PROJECT APPENDIX II

PROJECT APPENDIX II

TITLE: Investigating slope channel patterns and processes at Cerro Mirador: Punctuated or continuous lateral migration?

MOTIVATION AND OBJECTIVES:  The stratigraphic architecture of deep-water sinuous channel-fill deposits has been compared to that of fluvial systems, with reservoir targets focused on apparent lateral accretion packages. Here we use exceptional outcrop exposures of a deep-water multilateral channel complex to evaluate the competing hypotheses that 1) sinuous deep-water channel-fills comprise lateral accretion packages analogous to some fluvial channels indicative of gradual lateral migration, or 2) channel bends comprise stepped terraces indicative of punctuated lateral migration. Testing these hypotheses will contribute to current debate about the nature of fundamental processes that sculpt and fill submarine channels as well as providing high-resolution architectural data valuable for constructing reservoir models.

(A) Photo showing the stratigraphic succession of interest exposed at Cerro Mirador with the red box denoting the location of detailed photo shown in B, C, and D.(B) Un-interpreted photograph of the Cerro Mirador channel complex. (C) Photograph with preliminary characterization of bedding architecture. The red lines denote erosional surfaces interpreted as channel bases/margins; yellow lines denote intrachannel bedding surfaces. (D) Interpretation shown in C without photograph and showing an approximate scale.

GEOLOGIC CONTEXT: The stratigraphy exposed at Cerro Mirador (northern part of the Tres Pasos Formation outcrop belt; see Research Study Area map) provides the rare opportunity to investigate the architectural relationships of both fine- and coarse-grained facies in laterally offset channel-fill deposits. Preliminary analysis based on reconnaissance-level fieldwork and photography indicates the Cerro Mirador channel complex is expressed as generally upward-fining and upward-bed-thinning medium-grained sandstone to overlying siltstone. Internally, strata are truncated by erosional surfaces (>5 m relief) interpreted as channel bases/margins that systematically stack in a lateral direction (red lines in figure). Additionally, this channel complex is part of a thick succession (>500 m) of similarly well-exposed slope deposits stratigraphically above and below. Further work on this understudied part of the outcrop belt will improve km-scale correlations and sequence stratigraphic context for the Tres Pasos slope system evolution.

METHODS AND DATA: The architecture of the Cerro Mirador channel complex will be characterized with similar methods used to assess channelized strata at the Laguna Figueroa outcrops further south (e.g., Macauley and Hubbard, 2013; see also Appendices I and II). This characterization will include vertical sections that capture cm-scale sedimentology and measurement of paleocurrent indicators. Photomosaic interpretation combined with surveying of stratigraphic surfaces with differential GPS will provide accurate and high-resolution documentation of intrachannel facies heterogeneity. The resulting three-dimensional architectural model of the Cerro Mirador channel complex will also aid interpretation of the orientation of erosional surfaces, which will be used to address the primary question regarding the nature of channel migration.