TITLE: The variability of channel architecture and facies along a 25 km long paleoslope surface: Analysis of the upper through to lower reaches of the Figueroa Clinoform 

MOTIVATION AND OBJECTIVES: Numerous slope channel facies models have been developed, with variable records of deep erosion, shallow scouring, bypassing high-energy turbidity currents, mass wasting, and deposition of thin- and/or thick-bedded turbidites. How does position on paleoslope, or rather, distance from shelf-edge, control the facies distribution within slope channel deposits? Since the unique outcrop belt in the Magallanes Basin preserves near continuous ancient slope profiles from shelf edge to basin floor, it represents an ideal natural laboratory to test the hypothesis that along these surfaces a transitional record of near complete coarse sediment bypass at the upper slope to primarily deposition of sandy turbiditic units near the toe of slope. Regional-scale mapping has already confirmed this trend, but detailed outcrop investigations stand to develop more predictive insights. Questions we will attempt to answer include: Can unique facies models be deduced that provide the ability to pinpoint paleoslope position in more poorly constrained datasets? How are the main processes associated with sediment transfer (i.e., erosion, bypass and deposition) manifested along slope surfaces? Does key evidence for these processes change in character from the upper to lower slope? What is the relative importance of these processes, from proximal to distal locations? This project is linked to objectives 1 (Predictive Sedimentologic Models), 2 (3-D architectural models of reservoir-scale sedimentology) and 4 (Regional stratigraphy and paleogeography) of the overall JIP proposal.

GEOLOGIC CONTEXT: The stratigraphic architecture of the Tres Pasos–Dorotea transition in the vicinity of the town of Cerro Castillo is known to comprise a series of southward propagating, high-relief  (> 1 km) clinoforms (Fig. A) (Hubbard et al., 2010). Over the last few years, emphasis has been placed on development of lower slope channel models at Laguna Figueroa (Macauley and Hubbard, 2013). Following coeval strata up paleoslope, it is clear that channel stacking and internal architecture change significantly (Fig. B). 

METHODS AND DATA: Channel exposures along the Figueroa surface will be characterized using a similar approach to that we have used to assess channels at the lower portion of the surface (e.g., Macauley and Hubbard, 2012). This characterization will include traditional approaches such as cm-scale sedimentological section measuring and measurement of paleocurrent indicators. Photomosaic interpretation will foster description of channel stacking patterns and intrachannel heterogeneity. In selected areas of interest, construction of outcrop-constrained three-dimensional architectural models will be achieved by surveying stratigraphic surfaces with differential GPS, such that further extrapolation and interpretation can be achieved in Petrel. The digital datasets will be used to quantify channel stacking patterns, as well as provide foundations for comparison of facies information from site to site along the paleoslope surface (e.g., net:gross, amalgamation ratio, drape continuity, etc.).

Fig. A. Perspective image of satellite data draped on topography highlighting the extent of the Figueroa clinoform surface (yellow) and overlying deltaic topset strata (bright white). The paleobathymetric relief on the surface was at least 1 km. Red circles indicate channel deposits highlighted in Figure B.

Fig. B. Laterally offset channel bodies on the upper slope (location is Cerro Cazador). Inset shows 3 times vertical exaggerated trace of channel bodies. Middle: Channel body largely devoid of sandstone in fill with evidence for extensive sediment bypass in mudclast and pebble lag deposit (location is Cerro Sol). Base: Channel elements 10-15 m thick are vertically stacked and comprise channel complexes 30-50 m thick (location is Laguna Figueroa). Locations are indicated by red circles in Figure A.