Since about 20,000 years ago, the geography of the Earth has been profoundly modified by the gradual sea-level rise caused by the melting of continental ice sheets. Flat areas and regions ...characterized by very low gradients experienced, more than others, rapid flooding, with the progressive disappearance of vast coastal territories. Here we present a reconstruction of the late Quaternary coastline evolution of the north-western sector of the Sicilian Channel, constrained by high-resolution seismic profiles where the marker of the post-Last Glacial Maximum (LGM) marine transgression has been clearly identified and mapped. The locations of the post-LGM seismic horizon have been compared with predictions of a Glacial Isostatic Adjustment (GIA) model, which accounts for the migration of the shorelines in response to sea-level rise and for Earth's rotational and deformational effects associated with deglaciation. We have verified that most of the points mapped through seismic data interpretation fall along the palaeo-coastline that the GIA model predicts for the 21 kyrs B.P. time frame. However, the model shows a misfit in the marine sector between Mazara del Vallo and Sciacca, where the available data indicate a Quaternary tectonic uplift. The analysis of the seismic profiles provides useful constraints to current GIA models. These add on existing histories of relative sea level in the Mediterranean Sea, allowing to gain new insight into the evolution of the palaeo-geography of the region of study and of the whole Sicilian Channel since the LGM, even in areas where direct geophysical observations are not available yet. In this respect, one of the most attractive implications of the ancient coastline evolution is linked with the underwater archaeology. The sea-level rise heavily impacted the distribution of human settlements, possibly forcing site abandonment and migrations, and this is particularly relevant in the Mediterranean basin, the cradle of the western civilization. The underwater traces left by these ancient populations represent the fundamental proofs to reconstruct the early history of our precursors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Seismic reflection (2D/3D), borehole and bathymetric data are used to recognize a new gravitational complex in the Gulf of Squillace, Southern Italy, named the
Squillace Complex
. The ...complex has a NE-striking headwall connected to a basal detachment formed between Messinian evaporites and Tortonian shales. Its sense of movement changes to a W–E direction in the toe region. In plan view, the Squillace Complex is marked by the presence of sinuous and continuous seafloor scarps, just a few kilometers offshore, over an elongated morphological high. Seismic-well ties reveal that the complex was initiated in the Zanclean (~ 4 Ma) and continued its movement into the Gelasian (~ 2.1 Ma) at an average rate of 1.9 mm/year. Movement slowed down in the Calabrian (middle Pleistocene) and continued until the present day at a lower rate of 0.1 mm/year. Gravitational collapse of the
Squillace Complex
correlates with discrete contractional/transpressional events affecting the Calabrian region, which caused basin shortening and the temporary arrest of Calabrian Arc migration. These episodes resulted in tectonic uplift in the study area after 0.45 Ma (Late Pleistocene). Conversely, the complex’s slower movement recorded since the Calabrian (middle Pleistocene) is associated with slab rollback of the Ionian plate under the Calabrian Arc.
Submerged palaeo-shorelines on the central Mediterranean shelves, identified from high-resolution seismic profiles and bathymetric data, mark distinct water depths at which sea level stationed for a ...period of time during the relative sea-level rise that followed the Last Glacial Maximum (LGM). The shorelines are commonly represented by palaeo-coastal cliffs and barrier-beaches that lie today at water depths between −100m and −70m, and between −65m and −40m, in most places irrespective of the different tectonic contexts, even in the presence of significant vertical rates. These morphological features are thought to have been drowned during melt-water pulses 1A and 1B, which occurred between 15 and 10ka. The evidence presented here confirms drowned shorelines documented elsewhere at similar water depths and shows that melt-water pulses have punctuated the post-glacial relative sea-level rise with rates up to 60mm/yr. for a few centuries. The identification of morphological features related to melt-water pulses in the central Mediterranean Sea has important implications to improve our knowledge on episodes of rapid glacio-eustatic sea-level rise. This issue is critical to be able to forecast future sea-level rises in the Mediterranean, which is characterized by densely populated coasts and important coastal infrastructures.
•Palaeo-shorelines on the central Mediterranean shelves are found at distinct water depth intervals.•Palaeo-shorelines in several cases were drowned during melt-water pulse episodes.•Understanding the mechanisms causing MWPs is important to forecast future sea-level rise.
Sudden cardiac death and arrhythmia-related events in patients with non-ischaemic dilated cardiomyopathy (NICM) have been significantly reduced over the last couple of decades as a result of ...evidence-based pharmacological and non-pharmacological therapeutic strategies. Nevertheless, the arrhythmic stratification in patients with NICM remains extremely challenging, and the simple indication based on left ventricular ejection fraction appears to be insufficient. Therefore, clinicians need to go beyond the current criteria for implantable cardioverter-defibrillator implantation in the direction of a multiparametric evaluation of arrhythmic risk. Several parameters for arrhythmic risk stratification, ranging from electrocardiographic, echocardiographic, imaging-derived and genetic markers, are crucial for proper arrhythmic risk stratification and a multiparametric evaluation of risk in patients with NICM. In particular, integration of cardiac magnetic resonance parameters (mostly late gadolinium enhancement) and specific genetic information (ie, presence of
mutations) appears fundamental for proper implementation of the current arrhythmic risk stratification. Finally, a novel approach focused on both arrhythmic risk and prediction of left ventricular reverse remodelling during follow-up might be useful for effective multiparametric and dynamic arrhythmic risk stratification in NICM. In the future, a complete and integrated evaluation might be mandatory to implement arrhythmic risk prediction in patients with NICM and to discriminate the competing risk between heart failure-related events and life-threatening arrhythmias.
The spectacular water outburst occurring semi-periodically when the ice-dam formed by the external front of the Perito Moreno glacier collapses, is one of the most attracting events in the UNESCO ...‘Parque Nacional Los Glaciares’ of southern Patagonia. These occurrences have been documented since 1936. Instead, evidence of previous events has been only indirectly provided by dendrochronology analysis. Here we show for the first time radiocarbon-dated sediment cores collected within a small inlet of Brazo Sur, that is, the southern arm of Lago Argentino that record ice-dammings in the Little Ice Age, at 324–266 cal yrs BP, as measured on a vegetal fragment sampled at ca. 14 cm from the top of a core. A common characteristic of the three sediment cores is the abrupt change in the stratigraphic record found at variable depths of 14–18 cm from the top of the cores. This change is marked by a hiatus spanning ca. 3200 years, separating planar-laminated sediments below from an alternation of erosional and depositional events above it, indicating recurring high-energy conditions generated by the emptying of the lake basin. In addition, we observed significant changes in the abundance of environmental indicators as testate amoebae below and above the hiatus. These well-preserved stratigraphic records highlight the key role of glaciolacustine deposits in reconstructing the glacial dynamics and palaeoclimate evolution of a glaciated region.
The high-resolution sequence stratigraphy tackles scales of observation that typically fall below the resolution of seismic exploration methods, commonly referred to as of 4th-order or lower rank. ...Outcrop- and core-based studies are aimed at recognizing features at these scales, and represent the basis for high-resolution sequence stratigraphy. Such studies adopt the most practical ways to subdivide the stratigraphic record, and take into account stratigraphic surfaces with physical attributes that may only be detectable at outcrop scale. The resolution offered by exposed strata typically allows the identification of a wider array of surfaces as compared to those recognizable at the seismic scale, which permits an accurate and more detailed description of cyclic successions in the rock record. These surfaces can be classified as ‘sequence stratigraphic’, if they serve as systems tract boundaries, or as facies contacts, if they develop within systems tracts. Both sequence stratigraphic surfaces and facies contacts are important in high-resolution studies; however, the workflow of sequence stratigraphic analysis requires the identification of sequence stratigraphic surfaces first, followed by the placement of facies contacts within the framework of systems tracts and bounding sequence stratigraphic surfaces.
Several types of stratigraphic units may be defined, from architectural units bounded by the two nearest non-cryptic stratigraphic surfaces to systems tracts and sequences. The need for other types of stratigraphic units in high-resolution studies, such as parasequences and small-scale cycles, may be replaced by the usage of high-frequency sequences. The sequence boundaries that may be employed in high-resolution sequence stratigraphy are represented by the same types of surfaces that are used traditionally in larger scale studies, but at a correspondingly lower hierarchical level.
► Outcrop and core data allow to observe the physical attributes of units and surfaces. ► The types of units for high-resolution studies in shelf contexts are discussed. ► The use of high-frequency sequences simplifies the sequence stratigraphic methodology.
CHIRP subbottom profiles performed on the Ionian Calabrian margin, southern Italy, allow the recognition of an irregular step-like seabed topography and a marked variability in the geometry of the ...post-Last Glacial Maximum (LGM) transgressive wave ravinement surface (WRS). The WRS truncates an older unit showing locally an opaque seismic character, and displays both concave-up and concave-down profiles in any dip section and a local stepped geometry, with gradients between 1° and >
20°. A younger unit, characterized by high-amplitude reflectors onlapping or draping the WRS, is interpreted as a sediment wedge accumulated during the post-LGM glacio-eustatic rise. The WRS crops out forming steep slopes up to 12°, which are interpreted as relicts of palaeo-coastal cliffs generated by wave action during relative sea-level rise. In particular, the deeper slope is locally exposed between ca. 75 and 100
m water depth, corresponding closely with the depth range of melt-water pulse (MWP) 1A (14.3–14.0
ka BP), assuming no subsidence or uplift, and its generation is inferred to be related to this event.
A transgressive model for high-gradient settings and stepped sea-level rise is proposed. Coastal cliffs develop and retreat due to wave erosion during phases of slow relative sea-level rise. During phases of very high rate of relative sea-level rise, coinciding with melt-water pulses, cliffs tend to be overstepped, drowned and not completely eroded by the WRS. Such a ‘cliff overstep’ transgressive model is the equivalent in high-gradient settings of the ‘in-place drowning’ model, developed for low-gradient shelves. The present model may be effective in reconstructing stepped sea-level rises and the evolution of shelf areas during Late Quaternary time.
► CHIRP profiles show the irregular features of a high-gradient margin. ► A transgressive model for high-gradient settings is presented. ► Cliff retreat and overstep are related to changes in the rate of sea-level rise.
Both allogenic and autogenic processes may contribute to the formation of sequence stratigraphic surfaces, particularly at the scale of fourth-order and lower rank cycles. This is the case with all ...surfaces that are associated with transgression, which include the maximum regressive surface, the transgressive ravinement surfaces and the maximum flooding surface, and, under particular circumstances, the subaerial unconformity as well. Not all autogenic processes play a role in the formation of sequence stratigraphic surfaces, but only those that can influence the direction of shoreline shift. Any changes in shoreline trajectory, whether autogenic or allogenic in origin, influence the stratal stacking patterns in the rock record which sequence stratigraphic interpretations are based upon.
The discrimination between the allogenic and autogenic processes that may control changes in shoreline trajectory is a matter of interpretation and is tentative at best in many instances. For this reason, the definition and nomenclature of units and bounding surfaces need to be based on the observation of stratal features and stacking patterns rather than the interpretation of the controlling mechanisms. In this light, we extend the concept of ‘sequence’ to include all cycles bounded by recurring surfaces of sequence stratigraphic significance, irrespective of the origin of these surfaces. The updated sequence concept promotes a separation between the objective observation of field criteria and the subsequent interpretation of controlling parameters, and stresses that a sequence stratigraphic unit is defined by its bounding surfaces and not by its interpreted origin. The use of high-frequency sequences eliminates the need to employ the concepts of parasequence or small-scale cycle in high-resolution studies, and simplifies the sequence stratigraphic methodology and the nomenclature.
► The concept of ‘sequence’ as applied to meter- to decameter-scale cycles. ► The role of autogenic and allogenic processes in the definition of sequences. ► Field observations versus interpretations in the definition of sequences.
Malfunctions of cardiac implantable electronical devices (CIED) have been described after high-energy radiation therapy even in the absence of direct exposure to ionizing radiation, due to diffusion ...of neutrons (n) causing soft errors in inner circuits. The purpose of the study was to analyse the effect of scattered radiation on different types and models of CIED and the possible sources of malfunctions.
Fifty-nine explanted CIED were placed on an anthropomorphous phantom of tissue-equivalent material, and a high-energy photon (15 MV) radiotherapy course (total dose = 70 Gy) for prostate treatment was performed. All devices were interrogated before and after radiation. Radiation dose, the electromagnetic field, and neutron fluence at the CIED site were measured. Thirty-four pacemakers (PM) and 25 implantable cardioverter-defibrillators (ICD) were analysed. No malfunctions were detected before radiation. After radiation a software malfunction was evident in 13 (52%) ICD and 6 (18%) PM; no significant electromagnetic field or photon radiations were detected in the thoracic region. Neutron capture was demonstrated by the presence of the (198)Au((197)Au + n) or (192)Ir((191)Ir + n) isotope activation; it was significantly greater in ICD than in PM and non-significantly greater in damaged devices. A greater effect in St Jude PM (2/2 damaged), Boston (9/11), and St Jude ICD (3/6) and in older ICD models was observed; the year of production was not relevant in PM.
High-energy radiation can cause different malfunctions on CIED, particularly ICD, even without direct exposure to ionizing radiation due to scattered radiation of neutrons produced by the linear accelerator.
High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either vertical or horizontal changes between siliciclastics and carbonates. Vertical facies shifts occur ...between systems tracts and define a ‘reciprocal sedimentation’ pattern, typically consisting of transgressive/highstand carbonates and forced regressive/lowstand siliciclastics, although variations from this rule are common. Mixed systems with lateral facies change, usually typifying transgressive and/or highstand systems tracts, may exhibit proximal siliciclastics and distal carbonates or vice-versa, although variations may also occur along depositional strike. The marked variability of mixed siliciclastic-carbonate sequences makes the definition of a universal sequence stratigraphic model impossible, as the composition and geometries of systems tracts may change considerably, and sequence stratigraphic surfaces and facies contacts may vary in terms of occurrence and physical expression. However, some resemblance exists between siliciclastic sequences and mixed sequences showing lateral facies changes between siliciclastics and carbonates. In particular, these mixed sequences display 1) a stratal architecture of the clastic part of the systems tracts that is comparable to that of siliciclastic deposits, 2) a dominant role of the inherited physiography and of erosional processes, rather than carbonate production, in shaping the shelf profile, and 3) a local lateral juxtaposition of siliciclastic sandstones and carbonate bioconstructions due to hydrodynamic processes. These observations are helpful in predicting the location of porous and potential sealing bodies and baffles to fluid flow at the intra-high-frequency sequence scale, and ultimately they are useful for both petroleum exploration and production.
•A sequence stratigraphic model for mixed siliciclastic-carbonate sequences is elaborated.•Vertical and horizontal switches between siliciclastic and carbonate deposits are illustrated.•This work helps to better understand the partitioning of porous bodies within sequences.
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