Navegando por Assunto "Epicontinental sea"

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Diagênese da formação guia, Ediacarano da Bacia Araras -Alto Paraguai, sul do Cráton amazônico
(Universidade Federal do Pará, 2022-10-31) SANTOS, Caio Silva dos; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Guia Formation is a limestone unit of the Araras Group, exposed in central region of South America. They correspond to Ediacaran (622-614Ma) carbonate platform deposits, developed in an epicontinental sea. This deposits unconformably overlies diamictite of Puga Formation related to 635Ma Marinoan glaciation, also distributed over the metamorphic basement. The Guia Formation, aim of study, is composed of limestones interbedded with thin layers of black shales. The data were obtained from an analysis of a 350m stratigraphic profile in one of the best exposition of Guia Formation in a COPACEL mine open pit in Nobres town, State of Mato Grosso. The unit consist in six lithofacies, grouped in one facies association that records a deep carbonate platform: bituminous lime-mudstone, massive lime-mudstone and lime-mudstone rich in terrigenous grains, carbonate shale, carbonate breccias and deformed breccias. These rocks were intensive affected by diagenetic process such as aggrading neomorphism, organic matter maturation, physical compaction, spar calcite cement, dolomitization, chemical compaction and hydrocarbon migration. Aggrading neomorphism affect the matrix, turn it to microspar and pseudospar with hipidiotopic mosaic. The micrite rich in organic matter is partially dissolved by fluids capable of dissolving the matrix, generating the vug pores. That pores are cemented by spar calcite. This cement has coarse granulation, subhedral crystals, when it fills fractures it presents crystals with rhombohedral cleavage, with two directions. In cathodoluminescence, the cement has orange to red bright when it fills vug fracture, and it has zoned pink bright luminescence filling pore vug. The stylolites form serrated surfaces of low amplitude, insoluble material, composed by clays, quartz, and organic matter compound its. Dolomitization affects the rocks in three moments: the first one is the replacement of spar calcite filling fractures with subeuhedral dolomites in hipidiotopic mosaic and opaques minerals inclusions, the second on is the filling by the matrix replacement with anehedral dolomites; the third one is the formation of saddle dolomite associated with hydrocarbon. Spot analysis with SEM/EDS, shows a large amount of Ca, ang low range of Mg, Si, S, Ca, Mn, Fe, Ni, Zn, Sr, Cd, Ba and Pb. Reasserting that carbonate are scant changed by diagenetic/dolomitizing fluids. These rocks are part of the Araras Petroleum System, the Total Organic Content Analysis (TOC) indicated values between 0.04 and 0.50%, classified as a low to medium potential. The association among the petrographic and geochemistry data suggest that the bitumen migration occurred at 610 Ma, during thermal uplift of the Araras Intracratonic Basin, before the deposition of the Alto Paraguai Group, which led to exposure of the Araras Group and oxidation of the hydrocarbon, allowing the identification of type IV kerogen. Rock Eval pyrolysis, Hydrogen Index and Oxygen Index data of these rocks, do not have the potential to generate oil or gas, and are constituted by oxidized organic matter, with immature thermal evolution.
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Reconstituição Paleoambiental e Potencial Petrolífero da Sucessão Siliciclástica-Carbonática Permiana da Bacia do Paraná
(Universidade Federal do Pará, 2022-02-15) BRITO, Ailton da Silva; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian age was marked by extreme paleogeographic and paleoclimatic changes with predominances of arid conditions across the globe as a consequence of the eustatic sea-level fall from the end of the Carboniferous glaciation to the beginning of the Permian. The final phases of continental agglutination of the Pangea supercontinent caused uplifts accompanied by successive regressions of the epicontinental seas, culminating with the installation of desert systems at the end of the Permian. During the marine regressive phase, Western Pangea was the depositional site of a 50m thick mixed siliciclastic-carbonatic succession under restricted and shallow paleoenvironmental conditions, widely distributed in the Paraná Basin, SE of South America. The studied succession includes the top of the Palermo, Irati, and the base of the Serra Alta Formation, comprising a total of 120 m-thick. The Irati succession is essentially composed of dolomite intercalated with organic matter gray to black shale rich, which is considered an important source rock for hydrocarbons. This unit covers the heterolithic deposits from the Palermo Formation and is overlaid by shales from the Serra Alta Formation. The high content and good quality of organic matter present in Irati shales aroused economic interest since the 19th century. Although many works have contributed to the knowledge of the depositional paleoenvironment and generating potential of this unit, mainly from organic geochemical data, gaps remain regarding the paleoenvironmental understanding, previously interpreted as restricted sea or lacustrine. This research was carried out from 125 drill cores distributed in the center-north, center-south, and extreme south of the basin, provided by the company Irati Petróleo LTDA. complemented by outcrops from the northern region. Twenty-three drill cores were selected for sedimentological and stratigraphic study from facies/microfacies analyses, aided by XRD, SEM-EDS, and cathodoluminescence images. Total organic carbon (TOC), Rock-Eval pyrolysis, and biomarker analysis were performed on 102 cores. The integration of data allowed: the lateral correlation of the Irati Formation for more than 2,000 km in the SSW-NNE direction of the basin; the paleoenvironmental reconstitution; and lateral and vertical characterization of the generating potential. Twenty-one facies/microfacies were identified and organized into about 300 siliciclastic-carbonate couplet that are grouped into 59 high-frequency cycles representative of mid-outer ramp and offshore environments dominated by distal turbidity systems. The succession consists of four third-order sequences (S1, S2, S3, and S4). Sequence boundaries are type 2, with no evidence of subaerial erosion, marked by overlapping transgressive offshore deposits. Transgressive Systems Tracts are succeeded by Highstand Systems Tracts defined by the appearance of dolomite levels with a thickening upwards tendency, which indicates high carbonate productivity under normal to hypersaline conditions, evidenced by the presence of gammaceran, halite crystals. and pseudomorphs of gypsum. The transgressive deposits of sequences S3 and S4 (Assistance Member) form the two intervals (oil-shale) with the greatest generating potential in the Paraná Basin. Oil-shale S3 has the highest values of organic carbon and generating potential. The highest TOC peaks were 19.40% for the extreme south region, 22.23% for the center north, and 27.12% for the center-south of the basin. Kerogen predominates types I and II, which also presents an increased contribution, mainly from type I converging to the center-south. Oil-shale S4 presents lower TOC values for the extreme south region (8.82%), south-central (21.7%), and north-central (14.61%). The kerogen type is similar to oil-shale S3, it predominates type II, with a high contribution of type I in the south-central region and smaller proportions of type III. The organic matter of the Irati Formation is predominantly immature, however, occurrences of maximum pyrolysis temperature (Tmax) equal to or greater than 440 ºC in samples close to diabase sills show that there was localized maturation of organic matter, which corroborates the occurrence of a non-conventional petroleum system for mixed deposits of black shales (generators) - carbonates (reservoirs) of the Irati Formation. Regarding the quantity and quality of the source rock present in the Irati Formation, the center-south portion presents the highest values of organic carbon as well as the potential for hydrocarbon generation. The analysis of the stacking patterns associated with the previous ages of SHRIMP U-Pb from volcanic ash allowed the correlation of the succession with the global sea-level curve, allowing to estimate an age of 8.0 Ma for the Irati Sea and of 2 .7 Ma for 3rd order depositional sequences. Likewise, ages of 26.6 ka were calculated for the carbonate-siliciclastic couplets, 135.5 ka and 400 ka for the high-frequency cycles, whose origin is here attributed to the climatic cyclicity induced by the terrestrial orbital oscillation, compatible with the Milankovitch cyclicity. The characterization of the cycles based on faciological and organic geochemical data also demonstrates a strong climate control in the generation of intervals rich in organic matter.