Petrografía y ambiente sedimentario deposicional de la caliza San Antonio de la formación San Eduardo (eoceno), al suroeste de la comuna San Antonio de Playas, provincia del Guayas
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2020-10
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Facultad de Ciencias Naturales. Universidad de Guayaquil
Resumen
La caliza San Antonio, en la que no se han emprendido muchos estudios y de la cual se tiene muy poca información científica ha sido incluida dentro de la Formación San Eduardo (Eoceno Temprano - Eoceno Medio). Esta caliza aflora en la comuna San Antonio de Playas, cantón General Villamil Playas, provincia del Guayas. El objetivo del presente trabajo es definir la petrografía, bioestratigrafía y paleoambiente deposicional. Se estudiaron cuatro afloramientos y quince secciones delgadas. Se utilizó la metodología propuesta por Dunham (1972) y Folk (1962) para la clasificación de las rocas carbonáticas; los tipos de microfacies de Wilson (1975) y Flugel (2004) para identificar el ambiente deposicional; y mediante análisis químico se determinó el porcentaje de carbono en cuatro muestras de rocas. Las rocas calizas tienen entre 4,28% y 10,91% de carbono total. Se identificaron secuencias de somerización de medio orden en una plataforma carbonatada; litofacies packstone bioclástico, wackestone bioclástico, mudstone bioclástico, arcillolita y calcretas; parasecuencias gruesas dominantes y de engrosamiento proporcional hacia arriba; falla, fracturas, vetillas y cavernas. El análisis petrográfico al microscopio de la caliza San Antonio indicó que las rocas son packstone (bioesparita), wackestone (bioesparita y biomicrita) y mudstone (esparita). Los componentes ortoquímicos son 33% micrita y 67% esparita; y los componentes aloquímicos corresponden a 38,5% algas, 46,27% foraminíferos, 7,19% moluscos, 5,21% equinodermos, 2,59% briozoos y 0,7% serpulidos. La edad relativa es Eoceno Medio, pisos Luteciense al Bartoniense debido al hallazgo de macroforaminíferos, algas calcáreas, radiolarios, foraminíferos planctónicos y bentónicos. El paleoambiente sedimentario deposicional es Plataforma de Laguna Abierta a Plataforma Restringida de Rampa Interna.
The San Antonio limestone, in which not many studies have been undertaken and for which very little scientific information is available, has been included within the San Eduardo Formation (Early Eocene - Middle Eocene). This limestone outcrops in the San Antonio de Playas commune, General Villamil Playas canton, Guayas province. The objective of this work is to define the petrography, biostratigraphy and depositional paleoenvironment. Four outcrops and fifteen thin sections were studied. The methodology proposed by Dunham (1972) and Folk (1962) was used for the classification of carbonate rocks; the types of microfacies of Wilson (1975) and Flugel (2004) to identify the depositional environment; and by means of chemical analysis, the percentage of carbon in four rock samples was determined. Limestone rocks have between 4.28% and 10.91% of total carbon. Medium order somerization sequences were identified on a carbonate platform; bioclastic packstone lithofacies, bioclastic wackestone, bioclastic mudstone, claystone and calcretes; thick dominant and upwardly thickening parasequences; fault, fractures, veinlets and caverns. Petrographic microscopic analysis of the San Antonio limestone indicated that the rocks are packstone (biosparite), wackestone (biosparite and biomicrite) and mudstone (esparite). The orthochemical components are 33% micrite and 67% sparite; and the allochemical components correspond to 38.5% algae, 46.27% foraminifera, 7.19% mollusks, 5.21% echinoderms, 2.59% bryozoans and 0.7% serpulids. The relative age is Middle Eocene, Lutetian to Bartonian floors due to the discovery of macro-foraminifera, calcareous algae, radiolarians, planktonic and benthic foraminifera. The depositional sedimentary paleoenvironment is Open Lagoon Platform to Internal Ramp Restricted Platform.
The San Antonio limestone, in which not many studies have been undertaken and for which very little scientific information is available, has been included within the San Eduardo Formation (Early Eocene - Middle Eocene). This limestone outcrops in the San Antonio de Playas commune, General Villamil Playas canton, Guayas province. The objective of this work is to define the petrography, biostratigraphy and depositional paleoenvironment. Four outcrops and fifteen thin sections were studied. The methodology proposed by Dunham (1972) and Folk (1962) was used for the classification of carbonate rocks; the types of microfacies of Wilson (1975) and Flugel (2004) to identify the depositional environment; and by means of chemical analysis, the percentage of carbon in four rock samples was determined. Limestone rocks have between 4.28% and 10.91% of total carbon. Medium order somerization sequences were identified on a carbonate platform; bioclastic packstone lithofacies, bioclastic wackestone, bioclastic mudstone, claystone and calcretes; thick dominant and upwardly thickening parasequences; fault, fractures, veinlets and caverns. Petrographic microscopic analysis of the San Antonio limestone indicated that the rocks are packstone (biosparite), wackestone (biosparite and biomicrite) and mudstone (esparite). The orthochemical components are 33% micrite and 67% sparite; and the allochemical components correspond to 38.5% algae, 46.27% foraminifera, 7.19% mollusks, 5.21% echinoderms, 2.59% bryozoans and 0.7% serpulids. The relative age is Middle Eocene, Lutetian to Bartonian floors due to the discovery of macro-foraminifera, calcareous algae, radiolarians, planktonic and benthic foraminifera. The depositional sedimentary paleoenvironment is Open Lagoon Platform to Internal Ramp Restricted Platform.
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PLATAFORMA CARBONÁTICA, LITOFACIES, SECUENCIAS DE SOMERIZACIÓN, PARASECUENCIAS, CALIZAS, PALEOAMBIENTE DEPOSICIONAL