Navegando por Assunto "Carbonatos"

Agora exibindo 1 - 4 de 4

Acesso aberto (Open Access)
Depósitos carbonáticos-siliciclásticos da porção superior da Formação Piauí, carbonífero da bacia do Parnaíba, região de José de Freitas-PI
(Universidade Federal do Pará, 2015-07-22) MEDEIROS, Renato Sol Paiva de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The northwestern margin of the Gondwana, in the Neocarboniferous period, was influenced by a large transgressive-regressive event, depositing thin carbonate sequences from Andean basins to center-southern portions of the paleocontinent, such as the stratigraphic boundaries of the Parnaíba Basin. The Higher Member of the Piauí Formation in the Parnaíba Basin, studied in the region of José de Freitas, displays richly fossiliferous carbonate deposits overlapped by prograding clinoforms, defining the transition from a transgressive system tract to an highstand system tract. The facies and stratigraphic analysis of this succession allowed the individualization of 17 sedimentary facies and microfacies grouped in four facies associations (FA): the FA1 – Campo de Dunas – is below to the further FA and is composed by thin and average sandstone, with well selected and rounded grains, displaying plane parallel stratification with high level of bioturbation, cross-tubular stratification and translatant subcritically climbing ripple cross-lamination. The FA2 - Shallow sea deposits – is composed by a carbonate plain with tubular and continuous layers of solid carbonate and fossiliferous peloids interspersed with thin lenses of bituminous shale. The FA3 – Frente Deltaica and FA4 – Prodelta consist of pelitic layers and thin and average sandstones, arcosians and quartz sandstones, marked by surfaces of subaerial exposure with shrinkage cracks, cemented by carbonate, arranged in continuous tabular layers or in the form of sigmoidal lobes, as well as liquefaction structures of the types load cast and flame, and fluidization of the type disruption of layers, which distort the strata. The facies data corroborate the idea that the sea in the Pennsylvanian retrograded up to the border of the Parnaíba Basin, and later with the Appalachian orogeny (300 Ma) the top of the Parnaíba River arched and stepped back the marine incursion, followed by a progradational event on marine deposits.
Acesso aberto (Open Access)
O mar epicontinental Itaituba na região central da Bacia do Amazonas: paleoambiente e correlação com os eventos paleoclimáticos e paleoceanográficos do carbonífero
(Universidade Federal do Pará, 2019-03-14) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous paleogeography of the West Gondwana was dominated by epicontinental seas connected with the Panthalassa Ocean to the west. 50m-thick Pennsylvanian mixed siliciclastic-carbonate transgressive succession of the Amazonas Basin, Northern Brazil, were studied in outcrops and cores using facies and stratigraphic analysis in combination with O- and C-isotopic stratigraphy. Thirty-four facies, representative of coastal to shelf depositional systems grouped in three facies associations (FA): FA1) coastal desertic deposits, consisting of fine to medium-grained sandstone, mudstone and fine-grained dolostone that corresponds to a complex association of aeolian dunes, sand sheets, interdunes, fluvial channels and lagoon deposits bioturbated by Palaeophycus, Lockeia, Thalassinoides and Rosselia trace fossils; FA2) mixed tidal flat setting, constituted by fine to medium-grained sandstone, mudstone, shale, siltstone, lime mudstone and fine dolostone interpreted as supratidal, tidal channel, tidal delta and lagoon deposits with some brachiopod and echinoderm body fossils; and FA3) carbonate shelf deposits, consisting of lime mudstone, wackestone, packstone and grainstone with allochems (ooids and peloids), terrigenous grains and abundant and diversified open shallow marine benthic organisms, including, fish remains, foraminifers, brachiopods, echinoderms, gastropods, bryozoans, trilobites, corals, ostracodes, and conodonts, interpreted as bioclastic bars and carbonate shelf deposits. The conodonts species Neognathodus symmetricus, Streptognathodus sp. and Ellisonia sp. in the FA3 indicate the Baskirian-Moscovian age. The dolomitization affected the limestone and sandstone of AF1 and AF2 replacing the micritic matrix and occur as saddle dolomite indicating mixed of meteoric and marine waters and late burial. The neomorphism of opaque micritic matrix and bivalve shells are indicated by the growing of xenotopic mosaic of calcite crystals. In contrast, the secondary calcite cement is equant, fiber, bladed and espatic. Micritization is found in the bioclast shells exhibiting micritic coatings. The autigenesis of quartz and biogenic pyrite is commonly found in FA2 and FA3. The mechanic and chemical compaction in limestone caused the porosity reduction, cementation, fractures and development of dissolution seams and stylolite. The sandstones were cemented by quartz, calcite and iron hydroxides/oxides and show concave-convex and sutured contacts between quartz grains. The predominance of eodiagenetic and subordinate mesodiagenetic features in the Monte Alegre-Itaituba succession indicated less modified framework by the diagenesis corroborating the pristine signature of δ13C values ranging from ~ -2 to ~+5.28‰. This enriched trend upsection coadunate with high organic productivity triggered by massive flourishment of euphotic-controlled benthic organisms mainly in the FA3. Five types of shallowing upward asymmetric cycles characterize the Monte Alegre-Itaituba succession. Peritidal cycles in coastal desertic (Cycle I) were formed by alternance of dolostone and sandstone with δ13C values ranging from -1.5 to +0.3‰. Cycles II consist in interbedded of sandstone-mudstone and sandstone-mudstone-floatstone rhythmites and the Cycle III constitute dolostone interbedded with sandstone. These cycles II and III were interpreted as tidal flat and lagoon deposits with δ13C values ranging from +3,98%₀ to +4, 62%₀. The Cycle IV is a rhythmite formed by wackestones/mudstones couplets while the Cycle V consists of alternance of grainstones, wackestones and lime mudstone (ABC cyclicity) passing upsection for cycles composed by wackestones and lime mudstone (AB cyclicity). The cycles IV and V are shelf deposits with δ13C values ranging from +3,65%₀ a +5,28%₀. The stacking of 53 cycles with average thickness of 1,1 m, combined with Fisher plot diagram, indicated an aggradational to retrogradational stacking pattern inserted in the lowstand to early transgressive system tract (Cycles I-III) and late transgressive system tract (Cycles IV and V). The succession was deposited in ~13 Ma and individual cycles accumulated in an approximately 0.25 my typical of fourth order cycles related to high-frequency fluctuations of relative sea level. These data were correlated to the global δ13C and sea-level curves that positioned the Monte Alegre-Itaituba succession in the Late Serpukhovian to Early Moscovian age. The influence of Late Misssipian glaciation was negligible in these deposits but the post-glacial transgression combined with slow subsidence of the Amazonas basin caused the generation of allogenic cycles I, IV and V. The cycles II and III were formed by autochthonous processes during a period of equilibrium between supply and glacioeustasy. The Monte Alegre-Itaituba succession is the record of a large Amazonia epicontinental sea that was directly connected with the Panthalassa Ocean during Pennsylvanian.
Acesso aberto (Open Access)
Paleoambiente e diagênese da formação Itaituba, carbonífero da bacia do Amazonas, com base em testemunho de sondagem, região de Uruará, Pará
(Universidade Federal do Pará, 2014-08-04) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous Itaituba Formation represents expressive retrograding carbonate sedimentation included in the sedimentary evolution of the Tapajós Group of the Amazonas basin. These carbonate consist of fossiliferous limestones, fine grained dolostones, fine to coarse grained sandstones and subordinate reddish siltstones, black shales and evaporites. Facies and microfacies analysis of drill cores from the Uruará region, State of Pará , allowed to individualize nineteen facies grouped into five facies associations : tidal plain ( FA1 ) , tidal channel ( FA2 ), lagoon ( FA3 ), bioclastic bar ( FA4 ) and outer shelf ( FA5 ). FA1 is composed of fine grained sandstone with rip-up clasts and mud cracks , marl with quartz and feldspar grains, laminated dolomudstone with fine terrigenous grains and silicified dolostone with intercalation of mudstone and disseminated quartz grains dolomitized and locally with microcrystalline quartz. FA2 consists of medium to coarse grained sandstone with trough cross-bedding and mud drapes on foresets, very fine to fine grained sandstone with wavy bedding, laminated siltstone, synsedimentary faults and convolute lamination. FA3 consists of massive red siltstone, mudstone with fossils, brachiopods and floatstone with disseminated pyrite and massive mudstone with frequent quartz grains. AF4 and AF5 exhibit abundant bioclasts represented by spines and fragments of echinoderms, shells, spines and fragments of brachiopods, ostracods, foraminifera, red algae and bilvave shells. AF4 consists of fossiliferous oolitic grainstone and grainstone with terrigenous grains, mainly monocrystalline quartz grains and the AF5 consists of fossiliferous wackestone, wackestone with terrigenous grains and massive mudstone with monocrystalline quartz grains. Subarkoses (AF1), arkoses (AF2) and lithic arkoses (AF2) predominate in the Itaituba Formation and are composed by of polycrystalline and monocrystalline quartz grains, K-feldspar, plagioclase, pyrite, detrital muscovite, mudstone, metamorphic and chert fragments and rare bioclasts. The cement is of nonferrous calcite, iron oxides/hydroxides, silica overgrowth and intergranular, moldic and sometimes elongated porosities reaching up to 11 % of the rock. The diagenetic processes in sandstone are physical compaction, quartz overgrowth, non-ferrous calcite cementation, chemical compaction, grain replacement, pyrite autigenesis, formation of iron oxides/hydroxides and alteration of plagioclase. The diagenetic processes in carbonates are: micritization, neomorphism, dolomitization, fracturing, chemical compaction, calcite cementation, secondary dissolution and mineral autigenesis. The Itaituba succession is interpreted as a lagoon/tidal flat system linked to the marine carbonate platform. Tidal flats developed on the margins of the lagoons were periodically supplied by fine (silt) terrigenous influxes that inhibited the carbonate precipitation. Bioclastic bars were cut by tidal channels (inlet) connected the lagoon with the shallow platform rich in benthic organisms.
Acesso aberto (Open Access)
Paleoambiente e quimioestratigrafia da Formação Itaituba, carbonífero da borda sul da bacia do Amazonas, região de Uruará – Pará
(Universidade Federal do Pará, 2014-10-29) CAMPOS, Amélia Carolina Pimenta Parente de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/886783626882099; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Amazon Basin, characterized as an intracratonic basin of about 400,000 km2, has a Phanerozoic sedimentary record of four second- order sequences related to groups Trombetas; Urupadi and Curuá; Tapajós and Javari. The Itaituba Formation, the goal of this work, is part of the Tapajós Group, which represents the last transgressive -regressive cycle of this Paleozoic basin. The Itaituba Formation presents thick packages of subtidal limestones intercalated with thicker evaporite deposits toward the top of the formation, with shales, siltstones and sandstones that represent deposits transgressive – regressive deposits of moderate energy in shallow marine infra-tidal and subtidal environment. The formation is composed of the richest strata of marine fossils in the Amazon Basin, such as the conodonts, foraminifera, corals, bryozoans, crinoids, trilobites, ostracods, gastropods, brachiopods, bivalve, escolecodonts and fish fragments. In this work, it was studied samples from a drill core (FURO 5) obtained in Uruará area, east-central state of Pará. The main objectives of this study are to obtain the depositional age of Itaituba Formation by comparison with the century 87 Sr/86Sr curve and its chemostratigraphic characterization based on major and trace elements contentes, and C and O isotopes, as well as the facies description. The stratigraphic profile of the drill core is characterized by an intercalation between carbonatic facies rich in bioclasts , stylolites and quartz druses and dolomitic facies . At the base of the profile, terrigenous facies characterized by reddish silt with carbonate clasts were recorded. Microfaciologically the following lithotipes were identified: wackstone, packstone, and more rarely dolomudstone, mudstone and grainstone. Seven microfacies were defined: Bioclastic Mudstone (Mcb), Bioclastic Wackstone (Wb), Bioclastic Wackstone with stylolites (Wbe), Bioclastic Packstone (Pb), Bioclastic Packstone with Peloids (Pbp), Bioclastic Grainstone with Peloids (Gbp) and Fine Dolomite (Dl). Among the bioclasts are: brachiopods, echinoderms, foraminifera, pelecipods, bryozoans, gastropods and ostracods. As not skeletal components there are: quartz, clay minerals, feldspars, oóides and intraclasts. The matrix is micritic and there are three types of cement: "fringe", tile and sintaxial overgrowth. Much of the profile was affected by secondary processes such as dolomitization, dissolution and compaction. The results of geochemical analyses were performed on 46 samples collected at each 50 cm, approximately. The data confirm that the profile is predominantly calcitic with small variations in the Mg content, however, dolomitised levels are present. The high values of Si in some samples indicate the presence of terrigenous minerals, in addition to the druses and fractures filled with quartz. The Sr contents of the samples are satisfactory for the isotopic analysis, and varies from 30 to 293 ppm, some of the smaller values being related dolomitic rocks. Stable isotope studies were performed on 76 samples collected at intervals of 30 cm. The values obtained for 13C and 18O range from 1.602 to 5.422 ‰ and - 8.734 to 0.804 ‰, respectively. These values are in accord with those obtained in previous studies for the Itaituba Formation carbonates, pointing a marine environment with the typical isotopic signature of Carboniferous rocks. (13C ranging from 2 to 6 ‰, and 18O ranging from - 3 to 7‰). Therefore, the study carbonates have primary isotopic composition, except for some samples, which have their values affected by diagenetic processes, like the dolomitization. The depositional age was obtained from the leaching of two shells of brachiopods, which positioned the rocks from the Itaituba Formation in the Upper Pennsylvanian with two ages intervals, between 296 and 303 Ma (Virgiliano - Missourian), and between 293 and 307 Ma (Virgiliano - Desmoinesiano), and Lower Pennsylvanian aged between 313 and 318 Ma (Morrowan).