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Stratigraphic Architectures of Punctuated Deepwater Channel Migration, Upper Cretaceous Tres Pasos Formation, Magallanes Basin, Chile

Auchter, Neal C.; Romans, Brian W.; Hubbard, Stephen M.; Stright, Lisa

An improved understanding of the evolution of deep-water channel complexes and resultant stratigraphic architecture has important implications for evaluating reservoir distribution, continuity, and connectivity. Sinuous channels are significant components of deep-water depositional systems, and their stratigraphic architecture has often been compared to that of fluvial systems, with reservoir targets focused on apparent lateral accretion packages. While these deposits have been interpreted as point bars, recent studies of modern deep-water systems reveal more complex stratigraphic architectures than are typically identified with industry-standard seismic-reflection data. Interpretation of channel bend morphologies as stepped terraces casts doubt on the widespread applicability of fluvial point bars as architectural analogs for deep-water systems. Here we use outcrop exposures of a deep-water multilateral channel complex to evaluate the competing hypotheses that 1) sinuous deep-water channels comprise lateral accretion packages analogous to fluvial channels indicative of gradual lateral migration, or 2) channel bends comprise stepped terraces indicative of punctuated lateral migration.

Our study focuses on exceptional exposures of the Cretaceous Tres Pasos Formation, one of several turbiditic formations that filled the Magallanes foreland basin in southern Chile. Depositional shelf-to-basin relief of the Tres Pasos slope system is estimated to be at least several hundred meters. As such, these outcrops offer a unique opportunity to evaluate detailed facies architectures of a high-relief basin margin system. Data include high-resolution photomosaics and measured stratigraphic sections; 3-D mapping of stratigraphic surfaces provides subtle observations of intra-channel surface orientations and continuity. Channel deposits of the Tres Pasos Formation at the Cerro Mirador outcrop are expressed as generally upward-fining and upward-bed-thinning medium grained sandstone to overlying siltstone. Packages are truncated by erosional surfaces (>5 m relief) that systematically stack in one lateral direction. This architecture is interpreted to record discontinuous, punctuated lateral migration. These findings imply local-scale internal reservoir heterogeneity and motivate continued study of deep-water channel deposits utilizing surveys of seafloor and shallow-subsurface systems as well as detailed outcrop studies of analogous ancient systems.


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