2. Sedsim modelling of controls on confined mini basin fill by eustatic and halokinetic mechanisms (Gulf of Mexico)
Tristan SALLES1, Cedric GRIFFITHS1, David MCGEE2, Mihaela RYER2

3. Outline General Context Mini basin description and uncertainties
Sedimentary filling interpretations
Sedimentary structures
Control mechanisms
Numerical modelling
Building the Sedsim model
Testing scenarios
Model results
Processes through intervals
Cross-sections
Le but de l’etude est de simuler le remplissage sedimentaire de bassins confines et de reproduire l’heterogeneite des depots dans un contexte tectonique actif. Le modele est base sur un cas reel dans le Golf du Mexique sur des donnees de ConocoPhillips
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

4. General context Localization
Northern Gulf of Mexico Bathymetry
What is the architecture of the basin fill?
What depositional processes led to basin accumulation?
Can we simulate the way the basin filled ?
Can we reproduce the heterogeneity of the processes involved ?
≈ 29 km
≈ 43 km
What we want do understand
Presently the basins are confined but during deposition of
the interval of interest, there is evidence for a more unconfined system
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

5. General context Basin introduction
“Western Basin” A
Time /s 1 2 3 4 5 A’ 2 1 4 5 3 2 A A’
≈ 43 km
≈ 29 km
Salt, Fault, Basin names. Several intervals of deposition (5) during the Pleistocene based on seismic interpretation (horizons)
Simulation of the 5 intervals
Pleistocene period (-940,000 to -460,000 years)
after Heather MacDonald, (2009)
“Elongate Basin”
≈ 29 km
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

6. Sedimentary filling interpretations
Sedimentary structures
CHARACTER
INTERPRETATION
Chaotic
Variable to high reflectivity
Wavy with erosional basal contact
0.2 ms
0.5 ms
Transparent, wavy, mounded, erosional
Fully chaotic OR blocky
Debris Flows
Mass Transport
Complexes
Convergent
Leveed Channel
Overbank
Muddy Turbidites
By Thinning
0.2 ms
By Baselap
Ponded Mass Flows
Basin Floor Fans
0.5 ms
Draping
0.3 ms
after Heather MacDonald, (2009)
Draping
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

7. Sedimentary filling interpretations
Intervals summary
Interval 2 – Weakly Confined
Ponded sheets, MTDs, Channel complexes
-Salt emergence
-Increased channel confinement
-No fault movement
Interval 3 – Intermediate?
Draped sheet deposits, fault-steered channel complex
-Continued salt emergence
-Presence of fault
-Fault movement negligible
Interval 4 – Confined
Alternating sheet and mass-transport deposits
-Basin-wide deposition
-Extreme cyclicity in deposits
-Considerable fault movement
Interval 4 Sedimentary structure
1. Ponded sheets
2. Debris Flows
3. Channel complexes
* Salt emergence
4. Confined channel
after Heather MacDonald, (2009)
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

8. Controls on depositional style Sea level change
Relative sea level
Lowstand interval
High
Low
Time
condensed
section
interval when shoreline
is located near the shelf
edge (turbidity flows
dominate)
interval of upper slope
instability (debris flows
dominate)
leveed channels dominate
(relatively low sand:mud)
frontal splays dominate
(relatively high sand:mud)
Posamentier & Kolla, 2003.
interval of upper slope
instability (debris flows
dominate)
condensed
section
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

9. Controls on depositional style Halokinetic autocyclicity
Salt controlled structural high
Hemipelagites and muddy
turbidites mute topography
Pre-existing hemipelagites and
muddy turbidites
Head scarp
Intrabasinal MTC (pre-
existing hemipelagites
and muddy turbidites)
Run-up
Antecedent sea floor
MTCs stands for deep-water Mass Transport complexes
Madof et al., 2009.
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

10. Building the model General input and assumptions
4 siliclastic grainsizes :
1. coarsest 300 μm with a density of 2650 kg.m−3
2. medium μm with a density of 2650 kg.m−3
3. fine μm with a density of 2700 kg.m−3
4. finest μm with a density of 2700 kg.m−3
28 × 41 km plane divided into cells of 250 m
3 types of flow regime :
Highstand  linear sources composed of fine material (5% of fine and
95% of finest)
Transition  point sources corresponding to debris flows (high flow rate,
high flow velocity, high concentration, mainly coarsest and medium)
Lowstand  point sources corresponding to turbidity flows (medium flow
rate, high to medium flow velocity, medium to low concentration,
medium to fine grainsize)
The display interval in sedsim is set to 5000 years and flow sampling, sea-level and tectonic variations are refreshed every 250 years.
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

11. Building the model Pleistocene sea level fluctuations
Sea level curve used in the model
From Ron Waszczak.
Miller at al., 2005.
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

12. Building the model Interval Timing & Sedimentation Rates
0.46 Ma
Age (Ma)
Sea Level
0.54 Ma
4500 m/Ma
Time /ms ?
0.94 Ma
2000 m/Ma
Gives us the average flow concentration during the simulation
Depth / ft
Average deposition rate: 3250 m/Ma
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

13. Building the model Salt tectonic scenarios
High tectonic
activity during
deposition
Low tectonic
activity during
deposition
Example of 2 different tectonic scenarios (only the basement shows in the figures. The seascape was much smoother than present day that now reflects increased diapiric salt movement. Therefore, the initial bathymetry used for sedsim is based on the smoothed water bottom surface proposed by David.
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

14. Sedsim results 1st step mainly controlled by sea-level – Intervals 1 & 2 (beginning)
Partially dominated
by debris flows
We have approximated the sources input in such a way that we consider for the entire simulation 5 sea level hightstands, 4 periods dominates by turbidity currents and 5 periods dominated by debris flows.
Turbidity flow
dominated
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

15. Sedsim results 2nd step sea-level highstand and salt emergence – Interval 2
Muddy turbidity
flows due to salt
emergence
Muddy turbidity
flows due to salt
emergence
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

16. Sedsim results 3rd step sea-level transition and lowstand – Interval 3
Debris flows
dominated
Turbidity flow
dominated
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

17. Sedsim results 4th step sea-level transition and lowstand – Intervals 4 & 5
Debris flows
dominated
Turbidity flows
dominated
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

18. Sedsim results Halokinetic impact on deposit heterogeneity – Intervals 4 & 5
Slumped material induced
by salt tectonic
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

19. Sedsim results
Sections showing evolution in the mini-basin - Interval 2
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

20. Sedsim results Sections showing evolution in the mini-basin - End of interval 4
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

21. Sedsim results Average deposition rate
Average deposition rate of:
3500 m/Ma
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

22. Sedsim results Comparison to seismic1
Time /s 2 5 4 3 2 2 1 4 5
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

23. Conclusions
The model can simulate the different processes which filled the mini-basin:
Unconfined Turbidites
Channel Complexes
Debris Flows
2. The mini-basin fill is cyclic in nature and the cyclicity is controlled by:
(i) Salt interplay
(ii) Sea level changes
The model can reproduce the sedimentary layer heterogeneity however
the driving forces for tectonic activity is user imposed.
RST Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

24. Thank you… CSIRO Earth Science and Resource Engineering
Contact Us
Phone: or
Web:
CSIRO Earth Science and Resource Engineering
Dr Tristan Salles
Research Scientist
Phone:
Web:
Thank you…