Outcrop 8. Channel Margins in the Cerro Toro Formation, Cordillera Manuel Señoret

Abstract Outcrop accessibility: variable Outcrop Coordinates: 51.4716°S, 72.6508°W Refer to outcrop 8 on location map Conglomeratic deposits of the Cerro Toro Formation attributed to deposition in a large-scale basin axial channel belt are well exposed in the Cordillera Manuel Señoret, north of Puerto Natales between Cueva del Milodon and Lago Toro. The conglomeratic succession is informally called the “Lago Sofia Member” because of the presence of Laguna Sofia in this area (Scott, 1966). The large injectite complex that is the focus of Chapter 9 is present in the Cordillera Manuel Señoret on the south shore of Lago Sofia (Fig. 8.1A). The channel belt is characterized by low sinuousity, demonstrated with outcrop mapping and the collection of extensive paleocurrent data (Fig. 8.1A). Outcrop exposures of the channel belt margin are present on the north faces of Cerro Benitez and Cerro Mocho (Fig. 8.1B, C). Because of poor accessibility, the margin at Cerro Mocho cannot be easily visited. A levee interpretation for fine-grained material adjacent to the channel belt is based on a series of key observations: (i) paleocurrent measurements indicative of flow divergence (50° to 100°) measured from out-of-channel units as compared to those taken from inside the channel belt container; (ii) progressive thinning of sandstone beds away from the channel belt margin; (iii) evidence that the eroded channel margin was poorly indurated, including a stepped profile and injection of channel fill into out-of-channel strata; (iv) deposits that record slumping on the