1,721,064 research outputs found
Predicting early deterioration or improvement in ischemic stroke by transcranial Doppler - Response
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How to assess acute cerebral ischemia
No full textThere are different approaches to the assessment of acute stroke. Its causes, its severity, and/or its final prognosis may be investigated. The traditional approach is anatomoclinical. It is basically limited to finding out if the lesion is a hemorrhage or an ischemia, and its location. This approach is derived from and supported by the fact that acute stroke is still without a valid therapy. In our opinion, not stroke but individual patients presenting with stroke should be treated. The pathophysiology of the individual stroke should be investigated by means of new techniques: magnetic resonance, emission tomography, and transcranial Doppler. These new techniques will be important in the future, making it possible to create effective therapeutic strategies, designed for treating a particular subgroup of patients, as in the case of fibrinolytic agents. The main aspects of these new techniques for evaluating acute ischemic stroke have been reviewed in this article
Trace fossils in seep-impacted sediments as a tool to decipher the origin of fine-grained intervals of the Marnoso-arenacea turbidite succession (Miocene, northern Apennines, Italy)
No full textThe Marnoso-arenacea turbidite succession outcropping in northern Italy is one of the most studied deep-water
systems worldwide due to its excellent exposure. Despite the well-established sedimentology of the arenaceous
succession, the origin of fine-grained intervals within the Marnoso-arenacea Fm is reconsidered in the light of
methane-rich fluid expulsion, in particular as seep-carbonates are present. Fine-grained intervals are marked
by limited vertical and lateral extent, in the order of 102 m and 103 m respectively, and are often associated
with small-scale sediment deformation. In this study, we conduct a detailed sedimentological and stratigraphic
investigation of the well-exposed Prati Piani fine-grained interval (Serravallian in age) with particular focus on
the characterization of trace fossils and seep-carbonates. Trace fossils interpreted as Thalassinoides are widespread
throughout the interval and form a complex network testifying long-lasting burrowing activity of decapod
crustaceans. Seep-carbonates crop out at different stratigraphic levels and form meter-sized blocks with
δ13C from−33.2‰ to−18.2‰. The occurrence of aragonite cements and fossil chemosymbiotic fauna indicates
episodic carbonate precipitation close to the paleo-seafloor. Although crustaceans have been frequently reported
grazing microbial mats atmodern seeps and leaving a 13C-depleted isotopic signature in trace fossils, in our study
we found only one slightly depleted δ13C value (−9.5‰,) allowing us to exclude preferential authigenesis. Moreover,
burrows are filled by detrital fine-grained sediments and hemipelagic micrite that may have diluted the
methane-related signature. The association between in situ seep-carbonates and well-preserved trace fossils is
of use to interpret the interval as formed by fine-grained sedimentation draping a thrust-related anticline. In
this model, the stratigraphically- and laterally-confined deformed zones affecting the Prati Piani interval reflect
in-situ soft-sediment deformation and small-scale slumping induced by fluid seepage along the ridge, consistent
with present-day observations from several continental margins worldwide.
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Evidences for Paleo-Gas Hydrate Occurrence: What We Can Infer for the Miocene of the Northern Apennines (Italy)
Full text linkThe occurrence of seep-carbonates associated with shallow gas hydrates is increasingly
documented in modern continental margins but in fossil sediments the recognition of gas hydrates
is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and
geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to
investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such
as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics
and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly
oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by
the large dimensions of seep-carbonate masses and by the association with sedimentary instability
in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up
to +6h that are indicative of a contribution of isotopically heavier fluids released by gas hydrate
decomposition. The calculation of the stability field of methane hydrates for the northern Apennine
wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas
hydrates in the upper few tens of meters of sedimentary column
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