Caracterização estrutural do Lineamento de Piúma e sua influência na porção norte da Bacia de Campos

The detailed study of the Brazilian continental margin basins became possible with the advancement of geophysical tools, with emphasis on seismic reflection. Characterizing the structural and stratigraphic elements of Brazil’s marginal basins they realized that there was a relationship with structures present on the adjacent continental basement. So many works began to be made to understand this relationship and know the major factors that influenced the evolution of the continental margin. The study area of this work includes the northern portion of the Campos Basin and the continental outcropping adjacent areas, which corresponds to the northern of Rio de Janeiro state and the southern of Espirito Santo state. This area stands an important structural feature of NW-SE direction with a projection to the Campos Basin called Lineamento de Piúma. The outcropping basement rocks belongs to the Ribeira Belt which was bonded to other mobile bands forming the continent Western Gondwana during the Brasiliano Cycle, which later fragmented giving rise to the Atlantic Ocean. The opening of the ocean results on the formation of the marginal basins of Brazil. These basins have continental, transitional and marine facies. On Campos Basin the continental phase resulted on the formation of horsts and grabens bounded by synthetic and antithetic faults. Continuing rifting formed the saline lakes that deposited siliciclastic and carbonate sediments. The transitional phase resulted on thick packages consist of evaporites (halite and anhydrite) that was deposited in lagoon environment, tectonically quiet arid and semi-arid. The marine phase it deposited siliciclastic and carbonate in the Campos Basin resulting in shales, marls, limestones, ritmito, turbidites, sandstones and others. The objective of this study is to investigate the possible continuation... (Complete abstract click electronic access below)

Aspectos petrográficos dos carbonatos da Formação Riachuelo - Albiano, bacia de Sergipe

The carbonatic rocks have great importance in petroleum geology, since most hydrocarbons reservoirs in the world are associated to this kind of rock. The new giant petroleum fields discovered in the Brazilian southeast Atlantic margin are directly connected to calcareous rocks, which are subjacent to the Aptian evaporite pack. This demand an increase in the number of geologists able to study such deposits. The Aptian carbonatic platform is completely exposed only in the Sergipe-Alagoas Basin. Therefore, it works as a natural laboratory to the study and understanding of this kind of rock. The Sergipe Basin is situated in the east Brazilian coast, and has its evolutional history is intimately related to the formation of the South Atlantic Ocean, through the break-up of the Gondwana supercontinent. The marine sequence of the Brazilian marginal basins is of Albian age and is marked by the development of carbonatic platforms. In doing so, this paper aims to analyze the Albian limestones from Riachuelo Formation of the Sergipe Basin. The project gave to the student the opportunity to increase his knowledge in carbonates, due to the laboratory and outdoor activities. The studied deposits, within a regional outline, were petrografically described, allowing interpretations about the evolution of the former South Atlantic Ocean. Ten points were visited where samples were collected for making of thin sheets. In this work several carbonatic facies were identified totaling 116 laminates described.

Caracterização dos depósitos glaciais permo-carbonífero no sul de Minas Gerais, Brasil: Formação Aquidauana ou Grupo Itararé?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Association between post-orthodontic treatment gingival margin alterations and symphysis dimensions

Orthodontic therapy is known to be associated with the development of gingival recession. Several factors may be involved in the causal chain of this outcome, including anatomical and behavioral aspects. Among the anatomical aspects, the dimensions of the mandibular symphysis could play a predisposing role. This study evaluated the relationship between the mandibular symphysis dimensions prior to orthodontic therapy and the development of gingival recessions on the lower incisors and cuspids. Records from 189 orthodontically treated adolescents were evaluated, including radiographs, casts and intra-oral photographs. Symphysis dimensions were assessed by cephalograms. Gingival margin alterations were determined in photographs and cast models. Association between gingival margin alterations and symphysis dimensions was tested by chi-square (α=0.05). Occurrence of gingival recession increased after orthodontic therapy. No association was observed on average of symphysis dimensions and the occurrence of gingival recessions. It may be concluded that pretreatment symphysis dimensions may not be used as predictors of gingival recession after orthodontic therapy.

Biostratigraphy and paleoecology of an unusual palynological record from the Aquidauana Formation, Late Pennsylvanian of Paraná Basin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evolução tectônica e estratigráfica das bacias da margem continental do Uruguai

Pós-graduação em Geociências e Meio Ambiente - IGCE

Fire History at the Eastern Great Plains Margin, Missouri River Loess Hills

The purpose of this paper is to provide quantitative fire history information for a geographically unique region, the Loess Hills of northwest Missouri. We sampled 33 bur oak (Quercus macrocarpa Michx.), chinkapin oak (Q. muehlenbergii Engelm.), and black oak (Q. velutina Lam.) trees from the Brickyard Hill Conservation Area in northwest Missouri. The period of tree-ring record ranged in calendar years from 1671 to 2004 and fire-scar dates (n = 97) ranged from 1672 to 1980. Fire intervals for individual trees ranged from 1 to 87 years. The mean fire interval was 6.6 years for the pre-Euro-American settlement period (1672-1820), and 5.2 years for the entire record (1672-1980). A period of more frequent fire (mean fire interval = 1.6 for 1825 to 1850) coincided with Euro-American settlement of the area. The average percentage of trees scarred at the site was 16.8%, or about 1 in 7 trees sampled per fire. No significant relationship between fire years and drought conditions was found; however, events prior to 1820 may have been associated with wet to dry mode transitions.

Fire History at the Southwestern Great Plains Margin, Capulin Volcano National Monument

This study documents historic fire events at Capulin Volcano National Monument over the last four centuries using dendrochronologically dated fire scars at two sites: the lower volcano lava flows (the Boca) and the adjacent canyon slopes (Morrow Ranch). The mean fire interval (MFI) was 12 years at the Boca site (before 1890) and 5.4 years (1600-1750) and 19.1 years (1751-1890) at the Morrow Ranch site. Data from the Boca and Morrow Ranch sites combined with the extremely pyrogenic landscape position of the volcano slopes indicate that the volcano slopes likely burned more frequently (e.g., MFI <5 yr). Around 1750, the fire regime appeared to transition to longer fire intervals, greater temporal synchrony among fire-scarred trees, and a higher proportion of trees scarred in fire years. Temporal variability in the fire regime at Capulin Volcano may reflect changes in human populations, climate, and land use.

Vertical distribution of benthic invertebrate larvae during an upwelling event along a transect off the tropical Brazilian continental margin

Abundance and composition of marine benthic communities have been relatively well studied in the SE Brazilian coast, but little is known on patterns controlling the distribution of their planktonic larval stages. A survey of larval abundance in the continental margin, using a Multi-Plankton Sampler, was conducted in a cross-shelf transect off Cabo Frio (23 degrees S and 42 degrees W) during a costal upwelling event. Hydrographic conditions were monitored through discrete CDT casts. Chlorophyll-a in the top 100 m of the water column was determined and changes in surface chlorophyll-a was estimated using SeaWiFS images. Based on the larval abundances and the meso-scale hydrodynamics scenario, our results suggest two different processes affecting larval distributions. High larval densities were found nearshore due to the upwelling event associated with high chlorophyll a and strong along shore current. On the continental slope, high larval abundance was associated with a clockwise rotating meander, which may have entrapped larvae from a region located further north (Cabo de Sao Tome, 22 degrees S and 41 degrees W). In mid-shelf areas, our data suggests that vertical migration may likely occur as a response to avoid offshore transport by upwelling plumes and/or cyclonic meanders. The hydrodynamic scenario observed in the study area has two distinct yet extremely important consequences: larval retention on food-rich upwelling areas and the broadening of the tropical domain to southernmost subtropical areas. (C) 2009 Elsevier B.V. All rights reserved.

PALEOPRODUCTIVITY CHANGES DURING THE LATE QUATERNARY IN THE SOUTHEASTERN BRAZILIAN UPPER CONTINENTAL MARGIN OF THE SOUTHWESTERN ATLANTIC

Changes in the Brazilian continental margin`s oceanic productivity and circulation over the last 27,000 years were reconstructed based on sedimentological and microfaunal analyses. Our results suggest that oceanic paleoproductivity and the supply of terrigenous sediments to the Brazilian continental margin were higher during the Last Glacial Maximum (LGM) than during the Holocene. These changes may have been primarily influenced by significant sea level fluctuations that have occurred since the late Pleistocene. During the LGM, the lower sea level, higher productivity and lower sea-surface paleotemperatures may have been the result of the offshore displacement of the main flow of the Brazil Current. However, during the Holocene, the warm waters of the Brazil Current were displaced toward the coast. This displacement contributed to the increase in water temperature and prevented an increase in oceanic productivity. The decrease in terrigenous supply since the LGM could be related to the increase of the extension of the continental shelf and/or drier climatic conditions.

Paleoproductivity changes during the Holocene in the inner shelf of Cabo Frio, southeastern Brazilian continental margin: Benthic foraminifera and sedimentological proxies

Sedimentological and benthic foraminifera analyses carried out on a core (length 4.15 in, collected at 22 degrees 56`31 `` S and 41 degrees 58`48 `` W, at a water depth of 43 in) sampled from the inner shelf of Cabo Frio, southeastern Brazilian continental margin, allowed identification of different hydrodynamic and productivity regimes related to sea-level fluctuations and/or climatic changes, during the last 9.4 ka cal BP. Prior to 7.0 ka cal BP, a less intense hydrodynamic and lower productivity regime occurred at lower sea levels and under drier climatic conditions. Between 7.0 and 5.0 ka cal BP, relatively stronger local oceanic circulation and relatively high productivity were observed, in a scenario of rising sea levels and more humid conditions. From 5.0 to 3.0 ka cal BP, bottom currents weakened and input of nutrients increased, with productivity levels similar to the previous phase at lower sea level and in a drier climate. From 3.0 ka cal BP up to the present, stronger hydrodynamic conditions and a higher productivity regime are linked to the establishment of the upwelling process in Cabo Frio. From 2.5 ka cal BP to the present, upwelling enhancement has been recognized, resulting from the combined action of NE winds and the intensification of the meandering pattern of the Brazil Current (BC). (C) 2008 Elsevier Ltd and INQUA. All rights reserved.

Ordovician klippen structures of the Sierra de Umango: New insights on Tectonic evolution of the Western Sierras Pampeanas, Argentina

The basement rock of the Pampean flat-slab (Sierras Pampeanas) in the Central Andes was uplifted and rotated in the Cenozoic era. The Western Sierras Pampeanas are characterised by meta-igneous rocks of Grenvillian Mesoproterozoic age and metasedimentary units metamorphosed in the Ordovician period. These rocks, known as the northern Cuyania composite terrane, were derived from Laurentia and accreted toward Western Gondwana during the Early Paleozoic. The Sierra de Umango is the westernmost range of the Western Sierras Pampeanas.This range is bounded by the Devonian sedimentary rocks of the Precordillera on the western side and Tertiary rocks from the Sierra de Maz and Sierra del Espinal on the eastern side and contains igneous and sedimentary rocks outcroppings from the Famatina System on the far eastern side. The Sierra de Umango evolved during a period of polyphase tectonic activity, including an Ordovician collisional event, a Devonian compressional deformation, Late Paleozoic and Mesozoic extensional faulting and sedimentation (Paganzo and Ischigualasto basins) and compressional deformation of the Andean foreland during the Cenozoic. A Nappe System and an important shear zone, La Puntilla-La Falda Shear Zone (PFSZ), characterise the Ordovician collisional event, which was related to the accretion of Cuyania Terrane to the proto-Andean margin of Gondwana. Three continuous deformational phases are recognised for this event: the D1 phase is distinguished by relics of 51 preserved as internal foliation within interkinematic staurolite por-phyroblasts and likely represents the progressive metamorphic stage; the D2 phase exhibits P-T conditions close to the metamorphic peak that were recorded in an 52 transposition or a mylonitic foliation and determine the main structure of Umango; and the D3 phase is described as a set of tight to recumbent folds with S3 axial plane foliation, often related to thrust faults, indicating the retrogressive metamorphic stage. The Nappe System shows a top-to-the S/SW sense direction of movement, and the PFSZ served as a right lateral ramp in the exhumation process. This structural pattern is indicative of an oblique collision, with the Cuyania Terrane subducting under the proto-Andean margin of Gondwana in the NE direction. This continental subduction and exhumation lasted at least 30 million years, nearly the entire Ordovician period, and produced metamorphic conditions of upper amphibolite-to-granulite facies in medium- to high-pressure regimes. At least two later events deformed the earlier structures: D4 and D5 deformational phases. The D4 deformational phase corresponds to upright folding, with wavelengths of approximately 10 km and a general N-S orientation. These folds modified the S2 surface in an approximately cylindrical manner and are associated with exposed, discrete shear zones in the Silurian Guandacolinos Granite. The cylindrical pattern and subhorizontal axis of the D4 folds indicates that the S2 surface was originally flat-lying. The D4 folds are responsible for preserving the basement unit Juchi Orthogneiss synformal klippen. This deformation corresponds to the Chanica Tectonic during the interval between the Devonian and Carboniferous periods. The D5 deformational phase comprehends cuspate-lobate shaped open plunging folds with E W high-angle axes (D5 folds) and sub-vertical spaced cleavage. The D5 folds and related spaced cleavage deformed the previous structures and could be associated with uplifting during the Andean Cycle. (C) 2012 Elsevier Ltd. All rights reserved.

An additional basal sauropodomorph specimen from the Upper Triassic Caturrita Formation, southern Brazil, with comments on the biogeography of plateosaurids

We describe an additional saurischian specimen from the Caturrita Formation (Norian) of the Parana Basin, southern Brazil. This material was collected in the 1950s and remained unstudied due to its fragmentary condition. Detailed comparisons with other saurischians worldwide reveal that some characters of the ilium, including the low ventral projection of the medial wall of the acetabulum and its concave ventral margin, together with the short triangular shape of the pre-acetabular process and its mound-like dorsocaudal edge, resemble those of sauropodomorphs such as Plateosaurus and Riojasaurus. This set of traits suggests that MN 1326-V has affinities with basal Sauropodomorpha, probably closer to plateosaurians than to Saturnalia-like taxa. Previous records of this clade in the Caturrita Formation include Unaysaurus, which has been related to Plateosaurus within Plateosauridae. Alternative schemes suggest that plateosaurids include Plateosaurus plus the Argentinean 'prosauropods' Coloradisaurus and Riojasaurus. Both hypotheses raise biogeographic questions, as a close relationship between faunas from South America and Europe excluding Africa and North America is not supported by geological and biostratigraphical evidence. Additionally, the absence of plateosaurids in other continents suggests that the geographical distribution of this taxon is inconsistent with the geological history of western Pangaea, and this demands further investigations of the phylogeny of sauropodomorphs or improved sampling.

Neotectonics in the northern equatorial Brazilian margin

An increasing volume of publications has addressed the role of tectonics in inland areas of northern Brazil during the Neogene and Quaternary, despite its location in a passive margin. Hence, northern South America plate in this time interval might have not been as passive as usually regarded. This proposal needs further support, particularly including field data. In this work, we applied an integrated approach to reveal tectonic structures in Miocene and late Quaternary strata in a coastal area of the Amazonas lowland. The investigation, undertaken in Marajo Island, mouth of the Amazonas River, consisted of shallow sub-surface geophysical data including vertical electric sounding and ground penetrating radar. These methods were combined with morphostructural analysis and sedimentological/stratigraphic data from shallow cores and a few outcrops. The results revealed two stratigraphic units, a lower one with Miocene age, and an upper one of Late Pleistocene-Holocene age. An abundance of faults and folds were recorded in the Miocene deposits and, to a minor extent, in overlying Late Pleistocene-Holocene strata. In addition to characterize these structures, we discuss their origin, considering three potential mechanisms: Andean tectonics, gravity tectonics related to sediment loading in the Amazon Fan, and rifting at the continental margin. Amongst these hypotheses, the most likely is that the faults and folds recorded in Marajo Island reflect tectonics associated with the history of continental rifting that gave rise to the South Atlantic Ocean. This study supports sediment deposition influenced by transpression and transtension associated with strike-slip divergence along the northern Equatorial Brazilian margin in the Miocene and Late Pleistocene-Holocene. This work records tectonic evidence only for the uppermost few ten of meters of this sedimentary succession. However, available geological data indicate a thickness of up to 6 km, which is remarkably thick for an area regarded as a passive margin. (C) 2012 Elsevier Ltd. All rights reserved.

A new drought resistant gymnosperm taxon Duartenia araripensis gen. nov et sp nov (Cheirolepidiaceae?) from the Early Cretaceous of Northern Gondwana

A new gymnosperm taxon from the Lower Cretaceous (upper Aptian to possibly lower Albian) Crato Formation of Brazil, Duartenia araripensis gen. nov. et sp. nov. is described. The most prominent specimen, a branch with attached lateral branches of higher orders exhibits a distinct anisotomous branching pattern. The very dense wood is composed of tracheids with spaced and partly contiguous uniseriate pits and low rays with one pit per cross-field (mixed protopinaceous type). When foliage is not abraded, Duartenia exhibits coriacious Brachyphyllum-type leaves. Duartenia may be linked to cheirolepid conifers, however, the systematic affinity remains uncertain. The dense wood, characteristic growth pattern and thick, scale like, trichome bearing leaves may be related to ecological conditions that reflect a seasonally dry climate.