449 research outputs found
Genetically Related Incised Valleys and Deltas: Sequence and Modern Analogue Modeling From the Nonmarine Santa Barbara Coalfield, Late Pliocene, Italy
No full textDifferent source areas feeding the Early Pliocene marine Radicofani Basin (Siena): geological and paleogeographical implications
No full textMorphodynamics and facies architecture of streamflow-dominated, sand-rich alluvial fans, Pleistocene Upper Valdarno Basin, Italy
No full textPlanform architecture, stratigraphic signature and morphodynamics of an exhumed Jurassic meander plain (Scalby Formation, Yorkshire, UK)
No full textPliocene alluvial to marine deposits of the Val dâ€TMOrcia Basin (Northern Apennines, Italy): sequence stratigraphy and basin analysis
No full textSince the Middle-Late Miocene, the Apennine chain was characterised by the development of several basins. These basins have been alternatively explained as extensional post-orogenic basins or syn-orogenic compressional basins. In this framework, the Pliocene depositional history of the Val d'Orcia Basin (Southern Tuscany) is described, based on a sequence stratigraphic approach. Three depositional sequences (Vd3a-c) have been recognized. The Vd3a sequence records marine ingression and subsequent relative sea-level highstand in a narrow W-E trending depression. Subsequent relative sea-level fluctuations led to a progressive basin widening and deposition of Vd3b and Vd3c sequences. Basin scale sedimentation was mainly controlled by relative sea-level changes, although accumulation of bioclastic deposits of the Vd3c sequence could have been influenced by climatic factors. Based on its wide bowl-shaped geometry, the Pliocene Val d'Orcia Basin has been interpreted as an inherited depression. This depression is thought to be originated by erosion at the Late Miocene-Early Pliocene transition
Reconstruction of an extreme flood hydrograph and morphodynamics of a meander bend in a high‐peak discharge variability river (Powder River, USA)
No full textUnderstanding of morphodynamic processes associated with large-scale floods has recently improved following significant advances of modern technologies. Nevertheless, a clear link between flood discharge and in-channel sedimentation processes remains to be resolved. The hydrological and geomorphological data available for the meandering Powder River (Montana, USA) since 1977 makes it a perfect laboratory to investigate connections between flood discharge and point-bar sedimentation processes. This study focuses on a point-bar that accreted laterally ca 70 m during a 50-year recurrence flood, which lasted about 14 days in May 1978. In September 2018, a trench ca 2 m deep and 70 m long was excavated through the axial point-bar deposits, and the 1978 flood deposits were delineated based on georeferenced pre-flood and post-flood cross-section surveys. Sedimentological data show that point-bar deposits accumulated at the early and late flood stages, when the flow was confined to the channel..
Sediment–water flows in mountain streams: Recognition and classification based on field evidence
No full textSediment transport in mountain streams occurs through different flow types that are categorized in accordance with hydraulics and physical properties of a flowing material, and considering the dominant transport mechanism as debris flow, debris flood, hyperconcentrated flow, and water flow. Given that directly monitoring transport processes is often infeasible, a sound alternative to process recognition is to consider the morphological and sedimentological features of related deposits—attributes that chiefly depend on flow type. Accordingly, this work developed a post-flood survey protocol for distinguishing various flow types on the basis of the geomorphological and sedimentological features of deposits and their effects on vegetation. The case study selected for developing and applying the protocol is the Tegnas catchment (Dolomites, Italy), a mountain basin affected by an intense storm in October 2018. We conducted a literature review to identify diagnostic evidence for identifying different flow types and developed a survey form to ease data collection and interpretation. Field surveys were integrated with grain size analyses, measurements of the inclination angle (δ) of imbricated clasts, and estimations of organic content (OMLOI) in deposits. Field criteria allowed us to classify each channel sub-reach in accordance with the characteristics of flood deposits. The main stem of the catchment and its steep tributaries were characterized mainly by water and debris flow processes, respectively. Nevertheless, our survey also showed that debris floods occurred in several sub-reaches of the main stem and tributaries. The comparison of δ and OMLOI under different flow type deposits uncovered significant differences in δ and slight differences in OMLOI. The findings led us to conclude that a combination of field diagnostic criteria and quantitative measurements of additional parameters in a post-flood survey enables a reliable recognition of flow types
Sezione 309010, Foglio 309 Montepulciano, Carta Geologica Regionale, Scala 1:10.000, Regione Toscana
No full textMetadati Carta Geologica Regione Toscana scala 1:10.000. http://159.213.57.103/geoweb/listmet/lista_metadati_10k.ht
Morpho-sedimentary evolution of a microtidal meandering channel driven by 130-years of natural and anthropogenic modifications of the Venice Lagoon (Italy)
No full textAbstract Tidal channels form the pathways for tidal currents to propagate and distribute clastic sediments and nutrients, thus providing a primary control on tidal-landscape ecomorphodynamics. Most tidal channels in both estuarine and lagoonal environments have a tendency to meander, yet very few studies exist that investigate the full spectrum of processes controlling tidal meander morpho-sedimentary evolution. The Venice Lagoon (Italy) offers a unique opportunity to shed light on this topic, because a long record of morphological and sedimentary data is available, which allows one to relate tidal channel evolution to the hydrodynamic and morphological changes undergone by the lagoon. In particular, during the last 130 years, feedback between rising relative sea levels and anthropogenic interventions have caused severe modifications of the Lagoon hydro- and morpho-dynamics. Here we investigate how these modifications fed back into the morpho-sedimentary evolution of a meandering tidal channel located in the northern Lagoon. Combining extensive datasets of aerial photographs, topographic and bathymetric surveys, geophysical investigations, sedimentary core analysis, and numerical modeling, we show that enhanced local tidal ranges and water discharges determine adjustments of channel cross-sectional geometries proportional to increasing tidal prisms, while changes in local tidal asymmetries caused modifications of the local sediment transport regime, resulting in the development of bar-pool patterns according to the dominant tidal phase. Such bar-pool patterns eventually determine channel migration through a bar-push mechanism controlled by a fluvial-like, quasi-linear relationship between local channel curvature and lateral migration rates. Critical differences in sediment transport regime are however highlighted between fluvial and tidal meanders, the latter being potentially characterized by high concentrations of suspended sediment during periods of slack waters when wind-driven sediment transport processes are not negligible. This could hamper the formation of high-relief bedforms, with profound implications for the sedimentology of tidal point-bar deposits
Tidal Flow Asymmetry and Discharge of Lateral Tributaries Drive the Evolution of a Microtidal Meander in the Venice Lagoon (Italy)
No full textTidal landscapes are extensively characterized by the presence of meandering channels, the latter being important for the ecomorphodynamic evolution of these environments. It remains unclear whether changes in the relative strength of maximum flood and ebb currents (i.e., tidal flow asymmetries), together with the widespread presence of lateral tributaries, cause tidal meanders to evolve differently from their fluvial relatives. Here, we investigate the evolution of a meandering channel in the Venice Lagoon (Italy) that receives water from two major tributaries along its outer bank. Using a 2-D numerical model, we first analyze the changes in local tidal flow asymmetries, both natural and anthropogenically induced, which occurred during the last 120 years. The effects of these modifications on the meander morphodynamics are then investigated by means of a 3-D numerical model, and results are compared to modern and historical field data spanning more than one century. We show that under asymmetric tidal flows, tidal meanders develop depositional patterns according to the dominant flow direction, similar to that of fluvial meanders. In addition, the morphological effects of the nondominant tidal flow become increasingly negligible as tidal flow asymmetry increases. We also show that enhanced sediment and water fluxes from major lateral tributaries, sourced from wind-wave exposed tidal flats, can critically influence the development of erosional and depositional patterns within tidal meanders otherwise sheltered from wind action by the presence of salt marshes
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