Estratigrafía Del Neógeno Superior Al Sur De La Cuenca Tumaco (Pacífico Colombiano): La Formación Cascajal, Propuesta De Redefinición Litoestratigráfica

Abstract

S.A. 2016. Estratigrafía del Neógeno Superior al sur de la cuenca Tumaco (Pacífico colombiano): la Formación Cascajal, propuesta de redefinición litoestratigráfica. Boletín de Geología, 38(4): 43-60. RESUMENEl conocimiento estratigráfico del relleno sedimentario del segmento onshore de la cuenca de ante-arco Tumaco es poco conocido y los trabajos existentes se fundamentan en el estudio de líneas sísmicas y pozos para la exploración de hidrocarburos, haciendo poco énfasis en las unidades más superficiales. Se presenta el estudio detallado de las rocas del Mioceno superior -Plioceno expuestas en el sector sur de la cuenca Tumaco. Los nuevos datos estratigráficos del pozo ANH-Tumaco 1-ST-S representan la sección más completa y mejor preservada de este intervalo de tiempo. Se integró esta información con nuevos datos de ~200 m de secciones estratigráficas levantadas en afloramientos de los acantilados de la bahía de Tumaco y del río Patía. A partir de la descripción detallada de estas localidades, y siguiendo los parámetros de los códigos estratigráficos, se propone emplear el término Formación Cascajal para referirse a las rocas volcanoclásticas de edad Messiniense parte superior a Zancliense. Esta sucesión con un espesor observado de hasta 405 m está conformada principalmente por gruesos estratos lenticulares y ondulados de arenitas y conglomerados, con alto contenido de detritos volcánicos, en menor proporción, interestratificaciones de lodolitas y arenitas lodosas, localmente con icnofósiles y fósiles de bivalvos, gasterópodos, foraminíferos, equinodermos, crustáceos y restos de plantas bien conservadas, depositados en un ambiente de sedimentación deltaico influenciado por vulcanismo.Palabras clave: Pacífico colombiano, ante -arco, cuenca Tumaco, código estratigráfico, vulcanismo. UPPER NEOGENE STRATIGRAPHY IN THE SOUTH OF TUMACO BASIN (COLOMBIAN PACIFIC): CASCAJAL FORMATION, LITHOSTRATIGRAPHIC REDEFINITION PROPOSAL ABSTRACTThe stratigraphic knowledge of the sedimentary fill of the Tumaco onshore fore-arc basin is relatively poor. Previous works are based on the study of seismic lines and wells for hydrocarbon exploration with minor emphasis on the surface segments. We present a detailed study of the late Miocene -Pliocene rocks that outcrop in the southern Tumaco basin. New stratigraphic data from the ANH-Tumaco 1-ST-S well represent the most complete and best preserved sections for this time interval. This information is integrated with new data from descriptions of ~200 m of stratigraphic sections visited in the coastal cliffs of the Tumaco bay and the Patia river. The detailed descriptions of these locations following parameters from stratigraphic codes allow us to propose the use of the term Cascajal Formation to refer to volcanoclastic rocks of Messinian -Zanclean age. This succession, with an estimated thickness of up to 405 m, is composed mainly of thick lenticular and undulated layers of sandstones and conglomerates, with an important volcanic input. Minor interbedded mudstones and muddy sandstones are...

Chapter 8

“…The stratigraphic information was obtained from electrical logs, ditch cutting, and core samples from the Remolino Grande-1 (total depth (TD) 9080'-2767 m), Majagua-1 (TD 14 280'-4352 m), and Tumaco 1-ST-S (TD 1899.6'-579 m) wells. This information was also integrated with data from outcrops located in the Tumaco Bay (e.g., Echeverri et al, 2016), with previous results reported by Suárez (1990) and López-Ramos (2009) and data from the ANH Tumaco 1-ST-P well (Agencia Nacional de Hidrocarburos & Antek, 2013). The well cores and cuttings are stored at the national core repository of Colombia (Litoteca Nacional, Piedecuesta, Santander).…”

“…Subsequently, Nivia et al (2003) separated the youngest alluvial and deltaic deposits from the Guapi Formation, defining as Cascajal and Curay Members those underlying Pliocene and Miocene sedimentary deposits in the Nariño Department. Echeverri et al (2016) proposed the term Cascajal Formation for the volcanoclastic rocks of the Messinian -Zanclean age reported by Nivia et al (2003) (Figure 2). In contrast, in the northern part of the Tumaco Basin, Aspden (1984) and Aspden & Nivia (1985) proposed to divide the Neogene sedimentary cover into two formations: (i) Mayorquín Formation, composed mainly of mudrocks, and (ii) Raposo Formation, with conglomerates and sandstones.…”

“…A total of 1544 analyses were performed, including biostratigraphy (palynology, foraminifera, and calcareous nannofossils), petrography, and geochronology (U/Pb, Ar/Ar, and K/ Ar methods). The integration of these results along with unpublished reports and published data (Bedoya et al, 2013;Borrero et al, 2012;Echeverri et al, 2015aEcheverri et al, , 2015bEcheverri et al, , 2016) allowed an age model to be established and the provenance and paleoenvironment for the sedimentary rocks of the basin to be illustrated.…”

“…Finally, Agencia Nacional de Hidrocarburos & Antek (2013) informally proposed the names Tumaco and Tangareal del Mira Formations for upper Oligocene and Neogene deltaic deposits associated with the paleo-Patía and Mira Rivers (Figure 2). In this chapter, we will use the nomenclature of Borrero et al (2012), Echeverri et al (2011), andEcheverri et al (2016).…”

“…During the latest Miocene -Pliocene (Messinian -Zanclean), in the southern part of Tumaco Basin, more than 1300' (400 m) of thick lenticular layers of sandstones and conglomerates, with an important volcanic input (Cascajal Formation of Echeverri et al, 2016), were accumulated and interlayered with some mudrocks and muddy sandstone beds. Locally, bivalves, gastropods, fora-minifera, echinoderms, crustaceans, and well-preserved plant remains were found.…”