Caracterización sedimentológica de la Formación Guayaquil (Cretácico medio-Paleoceno inferior) en el Cerro Bellavista, Guayaquil-Ecuador
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2019
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Facultad de Ciencias Naturales. Universidad de Guayaquil
Resumen
El estudio se basó en determinar las características sedimentarias que se presentaron en la Formación Guayaquil y consistió principalmente en definir las litologías presentes en este afloramiento, así como también, clasificación y procedencia tectónica de las areniscas, condiciones ambientales de depósito y la edad relativa de la Formación. Se realizó una columna estratigráfica con un espesor de 172 m, en ella se exponen las variaciones en la composición de las rocas a lo largo del afloramiento, adicionalmente se realizó un muestreo para la elaboración de siete secciones delgadas y diez para análisis bioestratigráfico. La litología presente en la Formación Guayaquil está compuesta principalmente de Lutitas silicificadas con intercalaciones de Limolitas tobáceas, también aparecen estratos de areniscas turbidíticas a lo largo de las secciones de afloramiento. Las areniscas presentes se clasifican como: Arcosa Litica, Grauwacas Feldespáticas y Lítica Feldespática, obteniendo procedencias variadas como: de arco disectado, arco transicional, basamento elevado con tendencia a arco disectado y orógeno reciclado. La edad es de Maastrichtiano para el miembro inferior de la Fm. Guayaquil, confirmado por la ocurrencia del radiolario marcados zonal Amphipyndax tylotus, la Dictyomitra crassispina, se comprueba con la aparición de los nanofósiles calcáreos Watznaveria barnesae y Coccolithus paenepelugius cuyas edades llegan hasta el maastrichtiano: el ambiente es de Batial superior por la presencia y abundancia de radiolarios nassellarios (Dictyomitra crassispina, Dictyomitra andersoni, Amphipyndax tylotus), presencia de aglutinados como las Rzeakinas y Haplophagmoides; y aparición de escasas especies bentónicas.
The study was basesd on determining the sedimentary that were presented in the Guayaquil Formation and consisted mainly in defining the lithology present in this outcrop, as well as, classification and tectonic origin of the sandstones depositional environments and the relative age of the Formation. A stratigraphic column made with a thickness of 172 m was erected, it shows the variations in the composition of the rocks along the outcrop. In addition a sampling was made for the elaboration of seven thin sections and ten for biostratigraphic analysis. The lithology present in the Guayaquil Formation is composed mainly of silicified shales interbedded with tuffaceous siltstones, turbidite sandstone strata also appear the outcrop sections. The sandstones present are classified: as: Lithic Arenite, Feldspathic graywacke and Lithic Feldspathic, obtaining varied origins as: dissected arch, transitional arch, elevated basement with tendency to dissected arch and recycled erogeny. The age is Maastrichtian for the Lower Guayaquil Formation, confirmed by the occurrence of the zonal marker radiolarian Amphipyndax tylotus, and Dictyomitra crassispina, it is proven with the appearance of calcareous nanofossils Watznaveria barnesae and Coccolithus paenepelugius whose ages reach the Maastrichtian, the environment is upper Bathyal by the presence and abundance of nassellaria radiolarian (Dictyomitra crassispina, Dictyomitra andersoni, Amphipyndax tylotus), presence of agglutinates such as Rzeakinas and Haplophagmoides; and appearance of few benthic species.
The study was basesd on determining the sedimentary that were presented in the Guayaquil Formation and consisted mainly in defining the lithology present in this outcrop, as well as, classification and tectonic origin of the sandstones depositional environments and the relative age of the Formation. A stratigraphic column made with a thickness of 172 m was erected, it shows the variations in the composition of the rocks along the outcrop. In addition a sampling was made for the elaboration of seven thin sections and ten for biostratigraphic analysis. The lithology present in the Guayaquil Formation is composed mainly of silicified shales interbedded with tuffaceous siltstones, turbidite sandstone strata also appear the outcrop sections. The sandstones present are classified: as: Lithic Arenite, Feldspathic graywacke and Lithic Feldspathic, obtaining varied origins as: dissected arch, transitional arch, elevated basement with tendency to dissected arch and recycled erogeny. The age is Maastrichtian for the Lower Guayaquil Formation, confirmed by the occurrence of the zonal marker radiolarian Amphipyndax tylotus, and Dictyomitra crassispina, it is proven with the appearance of calcareous nanofossils Watznaveria barnesae and Coccolithus paenepelugius whose ages reach the Maastrichtian, the environment is upper Bathyal by the presence and abundance of nassellaria radiolarian (Dictyomitra crassispina, Dictyomitra andersoni, Amphipyndax tylotus), presence of agglutinates such as Rzeakinas and Haplophagmoides; and appearance of few benthic species.