Depositos estuarinos en la Formacion Rio Baguales (Chattiano-Aquitaniano), Provincia de Magallanes, Chile.

Abstract

ABSTRACT. Very little work has been done on the stratigraphy and sedimentology of the upper Oligocene-Lower Miocene Río Baguales Formation in the Magallanes Province of southern Chile since its original definition in 1957. A detailed stratigraphic section of the upper part of the formation exposed west of the Baguales River is presented, with an interpretation of depositional environments. This indicates a prograding shoreline in which estuary mouth, middle estuary (lagoon) and bay head delta facies are represented. Large-scale delta slope foresets indicate progradation towards the north and northwest, whereas southeast-directed cross-beds on the delta front probably suggest wave action. The general sequence reflects a gradual sea-level fall largely counteracted by tectonic subsidence, which provided the necessary accommodation space for thick tidal flat and subtidal deposits to accumulate. A longer period of transgression towards the top of the succession may be related to a rise in sea-level or accelerated tectonic subsidence, whereas a major regression commencing at around 23.3 Ma probably coincides with the opening of the Drake Passage and the growth of the East Antarctic Ice Sheet. RESUMEN. Depósitos estuarinos en la Formación Río Baguales (Chattiano-Aquitaniano), Provincia de Magallanes, Chile. Hay muy pocos trabajos sobre la estratigrafía y sedimentología de la Formación Río Baguales del Oligoceno superior-Mioceno inferior en la Provincia de Magallanes del sur de Chile, luego de su primera definición en 1957. Se presenta un perfil estratigráfico detallado de la parte superior de la formación al oeste del río Baguales, con una interpretación de los ambientes de depositación. Se identificó una costa progradante con facies de boca de estuario, medio de estuario (laguna) y delta de cabecera. Las grandes capas frontales del talud deltaico indican progradación hacia el norte y noroeste, mientras que la presencia de laminación cruzada inclinada hacia el sureste sugiere la acción de oleaje. La sucesión en general refleja una caída gradual del nivel del mar, acompañada por subsidencia tectónica con la creación del espacio de acomodación necesario para la acumulación de potentes facies mareales y submareales. Un período de transgresión hacia la parte superior de la sucesión indica una subida del nivel del mar o una aceleración en la tasa de subsidencia tectónica, seguida por una regresión mayor que comenzó alrededor de 23,3 Ma, probablemente coincidente con la apertura del Pasaje de Drake y el crecimiento de la calota de hielo de la Antártica del este. Oligoceno-Mioceneo, Polykladichnus. Palabras clave: Estuario, Delta tipo Gilbert, Cambios de nivel del mar del

Factors controlling alpine glaciations in the Sierra Baguales Mountain Range of southern Patagonia (50º S), inferred from the morphometric analysis of glacial cirques

“…In some parts of the SBMR the glacial cirques are developed over sedimentary rocks of the Eocene Man Aike Formation, a sequence of shales, sandstones and conglomerates with numerous mollusk fossils that overlies the Cretaceous Dorotea Formation and is, in turn, overlain by continental shales and sandstones rich in plant fossils belonging to the Río Leona Formation. The latter is followed by sandstones, conglomerates and mudstones of the Estancia 25 de Mayo and Santa Cruz Formations (Le Roux et al, 2010;Bostelmann et al, 2013). Gutiérrez et al (2013) mentioned that the Estancia 25 de Mayo Formation is intruded by laccolith-type plutons and olivine-gabbro sills.…”

Nuevos condrictios de niveles Bartoniano-priabonianos de Río de Las Minas y Sierra Dorotea, Cuenca de Magallanes, Patagonia Chilena.

“…Chondrichthyan records found in the locality were all recovered from a single level and they represent an assemblage of a well constrained age (Priabonian-Rupelian), while radioisotopic dates indicates a very well defined peak at 36.48±0.47 Ma, constraining the age of the fossil-bearing level exclusively to the Priabonian (Otero et al, 2012). Lower levels of the same section include coal seams representing stagnant marshes with abundant vegetation, and the large-scale cross-bedding of some sandstone units that is typical of Gilbert-type bayhead deltas or migrating barrier bars (Le Roux et al, 2010), consistent with an estuarine depositional environment. On the other hand, regional previous records of Megascyliorhinus are only known in the northern part of the Magallanes Basin, being recovered from Bartonian-Priabonian beds of Sierra Baguales (Otero et al, 2013a).…”