Anne Bernhardt, Zane R. Jobe Donald R. Lowe

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The evolution of an elongate foreland basin:

The deep- to shallow-marine filling of the Cretaceous Magallanes Basin, Chile

Anne Bernhardt, Zane R. Jobe

Donald R. Lowe

An industry affiliates program focused on the study of modern and ancient deepwater systems.

Co-Directors: Don Lowe, Steve Graham (Stanford University)

MEMBERS (2008)

Aera Energy Hess Rohol-Aufsuchungs A.G.Anadarko Husky Reliance Industries (India)Chevron Marathon Repsol YPFConocoPhillips Nexen ShellENI OccidentalExxonMobil Petrobras

ACKNOWLEDGMENTS

Michael Shultz (2004) Slope deposits-TPAndrea Fildani (2004) Basin evolution, slurry flows-PBWill Crane (2004) Conglomeratic basin-floor channels-CTSteve Hubbard (2006) Conglomeratic basin-floor channels-CTBrian Romans (2008) Upper Slope basins and channels-TPDominic Armitage (2009) Slope mini-basins-TPJake Covault (2009) Upper slope to delta plain transitionAnne Bernhardt (in progress) Conglomeratic basin-floor channels-CTZane Jobe (in progress) Conglomeratic basin-floor channels-CT Julie Fosdick (in progress) Structural evolution

Student Research in Magallanes Basin, Chile

Research Objectives

To develop an understanding of the facies,architecture, and controls on deepwater systems and of the processes by which they form

Explore and develop analogs for subsurfacedeepwater systems

Provide knowledge base for our affiliates toaid in understanding deepwatersystems in general and in evaluating their individual prospects

Key Observations

There are no perfect analogs, but . . .

Every outcropping deepwater system and every deepwateroutcrop has analog value.

One of the objectives in studying analogs must be to develop an understanding of deepwater depositsto the extent that we can consider applications of seemingly inappropriate analogs to understanding our own deepwater systems

Stratigraphy

Modified from Fildani et al., 2008

Generalized Cross-section of the Magallanes Basin

Map of study area

Modified from Fosdick, ongoing PhD project

Study area

Fildani and Hessler, 2005

It's a tough place to work but somebody's got to do it.

• Turbidites of the Punta Barrosa Formation record the onset of deep-water foreland basin sedimentation• Biostratigraphic assemblages indicate a paleo-water depth of 1000-2000 m • Paleocurrent measurements indicate a S-SE sediment dispersal pattern • Deposition within a narrow trough representing the axis of the early Magallanes foreland basin

Punta Barrosa Formation

Lower Punta Barrosa Formation

• The lower, shale-rich interval of the Punta Barrosa formation is incorporated into fold-and-thrust belt• •Characterized by laterally extensive turbidite sandstone beds interbedded with mud-rich intervals, with mudstone making up at least 50%

Upper Punta Barrosa Formation

•The upper, sand-rich interval is less affected by tectonism.

•Predominantly turbidites, some debris flows and sandy slurry flows

Fildani and Hessler, 2005

Sandy slurry flow deposits (sensu Lowe and Guy, 2000)

Upper Punta Barrosa Formation

Punta Barrosa Formation – Paleogeography

• Deposition mainly on the more distal parts of a longitudinally-fed deepwater system.

• Local sand bodies probably represent frontal splays to coarser, as-yet-unseen, perhaps more channelized upslope parts of the system

Cerro Toro Formation – Lithofacies

• Clast supported conglomerate– Avg. 1 m thick– Volcanic & meta-volcanic cobbles

• Up to 40 cm boulders!– Normal grading– Cobble imbrication– Raft blocks uncommon

• Emplaced by high-density

turbidity currents (R3)

Photo by Zane Jobe

field book

• Thick bedded sandstone– Avg. 75 cm thick– Usually amalgamated– Massive (S3)

• Dishes– Emplaced by high-density

turbidity currents

• Muddy-matrix supported conglomerate– Avg. 7 m thick– Clast supported base– Muddy matrix supported top– Emplaced by transitional,

turbulent slurry flows (Crane, 2004)

• Interbedded sandstone and mudstone– Flank channel margins– 5-50 cm sandstones

• Distinct whitish color• Tb-c, bioturbated

– Turbiditic mud• Sand filled burrows

– Narrow levees & other

out-of-channel deposits

Cerro Toro Formation – Stratigraphy

Modified from Crane and Lowe, 2008

Overview of the Silla Syncline looking south along Overview of the Silla Syncline looking south along the west limb. Park road in foreground. the west limb. Park road in foreground.

Cerro Toro Formation - Silla Syncline

Modified from Crane, 2004

Stratigraphic architecture of the Cerro Toro Formation along the west limb of the Silla Syncline.

Fining upward Fining upward conglomerate, sandstone, conglomerate, sandstone, and ss+mudstone channel and ss+mudstone channel fill of Pehoe Afill of Pehoe A

Stratigraphic relationships along the northern Stratigraphic relationships along the northern margin of the Paine C channelmargin of the Paine C channel

Generalized stratigraphic relationships and measured Generalized stratigraphic relationships and measured paleocurrent directions of major units in the Paine member paleocurrent directions of major units in the Paine member of the Cerro Toro Formation along the west limb of the Silla of the Cerro Toro Formation along the west limb of the Silla SynclineSyncline

Paine C- erosional surface

Pehoe A Pehoe B Paine A cgl

Paine BPaine A ss Paine CModified from Crane, 2004

Basin Models: Basin Models:

(A) Silla Syncline (A) Silla Syncline area as the main area as the main axial zone of the axial zone of the Magallanes Basin.Magallanes Basin.

(B) Silla Syncline (B) Silla Syncline area as a area as a structurally isolated structurally isolated slope basin lying slope basin lying west of the main west of the main axis of the axis of the Magallanes Basin.Magallanes Basin.

Cerro Toro Formation at Sierra del Toro

Cerro Toro Formation at Sierra del Toro - Architecture

Cerro Toro Fm at Sierra del Toro – Condor Margin

from Jobe et al., in press

Cerro Toro Fm at Sierra del Toro - Wildcat Axis Margin

from Jobe et al., in press

Cerro Toro Formation - Cordillera Manuel Señoret

Cerro Castillo

Cerro Toro Formation - Cordillera Manuel Señoret

Modified from Hubbard et al., 2008

Cerro Mocho

Giant cross-sets in Giant cross-sets in Cerro Toro Fm. Cerro Toro Fm. conglomerate near conglomerate near Lago Sophia, Lago Sophia, Cordillera Manuel Señoret

Cerro Toro Formation – Channel belt paleogeography

Cordillera Manuel Senoret

Sierra del Toro

Silla Syncline

38o 37o (Völker, 2004)

Peru-Chile Trench

Hikurangi Trough, New ZealandN

(Lewis and Pantin, 2002)

Puchkirchen Formation, Upper Austria

(courtesy of De Ruig)

Cerro Toro Analogues?

Tres Pasos Formation

Romans et al., 2008

Modified from Romans et al., 2008

Dorotea-Tres Pasos margin

Tres Pasos Fm at Cerro Divisadero

Modified from Romans (2008)

NORTH SOUTH

basal subunit thickens to the south

Tres Pasos Formation at Cerro Divisaderored-brown layers = Miocene igneous sills

Unit 1

Unit 2

Unit 3

Unit 4

Stratigraphic signature of the Tres Pasos prograding slope systemm

lower slope to base-of-slope

middle to upper slope

Romans et al., 2008

Cerro Escondido• Transition from Tres Pasos slope to Dorotea shelf-edge

delta• 2 sections (<300 m) at 10 cm-scale resolution• Depositional-strike perspective

basinward

Modified from Covault, ongoing PhD project

Dorotea shelf-edge delta architecture

• 4 lithofacies associations

• 2 upward-shoaling lithofacies successions (<200 m thick)

Dorotea shelf-edge delta architecture

• 4 lithofacies associations

• 2 upward-shoaling lithofacies successions (<200 m thick)– Thick, coarse-grained prodelta “sandwich”

– Thick, wave-reworked shoreface sandstone

– Thick subaqueous delta plain deposits

Delta front/shoreface

Prodelta

Subaqueous delta plain

Lithofacies association 2

• Amalgamated, thick sandstone units and mudstone packages overlain by thinner sandstone units

• Processes: turbidity currents

• Paleoenvironment: prodelta

• Hummocky, overlain by swaley, cross-stratified sandstone

• Processes: currents with wave reworking

• Paleoenvironment: delta-front/shoreface

• Lenticular, trough cross-stratified sandstone bodies encased in carbonaceous mudstone

• Paleoenvironment: subaqueous delta plain

Tres Pasos Formation - Sierra Contreras

Armitage et al., in review

Next slide

Tres Pasos Fm - Sierra Contreras

• Dominated by a thick sequence of stacked mass transport deposits

Tres Pasos Formation - Sierra Contreras

Armitage et al., in review

Sand was deposited in lows on top of MTDs

Tres Pasos Formation - Paleogeography

Basin Evolution

THE END

Anne Bernhardt, Zane R. Jobe Donald R. Lowe

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