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Facies 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
Sequence stratigraphy and architectural variability in growth fault-bounded basin fills: a review of Plio-Pleistocene stratal units of the Crotone Basin (southern Italy)
No full textCyclicity in non-marine foreland-basin sedimentary fill: the Messinian Conglomerate-bearing succession of the Venetian Alps (Italy)
No full textSpecial Publication of the International Association of Sedimentologist
Sequence stratigraphy in half-graben basins: examples from the Pliocene succession of Crotone Basin (Southern Italy)
No full textPolyphase tectonics through subsidence analysis: the Oligo-Miocene Venetian and Friuli Basin, north-east Italy
No full textArchitectural styles of prograding wedges in a tectonically active setting, Crotone Basin, Southern Italy
No full textThe lower Pliocene shallow-marine to continental succession of the Crotone Basin, a small forearc basin on the Calabrian Arc, Southern Italy, is represented by a mixed terrigenous–carbonate succession, up to 850 m thick, known as the Zinga Molasse, deposited in an active tectonic setting dominated by extensional structures and halokinesis. The succession may be informally subdivided into three main sequences, Zinga 1, Zinga 2, Zinga 3, each bounded by major unconformities produced by the interaction of tectonics and eustasy. The Zinga 1 sequence records terrigenous input into the basin leading to the development of stacked progradational wedges of shoreface and deltaic deposits. Spectacular thickness changes and progressive unconformities result from the activation of NE-trending growth folds and listric faults, and indicate that deposition occurred during extensional deformation and salt tectonics. However, the regional extent of the surfaces, the lack of evidence for changes in the local tectonic regime between sequences and the presence of listric faulting within sequences all favour eustatic sea-level change as the main control on the sequence development, although local tectonics strongly controlled sedimentary architecture
Vertically stacked Gilbert-type deltas of Ventimiglia (NW Italy): The Pliocene record of an overfilled Messinian incised valley
No full textOverfilled incised valleys develop when the rate of sediment supply outpaces the rate of accommodation. An overfilled incised valley presents simple or compound valley-fill architecture, depending on the depth of the valley incision, compared with the height reached by the following sea-level rise.
The Ventimiglia incised valley, exposed on the Ligurian coast, north-western Mediterranean margin, presents a spectacular example of compound incised-valley fill, developed in perennial “overfill” conditions. The valley was subaerially incised during the Messinian Salinity Crisis and rapidly flooded by the sea at the beginning of Pliocene, then filled by eleven coarse-grained Gilbert-type deltas during Early–Middle Pliocene time.
The basal Messinian unconformity is locally paved with subaerial scree breccias and bioclastic shallowmarine sandstones, and blanketed by bathyal marls. These deposits record the lowstand, transgressive and early-highstand systems tracts of the first valley-fill sequence. The subsequent progradation of Gilbert-type deltas occurred in four stages, or depositional sequences, separated by transgressive marine-marl intervals.
Within each depositional sequence, the deltaic bodies display offlapping architecture, recording falling shoreline trajectory, downward shifts in facies, and overall forced regression. The water depth and accommodation in the inundated coastal valley was gradually decreasing with time. The reduced accommodation allowed the youngest deltas to prograde out to the shelf edge, triggering mass collapses and subsequent filling into the newly created slump scars. Some of the deltas probably acted as “canyon perched deltas” and supplied sediment to the deep-water slope and floor of the Ligurian Basin.
The vertical stacking of Gilbert-type deltas is usually attributed, in tectonically active basins, to fault-related subsidence pulses. In Ventimiglia, the accommodation was created by high-frequency eustatic sea-level rises that, probably accompanied by climate controlled reductions in sediment supply, temporarily outpaced uplift, leading to the development of multiple cycles of infill
Anatomy and evolution of the normal-faulted Lower Pliocene fill of the northern Crotone Basin (southern Italy)
No full textThe complex development of the northern Crotone Basin, a forearc basin of the Calabrian Arc (Southern Italy), has been documented by sedimentological, stratigraphic and structural analyses.This Mediterranean-type fault bounded basin consists of small depocentres commonly characterized by a mix of facies that grades from continental to shallow marine.The lower Pliocene in¢ll of the Crotone Basin consists of o¡shore marls (Cavalieri Marl) that grade upwards into a shallow-marine to continentalsuccessionupto850mthick(ZingaFormation).Thesuccessionissubdividedintothree mainstratalunits:Zinga1,Zinga2,Zinga3boundedbymajorunconformities.TheZinga1stratalunit grades from the Cavalieri Marl to deltaic and shoreface deposits, the latter organized into several stacked progradational wedges that show spectacular thickness changes and progressive unconformities related to salt-cored NE-trending growth folds and listric normal faults.The Zinga 2 stratal unit records a progressive and moderate deepening of the area, marked by £uvial sedimentation at the base, followed by lagoonal deposits and by a stacking of mixed bioclastic and siliciclastic shoreface units, organized into metre-scale high-frequency cycles. Deposition was controlled by NE- trending synsedimentary normal faults that dissected the basin into a series of half-grabens. Hangingwall stratigraphic expansion was compensated by footwall condensed sedimentation. The extensional tectonic regime continued during sedimentation of the Zinga 3 stratal unit. Deposition con¢ned within structural lows during a generalized transgressive phase led to local enhancement of tidal £ows and development of sand-wave trains.The tectonic setting testi¢es the generalized structural domain of a forearc region.The angular unconformity at the top of the Zinga 3 stratal unit is regional, and marks the activation of a large- scale tectonic phase linked to strike- slip movements
From marginal to axial tidal-strait facies in the Early Pleistocene Siderno Strait
Full text linkThis geological guide presents the description of locations associated with a two-day field trip arranged in relation to the 10th International Congress of Tidal Sedimentology (Tidalites), Matera, Italy. The field guide describes sedimentological features of the largest among a series of tectonically controlled tidal straits that dissected the Calabrian Arc in southern Italy during the Early Pleistocene. The WNW-ESE trending, 50x20 km-wide Siderno Strait connected the Tyrrhenian with the Ionian seas. Due to tidal phase opposition between the two basins, continuous water-mass exchanges occurred through the strait, leading to powerful, bi-directionally flowing tidal currents. Sediments filling the Siderno Strait derived from both fluvial supply from the margins and intra-basinal autochthonous carbonate-factory debris. The main objective of the two-day field trip is to guide the visitor through a cross-section of the ancient strait, starting from one of the margins, ending in the deeper axial zone. The focus during the day one is on strait-margin deltaic fluvial-dominated deposits, shed from the tectonically-controlled, northern border and reworked by tidal currents in their distal reaches (delta front). Erosively-based, 4-5 m-thick pebbly-sandstone strata intercalated with 2-3 m-thick tidally-generated cross strata stack into a ca. 170 m-thick succession, exposed in a series of outcrops progressively located down-current with respect to the inferred entry point to the north. The focus of the day two is a ca. 150-190 m-thick succession consisting of cross-stratified mixed (bioclastic-siliciclastic) deposits, forming a series of WNE-ESE-oriented, elongated ridges that accumulated in the south-eastern axial zone of the Siderno Strait. The selected stops offer panoramic views of exceptionally continuous sections and close-up observations, revealing different scales of depositional architectures and a variety of sedimentary structures and trace fossils that record the development of these tidal sand ridges during the strait lifespan. The interplay between the tectonic uplift of a central bedrock sill and a number of syn-sedimentary faults and high-frequency relative sea-level changes (induced by glacio-eustacy and active tectonics) can be deciphered from the architecture of the tidally-generated cross strata composing the main body of the ridges
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