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his contribution provides new paleontological and stratigraphic data for the Eastern Precordillera (San Juan province, Argentina) Ordovician basin. This is based on the description of a group of olistoliths, interpreted herein as coming from the lower beds of the Ordovician Gualcamayo Formation, found embedded within the matrix of the Silurian-early Devonian Rinconada Formation. These olistoliths are characterized by variable dimensions and uniform lithologies, composed of black shales and marlstones or following hectometric limestone blocks related to the San Juan Formation. The Gualcamayo Formation blocks show a graptolite fauna characterized by Holmograptus spinosus, H. bovis, Cryptograptus schaeferi, Paraglossograptus tentaculatus, Archiclimacograptus spp., Atopograptus sp., Pseudophyllograptus sp., Tetragraptus sp., and Xiphograptus sp.; whereas on the bedding plane surfaces, conodont elements of Histiodella sp., Paroistodus horridus, Periodon macrodentatus, and Protopanderodus sp. are found. In the interbedded black shales-marlstones, the trilobites Annamitella sp., Mendolaspis sp., and Carolinites? sp. are observed. The presence of this graptolite fauna allows recording the middle Darriwilian H. spinosus Zone, representing the third record in South America, and enabling a correlation with other outcrops of Precordillera and North America, Australasia, and China. These middle Darriwilian deposits at the La Rinconada section represent the youngest age ever recorded for the drowning phase of the Ordovician carbonate platform (locally referred to as transfacies). This is coherent with a progressive drowning model from north to south and agrees with the diachronism of the base of the Gualcamayo Formation and equivalent units. In addition, the difference between the underlying units of the Rinconada Formation in different sections, together with contrasting thickness measurements, might indicate evidence of the Alto del Tambolar tectonic activity during the Rinconada Formation accumulation in Eastern Precordillera. These processes were also previously recognized for the deposition of the Tucunuco Group in the Central Precordillera. This study expands the knowledge regarding the carbonate drowning process of the Precordillera basin that occurred during the Middle Ordovician and the effects of the Guandacol Tectonic Phase in the La Rinconada area, never mentioned until this moment.

The Upper Cambrian-Tremadocian rocks exposed in the Alfarcito area of Cordillera Oriental, northwest Argentina reveal a series of transgressive-regressive cycles punctuated by incision of fluvio-estuarine valleys. An integrated sedimentologic, biostratigraphic and sequence stratigraphic study permits characterization of the sedimentary facies and stratal stacking patterns, and a revision of the stratigraphic framework of this succession. The Upper Cambrian-Tremadocian succession is included within the existing Santa Rosita Formation, which is formally subdivided here into six units, the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members. This scheme recognizes the internal complexities of the formation, in that the Tilcara and Pico de Halcón members record sedimentation in areally-restricted incised valleys and contain structures indicative of tidal dominance, whereas the Casa Colorada, Alfarcito and Rupasca members typify wave-dominated open-marine environments, where background suspension-fallout was punctuated by oscillatory flows during storms. The Tilcara Member is incised into the underlying Mesón Group. The Casa Colorada Member reflects a basinwide Late Cambrian transgression and subsequent progradation and consists of lower to upper offshore deposits. The Pico de Halcón Member is incised into the Casa Colorada Member. The Alfarcito Member is divided into three distinctly upward-coarsening and-thickening intervals. The sandstone-dominated intervals are composed of lower to middle shoreface deposits with minor amounts of offshore transition and upper shoreface deposits. The heterolithic, fine-grained intervals record more distal deposition, ranging from the lower offshore to the offshore transition. The Rupasca Member is a dominantly fine-grained unit that records a major late early to early late Tremadocian transgression. The lower interval of this member consists of lower offshore to offshore-transition deposits, while the upper part is made up of shelf to lower offshore deposits. The Humacha Member is not exposed in the study area. The importance of integrating biostratigraphy within a sedimentologic and sequence-stratigraphic framework is underscored here, in that it enables us to construct a more accurate stratigraphic framework which permits a clear understanding of the sedimentary dynamics of this system.

Abstract A comprehensive tectonic evolution of Proterozoic to Cambrian rocks that integrate the crystalline basement of Rio de Janeiro State, based on the new geological map, is presented. The map combines detailed geological data integrated to a 1:400.000 scale and new geochemical and geochronology data to characterize the distinct terranes amalgamated during three pulses of the Brasiliano orogeny. The Occidental terrane comprises the Tonian to Late Cryogenean passive margin of the São Francisco paleocontinent, including reworked cratonic basement. At the same period, two magmatic arc systems were developed outboard: The Continental Inner arc system represented by the dismembered terranes (Paraíba do Sul, Embú, and Cambuci domain) integrated now in the Central Superterrane: and the Intra-oceanic Outer Arc System, the Oriental Terrane, developed from 860 to 620 Ma. Related active basins were detected in association with the two arc systems that collided at ca. 620 - 595 and 605 - 550 Ma against the São Francisco passive margin. A later collision episode at ca. 535 to 510 Ma brought the Cabo Frio Terrane (Angola tip) and closed the Búzios back-arc basin. Finally, the collapse of the orogenic belt, probably related to slab detachment and asthenosphere upwelling marks transition to Gondwana stabilization.

La Formación La Silla (Cámbrico Superior - Ordovícico Inferior) fue definida en 1994 por Keller et al. a partir de los niveles inferiores de la Formación San Juan. Esta Formación consiste en una sucesión distintiva de calizas claras, con escasos fósiles y muy explotadas por su alta pureza. Basados en estudios detallados en la sección tipo cercana a Jáchal y siete secciones en el área sur cercana a la ciudad de San Juan, proponemos una subdivisión formal para la Formación La Silla en tres miembros. La división de la unidad está basada en la ubicación preferencial de bancos dolomíticos en el sector central de la Formación mientras que el sector superior e inferior son calizas monótonas. Los miembros se denominan, de base a techo: Miembro Río del Agua, Miembro Río Blanco y Miembro Río Salado (85, 140 y 81 m, respectivamente). Las dolomías en el Miembro Río Blanco son de dos tipos: macizas, potentes y generalmente asociadas a chert; y dolomías con laminación planar y/o entrecruzada, ambas fácilmente distinguibles a simple vista, otorgándole a este Miembro un aspecto bandeado debido a la alternancia entre calizas y dolomías. Esto contrasta con el aspecto macizo y monótono de los Miembros restantes con estratificación tabular y a veces suavemente ondulante. Se reconocen las facies de grainstone peloidal, grainstone oolítico, rudstone intraclástico, packstone peloidal, mudstone, microbiales laminadas y trombolíticas. Además se describen las nuevas facies de dolomías laminadas y dolomías macizas. De la misma manera que lo observado por Keller et al. (1994), la Formación La Silla representa una fase distinta en la sucesión cambro-ordovícica, con las dolomías perimareales de la Formación La Flecha por debajo y las calizas fosilíferas de plataforma abierta de la Formación San Juan por encima.The Cambro-Ordovician carbonate platform succession of the Precordillera Oriental of western Argentina is some 2000 m thick and consists of five formations, from base to top, La Laja, Zonda, La Flecha, La Silla and San Juan (Keller, 1999; Bordonaro, 2003). La Silla Formation (latest Cambrian-Early Ordovician) was defined by Keller et al. (1994) from the lower part of the San Juan Formation. It reaches some 350 m in thickness and consists of a distinctive succession of dominantly light-coloured, poorly fossiliferous limestones. The upper part of La Silla Formation is extensively quarried because of the remarkable purity of the limestones. Based on a detailed study of the type section in the northern outcrop area near Jáchal and seven sections in the southern area near San Juan (Fig. 1a), we propose a formal stratigraphic subdivision of La Silla Formation into three members. These are, from base to top, the Río del Agua Member, Río Blanco Member and Río Salado Member (Fig. 1b), which are 85, 140 and 81 m in their respective type sections. This subdivision is based in the preferential occurrence of creamcoloured dolostones interbedded in the middle part of the formation, whereas the lower and upper members are essentially monotonous limestones. Keller (1999) erected an informal tripartite subdivision conforming to three putative, shallowing-upward sequences, with the boundaries recording abrupt changes in relative sealevel. We do not detect this pattern and our proposed members do not coincide with this subdivision. We recognize nine individual lithofacies types (Fig. 2a-f). These are for the most part similar to those determined by Keller (1999) and Cañas (1999), but we consider that they over-estimated the abundance of muddy facies in the form of lime mudstone, wackestone and packstone. Limestones in all three members are dominantly thick- and massively bedded peloidal grainstones exhibiting tabular and gently undulating bedding. In the lower and upper members there are subordinate ooidal grainstones, along with rare peloidal packstone, intraclastic rudstone, mudstone, microbial laminites and thrombolite patch reefs. Dolostones are of two types: thick- and massively bedded and commonly cherty, and medium beds that are plane- and cross-laminated. The former is the dolomitized equivalent of the peloidal grainstone. The latter often occurs with thin intraclastic rudstones and represents relatively coarse grainstones that were preferentially dolomitized. These dolomites preserve evidence of unidirectional and oscillating currents. Our eight measured sections indicate that there was varying amounts of subsidence across the carbonate platform (Fig. 3), although precise correlation is impossible owing to the lack of biostratigraphic data. La Silla Formation represents a distinct phase in the Cambro-Ordovician evolution of the eastern Precordillera, with mainly lower energy peritidal limestones of La Flecha Formation below and open-shelf, fossiliferous muddy limestones of the (emended) San Juan Formation above. The dominance of peloidal grainstone suggests an open-shelf setting as well but one characterized by virtually continuous low-level turbulence yet absence of extreme events like major storms that would have formed deep scours and high-relief bedforms. While scoured surfaces do occur sporadically in the Río Blanco Member, large bedforms are not present in La Silla Formation (Fig. 4a-e).

The Upper Cambrian-Tremadocian rocks exposed in the Alfarcito area of Cordillera Oriental, northwest Argentina reveal a series of transgressive-regressive cycles punctuated by incision of fluvio-estuarine valleys. An integrated sedimentologic, biostratigraphic and sequence stratigraphic study permits characterization of the sedimentary facies and stratal stacking patterns, and a revision of the stratigraphic framework of this succession. The Upper Cambrian-Tremadocian succession is included within the existing Santa Rosita Formation, which is formally subdivided here into six units, the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members. This scheme recognizes the internal complexities of the formation, in that the Tilcara and Pico de Halcón members record sedimentation in areally-restricted incised valleys and contain structures indicative of tidal dominance, whereas the Casa Colorada, Alfarcito and Rupasca members typify wave-dominated open-marine environments, where background suspension-fallout was punctuated by oscillatory flows during storms. The Tilcara Member is incised into the underlying Mesón Group. The Casa Colorada Member reflects a basinwide Late Cambrian transgression and subsequent progradation and consists of lower to upper offshore deposits. The Pico de Halcón Member is incised into the Casa Colorada Member. The Alfarcito Member is divided into three distinctly upward-coarsening and-thickening intervals. The sandstone-dominated intervals are composed of lower to middle shoreface deposits with minor amounts of offshore transition and upper shoreface deposits. The heterolithic, fine-grained intervals record more distal deposition, ranging from the lower offshore to the offshore transition. The Rupasca Member is a dominantly fine-grained unit that records a major late early to early late Tremadocian transgression. The lower interval of this member consists of lower offshore to offshore-transition deposits, while the upper part is made up of shelf to lower offshore deposits. The Humacha Member is not exposed in the study area. The importance of integrating biostratigraphy within a sedimentologic and sequence-stratigraphic framework is underscored here, in that it enables us to construct a more accurate stratigraphic framework which permits a clear understanding of the sedimentary dynamics of this system.El análisis de las rocas del Cámbrico Superior-Tremadociano aflorantes en el área de Alfarcito, Cordillera Oriental, noroeste de Argentina, revela una serie de ciclos transgresivos-regresivos e incisiones de valles fluvio-estuarinos. Un estudio sedimentológico, bioestratigráfico y estratigráfico-secuencial integrado proporciona información para caracterizar las facies sedimentarias, analizar los patrones de apilamiento estratal y revisar el marco estratigráfico de estas sucesiones. La sucesión cámbrica-tremadociana es incluida en la Formación Santa Rosita, la cual es formalmente subdividida en seis miembros, Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca y Humacha. De este modo, este esquema retiene para el área de Alfarcito una unidad estratigráfica ampliamente aceptada como la Formación Santa Rosita y al mismo tiempo reconoce las complejidades internas de la misma, subdividiéndola en miembros. Los miembros Tilcara y Pico de Halcón registran depositación en valles incisos restringidos arealmente y contienen estructuras indicadoras de dominio mareal. Por el contrario, los miembros Casa Colorada, Alfarcito y Rupasca tipifican sedimentación en ambientes marinos abiertos dominados por el oleaje, donde la sedimentación por decantación alternó con flujos oscilatorios generados durante tormentas. El Miembro Tilcara está inciso en el subyacente Grupo Mesón. El Miembro Casa Colorada refleja una transgresión cámbrica tardía a escala de cuenca y la subsecuente progradación. En el área de estudio, esta unidad está representada por depósitos de offshore inferior a transición a offshore. El Miembro Pico de Halcón está inciso sobre el Miembro Casa Colorada. El Miembro Alfarcito está dividido en tres intervalos muy distintivos grano y estratocrecientes. Los intervalos arenosos están dominados por depósitos de shoreface inferior a medio con proporciones menores de depósitos de transición a offshore y shoreface superior. Los depósitos de los intervalos heterolíticos de grano fino registran depositación en un ambiente más distal, desde el offshore inferior a la transición al offshore. El Miembro Rupasca es una unidad dominantemente de grano fino, que registra una transgresión mayor de edad tremadociana temprana tardía a tardía temprana. El intervalo inferior del Miembro Rupasca consiste en depósitos de offshore inferior a transición a offshore, mientras que el intervalo superior consiste en depósitos de plataforma a offshore inferior. El Miembro Humacha no se encuentra expuesto en el área. La importancia de integrar estudios bioestratigráficos dentro de un marco sedimentológico y estratigráfico-secuencial es resaltada en este estudio. Este enfoque es esencial para construir un marco estratigráfico y correlaciones más precisas que ayuden a clarificar la nomenclatura estratigráfica de la cuenca.

Abstract U/Pb ages of detrital zircon from two samples of Ordovician sediments were determined and, based on similar published data, were compared with xenocrystal inheritance of Triassic and Oligocene granitoids of the Cordillera Real in order to better understand their genetic relationship and sources. The results show that the detrital zircon in the Ordovician sandstone and the inherited zircon cores in granitoids are statistically correlated. This correlation suggests assimilation of these sedimentary units by the felsic melts. Ages ranging from 300 to 2300 Ma are recorded in these inherited zircons. A high peak of Cambrian to late Neoproterozoic ages (500-750 Ma) is observed throughout metasedimentary units of the entire belt. Candidates for the main sources of these zircons include: Brasiliano or Pampean belts and/or an “in situ” hidden belt within the Central Andes or via recycling of detrital zircons in pre-existing sedimentary rocks. It is also possible that the sources lie below modern sedimentary covers but, at the time, formed high relief structures supplying recycled material into the Ordovician basins.

The Upper Cambrian-Tremadocian rocks exposed in the Alfarcito area of Cordillera Oriental, northwest Argentina reveal a series of transgressive-regressive cycles punctuated by incision of fluvio-estuarine valleys. An integrated sedimentologic, biostratigraphic and sequence stratigraphic study permits characterization of the sedimentary facies and stratal stacking patterns, and a revision of the stratigraphic framework of this succession. The Upper Cambrian-Tremadocian succession is included within the existing Santa Rosita Formation, which is formally subdivided here into six units, the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members. This scheme recognizes the internal complexities of the formation, in that the Tilcara and Pico de Halcón members record sedimentation in areally-restricted incised valleys and contain structures indicative of tidal dominance, whereas the Casa Colorada, Alfarcito and Rupasca members typify wave-dominated open-marine environments, where background suspension-fallout was punctuated by oscillatory flows during storms. The Tilcara Member is incised into the underlying Mesón Group. The Casa Colorada Member reflects a basinwide Late Cambrian transgression and subsequent progradation and consists of lower to upper offshore deposits. The Pico de Halcón Member is incised into the Casa Colorada Member. The Alfarcito Member is divided into three distinctly upward-coarsening and-thickening intervals. The sandstone-dominated intervals are composed of lower to middle shoreface deposits with minor amounts of offshore transition and upper shoreface deposits. The heterolithic, fine-grained intervals record more distal deposition, ranging from the lower offshore to the offshore transition. The Rupasca Member is a dominantly fine-grained unit that records a major late early to early late Tremadocian transgression. The lower interval of this member consists of lower offshore to offshore-transition deposits, while the upper part is made up of shelf to lower offshore deposits. The Humacha Member is not exposed in the study area. The importance of integrating biostratigraphy within a sedimentologic and sequence-stratigraphic framework is underscored here, in that it enables us to construct a more accurate stratigraphic framework which permits a clear understanding of the sedimentary dynamics of this system.

Abstract The Morro do Coco granite (MC) is a post-collisional intrusive body that was emplaced at Ribeira Belt, in the Cambro-Ordovician, succeeding the final stages of the Gondwana supercontinent amalgamation. This unit requires more studies, contrasting with similar best investigated occurrences of the central Ribeira Belt. This work presents a detailed investigation of such unit using petrography, Inductively Coupled Plasma (ICP), X-Ray Fluorescence (XRF) whole-rock geochemistry, U-Pb (SHRIMP) geochronology and Sm-Nd isotopes. The rock is a nearly undeformed syenogranite, geochemically classified as a high-K calc-alkaline magnesian, with metaluminous to slightly peraluminous affinity. Strongly light rare earth elements (LREE)-enriched patterns with significant negative Eu anomalies, typical of post-collisional granites, are identified. Similarly to other post-collisional granites of the central Ribeira Belt, U-Pb zircon data provide crystallization age of 496 ± 3 Ma . Sm-Nd isotopic data suggest crustal magma source as indicated by εNd(496) of -9, 143Nd/144Nd ratios between 0.511747 and 0.511752 and Mesoproterozoic TDM ages of 1.3 Ga. Based on its geochemical characteristics, morphology and geochronology, this unit is considered here as a member of Nova Friburgo Suite. Geochronological data defined three pulses of magmatism in this part of the orogen during the Cambro-Ordovician (515, 490 and 460 Ma).

Abstract The final consolidation of southwestern Gondwana during the Ediacaran–Cambrian resulted in the formation of a large landmass originally surrounded by the newborn Panthalassic Ocean. The Río de la Plata Craton is one of the last pieces that complete the geotectonic puzzle along the austral part of this supercontinent. However, the sedimentary record corresponding to the interval between the consolidation of SW Gondwana until the initial deposition in a large Ordovician cratonic basin is apparently missing. In this context, the Ediacaran–Cambrian epiclastic shallow-marine ramp of the Cerro Negro Formation, the uppermost unit of La Providencia Group, Tandilia System, is envisaged as the first known stratigraphic record of the hidden pericratonic basins of Gondwana. Geochronological and provenance data, coupled with robust stratigraphic and sedimentologic background, support that this unit keeps more tectono-sedimentary affinity with the Ordovician Balcarce Formation than the Neoproterozoic Sierras Bayas Group. The presence of similar Neoproterozoic source areas for both units, the absence of any metamorphism and deformation related to the Brasiliano cycle, and shallow marine deposition strongly suggest that the paleogeography and physiography of the original southernmost continental platform of Gondwana were similar to the Ordovician ones. Thus, the Cerro Negro Formation appears as the missing link between the ultimate stages of the Brasiliano Orogenic Cycle and the final stabilization of the continental platform from the SW part of Gondwana.

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ABSTRACT: Facies and stratigraphic analysis were carried out in Neoproterozoic-Lower Paleozoic carbonate-siliciclastic deposits of Cacoal and Pimenta Bueno formations exposed on basement rocks and into the Pimenta Bueno Graben, northwestern portion of Parecis Basin, southwesternmost Amazon Craton. The redescription and redefinion of this succession confirmed the previous interpretation for the Cacoal Formation as a Marinoan (~ 635 Ma) cap carbonate. The Cacoal Formation is subdivided here in two units separate by sharp contact found exclusively overlying Mesoproterozoic crystalline basement rocks: 1) a homonymous formation characterized by diamictites, sandstones and siltstones with dropstones interpreted as glacio-marine deposits; and 2) the Espigão d’Oeste Formation that consists of dolostone, dolomitic stromatolites, dolostone-siltstone rhythmite and siltstone interpreted as shallow to moderately deep platform deposits. The Ordovician to Silurian Pimenta Bueno Formation is a filling of Pimenta Bueno graben and overlies locally the Meso and Neoproterozoic rocks. This unit consists in diamictites, sandstones, siltstones and pelites interpreted as glacial-marine and tide- to storm-influenced platform deposits, recording a glacio-eustatic regressive-transgressive event. This new stratigraphic proposal modify the current stratigraphy for the Parecis Basin and suggest, at least, two levels of glaciation exposed in the sothwesternmost Amazon Craton related to the Marinoan and Late Ordovician-Early Silurian events.

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Copyright of Journal of Water Resources / Recursos Hídricos is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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The class Tentaculitoidea is an extinct group composed of small carbonate coniform-shaped invertebrates, distributed from Ordovician to Devonian. This group is more often recorded to the North Hemisphere, being less recorded to South Hemisphere deposits. This study aims (i) to analyze the species found in Brazilian Devonian outcrops, in addition (ii) to investigate their paleogeographic and stratigraphic distribution. The analyzed samples, which come from Paraná, Amazonas, and Parnaíba basins, are hosted in 9 Brazilian Research Centers. It was diagnosed 12 species of tentaculitoids: Tentaculites crotalinus, Tentaculites jaculus, Tentaculites kozlowskii, Tentaculites paranaensis, Tentaculites eldredgianus, Tentaculites trombetensis, Tentaculites stubeli, Tentaculites oseryi, Uniconus ciguelii, Homoctenus katzerii, Styliolina langenii, and Styliolina clavulus. The species from Paraná Basin are different from those recorded in Amazonas and Parnaíba basins, all present distinct stratigraphic ranges (Pragian to Givetian in Paraná Basin and Eifelian to Givetian in Amazonas and Parnaíba basins).

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Copyright of Comunicaçõe Geológicas is the property of Laboratorio Nacional de Energia e Geologia, I.P. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Rodriguésia is the property of Revista Rodriguesia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Efectuou-se um levantamento, a nível regional, que incidiu em soutos instalados em diversas formações geológicas, incluindo rochas ricas em manganês (Mn). Seleccionaram-se 38 soutos, 19 soutos com carência de magnésio (Mg) e outros tantos adjacentes com boas condições de produção. Determinaram-se as concentrações de nutrientes nas folhas e diversos indicadores da fertilidade dos solos. A concentração de Mg mais baixa observada em árvores que se desenvolviam em soutos em boas condições de produção foi 1,8 g kg-1 e o valor mais elevado em árvores com sintomas de carência de Mg foi 1,5 g kg-1. Na maioria dos soutos cloróticos, foi registado o valor do Mg permutável inferior a 0,20 cmolc kg-1 de solo. Todavia, nos soutos cujos solos apresentavam teores de Mn > 25 mg kg-1, os castanheiros exibiam sintomas de carência magnesiana para valores do Mg permutável superiores àquele valor e até 0,33 cmolc kg-1. Os soutos com os teores mais elevados de Mn no solo (Mn > 200 mg kg-1) estão instalados em xistos e grauvaques do Ordovício e do Silúrico.A regional survey was carried out in chestnut groves established in soils derived from bedrock of several geological formations, some with materials rich in manganese (Mn). A total of 38 chestnut groves were selected: 19 groves with several trees showing symptoms of Mg deficiency and 19 groves in their vicinity with vigorous tree growth. Foliar nutrient concentrations and several soil fertility indicators were determined. The lowest value of leaf Mg concentration in good growing conditions was 1.8 g kg-1 and the highest value in trees with evident symptoms of Mg deficiency was 1.5 g kg-1. In the majority of chlorotic groves, soil exchangeable Mg was below 0.20 cmolc kg-1. But the soils with Mn higher than 25 mg kg-1 exhibit symptoms of Mg deficiency up to 0.33 cmolc kg-1 of exchangeable Mg. In soils with the highest contents of Mn (>200 mg kg-1) the chestnut groves were established on Mn-rich schists and greywackes of the Ordovician and the Silurian.

El presente trabajo consiste en un estudio geológico detallado de las metamorfitas (Fm Puncoviscana s.l. o Complejo Puncoviscana) que constituyen el núcleo estratigráfico de la sierra de Mojotoro, Cordillera Oriental Argentina. El análisis integrado de este conjunto de rocas permitió dividir la clásica Fm Puncoviscana s.l. o Complejo Puncoviscana en tres unidades estratigráficas, que de más antigua a joven son: las Formaciones Chachapoyas, Alto de la Sierra y Guachos. La Formación Chachapoyas aflora en el flanco occidental de la sierra; está compuesta por facies de metapelitas y metaareniscas verdosas de grano muy fino, con un clivaje dominante de plano axial. Las rocas están fuertemente plegadas y afectadas por un metamorfismo dentro del campo de la anquizona alta-epizona. La Formación Chachapoyas esta intruida por diques ácidos de una edad de 533 ± 2 Ma. La facies arenosas son del tipo cuarzosas de grano fino clasto-soportadas y las facies pelíticas están compuestas por illita y clorita. La Formación Alto de la Sierra es una unidad metaarenosa, compuesta por metavaques cuarzosas, líticas y feldespáticas, donde la característica más notable es la presencia de material volcaniclástico, claramente identificable a través de corte delgado. Las arcillas de esta unidad son del tipo illita y escasos interestratificados de illita/esmectita. Las rocas fueron afectadas en un grado metamórfico tipo anquizona débil a intensa. La Formación Guachos constituye una secuencia heterolítica de metaarenisca-metapelita de coloraciones parda, pardo verdosas, en la cual se identificaron trazas fósiles de la icnofacies de Nereites. Las metaareniscas son del tipo cuarzosas donde se reconocen algunos líticos volcánicos de textura felsítica y las metapelitas están compuestas por illita, illita/clorita y clorita. Las rocas se encuentran plegadas y afectadas por un evento de deformación reconocible a escala de campo y en corte delgado. El grado de metamorfismo al cual estuvieron sujetas las rocas es dentro del campo de la anquizona intensa-epizona.The basement of Argentine Eastern Cordillera is an heterogeneous succession of siliciclastic and chemical rocks of Neoproterozoic-Early Cambrian age, identified as the "Precambrian basement" (Keidel, 1910) underlying with angular unconformity the Cambrian and Ordovician deposits of the Mesón and Santa Victoria Groups. The unit was defined as the Puncoviscana Formation (Turner, 1960) in the Santa Victoria range, and assigned to the Neoproterozoic-Cambrian (Mirré and Aceñolaza, 1972) due to the presence of Oldhamia, a trace fossil of the Lower Cambrian. However, the Puncoviscana Formation s.l. (Aceñolaza and Aceñolaza, 2005) is often adopted to identify all the basement of Eastern Cordillera, representing a heterogeneous group of rocks affected by low-grade metamorphism. The basement of the Mojotoro range is part of the 1a tecto-metamorphic zone, as defined by Willner (1990). They are part of a near-surface structural level in which the sedimentary characteristics and the original microfabric could be studied in detail (Fig. 1). From structural, stratigraphic and mineralogical information, a discontinuity (fault) could be inferred, and a new Early Cambrian stratigraphic unit named the Guachos Formation (Moya, 1998) in the Mojotoro Range can be defined. The main purpose of this contribution is to characterize the similarities and differences between the stratigraphic units of the basement in the Mojotoro Range (Lower-Middle Cambrian) in order to assess their relative stratigraphic position. The metamorphic grade was established from the cartographic material and sedimentological, petrographical and mineralogical characterization, and enabled the identification of three stratigraphic units (Fig. 1): the Chachapoyas, the Alto de la Sierra and the Guachos Formations. Satellite images and aerial photographs were used to build up a map of the studied area, with structures, lithologic contacts and sampling sites placed using GPS. The compositional studies of the field samples were carried out with a binocular magnifying lens, optic and scanning electronic microscope (SEM), and X-ray diffraction (XRD). The Chachapoyas Formation (nomen. novum.) crops out in the western flank of the range (Fig. 1), and consists of shales and very fine-grained, greenish sands, with a cleavage parallel to the axial plain (Fig. 3e). Rocks are strongly folded and affected by high anchizone-epizone grade metamorphism (Fig. 6). The unit is intruded by acidic dikes, dated at 533 ± 2 Ma, showing that the Chachapoyas Formation age is older than the other units in the Mojotoro basement (Fig. 2). Sandy facies are thin and mainly composed of grain-supported quartz arenites. Clay mineralogy corresponds to illite and clorite. Another described unit is the Alto de la Sierra Formation (nomen. novum.), composed by layers of purple and gray sands with parallel bedding, shales and feldespatic metawackes (Fig. 3a-c). Volcaniclastic material is recognized in thin sections (Fig. 4a-d), and clays mineralogy corresponds to illite and interlayer illite/smectite (Fig. 7c). The unit was affected by a weak to intense anchizone metamorphic grade (Fig. 6). A heterolitic sequence of brown to greenish brown shaly sands, with Nereites ichnofacies (Fig. 3f-h), was recognized as the Guachos Formation (Moya, 1998). The sandstones are mainly composed of quartz, and less proportions of volcaniclastic grains with felsitic texture (Fig. 3f-h). Shales are composed of illite, illite/chlorite and chlorite (Fig. 5b, d). The outcrops are folded and affected by a deformation event, a characteristic reflected in thin sections. The metamorphic grade corresponds to a high anchizone-epizone (Fig. 5a). The Guachos Formation can be correlated to the volcaniclastic rocks of Rancagua area, which presents similar facies and Nereites ichnofauna. The Rancagua succession has been studied by different authors (Lork et al., 1990; Adams et al., 2008) that described several rhyolitic detrital zircons in this unit and obtained a maximum age of sedimentation of Lower-Middle Cambrian. Finally, the fault between the Guachos Formation and the Chachapoyas Formation (Fig. 1) corresponds to a possible Neoproterozoic-Cambrian unconformity, and the acidic dikes intruded in the Chachapoyas Formation could correspond to a part of the calc-alkaline Pampean magmatic arc, defined in the Eastern Pampean ranges, with a great extension in NW Argentina, were the volcanic cover was eroded and could represent the source rock of the Alto de la Sierra and the Guachos Formations.

Este trabalho tem por objetivo apresentar os resultados da modelagem sísmica em meios com fortes descontinuidades de propriedades físicas, com ênfase na existência de difrações e múltiplas reflexões, tendo a Bacia do Amazonas como referência à modelagem. As condições de estabilidade e de fronteiras utilizadas no cálculo do campo de ondas sísmicas foram analisadas numericamente pelo método das diferenças finitas, visando melhor compreensão e controle da interpretação de dados sísmicos. A geologia da Bacia do Amazonas é constituída por rochas sedimentares depositadas desde o Ordoviciano até o Recente que atingem espessuras da ordem de 5 km. Os corpos de diabásio, presentes entre os sedimentos paleozóicos, estão dispostos na forma de soleiras, alcançam espessuras de centenas de metros e perfazem um volume total de aproximadamente 90000 Km³. A ocorrência de tais estruturas é responsável pela existência de reflexões múltiplas durante a propagação da onda sísmica o que impossibilita melhor interpretação dos horizontes refletores que se encontram abaixo destas soleiras. Para representar situações geológicas desse tipo foram usados um modelo (sintético) acústico de velocidades e um código computacional elaborado via método das diferenças finitas com aproximação de quarta ordem no espaço e no tempo da equação da onda. A aplicação dos métodos de diferenças finitas para o estudo de propagação de ondas sísmicas melhorou a compreensão sobre a propagação em meios onde existem heterogeneidades significativas, tendo como resultado boa resolução na interpretação dos eventos de reflexão sísmica em áreas de interesse. Como resultado dos experimentos numéricos realizados em meio de geologia complexa, foi observada a influência significativa das reflexões múltiplas devido à camada de alta velocidade, isto provocou maior perda de energia e dificultou a interpretação dos alvos. Por esta razão recomenda-se a integração de dados de superfície com os de poço, com o objetivo de obter melhor imagem dos alvos abaixo das soleiras de diabásio.This paper discusses the seismic modeling in medium with strong discontinuities in its physical properties. The approach takes in consideration the existences diffractions and multiple reflections in the analyzed medium, which, at that case, is the Amazon Basin. The stability and boundary conditions of modeling were analyzed by the method of the finite differences. Sedimentary rocks deposited since the Ordovician to the present, reaching depth up to 5 Km. The bodies of diabasic between the paleozoic sediments are layers reaching thickness of hundred meters, which add to 90.000 km3, form the geology of the Amazon Basin. The occurrence of these structures is responsible for multiple reflections during the propagation of the seismic waves, which become impossible a better imaging of horizons located bellow the layers. The representation this geological situation was performed an (synthetic) acoustic velocity model. The numerical discretization scheme is based in a fourth order approximation of the acoustic wave equation in space and time The understanding of the wave propagation heterogeneous medium has improved for the application of the finite difference method. The method achieves a good resolution in the interpretation of seismic reflection events. The numerical results discusses in this paper have allowed to observed the influence of the multiple reflection in a high velocity layer. It increase a loss of energy and difficult the interpretation of the target. For this reason the integration of surface data with the well data is recommended, with the objective to get one better image of the targets below of the diabasic layer.

Diversos estudos realizados no Norte de Portugal têm alertado para a ocorrência de carências de magnésio ou para a possibilidade de deficiente nutrição magnesiana nalgumas culturas. A partir de Julho-Agosto, pode observar-se a sintomatologia de carência de Mg em diversas zonas daquela região em culturas como o milho, em arbóreas e arbustivas, e ainda em espécies florestais. Em Trás-os-Montes e Alto Douro e no Entre-Douro e Minho, as deficiências de Mg nas culturas têm-se observado sobretudo em solos desenvolvidos em xistos do Silúrico e do Ordovício, em xistos do Precâmbrico e Câmbrico do complexo Xistograuváquico e em solos provenientes de granitos predominantemente alcalinos de duas micas. Nas formações silúricas, ordovícias e do complexo Xisto-grauváquico dominam as seguintes litologias: quartzofilitos feldspáticos, filitos, micaxistos, xistos grafitosos, ampelitos, liditos, psamitos, grauvaques, siltitos e, ainda, quartzitos xistóides e quartzitos. As unidades-solo onde, frequentemente, se tem observado baixas concentrações foliares de Mg, ou mesmo sintomas da carência de Mg são: os Cambissolos e Leptossolos úmbricos; os Cambissolos e Leptossolos dístricos; os Regossolos úmbricos; os Fluvissolos dístricos e úmbricos; e, ainda, os Antrossolos úmbricos, cumúlicos e áricos. Alguns dos dados aqui apresentados foram coligidos, não só em estudos em que o principal objectivo foi o da confirmação da deficiência de Mg, mas também em levantamentos do estado nutritivo de diversas culturas. Na maioria dos estudos utilizou-se como método de diagnóstico as concentrações foliares de Mg, mas também foram identificadas razões entre nutrientes, nomeadamente Mg/N e Mg/K, associadas à carência de Mg. Nalguns deles determinou-se o limiar a partir do qual se observaram as deficiências de Mg. Em quase todos os trabalhos se encontraram correlações entre as concentrações foliares de Mg e diversos parâmetros químicos do solo, como os teores de Mg2+ na solução do solo e o Mg2+ de troca, com as razões Mg2+/K+, Mg2+/Ca2+, Mg2+/Ca2+ + Mg2+, Mg2+/Ca2+ + Mg2+ + K+, Mg2+/CTC, Mg2+/NH4+ e Mg2+/Al3++H+, ou com o efeito combinado destas razões. A carência de Mg parece ser clássica em solos ácidos provenientes de material originário pobre em Mg, mas também pode ser despoletada por factores locais, ou por práticas culturais desajustadas.Several studies carried out in Northern Portugal have drawn attention to the occurrence of magnesium deficiencies or deficient Mg nutrition in different crops. From July-August onwards symptoms of Mg deficiency can be observed in certain areas of this region in maize, fruit crops, fruit-trees and forest species. In the Trás-os-Montes and Alto Douro region and in the Entre-Douro and Minho region, Mg deficiencies in crops have been detected predominantly in soils located on schists of the Siluric and Ordovician, on schists of Precambrian and Cambrian of the Schist and Greywacke complex, and soils derived from two-mica alkaline granite. The following lithology is found in the schists and in the Schist and Greywacke complex: feldspar quartz-phyllites, phyllites, micaschists, graphytic slates, siltstones, ampelites, lydites, psamites, greywackes, phyllito-quartzites and quartzites. The soil units where low foliar Mg concentrations or visible Mg deficiencies in crops more often observed are: Dystric and Umbric Leptosols, Umbric Regosols, Dystric and Umbric Cambisols, Dystric and Umbric Fluvisols, Umbric and Aric Anthrosols and Cumulic Anthrosols. Some of the data presented here were gathered from studies where the main purpose was the confirmation of Mg deficiencies and surveys to assess the nutritional status of various crops. The majority of the studies used, as a diagnostic tool, both the foliar Mg concentrations and, in some cases, the nutrient ratios Mg/N and Mg/K. In some studies, the threshold values for the occurrence of Mg deficiencies were determined. Most studies showed correlations between foliar Mg concentrations and several soil chemical parameters, such as soil solution Mg2+, exchangeable Mg2+, ratios between exchangeable cations Mg2+/K+, Mg2+/Ca2+, Mg2+/Ca2+ + Mg2+, Mg2+/Ca2+ + Mg2++K+, Mg2+/CTC, Mg2+/NH4+ and Mg2+/Al3++H+ or the combination of some of these ratios. Mg deficiency seems to be a classic problem in acid soils derived from parent material poor in Mg, but it can also be triggered by local factors or by inappropriate management practices.

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Copyright of Comunicaçõe Geológicas is the property of Laboratorio Nacional de Energia e Geologia, I.P. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Anuario do Instituto de Geociencias is the property of Universidade Federal do Rio de Janeiro, Instituto de Geociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Comunicaçõe Geológicas is the property of Laboratorio Nacional de Energia e Geologia, I.P. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Comunicaçõe Geológicas is the property of Laboratorio Nacional de Energia e Geologia, I.P. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recent methodological developments in the Hydrogeology of crystalline terrains demand detailed studies of rock fracturing, its chronological evolution and relationship to the regional geological framework. The example from Northeast Brazil idiscussed to illustrate the discrimination of different fracture sets, including their geometry, kinematics, crustal level and age. The crystalline brittle structures usually display a complex history, related to different deformation episodes. In the present case, an older, major event corresponds to the late-Brasiliano (Cambrian-Ordovician boundary) deformation, related to the exhumation of a neoproterozoic collisional belt. This setting can be described as a NNE-trending dextral transpressive belt, with brittle and brittle-ductile structures generated at 4-8 km crustal depth. A second, major deformation is associated to the rifting and development of passive margin basins lasting from Jurassic to early Tertiary times. The main structures of this stage were generated under a N to NW extensional regime and at shallower depths (2-4 km) as regards to the late-Brasiliano fracturing. These structures constitute a network of planar discontinuities which are reactivated under near-surface conditions (