1,721,044 research outputs found
Coarse sediments in Northern Apennine peat bogs and lakes: New data for the record of Holocene alluvial phases in peninsular Italy
No full textThis research was conducted in the Northern Apennines, in the upper valleys of the Cedra River and Parma River, occupied by glaciers during the last glacial maximum. The stratigraphy, the dating and the interpretation of the environmental significance of alluvial deposits interbedded between lacustrine sediments are reported. The data provide an overview of the periods of enhanced alluvial activity that occurred after the glacial retreat in the Apennine chain. The alluvial phases and the periods of environmental stability varied in frequency and length during the Holocene. In particular, starting from the beginning of the Apennine Neoglacial (about 4.2 kyr BP), the events became much more frequent but shorter. The elapsed time between alluvial phases (i.e. the length of the phases of stability) was greater during the Early Holocene, probably because of the values of insolation: when the insolation in July was lower, the length of the phases of stability was greater. Despite the uncertainty in the dating of some events, it is likely that many alluvial phases, later than about 8.5 kyr BP, started during ice rafted debris events in the North Atlantic. The overall analysis of the alluvial sedimentation indicates that periods of more frequent floods are associated with times of rapid climate change and not only with cool periods. The current increase in floods, linked to the ongoing climate change, confirms the data obtained from Holocene sediments. © The Author(s) 2014
Holocene palaeoclimate in the northern Sahara margin (Jefara Plain, northwestern Libya)
No full textThe palaeoclimatic evolution of northwestern Libya has been deduced from the study of the palustrine and aeolian sediments. The Holocene environmental variations have been recognized through geological and stratigraphic surveys and by pollen analysis and malacofauna content of the sediments. Some organic-rich horizons have been dated using the radiocarbon method. The data show that in general, the presence of marshes is linked with the period of higher humidity, which began around 9.4 ka BP and ended around 5.0 ka BP. From c. 5.0 ka BP up to about 4.4 ka BP, there was a simultaneous presence of marshes and vegetation of arid climate as a consequence of rainfall in the mountains and/or a decrease in temperatures. The Holocene wet period was interrupted by two arid spells dated about 8.2 and 5.5-5.4 ka BP. The end of the wet phase must have been gradual. The climatic events that occurred in the Jefara plain seem to be well correlated with those identified in Saharan Africa even if the Mediterranean is only 100 km away. © The Author(s) 2012
The upper pleistocene deglaciation on the apennines (Peninsular Italy) [La deglaciación del Pleistoceno Superior en los Apeninos (Península Italiana)]
No full textThe synthesis of the published data and new researches allow to establish a more reliable chronology of the phases of deglaciation that occurred after the Apennine last glacial maximum. The chronological framework was assured by radiocarbon dating and by the presence of four geochemically and chronologically characterized tephra layers and a quartz-rich loess, that were found on different mountain massifs, mainly in Central Italy. After the Campo Imperatore Stade (local LGM) dated 28-27 ka cal BP, a first retreat took place during the Campo Felice Arid Spell, followed by a glaciers advance (Le Capannelle Stade) that started between 26 and 25 ka cal BP. During the readvance the glaciers reached a length about 90% of the local LGM glacier. The readvance was followed by a retreat broken by at least two readvances (Piano Pietranzoni and Lago Pietranzoni readvances) and then by a very fast withdrawal at the beginning of the Fornaca Interstade, dated ca. 22-21 ka cal BP. The Fontari Stade glacier’s advance began ca. 18 ka cal BP and was followed by a retreat broken by at least three small readvances (Fontari 2; Fontari 3; M. Aquila 1). The M. Aquila 1 readvance ended ca. 15-14 ka cal BP. The Venaquaro Interstade, dated 14-13 ka cal BP, was followed by the M. Aquila Stade. This stade was the last Late Pleistocene small glacial expansion and can be correlated to the Younger Dryas. The variations in the atmospheric circulation in the Mediterranean area likely played a role during the first deglaciation phases (between 27-26 and 21-22 ka cal BP). During the period between 19-18 and 12 ka cal BP the glacial fluctuations were linked, very likely, to the climatic impact of the North Atlantic ice rafted debris events. It is possible, therefore, that during the Fornaca Interstade (between 22-21 and 19-18 ka cal BP), there has been such a change in atmospheric circulation and the Central Mediterranean area became more prone to be influenced by the effects of the North Atlantic D/O and IRD events. © Universidad de La Rioja
The climate-triggered western shift of the confluence between the Dora Baltea and Po rivers (north-western Italy) during the late Holocene
No full textThe study on the migrations of the confluence between the rivers Po and Dora Baltea was based on a detailed observation of aerial photographs, field surveys and sediment stratigraphy. The age of the sediments and morphological features was based on radiocarbon datings, on the presence of archaeological settlements and ancient artefacts and on historical data. The aerial photographs of the GAI 1954 flight of the Italian Air Force were used because in the year 1954, some low terraces were still clearly visible, while today are almost completely obliterated because of the works for the improvement of the rice fields. A succession of nine fluvioglacial and fluvial terraces and many abandoned riverbeds have been identified: the interpretation of the morphological features made it possible to identify the Po and Dora Baltea evolution during the late Holocene. The study established that during the last 3000 years, the confluence of the Dora Baltea into the Po has constantly migrated to the west and that this migration occurred during alluvial phases dating back to the Iron Age, 2nd century BC–1st century AD, 5th century AD, 6th–8th century AD and 15th–19th century AD. The alluvial phases occurred during periods of increased floods in northern Italy and advances of the Alpine glaciers in northwestern Italy and Switzerland. Neither tectonic deformations nor anthropic actions seem to have influenced fluvial evolution in the last 3000 years. The westward migration of the confluence between the rivers was therefore triggered by climatic changes, but caused by the different responses of the catchments of the Dora Baltea and the Po rivers to climatic changes, and by the greater slope of the Dora Baltea flood plain
The evolution of the Po river near Trino (Prov. of Vercelli - Piedmont, NW Italy) from the Bronze Age to the XVIIth Century [L'evoluzione del po nei pressi di trino (Prov. di Vercelli - Piemonte) tra l'età Del Bronzo ed il XVII secolo]
No full textThe study of the morphological features and sediments of the Po river bed and its banks, allowed the identification of several phases of erosion and deposition beginning from a period prior to the Middle Bronze Age. Radiometric datings of wooden poles found in the river bed give an indication of the fluvial evolution from the XIII century up to the present. A phase of stability of the river bed, inferred from geological proxy-data, seems to be typical of the period prior to the XIII century, and of the time interval including the XIII-XIV centuries and part of the XV century. During the same period, historical data report a limited number of flood events. There is a correlation between the sedimentation phases begun in the XV century which lasted until at least, the XVII century, and a period characterized by many huge floods, causing great changes in the riverbed. The depositional phase which started in the XV century was probably caused by the climatic changes that produced the so-called Little Ice Age. This period, characterized by a fresh and humid climate, lasted until the second half of the XIX century. During the XIII-XIV centuries phase, which represents the late part of the so-called "Medieval Climatic Optimum" and its phases of transition towards the Little Ice Age, no major depositional processes, nor erosion episode occurred
The effect of the Younger Dryas and of Heinrich Events on the climatic and environmental evolution of Central Italy [L'impronta del "Younger Dryas"e degli "Heinrich events "nell'evoluzione climatica e ambientale dell'ltalia centrale]
No full textPalaeoclimatic studies conducted in Central Italy on various sedimentary environments, have as their objective the identification of the palaeoclimatic changes contemporaneous with Heinrich Events, H1 (14,300 y B.P.) and H2 (21,000 y B.P.), and YD (ca. 11,000 y B.P.). Morphological and stratigraphical studies conducted in different Central Apennine sites, have identified the presence of lacustrine, eolian, alluvial, and stratified slope deposits, phases of pedogenesis, as well as evidence of discountinuous permafrost. The deposits taken into consideration are those which yielded a radiocarbon date between ca. 21,000 and 10,000 years ago. Correlation between sites and the dating of particular horizons was made possible by the presence of three tephra layers interposed within the various sediments that form the stratigraphical series. In correspondence with Heinrich Events and Younger Dryas, lake level oscillations, phases of fluvial and eolian activity (which allow an evaluation of the hydrological balance), stratified slope deposits (linked to arid phases, and also, in the Late Pleistocene, to intense gelifraction), solifluc-tions (indicators of cold-wet climates), traces of discontinuous permafrost at high elevations (which indicate that the annual mean temperature, at the moment of their formation, was around -1 - -2 °C), have been identified. From the data obtained, it is possible to state that climatic cooling and drying in Central Italy are contemporaneous with both Heinrich Events and the Younger Dryas. It has also been assumed the approximate value of the annual mean temperature difference compared to present-day values and the time when occurred HI (-6,7 - -7,7 °C) and YD (-6 - -7 °C)
Post-glacial deposits of the peschio di iorio lower valley (pescasseroli, national park of abruzzo, central Italy): Dating and paleoclimatic interpretation [I depositi post-glaciali della bassa valle peschio di iorio (Pescasseroli, Parco Nazionale D'abruzzo): Datazione e interpretazione paleoclimatica.]
No full textStrati graphical studies on the lower valley of Peschio di Iorio in Abruzzo assisted to define the depositional, erosive and pedogenetic phases that occurred after the last glacial maximum in the area. The chronology of deposits was obtained on the basis of sediments of glacial origin and a soil developed from the weathering of a tephra layer, which is widespread throughout Central and Southern Italy, and of three 14 C dates. The principal climatic and environmental events as indicated by sediments are: a) Presence of glaciers at the valley-head, which flowed into the Peschio di Iorio valley, with the snow line descending to altitudes markedly lower than 1800 m. b) A rise in temperature soon after 18,000 years B.P., which was accompanied by the rapid melting of glaciers and sedimentation of fluvioglacial deposits, c) A phase of stream activity, in presence of irregular precipitation and/or low temperatures hindering the development of abundant vegetation on the valley slopes, d) A phase of fluvial erosion favoured by probably rather regular precipitations and by a scarce contribution of material from the slopes, e) Tephra fall of "Neapolitan Yellow Tuff "(12,300±300 years BP.) and its partial colluvial re-sedimentation, in a time more recent than 8,990±80 years B.P. Re-sedimentation would have taken place during a period characterized by seasonal or irregular precipitations, f) A phase of pedogenesis with development of an andosoil all over the valley floor, which started after 8,990±80 years B.P. During the phase of pedogenesis, the area would have been under a regime of regular and/or abundant precipitations, g) A phase of colluvial deposition and covering of the andò soil on the valley floor which began around 6,900±85 years B.P. This phase indicates a negative variation or an increase - even if not much marked - of the rainfall seasonal regime, h) A phase of pronounced linear erosion, which was caused by abundant precipitations and occurred in a period well after 6,900±85 years B.P. and before 3,770±80 years B.P. i) A phase of alluvial and colluvial deposition with the covering of the andò soil still present at the foot of slopes. If due to natural causes, this phase, which occurred after 3,770±80 years B.P., would imply a rainfall decrease and/or a markedly seasonal rainfall regime
Tiber delta CO2-CH4 degassing: A possible hybrid, tectonically active Sediment-Hosted Geothermal System near Rome
No full textFiumicino town in the Tiber River delta, near Rome International Airport (Italy), is historically affected by large amounts of carbon dioxide (CO2) in the ground and gas eruptions triggered by shallow drilling. While it is known that CO2 originates from carbonate thermometamorphism and/or mantle degassing, the origin of methane (CH4) associated with CO2 is uncertain and the outgassing spatial distribution is unknown. Combining isotope gas geochemistry, soil gas, and structural-stratigraphic analyses, we provide evidence for a hybrid fluid source system, classifiable as Sediment-Hosted Geothermal System (SHGS), where biotic CH4 from sedimentary rocks is carried by deep geothermic CO2 through active segments of a half-graben. Molecular and isotopic composition of CH4 and concentration of heavier alkanes (ethane and propane), obtained from gas vents and soil gas throughout the delta area, reveal that thermogenic CH4 (up to 3.7 vol% in soil gas; δ13CCH4: -37 to -40‰ VPDB-Vienna Peedee Belemnite, and δ2HCH4: -162 to -203‰ VSMOW - Vienna Standard Mean Ocean Water in gas vents) prevails over possible microbial and abiotic components. The hydrocarbons likely result from known Meso-Cenozoic petroleum systems of the Latium Tyrrhenian coast. Overmaturation of source rocks or molecular fractionation induced by gas migration are likely responsible for increased C1/C2+ ratios. CO2 and CH4 soil gas anomalies are scattered along NW-SE and W-E alignments, which, based on borehole, geomorphologic, and structural-stratigraphic analyses, coincide with active faults of a half-graben that seems to have controlled the recent evolution of the Tiber delta. This SHGS can be a source of considerable greenhouse gas emissions to the atmosphere and hazards for humans and buildings. ©2015. American Geophysical Union. All Rights Reserved
The Late Pleistocene deglaciation on Mt Sirino and Mt Pollino (Basilicata, Calabria - Southern Italy) [La deglaciazione Tardo Pleistocenica sui M. Sirino e Pollino (Basilicata, Calabria - Italia Meridionale)]
No full textThe study undertaken indicated that the sediments present in some depressions on the moraines of Mt. Sirino and Mt. Pollino have analogous composition: they are formed in the lower part by deposit rich in aeolian quarz, while in the upper part they are rich in volcanic material. Only on the last moraine of Mt Sirino are there exclusively sediments formed mainly of volcanic material. Similar stratigraphy has been discovered also in some depressions on Mt. Matese and Mt. Greco moraines: on these massifs the presence of tephra and datable sediments allowed to ascertain that the transition from sediments rich in aeolian quarz and those rich in volcanic material took place around 13-14,000 years ago. All of the phases of glacial retreat, except the last at Mt. Sirino, would be datable to a period preceding ca. 14,000 years ago. The evaluation of the rise of the equilibrium line altitude (ELA) since the last glacial maximum indicated that at Mt. Pollino (2267 m) the glaciers disappeared before those at Mt. Sirino (2005 m). The presence of a glacier on the massif of lower altitude, when on the higher massif the glaciers had already disappeared, might have been attributed not so much to the slightly northernmost position, that appears unimportant, as to the different amount of precipitation. Still today the amount of precipitation that falls on Mt. Sirino is remarkably higher than that on Mt. Pollino
The evolution of the Northernmost Apennine Front (Piedmont, Italy): Plio-Pleistocene sedimentation and deformation in the Po Basin and Monferrato hills
No full textThe area under investigation includes the southern Vercelli plain and the lower Cerrina valley, in the northern central Monferrato hills. The comparison between the deformation of the sediments of the foredeep basin, north of the Monferrato thrust front, and of the Cerrina valley syncline, south of the front, enabled our understanding of the Pliocene and Pleistocene environmental and tectonic evolution to be improved. The study of the Plio-Pleistocene sedimentary successions allowed the phases of subsidence and deformation produced by the compressive tectonic to be dated. The subsidence involved the Po foredeep basin and the Cerrina valley syncline during the same periods, but with different intensity. A first phase of subsidence occurred before the sub-chron Olduvai, while the second phase can be dated between about 1.5 and 0.5 MA ago, but the maximum subsidence rate occurred around 1.07 and 0.99 MA ago. Also the main deformation phases of the Cerrina valley syncline are coeval with the activity of the Lucedio and Cavourrina faults, that correspond to two different buried thrust fronts. The Lucedio fault is linked to the Gaminella-Cerrina valley syncline through the NW-SE trending Crescentino fault (west) and the N-S trending Salera Line (east) acting as ramps, while the ramps linking the Cavourrina fault to the syncline are the NNE-SSW trending Fontanetto Po (west) and the N-S trending Trino (east) deformation zones. The tectonic frame indicates that the syncline corresponds to a trough behind the thrust front. However, the asymmetry of the Cerrina valley in its stretch with a W-E orientation, and the presence of a sequence of terraces only on the northern side, suggest that the hills north of the valley were gently uplifted at least until the upper Pleistocene. It follows that the syncline may have acted, until very recent times, as a boundary between two hilly areas (north and south of the valley) subject to different tectonic evolution. The results of the research suggest that the river, which entered the Cerrina valley during the Early and Middle Pleistocene, was probably fed by the Alpine valleys lying SW of the Aosta valley, or a collector of the streams that drained the Northern Monferrato
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