Stratigraphic Architecture of Deep - Water Leveed Channel Complexes of the Cerro Toro Formation, Upper Cretaceous, Southern Chile

R. T. Beaubouef, R. M. Lindholm, P. P. McLaughlin, and M. B. DeVries

The Cerro Toro Formation within the Torres del Paine National Park, southern Chile represents a deep-water leveed-channel complex deposited within an elongate Andean foreland basin during the Late Cretaceous. This stratigraphic interval represents an essentially continuous depositional record of a migrating leveed-channel complex. Channel fill units in the study area are 1 to 3 miles wide and up to 1,000 ft thick. The channels are filled by bedded conglomerate, and amalgamated sandstones interpreted to represent high density turbidites, and debris flow deposits. Channel fill facies commonly lie on an erosional surface that cuts into adjacent levee facies. Beds thin and onlap this surface toward the channel margins. Shale or siltstone drapes of the channel cuts are uncommo and laterally discontinuous. Bed continuity between channel and levee facies was not observed. Stratigraphy within the levee units consists of packages of upward fining and thinning, low density turbidites. Distal levee facies include thin-bedded, laterally continuous sandstones. Proximal levee facies include both thin- and thick-bedded sandstones; however, the thick-bedded sandstones have poor lateral continuity. The proximal levee facies have a higher sandstone percentage than the distal levee but also have a greater depositional and post-depositional complexity, with sand-filled crevasses, erosional truncation and slumped beds. Field observations suggest that these leveed channels formed in three stages: 1) aggradation of a confining levee resulting from overbank deposition as turbid ty flows bypass the area; 2) erosion as the channel becomes entrenched or migrates; and 3) filling of the channel margin relief by onlap of channel-fill sediments.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California