1,721,057 research outputs found
The sedimentary record of incised valleys: tidal dominated underfilling vs. fluvial dominated overfilling.
No full textA continental/siliciclastic to shallow-marine/carbonate system in the Upper Triassic of Dolomites (Travenanzes Formation, northern Italy)
No full textLa Formazione di Travenanzes (ex Formazione di Raibl Auctorum) è una
successione mista silicoclastico/carbonatica di ambiente da continentale a
marino-marginale e di clima arido che si depositò nel Sudalpino orientale
durante il Carnico superiore (Tuvalico). La deposizione avvenne in un’area
costiera a basso gradiente, alimentata da sedimenti provenienti da rilievi
meridionali e aperta verso nord-nordest alla Tetide.
L’ambiente deposizionale della Fm. di Travenanzes è stato ricostruito in
Dolomiti ed inquadrato nell’ambito di un sistema di piana alluvionale – piana
costiera inondabile - laguna a sedimentazione carbonatica.
La porzione continentale del sistema deposizionale carnico è costituita da
un sistema fluviale di tipo “terminal fan” caratteristico di clima arido con
precipitazioni stagionali, dove l’intensa evaporazione ed infiltrazione porta alla
diminuzione della portata e delle dimensioni dei canali fluviali verso mare, fino
alla totale scomparsa della rete idrografica superficiale in corrispondenza di
una piana fangosa costiera, prima della linea di costa.
La piana costiera fangosa costituisce la zona di interazione tra sistema
continentale e marino, essendo temporaneamente inondata durante le tempeste
marine e le piene fluviali maggiori. Localmente il clima arido porta allo
sviluppo di una “sabkha” costiera con precipitazione di anidrite nodulare e
“chicken-wire”, e gesso laminato.
La porzione marina del sistema deposizionale carnico è costituita da piane
tidali e lagune poco profonde a sedimentazione carbonatica, caratterizzate da
dolomie afanitiche, cristalline, laminate e marnose, organizzate frequentemente
in cicli peritidali metrici del tutto simili a quelli della soprastante Dolomia
Principale, e subordinate intercalazioni di peliti scure.
Distinti modelli di facies possono essere applicati separatamente alla
porzione continentale e marina del sistema, ma un modello deposizionale
comprensivo dell’intero sistema non è ancora stato descritto in letteratura.
Punto chiave per la sua elaborazione è la comprensione dei processi
deposizionali che avvengono sulla piana costiera inondabile.
In conclusione, la Formazione di Travenanzes è un esempio di sistema a
sedimentazione mista di clima arido e di ambiente di transizione continentaleparalico-
marino marginale, ed il suo confronto con casi analoghi, antichi e
attuali, potrebbe essere utile alla costruzione di un modello deposizionale di
validità generale e applicabile ad altri casi di studio nella storia della Terra
Sharp decoupling between continental/siliciclastic and shallow-marine/carbonate sedimentation in the Upper Triassic Travenanzes Fm. (Southern Alps, Italy)
No full textThe sedimentological response of sediments to the morphodynamic processes in the Venice Lagoon (Italy)
No full textPreliminary contribution to the CORILA project: sedimentological evidences of the present morphodynamic processes in the Venice Lagoon (NE Italy)
No full textLow trajectory clinoform sets at a basin margin and upper slope gullies (Brogniartfjellet, Svalbard).
No full text
Climatic control of arenites: an example from the Carnian (Upper Triassic) of the Dolomites (northern Italy).
No full textFacies and processes in a Gilbert-delta-filled incised valley (Pliocene of Ventimiglia, NW Italy)
No full textThe incised valley of Ventimiglia, located along the Ligurian coast (NW Italy), was cut by deep river erosion during the
Messinian sea-level fall and is connected seawards to a slope canyon. During Pliocene, the valley was flooded by the sea and
transformed into a coastal embayment or ria. The infill sequence of the incised valley is up to 500 m thick. The paleovalley floor is
locally paved by thin remnants of subaerial scree deposits, abruptly overlain by up to 150 m thick bathyal marls, above which a
number of stacked prograding conglomerate Gilbert-type deltas constitute most of the valley fill. Gilbert deltas present 15°–25°
dipping clinoforms, 50 to 250 m thick, and are alternated with up to 20–30 m thick marls intervals.
This unusual character of incised-valley-fill sequence, can be accounted for by the rapid and high-amplitude eustatic sealevel
rise that followed the Messinian event, and by the progradation occurring on a narrow and steep-gradient shelf, tectonically
controlled by the tilting and collapse of the margin. High and coarse sediment supply was provided by the uplifting Alpine
chain.
A remarkable analogy in facies patterns and depositional setting is observed with the high-latitude Holocene fan-delta systems
described by Prior and Bornhold [Prior, D.B., Bornhold, B.D., 1990. The underwater development of Holocene fan deltas. In:
Colella, A., Prior, D.B. (Eds.), Coarse-Grained Deltas: Spec. Publs. Int. Ass. Sedim., vol. 10, pp. 75–90.] in the fjords of the British
Columbia. Both examples are characterized by high rate of sea-level rise after the entrenchment stage, and predominance of massflow
processes and debris-avalanching in the first stage of progradation, followed, in the later stages of delta progradation, by
deposition of better-organized and stratified foreset beds on the delta slope predominantly by inertia and turbidity flows.
A large facies variability is observed in the Gilbert-type delta complex, recording deposition under a wide range of physical
conditions, both in individual and successive wedges. Long-term evolution of the valley fill shows a general trend from deep-water
to shallow-water deltas and from fluvial-dominated to wave-influenced deltas
Depositional canyon heads at the edge of narrow and tectonically steepened continental shelves: comparing geomorphic elements, processes and facies in modern and outcrop examples
No full textMarine geology data show that canyon heads can be the site of depositional processes and furnish the details of the geometry of their geomorphic elements. Canyon heads are usually floored by sediment with a prevailing coarse-grained nature and their sampling is very difficult thus preventing the characterization of the facies of their infill. Lithological and facies information is however available through outcrop studies. In this paper, we integrate modern seafloor and outcrop data to characterize the architecture of depositional canyon heads in tectonically active continental margins with a narrow shelf. The modern examples are located along the northeastern Sicilian margin (Milazzo and Niceto canyon-head systems), whereas the ancient one, Pliocene in age, is located onshore, along the Ligurian coast (Ventimiglia canyon-head system). The modern Milazzo canyon head is located at the coastline and has a steep slope. The flanking deposits are equivalent to the oldest Gilbert delta foresets of the Ventimiglia canyon head as the delta progrades directly into the upper slope. A deeply entrenched channel and a large chute mark the mostly erosional area directly facing the mouths of the rivers that enter the Milazzo canyon head. Laterally, the upper part of the foresets slope is characterized by a bulge with swales and ridges topography. These geomorphic elements are interpreted to be formed by debris flows and turbidity currents as suggested by the upper part of the Ventimiglia foresets, where chaotic, massive or graded deposits are observed. The swales and ridges topography gradually disapper downslope; this area is dominated by turbulent processes due to flow expansion from a confined to a more unconfined setting. An high turbulent flow environment is also confirmed by the formation of plunge pools, due to hydraulic jump, at the foresets-toesets transition. Similar features in the outcrop are infilled by bedsets facies with grain-size coarser than the eroded surroundings. The modern Niceto canyon head is connected landwards to a delta system that stretches across a 1 km wide shelf. Channelized delta distributaries are similar to the topset strata of the youngest deltas of the Ventimiglia canyon head. Channels are up to 200 m wide and 50 m deep and show axial bedform trains confirming that large scale trough cross beds are an important facies of channel infill. Wave reworking in the upper part of the topsets is also suggested by both the modern and outcrop data.
Our work shows how the nature of the infill and the depositional processes at the canyon heads are dependent on the shelf width and can give hints on the degree of evolution of the canyon itself. In addition, our work shows how the location and character of river entry points is important in dictating lateral facies variations within canyon heads
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