Navegando por Autor "TRUCKENBRODT, Werner Hermann Walter"

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Análise faciológica da Formação Alter do Chão (Cretáceo, Bacia do Amazonas), próximo à cidade de Óbidos, Pará, Brasil
(2012-03) MENDES, Anderson Conceição; TRUCKENBRODT, Werner Hermann Walter; NOGUEIRA, Afonso César Rodrigues
Cretaceous deposits of the Alter do Chão Formation, exposed on the banks of the Amazon river, near the town of Óbidos - PA, record a succession of sandstones, conglomerates and mudstones. Seven lithofacies have been recognized which comprise massive conglomerate (Cm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), climbing cross-laminated sandstone (Sl), massive mudstone (Mm), bioturbated mudstone (Mb) and deformed mudstone (Md). These facies are organized in fining-upward cycles, 1 to 6m thick, and have been grouped into two associations: channel fill and overbank deposits belonging to a fluvial meandering system. The channel-fill deposits include lenticular gravel bars composed of facies Cm and St, sandy bedforms with facies St, Sp and Sl, and lateral accretion bar, consisted of facies St, Sp and Mm, but with distinct migration with regard to that of the sandy bed forms. While paleocurrent measurements from facies St and Sp of sandy bedforms indicate a preferred orientation of paleoflow to SW and a subordinate flow to S, the lateral accretion bar migrates to E/ESE. The following overbank elements have been recognized based on their geometric relationships: muddy floodplain deposits including abandoned channel plug, crevasse splay channel filled with facies St and Sp and natural levee deposits composed of facies St, Sl and Mm. While the muddy channel plug overlies sandstones, the crevasse channel fill is in contact with mudstones of the floodplain and also cuts through fine-grained sandstones and mudstones interpreted as natural levee deposits. Adjacent muddy lenses in the same stratigraphic level on sandstone but with smaller width than that of the abandoned channel are attributed to swales, filled during floods, capping lateral accretion bar.
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Deformação das rochas siliciclásticas paleoproterozoicas do Grupo Araí como exemplo das reativações de falhas do embasamento, Serra do Tepequém, Roraima, norte do Brasil
(2012-12) FERNANDES FILHO, Lucindo Antunes; PINHEIRO, Roberto Vizeu Lima; TRUCKENBRODT, Werner Hermann Walter; NOGUEIRA, Afonso César Rodrigues
Serra do Tepequém region comprises paleoproterozoic siliciclastic rocks from Araí and Suapi Groups, which are part of Roraima Super-group. Field data indicate that bedding is dipping towards SE and NW in different domains limited by NE-SW sinistral oblique faults with both normal and also reverse displacements. The structural setting is formed by regional scale forced folds represented by kilometre scale kink bands and chevron folds. The proposed framework is compatible with upper-to-middle crustal level. The studied faults were controlled by reactivation of early ductile basement fabric. These findings differ from previous regional models, based on folding under ductile conditions related to colisional tectonics. Results evidence the importance of Guiana Shield early basement structures in controlling the geometry of the brittle structures, which were seen on the cover rocks of Serra do Tepequém.
Acesso aberto (Open Access)
Proveniência de arenitos albianos (Grupo Itapecuru), borda leste da bacia de São Luís-Grajaú, Maranhão, usando análise de minerais pesados e química mineral
(2009-04) MENDES, Anderson Conceição; TRUCKENBRODT, Werner Hermann Walter
Albian deposits from the São Luis-Grajaú Basin, formerly recognized only in the subsurface, have been recently found along the Itapecuru river, eastern part of this basin. These deposits consist of red, gray to greenish mudstones, cross-bedded and massive sandstone and subordinately limestones, interpreted as deposits of a to ENE/E and ESE prograding delta connected to a restricted platform. In order to understand the provenance of Albian sandstones, 18 samples were collected for heavy mineral analysis (fraction 0,062-0,125 mm) using a conventional petrographic microscope and scanning electron microscope. The sandstones have been classified as moderately to well sorted, dolomite-cemented quartz-arenites whose heavy-mineral suite consists of zircon (4-70%), garnet (12-74%), tourmaline (3-20%), staurolite (1-9%), rutile (1-8%) and baryte (0-55%), while kyanite, anatase (authigenic), calcic-amphibole, andalusite, sillimanite, spinel and ilmenite occur more rarely. The majority of the grains is angular irregular, but well rounded grains, particularly tourmaline and zircon, are also present. Surface textures include conchoidal fractures, percussion marks in V and diminute pits, the latter in rounded tourmaline and zircon grains, while corrosion features are mainly present in baryte (rhombic cavities), kyanite, staurolite (surface mammillae) and garnet (well-formed etch-facets). Zircon grains, with oscillatory zoning textures, U/Th ratio ≥ 0,5 and mean Zr/Hf ratio of 29, are mainly derived from granites and probably migmatites. Plots on Zr/Hf-Y and Hf-Y-Nb diagrams show that this mineral can be related to at least two different sources. The tourmaline types, determined as dravite and schorl, indicate provenance mainly from aluminous and/or Al-poor metapelites and metapsammites with smaller contribution from granitic and meta-ultramafic rocks. Garnet is rich in almandine and has relatively low spessartine, grossular and pyrope contents whose potential source rocks are low- to medium-grade metamorphic rocks and granites. Based on their heavy-mineral suite and the progradation of the delta system to ENE/E and ESE, the most likely source areas of the studied Albian sandstones are the São Luís Craton, the Neoproterozoic Araguaia and Gurupi belts as well as the Paleozoic Parnaíba Basin, the latter supplying sediments of rounded grains.