3D MODELING OF THE CERRO TORO DEEP-WATER AXIAL CHANNEL-BELT, SIERRA DEL TORO, MAGALLANES BASIN, CHILE: FROM OUTCROP OBSERVATIONS TO SUBSURFACE UNCERTAINTY.

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 GrahamGeological and Environmental Sciences, Stanford University

SUMMARYINTRODUCTION Observations Modeling Analysis 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 exposuresHubbard et al,

2008

SUMMARYINTRODUCTION Observations Modeling Analysis 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

EW

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

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Study Area – northern exposure of Sierra del ToroN

orth

~15 km

WE

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Study Area – southern exposure of Sierra del ToroN

orth

Looking to the north

~15 km1. Wildcat downcuts?

2. Guanaco south?

3. Undifferentiatedstratigraphic level?

4. Condor and undifferentiated relationship?

W E

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Structure and Stratigraphy: North (up-system)

500m

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Transformation Volume – Displacements in x, y and z

Northern

Central

Southern

N

E W

Southern

NorthernCentralN

-S Transect

Northern restoration

dz

dxdx, dy and dz

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Palinspastic restoration of mapped outcropping conglomerate units

N

WE

paleoflow

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Modeling the Channel Complexes

WE

~ 1.5 km

12001000 800 600 400 200 0

1400 mE W

SUMMARYINTRODUCTION Observations Modeling Analysis 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

12001000 800 600 400 200 0

E W

EW

SUMMARYINTRODUCTION Observations Modeling Analysis 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

12001000 800 600 400 200 0

1400 m

1400 m12001000southern section

WE

E W

northern section

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Wildcat Channel Complex

W E

SUMMARYINTRODUCTION Observations Modeling Analysis 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

N S12001000

0 500 1000m

800600400200

paleoflow

paleoflow

N

400m

SUMMARYINTRODUCTION Observations Modeling Analysis AAPG 2010

Undifferentiated Conglomerate

Position “tied” to the uppermost CondorSteps down similar to the Wildcat channel complexPoor outcrop exposure control

1400 m12001000 800 600 400 200 0

12001000 800 600 400 200 0

SUMMARYINTRODUCTION Observations Modeling Analysis 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

SUMMARYINTRODUCTION Observations Modeling Analysis 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– stackinguncertainty and ranges of

all of these parameters

15Hz

25Hz

INDUSTRY SPONSORSINDUSTRY 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