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
Flow
• Thick bedded sandstone– Avg. 75 cm thick– Usually amalgamated– Massive (S3)
• Dishes– Emplaced by high-density
turbidity currents
Cerro Toro Formation – Lithofacies
• Muddy-matrix supported conglomerate– Avg. 7 m thick– Clast supported base– Muddy matrix supported top– Emplaced by transitional,
turbulent slurry flows (Crane, 2004)
Cerro Toro Formation – Lithofacies
1.5 m
• 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 – Lithofacies
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
Cerro Toro Formation - Silla Syncline
Modified from Crane, 2004
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
Cerro Toro Formation - Silla Syncline
Paine C- erosional surface
Cerro Toro Formation - Silla Syncline
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
159°
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)
N
Peru-Chile Trench
Hikurangi Trough, New ZealandN
(Lewis and Pantin, 2002)
Puchkirchen Formation, Upper Austria
(courtesy of De Ruig)
Cerro Toro Analogues?
W E
Tres Pasos Formation
Romans et al., 2008
Tres Pasos Formation
Modified from Romans et al., 2008
Dorotea-Tres Pasos margin
Tres Pasos Fm at Cerro Divisadero
30 m
Modified from Romans (2008)
NORTH SOUTH
basal subunit thickens to the south
Tres Pasos Formation at Cerro Divisaderored-brown layers = Miocene igneous sills
Modified from Romans (2008)
Unit 1
Unit 2
Unit 3
Unit 4
Stratigraphic signature of the Tres Pasos prograding slope systemm
eter
s
lower slope to base-of-slope
middle to upper slope
Modified from Romans (2008)
Tres Pasos Formation
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)
1
2
Modified from Covault, ongoing PhD project
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
2
Delta front/shoreface
Prodelta
Subaqueous delta plain
Modified from Covault, ongoing PhD project
Lithofacies association 2
• Amalgamated, thick sandstone units and mudstone packages overlain by thinner sandstone units
• Processes: turbidity currents
• Paleoenvironment: prodelta
Modified from Covault, ongoing PhD project
Lithofacies association 3
• Hummocky, overlain by swaley, cross-stratified sandstone
• Processes: currents with wave reworking
• Paleoenvironment: delta-front/shoreface
Modified from Covault, ongoing PhD project
Lithofacies association 4
• Lenticular, trough cross-stratified sandstone bodies encased in carbonaceous mudstone
• Paleoenvironment: subaqueous delta plain
Modified from Covault, ongoing PhD project
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