Ritmitos de itu: Petrografia e considerações paleodeposicionais
Autor(a) principal: | |
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Data de Publicação: | 2006 |
Outros Autores: | |
Tipo de documento: | Artigo |
Idioma: | por |
Título da fonte: | Repositório Institucional da UNESP |
Texto Completo: | http://www.periodicos.rc.biblioteca.unesp.br/index.php/geociencias/article/view/456 http://hdl.handle.net/11449/69324 |
Resumo: | Rhythmite samples from Varvite Quarry and Park of Itu (SP), and well cores from Rafard (SP), were analyzed by optical microscopy to describe the petrographic characteristics of their light-colored (siltstone) and dark-colored (shale) laminae. The light-colored ones are essentially siltstones, commonly with traces of sands; the mineralogical composition is mainly quartz, with traces of feldspar and scarce mica; quartz or calcite cementation occurs in variable intensity, the first one being more intense in the Itu rhythmites; parallel laminations, internally normal graded or massive are the most common sedimentary structures in these rocks; bioturbations and dropstones are commonly observed in Itu rhythmites; contacts between siltstone laminae, and siltstone beds and shale laminae are commonly non-erosive and sharp. Considering this study and the macroscopic description of these rhythmites it was possible to clarify many questions about their composition, as the grain-size of the light-colored beds composed by silt with subordinate dropped sand, and the inappropriate use of the term varvite to the most of the Itu rhythmites. It was also important to reinforce their proglacial lacustrine origin, with random freezing of lacustrine surface water, and only sporadic ice-contact. |
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Ritmitos de itu: Petrografia e considerações paleodeposicionaisItu rhythmites: Petrography and paleo-depositional considerationsProglacial lacustrine sedimentationSubgroup Itararé rhythmitesVarvitesdepositionlacustrine depositpetrographyrhythmitesedimentary structuresedimentationsiltstoneRhythmite samples from Varvite Quarry and Park of Itu (SP), and well cores from Rafard (SP), were analyzed by optical microscopy to describe the petrographic characteristics of their light-colored (siltstone) and dark-colored (shale) laminae. The light-colored ones are essentially siltstones, commonly with traces of sands; the mineralogical composition is mainly quartz, with traces of feldspar and scarce mica; quartz or calcite cementation occurs in variable intensity, the first one being more intense in the Itu rhythmites; parallel laminations, internally normal graded or massive are the most common sedimentary structures in these rocks; bioturbations and dropstones are commonly observed in Itu rhythmites; contacts between siltstone laminae, and siltstone beds and shale laminae are commonly non-erosive and sharp. Considering this study and the macroscopic description of these rhythmites it was possible to clarify many questions about their composition, as the grain-size of the light-colored beds composed by silt with subordinate dropped sand, and the inappropriate use of the term varvite to the most of the Itu rhythmites. It was also important to reinforce their proglacial lacustrine origin, with random freezing of lacustrine surface water, and only sporadic ice-contact.Amostras de ritmito da Pedreira e do Parque de Varvito de Itu (SP) e de poço de Rafard (SP) foram analisadas ao microscópio óptico para descrição das características petrográficas de suas lâminas claras (siltito) e escuras (folhelho). As camadas ou lâminas claras são essencialmente sílticas, ocorrendo em geral apenas traços de areia; a composição é essencialmente quartzosa, com traços de feldspato e escassas micas; cimentação por sílica ou calcita ocorre em proporções variáveis, sendo a primeira mais intensa nos ritmitos de Itu; laminações plano-paralelas constituem as estruturas mais comuns; bioturbações e grãos caídos são freqüentes; contatos entre lâminas de siltito e entre lâminas de siltito e folhelho são em geral não-erosivos e abruptos. A partir deste estudo e das descrições desses ritmitos, foi possível clarificar várias questões relativas à composição destas rochas, como a composição dos estratos claros que são constituídos por siltito, com a fração areia ocorrendo apenas subordinadamente, na forma de grãos caídos, e a inadequação do uso da designação varvito para grande parte dos ritmitos de Itu, bem como reforçar sua origem proglacial lacustre, com congelamento esporádico da superfície do lago e apenas eventual contato direto com geleiras.Departamento de Geologia Aplicada Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista, Avenida 24-A, 1515. Bela Vista, CEP 13506-900. Rio Claro, SPHidroplan S/C Ltda., Avenida São Camilo, 476, CEP 06709-150. Cotia, SPDepartamento de Geologia Aplicada Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista, Avenida 24-A, 1515. Bela Vista, CEP 13506-900. Rio Claro, SPUniversidade Estadual Paulista (Unesp)Hidroplan S/C Ltda.Caetano-Chang, Maria Rita [UNESP]Ferreira, Silvia Maria2014-05-27T11:22:05Z2014-05-27T11:22:05Z2006-12-01info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/article345-358application/pdfhttp://www.periodicos.rc.biblioteca.unesp.br/index.php/geociencias/article/view/456Geociencias, v. 25, n. 3, p. 345-358, 2006.0101-9082http://hdl.handle.net/11449/693242-s2.0-342506720612-s2.0-34250672061.pdfScopusreponame:Repositório Institucional da UNESPinstname:Universidade Estadual Paulista (UNESP)instacron:UNESPporGeociências0,230info:eu-repo/semantics/openAccess2023-12-13T06:18:50Zoai:repositorio.unesp.br:11449/69324Repositório InstitucionalPUBhttp://repositorio.unesp.br/oai/requestopendoar:29462024-08-05T20:13:25.372336Repositório Institucional da UNESP - Universidade Estadual Paulista (UNESP)false |
dc.title.none.fl_str_mv |
Ritmitos de itu: Petrografia e considerações paleodeposicionais Itu rhythmites: Petrography and paleo-depositional considerations |
title |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
spellingShingle |
Ritmitos de itu: Petrografia e considerações paleodeposicionais Caetano-Chang, Maria Rita [UNESP] Proglacial lacustrine sedimentation Subgroup Itararé rhythmites Varvites deposition lacustrine deposit petrography rhythmite sedimentary structure sedimentation siltstone |
title_short |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
title_full |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
title_fullStr |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
title_full_unstemmed |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
title_sort |
Ritmitos de itu: Petrografia e considerações paleodeposicionais |
author |
Caetano-Chang, Maria Rita [UNESP] |
author_facet |
Caetano-Chang, Maria Rita [UNESP] Ferreira, Silvia Maria |
author_role |
author |
author2 |
Ferreira, Silvia Maria |
author2_role |
author |
dc.contributor.none.fl_str_mv |
Universidade Estadual Paulista (Unesp) Hidroplan S/C Ltda. |
dc.contributor.author.fl_str_mv |
Caetano-Chang, Maria Rita [UNESP] Ferreira, Silvia Maria |
dc.subject.por.fl_str_mv |
Proglacial lacustrine sedimentation Subgroup Itararé rhythmites Varvites deposition lacustrine deposit petrography rhythmite sedimentary structure sedimentation siltstone |
topic |
Proglacial lacustrine sedimentation Subgroup Itararé rhythmites Varvites deposition lacustrine deposit petrography rhythmite sedimentary structure sedimentation siltstone |
description |
Rhythmite samples from Varvite Quarry and Park of Itu (SP), and well cores from Rafard (SP), were analyzed by optical microscopy to describe the petrographic characteristics of their light-colored (siltstone) and dark-colored (shale) laminae. The light-colored ones are essentially siltstones, commonly with traces of sands; the mineralogical composition is mainly quartz, with traces of feldspar and scarce mica; quartz or calcite cementation occurs in variable intensity, the first one being more intense in the Itu rhythmites; parallel laminations, internally normal graded or massive are the most common sedimentary structures in these rocks; bioturbations and dropstones are commonly observed in Itu rhythmites; contacts between siltstone laminae, and siltstone beds and shale laminae are commonly non-erosive and sharp. Considering this study and the macroscopic description of these rhythmites it was possible to clarify many questions about their composition, as the grain-size of the light-colored beds composed by silt with subordinate dropped sand, and the inappropriate use of the term varvite to the most of the Itu rhythmites. It was also important to reinforce their proglacial lacustrine origin, with random freezing of lacustrine surface water, and only sporadic ice-contact. |
publishDate |
2006 |
dc.date.none.fl_str_mv |
2006-12-01 2014-05-27T11:22:05Z 2014-05-27T11:22:05Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/article |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://www.periodicos.rc.biblioteca.unesp.br/index.php/geociencias/article/view/456 Geociencias, v. 25, n. 3, p. 345-358, 2006. 0101-9082 http://hdl.handle.net/11449/69324 2-s2.0-34250672061 2-s2.0-34250672061.pdf |
url |
http://www.periodicos.rc.biblioteca.unesp.br/index.php/geociencias/article/view/456 http://hdl.handle.net/11449/69324 |
identifier_str_mv |
Geociencias, v. 25, n. 3, p. 345-358, 2006. 0101-9082 2-s2.0-34250672061 2-s2.0-34250672061.pdf |
dc.language.iso.fl_str_mv |
por |
language |
por |
dc.relation.none.fl_str_mv |
Geociências 0,230 |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
345-358 application/pdf |
dc.source.none.fl_str_mv |
Scopus reponame:Repositório Institucional da UNESP instname:Universidade Estadual Paulista (UNESP) instacron:UNESP |
instname_str |
Universidade Estadual Paulista (UNESP) |
instacron_str |
UNESP |
institution |
UNESP |
reponame_str |
Repositório Institucional da UNESP |
collection |
Repositório Institucional da UNESP |
repository.name.fl_str_mv |
Repositório Institucional da UNESP - Universidade Estadual Paulista (UNESP) |
repository.mail.fl_str_mv |
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1808129174994419712 |