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Andean geology

versión On-line ISSN 0718-7106

Resumen

LE ROUX, Jacobus P et al. Estuary deposits in the Río Baguales Formation (Chattian-Aquitanean), Magallanes Province, Chile. AndGeo [online]. 2010, vol.37, n.2, pp. 329-344. ISSN 0718-7106.

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 ne-cessary 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.

Palabras clave : Estuary; Gilbert-type delta; Oligocene-Miocene sea-level changes; Polykladichnus.

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