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The Oligocene-Neogene deep-sea Columbia Channel system in the South Brazilian Basin: Seismic stratigraphy and environmental changes

LIMA, Andrea Franca; FAUGERES, Jean-Claude; MAHIQUES, Michel
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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The Columbia Channel (CCS) system is a depositional system located in the South Brazilian Basin, south of the Vitoria-Trindade volcanic chain. It lies in a WNW-ESE direction on the continental rise and abyssal plain, at a depth of between 4200 and 5200 m. It is formed by two depocenters elongated respectively south and north of the channel that show different sediment patterns. The area is swept by a deep western boundary current formed by AABW. The system has been previously interpreted has a mixed turbidite-contourite system. More detailed study of seismic data permits a more precise definition of the modern channel morphology, the system stratigraphy as well as the sedimentary processes and control. The modern CCS presents active erosion and/or transport along the channel. The ancient Oligo-Neogene system overlies a ""upper Cretaceous-Paleogene"" sedimentary substratum (Unit U1) bounded at the top by a major erosive ""late Eocene-early Oligocene"" discordance (D2). This ancient system is subdivided into 2 seismic units (U2 and U3). The thick basal U2 unit constitutes the larger part of the system. It consists of three subunits bounded by unconformities: D3 (""Oligocene-Miocene boundary""), D4 (""late Miocene"") and D5 (""late Pliocene""). The subunits have a fairly tabular geometry in the shallow NW depocenter associated with predominant turbidite deposits. They present a mounded shape in the deep NE depocenter...

Palynostratigraphy and sedimentary facies of Middle Miocene fluvial deposits of the Amazonas Basin, Brazil

Dino, Rodolfo; Amaral Soares, Emilio Alberto; Antonioli, Luzia; Riccomini, Claudio; Rodrigues Nogueira, Afonso Cesar
Fonte: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD Publicador: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
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Palynostratigraphic and sedimentary fades analyses were made on sedimentary deposits from the left bank of the Solimoes River, southwest of Manaus. State of Amazonas, Brazil. These provided the age-elating and subdivision of a post-Cietaceous stratigraphic succession in the Amazonas Basin. The Novo Remanso Formation is subdivided into upper and lower units, and delineated by discontinuous surfaces at its top and bottom. The formation consists primarily of sandstones and minor mudstones and conglomerates, reflecting fluvial channel, point bar and floodplain facies of a fluvial meandering paleosystem. Fairly well-preserved palynoflora was recovered from four palynologically productive samples collected in a local irregular concentration of gray clay deposits, rich in organic material and fossilized wood, at the top of the Nova Remanso Formation upper unit. The palynoflora is dominated by terrestrial spores and pollen grains, an d is characterized by abundant angiosperm pollen grains (Tricolpites, Grimsdalea, Perisyncolporites, Tricolporites and Malvacearumpollis). Trilete spores are almost as abundant as the angiosperm pollen, and are represented mainly by the genera Deltoidospora. Verrutriletes, and Hamulatisporis. Gymnosperm pollen is scarce. The presence of the index species Grimsdalea magnaclavata Germeraad et al. (1968) indicates that these deposits belong to the Middle Miocene homonymous palynozone (Lorente...

Brachydelphis (pontoporiidae, odontoceti, cetacea) do neógeno do pacífico sul oriental

Gutstein, Carolina Simon
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
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Brachydelphis maseazi Muizon 1988, da Formação Pisco (Mesomiocene, Peru), corresponde a uma espécie de odontoceto conhecida por dois crânios incompletos e alguns elementos pós-cranianos associados. Uma revisão e estudo comparativo desta espécie foram realizados a partir de novos espécimes referidos a B. mazeasi provenientes dos depósitos neógenos da costa Sul-Pacífica do Peru e do Chile (Fms. Pisco e Bahía Inglesa respectivamente). Como dado complementar, nessa comparação, se estabeleceram hipóteses de correlações cronoestratigráficas para ambas as formações. Os fósseis aqui analisados ocorrem em rochas fosfáticas, cuja gênese ocorre sob condições muito específicas e está relacionada a eventos globais de variação de nível eustático. A presença dessas rochas em diversas formações neógenas do Pacífico, enfocando as Fms. Pisco e B. Inglesa, permitiu propor uma correlação cronoestratigráfica preliminar e constitui-se numa boa ferramenta para correlacionar eventos entre essas formações. Por outro lado, a tafonomia das mesmas é distinta, em um plano geral, com a Fm. B. Inglesa apresentando massiva quantidade de fósseis em uma camada retrabalhada de D-fosfato e a Fm. Pisco com amplos depósitos de sedimentos finos e fósseis esparsos. A fauna de vertebrados também já foi sugerida como sendo relacionada já que é notoriamente similar. A família Pontoporiidae está amplamente registrada em ambas as formações. A presença de B. mazeasi no Mesomioceno da Fm. Pisco reforçou a proposição da origem Pacífica para a família. Contudo...

Faunes ichthyologiques du Néogène Supérieur d’Angola, leur âge, remarques sur le Pliocène marin en Afrique Australe

Antunes, M. T.
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Artigo de Revista Científica
Publicado em 11/07/2008 FRA
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This note is concerned with fish remains from Upper Neogene beds at Farol das Lagostas (and nearby quarry of SECIL) and Baía Farta, mainly recovered by the author in 1960, 1961, 1963 and 1967. For further data see ANTUNES, 1964, pp. 213-215. All the forms identified until now (many of them for the first time) are show in «tableau I». Smaller ones are poorly represented. I. benedeni is provisorily accepted as a distinct species, though it may correspond to a dental morphotype that does exist equally in the extant I. oxyrhinchus (see text): therefore I. benedeni from Farol das Lagostas may after all represent only some dental variations that really belong in the form described as I. cf. oxyrhinchus. The presence of Aprionodon and Hypoprion could not be ascertained: Procarcharodon megalodon, Carcharodon carcharias, Isurus benedeni. Galeocerdo cuvieri, and Carcharhinus sp. I and sp. II are specially discussed. The whole fauna does not correspond either to a very shallow and coastal environment, or to deep waters far away from the coast. It clearly points out to warm waters: an acceptable model would be the fauna from the tropical Atlantic between Northern Angola and Senegal-Cape Verde. The age of this fauna was long regarded as Burdigalian. The data formerly presented (ANTUNES...

Faunes ichthyologiques du Néogène Supérieur d’Angola, leur âge, remarques sur le Pliocène marin en Afrique Australe

Antunes, M. T.
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Artigo de Revista Científica
Publicado em 25/07/2008 FRA
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This note is concerned with fish remains from upper Neogene beds at Farol das Lagostas (and nearby quarry of SECIL) and Baía Farta, mainly recovered by the author in 1960, 1961, 1963 and 1967. For further data see ANTUNES, 1964, pp. 213-215. All the forms identified until now (many of them for the first time) are show in «tableau I». Smaller ones are poorly represented. I. benedeni is provisorily accepted as a distinct species, though it may correspond to a dental morphotype that does exist equally in the extant I. oxyrhinchus (see text): therefore I. benedeni from Farol das Lagostas may after all represent only some dental variations that really belong in the form described as I. cf. oxyrhinchus. The presence of Aprionodon and Hypoprion could not be ascertained: Procarcharodon megalodon, Carcharodon carcharias, Isurus benedeni. Galeocerdo cuvieri, and Carcharhinus sp. I and sp. II are specially discussed. The whole fauna does not correspond either to a very shallow and coastal environment, or to deep waters far away from the coast. It clearly points out to warm waters: an acceptable model would be the fauna from the tropical Atlantic between Northern Angola and Senegal-Cape Verde. The age of this fauna was long regarded as Burdigalian. The data formerly presented (ANTUNES...

The Neogene of the Lower Tagus Basin (Portugal)

Pais, João
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Artigo de Revista Científica
Publicado em 25/03/2010 ENG
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Revista Española de Paleontologia 19 (2), 229-242; The Tertiary Lower Tagus Basin (LTB) occupies a large area in Portugal and constitutes a symmetric basin of the oriental huge Upper Tagus Basin, centered at Madrid (Spain). The LTB was an endorreic basin during the Paleogene. Marine connection occurred at the Lower Aquitanian; at the Lisbon – Setúbal Peninsula region the sedimentation was in the ocean/continent interface, with several changes in the coast line. Apparently, the first marine transgression came from South, originating a gulf with a N-S coral reef that attained the Lisbon area. Occidental communication to the sea was established after the Burdigalian.The sedimentary and palaeontologic record of the distal sector of the LTB (Lisbon –Setúbal Peninsula) is related to sea level changes. It is possible to correlate levels with planctic foraminifera and mammals, as well as to get isotopic ages (K/Ar in glauconites; 87Sr/86Sr). Good biostratigraphic data can be obtain from continental and coastal deposits. The fossil richness – dinoflagellates, spores, pollen, plant macrorremains, foraminifera, ostracoda, molluscs, echinids, fishes, reptiles, mammals – and O and C isotopes, constitutes a large source of information for environmental and palaeogeographical reconstitutions...

The Neogene of Algarve (Portugal)

Pais, João; Legoinha, P.; Elderfield, H.; Sousa, L.; Estevens, M.
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Artigo de Revista Científica
Publicado em 29/12/2010 ENG
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A synthesis about the Neogene and Quaternary of Algarve (Southern Portugal) is presented. New isotopic 87Sr/86Sr ages as well as biostratigraphic data about the Miocene deposits allow to present a new stratigraphic frame for the previously characterized units. The Lagos-Portimão Formation corresponds to deposits of temperate carbonate platform sedimentological type, developed during a long time span (Lower Burdigalian to Upper Serravallian). A major change in sedimentation conditions (carbonate to siliciclastic environments) occurred in the Lower Tortonian with the deposition of yellowish sands. Spongoliths rich in microfossils are represented in Algarve inland. Their age is not well established; calcareous nannofossils indicate the CN5a zone (Upper Serravallian) while foraminifera point out at least Nl6 zone (Lower Tortonian). In the Upper Tortonian, the sedimentation is widespread in Eastern Algarve, related with the Guadalquivir Basin infill. The deposits begin with detrital limestones, locally very rich in Heterostegina, passing to fossiliferous conglomerates and siltstones (Cacela Formation). Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±0.17 Ma. However, glauconites may be reworked from older deposits (Cacela Formation). The Galvana Conglomerate could be related to Pliocene deposits are not well characterized. Olhos de Água sands...

The three main marine depositional cycles of the Neogene of Portugal

Cachão, M.; Silva, C. M.
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Artigo de Revista Científica
Publicado em 29/12/2010 ENG
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The present work follows a stratigraphic model for the marine Neogene of Portugal based on the definition of three main marine sedimentary cycles. Conceptually the I, II and III Neogene Cycles can be defined as 2nd order sedimentary sequences with duration ranging from 5 to 8 Ma. The I Neogene Cycle is fully represented only in the Lower Tagus Basin. Ranging from the Early Aquitanian to the Late Burdigalian the I Neogene Cycle testify a transgressive episode in the region of Lisbon and Setúbal Peninsula. Rapid lateral facies variations suggest a shallowmarine basin. This cycle ends with an important Late Burdigalian tectonic compressive event expressed by uplift of the surrounding areas and deformation affecting the Early Miocene deposits of the Arrábida Chain. The II Neogene Cycle includes thick sedimentary sequences covering Paleozoic and Mesozoic formations in the Algarve and Alvalade-Melides regions and it extends as far north as Santarém in the Lower Tagus Basin. Mainly controlled by global eustasy, it was generated by the important positive eustatic trend that characterized the Middle Miocene worldwide to which the Portuguese continental margin acted more or less passively. This cycle ended with a second and the most important compression event starting after the end of the Serravallian affecting the entire Portuguese onshore and shelf areas. This led to an important depositional hiatus of marine sediments for more than 2.5 Ma. During the Early and the Middle Tortonian occurred the clockwise rotation of the Guadalquivir Basin. The thickmarine units deposited afterwards in this basin produced a litostatic load...

Delineating shallow Neogene deformation structures in northeastern Pará State using Ground Penetrating Radar

Rossetti,Dilce F.
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2003 EN
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The geological characterization of shallow subsurface Neogene deposits in northeastern Pará State using Ground Penetrating Radar (GPR) revealed normal and reverse faults, as well as folds, not yet well documented by field studies. The faults are identified mostly by steeply-dipping reflections that sharply cut the nearby reflections causing bed offsets, drags and rollovers. The folds are recognized by reflections that are highly undulating, configuring broad concave and convex-up features that are up to 50 m wide and 80 to 90 ns deep. These deformation structures are mostly developed within deposits of Miocene age, though some of the faults might continue into younger deposits as well. Although the studied GPR sections show several diffractions caused by trees, differential degrees of moisture, and underground artifacts, the structures recorded here can not be explained by any of these 'noises'. The detailed analysis of the GPR sections reveals that they are attributed to bed distortion caused by brittle deformation and folding. The record of faults and folds are not widespread in the Neogene deposits of the Bragantina area. These GPR data are in agreement with structural models, which have proposed a complex evolution including strike-slip motion for this area from the Miocene to present.

Low-temperature thermochronology from tunnel and surface samples in the Central and Western Alps; Niedrig-Temperatur Thermochronologie von Tunnel- und Oberflächenproben in den zentralen und westlichen Alpen

Glotzbach, Christoph
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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Low-temperature thermochronology owns the unique potential to derive rates of cooling, exhumation and denudation (erosional and tectonic). Furthermore it bears information about palaeotopography. This thesis comprises five low-temperature thermochronological studies conducted in the Western and Central Alps, i.e., one study in the eastern Lepontine dome and four studies along orogen-perpendicular transects through the Western and Central Alps. Main objectives of these studies are: (1) To unravel the structural-kinematic and exhumation history of the investigated regions, and (2) to estimate the shape of palaeo-isotherms under given boundary conditions. Three transects along tunnels (Mont Blanc, Lötschberg and Gotthard) and corresponding surface profiles were sampled in the external crystalline massifs (ECM) of the Mont Blanc, Aar and Gotthard. Sampling of the Lepontine dome was applied on a broader spatial scale. Samples were dated with the apatite and zircon fission track method (AFT and ZFT, respectively) and with the apatite (U-Th)/He method (AHe), which record the cooling of rocks between 330 and 40°C. The resulting two-dimensional sample transects along the tunnels were used to estimate the shape of palaeo-isotherms and to derive lateral and temporal differences in exhumation rates. Thermochronological data...

Biochronostratigraphy and paleoenvironment analysis of Neogene deposits from the Pelotas Basin (well 2-TG-96-RS), Southernmost Brazil

SILVA,WAGNER G.; ZERFASS,GEISE S.A.; SOUZA,PAULO A.; HELENES,JAVIER
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2015 EN
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This paper presents the integration of micropaleontological (palynology and foraminifera) and isotopic (87Sr/86Sr) analysis of a selected interval from the well 2-TG-96-RS, drilled on the onshore portion of the Pelotas Basin, Rio Grande do Sul, Brazil. A total of eight samples of the section between 140.20 and 73.50 m in depth was selected for palynological analysis, revealing diversified and abundant palynomorph associations. Species of spores, pollen grains and dinoflagellate cysts are the most common palynomorphs found. Planktic and benthic calcareous foraminifera were recovered from the lowest two levels of the section (140.20 and 134.30 m). Based on the stratigraphic range of the species of dinoflagellate cysts and sporomorphs, a span age from Late Miocene to Early Pliocene is assigned. The relative age obtained from the 87Sr/86Sr ratio in shells of calcareous foraminifers indicates a Late Miocene (Messinian) correspondence, corroborating the biostratigraphic positioning performed with palynomorphs. Paleoenvironmental interpretations based on the quantitative distribution of organic components (palynomorphs, phytoclasts and amorphous organic matter) throughout the section and on foraminiferal associations indicate a shallow marine depositional environment for the section. Two palynologicals intervals were recognized based on palynofacies analysis...

Burdigalian deposits of the Santa Cruz Formation in the Sierra Baguales, Austral (Magallanes) Basin: Age, depositional environment and vertebrate fossils

Bostelmann, J. Enrique; Le Roux, Jacobus P; Vásquez, Ana; Gutiérrez, Néstor M.; Oyarzún, José Luis; Carreño, Catalina; Torres, Teresa; Otero, Rodrigo; Llanos, Andrea; Fanning, C. Mark; Hervé, Francisco
Fonte: Servicio Nacional de Geología y Minería Publicador: Servicio Nacional de Geología y Minería
Tipo: Artigo de Revista Científica
EN
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Indexación: Scielo; ABSTRACT. A succession of marine and continental strata on the southern flank of Cerro Cono in the Sierra Baguales, northeast of Torres del Paine, can be correlated with stratigraphic units exposed along the southern border of the Lago Argentino region in Santa Cruz Province, Argentina. These include the Estancia 25 de Mayo Formation and the basal part of the Santa Cruz Formation. The lithological correlation is also confirmed by detrital zircon ages (maximum age of 18.23±0.26 Ma) and a rich assemblage of terrestrial vertebrate fossils, biostratigraphically equivalent to a postColhuehuapian, pre-Santacrucian South American Land Mammal Age (SALMA) fauna, suggesting a range of 19 to 17.8 Ma. Similar ages have been obtained from the basal part of the Santa Cruz Formation at Estancia Quién Sabe in southwestern Argentina, supporting the assumption of a regional continuity between these deposits. A measured lithostratigraphic column is presented and the depositional environment is interpreted as a coastal plain with small, meandering rivers and ephemeral floodplain lakes. The sedimentation coincides with intensified uplift of the Patagonian Andes during the ‘Quechua Phase’ of Andean tectonism, which is reflected by a change in paleocurrent directions from northwest to east-northeast. Keywords: Burdigalian...

Los depósitos sinorogénicos del sur de Mendoza y su relación con la faja plegada y corrida de Malargüe (35° -36°S), Mendoza. Argentina; The sinorogenis deposits of south of Mendoza and their relation with Malargüe fold and thrust belt (35° -36°S). Mendoza. Argentina

Arcila Gallego, Paula Alexandra
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2010 SPA
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En el extremo sur de la Cordillera Principal entre los 35º-36ºLS, los depósitos sinorogénicos y los estratos de crecimiento preservados en los depocentros sintectónicos de antepaís Horqueta, Pincheira y Ventana, registraron la historia de estructuración de la faja plegada y corrida de Malargüe desde el Neógeno hasta el Pleistoceno. Las secuencias sinorogénicas en los depocentros Horqueta, Pincheira y Ventana, alcanzan los 1.200 metros de espesor con depósitos de naturaleza volcánica, volcaniclástica, epiclástica, y en menor medida fluvial a lacustre, representados en las unidades litoestratigráficas Formación Molle, Agua de la Piedra, Butaló, Loma Fiera, Pincheira, Bramón y Coyocho. La evolución tectónica en los depocentros sinorogénicos de antepaís en función de la cronoestratigrafía, geoquímica y análisis de litofacies permite reconocer: (1) Estado inicial de cuenca de antepaís durante el Mioceno inferior. (2) Estado de depocentro de cuña frontal en el Mioceno medio. (3) La instalación de un arco volcánico local en el Mioceno superior y (4) Estado de cuenca de piggy-back durante el Mioceno superior a Plioceno. Los factores de control corresponden a la migración de la faja plegada y corrida de Malargüe con un estilo de deformación mixto hacia el antepaís...

Estratigrafía, sistemas depositacionales y aspectos composicionales del relleno neógeno de la cuenca Rodeo-Iglesia, San Juan, Argentina; Stratigraphy, depositional systems and compositional aspects of the neogene deposits of the Rodeo-Iglesia basin, San Juan province, Argentina

Alonso, María Susana
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2011 SPA
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67.23%
En este trabajo se estudió el relleno neógeno de la Cuenca de Rodeo- Iglesia, que comprende una potente sucesión continental. Estos depósitos pueden separarse en dos formaciones, Cuesta del Viento y Rodeo. La primera es una nueva unidad, definida originalmente para la vecina Cuenca de La Tranca, que registra la sedimentación proximal relacionada directamente con el levantamiento de la Sierra Negra. En este trabajo, se propone la separación de los términos basales de la secuencia neógena, anteriormente asignados a la Formación Rodeo y su nueva asignación a la Formación Cuesta del Viento. Esta unidad corresponde a depósitos de sistemas proximales, de alta pendiente y energía y a intervalos pelíticos y areno-pelíticos, correspondientes a una sedimentación distal de sistemas que drenan desde el Oeste. La Formación Rodeo ha sido dividida en dos Miembros: Lomas del Campanario, conformado por depósitos relacionados con actividad volcánica intracuencal y su retrabajo y Las Flores, que registra el impacto sobre la cuenca del levantamiento de la Cordillera de Colanguil, y la consecuente progradación de cuñas clásticas Hacia el techo de la unidad, un episodio evaporítico de importancia ha dado origen a depósitos de yeso de espesores considerables. El Miembro Lomas del Campanario...

Neogene-Quaternary coastal and offshore sedimentation in north central Chile: Record of sea-level changes and implications for Andean tectonism

Venegas, C.; Gómez, Christian; Lavenu, Alain; Fenner, J.; Marquardt, C.; Gregory Wodzicki, K. M.; Marchant, M.; Frassinetti, D.; Middleton, H.; Buchbinder, B.; Le Roux, J. P.
Fonte: PERGAMON-ELSEVIER SCIENCE Publicador: PERGAMON-ELSEVIER SCIENCE
Tipo: Artículo de revista
EN
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The stratigraphy, sedimentology, and paleontology of the Coquimbo Formation in a coastal section approximately 100km north of La Serena was Studied to establish relative low-order sea-level changes during the Neogene. During the Early-Middle Miocene, a wide coastal platform was bevelled onto Palaeozoic basement rocks, and marine sedimentation may have taken place within a deep coastal inlet later transformed into a submarine canyon. Transgression over this platform commenced during the late Burdigalian-early Langhian (16-15 Ma) and culminated in a sea-level highstand near the end of the Serravalian (11.8 Ma). This transgression was followed by regression during the rest of the Serravalian and Tortonian until approximately 9 Ma. Renewed transgression during the Messinian was Succeeded by regression lasting until 5.5 Ma, when another transgressive cycle bevelled a ravinement Surface into the underlying deposits. This cycle terminated in a marine highstand during the Zanclean at 4.9 Ma. Thereafter, the succession changed front enter platform to middle shoreface deposition. Rapid flooding at 3.9 Ma resulted in the formation of an extensively bored phosphatic hardground, which represents a condensed section. A lowstand during the Piacenzian is represented by inner-shelfdeposits...

Relación del índice de cristalinidad (IC) con la edad y el contenido de iones F y CO3 en muestras de vertebrados fósiles

Merino, Luis; Morales, Jorge
Fonte: Consejo Superior de Investigaciones Científicas (España) Publicador: Consejo Superior de Investigaciones Científicas (España)
Tipo: Artículo Formato: 21373 bytes; application/pdf
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[ES] Se ha determinado el índice de cristalinidad (IC) mediante difracción de rayos X de muestras actuales y fósiles pertenecientes a esmalte, dentina y hueso de metápodo de équidos, jiráfidos, rinocerótidos y proboscídeos de diferentes yacimientos neógenos españoles. Con estos valores de la cristalinidad del apatito se estima semicuantitativamente la evolución de los cambios diagenéticos ocurridos en el material óseo fósil. Se ha observado que el esmalte presenta un IC mayor que la dentina y hueso de metápodo, debido a su estructura más compacta. Sin embargo, no hay una correlación clara entre el incremento de la cristalinidad y la edad de las muestras. Además, el contenido de flúor aumenta durante los procesos de fosilización y como consecuencia aumenta el IC en las muestras fósiles. Por otro lado, el enriquecimiento diagenético de carbonato no está relacionado con la edad de los yacimientos, pero al aumentar su contenido en el esmalte, dentina y hueso de metápodo, disminuye en ellos su IC. Los sedimentos adyacentes juegan un papel clave en los cambios de cristalinidad de los huesos fósiles, como es el caso de los yacimientos con arenas, donde las muestras tienen un IC alto, por el contrario los yacimientos de margas y arcillas tienen un IC más bajo.; [EN] The crystalline fraction of enamel...

Review of Seismicity and Neogene Tectonics in Northeastern Brazil

Bezerra,F.H.; Ferreira,J.M.; Sousa,M.O.M.
Fonte: Revista de la Asociación Geológica Argentina Publicador: Revista de la Asociación Geológica Argentina
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
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Brazil comprises most of the continental intraplate part of South America, where seismicity is low but cannot be ignored. Both historical and instrumental seismological data indicate that northeastern Brazil has been one of the most seismically active parts of Brazil. This study presents an extensive review of both historical and instrumental seismicity and Neogene tectonics in this region. Systematic seismological monitoring started in 1986 with the João Câmara earthquake swarm. Seismicity concentrates around and to the west of the Potiguar basin, around the Recôncavo area, and along the Pernambuco shear zone. It occurs as swarms of events that may last for several years. Paleoseismological data from several sources point to paleoseismicity higher than that observed in the short present-day record. Raised marine terraces of late Pleistocene age indicate uplift and subsidence along the coast by as much as 12 m. Paleoliquefaction in late Neogene alluvial terraces indicates that it may have reached as much as magnitude M 7.0. The geological record presents evidence of faults that offset Neogene sedimentary deposits by as much as 260 m. Most of these faults correspond to reactivated Precambrian shear zones and Cretaceous faults. Geodetic monitoring is under way around the Potiguar basin. Most models that correlate intraplate seismicity with Neogene faults suggest that coseismic faulting occurs along preexisting zones of weakness. In a few places...

Paleoecological and paleoenvironmental implications of a high-density Chondrites association in slope deposits of the Neogene Santo Domingo Formation, Valdivia, south-central Chile

Encinas,Alfonso; Buatois,Luis A.; Finger,Kenneth L.
Fonte: Ameghiniana Publicador: Ameghiniana
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 EN
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36.64%
Neogene marine strata of the Santo Domingo Formation crop out in the vicinity of Valdivia, south-central Chile (40°S, 73°W). The succession is characterized by dark-gray sandy siltstone with abundant Chondrites isp. The occurrence of this ichnotaxon and lower-bathyal benthic foraminifers is consistent with a slope depositional environment. The abundance of Chondrites and the low ichnodiversity reveal poorly oxygenated bottom waters. The Santo Domingo Formation most likely accumulated in fault-controlled, intraslope silled minibasins, which werw formed during a major event of Neogene subsidence of the Chilean margin.

Acaciapollenites acaciae sp. nov., a new mimosoid polyad species from the Neogene of Colorado Basin, Argentina

Caccavari,Marta A.; Guler,M. Verónica
Fonte: Ameghiniana Publicador: Ameghiniana
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2006 EN
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46.56%
Fossil mimosoid polyads have been recently recovered from Neogene deposits in the Colorado Basin, Argentina, and the new species Acaciapollenites acaciae sp. nov. is described, which is closely similar to polyads of species included in Acacia Miller subgenus Acacia Vassal. It is characterized by colporate apertures on the distal face of the pollen grains, a typical polyad of the subgenus Acacia. The new polyad species is very similar to those of the extant Acacia curvifructa Burkart. Comparing the habitat of subgenus Acacia extant species, the Acaciapollenites acaciae occurrence suggests drier and warmer paleoclimatic conditions than today for the Late Miocene-Early Pliocene in the Colorado Basin. Paleogeographic data of Acacia pollen diversity are discussed. A similar early diversification and distribution of Acacia genus is recognized for the New and Old World.

Beidellite-nontronite clays in Neogene sediments from Cuitzeo-Charo lacustrine basin Michoacán, México: Geological setting and paleoenvironmental implications

Israde-Alcántara,Isabel; Robles-Camacho,Jasinto; Domínguez,José Manuel
Fonte: Sociedad Geológica Mexicana, A.C. Publicador: Sociedad Geológica Mexicana, A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
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36.74%
Lacustrine and fluviolacustrine deposits of the Charo sequence crop out extensively along tens of kilometres, and they overlie the Miocene volcanic sequences of the Mil Cumbres Complex in an E-W oriented basin. Eastwards of Morelia city (central Mexico), layers of non lithified clayey sediments of about 3 m in thickness are overlaid by massive diatomite deposits developed during the Miocene-Pliocene in the Cuitzeo palaeolake. Major outcrops are located south and east of the village of Charo at the Las Pulgas, Lomas Blancas and Tzitzimeo sites; all having similar mineralogical facies and strati graphic correlation. Field studies, petrography and X-ray fluorescence spectrometry (XRF) indicated that the parent rock was mainly of andesitic composition with minor daciticrhyolitic components. The source of the raw material was located in the upper topographic levels of the present horst-graben system. The diagenetic clays were identified as smectites. The central part of the Las Pulgas column shows a beidellite-nontronite (B-N) association. Likewise, 27A1-NMR and Móssbauer spectroscopies confirm the B-N character. Interlaid and overlying diatomite strata indicate a lacustrine environment, favourable to the development of secondary clays. The stability of lacustrine conditions gave place to an incipient stratification (smectite-illite)...