1. 3D MODELING OF THE CERRO TORO DEEP-WATER AXIAL CHANNEL-BELT, SIERRA DEL TORO, MAGALLANES BASIN, CHILE: FROM OUTCROP OBSERVATIONS TO SUBSURFACE UNCERTAINTY Lisa Stright, Zane Jobe, Anne Bernhardt and Steve Graham Geological and Environmental Sciences, Stanford University

2. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Axial deep-water channel belt in the Andean foredeep Retro-arc foreland basin Deep-water sedimentation of arc derived detritus in elongate foreland trough Gentle folding and faulting during post-depositional (Miocene) uplift and deformation Late Cenozoic glaciation has led to spectacular 3D exposures Hubbard et al, 2008

3. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Condor Conglomerate (Barton et al., 2007; O'Byrne et al, 2007) Silla Syncline (Bernhardt et al., in review; Crane and Lowe, 2008; Beaubouef, 2004) Sierra del Toro: Looking to the south >1000 m E W Wildcat Conglomerate (Jobe et al., in review; Hubbard et al., 2007, 2008) At least 3 channel complex sets– Condor (Barton et al. 2008), Guanaco, Wildcat (Jobe et al. 2009) Condor: (Barton et al., 2008; O’Byrne et al. 2007b) 3 distinct channel complexes aggrade and stack to the west conglomeratic channel fill comprised of dune and bar forms complexes 50-80m thick, 1.0 - 1.5km wide Guanaco: (Jobe et al., in review) at least 5 individual channels, 5 - 70m thick and 0.1 – 1.0 km wide aggrade and stack vertically and to the east observed on northern sections only Wildcat: (Jobe et al., in review) downcuts to the south (?) and amalgamates the Guanaco max thickness 300m, width 3.5 km along 6 km outer bend margin angle 9° and inner bend margin angle 7 ° paleoflow divergence in uppermost sections, loss of confinement (?) ~12 km

4. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Study Area – northern exposure of Sierra del Toro North ~15 km W E

5. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Study Area – southern exposure of Sierra del Toro North Looking to the north ~15 km 1.Wildcat downcuts? 2.Guanaco south? 3.Undifferentiated stratigraphic level? 4.Condor and undifferentiated relationship? W E

6. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Structure and Stratigraphy: North (up-system) 500m

7. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Transformation Volume – Displacements in x, y and z Northern Central Southern N E W Northern Central N-S Transect Northern restoration dz dx dx, dy and dz

8. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Palinspastic restoration of mapped outcropping conglomerate units N W E paleoflow

9. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Modeling the Channel Complexes WE ~ 1.5 km 1200 1000 800 600 400 200 0 1400 m E W

10. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Condor Channel complex Total thickness of 3 channel complex: 500m Lowest: vertically aggrades and stacks to the west Middle: shift to the west, aggradation Upper: shift back to the east Strong structural control along these sections 1400 m paleoflow N 1200 1000 800 600 400 200 0 E W E W

11. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Guanaco Channel complex Smaller and thinner exposures Upper 4 Guanaco channels eroded/incorporated into the Wildcat At or below the resolution of the modeling 800 600 400 200 0 paleoflow N northern southern 1200 1000 800 600 400 200 0 1400 m 1200 1000 southern section W E E W northern section

12. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Wildcat Channel Complex WE

13. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Wildcat Channel Complex Because the Guanaco is not observed on the southern section, downcutting is at least Modeling reveals a 600m erosion over a distance of 8km The magnitude of erosion predicted by the model is tightly coupled with structural interpretation NS 1200 1000 0 500 1000m 800 600 400 200 paleoflow N 400m

14. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Undifferentiated Conglomerate Position “tied” to the uppermost Condor Steps down similar to the Wildcat channel complex Poor outcrop exposure control 1400 m 1200 1000 800 600 400 200 0 1200 1000 800 600 400 200 0

15. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Biased sampling generate uncertainty in interpretation –Limited exposures –Eroded section –Limited ability to measure and describe all data Visually data digitally in 3D –Helps to reduce the uncertainty in stratigraphic relationships –Analyze potential stacking patterns –Platform for discussion Stratigraphic uncertainty tightly controlled by uncertainty in structural interpretation and restoration –Magnitude of downcutting of the uppermost channel complex –Width and thicknesses of channel complexes No outcrop exposure is truly 3D -> interpretation uncertainty Modeling the deep-water channel belt deposits of Sierra del Toro

16. SUMMARYINTRODUCTIONObservationsModelingAnalysis AAPG 2010 Future Work Channel-fill architecture modeling (after Jobe et al., in press) 3D forward seismic reflectivity modeling to use as analog for subsurface seismic surveys Dimensional characterization of the channel complexes: –width –height –asymmetry –sinuosity –stacking uncertainty and ranges of all of these parameters 15Hz 25Hz

17. INDUSTRY SPONSORS SPODDS Students: Julie Fosdick, Anne Bernhardt, Zane Jobe, Katie Maier, Jon Rotzien, Larisa Masalimova, Glenn Sharman, Blair Burgreen Advising Committee: Stephen Graham, Andre Journel, Gary Mavko, Don Lowe