Dissertações em Geologia e Geoquímica (Mestrado) - PPGG/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2604

O Mestrado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

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Datação pelo método de traços de fissão em apatita da região da estrutura dômica de Monte Alegre, Bacia do Amazonas (PA)
(Universidade Federal do Pará, 2011-04-05) NEGRÃO, Sílvia Cristina Barroso; LELARGE, Maria Lidia Vignol; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
In the northern portion of the Amazonas Sedimentary Basin, south of the Monte Alegre city (PA), a semi-elliptical structure defined by a group of small hills occurs, which is known as the Monte Alegre Dome. In the central portion of the dome, Devonian rocks of the Ererê Formation crop out, while toward the edge of the structure the Neodevonian to Mesocarboniferous successions, represented by the Barreirinha, Curiri, Oriximiná, Faro and Monte Alegre formations, are exposed. Diabase dykes and sills of about 200 Ma (Penatecaua Magmatism) cut this set of rocks. The formation of this dome structure has been related to the emplacement of dykes and sills of diabase. However, the contribution of Tertiary tectonism, present throughout the Amazon Basin, cannot be ruled out for the formation of the dome, since in the eastern and southern portions of this structure the Cretaceous to Tertiary rocks of the Alter do Chão formation are in faulting contact with rocks of the Ererê formation. In this study we applied the apatite fission track thermochronology in the diabase of the Penatecaua Magmatism in order to determine the age of formation of the dome structure, and to investigate the role of the Tertiary tectonics in the development of this structure. The apatite fission track method (AFT) is applied to study the thermotectonic evolution of a region, since the quantification of the fission tracks present in the mineral permits to estimate the age at which the rock passed through a given temperature (blocking temperature), which may be related to a tectonic event (uplift / subsidence) that occurred in the area. The mafic rocks studied in the region of Monte Alegre provided ATF apparent average ages between 53.2 and 43.6 Ma. These ages are interpreted as representing major tectonic events that occurred in the Tertiary (Early to Middle Eocene) that uplifted to shallower crustal levels and the diabases and the country rocks. The thermal histories obtained after modeling the AFT data allowed the recognition of four events of cooling, which occurred at 140-110 Ma, 110-100 Ma, 55-45 Ma and 30 Ma-recent. Just one sample (TFMA-12), located outside of the dome structure, did not record the Eocene tectonic event. The ATF data modeling also permitted to estimate cooling rates ranging from 0.4ºC / Ma for slower events, up to 2.82°C / Ma for faster events. Based on these cooling rates it is suggested that 3 to 3.35 km of rocks section was removed due to the reactivation of faults at different moments during the geologic evolution of the region, mainly along the Cenozoic. The apparent ATF ages between 43.6 and 53.2 Ma, as well as the significant cooling thermal event recorded in the Eocene by the data modeling revealed the important role that the Tertiary (Eocene) tectonic in the formation of dome structure of Monte Alegre. It is believed that the apparent ages of fission tracks (43.6 and 53.2 Ma) would place limits on the age of this Tertiary tectonics.
Acesso aberto (Open Access)
Morfologia e sedimentologia da praia de macromaré de Ajuruteua, Pará: um estudo para definição de índices de sensibilidade ambiental ao derramamento de óleo
(Universidade Federal do Pará, 2007-10-28) BRAGA, Francisca de Paula da Silva; SOUZA FILHO, Pedro Walfir Martins e
The Ajuruteua macrotidal beach located in Northern Brazil is subject to oil pollution in response to the routes of tanker ships. Hence, it is very important to know the environmental characteristics to establish contingency plans. The aim of this work is to investigate the spatial and seasonal changes in grain size and morphologic properties along the intertidal zone (IZ) to define environmental sensitivity index (ESI) to oil spill in this beach zone. During this research it was carried out 23 beach profiles from foredunes to 1 m in deep in the subtidal zone under low spring tide condition. Along this profiles, sedimentary samples were collected in June, September and December 2005 (solsticious) and March 2006 (equinoctials). Sedimentary samples were analyzed in laser granulometer (Malvern Mastersize 2000) in 1/8φ interval. Topographical data were collected by TOPCON total station and processed using TOPOGRAPH 98SE and GOLDEN SOFTWARE (SUFER 8.0). The results show seasonal variations in the grain size and morphologic distribution in the IZ. On June and December the IZ is flat, while on March and September we observe the occurrence of a ridge and runnel system. On June and December, the upper IZ sediments are fine, well sorted, with positive skewness, tending to be coarser in direction to lower IZ, where the sediments are moderately to poorly sorted, with negative skewness. On September and March, it was observed heterogeneity on IZ sediment distribution; the grain size changes from fine to medium, from well to poorly sorted, with negative skewness. In the runnel, the sediments tend to be coarser with negative skewness and moderately sorting. To Ajuruteua beach ESI map elaboration we classified the index 3A as less sensible and the index 3E as more sensible. On June and December the lower IZ is more sensible (index 3D) to oil spill than upper IZ (index 3A). On March and September, the sensibility is higher, mainly along the runnel (3E), that work out as a trap, difficulting the oil cleaning.
Acesso aberto (Open Access)
Paleoambiente dos calcários e folhelhos betuminosos da Formação Guia, Neoproterozóico, Sudoeste do estado do Mato Grosso
(Universidade Federal do Pará, 2012-05-02) BRELAZ, Luciana Castro; LOPES, Renata Lourenço; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The establishment of large carbonate platforms worldwide linked to the sudden increase in global temperature after the last Cryogenian glaciation (~ 635 Ma) was concomitant with the ice-melting and transgressive events. In Brazil, one of the best examples of these post-glacial transgressive Ediacaran deposits is the Guia Formation, the calcareous unit of Araras Group, exposed for hundreds of kilometers in the North Paraguay Belt and Southern Amazon Craton. The Guia Formation consists predominantly of limestone and bituminous shale, more than 400 m thick. It was investigated in open pits of quarries in the Cáceres, Nobres and Cuiabá region, southwestern of the State of Mato Grosso, Brazil. The facies and stratigraphic analysis of the Guia Formation allowed recognizing of three facies associations (FA) representative of a retrogradational platform succession: FA1- lower shoreface influenced by storms, FA2- proximal offshore and FA3- distal offshore with slope facies. The association FA1 up to ~ 150 m thick, and includes marl and grey terrigenous-rich fine-grained limestone with megaripple bedding, wavy bedding and hummocky cross-stratification, produced by oscillatory and combined flow related to fairweather and storms wave in the shoreface zone. The association FA2 corresponds to the thickest deposits of the Guia Formation, reaching almost 200 m in thickness and consists of grey to black organic-rich ribbon limestone interbedded with shale. The remarkable lateral monotonous continuity of these deposits, extensive by hundreds of kilometers, suggests low energy conditions, below the storm wave base, related to the offshore zone. The large amount of organic material accumulated in these deposits associated with pyrite crystals implies stagnant and anoxic deep waters. Palynomorphs in these facies include a few species of leiosphaerids, indeterminate sphaeromorph acritarchs and probable algae fragments. The brown colour of amorphous organic material and acritarchs indicates moderate degree of maturation. The rarity of preserved organic forms and the large amount of amorphous organic matter indicate moderate degree of degradation. The association AF3 has 70 m thick and consists of limestone breccias with tabular clasts and slump features interbedded with fine-grained limestone. The intraformational breccias were formed by gravity flows generated during instability of carbonates in the distal offshore zone. These episodic gravity flows alternated with cyclic hemipelagic sedimentation (forming lime and terrigenous mud). Three aspects were considered to define the morphology of the platform: 1) the transition from shallow to deep deposits without an abrupt facies change; 2) the absence of brittle sinsedimentary deformation; and 3) the lateral continuity of these deposits over hundreds of kilometers, suggesting sedimentation in a homocline ramp. The existence of a wide carbonate ramp in the margin at the Amazon Craton during the Ediacaran, site of organic matter-rich lime mud deposition, opens perspectives for prospection of source rocks of a probable Neoproterozoic petroliferous system developed in the Central Brazil region.
Acesso aberto (Open Access)
Paleoambiente e quimioestratigrafia da Formação Serra do Quilombo, Neoproterozóico da Faixa Paraguai Norte, regiões de Cáceres e Nobres (MT)
(Universidade Federal do Pará, 2012-05-03) MILHOMEM NETO, João Marinho; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
After the last criogenian glaciation (ca. 635 Ma), large carbonate platforms were developed in several cratonic regions of the Earth and, despite of the intense dolomitization of these deposits, many of paleoceanography and sedimentary processes can still be rescued, contributing to the understanding of the paleoenvironment and the isotopic geochemistry of the Neoproterozoic seawater. One of the most important testimonies of this period in Brazil is the Serra do Quilombo Formation, upper portion of the Araras Group, exposed in the northern Paraguay Belt, southern of the Amazonian Craton. This unit has been interpreted in its type section in the Caceres region, Mato Grosso, as deposits of shallow to moderately deep platform influenced by storms and earthquakes. The stratrigraphic and facies revaluation in combination with C, O and Sr isotopes data in the Caceres (type-section) and Nobres regions, allowed enlarging the paleoceanography and paleoenvironmental interpretations, aiming at building a chemostratigraphic framework for the unit. The 140 m thick of the study succession includes the Serra do Quilombo Formation in sharp basal contact with the Guia Formation and the gradual contact, to the top, with the Nobres Formation. In this succession were described five depositional facies that correspond the organic matter rich laminated dolostone (Dl), massive to laminated dolostone (Dml), hummocky/swaley to planar stratified sandy dolostone (DAh), sandy/oolitic dolostone with wave cross laminations (DAl) and matrix-supported dolomitic breccia (BDm). The sedimentary facies were grouped into two facies associations (FA) that indicate environments of deep to moderately shallow carbonate platform (FA1: Dl and Dml) and storm influenced shoreface (FA2: DAh, DAl and BDm). The Serra do Quilombo Formation comprises a shallowing upward succession, which represents the progradational record of a highstand system tract, in a homoclinal carbonate ramp, installed on the southern part of the Amazonian Craton during the Ediacaran. C and O isotopic analyses were performed in 141 samples (among laminated limestones and dolostones, sandy/oolitic dolostones and clasts, cement and matrix of dolomitic breccias), of which 6 were also selected for the Sr analysis. Major (Ca, Mg and Fe) and trace (Rb, Sr and Mn) elements contents, performed on 20 samples, assisted in the selection of those for Sr isotopic analysis and evaluation of the primary nature of the isotopic signal of study carbonates. The δ13C values, interpreted as representing the original sea water, showed a trend ranging from negative, around -2 ‰ at the base of the succession (Guia Formation) to above 0‰ at the top of the succession. The type-section of the Serra do Quilombo Formation presents a homogeneous C-isotope curve, with δ13C values around 0 ‰, which allows its perfect correlation with other sequences, for example, its section reference in Nobres, far about 200 km. The 87Sr/86Sr follow the general C-isotopes trend, increasing towards the top of the succession, ranging from 0.7077 to 0.7083, directly related to the environmental shallowing and the consequent influx of siliciclastic grains recorded in the top portion of the unit (AF2). The δ13C and δ18O data obtained for the dolomitic matrix-supported breccias (BDm) indicate, in general, a similarity between the isotopic signal of both matrix and clasts, suggesting a sindeposicional and primary process. On the other hand, for the dolomitic cemented breccia, the values obtained for the sparry dolomite cements indicate lower values of δ13C and, notably, of δ18O in relation to the clasts, suggesting that its origin is secondary, probably resulting from the interaction with meteoric water or hydrothermal fluids during the breccias formation. The establishment of a moderately deep to shallow carbonate platform environment with C isotopic patterns, tending to positive values, is clearly distinct of the postglacial deposits of the base of the Araras Group, with strongly negative values of C, and may represent the restoration of normal sedimentation conditions. Likewise, the growing trend of Sr isotopic ratio indicates the increasing in the influx continental in a scenario completely devoid of glacial influence (Snowball/slushball Earth hypothesis). Sr values indicate ediacaran age, between 560 and 580 Ma for the Serra do Quilombo Formation deposition.
Acesso aberto (Open Access)
Rochas geradoras da Formação Guia, Neoproterozoico do sul do Cráton Amazônico, região de Cáceres e Nobres, estado do Mato Grosso
(Universidade Federal do Pará, 2018-10-24) BEZERRA JUNIOR, Alexandre Castelo Branco; SILVA JUNIOR, José Bandeira Cavalcante da; http://lattes.cnpq.br/8615194741719443
Extensive epeiric seas installed in the western Gondwana at the Upper Neoproterozoic were influenced by the last global glacial Marinoan event (635 Ma) linked to the Snowball Earth hypothesis. The rapid change in icehouse for greenhouse conditions favored the development of wide carbonaceous platforms on the southeastern margin of the Amazonian Craton, in the context of the Intracratonic Basin, reversed at the beginning of the Paleozoic. In this region, the deposits of the Araras Group are exposed, which record the evolution of the post-glacial carbonaceous platforms. The Araras Group is composed, from the base to the top, by the Mirassol d'Oeste (cap dolomitic), Guia (cap limestone), Serra do Quilombo and Nobres formations. The Guia Formation, object of this study, has its base interpreted as limestone cap with up to 30 meters thickness in the occurrences on the Craton and platform deposits with up to 225 meters in the Intracratonic Basin. This unit consists of micritic limestones and transgressive shales rich in organic matter presenting excellent exposures in the regions of Cáceres and Nobres, State of Mato Grosso, consisting of the following facies/microfacies: limemudstone; wackestone with terrigenous; mudstone with intraclastic; and limestone breccia. This monotonous set of facies/microfacies was interpreted as a shallow marine platform paleoenvironment below the level of storm waves in the offshore zone under reducing conditions. Stilolytes and dissolution seams are common in Mc and Wt microfacies, as well as the presence of bitumen and pyrite filling inter-crystalline pores. The facies Wt presents a variation of terrigenous content of 5% to 35%, represented by grains of quartz and muscovite, both varying from silt to fine sand. The analysis of the quartz grains by cathodoluminescence indicate the origin of igneous and metamorphic sources from medium to high grade. The anomalous amount of terrigenous disseminated in the micritic facies, considered a textural inversion, suggests siliciclastic influx of margins close to the basin, consistent with a paleogeographic context of epeiric seas proposed by previous studies for the core of West Gondwana. The analysis of Total Organic Content (TOC) indicated in the outcropping succession in the region of Cáceres TOC values between 0.06% and 0.23%, while in the Nobres region, the deposits presented values between 0.05 and 0.27%, consistent with neoproterozoic accumulations around the world (generally less than 1%). This hydrocarbon accumulation, although economically irrelevant, composes an unconventional petroleum system called Araras. In such a way that the studied succession (Fm. Guia) constitutes the generating and reservoir rock of this system and the dolomites of the Serra do Quilombo Formation represent the sealing rock. At least two stages of hydrocarbon migration are recorded, associated to the tectonic events in the Upper Ediacaran and Early Paleozoic, with the opening of the Parecis and Paraná basins.
Acesso aberto (Open Access)
A sucessão siliciclástica-carbonática neocarbonífera da bacia do Amazonas, regiões de Monte Alegre e Itaituba (PA)
(Universidade Federal do Pará, 2010-03-14) LIMA, Hozerlan Pereira; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Neocaboniferous deposits of Morrowanian age in the Amazon Basin, northern Brazil, characterize the transition zone between Monte Alegre (siliciclastic rocks) and Itaituba (carbonate rocks) formations. The outcrop-based facies and stratigraphic analyses of this up to 40m thick succession, exposed in the Monte Alegre and Itaituba regions, State of Pará, allowed the recognition of five facies associations (FA), representative of a transitional desertic to coastal system, comprising: eolian dune/interdune (FA1), sandy sheet/wadi (FA2), lagoon/washover (FA3), beach/tidal flat (FA4) and lagoon/tidal delta (FA5). FA1 contains bimodal fine to medium-grained sandstone with medium-scale trough cross-stratification, subcritically climbing translatent stratification and inversely graded lamination (dune deposits). Massive fine sandstones with root marks suggest development of paleosols, while adhesion warts indicate eolian grain migration on wet interdune surface. FA2 comprises fine to medium-grained sandstone with even-parallel stratification and subcritically climbing translatent stratification, related to deflation, while fine to medium-grained sandstone with tangential and recumbent-folded cross-stratification and convolute bedding suggest migration of high-energy ephemeral rivers. FA3 with laminated mudstone and fine-grained sandstone with climbing-ripple cross lamination, hosting the ichnofossil Palaeophycus, suggests a low-energy environment of lagunar/washover type. FA4 is characterized by fine to medium-grained sandstones with planar and low-angle cross-stratification, interbedded with lenticular dolomite, locally truncated by fine to medium-grained sandstones. These facies correspond to the zone of swash and backwash on beach environment, locally cut by small channels, while the carbonate is interpreted as precipitated in ponds. FA 4 also comprehends mudstones with mudcracks and mud curls as well as small to medium-scale planar cross-bedded sandstones with mud drapes lining foresets and reactivation surfaces, suggesting migration of sandwaves in intertidal zones. FA5 is represented by dolomitized limestones (mudstones, wackestones, packstones and grainstones) containing vuggy and moldic porosities. Bioclasts include brachiopods, echinoderms, foraminifers, ostracodes, bryozoans, trilobites, mollusks and non-fragmented corals, and furthermore the trace fossil Thalassinoides. Additionally, this facies association comprises conglomerates with pebbles of dolomitized limestones, fine-grained sandstones with low-angle cross-stratification and reactivation surfaces, locally overlaid by fine sandstones with sigmoidal cross-stratification and climbing cross-lamination, which were interpreted as tidal inlet and tidal delta deposits. The facies/microfacies associations and paleontological data presented here point to a lagoonal environment, connected in part to a coastal desert zone, and characterize the transition between Monte Alegre and Itaituba formations. The abundance of fine sands with rounded grains in carbonate facies is consistent with siliciclastic influx from the desert adjacent to coastal environment. Warm tropical conditions for the environments can be inferred from the limestones and their diverse fauna as well as from the clay minerals, principally smectite. The interbedding of siliciclastic and carbonate rocks which characterizes the end of the deposition of the Monte Alegre Formation and the beginning of the sedimentation of the Itaituba Formation justifies a unique system representation for this interval.

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