Ambiente sedimentario, bioestratigrafía y petrotectónica de la Formación Punta Ancón (Eoceno medio), Acantilado Ballenita - Punta Murciélago, Península de Santa Elena
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2019
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Facultad de Ciencias Naturales. Universidad de Guayaquil
Resumen
La formación Punta Ancón es la unidad superior del Grupo Ancón (Eoceno medio) que sobreyace a la formación Seca. Se definió el ambiente sedimentario deposicional, edad y marco tectónico de deposición de las areniscas de la formación Punta Ancón, sector Ballenita - Punta Murciélago. Se interpretaron ocho afloramientos, catorce muestras bioestratigráficas y quince láminas delgadas. La formación consiste de areniscas tobaceas con estratificación cruzada, laminadas o masivas; y areniscas fisuradas. Se identificaron ocho especies de radiolarios en el afloramiento PA5. Las especies Podocyrtis diamesa y Podocyrtis ampla indicaron una edad relativa de Eoceno Medio - medio. El ambiente de depositación fue interpretado como Marino somero: Litoral y Sublitoral. Las areniscas de la formación Punta Ancòn son sublitarenitas y litarenitas: 88.4% cuarzo, 11.2% fragmentos líticos y 0.4% feldespatos. El cuarzo aumenta en dirección Oeste de 83.8 a 93.0%; y los fragmentos líticos hacia el Este de 6.7% a 15.7%. Los componentes monocristalinos son: 86.7% cuarzo monocristalino, 12.9% fragmentos líticos y 0.5% feldespatos. El cuarzo aumenta en dirección Oeste de 81.3 a 92.1% y los fragmentos líticos totales hacia el Este de 7.5% a 18.2%. Los componentes policristalinos son: 55.6% cuarzo policristalino, 24.4% fragmentos líticos sedimentarios y 20% fragmentos líticos volcánicos. En dirección Oeste aumentan el cuarzo de 51.3 a 60% y líticos volcánicos de 18.5 a 21.4%; los líticos sedimentarios hacia el Este de 18.6 a 30.2%. La procedencia tectónica es orogenia reciclada (cuarzosa) e interior cratónico; complejo de subducción y tendencia entre orógeno de arco y orógeno de colisión, según diagramas triangulares de procedencia.
The Punta Ancón formation is the upper unit of the Ancón Group (Middle Eocene) that overlies the Seca formation. The depositional sedimentary environment, age and tectonic provenance of sandstones of the Punta Ancón formation, in the Ballenita - Punta Murciélago sector, was defined. Eight outcrops, fourteen bioestratigraphic samples and fifteen thin sections were interpreted. The formation consists of tuffaceous sandstones with cross stratification, laminated or massive and fissured sandstones. Eight radiolarians species were identified in the PA% outcrop. The species Podocyrtis diamesa and Podocyrtis amplaindicated a relative age of middle - Middle Eocene. the depositional environment was interpreted as shallow marine: Foreshore and Shoreface. The sandstonesof the Punta Ancón formation are sublitharenite and litharenite: 88.4% Quartz, 11.2% lithic Fragment and 0.4%Feldspars. Quartz increasrs westward from 83.8% to 93%, and Lithic Fragments eastward from 6.7% to 15.7%. the monocrystalline components are: 86.7% monocrystalline Quartz, 12.9%Lithic Fragments and 0.5% Feldspars. Quartz increases in a western direction from 81.3 to 92.1% and the Total Lithic Fragments towards the east from 7.5 to 18.2%. The polycrystallibe components are: 55.6% polycrystalline Quartz, 24,4% Lithic Sedimentary Fragments and 20% Lithic Volcanic Lithics from 18.5 to 21.4%; and Sedimetary Lithics to east from 18.6 to 30.2%. The tectonic provenance is recycled orogen (quartzose) and cratonic interior, subduction complex and tendency between arc orogen and collision orogen, according to triangular diagrams of provenance.
The Punta Ancón formation is the upper unit of the Ancón Group (Middle Eocene) that overlies the Seca formation. The depositional sedimentary environment, age and tectonic provenance of sandstones of the Punta Ancón formation, in the Ballenita - Punta Murciélago sector, was defined. Eight outcrops, fourteen bioestratigraphic samples and fifteen thin sections were interpreted. The formation consists of tuffaceous sandstones with cross stratification, laminated or massive and fissured sandstones. Eight radiolarians species were identified in the PA% outcrop. The species Podocyrtis diamesa and Podocyrtis amplaindicated a relative age of middle - Middle Eocene. the depositional environment was interpreted as shallow marine: Foreshore and Shoreface. The sandstonesof the Punta Ancón formation are sublitharenite and litharenite: 88.4% Quartz, 11.2% lithic Fragment and 0.4%Feldspars. Quartz increasrs westward from 83.8% to 93%, and Lithic Fragments eastward from 6.7% to 15.7%. the monocrystalline components are: 86.7% monocrystalline Quartz, 12.9%Lithic Fragments and 0.5% Feldspars. Quartz increases in a western direction from 81.3 to 92.1% and the Total Lithic Fragments towards the east from 7.5 to 18.2%. The polycrystallibe components are: 55.6% polycrystalline Quartz, 24,4% Lithic Sedimentary Fragments and 20% Lithic Volcanic Lithics from 18.5 to 21.4%; and Sedimetary Lithics to east from 18.6 to 30.2%. The tectonic provenance is recycled orogen (quartzose) and cratonic interior, subduction complex and tendency between arc orogen and collision orogen, according to triangular diagrams of provenance.