科研之友
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摘要
very little work has been done on the stratigraphy and sedimentology of the upper oligocene-lower miocene r赤o 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.
