Ambiente sedimentario y petrotectónica de las areniscas de la formación seca (eoceno medio), acantilado Anconcito, provincia de Santa Elena.
Fecha
2021-03
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Facultad de Ciencias Naturales. Universidad de Guayaquil
Resumen
La Formación Seca en el sector de los acantilados de Anconcito carece de estudios geológicos actualizados, en cuanto a su edad, ambiente deposicional y petrotectónica. Se identificaron siete afloramientos, con las siguientes litologías: arcillolita, lodolita, arenisca masiva, arenisca laminada, arenisca con figuras de ondulación granodecreciente y limolita. Se interpretaron secuencias de Bouma: truncada incompleta conformadas por arenisca laminada que se encuentra entre las capas de arcillolita y lodolita (Te; Tb – e); secuencia truncada interrumpida por no presentar unidades inferiores ni superiores (Tc-b) y secuencias completas (Ta - e). Para los análisis bioestratigráficos se seleccionaron dieciséis muestras de rocas; y para el análisis petrográfico se elaboraron diez secciones delgadas. La edad relativa de la Formación Seca es Eoceno Medio medio, por la presencia del radiolario del orden nassellarios Podocyrtis ampla; y el ambiente de depositación es marino de plataforma externa a talud superior, por los foraminíferos bentónico Bathysiphon eocénica, Nodosaria sp., Uvigerina hispida, Lenticulina sp. Las areniscas de los acantilados de Anconcito son Sublitarenitas, y tienen una procedencia tectónica de Orógeno reciclado por sus componentes esenciales: (82,96%) cuarzo, (15,9%) fragmentos líticos, y (1,14%) feldespatos; Orógeno reciclado tipo cuarzoso por sus componentes monocristalinos: (82,04%) cuarzo monocristalino, (16,72%) fragmentos líticos totales, y (1,24%) feldespatos; y Orógeno de colisión por sus componentes policristalinos: (31,23%) cuarzo policristalino, (63,77%) líticos sedimentarios, y (5%) líticos volcánicos.
The Seca Formation in the Anconcito cliffs sector lacks updated geological studies regarding its age, depositional environment and petrotectonics Seven outcrops were identified, consisting of the following lithologies: claystone, mudstone, massive sandstone, laminated sandstone, sandstone with fining-up, ripple figures and siltstone. Bouma sequences were interpreted: incomplete truncated sequences formed by laminated sandstone between claystone and mudstone layers (Te; Tb - e); truncated sequence interrupted with no lower or upper units (Tc-b) and complete sequences (Ta - e). Sixteen samples were selected for biostratigraphic analysis and ten thin sections were elaborated of rocks for petrographic analysis. The relative age of the Seca Formation is Middle Middle Eocene, due to the radiolarian order nassellarios Podocyrtis ampla; and the depositional environment is marine from external platform to upper slope because of the benthic foraminifera Bathysiphon eocénica, Nodosaria sp., Uvigerina hispida, Lenticulina sp. The sandstones of the cliffs of Anconcito are Sublitarenites, and have a depositional tectonic origin of Orogen recycled due to its essential components: (82.96%) quartz, (15.9%) lithic fragments, and (1.14%) feldspars; Recycled quartz-type Orogen due to its single-crystalline components: (82.04%) single-crystalline quartz, (16.72%) total lithic fragments, and (1.24%) feldspars; and Collision orogeny because of its polycrystalline components: (31.23%) polycrystalline quartz, (63.77%) sedimentary lithics, and (5%) volcanic lithics.
The Seca Formation in the Anconcito cliffs sector lacks updated geological studies regarding its age, depositional environment and petrotectonics Seven outcrops were identified, consisting of the following lithologies: claystone, mudstone, massive sandstone, laminated sandstone, sandstone with fining-up, ripple figures and siltstone. Bouma sequences were interpreted: incomplete truncated sequences formed by laminated sandstone between claystone and mudstone layers (Te; Tb - e); truncated sequence interrupted with no lower or upper units (Tc-b) and complete sequences (Ta - e). Sixteen samples were selected for biostratigraphic analysis and ten thin sections were elaborated of rocks for petrographic analysis. The relative age of the Seca Formation is Middle Middle Eocene, due to the radiolarian order nassellarios Podocyrtis ampla; and the depositional environment is marine from external platform to upper slope because of the benthic foraminifera Bathysiphon eocénica, Nodosaria sp., Uvigerina hispida, Lenticulina sp. The sandstones of the cliffs of Anconcito are Sublitarenites, and have a depositional tectonic origin of Orogen recycled due to its essential components: (82.96%) quartz, (15.9%) lithic fragments, and (1.14%) feldspars; Recycled quartz-type Orogen due to its single-crystalline components: (82.04%) single-crystalline quartz, (16.72%) total lithic fragments, and (1.24%) feldspars; and Collision orogeny because of its polycrystalline components: (31.23%) polycrystalline quartz, (63.77%) sedimentary lithics, and (5%) volcanic lithics.
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FORMACIÓN, SECUENCIAS, AMBIENTE DE DEPOSITACIÓN, COMPONENTES