids. In the Secca del Capo area, which is free from recent emission activity, the
benthic foraminiferal population is indicative of a normal marine environment, with Globocassidulina subglobosa, Cassidulina
crassa, and Gavelinopsis lobatulus. In the Basiluzzo, Secca dei Pesci, and Panarea areas, which are characterized by different
degrees of hydrothermal activity, three distinct assemblages have been recognized. The first assemblage is dominated by
Ammodiscus catinus, Glomospira charoides, and Glomospira gordialis and indicates hydrothermal influence. The second
assemblage, with Lobatula lobatula, Asterigerinata mamilla, Rosalina globularis, and Quinqueloculina spp. as main constituents,
indicates a seagrass environment influenced by diffuse emissions. The third assemblage with abundant A. catinus,
Ammoglobigerina globigeriniformis, G. gordialis and Haplophragmoides canariensis suggests low pH conditions resulting
from acidic hydrothermal emissions, leading to the dissolution of calcium carbonate tests
Benthic foraminifera from recent shallow-water hydrothermal emissions in the Aeolian Arc (Tyrrhenian Sea)
No full text
Volcanological and petrological evolution of Marsili seamount (southern Tyrrhenian Sea).
No full textMagma Plumbing System at a Young Back-Arc Spreading Center: The Marsili Volcano, Southern Tyrrhenian Sea
No full textAlthough spreading rate is commonly taken as a proxy for decompression mantle melting at
mid-ocean ridges (MORs), magmatism at back-arc spreading centers (BASCs) is further influenced by the
subduction-related flux melting of the mantle. These regions consequently show a diversity of crustal structures,
lava compositions, and morphologies not typically found in MORs. Here we investigate the crustal
plumbing system of the small-scale, Marsili back-arc spreading center of the Southern Tyrrhenian Sea using
plagioclase data from a wide spectrum of lavas (basalts to andesites) dredged from its summit and flanks.
We employ petrological modeling to identify the plagioclase populations carried in the individual lavas, allocate
them to plausible magmatic components present within the plumbing system, and trace the processes
occurring during magma ascent to the surface. The properties of the system, such as mush porosity and
abundance of the melt bodies, vary from one magma extraction zone to another along the BASC, evidencing
the local variability of melt supply conditions. The plagioclase crystals document a range of relationships
with the host lavas, indicating magma extraction from a composite, vertically extensive mush and melt-lens
system resembling that of MORs. At the same time, however, in small BASCs, such as in the case of the Marsili
Basin, crustal accretion and resulting morphology are significantly influenced by the three-dimensional
setting of the basin margins. This is an important deviation from the conventional model based on the linear
continuity and essentially two-dimensional framework of MORs
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