Claudio Limeira Mello

Fácies sedimentares e ambientes deposicionais associados aos depósitos da Formação Barreiras no estado do Rio de Janeiro

This paper characterizes the facies, sedimentary processes, and environments of the Barreiras Formation in the state of Rio de Janeiro between Marica and Barra de Itabapoana. It also attempts to correlate the Barreiras deposits to well-defined Tertiary stratigraphic units in Rio de Janeiro, thereby contributing to the reconstruction of the Cenozoic sedimentary evolution of a continental area adjacent to important oceanic basins. Three gravelly facies, three sandy facies, and two muddy facies were recognized. The facies associations record high-energy traction deposits and suspension and debris-flow deposits, related to sandy to locally gravelly braided rivers, with varied occurrence of debris-flows. In Buzios, polymictic matrix-supported gravels interbedded with muddy sands occur adjacent to the Pai Vitorio fault. These gravelly deposits were associated with syntectonic movements during the evolution of the Barra de Sao Joao Graben. Muddy-sandy sediments unconformably cap the Barreiras Formation. Their contact with the Barreiras Formation is generally marked by stone-lines of quartz and reworked Fe-oxide clasts. The deposits of the Barreiras Formation described here are faciologically similar to the Macacu and Resende formations (Eocene-Oligocene units). The main difference between them is the high-Fe oxidation in the Barreiras Formation deposits. Reliable geochronologic markers were not recognized in the Barreiras Formation, hence, its correlation with the Macacu and Resende formations can not be confirmed.

Quaternary sedimentation, neotectonics and the evolution of the Doce River Middle Valley lake system (Southeastern Brazil)

The Doce River Middle Valley (State of Minas Gerais, Southeastern Brazil) is one of the most important areas in Brazil in the study of Quaternary evolution of the humid tropics. This area preserves a singular barred-Iake system which has been previously investigated by several authors, particularly on the 70s. Most previous studies have considered paleoclimatic controls as responsible for the origin and the evolution of the lake system. Some authors have also recognized evidences of neotectonic influence on the lacustrine development. In the present study, a new approach to the Quaternary evolution ofthis area is discussed. The origin and the evolution of the lake system are interpreted according to regional stratigraphic and structural investigations. Geophysical (seismic stratigraphic) data provide new insights about the lake stratigraphy. Detailed structural analyses of joints and faults affecting Quaternary sediments support neotectonic interpretations. Stratigraphic analyses confirm the beginning of the lacustrine sedimentation around 9,000 years BP, simultaneously with an important regional alluvial sedimentation. Seismic stratigraphic analysis performed at the dam of Dom Helvecio Lake shows a normal fault affecting Holocene alluvial sediments. It explains the damming of this lake and suggests neotectonic mechanisms as the main control for the origin of the Doce River Middle Valley lake system.

Rio de Janeiro: A Metropolis Between Granite-Gneiss Massifs

The city of Rio de Janeiro is well-known for its outstanding landscape, particularly the several steep rocky domes that emerge close to the coast. Such a wonderful scene results from a combination of differential weathering controlled by the presence of a variety of Neoproterozoic gneisses and Cambrian granites and strong valley incision along subvertical faults and fractures. In this chapter we present the geological and geomorphological aspects that influence the daily life of more than 12 million inhabitants of the Rio de Janeiro metropolitan region, in two areas around Guanabara Bay: Coastal Massifs and the Serra dos Orgaos escarpment. The combination of such topographic constraints, intense summer rainstorms, and dense occupation frequently creates a scenario with a high potential for landslide-derived hazards.

Mapa geológico do cenozoico da região da bacia de Volta Redonda (RJ, segmento central do Rifte Continental do Sudeste do Brasil): identificação de novos grabens e ocorrências descontínuas, e caracterização de estágios tectonossedimentares

This work aims to present new results of geological mapping and tectonosedimentary analysis of the cenozoic of Volta Redonda basin region, inserted in the central segment of the Continental Rift of Southeast Brazil (CRSB). Were recognized three paleogenic depocenters (grabens of Colonia Santo Antonio, Dorândia, Casa de Pedra - most importantly, for its volcanic and sedimentary record) and discontinuous paleogenics deposits (areas of Belmonte, Jardim Amalia, Cafundo, Vargem Alegre), and two expressives quaternary grabens (grabens of the Rio Bananal and the Usinal), distributed in the NE-SW direction. The paleogenic filling was related to three tectonic stages: Pre-Rift phase, linked to the deposition of the Ribeirao Quatis Formation (fluvial); Rift phase I (main), related to Resende Formation, characterized by a fluvial and alluvial fan systems associated with major fault edges, and basanitic volcanism (Casa de Pedra Basanite); Rift phase II (final) relating to Pinheiral Formation fluvial deposits, responsible for clogging of paleogenics depocenters. Significant accumulations of recent alluvial deposits are linked to the fulfillment of the Quaternary grabens. The current configuration of the Volta Redonda basin region is the results of a generation of several brittle structures associated to paleogenic opening and neotectonic deformation. Thus, this segment of the CRSB is represented by a mosaic of paleogenic dpocenters and discontinuous occurrences significantly compartmentalized by recent deformation, and quaternary depocenters, mainly linked to the Holocene extension event. The identification and characterization of these feautures, brings a new arrangement of cenozoic record in the region of the Volta Redonda basin, measuring around 40 km in the NE-SW and 10 km in the NW-SE direction.

Coberturas cenozóicas e estruturas deformadoras na Depressão Periférica Paulista, Campinas, São Paulo

The study area is located in the Metropolitan Region of Campinas, on the contact between the Depressao Periferica Paulista and the Atlantic Plateau. The work here presented aims at mapping the Cenozoic deposits and also the tectonic structures that deform them. Three Cenozoic deposit units, associated to hill tops and slopes, were identified; from the oldest to the youngest, they correspond to: Rio Claro Formation (Trc), planation surface deposits (TQsp), and gravitational flow deposits (Qfg). The Trc deposits consist of meandering fluvial facies intercalated, or in lateral contact, with gravitational flow facies. The TQsp occurs at the top or on gently sloping divides of gentle and rolling hills. It consists of sandy-clayey or sandy deposits underlain by a stone line. The Qfg occurrences are very restrict, associated to the lower portion of slopes, and its thickness increases towards current valleys; it consists of both colluvial, with a basal stone line, and fluvial terrace deposits. This stone line sometimes contains ferruginous fragments originated from ferricretes of the Trc sediments. Two older strike-slip Cenozoic events and a younger extensional one affect the Cenozoic deposits. The older, with σ1 trending around EW, has generated strike-slip NE and NW faults, and normal EW ones. It was probably contemporaneous with the deposition of the Trc. The second event, whose σ1 trends around NW, has generated EW to WNW and NS to NNW faults, and is probably of transtensional nature. This event affects the Trc and TQsp deposits and has produced vertical tectonic offsets of the basal surface of the Trc totalizing at least 50m. The younger event, with a sub-horizontal σ3 trending around NE, has generated NE normal faults, which affect the Trc and TQsp sediments.

Estudo de depósitos da formação barreiras com base em reflexão por ondas de radar

This paper integrates radar reflection sections (GPR - Ground Penetrating Radar) with lithologic profiles based on sounding logs in deposits of the Barreiras Formation at selected points in the northern part of Rio de Janeiro State and southern part of Espirito Santo State. Three radar survey lines were investigated by common-offset mode using PulseEkko IV radar system and 50 MHz antennas. Based on interpretation of the main radar facies and units evident in the GPR lines, sampling points were selected for obtaining sounding logs using a mechanical auger. The Barreiras Formation deposits here described correspond to fining-upward sandy successions. In the geophysical survey, these sandy deposits are associated with more-or-less continuos wavy reflection patterns presenting a cross-bedded aspect and concave-upward geometry (radar facies II). Argillaceous mudstone layers interbedded with the sandy deposits are associated with a continuous, parallel reflection pattern (radar facies I). The Barreiras Formation sediments are interpreted as fluvial channel deposits, with little contribution of suspended sediments or gravitational flow deposits, in agreement with previous interpretations based on outcrop deposits in these regions.

Mapping neotectonic features using ground penetrating radar in southeastern Brazil

The Quaternary record of the Southeastern Brazil presents several tectonic structures that are related to two main tectonic phases during Pleistocene and early to middle Holocene ages. The first phase is related to an E-W dextral transcurrent tectonic regime producing NW-SE transtensional structures. The second phase is characterized by a NW-SE extension that produced NE-SW normal faults. The Holocene sedimentary evolution is marked by an important episode of environmental instability as being related to an alluvial fan system, that are the framework of amphitheater-like headwaters and flat valley floors. This work aimed to map the tectonic signatures in GPR profiles and to establish their relationships with the stratigraphical and geomorphological evolution. To this survey it was used 50 MHz antenna frequency. The GOCAD software was used for 3D reconstruction of reflection surfaces. It was recognized a northeastern dip, NW-Se normal fault set, that are probably related to the headwater evolution due to syn-depositional E-W dextral transcurrent tectonic phase. In a site studied on a flat valley floor were mapped several NE-SW conjugate faults. These NE-SW fault sets are due to a post-depositional the NW-SE extensional tectonic phase. All of the tectonic features do not affect the upper beds marked by the shallower reflector. It documents a post-deformation depositional sequence.