1,721,573 research outputs found
The role of Late Quaternary incised valley systems in coastal-plain aquifer geometry: A case study from the Arno Plain (Ligurian Sea, Italy).
Full text linkThe Late Quaternary subsurface successions buried beneath several delta-coastal plains exhibit distinct cyclic facies patterns
that reflect the predominant control exerted by climate-eustatic factors on sedimentation, at Milankovitch and sub-
Milankovitch scales. However, local subsidence co-operates with Late Quaternary glacio-eustatic fluctuations in determining
changes in accommodation space through time and space. During phases of sea-level rise (interglacial periods), subsidence
further increases the accommodation space. On the other hand, during the subsequent phases of sea-level fall (glacial periods) subsidence works to mitigate the accommodation space reduction, resulting in a better preservation of the
depositional record.
In the case of rapidly subsiding regions, such as the Po Plain (N Adriatic Sea, Italy), the combined tectonic-eustatic effect led
to a vertically stacked succession of transgressive-regressive (T-R) sequences forming a multilayered aquifer system (Amorosi
and Colalongo, 2005; Amorosi and Pavesi, 2010). In a hydrostratigraphic view, sheet-like, channel-belt fluvial bodies, tens of
m-thick in the regressive portion of the T-R sequences represent major aquifers. In contrast, pronounced fluvial incisions
occurred during glacial periods in coastal plains characterized by lower rates of subsidence, as those facing the Ligurian-
Tyrrhenian margin (e.g. Arno Plain, Ombrone Plain, Tiber Plain, Volturno Plain). These erosive processes led to the formation
of km-wide and tens of m-thick paleovalleys able to erode confined aquifers, reducing their lateral continuity. In these
contexts, the reconstruction of the aquifer systems is further complicated by the incised valley fill (IVF) successions formed
during the subsequent interglacial periods. These IVFs, which consist predominantly of estuarine muddy deposits, represent,
in fact, localized impermeable barrier to ground-water circulation. A high-resolution multiproxy approach (sedimentological,
faunal and chronological data) and the application of sequence stratigraphic principles can furnish a successful threedimensional
representation of such complex aquifer systems.
The Arno coastal plain (Ligurian Sea, Italy) represents an ideal setting where to investigate the hydrostratigraphic role of
incised valley systems (IVSs), as two well-preserved IVFs have been identified within the uppermost 100 meters and dated to
two non-consecutive interglacial cycles (MIS 7 and MIS 1; Amorosi et al., 2008; Rossi et al., in press). Based on a large
subsurface stratigraphic dataset, composed of hundreds of > 50 m long cores, 14C and ESR chronological data, and
stratigraphic correlation, a representation of the Arno Plain aquifer system is outlined. We focused on the identification and
mapping of potential aquitards/aquicludes (IVFs) and aquifers. These latter include: (i) laterally discontinuous gravel terrace
deposits developed at different stratigraphic levels along the paleovalleys flanks, (ii) lenticular channel-belt sand bodies
formed during the glacial phases that preceded IVSs formation, and (iii) post-valley fill coastal-marine sands showing a
landward-wedging geometry.
References
Amorosi A. and Colalongo M.L. (2005). The linkage between alluvial and coeval nearshore marine successions: evidence from
the Late Quaternary record of the Po River Plain, Italy. In: M.D. Blum, S.B. Marriott & S.F. Leclair (Eds.) Fluvial Sedimentology
VII. Int. Assoc. Sedimentol. Spec. Publ. 35, 257–275.
Amorosi A. and Pavesi M. (2010). Aquifer stratigraphy from the middle-late Pleistocene succession of the Po Basin. Mem.
Descr. Carta Geol. d’It. XC, 7–20.
Amorosi A., Sarti G., Rossi V. and Fontana V. (2008). Anatomy and sequence stratigraphy of the late Quaternary Arno valley fill
(Tuscany, Italy). In: A. Amorosi, B.U. Haq & L. Sabato (Eds.) Advances in Application of Sequence Stratigraphy in Italy.
GeoActa Spec. Publ. 1, 55–66.
Rossi V., Amorosi A., Sarti G. and Mariotti S. (in press). Late Quaternary multiple incised valley systems: an unusually wellpreserved
stratigraphic record of two interglacial valley fill successions from the Arno plain (northern Tuscany, Italy).
Sedimentology
Anatomy and sequence stratigraphy of the late quaternary Arno valley fill (Tuscany, Italy)
No full text"The late Quaternary Arno valley fill, in western Tuscany, was formed during the last glacio-eustatic cycle. It"
"exhibits a total thickness of 35-40 m, and is 5-7 km wide. It consists almost entirely of a single transgressive succession emplaced during the post-Last Glacial Maximum transgression, between latest Pleistocene (13 cal. ka"
"BP) and early Holocene (8 cal. ka BP). An indurated horizon, intensively reworked by pedogenic features, occurs lateral to the deep incision."
"Above a fluvial deposit flooring the valley, the incised valley fill includes an early transgressive succession of"
"coastal plain, bay head-delta, and estuarine deposits. As sea-level rise continued, the valley was filled and the interfluves flooded. Above the interfluve sequence boundary, the late transgressive Holocene succession is about"
"17 m thick, and includes a transgressive-regressive succession of coastal, shallow-marine and modern deltaic deposits."
"Facies analysis of continuous cores and stratigraphic correlation of borehole data from the lower Arno coastal plain allow detailed reconstruction of three-dimensional facies architecture of the valley body. Alternating"
"freshwater and brackish deposits form the valley fill at proximal-most locations. West of Pisa, the valley fill includes amalgamated estuary-mouth sand bodies, whereas at distal locations (beneath the present shoreline) it consists almost entirely of estuarine mud."
"Subtle vertical facies changes within the valley fill allow identification and lateral tracing of three vertically stacked, shallowing-upward successions, about 10 m thick and bounded by flooding surfaces, which are inter-"
"preted as parasequences. Parasequence architecture suggests that sea-level rise close to the Pleistocene-Holo- cene boundary was punctuated by at least two distinct stillstand phases.
Destrutturazione nei terreni coesivi naturali. Aspetti costitutivi e numerici
Full text linkIn questa nota viene descritto un modello costitutivo in grado di simulare il processo di destrutturazione che si verifica nei terreni coesivi naturali soffici sottoposti a carichi di tipo statico. Viene inoltre descritta la strategia di implementazione del modello costitutivo in un codice di calcolo agli elementi finiti basata sul metodo di Eulero Generalizzato di tipo implicito. Le principali caratteristiche del modello costitutivo sono evidenziate attraverso una serie di esempi numerici realizzati su un singolo elemento finito 3D
SANICLAY-T: simple thermodynamic-based anisotropic plasticity model for clays
Full text linkIn this work the anisotropic model for clays SANICLAY proposed by Dafalias and Taiebat (2013) is reformulated within the framework of hyper-elastoplasticity. The model, called SANICLAY-T, is fully defined by two scalar potential functions, the free energy and the rate of dissipation. It is first presented in the triaxial space and then generalised in the multiaxial one. The model reproduces exactly the original one for the case of associate flow rule, while leads to a different outcome for non-associated flow. When compared to existing hyperplastic models accounting for rotational hardening, the proposed one proves to be more versatile, as characterised by less restrictive constraints on the hardening and asymptotic behaviour of the soil. The predictive capability of the model is illustrated with reference to experimental data on natural and reconstituted clays, highlighting its merits and limitations
Development and evolution of a Late Quaternary fluvial channel belt: implicationsfor the interpretation of ancient analogues
No full textOnly sparse data sets, if any, are available to constrain the age attribution of ancient fluvial deposits. In this respect, Quaternary stratigraphy may provide an important chronostratigraphic framework within which to develop a generalized model of channel belt formation and evolution.
Detailed stratigraphic analysis of middle-late Quaternary fluvial deposits from the Po River Basin, in Northern Italy, reveals distinctive cyclic changes in lithofacies and channel stacking patterns, falling in the Milankovitch (100 kyr) band . Stratigraphic correlations with the coeval nearshore successions document that the lower portions of fluvial cycles, characterized by isolated sand bodies, were deposited during phases of relatively high-accommodation (episodes of sea-level rise under interglacial conditions). In contrast, accumulation of laterally amalgamated fluvial bodies (channel belts) took place during phases of relatively low accommodation, marking the “regressive” maxima (i.e., OIS 2 and OIS 6). A well constrained chronostratigraphic framework indicates that eight major channel belts (aquifer systems), separated by thick mud-prone floodplain successions, were deposited during the last 870 ka, while development of the youngest (LGM) channel-belt took place during an interval of time of about 20 ka.
Comparison of the late Quaternary succession of the Po Basin with the fluvial analogue Escanilla Formation, an Eocene formation commonly applied for reservoir studies, documents striking analogies in terms of both tectonic setting and fluvial architecture. These include: i) sedimentation in a highly subsiding, actively folded basin; ii) overall thickness of about 800 m; iii) similar cyclic architecture (100 m-thick cycles), with development of 6-8 laterally extensive channel belts.
Whilst new data are increasingly capable of providing a refined stratigraphic framework for the Escanilla Formation, no direct dating is available, and duration of its deposition (1.5 or 7 Ma?) is still problematic. Based upon similarities with modern channel belts, we suggest that most of the Escanilla Formation (i.e., the 550 m-thick Olson Member) is likely to span less than 1 My, and that the unconformities with both underlying Mondot Member and overlying Collegats Formation could account for major stratigraphic hiatuses. This interpretation is consistent with the remarkable homogeneity in terms of both lithology and facies architecture observed across the Olson member, along with lack of highly mature palaeosols throughout the formation
Small-strain stiffness of reconstituted clay compressed along constant triaxial effective stress ratio paths
No full textThe work described in the paper is an experimental investigation of the effects of anisotropic stress states and histories on the small-strain shear stiffness of reconstituted clays as measured with bender element tests. A brief review is made of previous work dealing with the dependence of small-strain shear modulus on stress state and history in isotropic conditions of confinement, and the rational link that exists between void ratio, e, effective stress, sigma', and overconsolidation ratio, OCR, is considered. Under isotropic stress conditions, only two out of the three variables e, sigma' and OCR are required to describe the dependence of the small- strain stiffness of a clay on current state and history. The same approach proved useful in the analysis of the data from tests with anisotropic stress conditions. The values of the small- strain shear modulus of reconstituted samples compressed along stress paths with constant triaxial effective stress ratios were higher than those measured on isotropically compressed samples. The observed differences increased with increasing stress ratio and could be explained only in part in terms of the smaller void ratios of the anisotropically compressed samples at the same mean effective stress. Simple relationships to evaluate the stiffness indexes of clays that have undergone anisotropic stress histories are proposed
Analisi numerica della risposta sismica locale di un comune della Daunia secondo approcci 1D, 2D e 3D
No full textNel presente lavoro è sintetizzato lo studio degli effetti di sito sulla risposta sismica locale dell’area urbana del comune di Bovino, situato nel subappennino Dauno (FG), caratterizzato da una zona di valle e da rilievi di al-tezza massima pari a circa 400 m. Al fine di valutare l’influenza della topografia e delle condizioni geomorfo-logiche locali, sono state eseguite analisi numeriche agli elementi finiti nel dominio del tempo secondo schemi mono- (1D) e bidimensionali (2D) con i codici QUAKE/W e PLAXIS 3D. Quest’ultimo codice ha inoltre consentito di condurre anche simulazioni tridimensionali (3D). La componente orizzontale di un evento sismi-co reale è stata selezionata come input all’affioramento della formazione rocciosa.
Il confronto tra gli accelerogrammi determinati in superficie, in termini di ampiezza e contenuto in frequenza, ha permesso di evidenziare una notevole dipendenza del risultato dallo schema geometrico considerato. In par-ticolare, nelle analisi 2D e 3D si è registrata una maggiore amplificazione del moto al centro della valle ed in cresta al rilievo sui quali sorge l’abitato rispetto all’approccio 1D
Microzonazione sismica di livello 3 di un comune della Daunia: analisi preliminari
No full textNella presente nota sono illustrati i risultati di analisi preliminari svolte nell’ambito di uno studio di microzonazione sismica di terzo livello del comune di Bovino (FG), finalizzato alla valutazione della pericolosità sismica dell’area attraverso il riconoscimento di aree sismicamente omogenee. La redazione di tale studio ha richiesto una descrizione sufficientemente dettagliata sia del modello geologico sia del modello geotecnico, lo studio di pericolosità di base per l’area in esame e la quantificazione degli effetti indotti dalle condizioni locali sulla risposta sismica. Nello specifico, nella nota sono riportati i risultati di analisi monodimensionali (1D) e bidimensionali (2D) relative al suddetto abitato della Daunia, eseguite secondo l’approccio lineare equivalente implementato nel codice agli elementi finiti QUAKE/W
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