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The Stratigraphic Architecture Preserved at the Channel-Lobe Transition Zone: Tres Pasos Formation Outcrop Belt, Southern Chile

Pemberton, Erin; Hubbard, Stephen M.; Fletcher, Sean; Romans, Brian W.

Deep-water turbidite systems and the evolution of various stratigraphic architectures within slope settings is an active area of research, with much focus put on two end members, slope channels and submarine fan lobes. However, the intermediate architecture of deep-water depositional systems, the channel-lobe transition zone, remains elusive or poorly documented. While recognition of this zone has been historically difficult, new high-resolution seismic and modern seafloor datasets offer insight into the intricacies of these systems. The channel-lobe transition zone marks the shift from confined to unconfined flow, and the objective of this study is to document the stratigraphic architecture associated with this shift in flow conditions in the Tres Pasos Formation, which crops out in southernmost Chile (Cretaceous Magallanes Basin). The vertical and horizontal continuity of beds and sedimentary bodies are a focus of the outcrop investigation, with a goal to better constrain subsurface reservoirs in analogous deposits.

The framework for this study is a high-resolution analysis of a 1.4 km long and 100 m thick three-dimensionally exposed, oblique-strike oriented outcrop at Arroyo Picana, which is located stratigraphically beneath (and presumed down-dip of) large slope channel complexes. The stratigraphic architecture in the Arroyo Picana outcrop is highly variable with respect to sandstone sedimentary body geometry, ranging from channelized (low aspect ratio with incisional relief up to 25 m) to broad and more tabular, (high aspect ratio; ~5 m thick and extending over 650 m laterally). Stratigraphic sections were measured at roughly 20 m spacing and capture subtle lateral changes in stratigraphy and facies architecture. Major sandstone packages and mappable surfaces were walked out and surveyed using differential GPS in order to constrain their lateral extent and variation. The channel-lobe transition zone is characterized by the stratigraphic juxtaposition of high and low aspect ratio sedimentary bodies; sandstone bed extent is difficult to predict, however, abundant scours and channelization results in an interconnected stratigraphic architecture.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013