Página 1 dos resultados de 13 itens digitais encontrados em 0.001 segundos

Idades de Soterramento 'ANTPOT.26 AI/''ANTPOT.10 Be' em grãos de quartzo e o assoreamento de sistemas de cavernas na região de Iraquara, (BA): 2 milhões de anos de registro sedimentar no Quaternário; not available

Laureano, Fernando Verassani
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/12/2014 PT
Relevância na Pesquisa
16.92%
Idades de soterramento de grãos de quartzo pelos isótopos cosmogênicos 'ANTPOT.26 Al' e 'ANTPOT.10 Be' foram obtidas em depósitos sedimentares que assorearam os sistemas de cavernas associados aos vales cegos dos riachos das Almas e Água de Rega, região de Iraquara (BA). Os resultados também incluem a caracterização faciológica e uma abordagem preliminar sobre a arquitetura dos depósitos, além do mapeamento em campo do contexto geomórfico dos sistemas de condutos e seu preenchimento sedimentar. Coberturas terciárias assentadas sobre todas as unidades pré-cambrianas testemunham que a superfície cárstica e os sistemas de condutosfazem parte de uma longa história de evolução, envolvendo episódios de exposição, soterramento e exumação. Durante os dois últimos milhões de anos, a drenagem superficial e os sistemas de cavernas estavam plenamente articulados na condução de água e sedimentos, com rotas de fluxo subterrâneas que incluíam ainda trechos labirínticos pré-existentes, que serviam de repositório de sedimentos durante os eventos de inundação, proporcionando também, rotas alternativas ao canal,na medida em que o sistema agradava. A sucessiva migração do canal por estas redes labirínticas originou o padrão distributário observado na Lapa Doce e na Gruta da Torrinha. Os depósitos sedimentares estudados nas cavernas dividem-se em dois grupos: fluviais e de água estagnada. Osdepósitos fluviais ocorrem na base e são constituídos por fácies de canal e fácies de inundação. As idades de soterramento de grãos de quartzo destes sedimentos apontam para um período de assoreamento fluvial compreendido entre 1...

Loess and floods: late Pleistocene fine-grained valley-fill deposits in the Flinders Ranges, South Australia.

Haberlah, David
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2009
Relevância na Pesquisa
26.48%
Terrace remnants of late Pleistocene fine-grained valley-fills, at present eroded by ephemeral traction-load streams, are reported from many semi-arid and arid parts of the world. While they present promising palaeo-environmental archives for recent geological times such as the Last Glacial Maximum (LGM) for which few other terrestrial depositional records exist, their poorly understood nature has limited their significance. This study examines the fine-grained valley-fill deposits from the Flinders Ranges in South Australia, here called Flinders Silts. It establishes the timing, mode and environmental controls of deposition as opposed to their advancing erosion under the current climate. A regional chronostratigraphy based on 124 numerical dates is discussed, of which 43 radiocarbon and 22 luminescence ages were obtained from 12 sections across three major catchments within the scope of this thesis. Regionally significant intervals of rapid aggradation, relative surface stability and erosion are established. Regional climatic controls are differentiated from intrinsic catchment- and site-specific effects on the system. Further, individual age proxies and age models are critically assessed in how far they reflect depositional events. The final aggradational interval bracketing the extended LGM is discussed in detail on a continuous layered to laminated stratigraphic sequence. The provenance question of the fine-grained sediments and the depositional environment of the Flinders Silts are further addressed by high-resolution particle-size analysis. In order to study the subtle variations within the fine-grained partially-aggregated material...

Large floods during late Oxygen Isotope Stage 3, southern Negev desert, Israel

Greenbaum, Noam; Porat, Naomi; Rhodes, Edward; Enzel, Y
Fonte: Pergamon-Elsevier Ltd Publicador: Pergamon-Elsevier Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.65%
Slackwater deposits were found in a cave in the Nahal Netafim catchment (35 km2), near the head of the Gulf of Aqaba in the southern Negev, Israel. The sedimentological record includes 27 large paleofloods, dated by infrared stimulated luminescence to 33,

Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes

Benito, Gerardo; Thorndycraft, V. R.; Rico, María Teresa; Sánchez Moya, Yolanda; Sopeña, Alfonso
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
67.19%
10 páginas, 5 figuras, 1 tabla.-- El PDF del artículo es la versión manuscrita del autor.; Palaeoflood chronologies from seven Spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed. These fluvial records were divided in to two sub-sets, namely Atlantic (10 ka record) and Mediterranean (3 ka record) river basins, which represent distinct modern hydroclimatic conditions. In Atlantic basins floods result from intense, widespread rainfalls associated with Atlantic frontal systems transported by westerly airflow. Mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems (MCSs) during autumn months. Evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10,750–10,240; 9550–9130; 4820–4440; 2865–2350; 960–790; and 520–290 cal BP. Despite the different flood-producing weather conditions in Atlantic and Mediterranean rivers, the radiocarbon sample clusters overlap and indicate changes in large-scale atmospheric circulation and climatic conditions in the Iberian Peninsula. Comparison with proxy records of mean temperature for the Northern Hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases (e.g. the 2650 yr BP climatic event or AD 1590–1650 period of the Little Ice Age). Radiocarbon dates from aggraded floodplain sediments were clustered at 2710–2320...

The palaeoflood record of the Gardon river, France: A comparison with the extreme 2002 flood event

Sheffer, N. A.; Rico, María Teresa; Enzel, Y.; Benito, Gerardo; Grodek, T.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
66.77%
13 páginas, 8 figuras, 3 tablas.-- El PDf del artículo es su versión post-print.; A paleoflood study in the Gardon River gorge in southern France identified extreme floods larger than any modern or historically gauged flood. During the course of our study, an extreme flood on the 8–9th of September 2002 claimed the lives of 21 people and caused millions of Euros worth of damage to the towns and villages along the river. The magnitude of this flood was larger than any known historical flood on record,. However, there is evidence of greater magnitude flood events in the form of slack-water flood deposits preserved in caves elevated 17–19 m above the normal base flow, and up to 3 m above the level reached by the 2002 floodwaters. The stratigraphy and radiocarbon dating show that at least five extreme events occurred during the past 500 years. The discharge estimation associated with these flood units, achieved using the HEC-RAS one dimensional model, indicates that at least three floods were bracketed by discharges between 6850 and 7100 m3 s− 1, and at least two floods reached a magnitude above 8000 m3 s− 1. Therefore, the extraordinary flood of 2002 was not the largest in the basin.; This project was totally funded by the European Commission...

Late Holocene fluvial chronology of Spain: The role of climatic variability and human impact

Thorndycraft, V. R.; Benito, Gerardo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
67.04%
A database of published and unpublished radiocarbon dates from Late Holocene fluvial environments in Spain was critically analysed in order to obtain a fluvial chronology for this period. The principal types of depositional environment represented in the record were slackwater flood deposits (28 dates), alluvial overbank facies (12 dates) and alluvial channel facies (7 dates). The sedimentary context of each date was classified in order to identify those samples that specifically dated change in the fluvial environment. Analysis of the different depositional environment data-sets using summed probability plots identified phases of alluviation at 2800–2350 and 800–500 cal. BP. Increased frequency of large magnitude floods occurred at 2850–2500, 1000–800 and 520–250 cal. BP. The results indicate that in Mediterranean regions slackwater flood deposits are valuable archives of climatic variability even during periods of increased human impact.; This research was funded by the International Council for Science (ICSU) project “Past hydrological events related to understanding global change” and the INQUA project “The significance of past hydrological events: using existing 14C data to reconstruct Holocene fluvial activity in temperate and tropical regions.”; Peer reviewed

The Holocene fluvial chronology of Spain: Evidence from a newly compiled radiocarbon database

Thorndycraft, V. R.; Benito, Gerardo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
37%
A critical analysis of 74 radiocarbon dates, selected from a total of 102 published and unpublished dates from Holocene fluvial environments in Spain, has identified a number of periods of increased fluvial activity in Spain, namely: 11,170–10,230; 9630–8785; 7980–6860; 5800–4800; 3880–3085; 2895–1820; 1300–0 cal BP, the latter period reflecting sustained fluvial response to increased human impact. The radiocarbon samples were classified according to type of depositional environment: (a) alluvial overbank, (b) flood basin, (c) alluvial channel gravels, (d) fluvio-torrential deposits and (e) slackwater flood deposits (palaeofloods). Dates from slackwater flood deposits indicated at least five phases of increased frequency of large magnitude floods during the Holocene: 10,855–10,230; 9530–8780; 2880–2430; 975–790; and 520–265 cal yr BP. Flood basin type deposition occurred from 7980 to 4830 cal yr BP. The main clusters of dates from alluvial floodplain deposits occurred at 2750–2150 and 930–520 cal yr BP. The record is discussed in relation to other palaeoenvironmental archives including pollen records of Holocene vegetation change and palaeoclimatic proxies such as the North Atlantic drift ice record. Comparison with the latter indicates that major Holocene flooding coincided with cold climate phases during 9530–9280...

A long-term flood discharge record derived from slackwater flood deposits of the Llobregat River, NE Spain

Thorndycraft, V. R.; Benito, Gerardo; Rico, María Teresa; Sopeña, Alfonso; Casas Planes, M. A.; Sánchez Moya, Yolanda
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
87.22%
16 páginas, 7 figuras, 4 tablas.-- El PDF del artículo es su versión post-print.; Slackwater palaeoflood deposits were identified along two bedrock gorge study reaches of the Llobregat River, at Pont de Vilomara and Monistrol de Montserrat. The compiled palaeoflood record consists of two principal flood series: (a) a relatively complete record of low to high magnitude flood events from the last ca. 100 years and (b) evidence of the largest palaeoflood events that have occurred over the last ca. 2700 years. The longer term extreme palaeoflood record indicates that the discharge of the 1971 flood, the largest on record, was exceeded on at least eight occasions, with two periods of high magnitude flooding identified: (a) the Late Bronze Age (2500–2700 years ago) and (b) the Little Ice Age (AD 1500–1700). At Pont de Vilomara, palaeodischarge estimates of 3700–4300 m3/s compare to a discharge of 2300 m3/s for the 1971 event. Downstream at Monistrol, an estimate of 4680 m3/s for flood deposits dated as AD 1516–1642, and believed to be those of the AD 1617 flood, compared to 2500 m3/s for the 1971 flood.; The research was carried out as part of the SPHERE Project (Systematic, Palaeoflood and Historical data for the improvEment of flood Risk Estimation)...

Caesium-137 dating applied to slackwater flood deposits of the Llobregat River, NE Spain

Thorndycraft, V. R.; Benito, Gerardo; Walling, D. E.; Sopeña, Alfonso; Sánchez Moya, Yolanda; Rico, María Teresa; Casas Planes, M. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
97.48%
14 páginas, 6 figuras, 1 tabla.-- El PDF del artículo es su versión post-print.; During a palaeoflood study of the Llobregat River (NE Spain), analysis of 137Cs was carried out on slackwater flood deposits to obtain an improved flood chronology for the most recent flood sediments. At the Monistrol study reach, 137Cs was measured in flood deposits preserved in valley side rock alcoves, with a range of 137Cs concentrations of 2.80–10.06 mBq/g measured. The 137Cs was associated with sediment mobilised from the upstream catchment by erosion and transported to the alcoves during floods. The onset of measured caesium activity in the sedimentary profiles permitted the deposits to be divided between those from floods that occurred before the mid-1950s and those from events after this period. Combining the information derived from the slackwater flood stratigraphy, the minimum discharge estimates associated with the flood deposits, 137Cs analysis and the instrumental peak discharge series, it was possible to identify the particular flood events responsible for the majority of the slackwater flood units. At Vilomara, however, 137Cs activity was measured in palaeoflood deposits dated to the Late Bronze Age and located at an elevation not reached by the floodwaters of the largest modern events. The data from this site indicated that the 137Cs was not associated with sediments transported by floods but was rainfall-derived...

Palaeoflood hydrology and its role in applied hydrological sciences

Benito, Gerardo; Thorndycraft, V. R.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 5160 bytes; image/gif
ENG
Relevância na Pesquisa
46.65%
This paper is a review of the methodology of palaeoflood hydrology. In particular, we focus on recent developments and the credibility of the palaeoflood data produced. The use of slackwater flood deposits as a physical record of water surface elevations reached by past floods enables the calculation of robust palaeodischarge estimates for floods that occurred during recent centuries or millennia. Over these time intervals the chronological precision from numerical age dating, such as radiocarbon, is sufficient for the structuring of the palaeoflood discharge data into different threshold levels that are exceeded by floodwaters over specific periods of time, the input data necessary for new methodologies of flood frequency analysis. The value of palaeoflood hydrology to hydrological sciences is discussed through its application in varying multidisciplinary research themes. We demonstrate the use of palaeoflood hydrology in: (1) flood risk estimation; (2) determination of the maximum limit of flood magnitude and non-exceedances as a check of the probable maximum flood (PMF) and its application in producing regional, long-term envelope curves; (3) Holocene climatic variability and (4) assessing sustainability of water resources in dryland environments where floods are an important source of water to alluvial aquifers.; Our palaeoflood research has been funded by the European Commission through the projects ‘Systematic...

Palaeoflood record of the Tagus River (Central Spain) during the Late Pleistocene and Holocene

Benito, Gerardo; Sopeña, Alfonso; Sánchez Moya, Yolanda; Machado, María José; Pérez-González, Alfredo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 817 bytes; image/gif
ENG
Relevância na Pesquisa
16.58%
Palaeoflood hydrology of the Tagus River (Central Spain) was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at El Puente del Arzobispo in the central part of the catchment (35,000 km2 in drainage area) and in Alcántara, at the lower part of the catchment (52,000 km2 in drainage area) near the Portuguese border. The palaeoflood record, with more than 80 flood events, shows clusters of floods at specific periods from 9440 to 9210 14Cyr BP (8540–8110 BC), 8500 to 8000 14Cyr BP (7500–7000 BC), 6750 14Cyr BP (5000 BC), 1200 to 950 14Cyr BP (AD 785–1205), 410 14Cyr BP (AD 1450–1500), 170 to 80 14Cyr BP (AD 1670–1950). The largest flood(s) occurred during the periods 9440 to 9210 14Cyr BP, 6750 14Cyr BP and 1200 to 950 14Cyr BP reaching minimum discharge estimates of between 4000 and 4100 m3 s−1 in the El Puente del Arzobispo reach and 13,700–15,000 m3 s−1 in the Alcántara reach. These periods with increased flood magnitude and/or frequency in the Tagus River are strongly related to increased moisture influx and winter precipitation in the Iberian Peninsula, especially in the western zone. Proxy records sensitive to winter precipitation such as lake levels and vegetation changes (indicated by pollen records) are in good agreement with the clusters of floods found in the Tagus River. This flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the Iberian Peninsula.; This research was supported by the Spanish Committee for Science and Technology (CICYT) grant HID99-0850...

Sedimentology of high-stage flood deposits of the Tagus River, Central Spain

Benito, Gerardo; Sánchez Moya, Yolanda; Sopeña, Alfonso
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
87.35%
This paper details the sedimentology of high-stage flood deposits, with the definition of sedimentary environments and their characteristic sequences, along two bedrock reaches of the Tagus River (Central Spain). High-stage flood deposits accumulated in bedrock canyons include slackwater flood deposits (SWD) and other types of deposits located at flow separation zones and associated with slow-moving flow (<1 m s−1). These flood deposits are common indirect indicators of flood stages used in palaeoflood studies for estimating the discharges associated with Quaternary floods. Depositional environments of flood deposits include (1) channel widening, (2) canyon expansion, (3) bedrock obstacles, and (4) backflooded areas along tributary streams. These flood deposits can be found associated with other non-fluvial environments, namely aeolian reworked and slope washflow facies. Channel widening, due to flood stage variations, comprises internal and external zones of the channel margins, and their characteristic sequences contain similar facies to those of alluvial floodplains. Canyon expansion environments favour vertical accretion of slackwater units and the development of flood deposit benches, which contain four sequences related to bench elevation and distance from the channel's main thread of flow. At the lee side of bedrock obstacles...

Relación entre periodos frios y cambios de patrón de macroescala (oscilación del Atlántico Norte) en las inundaciones en el Río Guadiana; Relationship betwen cold periods and changes in macroscale patterns (North Atlantic oscillation) in Guadiana River floods

Ortega, A.; Garzón Heydt, G.
Fonte: Sociedad Geológica de España Publicador: Sociedad Geológica de España
Tipo: Artículo Formato: 190981 bytes; application/pdf
SPA
Relevância na Pesquisa
16.51%
43ª Sesión Científica. Móstoles, Noviembre de 2007; Global changes in climate have been widely documented but the relationships between these changes and floods are not easy to establish. Hydroclimatology offers an important tool in order to improve our knowledge about the flood producing mechanisms, which can be used to explain historical and palaeohydrological events. Storm cells and mesoscale systems develop into small floods, mainly at tributary streams. But a synoptic scale relates better to Guadiana River floods, dominant in winter. At a higher level, macroscale atmospheric configuration can also explain flood generation at the Guadiana River and, particularly, the North Atlantic Oscillation (NAO) that is one of the most important recurrent patterns of atmospheric circulation. There is no reliable evidence, however relating NAO and historical floods in Europe, especially for central European countries. This situation changes in the Iberian Peninsula, specially in the Southwest that shows a good relationship between winter floods and a negative NAO phase. Recent Guadiana River floods (XX century) could be related to these phenomena, but there´s not and index who covers previous events. Guadiana palaeoflood records compiled using slackwater deposits are dated by 14C radiometric methods and associated...