Depósitos marinhos juro-cretácicos em afloramentos de cuba: nanofósseis calcários e microfácies carbonáticas
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Data
2005-10-27
Autores
Castro, Ana Marina Escobar [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Rochas do Jurássico Superior e Cretáceo, dominantemente carbonáticas e comumente intercaladas a folhelhos e margas, afloram em Cuba central e ocidental. O estudo de 31 afloramentos é o objeto desta tese, que investiga, centralmente, o seu conteúdo nanofossilífero e as características das suas microfácies carbonáticas. Informações quimioestratigráficas de carbono e oxigênio também foram obtidas. O Neojurássico apresenta pobre conteúdo de nanofósseis, freqüentemente mal preservados, seja pela forte recristalização dos calcários seja pela oxidação dos folhelhos, o que impediu seu biozoneamento. Todavia, combinando-se os dados de nanofósseis com os dados paleontológicos prévios (calpionelidos, calcisferas e crinóides da família Saccocomidae) reconhece-se a ocorrência de 4 afloramentos mesothitonianos e 4 neotithonianos. Tais seções neojurássicas teriam sido acumuladas em piso marinho profundo anóxico (rampa externa a batial), conforme sugerem as microfácies dominantemente pelágicas [mudstones, wackestones e margas com radiolários, espículas de esponjas, calcisferas e crinóides (e.g., Saccocoma), equivalentes às microfácies-padrão SMF 1 e SMF 3 de Wilson]. Episódios de aloctonia foram registrados ao longo do intervalo, como sugere a presença de calcários de águas rasas interrompendo a seção pelágica (packstones e grainstones com oóides, pelóides, miliolidos e moluscos). Dados isotópicos de carbono e oxigênio sugerem que águas frias e produtivas estiveram associadas à deposição pelágica. Nos 10 afloramentos pertencentes ao Eocretáceo a nanoflora também é pobre e mal preservada, ocorrendo algumas espécies de forma esporádica ao longo do intervalo. Contudo, foram detectados 9 bioeventos de surgimento ou extinção de espécies de nanofósseis...
Late Jurassic and Cretaceous carbonate rocks and associated marls and shales crop out in central and western Cuba. This thesis objectives, through the study of thirty-one outcrops, to investigate the nannofossil content and carbonate microfacies of these rocks. Also it aims to obtain chemostratigraphic data from carbon and oxygen isotopes. The Late Jurassic has a poor nannofossil content, badly preserved due to the strong limestone recrystallization or to shale oxidation, which obscures the biostratigraphic zoning. However, through the combination of nannofossil and previous paleontologic data (calpionelids, calcispheres and crinoids of the Saccocomidae family), it was possible to recognize the occurrence of four Mesothitonian and four Neotithonian outcrops. Such Late Jurassic sections were accumulated in a deep, anoxic marine environment (outer ramp to bathial), as suggested by the dominant pelagic microfacies [mudstones, wackestones and marls with radiolarians, sponge spicules, calcispheres and crinoids (for instance, Saccocoma), which are equivalent to the Wilsonþs standard microfacies SMF 1 and SMF 3]. Alloctonous episodes were recorded along the interval, as suggested by the presence of shallow water limestones which interrupts the pelagic domain (packstones and grainstones with ooids, peloids, miliolids and mollusks). Carbon and oxygen isotopic data suggest that cold and productive waters were closely associated with the pelagic deposition. In ten Early Cretaceous outcrops the nannoflora is poor and badly preserved, but with sporadic occurrence of some species in the interval. However, nine bioevents of nannofossil appearance or extinction were detected, and when integrated to certain nannofossiliferous associations allowed to recognize... (Complete abstract, click electronic address below)
Late Jurassic and Cretaceous carbonate rocks and associated marls and shales crop out in central and western Cuba. This thesis objectives, through the study of thirty-one outcrops, to investigate the nannofossil content and carbonate microfacies of these rocks. Also it aims to obtain chemostratigraphic data from carbon and oxygen isotopes. The Late Jurassic has a poor nannofossil content, badly preserved due to the strong limestone recrystallization or to shale oxidation, which obscures the biostratigraphic zoning. However, through the combination of nannofossil and previous paleontologic data (calpionelids, calcispheres and crinoids of the Saccocomidae family), it was possible to recognize the occurrence of four Mesothitonian and four Neotithonian outcrops. Such Late Jurassic sections were accumulated in a deep, anoxic marine environment (outer ramp to bathial), as suggested by the dominant pelagic microfacies [mudstones, wackestones and marls with radiolarians, sponge spicules, calcispheres and crinoids (for instance, Saccocoma), which are equivalent to the Wilsonþs standard microfacies SMF 1 and SMF 3]. Alloctonous episodes were recorded along the interval, as suggested by the presence of shallow water limestones which interrupts the pelagic domain (packstones and grainstones with ooids, peloids, miliolids and mollusks). Carbon and oxygen isotopic data suggest that cold and productive waters were closely associated with the pelagic deposition. In ten Early Cretaceous outcrops the nannoflora is poor and badly preserved, but with sporadic occurrence of some species in the interval. However, nine bioevents of nannofossil appearance or extinction were detected, and when integrated to certain nannofossiliferous associations allowed to recognize... (Complete abstract, click electronic address below)
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Geologia estratigráfica, Geology
Como citar
CASTRO, Ana Marina Escobar. Depósitos marinhos juro-cretácicos em afloramentos de cuba: nanofósseis calcários e microfácies carbonáticas. 2005. xiv, 159 f. Tese (doutorado) - Universidade Estadual Paulista, Instituto de Geociências e Ciências Exatas, 2005.