Reconstructing the alluvial burying process of a tree in life position, Paleogene of south Patagonia, Argentina

RODRÍGUEZ BRIZUELA, RAFAEL; PUJANA, ROBERTO ROMÁN

Bariloche

Congreso; IV Congreso Latinoamericano de Sedimentología y XI Reunión Argentina de Sedimentología; 2006

The Rio Guillermo Formation crops out at southwest of Santa Cruz province, Argentina, representing part of the Paleogene fill of the Austral basin. The age of this unit is not precisely defined. It was assigend to Upper Eocene and to Upper Middle Oligocene. In the studied section (Cancha Carrera locality) the sedimentation is dominated by gravel bed braided and anastomosed fluvial systems. The fluvial channels contain mainly transported (paraautochtonous) fossil trunks and in some rare cases autochtonous trees. This contribtuion is based in one of these cases. Two gravel lithofacies are used to describe the fill within the channel, which has 20 m wide. Facies A: planar cross beded thin gravel (1.15 m of thickness). Characterised by poorly sorted pebble gravel and sandstones with planar cross bed sets less than 15 cm. Aroun the tree this facies present downlaping arrangement, interpreted as scour pool fill produced by flow erosion around the trunk. Facies B: class-supported horizontally stratified thick gravel (2 m of thickness)